Total Syntheses of (-)-Conidiogenone B, (-)-Conidiogenone, and (-)-Conidiogenol.

Cyclopianes are novel diterpenes featuring a highly strained 6/5/5/5 tetracyclic core embedded with 6-8 consecutive stereocenters. The concise total syntheses of (-)-conidiogenone B, (-)-conidiogenone, and (-)-conidiogenol have been accomplished in 14-17 steps. The present work features a HAT-mediated alkene-nitrile cyclization to access the cis-biquinane, a Nicholas/Pauson-Khand reaction to construct the linear triquinane, and a Danheiser annulation to afford the congested angular triquinane skeleton.