Syntheses of cyanines: a review

Tetrahedron 68 (2012) 781e805

Contents lists available at SciVerse ScienceDirect

Tetrahedron journal homepage: www.elsevier.com/locate/tet

Tetrahedron report number 960

Syntheses of cyanines: a review Mallika Panigrahi a, Sukalyan Dash b, Sabita Patel c, Bijay K. Mishra a, * a

Centre of Studies in Surface Science and Technology, School of Chemistry, Sambalpur University, Jyoti Vihar, Burla 768 019, India Department of Chemistry, Veer Surendra Sai University of Technology, Burla 768 018, India c Department of Chemistry, National Institute of Technology, Rourkela 769 008, India b

a r t i c l e i n f o Article history: Received 6 October 2011 Available online 3 November 2011 Keywords: Cyanine dyes Polymethine dyes Squarines Chiral cyanine dyes Fullerenes Cyclodextrins

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 781 Synthesis of cyanine dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782 2.1. Synthesis of non-chiral polymethine cyanine dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782 2.1.1. Synthesis in organic medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782 2.1.2. Solid-phase synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787 2.1.3. Water-mediated synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792 2.2. Syntheses of chiral polymethine dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793 2.3. Syntheses of squaryl polymethine dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797 Future prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803 References and notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803 Biographical sketch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805

1. Introduction

Abbreviations: BSA, bovine serum albumin; a-CD, a-cyclodextrin; DBF, di-nbutylformamide; DBHT, di-O-benzoyl hydrogen tartrate; DCC, dicyclohexylcarbodiimide; DIEA, diisopropyl ethylamine; DMF, dimethyl formamide; DMSO, dimethyl sulphoxide; DPFA, N,N0 -diphenylformamidine; DSSC, dye-sensitized solar cell; DVD-R, recordable digital versatile disk; IPCE, incident photon-to-current conversion efficiencies; NHS, N-hydroxysuccinamide; NIR, near-infrared; NMR, nuclear magnetic resonance; PEG, polyethylene glycol; pip, piperidine; rt, room temperature; TO, thiazole orange; UVevis, ultra violet-visible. * Corresponding author. Tel.: þ91 6632430093, þ91 9861046813 (mobile); fax: þ91 663430158; e-mail address: [email protected] (B.K. Mishra). 0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2011.10.069

Cyanine dyes came to the limelight during 1856 for their application in the field of photography and have now received wide attention due to their applications in photodynamic therapy.1 Cyanine dyes (a class of polymethine dyes) are planar, conjugated, open-chain (sometimes ring) systems of sp2-hybridized carbon atoms with an odd number of methine groups and an even number of p electrons according to the general formula: XeðCRÞn eX0 with n¼1, 3, 5, .; R¼H or substituents;

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M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

X and X0 ¼terminal chain atoms (e.g., N, O, P, S) or atom groups (e.g., NR2, CH]O). These are usually called cyanine dyes with X¼X0 ¼N and represented by vinylogous amidinium salts; oxonol dyes with X¼X0 ¼O and represented by vinylogous carboxylate salts; and merocyanine dyes with X¼N and X0 ¼O and represented by vinylogous carboxamides. Together with aromatics and polyenes, polymethines (cyanines) belong to a particular group or organic compounds with conjugated p-systems, which can be advantageously classified by the triad €nhe et al.,2 which describes the common system, introduced by Da and the different electronic properties, such as delocalization energy and polarizability, as well as p-electron densities and bondlength alternation along the polymethine chain of these three archetypal p-systems. The chromophoric stereochemical alignment is usually transoid, which leads to stability due to attenuation of steric hindrance. However, cisetrans isomerization has also been observed, under some specific conditions.3 This class of dyes, besides having applications in photography and photodynamic therapy, possesses versatile applications in inorganic large band-gap semiconductor materials,4e6 laser materials,7 light harvesting systems of photosynthesis8 and photovoltaics,9 photorefractive materials,10e13 as fluorescence probes for monitoring photochemically initiated polymerization,14 as antitumor agents,15e19 in optical data storage,20 in organic solar cells,21 proteomics,22 and biomolecular labeling.23e27 Of particular interest are molecules that can reversibly switch between a nonemissive and an emissive state. Some representative examples are fluorogenic unsymmetrical cyanine dyes, which become fluorescent upon interaction with specific proteins,28 and photochromic compounds,29 which can undergo a reversible change in their optical properties under illumination. Such dynamic systems can find valuable applications as fluorescent supramolecular devices, for the design of smart materials.30 2. Synthesis of cyanine dyes A number of synthetic procedures for polymethine dyes of diverse molecular structure have been reported in the literature.31e34 Synthetic processes have been proposed extensively for monomethines,35e41 dimethines,42e46 trimethines,47e50 tetramethines,51 pentamethines,52e56 heptamethines,57e59 squarylium cyanines,60e64 and various other cyanine dyes.65e67 2.1. Synthesis of non-chiral polymethine cyanine dyes 2.1.1. Synthesis in organic medium. Generally, for the generation of a methine dye, the prestruct has a synthon component containing a methylene group activated by a quaternized nitrogen atom and another component having a carbonyl group with an auxochrome. By using this strategy, large numbers of styryl pyridinium dyes (1) have been synthesized with varying alkyl chains R and electrondonating groups Y. (Scheme 1).68 Fused pyridinium ring systems, such as substituted quaternary imidazo[1,2-a]pyridinium salts were condensed with 4-

(dimethylamino)benzaldehyde in the presence of 1-butanol and piperidine (pip) as base at reflux temperature by Yarmoulk et al.69 to obtain a fluorophore probe (2) for the study of the behavior of nucleic acid and bovine albumin serum (BSA) proteins (Scheme 2).

1 R

X Me

X

N

-H2O

Δ

(Me)2N

R1 N

R2

X

N

2 Scheme 2.

An extended series of mono- and bis-cyanine dyes with monoand trimethine chains were prepared by Shindy et al. (Scheme 3).70 The synthon components were p-chloranil (3) and 4-amino-5(hydroxy, mercapto, or imino)-3-methyl-1-phenylpyrazole (4aec), taken in 1:2 molar ratios to afford (5aec) as the stationary material for all the dyes. To introduce heterocyclic auxochromes, methylene groups are activated in (5aec) by quaternizing the molecule with iodoethane to produce (6aec) and (7aec). The reactions were carried out using piperidine as the base and iodoethane quaternary salts of pyridine, quinoline and isoquinoline (8) in ethanol at suitable places to yield monomethine dyes (9aee), bismonomethine dyes (10aee) and (11aee), trimethine dyes (12aee) and bistrimethine dyes (13aee). An isoxazole unit was fused to the pyrazolidinone (14) to afford a biheterocyclic compound (16) through (15). The pyrazoloisooxazole derivative has been used as a starting material for the synthesis of some photosensitizer trimethines (17aee), monomethine mixed cyanines (18aec), monomethines (19aec and 20aec), and azamethine cyanines (21aec) (Scheme 4).71 Imide functional groups are important structural constituents in pigment dyestuffs because these functional groups form hydrogenbonded networks, which contribute to the high lattice energies, providing the desired insolubility of pigment particles. Some monomethine dyes, (24e27) and (30e32), with these characteristics have been prepared by condensation of the CH acidic heterocycles, 4-alkyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile (22), and barbituric acid (29), with electron-rich thiophene aldehydes (23aec) and benzaldehyde derivatives.72 The formylation of (22) and (29) with N,N0 -diphenylformamidine or N,N-di-n-butylformamide in acetic anhydride and further reaction with 4picolinium salts engendered the dimethine dyes (28) and (33a,b) (Schemes 5 and 6).

N

in EtOH/pip/Δ

X

+ Y

R2

CHO

R CH

N

N

+

O

R

Me

(Me)2N

-H2O

1

pip = piperidine Scheme 1.

