Gold-Catalyzed Hydrative Carbocyclization of 1,5- and 1,7-Allenynes Mediated by π-Allene Complex: Mechanistic Evidence Supported by the Chirality Transfer of Allenyne Substrates
摘要:
We report PPh3AuCl/AgOTf-catalyzed hydrative carbocyclization of 1,5- and 1,7-allenynes to give cyclized ketones chemoselectively. In this transformation, hydration occurrs regioselectively at the C CPh carbon, accompanied by addition of the C CPh carbon to the two terminal allenyl carbons. This method is effective for the construction of a quaternary carbon center. On the basis of the chirality transfer of allenyne substrates, control experiments, and theoretic calculations, we propose that this hydrative carbocyclization proceeds through an initial pi-allene complex with a small energy barrier.
Direct and Stereospecific Synthesis of Allenes via Reduction of Propargylic Alcohols with Cp<sub>2</sub>Zr(H)Cl
作者:Xiaotao Pu、Joseph M. Ready
DOI:10.1021/ja8035527
日期:2008.8.1
Allenes can be synthesized via the direct SN2' addition of hydride to propargylicalcohols. Previous examples of this approach, however, have involved harsh reaction conditions and have suffered from incomplete transfer of central chirality to axial chirality. Here we show that Cp2Zr(H)Cl can react with the zinc or magnesium alkoxides of propargylicalcohols to generate allenes in good yield and in