The Acylation of Acetylenes with β,γ‐Unsaturated Acid Chlorides, A New Synthesis of 5‐Substituted 2‐CyclopentenonesThe acylation of acetylenes with α,α‐disubstituted, β,γ‐unsaturated acid chlorides underFriedel‐Crafts‐type conditions leads to 5‐substituted 2‐cyclopentenones. Phenols are formed with β,γ‐unsaturated acid chlorides bearing at least one α‐H‐atom. These transformations are explained by the intramolecular cyclization of the initially formed vinyl cation, which, in the cases of α,α‐disubstituted acid chlorides, is followed by ring contraction. The reaction leading to 2‐cyclopentenones is applied to the synthesis of some spiro[4.4