Synthesis and stereochemistry of occidenol, a 4,5-dihydrooxipin-containing sesquiterpene: a pericyclic approach

The first synthesis of occidenol (1), a 4,5-dihydrooxipin-containing sesquiterpene, is reported. The stereochemistry is corrected from that postulated by Tomita and Hirose, by a synthesis starting with natural occidentalol (4), the stereochemistry of which was also initially in error. The route (schemes 1 and 2) utilizes a retro-electrocyclic [2+2+2] fragmentation with N2 expulsion from 9 to produce, quantitatively, the acid sensitive dihydrooxipin system.