Cyclization of cembrane diterpenoids: IX. Electrophilic cyclization of 5 alpha-acetoxyisocembrol

Cyclization of diterpenoid alcohol 5 alpha -acetoxyisocembrol catalyzed by formic acid occurs along two pathroutes resulting in compounds with carbon skeleton of 2,11:3,8-dicyclocembrane and eunicillane derivatives, 5 alpha - acetoxy-2,11-cyclocembranoids, potential intermediates in the synthesis of eleutherobin analogs. All newly prepared eunicillanoids in solution exist a s pairs of conformers slowly (in the NMR time scale) interconverting. The c onformers are distinguished by the orientation of the triple-substituted De lta (7) double bond.