Highly selective hydrohalogenation reaction of substituted 2,3-allenoates

The hydrohalogenation reaction of 1-alkyl substituted 1,2-allenyl carboxylic acid esters (1) with MX (M= Na, or Li, X= Cl, Br, I) afforded a mixture of β,γ-unsaturated 3-halo–3-alkenoates (2) and Q,P unsaturated 3-halo-2-alkenoates (3) in HOAc, while using a mixture of HOAC-CF₃CO₂H (1:1) or CF₃C₂H as the reaction medium the corresponding reaction cleanly produced β,γ -unsaturated 3-hale3-alkenoates (2) as the sole products in high yields. The subsequent coupling reactions were studied.