4-(Dimethylamino)pyridine as a Catalyst for Carbon Acylation. 2. Control of Carbon vs. Oxygen Acylation in Benzofuranones

Article abstract of DOI:10.1021/jo00233a022

3-Phenylbenzofuranone (1), when deprotonated with sodium hydride and treated with excess chloroformates, generally affords products arising from oxygen acylation (enol carbonates 4).Such molecules, when treated with a catalytic quantity of 4-(dimethylamino)pyridine (DMAP, 6) in halogenated solvents, rearrange to the carbon-acylated isomers 3.These migrations are proposed to involve the intermediacy of an acylated (dimethylamino)pyridinium species (10), which transfers the ester functionality from oxygen to carbon.Inclusion of DMAP in the acylation reaction mixture, however, leads to direct carbon acylation.Thus, complete regiocontrolled acylation of these substrates is attainable.