One‐Step Synthesis of 2‐Amino‐5H‐pyrimido[5,4‐b]indoles, Substituted 2‐(1,3,5‐triazin‐2‐yl)‐1H‐indoles, and 1,3,5‐Triazines from Aldehydes

Abstract An efficient one‐step synthesis of 2‐amino‐5 H ‐pyrimido[5,4‐ b ]indoles through a copper‐catalyzed cascade reaction between 3‐haloindole‐2‐carbaldehydes and guanidine hydrochloride is described. In contrast, the base‐mediated reactions of either 3‐haloindole‐2‐carbaldehydes or substituted indole‐2‐carbaldehydes with substituted amidine hydrochlorides in DMSO result in the formation of 2‐(1,3,5‐triazin‐2‐yl)‐1 H ‐indole derivatives in one step in excellent yields. Studies toward exploring the utility of the method demonstrate that even substituted benzaldehydes undergo a similar reaction to efficiently yield 2,4,6‐trisubstituted 1,3,5‐triazines. A plausible mechanism for the formation of substituted 1,3,5‐triazines identifies the role of DMSO as an oxidant during the reaction.