Oxidative Heterocoupling of Lithium Acylate α-Carbanions by the Action of 1,2-Dibromoethane

Pairs of alpha-carbanions generated from lithium 2-methylpropanoate, butanoate, pentanoate, hexanoate, heptanoate, and phenylacetate by the action of lithium diisopropylamide on the corresponding acids (AH, BH) in THF reacted with 1,2-dibromoethane to give mixtures of oxidative homo- (2,2,3,3-tetramethyl-, 2,3-diethyl-, 2,3-dipropyl-, 2,3-dibutyl-, 2,3-dipentyl-, and 2,3-diphenylbutanedioic acids) and heterocoupling products (3-ethyl-2,2-dimethyl-, 2-ethyl-3-propyl-, 2-butyl-3-ethyl-, 2-ethyl-3-pentyl-, 2-ethyl-3-phenyl-, 2-butyl-3-propyl-, 2-pentyl-3-propyl-, 2-phenyl-2-propyl-, 2-butyl-3-pentyl-, 2-butyl-3-phenyl-, and 2-pentyl-3-phenylbutanedioic acids) in overall yields of 83-99%. The ratio of the homo- and heterocoupling products depended on the structure of the initial alpha-carbanions.