Butenolide synthesis by molybdenum-mediated hetero-Pauson-Khand reaction of alkynyl aldehydes

The highly reactive complex Mo(CO)(3)(DMF)(3) promotes the CO gas-free cyclocarbonylation of 1,5- and 1,6-alkynyl aldehydes under very mild reaction conditions to provide fused butenolides in good yields. This novel Mo-mediated hetero-Pauson-Khand reaction is very general with regard to the substitution at the alkyne terminus and tether (18 tested cases). Using readily available chiral alkynyl aldehydes, this procedure has been applied to the enantio- and stereoselective synthesis of highly substituted bicyclic butenolides, including an intermediate in natural product synthesis.