Development of palladium catalyzed-reaction and its synthetic application

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An allenic ester, produced by palladium-catalyzed carbonylation of a propargylic carbonate, provides a further synthetically useful transformation because of a reactive allenic SP carbon. To demonstrate the utility of the allenic ester, we designed a following domino-type carbonylation/Diels-Alder reaction sequence. Carbonylation of a propargylic carbonate having a vinyl group in place of acetylenic proton provides an alpha-vinyl allenic ester which can be recognized as an electron-defficient conjugated diene. This alpha-vinyl allenic ester undergoes intramolecular Diels-Alder reaction with a methyl enol ether as an electron-rich dienophile, affording an indene skeleton. This synthetically interesting reaction was applied to an efficient construction of vitamin D_3 intermediate.