Patent ID: 8691989

Claim:
A method for preparing a diastereomerically enriched morphinan comprising: (a) providing morphine or an analog thereof; (b) converting one or more hydroxyl groups on the morphine to one or more ester groups, in an esterification reaction, to prepare an esterified product; (c) converting the N-methyl group on the esterified product to an N—H group, in a demethylation reaction, to prepare a demethylated product, using a demethylation reagent comprising a mild oxidizing agent; (d) converting the N—H group on the demethylated product to an N-alkyl group, in an alkylation reaction, to prepare an alkylated product; and (e) purifying the alkylated product in a purification step, wherein the morphinan has the structure of formula (Ia) wherein, in formula (Ia): R 1 and R 2 and R 7 to R 9 are H; R 10 is an alkyl having the formula —CH(R 11 )(R 12 ), where R 11 and R 12 are independently methyl, ethyl, propyl, cyclopropyl, butyl, cyclobutyl, pentyl, cyclopentyl, hexyl, or cyclohexyl; and R 3a and R 6a are independently selected from H, substituted or unsubstituted C 1 -C 12 alkyl, and hydroxyl protecting groups.