Transition metal catalyzed stereospecific intramolecular [3+2] cycloadditions of methylenecyclopropanes with alkynes

Palladium catalyzed intramolecular [3 + 2] cycloadditions of diastereomerically pure methylenecyclopropanes MCPs have been investigated. The reaction was found to be stereospecific and occurred with retention of configuration at the carbon center undergoing reaction. A variety of substitution patterns were tolerated on and around the MCP. Deuterium labeling studies have been conducted, and information about the rate of the reaction was obtained. A mechanism has been proposed involving pi-allyl intermediates. Pd-2(dba)(3)/P(OiPr)(3) was a suitable catalyst for most cycloadditions, but molecular sieves or Pd(PPh(3))(4) improved the reaction with some substrates. 1,4-Addition of hydride or a carbanion to the enoate was achieved with high selectivity at the newly formed stereocenter. The allylic alcohol was selectively epoxidized with VO(acac)(2)/t-BuOOH.