Y

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

O Cl

Ph H2N Me N X 2 EtOH/Py N + XH N N -4HCl Cl N Me Ph H

O

Cl

Cl O

4a-c

3

N

EtOH/pip I

N H

Me

H N

Me

N

N H

O

Me I

N N Et Ph

EtI EtI

O

Ph N X

H N

O

A Et N N N Et Ph Ph

I

O

N H

H N

Me N N Et Ph

O

2I

7a-c +2 8 EtOH/pip

+8 EtOH/pip

A

H N

Et

+8 N

N Ph

O

N

Ph N X

Me

9a-e

Et

O

6a-c

+8 N

+EtI

N H

N Ph O

N Ph

O

Ph N X

Me

Me N

5a-c

A

Ph N X

H N

783

N Et Ph

2I

A

EtOH/pip

N

Ph N X N H

N Ph

10a-e

OEt Et +2(OH)CH(OEt) 2 EtO EtOH/pip

N

Ph N X N H

+8

O

O

H N

O

A N N N Et Ph Ph

11a-e A

H N N N Et Ph

O

2I

N Ph

12a-e +8

7a-c

EtOH/pip

+2 8 EtOH/pip

Et N

A

Ph N X

O

N H

N Ph

O

A

H N N N Et Ph

N Ph

2I

13a-e

4a-c, 5a-c, 6a-c, 7a-c

: a X=O, b X=S, c X=NH

9a-e, 10a-e, 11a-e

: a X=O, A=1-ethylpyridinium-4-yl salt : b X=O, A=1-ethylquinolinium-4-yl salt : c X=O, A=1-ethylisoquinolinium-4-yl salt : d X=S, A=1-ethylquinolinium-4-yl salt : e X=NH, A=1-ethylquinolinium-4-yl salt

12a-e, 13a-e

: a X=O, A=1-ethylpyridinium-2-yl salt : b X=O, A=1-ethylquinolinium-2-yl salt : c X=O, A=1-ethylpyridinium-4-yl salt : d X=S, A=1-ethylquinolinium-2-yl salt : e X=NH, A=1-ethylquinolinium-2-yl salt Scheme 3.

Rhodacyanine dyes, such as (35), having two different conjugated systems (a neutral merocyanine and a cationic cyanine moiety) and three heterocyclic components, in which two terminal heteroaromatic rings flanked by a rhodanine moiety, were obtained in a one-pot synthetic protocol through (34) as the intermediate

(Scheme 7).73 These dyes show strong in vitro antimalarial activity against Plasmodium falciparum. Inagaki et al.74 synthesized some pentamethine (36aed) and heptamethine (37a,b) oxonol dyes based on Meldrum’s acid with a variation of the countercations (Fig. 1). These dyes possess large

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M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

Me N

N Ph

Ph O Ph HN NH OH EtOH/pip -HBr

Me

Br

Br

N

O

14

Ph N

Me N

H2O

N Ph

O

N Ph

A

15

N Ph N

N

N Ph

O

N Ph

N Me I

Me N

I

N

O CH C R

EtOH/pip

I

CH

Ph N

N

N Ph

OH OH

N Ph

Me

Me R EtOH/pip

O N Ph 16

A

O

N

O O

Ph N

Me

O OH

N Ph

Ph N

H N Ph

I

Me

Me

N

H2SO4 Me EtOH N

N Ph

Ph N

Me

N Ph

Ph R N CH C CH O

N

Me I

17a-e

20a-c Ph N

Me

16 EtI

N

O

I

O

N Ph

(OEt)2HC

(EtO)2CHOH EtOH/pip -H2O

Ph N

CH2 N

O

O

N Ph

A

A

I

Me

NO2

A

Ph N

CH N N R

N Ph

N A

A CH N

O

Ph N

N

I

N

19a-c Ph N

N HC N

N Ph

O

I

Me

N

R

I

N Ph

O

A CH N

I

18a-c

I

O

21a-c

17

a

b

c

d

e

R

H

Me

Ph

4-MeO-C6H4

4-NO2-C6H4

(18) A = a: 1-ethylpyridinium-2-yl salt. b: 1-ethylquinolinium-2-yl salt, c: 1-ethylpyridinium-4yl salt; (19) A = a: 1-ethylpyridinium-4-yl salt, b: 1-ethylquinolinium-4-yl salt, c: 1ethylisoquinolinium-1-yl salt; (20) A = a: 1-ethylpyridinium-2-yl salt, b: 1-ethylquinolinium-2yl salt, c: 1-ethylpyridinium-4-yl salt; (21) R = a: 4-OH, b: 2-OH, 5,6-benzo substituent, c: 2OH, 3,4- benzo substituent. Scheme 4.

extinction coefficients of the order of 105 dm3 mol1 cm1, narrow bandwidths, and wide variation of absorption wavelengths over the ultraviolet to near-infrared region. As a standard for lightfastness, a nickel-azo dye was employed, which is used in commercial DVD-Rs with recordable digital versatile disks with practically sufficient light-fastness. In the course of development of these dyes for DVD-Rs, which requires resistance to ambient light and a reading laser beam, the light-fastness of oxonol dyes increases by quenching the excited state of the oxonol anion by the onium counterion? Although the triethylammonium salts (36a)

and (37a) faded rapidly, in striking contrast, the oxonol dyes with bipyridinium countercations, (36c,d) and (37b) showed enhanced light resistance. For the sensitization of nanocrystalline TiO2 electrodes, a series of new benzothiazolium hemicyanine dyes (42e46) and a naphthothiazolium hemicyanine (47) with pendent sulfonate anchoring groups have been synthesized by Chen et al.75 Compounds (42e45) were synthesized by condensation of (40a,b) (obtained from 38 and 39) with (41a,b), and compounds (46) and (47) were obtained from the condensation of (40c,d) with (41a) in ethanol in the presence of

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

C9H19

C9H19

C9H19 CN

N

O

Ph

CN

O

N

HO

H

785

DPFA

O

CN

N H N

O

H2N-Ph

O

H

H

22 R

Bu

S

N

O

23a-c

ii

i

H2O

ClO4

N

Bu

O

iii

C12H25

H2O

Ph, NH2, HClO4

Bu R

C9H10

S

N

C9H19

C9H10

CN

Bu CN

O H

O

CN

O

N

C12H25 N

N H

O

24-26

N H

O

O

27

28

23a: R = H, b: R= OMe, c: R = n-Bu2N; 24: R = H; 25: R = OMe; 26: R = n-Bu2N (i) Ac2O, 90 oC, 0.5-2 h, (ii) Ac2O, 120 oC, 2 h; (iii) Ac2O, rt, 0.5 h, and 90 oC, 2 h, DPFA = N,N’–diphenylformamidine Scheme 5.

n-Bu O

Bu O

Bu O

O O

NH N H

H2O

O i

N

N

N

i R C12H25

(a: R = iPr, b: R = H)

N H

O

N H N H

N

R

N H

Bu

O

Bu

ClO4

S O

Bu ii

O Bu

H2O

O i

O

29

30 Bu2N

N Bu

H

O

O

O

H

O

O

31

R H

O

C12H25 N

N

R

N

O

32

33a, b

H

O

(a: R = iPr, b: R = H)

(i) Ac2O, 90 oC, 1.5-2 h, (ii) Ac2O, 90 oC, 1 h, DBF= di-n-butylformamide. Scheme 6.

R R

N

S

N

ToS

O

SMe

(i)

S

+ N R'

N Me

R"

S SMe O

N R'

34

S

-MeSH -H2

R N

(ii)

S N R'

O

TsO

R N S

TsO (iii) -MeSH -H2

O

N R"

N R'

35

R = Me, R’ = R” = Me, Et, Ph (i) NEt3, MeCN, rt, (ii) TsOMe, DMF, 120 oC, (iii) NEt3, MeCN, 70 oC Scheme 7.

