Synthesis of isocoumarins and alpha-pyrones via palladium-catalyzed annulation of internal alkynes

A number of 3,4-disubstituted isocoumarins and polysubstituted alpha-pyrone s have been prepared in good yields by treating halogen- or triflate-contai ning aromatic and alpha,beta-unsaturated esters, respectively, with interna l alkynes in the presence of a palladium catalyst. Synthetically, the metho dology provides an especially simple and convenient, regioselective route t o isocoumarins and alpha-pyrones containing aryl, silyl, ester, tert-alkyl, and other hindered groups. The reaction is believed to proceed through a s even-membered palladacyclic complex in which the regiochemistry of the reac tion is controlled by steric factors. A number of 3,4-disubstituted isocoum arins and polysubstituted alpha-pyrones have been prepared in good yields b y treating halogen- or triflate-containing aromatic and alpha,beta-unsatura ted esters, respectively, with internal alkynes in the presence of a pallad ium catalyst. Synthetically, the methodology provides an especially simple and convenient regioselective route to isocoumarins and alpha-pyrones conta ining aryl, silyl, ester, tert-alkyl, and other hindered groups. The reacti on is believed to proceed through a seven-membered palladacyclic complex in which the regiochemistry of the reaction is controlled by steric factors.