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

An efficient one-step synthesis of 2-amino-5H-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)-1H-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.