Studies on the mechanism of reactions of substituted acetophenones with dibromocarbene

Mechanistic study on the reactions of dibromocarbene with para-substituted acetophenones suggests that the reactions proceed via the formation of a tw isted carbonyl Ylide intermediate which causes two competitive pathways, i. e., (1) deoxygenation(in the form of losing CO) and (2) electrocyclization. Although deoxygenation was observed not to be the major reaction path, it is clear that the extent of this reaction is increased substantively with r espect to electron-donating substituents. This phenomena is rationalized ba sed mainly on the electronic effect of substituents on each reaction path i nvolved as well as the twisted confirmation of Ylide intermediate.