Synthesis of α- and β-Carbolines by a Metalation/Negishi Cross-Coupling/SNAr Reaction Sequence

Carbolines are considered to be privileged scaffolds in medicinal chemistry. An efficient method for the synthesis of α- and β-carbolines from fluoropyridines and 2-haloanilines is reported. This streamlined procedure consists of a four-step directed ortho-lithiation, zincation, Negishi cross-coupling, and intramolecular nucleophilic aromatic substitution, providing access to a diverse set of functionalized carbolines. While the procedure is applicable to batch conditions, the generation of arylzinc intermediates in continuous flow has been demonstrated.