Chemistry of the Podocarpaceae. XVII. Ring-A modifications of O-methylpodocarpic acid

Abstract

Methods for the conversion of 0-methylpodocarpic acid (I) into 12-methoxy-16-norpodocarpa-8,11,13-trien-4-amine (11) have been examined, a Curtius reaction on the acid chloride (IV) followed by hydrolysis of the isocyanate (111) with 85% w/w sulphuric acid affording the highest overall yield (44%). Some "simple deaminations" involving no change in oxidation state, have been investigated as possible routes to alkenes suitable for further modification of the A ring of podocarpio acid. These include nitrous acid deamination, treatment of the N-benzoate (VIII) with phosphorus pentabromide or pentachloride, and pyrolysis of the tertiary amine oxide (VII) or quaternary methylammonium iodide.