Development of the practical organic reactions based on the π-coordination of alkyne to Lewis acid

点击翻译按钮获取中文摘要

Lewis acid mediated chelatipn control is one of the most fundamental and efficient methodologies for effecting the selective carbon-carbon bond formation in modern organic synthesis. It is well accepted that the chelation-controlled feactions proceed through the coordination of a lone pair of heteroatoms, such as an oxygen of an aldehyde br a nitrogen atom of an imine, to a Lewis acid, which is recognized as a σ-σtype chelation. On the contrary, we found that chemo- and regioselective reactions of certain alkynyl and alkenyl aldehydes were accomplished through a σ-π chelation between a lone pair of the carbonyl compounds and π-electrons of the C-C multiple bond. We also found that the chemoselective ring opening of alkynyl epoxides in the co-existence of the corresponding alkyl epoxides is achieved in a Me_3Al mediated reaction with alkynyl lithium reagents; this interesting chemoselectivity is most probably a reflection of bidentate complexation to an n-electron pair of the oxygen atom of the epoxide and π-electrons of the C-C triple bond.