INVESTIGATIONS OF NOVEL AZOMETHINE YLIDE-FORMING PHOTOREACTIONS OF N-SILYLMETHYLIMIDES

The scope of a recently discovered (Yoon, E. C. et al. J. Am. Chem. Se c. 1995, 117, 2698), azomethine ylide-forming photoreaction has been e xplored by probing the excited state chemistry of several N-trimethyls ilylmethyl substituted cyclic and acyclic imides and amide analogs. Ph otolysis of N-[(trimethylsilyl)methyl]maleimide (4) in acetonitrile le ads to efficient production of the tricyclic product 16, formed by tra pping of the photogenerated azomethine ylide intermediate 15 through c ydoaddition with 4. Irradiation 4 in solutions containing high concent rations of the dipolarophiles, acrylonitrile or fumaronitrile, results in production of the products (19-21 and 23-24, respectively) arising by cycloaddition of the ylide 15 with the added dipolarophiles. In co ntrast, photolysis of the nonconjugated cyclic imide, N-[(trimethylsil yl)methyl]succinimide (5), brings about N-acyl migration resulting in the exclusive production of the unstable, iminolactone 30. On the othe r hand, acyclic, N-trimethylsilylmethyl aroyl imides 6-8 undergo the e xcited state C to O silyl migration reaction to produce azomethine yli de intermediates 35. Both in the presence or absence of added dipolaro philes, these ylides undergo electrocyclization to form transient azir idine intermediates 36 which react further by ring opening to generate N-phenacylamide products 32-34. In contrast, the nonconjugated imide, N-[(trimethylsilyl)methyl]-N-acetylacetamide (9), is unreactive upon irradiation. Similarly, simple N-[(trimethylsilyl)methyl] amides 10-13 , while being photochemically labile, do not react to form ''trappable '' ylide intermediates upon irradiation. The results outlined above ar e presented and discussed in terms of the scope and limitations of the new, azomethine ylide-forming photoreaction of silylmethyl imides.