A novel 1,2-migration of arylzincates bearing a leaving group at benzylic position: Application to a three-component coupling of p-iodobenzyl derivatives, trialkylzincates, and electrophiles leading to functionalized p- substituted benzenes

Article abstract of DOI:10.1016/S0040-4020(98)00569-9

A three-component coupling of p-iodobenzyl derivatives, trialkylzincates, and electrophiles is described. Lithium trialkylzincates (R₃ZnLi) react with p-iodobenzyl methanesulfonate to give benzylzinc reagents p-RC₆H₄CH₂Zn(L). The reaction proceeds through a mechanism involving initial iodine/zinc exchange and the 1,2-migration of the resulting arylzincates. The benzylzinc reagents, thus prepared, are subsequently used in coupling reaction with electrophiles such as aldehydes, ketones, acyl chlorides, tosyl cyanide, and chlorosilanes to give a variety of functionalized p-substituted benzenes. Reactions under Barbier conditions in which the corresponding benzylzinc reagents are generated in the presence of electrophiles work well for Me₃ZnLi and for magnesium zincates R₃ZnMgBr derived from Grignard reagents. Generation of secondary benzylzinc reagents starting from diethyl 1-(p-iodophenyl)ethyl phosphate and their reaction with electrophiles are also achieved under Barbier conditions. Ketones, allyl bromides, and chlorosilanes are successfully used as electrophiles under these conditions.