TsO

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M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805 O

O

O

O

O

n

O

M

O

n

M+

36 a

2

Et3NH+

b

2

Me4N+

c

2

N,N’-diphenyl-4,4’-bipyridinium2+

d

2

N,N’-di(1-naphthyl)-4,4’-bipyridinium2+

37 a

3

Et3NH+

b

3

N,N’-diphenyl-4,4’-bipyridinium2+

Compound

(IPCEs) for the dye-sensitized TiO2 electrodes, and (iii) the overall photoelectric conversion efficiencies (h) for the dye-sensitized solar cells (DSSCs), based on these hemicyanines, depend strongly on the type of anchoring groups and decrease in the order: carboxylzhydroxyl>carboxyl>sulfonatezhydroxyl, indicating the importance of the dye adsorbing groups for their sensitization effects in DSSCs. Meguellati et al.76 have introduced a new family of dynamic fluorophore analogues (51) and (52) of some well-known tri- and pentamethine cyanine dyes that can be obtained via a reversible condensation between non- and/or weakly fluorescent benzothiazolium amine and indolenin aldehydes building blocks (Scheme 9). A mixture of amine (48) and Fischer’s base aldehyde (49) or (50) was heated (50  C) in DMSO-d6 for three days to produce the a-aza-tri- and a-aza-pentamethinium dyes (51) and (52), respectively. These cyanine dye analogues (51 and 52) differ from the original tri- and pentamethine dyes solely by the introduction of an imine bond into the polymethine chain, making their formation reversible and adaptive to the pressure of external conditions. It is noteworthy that both imino dyes (51) and (52) proved to be stable in their solid state, while slowly regenerating the amine and aldehyde precursors when stored in solution for more than 1 h. This dynamic system could re-organize in response to an external stimulus, leading to a measurable perturbation of the global UVevis and fluorescence spectra of the equilibrating

O

Fig. 1. Structures of oxonol dyes 36aed and 37a,b.

piperidine as base, as shown in Scheme 8. Photophysical and photoelectrochemical studies revealed that (i) the fluorescencequenching efficiencies of these dyes by colloidal TiO2, (ii) the monochromatic incident photon-to-current conversion efficiencies

S

S N

benzene

+ Br(CH2) nCOOH n = 1, 2

N

reflux

+ OHC

EtOH pip S NEt2

N X

(CH2)nCOO

42

43

44

45

X

OH

H

OH

H

n

1

1

2

2

S R1

S

benzene O

+

S O O

N 2 R

reflux

+ 2 R

CH2-CH2-CH2-SO3

40c: R1, R2 = H 40d: R1, R 2 = -CH=CH-

38a: R1, R2 = H 38b: R1, R 2 = -CH=CH-

EtOH pip S R1

N 2 R

41a

N

R1

CH C H

NEt2

CH2-CH2-CH2-SO3 46: R 1, R 2 = H 47: R1, R 2 = -CH=CH-CH=CHScheme 8.

a: X = OH

41 b: X = H

40

HC HC

NEt2 X

(CH2)nCOOH n = 1, 2

39

38

Br

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

787

S NH2 X N +

O

+

48

O

N

N

49

50

+H2O

-H2O +H2O

N S

-H2O

N I

I S

N

N

N

N

51

52 Scheme 9.

mixture. This concept can be used in the development of smart materials. In order to enhance the fluorescence probing of nucleic acids, some novel asymmetric analogues of thiazole orange (TO) (56aeq) with amide substituents in the benzothiazole moiety have been synthesized77 (Scheme 10) by condensation of (53aed) with (54aeg) and (55a,b) in the presence of N-diisopropylethyl amine and appropriate solvents (ethanol or acetic anhydride) at room temperature. The dyes (56aeq) show absorption bands in the range of 453e519 nm and almost no fluorescence in the free state. However, the fluorescence intensity increases significantly when bound to DNA. For the preparation of some neutral monomethine cyanine dyes (60aef), Deligeorgiev et al. have used two methods, one involving melting of a mixture of (57aec) with heterocyclic compounds (58a, 59bed) having an active methyl group, followed by dilution with ethanol, and the other involving the treatment of the mixtures of the above compounds in the presence of acetic anhydride at the appropriate temperature78 (Scheme 11). Romieu et al.79 have reported the synthesis of a new fluorescent pentamethine cyanine dye with an amino acid derivative. Further derivatization with a trisulfonated linker has led to a novel watersoluble near-infrared (NIR) dye suitable for covalent labeling of biomolecules. Synthesis of the cyanine-based amino acid (61) was accomplished in five steps, starting from 2,2,3-trimethyl-1H-benz [e]indole as a common precursor for the two moieties (Scheme 12). Firstly, this indole undergoes quaternization with N-(4bromobutyl)phthalimide to afford the iminium quaternary salt (62) in 90% yield. The readily formed second indole unit (63) bearing a carboxylate group was treated with malonaldehyde dianilido hydrochloride in a 1:1 mixture of acetic acid and acetic anhydride under reflux to give (64) in quantitative yield. Reaction of (62) with (64) in a 1:1 mixture of acetic acid and pyridine under reflux furnished the pentamethine cyanine derivative (65), which was isolated in 82% yield by silica-gel chromatography. Finally, the removal of the phthalimide protecting group was achieved by treatment with a 10-fold excess of hydrazine monohydrate in a mixture of dichloromethane and methanol to afford the targeted dye (61) as the trifluoro acetate salt.

A functionalized derivative of (69) was achieved by coupling (66) with (68) obtained by treating (67) with N-hydroxysuccinamide (NHS) (Scheme 13 and 14).80 The synthesis of some water-soluble N-1,5-phosphosubstituted pentamethine cyanine dyes (73aec) was achieved by the condensation of 2 equiv of the N-phosphonate quaternary heterocyclic ammonium salts (72aec) with ethyl orthoformate in dry pyridine.57 The salt was prepared by refluxing the 2-methylsubstituted heterocyclic base (70aec) with diethyl 3bromopropyl phosphonate (71) in acetonitrile as solvent (Scheme 15). The phosphonate moiety in 72a was transformed into the phosphonic compound 74 by refluxing the salt in a mixture of acetic acid and hydrochloric acid for 48 h in order to get a better solubility of the dye in an aqueous medium and to enhance the complexing ability of the phosphorus moiety at different pH values (Scheme 16). Recently, a number of cyanine dyes having complex heterocyclic moieties,81,82 fluorinated polymethine chains,83 protein labeling capability,84 and nucleic acid binding activity85 were synthesized by various workers. These dyes excel in their applications to the multifaceted modern researches in dye chemistry. 2.1.2. Solid-phase synthesis. By the condensation of aldehyde (75) containing functionalities of various sizes, conjugation lengths, and electron-donating or -withdrawing capabilities with 2- or 4methylpyridinium salts (76), a fluorescent library of dyes (77) based on a styryl scaffold was created by Chang et al. (Scheme 17).86 The condensation of (75) and (76) with a secondary amine as catalyst was performed in 96-well plates, and the dehydration reaction was accelerated by microwave irradiation for 5 min to give 10e90% conversion. The structural diversity of the styryl dyes resulted in a broad color range from blue to red, representing practically all visible colors. The advantages of the synthetic method include (i) no further purification for primary analysis, as the fluorescent properties of the products are easily distinguishable from those of the leftover building blocks (75) and (76), due to their weak fluorescence or much shorter lex and lem; (ii) direct use of the reaction mixture in biological screening; (iii) avoiding of toxic catalysts (such as strong

788

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

Me

N R1 O

X

R-C-N O

54a-54g

R-C-N

S

H

S HC

H

EtOH/Ac2O

SMe N H

N Et

MeSO 4

56a, 56c-56m, 56q

O R-C-N N R1

Me

53a-53d

N R1

N X Me

S HC

H

X

N R1

N X Me

55a-55b

56b, 56n

54 X=Br/I R1

53 R

55 X=Br/I R1

Me

a

O (H2C)2OCOHN

(H2C)3 N O

Ph

b

O (H2C)3

S

(H2C)3 N O

c

Cl

H2 C

d

F (H2C)2

e f

(CH2)2OH

(H2C)3 S

g

-(CH2 ) 5COOH Scheme 10.

