Lanostane to cucurbitane transformations

Transformation of 3,7,9,11-tetraoxygenated lanostane derivatives into 3,7,11-trioxygenated cucurbit-1(10)-enes and cucurbit-5(10)-enes has been achieved. Attempts to convert the latter in good yield into cucurbit-5-enes are documented. The steric and electronic factors influencing the course of dehydration, under Westphalen conditions, of 9α-hydroxylanostane derivatives are discussed. Unusual autooxidation and dehydrogenation promoted by rhodium trichloride and iron pentacarbonyl are described.