Photochemistry of hemicyanines Part VII. Photochemistry of 2,3-diaryl-1H-isoindolium salts

35

.I. Photochem. Photobiol. A: Chem., 73 (1993) 35-45

Photochemistry of hemicyanines Part VII. Photochemistry of 2,3-diary]-lH-isoindolium

salts

Jacek A. Soroka+, Irena W. Bogdafiska, Andrzej R. KoSmider and Krystyna B. Soroka Technical Universily, PL 71-065 Srczecin (Poland)

(Received July 20, 1992; accepted February 18, 1993)

Abstract l,l-Dimethyl-2,3-diary&lH-isoindolium salts undergo two-step phototransformation with the first step being photoreversible. The photoreaction, which is characteristic of the 3-azoniahexa-1,3,5-triene system, leads through a “dihydro” intermediate to 10,10-dimethyl-10H-isoindolo[3,2-flphenanthridinium salts, the first known derivatives of the new heteropolycyclic system. The primary product of phototransformation undergoes oxidation by three competitive routes or is stabilized by @elimination of a stable molecule (e.g. methanol). The direction of phototransformation is strongly dependent on the acidic-basic properties of the solvent.

2. Experimental details

1. Introduction The photocyclization of hexatriene derivatives is a very useful selective preparative method. A series of papers [l-6], supplemented by this work, have focused on the 3-azoniahexa-1,3,5-triene system which is a common reagent present in molecules of numerous different classes of compound. The photoreactivity of this system was reported for the first time by Van Binst et al. [7], Tymyanskii et al. [S] and independently by our group [9]. The presence of this system leads to photocyclization producing the 3,4-dihydropyridinium cation. Depending on the structure of the substrate and/or the solvent, the transformations of the latter system involve a sigmatropic hydrogen shift or a two-step process catalysed by weak bases [5]. Depending on the stereochemistry of the primary product further transformations do or do not occur [4] or oxidation takes place with the participation of singlet oxygen and a catalytic amount of base [5] leading to more stable heteropolycyclic compounds. As a continuation of studies on the photochemistry of derivatives of N-phenylpyridinium [4], 1-a#-3H-indolium [Z, 31, benzo[cJquinolizinium and pyrido[l,Z-flphenanthridinium cations [S], the derivatives of 2,3-diaryl-lH-isoindolium salts are the subject of the present investigation. +Author

to whom correspondence

lOlO-6030/93/$6.00

should be addressed.

2.1. Photochemical

investigations A gas-tight quartz spectrophotometric cell with an optical width of 1 cm and a volume of 3 ml was used for the investigations. A high-pressure mercury arc lamp (VP60) with or without a Wood filter, an HQE 40 mercury lamp in a glass jacket and a halogen lamp with a set of glass filters were used as light sources. Some experiments were performed using a pulse xenon lamp supplemented by a set of glass filters (A>290 nm). 2,2. Photochemical reactions A tube reactor {volume, 185 ml; Pyrex glass; A> 290 nm) with convective recirculation of solution, equipped with a gas inlet for operation in the chosen gas atmosphere (argon or air), was used for preparative purposes. A high-pressure mercury arc lamp (LRF 250 VA, POLAM, PoIand), equipped with an elliptical aluminium reflector, was used as an external light source. 2.3. Spectra and analysis The UV-visible spectra were recorded on Specord UV-VIS and Specord M40 spectrophotometers (Carl Zeiss, Jena, Germany). The proton nuclear magnetic resonance (‘H NMR) spectra were measured using Tesla BS 487C (80 MHz) and Bruker (300 MHz) spectrometers. CF,COOH, CF,COOD, CD,CN and CDCIB were used as solvents and tetramethylsilane (TMS) was used as internal standard.

B 1993 - Elsevier

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I. A. Soroka et al. I Photochemistry of 2,3-diaryl-lH-isoindolium salts

36

The electron spin resonance (ESR) experiments were performed using an SEX 204 spectrometer (Radiopan, Poland) with a spin sensitivity of 1011 and a frequency of 9.303 GHz. The purity of the products was checked using ‘H NMR and thin layer chromatography (TLC) (Merck, Kieselgel Alufolien 60 F2.54, n-pro:?l-butan-2-one-acetic acid (1:2:2, v/v)) meth-

2.4, Syntheses 2.4.1. 2-Aryl-3,3-dimethyiphthalimidines (3a and 3b) A mixture of the chosen aniline (OS mol), the hydrochloride (0.5 mol) and 3,3_dimethylphthalide (2) (0.25 mol) was refluxed for 3-8 h using a short, wide air condenser. The sublimated product formed was periodically removed from the condenser. The crude reaction mixture was dissolved in 50-100 ml of boiling methanol and left to crystallize. The crude product (3) was recrystallized from methanol or benzene (yield, 60%-70%). The characteristics of these products are described in Table 1 (see Section 3).

peared from the solution and no changes in the UV-visible spectra were observed. The irradiation generally lasted l-3 h. The excess solvent was evaporated and the concentrated solution (30 ml) of product 7 was left to crystallize. The product formed was filtered off and recrystallized from a small volume of hot acetonitrile (yield, approximately 95%). The characteristics of the products are given in Section 3.

