A new access to phosphaindolizines by [3+2] cycloaddition of azomethine ylides onto phosphaalkynes

0040.4039192

TetrahedronLetkrs, Vol. 33. No. 8, pp. 1049.1052, 1992 Printed in Great Britain

Pcrgmon

A NEW ACCESS TO PHOSPHAINDOLIZINES

BY [3+2]

CYCLOADDITION

$3.00 + .oo

Press plc

OF AZOMETHINE

YLIDES ONTO PHOSPHAALKYNES’

Uwe BergstrBOer, Andreas Hoffmann, Fachbereich

Chemie der Universitht

Kaiserslautern,

and Manfred

Regitz*

Erwin-Schr6dinger_Stasse,

D-6750 Kaiserslautern,

Federal Republic of Germany

Abstract: Azomethine ylides such as 1 and 4 in which the nitrogen atom is incorporated undergo regiospecific [3 + 21 cycloadditions

with the phosphaakynes

in a six-membered heterocyclic ring

2a and b at 130-l 40 “C to furnish the phosphaindolizines

3 and 5a-c after elimination of ethyl formate or hydrogen cyanide, respectively.

In contrast. dipoles of the type 6 react

unspecifically with the phosphaalkyne 2a to yield the regioisomers 7 and 8.

Phospholes

with a X3,&phosphorus

role in the development are a structural

component

cyclocondensation4, cycloadditions

and other heteroatoms

of the chemistry

of all the phosphaindolizines

by O/P exchange

of mesoionic

both the latter procedures, With the previously alkynes 2, we now describe

of low coordinated

in oxazolium

compounds elimination

unknown

in the ring system play an important

phosphorus213.

to be discussed

salts with tris[trimethylsilyl]phosphine5,

to phosphaalkyne@

applicable

synthesis

c’

‘COzEt

1’

1A +

t5u-C,P

t

CO,Et A!!

2a

-

and by [3+2] In

reaction.

of the title compounds.

le

N’

by

ylides of the types 1, 4, and 6 with phospha-

@ CJ H

which

or of nitrile ylides to phosphaalkenes7.

reactions follow the actual ring-forming reaction of azomethine

a new and generally

1,3-Azaphospholes,

here, have been prepared

toluene, 130-1LOOC (glass pressure tube) -HCO*Et

1050

When

the

cycloaddition8 elimination

pyridinium

reaction

ylide

1 is heated

with

takes place and is followed,

of ethyl formate

the

phosphaalkyne

under the harsh reaction

to furnish the [1,3]azaphospholo[l,5-alpyridine

2a, a regiospecific

[3+2]

conditions

by an

3 (30% yield). The 3rP-NMR

chemical shift (6 = + 162.4) as well as the 13C-NMR signals of the azaphosphole coupling

constants

ring and their respective

[A = 133.4 (‘JC p = 47.3 Hz, C3); 155.1 (‘JC P = 45.1 Hz, Cl);

C8a)] agree very well with the values for the independently

preiared

employed,

142.1 (*Jcp

methyl derivative

= 9.2 Hz,

(3; Me in place of

tBu)g. lsoquinolinium

and phthalazinium

phosphaalkynes

2a and 2b via [3+2]

which, however,

necessitates

are obtained

(4a and b, respectively)

methylides cycloaddition

the addition

and elimination

of triethylamine)

react

similarly

(in this case of hydrogen

and the condensed

1,3-azaphospholes

with the cyanide

5a-c

(2.540% yield).

8 +

6

R-C,P tube)

-HCN

2

These reactions reactions

1 + 2a=e

The constitution unequivocally

Fig. 1.

are also regiospecific

5

although

the dipole orientation

is the reverse

R

of that in the

3. of 5b - and thus the direction

by an X-ray structure

of addition

of 4b to 2a - has been confirmed

analysis (Fig. 1)‘O.

Crystal structure of the phosphaindolizine and bond angles [“I

5b. - Selected bond lengths [A]

1051

Bond lengths N2 -Nl 1.375(4)

P -c2 N2 -03 Cl 2 -Cl3 Nl -Cl3

c3 C7 P c3

1.754(3) 1.286(4) 1.431(5) 1.365(4)

Bond angles c13-P -c2 C3 -c2 -P C2 -C3 -Nl C31 -C3 -Nl c21 -c2 -P

-c31 -C6 -Cl3 -c2

1.419(5) 1.428(5) 1.734(4) 1.371(5)

C12-Cl3 Cl3-Ni Nl -Cl3 Cl3-Ni c31 -c3

89.9(2) 111.5(3) 112.9(3) 117.6(3) 123.8(2)

-P -C3 -P -N2 -c2

c7 -Cl2 Nl -C3 C31 -N3 c2 -c21

131.2(3) 114.0(3) 111B(2) 126.5(3) 129.5(3)

c21 C3 N2 Cl2

-c2 -C31 -Ni -Cl3

1.392(5) 1.372(4) 1.140(5) 1.533(5)

-c3 -N3 -C3 -Nl

124.7(3) 178.6(4) 119.4(3) 117.1(3)

The bond lengths for P-C2 and P-Cl3 [1.754(3) and 1.734(4) A, respectively] are intermediate between those of P/C single and P/C double bonds and are indicative of electron delocalization in the phosphorus-containing

heteroaromatic

ring. The bond angle C13-P-C2 [89.9(2)“]

is in the region

characteristic for 1,3-azaphospholes2. When the 31P- and 13C-NMR data of the 1,9azaphosphole

systems of 5a-c are considered, it is

seen that they all lie in narrow absorption ranges [31P: 6 = +72.9 to +83.3; 13C: 6 = 104.9-109.7 (2Jc P = 5.5-6.1 Hz, C3); 153.9-161.8 (‘& = 42.3-59.9 Hz, C12a); 172.8-175.3 (1Jc,p = 54.3-55.3 Hz, C2)]. in conjunction with the crystal structure analysis of 5b, these data confirm that the products 5a-c all belong to the same structural type. Although the pyridinium, pyridazinium, and 1,4-diazinium dicyanomethylides

6a-c all react with the

phosphaalkyne 2a in the manner described above (the elimination of HCN is again promoted by the addition of 1 mol of NEt.J, the primary step is completely non-selective so that 1:l mixtures of 7a-c with 8a-c are formed (40-60% yield).

