Some reactions of benzaldehyde acetals with alkyl-lithium reagents; a stereospecific olefin synthesis from 1,2-diols

Abstract

In certain cases the reaction of 2-phenyl-1,3-dioxolans with n-butyl-lithium gives olefins in a highly Stereospecific fragmentation reaction. In particular, the reaction constitutes the crucial step in a convenient preparation of trans-cyclo-octene from cis-cyclo-octene.

A mechanism is proposed involving initial metallation of the dioxolan followed by concerted cycloelimination to olefin and benzoate ion. Support for this mechanism, in three instances, is provided by the isolation of products derived by in situ trapping of the lithium derivative of the dioxolan by benzoate ion.