A. Sidduri et al., SELECTIVE MONOMETHYLENE AND POLYMETHYLENE HOMOLOGATIONS OF COPPER REAGENTS USING (IODOMETHYL)ZINC IODIDE, Journal of organic chemistry, 58(10), 1993, pp. 2694-2713
A wide range of unsaturated aryl-, alkenyl-, alkynylcopper compounds c
an be selectively homologated by a methylene unit using (iodomethyl)zi
nc iodide or bis(iodomethyl)zinc. These reactions allow the generation
of mixed allylic zinc-copper compounds which can be efficiently trapp
ed 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 presen
ce 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 cop
per reagents. The homologation of other types of copper reagents is al
so possible, and carbanions at the alpha-position to amines as well as
homoenolates of aldehydes or ketones can also be prepared by this met
hod.