Total Synthesis of Calothrixin B via an Intramolecular Baylis‐Hillman Cyclization/6π Electrocyclization/Dehydro‐aromatization Sequence and a Specific Oxidative Quinone Formation

Abstract A short total synthesis of bioactive alkaloid calothrixin B have been accomplished with atom and step economy from commercially available starting materials. The key cyclization involved a Baylis−Hillman/6π electrocyclization/dehydroaromatiz‐ation sequence to construct the pentacyclic skeleton. Reduction of the resulting lactam followed by oxidation led to the characteristic quino[4,3‐ b ]carbazole framework. This intermediate underwent a direct oxidation with high regioselectivity to yield the final product. magnified image