3. Results

and discussion

The general structure is presented below.

of the compounds

studied

H

H

H

H

CII,

H

H

H

” ”

H

H

C”,

H

H

H

H

H

CHJ

H

H

H

cm3

H

H

H

w

n

OcHl

H

H

H

”

”

OCH3

(II 2.4.2. 2, I-Dialyl-1, I-dimethyi-lH-isoindolium (la-&) In a250 ml flask equipped with a stirrer, dropping funnel, thermometer and an inert gas inlet (argon), 10 ml of a 1.6 M solution of butyl-lithium in hexane was introduced. A solution of 0.014 mol of chosen arylbromide dissolved in 25 ml of diethyl ether was then added dropwise at 20 “C. To this solution of aryl-lithium, a solution of chosen phthalimidine (3) (0.01 mol) dissolved in 100 ml of benzene was added, and the reaction mixture was stirred under reflux for 2 h. Finally, 100 ml of water was added. The separated organic layer was dried using magnesium sulphate, and the solvents were evaporated under reduced pressure. The residual oil was dissolved in 7 ml of acetic acid and 0.7 ml of 72% perchloric acid was added. The solution of crude product was left to crystallize in a refrigerator and was recrystallized from a small volume of hot acetonitrile (yield, approximately 30%). The characteristics of the products are given in Table 1 (see Section 3). perchlorates

2.4.3. lU,IO-Dimethyl-IOH-koindolo[3,2-f]phenanthtidinium perchlorates (7a-7g) The corresponding isoindolium derivative (I) (300 mg) dissolved in 185 ml of methanol was irradiated in a tube reactor (see Section 2.1) with air bubbling (40 ml rnin-l). The irradiation was stopped when the starting compound had disap-

The synthesis of the lH-isoindolium derivatives (1) involved the transformation of 3,3-dimethylphthalide (2) into related 2-aryl-3,3-dimethylphthalimidines (3), according to the procedure described by Pavlova and Yakovlev [lo] with some improvements 111-141; this was followed by reaction with the chosen aryhnetallic compound and finally acidification of the intermediate carbinol derivatives (Scheme 1).

(II

Scheme 1.

The characteristics of the synthesized phthalimidines (3) and l,l-dimethyl-2,3-diaryl-lH-isoindolium salts (1) are presented in Table 1. For compounds la-le the course of the reaction performed in acidic methanol or pure acetonitrile

J. A. Soroka~ et ul. I Photo&hen&y

TABLE 1. Characteristics (3a and 3b) Compound (melting point, “C)

of 2,Pd~ryl-lH-irakdolium

of the 2,3-diaryl-l,l-dimethyl-lH-isoindolium

perchlorate

(la-lg)

salts

37

and 2-aryl-3,3-dimethylphthalimidines

UV-visible ; (loo0 cm-‘) log l (MeCN, 298 K)

‘H NMR, 6 @pm), J (Hz) (solvent, frequency)

Maximum: Minimum: Shoulder:

34.16j4.24 41.50/3.28 43.30/3.68

1.792 (s. 6H, l-Mea) 7.X-7.85 (m, lOH, H2’-6’, 7.85-8.06, (m, 4H, H4-7) (CD&N, 80 MHz)

Maximum: Minimum: Shoulder:

34.1Okl.30 41.32/3.30 43.30/X87

1.792 (s, 2.330 (s, 7.10-7.79 7.87-8.10 (CD&N,

Maximum: Minimum: Shoulder:

34.00/4.26 41.70/3.31 44.201’382

1.791 (s, 6H, l-Me,) 2.306 (s, 3H, 3”-Me) 7.25-7.80 (m. 9N, H2’6’, 7.8CW3.07 (m, 4H, H4-7) (CD&N, 80 MHz)

4”-6”)

Maximum: Minimum: Shoulder:

33.50/4.17 41.00/3.45 440013.88

1.774 (s, 2.374 (s, 7.19-7.79 7.80-8.07 (CD&N,

6H, 1-Mez) 3H, 4”-Me) (m, 9H, H2’-6’, (m, 4H, H47) 80 MHz)

2”, 3”, 5”, 6”)

Maximum: Minimum: Shoulder:

34.20/4.21 41.60/3.45 X20/3.32 38.10/X87

1.805 (s, 3.680 (s, 7.07-7.79 7.W.06 (CD&N,

6H, l-Mea) 3H, 3”-OMe) (m, 9H, H2’-5, (m, 4H, H47) 80 MHz)

2”, 4”-6”)

