二溴卡宾与取代苯乙酮反应机理的研究

Studies on the Mechanism of Reactions of Substituted Acetophenones with Dibromocarbene

研究了二溴卡宾与取代苯乙酮的反应机理．在取代苯乙酮与二溴卡宾的反应中，由于形成的羰基叶立德中间体的非平面构象，使得１，３－偶极加成难以发生，其主要反应途径为电环化和脱氧反应的竞争．当增大苯环上取代基的供电子能力时，原处于次要地位的脱氧反应的程度有所增强，但变化程度有限。

Mechanistic study on the reactions of dibromocarbene with para substituted acetophenones suggests that the reactions proceed via the formation of a twisted 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 respect to electron donating substituents. This phenomena is rationalized based mainly on the electronic effect of substituents on each reaction path involved as well as the twisted confirmation of Ylide intermediate.