Organometallic intermediates. Part I. The influence of electronic and steric effects on the direction of hydrocarboxylation of acetylenes

Abstract

The relative proportions of isomeric cinnamic acids obtained by the hydrocarboxylation of meta- and para-mono-substituted diphenylacetylenes can be correlated with the σ-constants of the substituents. The direction of addition of the elements of formic acid in this reaction obeys the generalised Markownikof rule. However, ortho-substituents, irrespective of their electronic properties, cause preferential formation of the α-arylcinnamic acid. Possible mechanisms for the hydrocarboxylation reaction are discussed.