Formic acid catalysed rearrangement of 5beta-methyldihydrothevinols (= 3,6-dimethoxy-5,17-dimethyl-4,5-epoxy-6,14-ethanomorphinan-7-methanols): synthesis of new doubly bridged morphinan derivatives.

We recently showed that substitution of a 5beta-methyl group allows the isolation of 14-alkenyldihydrocodeinones from the action of hot formic acid on certain dihydrothevinols. It has now been shown that, in those dihydrothevinols which are converted to stable side chain olefins by such treatment, introduction of a 5beta-methyl group results in the formation of new doubly bridged morphinan derivatives in addition to the dihydrocodeinones or olefins. The new morphinans have low affinities for opioid receptors.