Total Synthesis of Calothrixin B and Its Analogs

The total synthesis of calothrixin B and its analogs was achieved starting from 2‐methylindole. The synthesis involved an electrocyclization of 2‐nitroarylvinyl‐3‐phenylsulfonylvinylindoles as a key step to give 2‐nitroaryl‐4‐methoxy‐3‐methylcarbazoles. Oxidation of these compounds followed by reductive cyclization led to N‐phenylsulfonylquinocarbazoles. These quinocarbazoles underwent hydrolysis and aerial oxidation in one pot to give the target compounds. A linear synthesis of calothrixin B and its analogs has been established from commercially available 2‐methylindole. The thermal electrocyclization of 2‐nitroarylvinyl‐3‐phenylsulfonylindole was a key step in the synthesis. The synthesis of calothrixin B and its analogs was achieved in 12–22 % overall yield over twelve steps.