Synthesis of racemic and chiral codeine and morphine via the dihydrothebainones. (Chemistry of opium alkaloids, part XI)

Article abstract of DOI:10.1002/recl.19790980612

Racemic and chiral 1-(3,5-dibenzyloxy-4-methoxybenzyl)-1,2,3,4-tetrahydro-6-methoxy-isoquinoline (1, Scheme) were N-methylated, which gave 2a. A Birch reduction converted 2a, via 2b, into the 1,4-diene 3. Acid-catalysed cyclization of 3 gave the morphinan 4. Selective removal of the hydroxyl group in position 2, via the 1-phenyl-5-tetrazolyl ether (5), by hydrogenolysis, yielded (-)-dihydrothebainone-(6). The conversion of 6 into (-)-codeine and (-)-morphine is known. In this way our preceding synthesis is shortened by two steps.