Palladium-catalyzed asymmetric construction of vicinal all-carbon quaternary stereocenters and its application to the synthesis of cyclotryptamine alkaloids

We report the use of a two-fold Pd-catalyzed decarboxylative allylic alkylation (Pd-DAAA) to construct two vicinal all carbon quaternary stereocenters in a diastereo- and enantioselective fashion. To demonstrate the synthetic utility of this process, the products of the Pd-DAAA were elaborated to complete the formal syntheses of the cyclotryptamine alkaloids. Mechanistic investigations have revealed that the two-fold Pd-catalyzed transformation proceeds through an initial matched first allylation followed by a second mismatched allylation to deliver the desired product.

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.