W22C~05 (427.89) C (%): 64.56

Maximum:

(64.6) 5.18 (5.2)

Minimum: Shoulder:

29.CW3.98 34.5tY4.01 44.10/4.08 30.W3.87 40.50/3.54 39.20/3.60

1.794 (s, 3.811 (s, 7.024 (d, 7.374 (d, 7.34-7.76 7.76-8.04 (CD&N,

6H, l-Me3 3H, 4’-OMe) J=9. 2H, H3”, 5”) I=9, 2H, H2”, 6”) (m, 5H, H2’-6’) (m, 4H, H4-7) 80 MHz)

CuH,CINO, (427.89) C (%): 64.56

Maximum: Minimum: Shoulder:

34.60t4.16 41.90/3.33 28.10/3.42

1.724 (s, 1.836 (s, 3.636 (s, 6.97-7.16 7.20-7.84 7.84-8.05 (CD&N,

3H, l-Me) 3H, l-Me) 3H, 2”-0Me) (m, lH, H3”) (m, SH, H2’-6’, (m, 49 H4-7) 80 MHz)

1.499 (s, 7.167.71 7.89-7.90 (CD&,

6H, 3-Me,) (m, 8H, H4-6. (m, lH, H7) 80 MHZ)

Molecular formula (molecular weight) Elemental analysis: calculated (found)

;3801-302)

C&H&lNO., (397.84) C (%): 66.42 (66.5) H (%): 5.07

2”-6”)

(5.2) :z44.5-215.5)

C&H,ClNO., (411.89) C (%): 67.07 (67.0) H (%): 5.38

6H, l-Me,) 3H, 3’-Me) (m, 9H, HZ’, 4’-6’, 2”-6”) (m, 4H, H4-7) 80 MHz)

(5.5) ;;69-*70)

;;3&237)

C&H&NO., (411.89) c (%): 67.07 (67.1) H (%): 5.38 (5.5) GH,ChW (411.89) C (%): 67.07 (67.0) H (%): 5.38 (5.4)

;;2cc221)

‘&H,ClNOs (427.89) C (%): 64.56 (64.6) H (%): 5.18 (5.3)

;f9-5-l”)

H (%):

$2>225)

H (%):

&3-194)

(64.7) 5.18 (5.1)

C&isNO (237.30) c (%): 80.98 (81.1) H (a): 6.37 (6.5)

Maximum:

Minimum:

36.00/3.50 40.60/3.85 44.80/4.06 36.2OJ3.50 41.80/3.83 44.00/4.06

H4”-5”)

H2’6’)

L A. Soroka et al. r Photochenkhy of 2,3-diaryl-IH-isoindoliumsalts

38 TABLE

1. (continued)

Compound (melting point, “C)

Molecular formula (molecular weight)

UV-visible D (1W cm-‘) log E (MeCN, 298 K)

‘H NMR, S (ppm), J (Hz) (solvent, frequency)

Maximum:

1.490 (s, 2.372 (s, 6.91-7.40 7.40-7.70 7.82-7.98 (CDClp,

Elemental analysis: calculated (found) 3b (157.5-157.8)

CtP1,NQ (251.33) C (%): 81.24 (81.3) H (%): 6.82 (7.0)

Two

signals due to non-coplanarity

36.00/3.52

40.83/3.85 Minimum:

Shoulder:

43.6514.06 36.23/3.51 41.70/3.x4 43.85/4.05

6H, 3-Me*) 3H, 3’-Me) (m, 4H, H2’, H4’-6’) (m, 3H, H4-6) (m, lH, H7) 80 MHz)

37.2OE5.67 38.2w3.75 45.32/4.10

of the molecule.

was very similar. A two-stage

process was observed, demonstrated by isosbestic points. Typical spectra for irradiated Id are presented in Fig. 1. Table 2 contains the isosbestic points characteristic of each of the two reaction stages: isoindolium salt (1) -primary product and primary product + final photoproduct. The reaction performed in neutral methanol or slightly basic acetonitrile (diazabicyclo[2.2.2]octane (DABCO) added) was a one-stage process. In none of the cases described above was the intermediate long-wave absorption observed (wavelength longer than that characteristic of the final photoproduct). The lack of long-wave absorption, which should be shown by the primary product of photocyclization (4), suggests the reaction mechanism shown in Scheme 2.

Fig. 1. Changes in the W-visible spectra of Id during irradiation in a methanolicsolution (c=8~lO~~mol I-‘,d= 1 cm) containing 0.12% of perchioric acid. An HQE 40 mercury arc lamp in a glass jacket was used as external light source (distance, 7.5 cm). (a) General picture of changes. (b) First stage of phototransformation. (c) Second stage of phototransformation. (d) Comparison of the absorption spectrum of Id after complete phototransformation with the spectrum of a pure crystalline photoproduct (7d). By subtraction of the two curves the absorption spectrum of the byproduct or intermediate was found. Scheme

2.

