Rapid access to diverse α-carbolines through sequential transition metal catalyzed amination and direct C-H arylation

An efficient sequence of Pd catalyzed amination and direct C-H arylation for a synthesis of pharmacologically important α-carbolines is described. The outstanding feature in the synthetic sequence is that a combination of DBU and 2-(dicyclohexylphosphino)biphenyl (DCHPB) plays a critical role to not only enhance the reactivity but also suppress hydrodehalogenation in the direct C-H arylation step. The reaction protocol provides α-carbolines with various substituents including base-sensitive ester and ketone moieties in moderate to excellent yields. Moreover, combination with Cu catalyzed amination further enhanced the versatility of the α-carboline synthesis.