Rhodium-Catalyzed Asymmetric (3 + 2 + 2) Annulation <i>via</i> N–H/C–H Dual Activation and Internal Alkyne Insertion toward <i>N</i>-Fused 5/7 Bicycles
Chao Yang, Lijun Shi, Fang Wang, Yijin Su, Ji‐Bao Xia, Fuwei Li
Abstract
N-Fused 5/7-membered bicycles have witnessed apparent importance in many bioactive molecules, but there are rare examples to construct these privileged scaffolds by asymmetric catalysis due to the unfavorable steric hindrance, transannular interactions, and congested bridgehead stereocenter. We herein report rhodium-catalyzed (3 + 2 + 2) annulation of alkenylamides with alkynes for the efficient synthesis of stereogenic 1-azabicyclo[5.3.0]decanes through N–H/C–H bond dual activation. Moreover, the corresponding asymmetric catalytic reaction has been realized leading to enantioenriched products bearing bridgehead quaternary stereocenter in moderate-to-good yields with up to 96% ee. Mechanistic studies and density functional theory calculations have revealed that rhodium experienced a preset unique catalytic pathway via amino rhodation of tethered ene to produce a stereogenic alkyl-Rh species, which undergoes the following C–H activation and alkyne insertion to provide the key 8-membered rhodacycle intermediate. This protocol discloses a highly valuable asymmetric rhodium-mediated C–H functionalization mode and validates a de novo cascade construction of chiral 1-azabicyclo[5.3.0]decanes.