Morphinans stereoselectivity

Stereoselective reduction of 6-keto-compounds in the morphine, codeine, and morphinan series to 6-a- and 6-/S-hydroxy-compounds by formamidine-sulphinic acid has been reported. Dihydrocodeinone pyrrolidine enamine (141) has been shown to react with 2,4-dinitrofluorobenzene in the presence of potassium hydroxide to give the aci-nitro-salt (142), accessible also directly from dihydrocodeinone and m-dinitrobenzene in alkali. 

The vast majority of biosynthetic reactions are enzyme-catalyzed and, therefore, show considerable stereoselectivity and substrate specificity. In general, stereoselectivity is more important than substrate specificity, and many unnatural morphinan derivatives have been produced biosynthetically (Kirby et al. 1972, Brochmann-Hanssen and Okamoto 1980, Brochmann-Hanssen and Cheng 1982, 1984, Brochmann-Hanssen et al. 1982). The oxidative coupling of reticuline to salutaridine as well as the succeeding biotransformations are not very substrate specific. Several reticuline analogues have been converted to the corresponding morphine and codeine... 

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