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Strategies for the generation of noroxymorphone from 14-hydroxymorphinone are presented. Noroxymorphone is the key intermediate in the synthesis of various opioid antagonists, including naloxone, naltrexone and nalmefene, as well as mixed agonists-antagonists like nalbuphine. The transformation requires removal of the N-methyl group from the naturally occurring opiates and a double bond hydrogenation. The pivotal reaction step thereby is a N-methyl oxidation with colloidal palladium(0) as catalyst and pure oxygen as terminal oxidant. The reaction produces a 1,3-oxazolidine intermediate, which can be readily hydrolyzed to the corresponding secondary amine. Different reaction sequences and various phenol protection groups were explored. The most direct route consumes only H2, O2 and H2O as stoichiometric reagents and produces only H2O as by-product. Challenges inherent in gas-liquid reactions with oxygen as oxidant were addressed by developing a continuous flow process.

The palladium-catalyzed N-demethylation of the opioid alkaloids oxymorphone 3,14-diacetate and 14-hydroxymorphinone 3,14-diacetate to their nor-derivatives with oxygen as the terminal oxidant has been investigated. Palladium(II) acetate forms colloidal palladium(0) particles upon heating in N,N-dimethylacetamide. The palladium(0) particles are effective catalysts for the aerobic N-demethylation of these opiate alkaloids. Demethylation of 14-hydroxymorphinone 3,14-diacetate with pure oxygen as oxidant in a continuous flow reactor provided the demethylated product with excellent selectivity after residence times of only 10–20 min with 2.5–5 mol % palladium acetate as catalyst on a laboratory scale. Scale-up of the oxidation in a 100 mL flow reactor (combination of FlowPlate A6 and coiled tube to enhance the gas–liquid mass transfer), hydrogenation in a packed bed reactor, and subsequent hydrolysis afforded the desired noroxymorphone in high quality and good yield on a kg scale. The reaction sequence consume...

Oxymorphone was converted to naltrexone in three steps by palladium-catalyzed oxidative N-demethylation and intramolecular acyl transfer from C-14 hydroxy to N-17. Vitride™ reduction of N-acylamide to N-alkylamine proceeded with concomitant reductive deprotection of C-6 and O-3 functionalities.

An improved preparation of buprenorphine via palladium-catalyzed N-demethylation/acylation is reported. Three routes were investigated and compared in overall yield. The first involved N-demethylation/acylation of an advanced intermediate obtained from thebaine followed by hydrolysis of the N-acetamide and alkylation with cyclopropylmethyl bromide and/or reduction of the N-acetyl group with the Schwartz reagent followed by N-alkylation. The second route employed cyclopropylcarboxylic acid anhydride in the N-demethylation/acylation protocol and subsequent reduction of the cyclopropylcarboxamide by either lithium aluminum hydride or under hydrosilylation conditions. Both of these routes originated in thebaine and therefore required O-demethylation as a final step. The third route employed an N-demethylation/acylation sequence starting from oripavine rather than thebaine, thus avoiding the O-demethylation. The routes are compared for overall efficiency and experimental and spectral data are provided for all new compounds.

Morphine alkaloids and some of its derivatives (morphine, codeine, thebaine, oripavine, hydrocodone, and oxycodone) were subjected to fermentations with six fungal strains. The alkaloids were transformed to a variety of products via biological oxidations, reductions, and oxidative demethylations. The strain Cunninghamella echinulata proved to be the most effective for demethylations of all of the above compounds, except for morphine. The time profile of the conversion of 3-[14CH3]thebaine to 3-[14CH3]northebaine by C. echinulata cultures was also determined.

Hydrocodone was converted to various N-acyl derivatives via a one-pot N-demethylation/N-acylation protocol catalyzed by palladium(II). The procedure has also been successfully applied to several N-methyltropane alkaloids. A plausible mechanism is suggested.

Thebaine was converted into its iron tricarbonyl complex, which underwent successive N- and O-demethylation with BrCN and BBr 3 , respectively. Decomplexation of the iron tricarbonyl moiety was accomplished with ammonium cerium(IV) nitrate (CAN) and base-catalyzed hydrolysis furnished nororipavine. When excess CAN was used the methoxydiene unit was converted into its C-14 nitrate that on hydrogenation and further hydrolysis furnished noroxymorphone. Full experimental and spectral data are provided for all key compounds.

The synthesis of nalbuphine (VI) from oripavine (I) requires only five chemical transformations and is conducted with an overall yield of 45%, in contrast to current methods requiring seven to ten steps.

Buprenorphine was synthesized from oripavine by a sequence involving the conversion of oripavine into its cyclopropylmethyl quaternary salt, N-demethylation with thiolate to N-cyclopropylmethyl nororipavine, and conversion of this material to the title compound by previously available methods. The new synthesis avoids toxic reagents used previously, is shorter, and proceeds in comparable yields. Experimental and spectral data are provided for all new compounds.