Metalation of Alkynes. 4. The Methoxymercuration Reaction

Article abstract of DOI:10.1021/jo00286a027

Methoxymercuration of symmetrically and unsymmetrically substituted alkynes (4-octyne, 2-heptyne, 2-nonyne, 1,4-dimethoxy-2-butyne, 1,4-diacetoxy-2-butyne, methyl-2-octynoate, methyl phenylpropynoate, 1-phenylpropyne, 1-phenyl-1-pentyne, diphenylethyne) was investigated.The corresponding α-mercurated enol ethers were generally isolated and characterized except for 4-octyne, 2-heptyne, and 2-nonyne, which yielded α-acethoxymercurio ketones.Methoxymercuration was investigated kinetically.The rate law is second order, first order in both alkyne and mercuric acetate.Arylalkynes are less reactive than alkyl derivatives and the reaction rate is decreased by electron-withdrawing substituents.Activation parameters were determined for selected substrates.The kinetic data are in agreement with an electrophilic associative rate-determining step.Product analysis results suggest the formation of a cationic intermediate, the nature of which may vary from an unsymmetrically bridged species to an open carbocation, depending on the substrate.