A solvent controlled regioselective synthesis of 2- and 4-substituted α-carbolines under palladium catalysis.

A facile method for the chemodivergent synthesis of α-carbolines 1 via palladium catalyzed [3+3] annulations of tosyliminoindolines 6 with α, β-unsaturated aldehydes 7 is described. Mechanistically, this cascade reaction proceeds through either a carba -Michael (in DMF) or aza -Michael (in NMA) pathway followed by intramolecular cyclization of the intermediate. A preliminary photo-physical study on selected products is also reported.