Synthesis of Isocoumarins and α-Pyrones via Palladium-Catalyzed Annulation of Internal Alkynes

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Abstract
A number of 3,4-disubstituted isocoumarins and polysubstituted α-pyrones have been prepared in good yields by treating halogen- or triflate-containing aromatic and α,β-unsaturated esters, respectively, with internal alkynes in the presence of a palladium catalyst. Synthetically, the methodology provides an especially simple and convenient, regioselective route to isocoumarins and α-pyrones containing aryl, silyl, ester, tert-alkyl, and other hindered groups. The reaction is believed to proceed through a seven-membered palladacyclic complex in which the regiochemistry of the reaction is controlled by steric factors. A number of 3,4-disubstituted isocoumarins and polysubstituted α-pyrones have been prepared in good yields by treating halogen- or triflate-containing aromatic and α,β-unsaturated esters, respectively, with internal alkynes in the presence of a palladium catalyst. Synthetically, the methodology provides an especially simple and convenient regioselective route to isocoumarins and α-pyrones containing aryl, silyl, ester, tert-alkyl, and other hindered groups. The reaction is believed to proceed through a seven-membered palladacyclic complex in which the regiochemistry of the reaction is controlled by steric factors.