Preparation of δ-Chloro-α-allenyl Ketones by Acylation of 3-Buten-1-ynes

AlCl 3 -mediated acylation of 3-buten-1-yne derivatives with acyl chlorides yields a mixture of 5-chloro-2,3-pentadienones and 3-chloro-2,4-pentadienones. The proportion of allenyl ketones vs conjugated dienic ketones depends on the substitution pattern of the starting enyne. Acylation of 5-acetoxy-3-buten-1-ynes leads to the corresponding allenyl ketones (6-acetoxy-5-chloro-2,3-pentadienones).