Syntheses and Crystal Structures of Three Electron Poor N-Vinyltheophylline Derivatives

Abstract

Protonation of the highly reactive 1:1 interme- diates, produced in the reaction between triphenylphosphine and alkyl acetylenecarboxylates (or dialkyl acetylenedi- carboxylates) by theophylline leads to vinyltriphenylpho- sphonium salts, which undergo Michael addition reaction with conjugate base to produce phosphorus ylides. Silica gel was found to catalyze conversion of the phosphorus ylides to electron-poor N-vinyl imidazoles in solvent-free conditions under thermal (90 � C, 1 h) conditions. The structures of these compounds were confirmed by IR, 1 H, and 13 CN MR spectroscopy, and single crystal X-ray structure determina- tion. The structural analysis of the products indicated that the reaction is completely regio- and stereoselective.