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Asymmetric Total Synthesis of Twin Bufogargarizins A and B
Li-Ping Zhong1, Rui Feng1, Jing-Jing Wang1
1Shenzhen Grubbs Institute, Department of Chemistry, Guangdong Provincial Key Laboratory of Catalytic Chemistry, Southern University of Science and Technology, Shenzhen 518055, China.
Abstract:
The first and asymmetric total synthesis of bufogargarizins A and B, two unusual and highly oxygenated twin steroids with rearranged A/B rings, was achieved. The synthetically challenging [7-5-6-5] tetracyclic ring system of bufogargarizin A was efficiently constructed by the first intramolecular Ru-catalyzed [5 + 2] cycloaddition reaction of a vinyl ether cyclopropane-yne. Notably, the interesting [5-7-6-5] tetracyclic skeleton of bufogargarizin B was diastereoselectively reassembled by unique retro-aldol/transannular aldol cascade reactions from the [7-5-6-5] tetracyclic framework.
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