+2a,

toluene, 130-lLO°C

(glass -HCN

pressure

tube1

6-8 X Y

8

7

6 a

b

c

d

t

f

Q

h

i

CH CH

N CH

CH N

CH CMe

CH cteu

CH OiPr

CH C-CO,Me

CH C-CEN

CH C-COPh

When donor-substituents

were introduced into the 4 position of 6a, is was found that a methyl

group had no effect on the product ratio (7d:8d = 50:50) whereas tert-but+ and isopropoxy groups favoured the formation of the isomer 7 (7e:6e = 80:20; 7f:8f = 1OO:O).Acceptor substituents exhibited

1052

neutral effects (7g-i:8g-i = 50:50)“. 60, 0.015-0.049

Acknowledgements:

lndustrie for generous

References

and Notes

Organophosphorus

mixtures

can be separated

2:1), as has been demonstrated

We thank

Chemischen

1.

The product

mm, ether/pentane,

the

Deutsche

by MPLC (Merck silica gel 7a/8a.

for the example

Forschungsgemeinschaft

and

the

Fonds

der

financial support.

Compounds;

Part 54. For Part 53, see: Breit, B.; Memmesheimer,

H., Boese,

R.; Regitz, M. Chem. Ber. 1992, 725, in press. 2.

Schmidpeter,

A.; Karaghiosoff,

Elements (Roesky, 3.

Schmidpeter,

K. in Rings, Clusters and Polymers

H. W., ed), Elsevier, Amsterdam

A. in Multiple

of h-lain Group and Transition

1989, pp. 307-343.

Bonds and Low Coordination

in Phosphorus

Chemistry

(Regitz,

M.,

Scherer, 0. J., eds.), Thieme, Stuttgart 1990, pp. 258-286. 4.

See, e.g., Issleib, Issleib,

K.; Vollmer,

R. L

R.; Oehme,

Anorg.

A//g.

H.; Meyder, Chem.

Lett. 1978,

H. Tetrahedron

198:,

481,

22-32;

Heinicke,

79, 441-444;

J.; Tzschach,

A.

Lett. 1982, 23, 3643-3646.

Tetrahedron 5.

K.; Vollmer,

See, e.g., Mtirkl, G.; Dorfmeister,

G. Tetrahedron

Leff. 1986, 27, 4419-4442

as well as Tetrahedron

Lett. 1987, 28, 1089-1092. 6.

RGsch, W.; Richter, H.; Regitz, M. Chem. Ber. 1987, 120, 1809-1813;

Fuchs, E. P. 0.; Hermesdon, Chem. 1988, 338, 329-

M.; Schnurr, W.; Rosch, W.; Heydt, H.; Regitz, M.; Binger, P. J. Organomet. 340; see also Regitz, M. in Ref.3, pp. 73-74. 7.

M%kl, G.; Troetsch-Schaller, B. unpublished

8.

1990,90,

Lett. 1988, 29, 785788;

results with RC(OTms) = PTms, University

Reviews on the cycloaddition 1988, 100, 1541-1565;

9.

I.; Holzl, W. Tetrahedron reactivity

of Kaiserslautern,

of phosphaalkynes:

1989.

Regitz, M.; Binger,

Chem. lnt. Ed. Engl. 1988, 27, 1484-1508;

Angew.

Regitz M.; Burkhardt, P. Angew.

Chem.

Regitz, M. Chem. Rev.

191-213.

Cyclocondensation Schmidpeter,

of pyridinium

A.; Spindler,

salts with

PCI,:

Bansal,

R. K.; Karaghiosoff,

C. Chem. Ber. 1991, 124, 475-480. Further examples

K.; Gupta,

N.;

of this methodo-

logy are given therein. 10.

C,,H;,N,P.

M = 267.3 g.mol-‘,

orthorhombic.

13.780(2) A, V = 1325.5(6) A3, Z = 4, d,,,,. The measurements MO K,

radiation;

were performed

Pnma (No.62);

with an Enraf-Nonius

1116 independent

and the subsequent

refinement

CAD4 diffractometer

number of parameters

by direct

methods

bond

11.

angles,

as well as temperature Crystallographic

Cambridge

CB2 1 EW, U.K.

Phosphaindolizines

Data

of the structural

salts: MBrkl, G.; Pflaum, S. Tetrahedron

(Received in Germany 27 November

1991)

factors Centre,

c =

p = 1.9 cm-‘.

with monochromatic

are available University

type 8a were also obtained Lett. 1987,28,

151 l-1514.

converged

solution at R =

tables of bond lengths and

on request

Chemical

134. The structure

[SHElX-761

0.0474 and Rw = 0.0470. Further details such as atomic coordinates, Cambridge

b = 6.948(2),

coefficient

[h: 0 - > + 16; k: 0 -> + 7; I: 0 -> + 161 with 4.0” 5 28

reflections

I 50”, of which 985 with I > 2u(l) were observed; [SHElX86]

a = 13.844(4),

= 1.339 g cm3, absorption

from The Director

Laboratory,

Lensfield

by O/P exchange

of the Road,

in oxazolium