Reaction of (1S,6S)-1,7,7-trimethyl-2,3-dimethylene-trans-bicyclo[4.4.0]decane with thallium(III) acetate; a new route to (–)-warburganal and (+)-euryfuran

Oxidation of the diene (2a), obtainable in two steps from manool, with thallium(III) acetate in acetic acid yielded five products. After alkaline hydrolysis they were shown on the basis of spectroscopic evidence to be (2b), (3a), (4), (5a), and (6a). These compounds may be considered as useful intermediates to naturally occurring drimanes. On oxidation with pyridinium dichromate compound (3a) afforded the aldehyde (3b), whose acetal (3c) had previously been employed in the synthesis of warburganal (7a). Oxidation of compound (4) with pyridinium chlorochromate yielded in one step the (+)-form (8) of euryfuran.