Pd(II)-catalyzed annulation of terminal alkynes with 2-pyridinyl-substituted -quinone methides: direct access to indolizines.

A Pd-catalyzed direct method has been developed to access 1,3-disubstituted indolizines. This reaction proceeds through a regiospecific annulation of terminal alkynes with 2-pyridinyl-substituted -quinone methides and, in most of the cases, the desired 1,3-disubstituted indolizines were obtained in moderate to good isolated yields. The control experiments suggested that the reaction does proceed through a substrate-controlled regiospecific formal [3 + 2]-annulation pathway.