Enantioselective Synthesis of Dihydro-1H-benzindoles

The first examples of dihydro-1H-benzindoles by enantioselective gamma-lactamization reaction of naphthyl sulfilimines with trichloroacetyl chloride in the presence of ZnCu as catalyst (>= 98:2 er and 65-80% yields) are described. Products are obtained by [3,3]-sigmatropic rearrangement of the azasulfonium enolate or followed by a second allylic rearrangement that transfers chirality. The absolute stereochemistry was confirmed by X-ray crystallography, which provides support for the mechanisms proposed.