Chromium(II)-Catalyzed Diastereoselective and Chemoselective Csp2–Csp3 Cross-Couplings Using Organomagnesium Reagents

A simple protocol for performing chromium-catalyzed highly diastereoselective alkylations of arylmagnesium halides with cyclohexyl iodides at ambient temperature has been developed. Furthermore, this ligand-free CrCl2 enables efficient electrophilic alkenylations of primary, secondary, and tetiary alkylmagnesium halides with readily available alkenyl acetates. Moreover, this chemoselective C–C coupling reaction with stereodefined alkenyl acetates proceeds in a stereoretentive fashion. A wide range of functional groups on alkyl iodides and alkenyl acetates are well tolerated, thus furnishing functionalized Csp2–Csp3 coupling products in good yields and high diastereoselectivity. Detailed mechanistic studies suggest that the in situ generated low-valent chromium­(I) species might be the active catalyst for these Csp2–Csp3 cross-couplings.

本研究开发了一种简单的反应方案，可在室温下实现铬催化芳基卤化镁与环己基碘化物的高非对映选择性烷基化反应。此外，该无配体氯化铬(II)能够高效实现伯、仲、叔烷基卤化镁与易得烯基乙酸酯的亲电烯基化反应。进一步来讲，该化学选择性C-C偶联反应在使用立体规整烯基乙酸酯时，可按立体保持的方式进行。烷基碘化物与烯基乙酸酯上的多种官能团均具有良好的兼容性，因此可获得官能化的Csp²-Csp³偶联产物，且收率优良、非对映选择性优异。详细的机理研究表明，原位生成的低价铬(I)活性物种或许是此类Csp²-Csp³交叉偶联反应的活性催化剂。