Magnesium-promoted reductive acylation of aromatic conjugated ynones accompanying with transposition of the triple bond

Reductive acylation of aromatic conjugated ynones with acid chlorides in the presence of magnesium metal in N,N-dimethylformamide gave the corresponding enyne derivatives as the main compounds in moderate yields. Selective transposition of the ynone triple bond to the neighboring position was observed by allene intermediate formation. The existence of an aromatic ring of the starting material played an essential role in the reaction. Moreover, the acylation produced corresponding lactones in the presence of diacid chlorides. Final product structures were fully characterized and one product, 3,5-diphenyl-2-penten-4-yn-2-yl acetate was analyzed by single-crystal X-ray diffraction.