Abstract:
The optically active ketone 12-methoxy-15,l6-dinorpodocarpa-4,8,11, 13-tetraen-3-one (9) * has been synthesised from podocarpic acid (1a) via the methoxy-alkene, 12-methoxy-16-norpodocarpa-4(15),8,11,13-tetraene (2). Preparation of the methoxy-alkene intermediate (2) was achieved by decarboxylating 12-methoxypodocarpa-8,11,13-trien-16-oic acid (1b) with lead tetra-acetate, and also by deaminating 12-methoxy-l6-norpodocarpa-8,11,13-trien-4-amine (33) with nitrous acid. Other products obtained from the lead tetra-acetate decarboxylation reaction were the alkenes (10) and (11), the tertiary acetate (12b), and the lactones (15a) and (16). Evidence for the stereochemistry of these compounds is presented and pathways for their formation are suggested. Nitrous acid deamination of the primary amine (33) afforded the methoxy-alkenes (2), (10) and (11), together with the epimeric alcohols (12a), and (14), and the tertiary acetate (12b). It is suggested that substitution products from this reaction arise from an SN1 mechanism while an E1 mechanism is proposed to account for the products from elimination. Ozonolysis, and potassium permanganate or osmium tetroxide - sodium metaperiodiate oxidations of the methoxy-alkenes (4) give inter alia the cis-A/B-ring fused ketone, 12-methoxy-15,16-dinor-5B-podocarpa-8,11,13-trien-4-one (3), an intermediate in the synthesis of the ketone (9). * Normal steroid numbering is used throughout this thesis.