Selective Mono- and Polymethylene Homologations of Copper Reagents Using (Iodomethyl)zinc Iodide

Article abstract of DOI:10.1021/jo00062a010

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 α-methylene-γ-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 α-position to amines as well as homoenolates of aldehydes or ketones can also be prepared by this method.