Methoxide-induced fragmentation of 2,2,3-trihalogeno- and 2,2-dihalogeno-3-methoxy-1,3-diphenylpropanones

Abstract

The reaction of 2,2,3-trihalogeno-1,3-diphenylpropanones with sodium methoxide in methanol occurs with exclusive formation of fragmentation products. Kinetic and stereochemical evidence is interpreted in terms of a concerted intramolecular process promoted by initial attack of methoxide anion at the carbonyl carbon. In the case of 2,2-dihalogeno-3-methoxy-1,3-diphenylpropanones the reaction gives fragmentation, rearrangement, and elimination products. The former products are believed to be formed through competing reactions involving an intermediate formed on addition of methoxide to the substrate. For the fragmentation pathway the results are consistent with a carbanionic-intermediate mechanism.