Successive Carbon-Carbon Bond Formation by Sequential Generation of Radical and Anionic Species with Manganese and Catalytic Amounts of PbCl2 and Me3SiCl

Three-component coupling reactions of iodoalkanes, (alpha),(beta)-unsaturated nitriles (or esters), and carbonyl compounds are achieved in good to excellent yields with a moderate reducing system derived from manganese metal and a catalytic amount of PbCl2 and Me3SiCl. Although the role of PbCl2 is unclear, addition of a catalytic amount of the salt is essential for reducing the iodoalkane. The reaction proceeds with primary, secondary, and tertiary iodoalkanes. Both acrylonitrile and acrylic esters can be employed as activated olefins, while the reaction with an alkyl vinyl ketone gives a complex mixture. Ketones and aldehydes can be used as the third component and the diastereoselectivity of the anionic addition is approximately 1 : 1-2 : 1 ratio. By using the heterogenerative process, i.e., successive 1,4-addition by radical and anionic internal addition, cyclopropanation of electron-deficient olefins is achieved with chloroiodomethane, manganese, PbCl2, Me3SiCl, and DMAP.