J. A. Son&a et al. I Photochem&y TABLE

2. Locations (1000 cm-‘)

of Z,3-diatyl-lH-~oindolium

salts

39

of isosbestic points for both stages of phototransformation

Compound

Solvent

stage I

Stage II

la

CH,OH + 0.04% HClO,

30.4 f 0.1 35.0f0.2

31.5 f 0.3 34.8+0.1

Ic

CH,OH+O.W%

30.5 f 0.1 35.1 f0.2

31.2fO.3 34.4 * 0.1

Id

CH,OH+ 0.04% HClO,

29.7rt0.1 34.9 *0.2

32.0 * 0.3 34.5zkO.l

CH,OH+ 0.12% HCIO,

29.7+0.1 35.6 f 0.2

32.8 zt 0.3 34.4fO.l

CH,OH+0.04%

31.0*0.1 34.5 *0.2

31.4 f 0.3

le

HCIO,

HCIO,

The observation that the characteristic absorption of the intermediate compounds 4a-4e does not appear in acidic medium leads to the conclusion that these compounds must undergo an instantaneous rearrangement, most probably an adiabatic [1,3]-sigmatropic hydrogen atom shift (as is shown in Scheme 2 for compound 5) or higher [1,5]-, [1,7]- or [1,9]-hydrogen atom shifts. Structure 6 is only one of the few which can be proposed. The spectral properties of the homocyclic analogues of these systems have been studied by different workers and are reviewed by Muszkat [15]. It has been proposed that the colour of these compounds is influenced by free radicals [16]. However, precise ESR investigations of compounds 4f and 4g (12-r-electron coloured intermediates) contradict this. Despite the high concentration of coloured intermediates (3 X10s4 mol l-‘, approximately 1014 molecules within the active part of the spectrometer (spin sensitivity, loll) no resonance signals were observed. Because the reaction stops after the first stage and does not proceed in the absence of light, we can conclude that, for the oxidation of compound 6 leading to the final product 7 (the IO,lO-dimethyl-lOH-isoindolo[3,2-flphenanthridinium salt (DIIP)), singlet oxygen is necessary. The requirement of singIet oxygen in similar systems has been noted previously [5]. A similar experiment (the oxidation of 2,2,6,6-tetramethylpiperidine-4-one (TEMPO) by singlet oxygen into the well-known 4-0x0-TEMPO free radical in the presence of la in acetonitrile solution} provides support for this conclusion. A distinct acceleration of the process caused by the presence of DABCO (or another Lewis base, e.g. methanol) indicates the parallel mechanism of rearrangement and oxidation, identical with that presented previously [S] (Scheme 3). In

the absence of a base the photo-oxidation process is about three orders of magnitude slower. Unfortunately, the attempts to isolate pure intermediate compound 6 failed due to its good solubility. Similar intermediate compounds, but less soluble, found during investigations of the photocyclization of l-(3,5-dimethoxyphenyl)-4,6-diphenyl-2-styryl-pyridinium perchlorate, were isolated (in 95% purity only} and identified by spectral, microanalytical and chemical methods [S].

(IO)

Scheme 3.

The structure of compound 7 was proven by instrumental methods. The part of the ‘H NMR 300 MHz spectrum of compound 7a covering the range of aromatic proton absorption is presented in Fig. 2. The elemental microanalysis data (C, H) and ‘H NMR data of the product 7 obtained from lc and le indicate that it is an equimolar mixture of possible isomers. This means that the photocyclization of both rotamers is equally possible, as is shown in Scheme 4.

1. A. Soroka et al. I Photochemirtty of 2,3-dia~l-lH-isoindolium salts

40

Fig. 2. Aromatic proton region in 300 MHz ‘H NMR spectrum of compound 7a. The single signal of two equivalent methyl groups is located at 2.3731 ppm. The detailed assignments of the chemical shifts and the relevant coupling constants arc collected in Table 3.

hv /

[I) c1s -

Scheme

rotanar

O2

-

substituted

(71

2

(7)

4 - .mbstItuted

.

4.

For methoxy derivatives, the separation of the two isomers 2-OMe-DIIP (7el) and 4-OMe-DIIP (7e2), despite the very similar retention indices, is possible by fractional crystallization. For reaction of compounds lb and lc (R’ or R3=CHs), the chromatographic separation of photoproducts 7b1, 7b2 and 7~1, 7~2 was not possible because the product had practically the same retention indices (in each of the two pairs). Moreover, they crystallized to form molecular complexes of stoichiometry 1:l. The NMR data for each isomer (four isomers: 2-Me-DIE’, 4-Me-DIIP, 5

