Synthesis of α‐Carbolines Starting from 2,3‐Dichloropyridines and Substituted Anilines

Abstract

Abstract 9 H ‐α‐Carbolines have been prepared via consecutive intermolecular Buchwald–Hartwig reaction and Pd‐catalyzed intramolecular direct arylation from commercially available 2,3‐dichloropyridines and substituted anilines. The combination of a high reaction temperature (180 °C) and the use of DBU were found to be crucial for the intramolecular direct arylation reactions of the 3‐chloro‐ N ‐phenylpyridin‐2‐amines as no reaction was observed at 120 °C and 180 °C using different inorganic and other organic bases. On the other hand, nitrogen‐methylated pyridine analogues of these substrates { N ‐[3‐chloro‐1‐methylpyridin‐2(1 H )‐ylidene]anilines} do undergo ring closure at 120 °C, with K 3 PO 4 as base, affording the respective 1‐methyl‐1 H ‐α‐carbolines in good yields.