Azomethine Ylide Cycloaddition/Reductive Heterocyclization Approach to Oxindole Alkaloids: Asymmetric Sinthesis of (-)-Horsfiline

The intermolecular [3 + 2] annulation of azomethine ylides with 2(2-nitrophenyl)acrylate dienophiles followed by reductive heterocyclization affords the spiro(indole-pyrrolidine) ring system. Hence, this enable us to accomplish a concise and highly enantioselective synthesis of (−)-horsfiline 1, based on chiral auxiliary-directed π-face discrimination in the 1,3-dipolar cycloaddition of (1S,2R)-2-phenyl-1-cyclohexyl ester 4f with N-methylazomethine ylide.