Me R1 N

A

SMe A

N

+

Y

57a, 57b, 57c R3

57a:X = S, R = H, A = MeSO4 57b:X = O, R = H, A = ClO4 57c:X = S, R = Cl, A = MeSO4

o (MeCO)2O, 70-100 C 15-30 min

Me

N

H C

NH

N

58a

X

X

100-110oC 10-15 min

Me

60a, 60b, 60e R2

R2

R1

X

59b, 59c, 59d

H C

Y NH

N

59b: R2 = pyrrolidyl, R3 = Me, Y = N 59c: R2 , R3 = H, Y = N 59d: R2 , R3 = H, Y = CH

A

Me

R3

60c, 60d, 60f

60a: X = S, R1 = H, A = MeSO 4 60b: X = O, R1 = H, A = ClO4 60c: X = S, Y = N, R1= H, R2 = pyrrolidyl, R3 = Me, A = I 60d: X = S, Y = N, R1 , R2 , R3 = H, A = I 60e: X = S, R1 = Cl, A = MeSO 4 60f: X = S, Y = CH, R1 = Cl, R2 , R3 = H, A = MeSO4 Scheme 11.

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

sealed tube o 140 C

789

Br

O

N

N N

Br

62 O

O Br

HO

O

N

O

Br O

N H N

63

N

N

Br

N

64 CO2H

Ac2O,AcOH reflux CO2H

AcOH, Pyridne, reflux

X N

N

1.NH2NH2, MeOH, CH2Cl2 2 trifloroacetic acid on RP-C16 silica column

65 N 1 R R

CO2H R,R1 = phthalimidyl X = Br

N

N

X

NH2

CO2H

61 X = CF3CO2 (57%) Scheme 12.

H2N

oleum

OH β-alanine

4oC

H2N

O

O

O

O

Fmoc-OSu OH

SO3H α-sulpho β-alanine

O

1,4-dioxane

N H

OH SO3H

aq Na2CO3 DCC, NHS, DMF α-sulpho β-alanine aq Na2CO3 4 oC O

O O H2N SO3H

O

O N H

OH SO3H

Et2NH DMF

66 Scheme 13.

O

N H

SO3H

N H

OH SO3H

790

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

N

N

N

N

uronium reagent

O SO3

SO3

67

68 C

COOH

r ffe bu H 8.2 a te P r bo o aq 4 C

O N

O

O

N

N

SO3

SO3H

H C N

69

SO3H OH

O

O

O

Scheme 14.

Y Y 2

X + 2Br(CH2)3-PO(OEt)2

MeCN

X N

2

Br

N 71 70a : X = S, Y = H

O P O

70b: X= C(Me)2, Y = H

O

70c: X= C(Me)2, Y = SO3 K Y

HC(OEt)3 in pyridine

X

X

N

N

Y

72a: X = S, Y = H 72b: X= C(Me) , Y = H 2 72c: X= C(Me) , Y = SO3K 2

Br O P O O

O P O O

73a: X = S, Y = H 73b: X= C(Me)2, Y = H 73c: X= C(Me)2, Y = SO3 K Scheme 15.

acids, bases, or metals); and (iv) removal of most of the low-boiling point solvent and catalyst (pyrrolidine) during the microwave reaction, leaving only dimethyl sulphoxide (DMSO), a common solvent for biological sample preparation. Microwave irradiation was also used for the condensation of 1,2,3-trimethylbenzimidazolium or 1,4-dimethylpyridinium salts

S

S

with aromatic aldehydes in the presence of piperidine under solvent-free condition to yield 1,3-dimethyl-2-substituted styrylbenzimidazolium salts and 1-methyl-4-substituted styryl pyridinium salts.87 The approach provides a fast and environmentally benign pathway to several useful hemicyanine dyes. Balasubramanian and Mason88,89 proposed a solid-phase synthetic route for unsymmetrical trimethine cyanine dyes (e.g., 79) by capturing and activating the hemicyanine intermediate (78) on a polystyrene sulfonyl chloride resin, followed by reaction and

N

N Br AcOH/Hcl Δ

HO P O HO

O P O O

R Br

O R C H +

75

Me N

DMSO-EtOH -H2O

R

74

72a Scheme 16.

pyrrolidine cat. X

76

X N R

77 Scheme 17.

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

MeO

I

OMe

MeO

791

N

N

N

H

i

I

N

N

78

H SO2Cl

ii

-HCl I N

N

MeO I

N

I N

N

iii

SO2

79

(i) (EtO)3CH, EtOH, 80 oC, 2 h, (ii) diisopropylethylamine (DiEA), rt, 4 h, (iii) DiEA, pyridine, rt, 30 min Scheme 18.

A dumbbell-type 60-fullerene dimer linked with a cyanine spacer (81) having sulfur in the acceptor unit was synthesized93 through a coupling reaction of (80), which was a 1,3-dipolar addition product of azomethine ylide and 60-fullerene. When n-butyl alcohol and squaric acid were used in the second step, a 60fullerene dimer (82), with two C60 units covalently attached to a squarylium cyanine dye, was obtained94 (Scheme 19). Synthesis of some sulfo-indocyanine dyes (96 and 97) with high water solubility was attempted from a solid-supported aniline scaffold (86) and two key intermediates (90) and (91). The synthesis of (86) was achieved by a stepwise process. Initially, the amino group of p-aminobenzoic acid (83) was blocked by using di-

concomitant cleavage by a heterocyclic carbon nucleophile (Scheme 18). The chemistry in this method has been designed to minimize purification steps and the approach appears to be a robust and a versatile strategy for delivering a wide range of cyanine-based dyes in high purity. Such methods, involving a combination of microwave and solid-phase protocols, have recently been adopted by many workers90,91 to synthesize unsymmetrical functionalized cyanine dyes, covering the whole visible color range. Some solventfree methodologies allowing for a greener approach92 have also been suggested for the synthesis of cyanine dyes.

Me N

S Me N

S C60

CH2COOH toluene NHMe N2, reflux

Me N

OHC

Me N

S N Me

80

Me N

S CH CH C H

N Me

1 Me2SO4 2 Py, CH(OEt)3 KI I

81 O Me N

S

S CH

CH N Me

O

N Me

82 Scheme 19.

Me N 1 Me2SO4 2 Py, n-BuOH, squaric acid

792

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

tert-butyl dicarbonate to afford (84), which was further condensed with PEG in the presence of DCC to obtain (85). Deblocking of (85) by using trifluoroacetic acid yielded (86) (Scheme 20).95

HOOC

To obtain the other synthon components, (87) was converted into indole derivative (88), which through (89) afforded (90) and (91) (Scheme 21).

di-t-butyl dicarbonate

NH2

HOOC

NHBoc

THF, reflux, 24 h

84

83

PEG, DCC, DMAP CH2Cl2, rt.12 h O

CH2Cl2

O C

O

NH2

O C

THF, rt. 5h

NHBoc

86

85 Scheme 20.

N H

The polyethylene glycol (PEG)-bound aniline (86) when treated with 1,1,3,3-tetramethoxy-propane or triethyl orthoformate in glacial acetic acid yielded the PEG-bound 4-(3methoxyallylideneamino)benzoic acid ester (92) or the PEG-bound formamidine (93), respectively. Subsequent reaction of (92) with the heterocyclic carbon nucleophile (90) resulted in the formation of the PEG-bound tetramethine hemicyanine dye (94), and treatment of (93) with (90) in ethanol produced a dimethine dye (95). The immobilized PEG-bound tetramethine hemicyanine (94) or the PEG-bound dimethine hemicyanine (95) reacted with a substoichiometric quantity of the second heterocyclic nucleophile (91) in a mixed solution of acetic anhydride and pyridine to form the unsymmetrical cyanine dye (96) or (97), respectively (Scheme 22).

