A versatile synthesis of unsymmetrical 3,3'-bioxindoles: stereoselective Mukaiyama aldol reactions of 2-siloxyindoles with isatins.

A new synthesis of 3,3'-bioxindoles is reported that is well suited for the preparation of unsymmetrical structures. In the key step, 3-hydroxy-3,3'-bioxindoles are constructed by Mukaiyama aldol reaction of 2-siloxyindoles with isatins. These tertiary carbinols are formed in high diastereoselectivities, with substitution at various positions of the isatin and the 2-siloxyindole being tolerated.