Me-DIIP and 7-Me-DIIP) were deduced from two spectra only. The spectra were analysed by comparison with the spectral data of other purified derivatives (7a and 76). The UV-visible spectra obtained can be attributed to an equimolar mixture of the corresponding compounds. The phototransformation of If and lg differs significantly from that of the other salts. During irradiation, coloured intermediates are observed: a red one in the case of If (A,, = 490 nm, MeOH) and an orange one in the case of lg (A_=450 nm, MeOH). Because of their different reactivities, each will be described separately. During the irradiation of an acidic methanolic solution of lf, isosbestic points at 28 300 and 35 000 cm-’ were observed. The colour of the solution decreased slowly in the dark in aerobic conditions with a pseudo-first-order rate constant &,s= 1.4(2)X lop5 s-l (concentration, 2 X 10v5 mol 1-l; 0.3% HClO_, in MeOH) and was accompanied by distinct isosbestic points at 24 100 and 34 200 cm-‘. When a Wood glass filter was used during irradiation the newly formed absorption band was over three times more intense than the band obtained without use of the filter. A subsequent selective irradiation through a green filter (A=480 nm) caused photobleaching. Renewed irradiation using a Wood filter caused the repeated formation of the red colour. The same isosbestic points at 28 300 and 35 000 cm-’ were observed. In our opinion, this provides proof for the full photoreversibility of the first stage of the process. When DABCO was added to the photocoloured solution obtained from lf, the solution was quickly discoloured and an isosbestic point at 22 800 cm- ’ was observed (unfortunately, the short-wavelength part of the spectrum was not measured). This provides proof for the occurrence of a rearrangement similar to that described previously [6]. Further irradiation of the coloured acidic solution using the full spectrum of the mercury arc lamp led to the expected final product (71) and was accompanied by isosbestic points at the same wavelengths as in the dark process. This means that, in both cases, oxidation occurred, involving triplet oxygen in the dark process and singlet oxygen or the organic compound in its triplet excited electronic state in the photochemical process. This problem has not been studied further. The final product was formed instantaneously after DABCO was added to a solution of If in daylight. The coloured intermediates were not observed for solutions in pure methanol or acetonitrile containing traces of DABCO. In both

J. A. So&u TABLE

3. Characteristics

Compound (melting point, “C)

et al. / Photochemistry

of 2,3-diaryl-IH-isoinda[ium

of 10,10-dimethyl-10H-isoindolo[3,2-flphenanthridinium

Molecular formula (molecular weight)

(DIIP)

salts

perchlorates

41 (7a-7g)

W-visible G (1000 cm-‘) log E (MeCN, 298 K)

‘H NM& S (ppm), (solvent, frequency)

Maximum:

H-l, J(1, H-2, J(2, H-3, J(3, H-4, H-5, J(5, H-6, J(6, H-7, 1(7, H-8,

J (Hz)

Elemental analysis: calculated (found)

CUHmClNOa (395.85) C (%): H (%):

66.75 (66.8) 4.58 (4.6) Minimum:

Shoulder:

7b (324-325)

c;H&lNO, (409.87) C (%): 67.40 H (%):

(67.5) 4.92

Maximum:

38.70/4.41, 39.80/4.38, 41.40/4.42 25.7W3.97, 29.6013.84, 34.00/4.02, 37.6W4.27, 39.3or4.37, 40.20/4.38, 44.2IY4.07 27.8013.89, 35.70/4.31

25.56/4.00, 35.44r4.37,

38sW4.44, 41Jw4.43 Minimum:

(5.0)

Shoulder:

Molecular complex of S- and ‘I-methyl DIIP derivatives (StoichiometIy 1:l)

25.10/4.09, 26.3014.02, 32.40/4.11, 36.4Ot4.33,

29.96/3.81, 37.2Of4.29, 40. W4.38, 43.60/4.14 27.4Y3.90 32.W4.10, 36.45f4.33

9.505, dd 2) =8.3, J(1, 8.235, dd 3)=8.1, J(2, 8.430, ddd 4) = 8.4 9.087, dd 9.101, dd 6) =8.2, J(5, 8.230, ddd 7)=8-l, J(6, 8.102, ddd 8) =7.7 9.000, dd

3) =l.O 4)=0.9

7) = 1.2 8)=1.5

lo-Met, 2.373, s, 6H H-11, 7.985, dd J(11, 12)==8.0, J(11, 13)=0.8 H-12, 8.127, ddd J(12, 13)=7.4, J(12, 14)=1.0 H-13, 7.942, ddd J(13, 14)=8.6 H-14, 8.754, dd (CF,COOD, 300 MHz)

7hl: 5-Me-DIIP 2.36 (s, 6H, IO-Me,) 3.313 (s, 3H, 5-Me) 7.66-8.08 (m. 7H, H3, H6-8, 8.24 (t, J=8.5, lH, H2) 8.46 (m, lH, H8) 8.77-9.06 {m, IH, H14) 9.200 (d, J=8, lH, H4) 9.425 (d, J=8, lH, Hl)

11-13)

