Total synthesis of racemic lasidiol via intramolecular [4+3] cycloaddition

Lasidiol, a sesquiterpenoid with a carotane skeleton, and its 8a-epimer have been synthesized in 12 steps starting from 2-methylfuran. Key elements in the synthesis are constructions of the carbon framework in an intramolecular [4+3] cycloaddition and cleavage of the epoxy-bridge by reductive elimination with sodium naphthalenide after reduction and hydrogenation of the bromo-substituted cycloadducts.