Solvolysis of caryophyllen-8 beta-yl derivatives: Biomimetic rearrangement-cyclization to 12-nor-8 alpha-presilphiperfolan-9 beta-ol

The solvolyses of caryophyllen-8 beta-yl p-nitrobenzoate (14-OpNB) and 15-n orcaryophyllen-8 beta-yl tosylate (15-OTs) were investigated as potential m odel reactions for the biogenesis of the tricyclic presilphiperfolanol sesq uiterpenes. Buffered solvolysis of 14-OpNB in 60% aqueous acetone at 125 de grees C afforded caryophyllene (3) as major product, accompanied by small a mounts of caryophyllen-8 beta-ol (14-OH) and 5,8-cyclocaryophyllen-4 alpha- ol (16). In contrast, 15-OTs underwent a stereospecific rearrangement-cycli zation to 12-nor-8 alpha-presilphiperfolan-9 beta-ol (17) upon solvolysis i n 60% aqueous acetone at 75 degrees C. The structure and stereochemistry of this trans,cis,trans-tricyclo[6.2.1.0(5,11)]undecane derivative were estab lished by NMR correlation spectroscopy and X-ray crystallography. Two diffe rent mechanisms (paths A and B) for the conversion of 15-OTs to 17 by initi al 1,2-migration of either the external or internal cyclobutane ring bonds (C10 and C1) followed by pi-sigma cyclization onto the trans double bond ar e discussed.