Preparation of γ-Keto Phosphonates via a Zinc-carbenoid Chain Extension Reaction

A variety of β-keto phosphonates can be converted to γ-keto phosphonates through reaction with ethyl(iodomethyl)zinc. The presence of α-alkyl substituents, Lewis basic functionality, and modestly acidic NH-protons are accommodated in substrates of this reaction. Chain extension of β-keto phosphonates that contained olefinic functionality proceeded more quickly than cyclopropanation; however, it was not possible to effect the chain extension to the exclusion of cyclopropane formation. A primary reason for this imperfect chemoselectivity appears to be the slow chain extension of β-keto phosphonates. Nevertheless, the simplicity, the scope, and efficiency of this method serve to make it an attractive alternative to the established methods for γ-keto phosphonate formation