(CH2)5COOH

2.1.3. Water-mediated synthesis. Water has been a rare medium for use in condensation reactions to synthesize cyanine dyes. However, this medium has been successfully used to carry out the reaction of 3-(9-julolidinyl)prop-2-en-1-al (98) with N-(1adamantyl)-4-methylpyridinium chloride (99) and a-cyclodextrin (a-CD) in the presence of aqueous sodium hydroxide to afford the cyanine dye rotaxanes (100a and 100b) as well as the free dye (101) (Scheme 23).96 a-Cyclodextrin, a cone-shaped molecule having a narrow 6-rim (with primary OH groups) and a wide 2,3-rim (with secondary OH

O Me C HO3S

O3S

iPr

NHNH2

87 88

KOH KO3S N

Br(CH2(CH2)4COOH

89

EtI

O3S

O3S N

N

90 91 Scheme 21.

O O C

1,1,3,3-tetramethoxy-propane, glycerol acetic acid,

NH2

Triethylorthoformate, glycerol acetic acid, o 55 C. 55 h O

86

o 55 C. 55 h

O

O O C

N

O C

OMe

93

92 acetic acid 80oC 1h

90

90 O

SO3

O N

triethyl orthoformate EtOH reflux, 2.5 h H N C H 95

O C

O C

C O

N CH NH

N

SO3

H C N

94 91

acetic anhydride, pyridine 91 o 110 C,15 min

O3S SO3

O3S

SO3 N

N

(CH2)5COOH

N

N

acetic anhydride o pyridine, 100 C, 15 min

(CH2)5COOH

97

96 Scheme 22.

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

N

793

N

N

N

+

α - CD

N

+

Cl

NaOH aq o 95 c

Cl +

O

Cl +

N

98

99

100a

Cl

N

N

100b

101

Scheme 23.

groups), provides a nonpolar environment for the reaction site, mimicking enzymes in bringing the reactants into close proximity. Due to its asymmetric facial structure, there are two possible orientations of the cyclodextrin unit, giving rise to the two stereoisomers (100a and 100b). Both stereoisomers were efficiently separated by reverse-phase chromatography.97 2.2. Syntheses of chiral polymethine dyes Some well-known chiral polymethine dyes with chiral centers have been isolated from natural sources, such as (102) from Beta vulgaris and (103) from Amanita muscaria where both dyes contain pentamethinium cyanine chromophores. Their chirality is mostly due to the presence of L-a-amino acids.98,99 However, investigation on chiral polymethine dyes with potentially new chiroptical properties (e.g., as sensitizers, or having different sensitivities for plane- or circular-polarized light) are sparse.100,101 Me +

The pioneering reports on the synthesis of chiral polymethine € nig102 in 1928. In this yearly paper, the first synthetic dyes were by Ko chiral pentamethine cyanine dye was given the old-fashioned formula (104) with so-called ‘partial valencies’ (mesomeric structures were not known at that time). A present-day notation of this polymethine dye is given by the formulas 104a (S,S) and 104b (S,R): H3C

Sulfo mix

O

-H2O, -H2

Me

NH2

N

Me

NaBH4/NiCl2/MeOH

Me N H2

Me

SO3

Me O

HCl in Et2O

Me

N H

+ bromocamphor sulphonate

Me

Me

Br NH3 in H2O Me

Me Br

Pyridine/BrCN in EtOH,Et2O

Me N H

N

Me

N Me

Me

104a H2O/MgO Me

Me N *

N

-H2O

Me

ClO4 Me

Me

106(S)

Me ClO4

H2N

105(S) Scheme 24.

O

N *

794

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

}tze104 in 1938 synthesized some unSubsequently, Go symmetrical chiral monomethine cyanine dyes (107aec) with thiazolyl and quinolyl end groups, using 1-phenyl-ethylamine as a monochiral starting material (Scheme 25).105 Reichardt106 tried to synthesize a sterically hindered, possibly nonplanar trimethine cyanine dye (109) with indolyl end groups from (108). However, a careful analysis of its 1H NMR spectrum and a single-

Me

Me N

*

Me

Me

*

N

Br

CH

HC CH CH CH

104

Me

Me N *

Me

Me

Me

Br

N *

N * Me

N * Me

Me

104a: (S,S)

Me

Me N *

Me

Me

Me

Br

N *

N * Me

N * Me

Me

104b: (S,R) or meso form A reaction scheme has also been proposed to synthesize the monochiral (þ)-(S)-pentamethinium cyanine dye (106) from (105) with only one chiral center (Scheme 24).102,103

NH2 Ac2O in benzene CH -Ac2OH Ph * Me

Ph Me CH N

crystal X-ray determination showed the condensation product was to be (110) (with a stereogenic center) instead of the symmetrical dye (109) (Scheme 26). The formation of (110) was attributed to the ethyl

O

S

HN C Me

HN C Me

Lawesson's

CH Ph * Me

I

Me

MeCOCH2Cl, -H2O

CH Ph * Me

reagent

HClO4, -HCl

I

N

S Me

Me

ClO4

N

Me

N

S

CH

in PrOH/Et3NH

Me

Ph

ClO4 Me

107:a: (-)-(R)-; b: (+)-(S)-; c: ( )-[(R)+(S)] Scheme 25.

Me Me

Me Me CH2Me

N Me

HC(OEt)3 BF4

Me BF4

N

N

Me Me 2

Me

Me Me

109

115 oC in pyridine Me CH Me Me 2

108

N

N

Me Me

Me

110 Scheme 26.

Me BF4

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

This shows that replacement of one of the methyl groups at C-3 of the indolyl group by sec-butyl has only a small influence on the UVevis absorption maxima of these dyes. Earlier, the synthesis of chiral polymethine dyes required costly separation of diastereoisomeric salts (e.g., 3-bromocamphor-8-

group at C-2 changing its position with one of the methyl groups at C3. A twofold anionotropic WagnereMeerwein 1,2-alkyl rearrangement, starting from (108), leads via an intermediate eventually to an isochiral (racemic) mixture of the iminium salts (111a and 111b) presented as (111c) (Scheme 27).107,108

Me

Me

Me

2

Me

Me

Et

Et

N

N

Me

795

Me Me

BF4

Me

Me

Et

N

Et

BF4 N Me

Me

108 2 BF4 Et

Me

N

N

Me

o 150 C

N Me

Me

Me

Et

pyridine

Me BF4

BF4 +

Me

Me

Me

Et

111b: (-)-(S)

111a: (+)-(R)

Scheme 27.

sulfonates)103,111 into enantiomers. In order to avoid this problem, several attempts have been made to find natural monochiral compounds with a known absolute configuration at their stereogenic centers with 1,2,3,4-tetrahydroquinoline rings. Wolf et al.112

The isochiral salt (111c) possesses a new stereogenic center at C3 of the indolinium ring, producing a symmetrical chiral trimethinium cyanine dye (115) through the intermediacy of (112), (113), and (114) (Scheme 28). Me

Me

Et

Et

NaOH

2

CH3 N

2

BF4

NaBF4 H2O

Me

111c Me

CH2 N Me 112 (+)-[(R)+(S)] -

Me

Et

2

2

DBHT

N Me

Et CH3

N Me

2 HBF4

CH3

from ethanol and acetone

DBHT

N

-2 DBHT

Me

113: (+)-[(R)+(S)] -

2

Et

fractional- cryst

CH3

Me

DBHT

114:(S) Me

HC(OEt)3 in pyridine BF4 -3 EtOH -HBF4

111b: (-)-(S)

Et Et

Me

N

N

Me

Me

BF4

115:(+)-(S,S)-

(DBHT = di-O-benzoyl hydrogen tartrate) Scheme 28. 109

synthesized a monochiral heterocyclic imiReichardt et al. nium salt, (þ)-(3R,15S)-1,2,3-trimethylindolinium tetrafluoroborate (116), in an eight-step reaction sequence starting from natural monochiral ()-(2S)-2-methyl-1-butanol (generated by alcoholic fermentation), as given in Scheme 29. Iminium salt 116 can be finally used to prepare some chiral polymethine cyanines (117e119), the absolute configuration of which at the indoline C-3 and stereocentre at C-15 was confirmed by means of a single-crystal X-ray analysis. In spite of the fact that the stereocentres in all the di- and trinuclear dyes are not directly part of the light-absorbing system, these contribute to large specific rotations. The absorption wavelengths of (117) and (118) in acetonitrile, lmax¼546 and 642 nm, respectively, are nearly the same as those of the corresponding trimethinium (553 nm) and pentamethinium (636 nm) cyanine dyes in methanol,110 with only two monochiral 1,2,3-trimethylindolyl end groups.

have found an entirely different access to chiral pentamethinium cyanine dyes (120) using monochiral ephedrine as the chiral starting material (Scheme 30). Chemoselective reduction of the pyridine moiety of cinchona alkaloids, such as quinidine (121) and quinine (123), or their 10,11-dihydro derivatives, leads to the corresponding 10,20 ,30 ,40 ,10,11-hexahydro derivatives (122 and 124, respectively), which are used for the preparation of new chiral polymethine dyes113 (Scheme 31). In the 1H NMR spectrum of (124) (mixture of diastereomers), two multiplets occur at d¼3.57e3.67 and 3.99e4.02 ppm for 9-H, whereas pure 124a and 124b show only one multiplet at d¼3.60 and 4.07 ppm, respectively, for the same 9-H. From the complete absence of the other 9-H signal, the diastereomeric ratio was estimated to be in excess of 99:1 in both cases.

