Formal syntheses of (±)-Asterisca-3(15),6-diene and (±)-Pentalenene using Rh(I)-catalyzed [(5+2)+1] cycloaddition

Efficient formal syntheses of (+/-)-Asterisca-3(15),6-diene, a natural product with a bicyclo[6.3.0]undecane skeleton, and (+/-)-Pentalenene. a natural product with a tricyclo[6.3.0.0(4,8)]undecane skeleton, have been achieved by using Rh(I)-catalyzed [(5+2)+1] cycloaddition. The [(5+2)+1] reaction provides an expeditious approach to reach the bicyclic cyclooctenone 4, which was quickly transformed (via hydroboration then oxidation) to diketone 14, a key advanced intermediate for the total synthesis of (+/-)-Asterisca-3(15),6-diene. Through further transformations, 14 was converted to diene 18, an advanced intermediate for the total synthesis of (+/-)-Pentalenene. (C) 2009 Elsevier Ltd. All rights reserved.