7b:2 7-Me-DIIP 2.36 (s, 6H. lo-MeJ 2.863 (s, 3H. 7-Me) 7.66-8.08 (m, 6H, I-U, H6, 8, 11-13) 8.24 (t, J=8.5, lH, H2) 8.913 (d, J==8, IH, H5) 8.46 (d, 5=8, lH, H5) 8.77-9.06 (m, 2H, H4, 14) 9.425 (d, 1=8, lH, Hl) (CF,COOH, 80 MHz)

J. A. Soroka et al. I Photochemishy of 2,3-dimyl-lfbisoindolium salts

42 TABLE

3. (continued)

Compound

Molecular

UVvisible

(melting point, ‘C)

formula (molecular weight)

log E (MeCN,

P (1000 cm-‘) 298 K)

‘H NMR 8 @pm), J (Hz) (solvent, frequtincy)

Elemental analysis: calculated (found)

;;49-295

)

r&H&IN04 (409.87) C (%): 67.40 (67.6) H (%): 4.92

Maximum:

24.70/3.99, 25.7X3.96, 31.90/4.13, 35.40/4.39, 38.8Of4.45, 40.9ot4.39

Minimum:

25.30/3.96, 27.1013.82, 33.70/4.02, 37&l/4.31, 40.1cY4.37, 43.w4.10 36.10/4.38

(5.0)

Shoulder: Molecular complex of Z- and 4-methyl DIIP derivatives (stoichiometry 1:l)

7d (302-304) (decomp.)

C&H,ClNO, (409.87) C (%): 67.40 (67.4) H (%): 4.92

7~2: 4-Me-DIIP 2.224 (s, 6H, lo-Me,) 3.174 (s, 3H, 4.Me) 7.69-8.25 (m, 7H, H2, H3, 6, 7, 11-13) 8.44-9.14 (m, 4H, H4, 5, 8, 14) 9.324 (dd, J1=8.5. J2=1.5, 3H, Hl) (CF,COOH, 80 MHz) Maximum:

(5.1)

Minimum:

Shoulder: 7el (2-OMe-DIIP) (288.5-289.5)

WzoClNQ (425.87) C (%): 64.87 H (%):

(64.9) 4.73

7~1: 2-Me-DIIP 2.224 (s, 6H, 10-Me,) 2.761 (s, 38, Z-Me) 7.69-8.25 (m, 6H, H3, 6, 7. 11-13) 8.44-9.14 (m, 4H, H4, 5, 8, 14) 9.161 (s, lH, Hl)

Maximum:

Minimum:

(4.9)

Shoulder:

25.30/4.05, 26.50/4.03, 28.10/3.95, 31.40/4.27, 35.20/4.37, 36.50/4.35, 37.00/4.49, 38.OOf4.46, 41.20/4.38 2.5.80/3.98, 27/X1/3.93, 29.3013.92, 33.9Ol4.01 35.7014.34, 36XV4.35, 40.20/4.31 43.80/4.10 32.30/4.22 23.3213.96, 28.8013.87, 37.4414.62, 40&l/4.26 26.32/3.55, 30.30/3.83, 39.80/4.20, 42.60/4.M 24.10/3.91, 32.6W4.09, 36.4Of4.54, 41.3w4.15

2.388 (s, 6H, lo-Mez) 2.900 (s, 3H, 3-Me) 7.81-8.31 (m, SH, H6, 7, 11-13) 8.119 (dd, J1=8.8, J2= 2, lH, H2) 8.700 (dd, J1=7.5, J2==2, lH, H14) 8.81-9.00 (m, lH, H8) 8.36-9.15 (m, lH, H5) 9.358 (d, /=8.8, lH, Hl) (CFjCOOH, 80 MHz) 2.211 (lo-Me,) 2.799 (3-Me) 9.300 (Hl) (CD&N, 80 MHz)

2.360 (s, 6H, lo-Me,) 4.270 (s, 3H, 2-OMe) 7.79-8.34 (m, 6H, H3, 6, 7. 11-13) 8.62-9.09 (m. 4H, H4, 5, 8. 14) 8.944 (d, J = 1, lH, Hl) (CF&OOH, 80 MHz) 2.18 (lo-Me,) 4.11 (Z-OMe) 8,82A (Hl) (CD&N, 80 MHz)

(conrinued)

J. A. Soroka et al. I Photochemistry of 2,3-diaryl-IH-isoindolium salts TABLE

43

3. (continued)

Compound (melting point, ‘C)

Molecular formula (molecular

W-visible V (1000 cm-‘) log E (MeCN, 298 K)

‘H NMR, S (ppm), J (Hz) (solvent, frequency)

Maximum:

23.8W3.85, 29.9214.17, 33.3614.34, 352814.39, 39.8014.34 26&l/3.58, 31.76i4.14, 34.3214.27, 37.6813.98, 42.W4.24 27.70/3.69, 30.60/4.16, 36.30/4.21, 42.W4.25