796

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

H

H H

H

N OH 9 H OH

9

N OH H OH

HN

HN

OMe

OMe o

M.P = 42 C, [

D=

o

+76

M.P = 55 C, [

(+)-(3R,4S,4’R*,8S,9R)-hexahydroquinine

D=

(-)-(3R,4S,4’S*,8S,9R)-hexahydroquinine

124a

*

124b

PH3 in pyridine

OH

-28

*

(-)-(2S) i) PhNHNH2, NH3

*

Mg2 in Et2O

Br

MeCHO H2O

(+)-(2S) 52%

*

Na2Cr2O7

*

OH in H2SO4/H2O

*

O (+)-(4S) 85%

(2R,4S) and (2S,4R)

* *

i) MeI in MeOH, HI

ii) heat in xylene with zeolite

*

Me N

ii) NaOH/H2O, -HI

H

iii) (-)-(2R,3S) -DBHT 86%

Me

DBHT

N Me

116 (3R,15S)

+ CH2(CH(OMe)2I2

*

3 EtOH,- HBF4

Me BF4 N

Me

i) NaOH

* *

DBHT

* N

ii) HBF4

Me (+)-(3R,15S) 116

*

*

4-fold cryst from ethanol

*

Me (3S,15R) HC(HC=O)3 in Ac2O/NaOAc -H2O, -HBF4

* BF4

N Me

HC(OEt)3 in pyridine 2EtOH,-HBF4

(3R,15S,3'R,15'S 25% blue metallic cryst

118

Me

*

N

*

*

N

* *

*

*

(BF4)2

Me Me

*

N

BF4

N

*

Me

117 (3R,15S,3'R,15 S)

*

119 (3R,15S,3'R,15'S,3"R,15"S)

61% red crystal

34% Scheme 29.

O C

Me

2

H HC(OEt)3

Me

O

O

HClO4

ClO4

-EtOH -H2O

(i) (1R,2S)-ephedrine, -EtOH

H

Me

Me Me Me N Ph Me

Et2N

(ii) Et2NH, -EtOH

ClO4 Me

Me

120 (+)-(R,S) Scheme 30.

Therefore, both diastereomerically pure hexahydroquinines were used for the synthesis of chiral polymethine dyes (125e127) (Scheme 32). However, attempts have been made to separate the hexahydroquinidine (124) into the corresponding pair of diastereomers with bare success. The 1H NMR coupling constants of the methine hydrogens 13-H/14-H (J¼11.7 Hz) and 14-H/15-H (J¼12.6 Hz) confirm the all (E)-configuration along the polymethine chain of (127) in DMSO solution. Recent studies on chiral polymethine dyes include experimental and theoretical studies regarding their spectroscopic response toward protons and various metal ions,114 and their diastereoselective supramolecular ion pairing with (tris(tetrachlorobenzenediolato) phosphate) anions to evaluate the presence of chirality in the dye molecules.115

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

OMe

H

797

OMe

H

3 H2/Ni in EtOH H OH

H OH N

N

i) 55 bar, rt. 4 h

4' 3'

OH H H ii) 70 bar, 70 oC, 24 h. HN 2' (+)-[3R,4S,(4'R+4''S),8R,9S]-hexahydroquinidine (+)-(3R,4S,8R,9S)-quinidine N 1'

122

121 10 11 7 3' 2'

10 3 H

2 4

11 7

5

N 6 8 1 9 OH 4' H

N 1' 8' 7'

5

N 6 8 1 3' OH 9 4' 2' H H HN 5' 1'

3H2/Ni in EtOH i) 55 bar, 70oC, 24 h

5'

3 H 2 4

ii) 70 bar, 70o C, 24 h.

8'

6' OMe 7' (+)-[3R,4S,(4,R+4,S)8S,9R]-hexahydroquinine

6' OMe

(+)-(3R,4S,8S,9R)-quinine

124

123 Scheme 31.

2

Et2O

Br CN NH Me

N Me

-NC-, -NH2

N

NaOH in MeOH/H2O -PhNHCH

N Me

Br

124a,b in HBF/Br2O/EtOH O Na

O

-2H2O, NaBF4 H NH H H

H

NH

H

H OH

N

N

H

MeO

(BF4)3

OMe

125: (-)-(3R,4S,4’R*,8S,9R) 126: (+)-(3R,4S,4’R*,8S,9R) 127: (-)-[3R,4S,(4’R*+4’S),8S,9R] Scheme 32.

2.3. Syntheses of squaryl polymethine dyes Squarines are analogues of cyanines with respect to their strong electron-donating and -accepting groups present at the two termini of a p-conjugated system. The squaryl polymethine dyes possess a cyclobutene core in the middle of the conjugated systems.116 Their electronic structures are quite interesting from the scientific and technological viewpoints. In contrast to conventional polymethines, and oxygen-based squarines, ring-substituted squarines can be excited not only with red lasers, but also with blue lasers or light-emitting diodes. Due to their favorable spectral

and photophysical properties, these dyes are useful for fluorescence lifetime-based biomedical applications. Squarines are among the promising classes of dyes that can be utilized to synthesize probes and labels for the red and nearinfrared (NIR) spectral region.117e119 Their unique photochemical and photophysical properties120 make them useful in a variety of applications, such as in copiers,121 solar cells,122 optical discs,123 and sensors.124 The general tendency of the dyes to form aggregates in the solid state and within heterogeneous environments present in most of the above-mentioned applications results in drastic changes in their absorption and photophysical properties.125e128

798

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

O

O

DDQ ,THF HO

O

O

O2N

NO2

79%

O

O2N NO2

78%, pip

O

Sn, HCl

C5H11

O

H2N

90% O

131

N

C5H11

C5H11

O

132

C5H11

O

OH

N C5H11

38%

C5H11

32%

NH2

O

N

n-C5H11Br, K2CO3

NaBH4, Pd(PPh3)4, THF

O

130

129

128

N C5H11

C5H11

O

HO

OH

OH

n-butanol, THF 4.5%

133 OC5H11

HO

OH

N C5H11

N C5H11

C5H11

N

2+ C5H11

C5H11 C5H11 N

HO

OH O

H11C5

-

134 Scheme 33. 129

Petermann et al. reported the synthesis of two squarine dyes (134 and 141), starting from an aromatic alcohol (128) and an aminophenol (135). The preparation of 134 (Scheme 33) requires the

NH2

oxidation of 128 with DDQ, affording an aldehyde (129), which on condensation with 3,5-dinitrotoluene gives a dinitro stilbene (130). The compound (130) on reduction gives a diamino stilbene (131). N(C7H15)2

N(C7H15)2 POCl3, DMF

n-C7H15Br, K2CO3

OC7H15

60%

OH

OC7H15

135

H

136

O

137

O NaH, DMF 64% O P EtO OEt

O

138 (C7H15)2N

(C7H15)2N

OC7H15 OH

89%

O

139

OH

n-butanol, toluene 0.3% HO

(C7H15)2N

O

NaBH4, Pd(PPh)3,THF

140 O

OC7H15

OH

OC7H15 OH O

OH

+ 2 OH

O-

HO

141 Scheme 34.

C7H15O

N(C7H15)2

O

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

Alkylation of (131) to (132) followed by deprotection yields an unstable diol (133), which is condensed with squaric acid to yield (134). The dye (141) was synthesized from m-nitrophenol (135), which on alkylation produced (136), followed by a Vilsmeier reaction to afford (137). A Horner reaction of the resulting aldehyde (137) with the phosphonate (138) produced the stilbene (139). The selective deprotection (alkoxy vs allyloxy) of (138) was effected with NaBH4/ Pd(PPh3) resulting in the formation of an unstable diol (140), which on condensation with squaric acid afforded the dye (141) (Scheme 34).

