Transpositions a etapes multiples d'epoxydes sesquiterpeniques—II : Action d'acides de lewis sur l'epoxyde de cyperene

Cyperene epoxide 1, on treatment with stannic chloride, gives the cyclopentanone 2 (70% yield) and the methyl ketone 3 (10% yield) by multi-step rearrangements comprising six elementary rearrangements. At least two of these elementary rearrangements cannot be concerted and it seems that in such compact globular polycyclic systems, the bond which migrates is not necessarily the one which is the better geometrically disposed for migration, but the one which would give a thermodynamically more stable product.Treatment of cyperene epoxide 1 with activity grade 1 alumina leads to two conjugated dienes which are the dehydration products of a rearranged allylic alcohol.