2.369 (s, 6H, IO-Me,) 4.350 (s, 3H, 4-OMe) 7.81X3.21 (m, 6H, H2, 6, 7, U-13) 8.225 (dd, J1=8.1, JZ=2.5, lH, H3) 8.62-9.09 (m, 3H, H5, 8, 14) 9.100 (dd, Jl=8.5, J2=1.3, lH, Hl)

27.50/4.24, 30.W4.25, 34.3514.34, 357014.26, 37.4014.44, 41.50/4.30 29.70/4.09, 31.10/4.06, 33X/4.23, 36.30/4.23, 40.30/4.18, 44.10/4.13 26.4W4.14, 31.7014.18, 38.4014.34, 42.4014.24

2.186 (s, 6H, lo-MeZ) 4.198 (s, 3H, 3-OMe) 7.81-8.15 (m, 4H, H6, 11-13) 7.686 (dd, Jl = 9. J2=2.2, lH, HZ) 8.286 (d, J=2.2, 1H. H4) 8.368.56 (m, lH, H7) 8X-8.71 (m, lH, H14) 8.77-8.81 (m, lH, H8) 9.011 (dd, J1=8, J2- 1.8, lH, H5) 9.300 (d, I=9.5, lH, Hl) (CD,CN, 80 MHz)

23.7613.85, 29.0414.22, 33.4814.25, 35.04/4.35, 39.32f4.35 26X/3.52, 32.04/3.99, 34.1214.20, 37x/4.01, 42.48/4.21 36.W4.16, 41.45f4.25

2.318 (s, 6H, lo-Me,) 4.274 (s, 3H, LOMe) 7.60 (d, /=8, lH, HZ) 7.75-9.19 (m, lOH, H3-8, (CF,COOH, 80 MHz)

weight) Elemental analysis: calculated (found) 7e2 (4-OMe-DIIP) (303-304)

&-,H,ClNO, (425.87) C (%): 64.87 H (%):

(64.9) 4.73 (4.9)

Minimum:

Shoulder:

If

~iflC~O5

(2975299.5)

(425.87) C (%): H (%):

Maximum:

64.87 (65.0) 4.73 (4.7)

Minimum:

Shoulder:

Iis (231-232)

GH&lN@ (425.87) C (%): 64.87 H (%):

Maximum:

(64.9) 4.73 (4.7)

Minimum:

Shoulder:

casesthe reaction was similar to a one-step process, despite the complex mechanism (Scheme 3) involving a series of very fast subprocesses, such as enamine (8) formation due to the attack of a weak base, singlet oxygen cycloaddition, protolysis of cycloperoxide 9 and, finally, p-elimination of hydrogen peroxide from hydroperoxide 10 [6].

(CF,COOH, 80 MHz) 2.18 (IO-Me,) 4.20 (4-OMe) 8.986 (HI) (CD@, 80 MHz)

11-14)

The data indicate that, in contrast with the phototransformations of compounds la-le, the exceptionally stable, red-coloured primary photoproduct 3-methoxy-4a, 4b-dihydro-IO,lO-dimethyl-isoindolo[2,3-flphenanthridinium cation (4f9 is formed. Due to the photoreversibility of the process we can conclude that compounds If

44

.I. A. Soroka et al. I Photochemistry of 2,3-diaryi-IFi-isoindolium subs

and 4f form a photochromic system. Unfortunately, because of the susceptibility to oxidation of 4f this system is not of interest from a practical point of view. In the case of the o&o-methoxy derivative (lg), despite some similarities with the former case, the phototransformation led surprisingly to two final products: the expected compound 7g and an unexpected compound without a methoxy group (7a). The relative yield of both photoproducts strongly depends on the basic-acidic character of the solvent used. In neutral or basic medium both isomers were formed in almost equal amounts, whereas in acidic medium compound 7a prevailed. The influence of the solvent properties on the yield of both photoproducts is presented in Table 4. The results may be explained, as in the case of compound le, by the equal chance of photocyclization of both rotamers, and by the photochemical reversibility of the first stage of the process. In the discussed case only one of the two primary photoproducts is the true “dihydro” compound and only this product reacts normally. The second product of photocyclization, 4a-methoxy-4b-hydro-10,10-dimethyl-lOH-isoindolo[3,2-fJphenanthridinium cation, may be transformed through p-elimination of methanol into 7a (Scheme 5).

Scheme

5.

TABLE 4. Yield of photoproducts of compound lg formed in methanol solutions containing various amounts of acid or base Acid/base

w/w (%)

Yield (%)

7g

7a 80 74 54 52_ 51

HCIOl HCIO.