The dyes (134) and (141) in solution displayed absorption maxima located above 900 nm. The absorption spectra of spincoated films showed red-shifted absorption bands belonging to J-like aggregates. The nonlinear optical measurements of one dye indicated that this type of colorant was potentially useful for application in optical switches operating in the infrared region. Tatarets et al.130 reported the synthesis of some water-soluble, ring-substituted squarines, which can be used as labels for

O

Me

O

O N R1

OBu Me

SO 3

NEt 3 CN

O

143b, d

143a

Me

143b

Me (CH2)3CHOOEt

144a

.....

144b

.....

X

Me

R2 ......

(CH2)3CHOOEt

143d

144a, b

Me

Me

Me SO 3

HNEt 3

O

1 R Me

142d

BuOH/toluene

144a

R2

Me

N R1

142a

N

pyridine

NC Me

S Na

143a

Me

CN

NC

Me

NaSH ethanol

142a, d

O

Me

Me

N R1

799

N R1

145

O

N R2

Na

.....

145

X

R1

.....

a

S

Me

.....

b

C(CN2) Me

(CH2)5CHOOH

.....

c

O

Me

(CH2)5CHOOH

d

C(CN2)

(CH2)3CHOOH

Et

(CH2)5CHOOH

R2 (CH2)5CHOOH

Et Scheme 35.

COOH Me

Me

O3S

O

X

2 R

1 R

N

SQ

X

Me Me

O3S

N

K N

BuOH/toluene or pyridine

2 R

K SO3

Me Me

O HOOC

144a

146

TSTU DIPEA

R1 R2 - + - + a O S Na S Na b C(CN) 2OBu O HNEt 3 SQ X

c

O

O O C O N

Me

O3S 146, 147 X a b c

S C(CN) 2 O

O

X

Me

OH OH

N

K N O

O

N O C O O Scheme 36.

K SO3

Me

147a-c

Me

800

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

Me

NH2 MeI, MeCN

N

Me

O

OH

O

OH

fluorescence-binding assays. Synthetic protocols for both unsymmetrical and symmetrical squarines have been described in Schemes 33 and 34. Unsymmetrical squarines were synthesized from (142aed), which can easily undergo substitution reactions with NaSH or CH-acids, such as malononitrile using triethylamine (TEA) as a base to produce (143aed). The ring-substituted compounds (142aed) were subsequently treated with a second indolenine (144a) to yield the unsymmetrical squarine dyes (145) (Scheme 35). Symmetrical squarines (146aec) are synthesized from (144a), which are converted into water-soluble esters (147aec) (Scheme 36). Another class of symmetrical and unsymmetrical anthracenebased squarines has been synthesized131 through the protocol shown in Scheme 37. On heating N,N-dimethyl-1-aminoanthracene and squaric acid at 120  C for 12 h in n-butanol/toluene, a symmetrical squarine (148) as a single product with an absorption maximum centered around 800 nm was formed. Condensation of 3-[4-(N,N-dialkylamino)anthracene]-4hydroxy-cyclobutene-1,2-diones with the appropriate dialkylanilines afforded unsymmetrical squarines (149 and 150).

+

reflux, 30 h Me

N

Me toluene/n-butanol reflux, 12 h

2+

O

Me

N

O

Me

148 Scheme 37.

O

Br-Ar-Br or I-Ar-I

OiPr

OiPr

O cat. Pd(PPh ) O SnBu3 CuI/MeCN3or4 toluene reflux 151

OH

OiPr Ar

HClaq

O

O

Ar

THF, rt O

OH

O

O

O

153a-e

152a-e O

OAr NI Bu

N Bu

O

N Bu

O

154a-e

S

S

NI N Bu 1-butanol, benzene Bu (4/1 v/v)

153a-c +

S

Ar O

N Bu

O

155a-c _

quinoline or NEt3 reflux

O

O

O

O

O

_

O

O Ar

N Bu

NI Bu

O

N Bu

O

156b and 156d O N Bu

N I Bu

_

O

_

Ar O

O

N Bu

157c and 157d

a

b

c

d

e

Ar

N Bu

Scheme 38.

O

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

-

O

n-Bu

N

+ N

HO

Me + Me N

-

O

Me

n-Bu

N

where they can be used for imaging hydrophobic domains, such as cell membranes. Some bis-squarylium dyes bearing arene and thiophene spacers were found to exhibit large and intense electronic absorptions ranging from the visible to the near-infrared region, and some of them were fluorescent emissive.132 Stille-type Pd-catalyzed crosscoupling reactions of diiodo- or dibromoarenes with tributylstannylsquarate (151) afforded the bis-squarates (152aee) from the corresponding dihalogenated arenes, which were subsequently hydrolyzed under acidic conditions to afford the bis-squaric acids (153aee).133 These bis-squaric acids were converted into the bissquarylium dyes by reaction with a series of heterocyclic methyl quaternary salts, such as N-butyl-2,3,3-trimethylindolium, Nbutylbenzothiazolium, N-butylbenzoxazolium, and N-butylbenzoindolium. Under azeotropic conditions, the arene-bridged bissquarylium dyes (154aee and 157ced) were obtained (Scheme 38). The Pd-catalyzed cross-coupling reaction of some dibrominated thiophene derivatives, such as 2,5-dibromothiophene, 5,50 dibromo-2,20 -bithiophene, and 5,50 -dibromo-2,20 :50 ,20 -terthio-

OH

O

O

Me

150

149

The water compatibility and substantial enhancement of the fluorescence of (150) in micellar media suggest that these dyes can be potentially useful as fluorescent probes in biological applications

O

OiPr

O

SnBu

OiPr

OH

OiPr

HClaq

Br-Ar-Br O 3

151

Ar

O

O

OH Ar

O

THF, rt

cat. Pd(PPh3)4 CuI/MeCN or toluene reflux

O

O

O

O

158a-d

159a-d O

O

-

Ar

N Bu

NI Bu

O

N Bu

O

160a-d butanol /benzene (4/1 v/v)

S

159a-d +

801

NI Bu

S N Bu

quinoline reflux

O

O

S

Ar O

N Bu

O

161a-c

O N Bu I

N Bu

_

O

_

Ar O

N Bu

O

162a

a

b

Ar

c S

S

d S

S

S

S

S

S

S

Scheme 39.

OH O3S

KO3S

HO

R-X N R

N

163

O O

164a-f

O

-

O3S

N

N R

OH

165a-f

a: R = p-CH2C6H4COOH b: R = (CH2)5COOH c: R=C2H5 d: R = CH2C6H5

e: R = p-CH2C6H4Me f: R = p-CH2C6H4F Scheme 40.

