Selective mono- and polymethylene homologations of copper reagents using (iodomethyl)zinc iodide
摘要:
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.
Regioselective reaction of allylbenzotriazoles with aldehydes and ketones in the presence of lithium
作者:Alan R. Katritzky、Clara N. Fali、Ming Qi
DOI:10.1016/s0040-4039(97)10601-3
日期:1998.1
The reactions of α- and γ-substituted allylbenzotriazoles 2, 3 and 4 with an excess of lithium in THF at −78 °C generate various allyllithiums, which react readily with aldehydes and ketones with high regioselectivity to give predominantly the branched products 5 in excellent yields.