Radical transfer catalysis versus Lewis acid catalysis by the copper(I) chloride–2,2′-bipyridine complex: the effect of the structure of the ligand

Abstract

Cyclization of O-(but-3-enyl)-α-chloroglycolic acid methyl ester 4 catalysed by copper(I) chloride–2,2′-bipyridine 8 leads primarily to the 5-exo product 5, whereas using copper(I) chloride–6,6′-dimethyl-2,2′-bipyridine as catalyst leads to the 6-endo product 6. This is interpreted in terms of a change from a radical to an ionic mechanism.