SELECTIVE MONOMETHYLENE AND POLYMETHYLENE HOMOLOGATIONS OF COPPER REAGENTS USING (IODOMETHYL)ZINC IODIDE

A wide range of unsaturated aryl-, alkenyl-, alkynylcopper compounds can be selectively homologated by a methylene unit using (iodomethyl)zinc iodide or bis(iodomethyl)zinc. These reactions allow the generation of mixed allylic zinc-copper compounds which can be efficiently trapped with carbonyl compounds. An application to a general preparation of functionalized alpha-methylene-gamma-butyrolactones is described. The homologation of alkynylcoppers with (iodomethyl)zinc iodide allows a one-pot preparation of propargylic copper reagents which in the presence of a carbonyl compound provide various homopropargylic alcohols in excellent yields. In the absence of an electrophile, a clean quadruple methylene homologation of alkynylcoppers occurs to furnish dienic copper reagents. The homologation of other types of copper reagents is also possible, and carbanions at the alpha-position to amines as well as homoenolates of aldehydes or ketones can also be prepared by this method.