Carbon-carbon bond formation in regio- and stereoselective palladium-catalyzed cyclization of allene-substituted conjugated dienes

Regio- and stereoselective palladium-catalyzed reactions of allene-substitu ted 1,3-dienes 1 in acetic acid at room temperature lead to cyclization wit h formation of a carbon-carbon bond between the middle carbon of the allene and the terminal carbon of the 1,3-diene. Two different types of reactions , both that constitute 1,4-carboacetoxylations of the 1,3-diene, have been developed. In one of the reactions, Pd(II) catalyzes the oxidation of 1 to bicyclic compounds 2, and in the other, Pd(0) catalyzes the transformation of 1 to bicyclic compounds 3. The products 2 are useful for further synthet ic transformations and undergo Diels-Alder reactions with dienophiles to gi ve polycyclic ring systems.