A General Carbazole Synthesis via Stitching of Indole-Ynones with Nitromethanes: Application to Total Synthesis of Carbazomycin A, Calothrixin B, and Staurosporinone.

A new, one-pot domino benzannulation reaction between indole-3-ynones and various nitromethane derivatives has been explored for a general entry to diversely functionalized carbazole frameworks (28 examples). The scope of this new benzannulation has been extended to variants like 2-chloroindole-3-ynones to eventuate in chemo-differentiated 1,2,3,4-tetrasubstituted carbazoles with retention of the nitro group. The efficacy of this strategy has been demonstrated through concise total synthesis of natural products, viz. carbazomycin A, calothrixin B, and staurosporinone (K252c).