Exploiting the Multidentate Nature of Chiral Disulfonimides in a Multicomponent Reaction for the Asymmetric Synthesis of Pyrrolo[1,2-a]indoles: A Remarkable Case of Enantioinversion

A new multicomponent coupling reaction for the enantioselective synthesis of pyrrolo[1,2-a]indoles under the catalysis of a chiral disulfonimide is described. The high specificity of the reaction is a consequence of the multidentate character of the BrOnsted acid catalyst. Insights from DFT calculations helped explain the unexpected high enantioselectivity observed with the simplest 3,3-unsubstituted binaphthyl catalyst as a result of transition-state stabilization by a network of cooperative noncovalent interactions. The remarkable enantioinversion resulting from the simple introduction of substituents at 3- and 3-positions, the first reported example of this phenomenon in the context of binaphthalene-derived BrOnsted acid catalysis, was instead attributed to destabilizing steric interactions.