Reaction of pyrrolo[1,2-c]imidazole mesomeric betaines with diphenylcyclopropenone derivatives
摘要:
The cyloaddition reactions of title mesomeric betaines to diphenylcyclopropenone and diphenylcyclopropenethione have been studied. Cycloadditions lead to either 2(1H)-pyridone, 2(1H)-pyridinethione, or bicyclo[3.1.0]hex-3-en-2-one derivatives. Formation of the bicyclo[3.1.0]hex-3-en-2-ones is highly stereoselective with exclusive formation of C-6 exo-alkoxycarbonyl or the exo-acetyl diastereoisomer. Diphenylcyclopropenone and its thione enriched with C-13 at both the 2- and 3-positions were prepared and used to determine the structures of the cycloaddition products. Possible mechanistic pathways for these reactions are considered and compared with previous postulated mechanisms for the cycloadditions of cyclopropenones to N-heterocycles and enamines.