Preparation and Cytotoxic Evaluation of Vouacapane Oxidation Products

Treatment of (−)-(5S,6R,8S,9S,10R,14R)-6-acetoxyvouacapane (1) with DDQ, mCPBA, or Cr(VI) reagents afforded diterpenoids with various degrees of oxidation at the furan and C rings. Oxidation of 1 using DDQ provided the known benzofuran 2, together with the new derivatives dimer 3, lactone 4, and aldehyde 5, while mCPBA oxidation gave 2, spirocassenolide 6, and cassenolides 7 and 8a. Oxidation of 1 with CrO3 gave 4, 6, 8a, and spirocassenolide 9,...