Studies in group IV organometallic chemistry XXVII. Isomerization of the primary trans-addition products formed in the hydrostannation of ethynes

Abstract

The isomerization of the primary trans-addition products formed in the hydrostannation of ethynes has been shown to proceed under the influence of organotin radicals. Attack of such radicals on the carbon-carbon double bond produces an ethyl radical containing two organotin groups. Elimination of one of the organotin moieties as a radical may result in the formation of the isomerized product. The course of the latter step is determined by several factors. One of these seems to be a preference for those conformers of the free radical intermediate in which both tin atoms at the β-carbon atom are in gauche-position with respect to the polar substituent at the α-carbon atom.

At the same time these studies reveal that in hydrostannations of certain carbon-carbon double bonds the hydrogen transfer, following the reversible attack of an organotin radical, is the rate-determining step in the propagation reaction.