摘要
Herein,we report an organocatalytic asymmetric[8+2]higher-order cycloaddition of tropones with azlactones employing bifunctional guanidines as hydrogen-bond-mediated catalysts via a 1,8-addition/annulation process.The reaction has a broad scope with respect to both cycloaddition partners and hence offers rapid access to an array of[5.3.0]bicyclic compounds with excellent outcomes[up to 95%yield,>19:1 diastereomeric ratio(dr),and 96%enantiomeric excess(ee)].Besides,the synthetic utility of the protocol provides rapid transformation into enantioenrichedα-amino acid derivatives.Moreover,the isolated[1,5]-H shift isomer,X-ray crystal structure of chiral guanidinium salt,and density functional theory(DFT)calculations provide convincing evidence for the interpretation of diastereo-and enantioselection.
