Reactions of xanthinium N(7)-ylides with olefinic dipolarophiles

Abstract

The stereo- and regio-chemical aspects of the reactions of xanthinium N(7)-methylides (2) with olefinic dipolarophiles were elucidated. The reactions of ylides (2) with N-phenylmaleimide afforded stereoselective endo adducts, and with acrylates and acrylonitrile afforded stereo- and regio-selective 6-endo adducts. On the other hand, the reactions of ylides (2) with trans-olefins afforded mixtures of two stereoisomers, the 8-endo-7-exo and 8-exo-7-endo pyrrolo[2,1-f]purine derivatives. Stereochemistry of the adducts was elucidated by ¹H n.m.r. and X-ray analysis. The stereoselectivity of the adducts was governed by the balance of steric and electronic effects. The ylides (2) reacted in their Z-form in all reactions investigated. The steric factors of the dipolarophiles were also closely examined.