SO3H

R

802

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

phene with tributylstannylsquarate (151) afforded the bissquarates (158aed), which were converted by acid hydrolysis into the bis-squaric acids (159aed). The reaction of these bis-squaric acids with 1-butyl-2,3,3-trimethylindolium iodide and 1butylbenzothiazolium iodide under azeotropic conditions in 1butanol/benzene afforded the thiophene-, bithiophene-, and terthiophene-bridged bis-squarylium dyes (160aed) and (161aed). For the monothiophene-bridged dye, the benzindolino derivative (162) was also synthesized (Scheme 39). Some water-soluble, squarylium indocyanine dyes with various N-substituents on 3H-indolenine (165aef) were synthesized134 using a protocol involving condensation of the potassium salt of 2,3,3-trimethylindoleninium-5-sulfonate (163) and 1-(bromomethyl)benzene to produce intermediates (164aef), which were further condensed with squaric acid affording the dyes 165aef (Scheme 40). Renard et al.27 have reported the synthesis of some fluorinated squarine dyes, by a two-step condensation process. Initially the dibutyl ester of squaric acid (167) and either the methylated benzothiazole derivative (166a) or the corresponding fluorinated derivative 166b, were condensed to obtain hemisquarines (169a or 169b), which were then treated with benzothiazole nuclei involving an iodohexyl linker attached to the nitrogen atom [(170a) or (170b)], obtained by reaction of the benzothiazole or the fluorobenzothiazole with 1,6-diiodohexane, to give the squarines (171 or 172) in moderate yields. For the synthesis of squarine (173) involving a dicyanomethylene group on the squaric acid, the monobutyl ester of the dicyanomethyl squaric acid (168) was reacted with the methylated benzothiazole (166a) to give hemisquarine

(169c). The dicyanomethylated squarine (173) was then obtained by reaction of (169c) with the benzothiazole linker derivative (170a) (Scheme 41). For the fabrication of DSSCs based on nanoporous TiO2, some symmetrical squarine dyes 180e182 were synthesized by refluxing a mixture of the corresponding trimethylindolium iodide salts (175e177) obtained from (174a) and squaric acid in a ratio of 2:1 in HOOC

HOOC MeCN R1-I

N

N

174a O

R1

O

175 R1= C2H5 HO

ne ue tol / l no

OH uta n-b

N R1

180-182

Symmetrical squarine dyes Scheme 42.

N I

BuO

O

167

CN

NC b

a

BuO

O O HNEt3 168

OBu Y

S

X = H, Y = O, Z = OBu 169a (40%) O

N

X

Z

X = F, Y = O, Z = OBu 169b (80%) - + X = H, Y = C(CN)2 , Z = O HNEt 3 169c (50%)

S c

S X

N I (CH2)6I

X

Y I(H2C)6 I N

N

X = H 170a (45%) X = F 170b (45%)

X

S O

171 X = H, Y = O; 172 X = F, Y = O; 173 X = H, Y = C(CN)2 Synthesis of squarine dyes ( 171-173). Reagents and conditions: (a) EtOH, TEA, 650C, 90min; (b) EtOH, TEA, 650C, 60min; (c) butanol, toluene, 1200C, 10 h, or 1000 C, 8 h for X = H, Y = C(CN)2. Scheme 41.

177 R1= (CH2)3CF3

COOH O

X = H 166a (64%) X = F 166b (83%) O

176 R1= C4H9

O R1 N

HOOC

S X

I

M. Panigrahi et al. / Tetrahedron 68 (2012) 781e805

O

O

BuO

MeCN

OBu

OBu N

R2I

N

803

N

I

R2 O

EtOH/NEt 3

R2

174b

O

183, 184

178, 180 1. EtOH/NaOH 2. HCl R2

COOH

O

OH

n-butanol/toluene

N

N N O

R2 O

HOOC

O

R1 185, 186

187, 188

N

Unsymmetrical squarine dyes

I

R2

180: R1 = R2 = Et 181: R1 = R2 = Bu 182: R1 = R2 = (CH2)3-CF3 185: R1 = R2 = Et 186: R1 = Bu and R2 = (CH2)3-CF3 Scheme 43.

a 1-butanol/toluene mixture (1:1 v/v) for 18 h (Scheme 42).135 Unsymmetrical squarine dyes (187) and (188) were obtained by condensing the salts (178 and 179) prepared from (174b) with semisquarine esters through the intermediate formation and reactions of (183e186) (Scheme 43). By introduction of molecular asymmetry and increasing the alkyl chain length of the squarine sensitizers, the photovoltaic performance was found to be enhanced.

3. 4. 5. 6. 7. 8. 9.

3. Future prospects

10.

Due to flexibility in the structural artifact in cyanines, a wide variety of these dyes can be generated with novel molecular architectures. Consequently, new synthetic procedures will be inevitable, and these invented methods will open up new vistas in organic synthesis. This will lead to a more colorful world with many beautiful applications spanning from analytical chemistry to medicinal chemistry. Not only can these dyes trace a tumor cell and quantify it through its specific binding with the protein, but they can also clean up the tumor cell though photoemission.

11.

Acknowledgements

12. 13. 14. 15. 16. 17. 18. 19. 20.

B.K.M. thanks the University Grants Commission, New Delhi and the Department of Science and Technology, New Delhi for financial assistance through the DRS and FIST programmes, respectively. M.P. thanks the Council of Scientific and Industrial Research, New Delhi for a Senior Research Fellowship. References and notes 1. Mishra, A.; Behera, R. K.; Behera, P. K.; Mishra, B. K.; Behera, G. B. Chem. Rev. 2000, 100, 1973 and references therein. 2. D€ anhe, S. Z. Chemosphere 1965, 5, 441; D€ anhe, S.; Leupold, D. Ber. Bunsen-Ges. €nhe, S.; Moldenhauer, F. Prog. Phys. Org. Chem. Phys. Chem. 1966, 70, 618; Da € €nhe, S. Cyanine Dyes 1985, 15, 1; Danhe, S. Chimia 1991, 45, 288; Bach, G.; Da and Related Compounds. In Rodd’s Chemistry of Carbon Compounds

21. 22. 23. 24. 25. 26. 27. 28.

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Biographical sketch

Mallika Panigrehi was born in Khariar, India, on 15th October 1982. She received her M.Sc. (2004) and M.Phil. (2005) degrees from the Department of Chemistry, Sambalpur University, India. In 2006 she joined Regional Research Laboratory (RRL) Bhubaneswar as a research fellow to work on the isolation of natural products from ocean and their identification through different techniques. Subsequently she joined in Prof. B K Mishra’s Laboratory as a Senior Research Fellow (CSIR) in the Chemistry Department of Sambalpur University.

Dr. Sukalyan Dash was born in 1967, at Bargarh. He completed his M.Sc. in 1989, M.Phil. in 1991 and was awarded Ph.D. in 1996, under the guidance of Prof. Bijay K. Mishra, in Physical-Organic Chemistry from Sambalpur University. He served in Womens’ College, Bargarh, Anchal College, Padampur and is presently continuing his service in the University College of Engineering, Burla, as a Reader in Chemistry. His research interests focus on Surface Chemistry, Oxidation Kinetics and Organic Synthesis. He has been awarded Prof. R. C. Tripathy Young Scientist Award and Prof. Dayanidhi Pattnaik award for best paper of the year by the Orissa Chemical Society.

Dr. Sabita Patel was born in 1977, in Jamuna, Orissa, India. She received her M.Sc. degree (1999) and M.Phil. degree (2000) from Sambalpur University. After qualifying NET, she joined as a CSIR Fellow in the research school of Prof. B. K. Mishra for Ph.D. programme. She is the recipient of Prof. R. C. Tripathy Young Scientist Award (2005) and Prof. Dayanidhi Pattnaik best paper award (2006) from the Orissa Chemical Society. Her research area covers Organic Reaction Mechanism and Surface Chemistry. At present she is a Lecturer in Chemistry, NIT, Rourkela, Orissa, India.

Prof. B. K. Mishra was born in 1954 in Kuchinda, Orissa, India. He received M.Sc. (1975), Ph.D. (1981) and D.Sc. (2003) from Sambalpur University. His research interests focus on Organic Synthesis, Surface Chemistry, Reaction Mechanism, Correlation Analysis and Graph Theoretical applications in Chemistry. He was an INSA visiting scientist at IISc, Bangalore and a UGC Research awardee in ninth plan period. He has been awarded Samanta Chandra Sekhar Award-2006.