3372-02-9

An investigation into the influence of oxidative conditions on the efficiency of opiate N-demethylation using iron powder has been carried out under non-classical Polonovski conditions. This approach involves a two-step process of N-oxidation and subsequent treatment of the intermediate N-oxide hydrochloride with the redox catalyst. Significant improvements in rate and yield have been realized for these reactions in the presence of molecular oxygen. In this context, further rate enhancement was achieved by the judicious addition of small amounts of ferric ions, leading to a concomitant reduction in the amount of the zero-valent iron primary catalyst that is required. This has led to a generalized improved methodology for the N-demethylation of oripavine, codeine, morphine, and thebaine. This protocol can also be carried out in one-pot without the need to isolate the intermediate N-oxide.

(Figure Presented) A mild and simple two-step Fe(0)-mediated N-demethylation of a number of tertiary N-methyl alkaloids is described. The tertiary N-methylamine is first oxidized to the corresponding N-oxide, which is isolated as the hydrochloride salt. Subsequent treatment of the N-oxide hydrochloride with iron powder readily provides the N-demethylated amine. Representative substrates include a number of opiate and tropane alkaloids. Key intermediates in the synthesis of semisynthetic 14-hydroxy pharmaceutical opiates such as oxycodone and oxymorphone are also readily N-demethylated using this method.