0.20 0.04

None

_

20 26 46

DABCO DABCO

0.04 0.40

48 49

If the proposed mechanism is accepted, then, in addition to the effect of the solvent, the light wavelength used should also play a role. In fact, the use of a Wood filter, which inhibited the reverse reaction of the coloured intermediate, resulted in an increase (by about 5%) in the yield of 7g. A model study (Dreiding’s stereomodels) shows that compound 7g, due to steric hindrance, may occur in the form of two isomers, which differ in the direction of the methyl moiety of the methoxy group in relation to the molecular plane, which may be reflected in the optical activity. The results of a corresponding crystallographical study will be published [17].

4. Conclusions (1) 1,1-Dimethyl-2,3-diaryl-lH-isoindolium perchlorates, which include the photoactive system 3-azoniahexa-1,3,5-triene, undergo photocyclization forming the lOJO-dimethy14a,4b-dihydrolOH-isoindolo[3,2-flphenanthridinium salts. (2) For the 3-(2-methoxyphenyl) and 3-(4-methoxyphenyl) isoindolium derivatives the coloured photocyclization products formed are relatively stable in acidic solutions. (3) The coloured photocyclization products undergo photocycloreversion forming the starting isoindolium salts. (4) With the exception of the stable photoproducts mentioned above, the products of photocyclization transform rapidly into colourless isomers, most probably by a sigmatropic rearrangement based on the energy from the previous adiabatic process of photocyclization. (5) All products of photocyclization undergo oxidation, involving triplet oxygen (dark process, less effective) or singlet oxygen (photoprocess catalysed by weak bases, such as pure methanol or DABCO, more effective) or the triplet excited electronic state of the oxidized molecules. (6) For isoindolium salts with a methoxy substituent located at the site of ring closure, the photoproduct will be stabilized by p-elimination of methanol. (7) For asymmetrically substituted isoindolium compounds (ortho or para positions) both rotamers have an equal chance of photocyclization. (8) The presence of an acid in the medium inhibits the stabilization of the primary photoproduct by the elimination of perchloric acid and the formation of enamine. Due to the reversibility of the process the presence of an acid influences

1. A. Soroka et al. I PhotochemistT

the yield and composition of the products, which is spectacularly illustrated for the o&o-methoxy derivative. (9) For asymmetrically substituted methyl-isoindolium derivatives, an equimolar mixture of all possible isomers is formed during the photoprocess. The products crystallize in the form of molecular complexes of stoichiometry 1:l. (10) All the photoproducts described in this paper are the first examples of the previously lOH-isoindolo[3,2-flphenanthridinium unknown cation heteropolycyclic system.

Acknowledgments

The authors are indebted to Dr. Janusz A. Baran (Technical University) for his help in obtaining the ‘H NMR spectrum and for discussions and to Wojciech Jacobson (Technical University) for is help in the preparation of the manuscript. This work was supported by KBN research grant No. 2 1326 91 01.

of 2,3-diaryl-IH-isoindolium

salts

45

References 1 K. B. Soroka, A. R. KoSmider and J. A. Soroka, IXfh Inf. CongzssofHeteroqxlic Chemtiq, Tokyo, 1983, Pharmaceutical Society of Japan, Tokyo, 1983, Book of Abstracts, F-135. K. B. Soroka and 5. A. Soroka, Tetrahedron L&t., 21 (1980) 4631-4632. K. B. Soroka and J. A. Soroka, Chem. SW., 29 (1989) 167-171. J. A. Soroka, Chem. Ser., 29 (1989) 361-365. J. A. Soroka, Chem. Ser., 29 (1989) 367-373. .I. A. Soroka, .I. Photochem. Photobiol. A: Chem., 64 (1992) 171-182. G. Van Binst, R. B. Baert and R. Salsmans, Synth. Commun., 3 (1973) 59-61. Y. R. Tymyanskii, M. I. Knyashanskii, Y. P. Andreychikov, G. E. Trukhan and G. N. Dorofeenko, Zh. 0~. Khim., 12 (1976) 1126. 9 K. B. Soroka and J. A. Soroka. Pr Nauk Inst. Chem. Ora Fir. Polifech. Wroclaw., I8 (Ser.‘Konf. 5) (1979) 14. 10 L. A. Pavlova and S. W. Yakovlev, Zh. Obsch. Khim., 33 (1963) 3377. 11 A. Fabtycy and A. KoSmider, Rocz. Chem., 48 (1974) 1069-1071. 12 W. Zitikowska, Most& Thesis, Technical University of Szczetin, 1964. 13 1. BogdaAska, Master’s Thesis, Technical University of Szczecin, 1969. 14 1. Skbrzewska, Master’s The& Technical Universitv of Szuetin, 1969. 15 K. A. Muszkat, Top. Curr. Chum., 88 (1980) 91-143. 16 M. I. Knyazhanskii, Y. R. Tymyanskii, V. M. Feigelman and A. R. Katritzky, Heteroqcles, 26 (1987) 2963-2982. 17 R. Anulewicz, J. A. Soroka and K. Wofniak, in preparation.