Efficient Catalytic Insertion of Acetylenes into a Carbon−Carbon Single Bond of Nonstrained Cyclic Compounds under Mild Conditions

A rhenium complex, [ReBr(CO)3(thf)]2, catalyzes the reaction of a 1,3-dicarbonyl cyclic compound with an acetylene to give a medium-sized cyclic compound in excellent yield. By using isocyanide as an additive, the catalytic activity of the rhenium complex changes dramatically, and the insertion of acetylenes into a carbon−carbon single bond occurs under mild conditions. A plausible mechanism is that the reaction proceeds via the formation of a rhenacyclopentene intermediate, ring opening by a retro-aldol reaction, isomerization, and reductive elimination.