The total synthesis of (±)-arisugacin A

A 20-step total synthesis of (±)-arisugacin A with an overall yield of 2.1% is described here in detail. This synthesis features a formal [3+3] cycloaddition reaction of α,β-unsaturated iminium salts with 6-aryl-4-hydroxy-2-pyrones through a highly stereoselective 6π-electron electrocyclic ring-closure of 1-oxatriene. A strategic dihydroxylation–deoxygenation protocol leading to the desired angular C12a–OH was developed to serve as a critical step in leading to the final total syntheses of arisugacin A. This synthetic endeavor also led to an interesting and unexpected retro-aldol–aldol sequence in the AB-ring.