Cyclization of cembrane diterpenoids. VI. Products of the cyclization of 5β-acetoxyisocembrol

The structures and the stereochemistries of all the main products of the carbocyclization of 5β-acetoxyisocembrol on its interaction with aqueous formic acid in chloroform have been established. This reaction takes place more selectively than the cyclization of cembrene under the same conditions and is distinguished by the complete predominance in its last stage of the 1,5-hydride shift from C-15 to C-4 over the splitting out of a proton from the C(4)-methyl group.