Synthetic Studies Utilising Dehydroabietic Acid
This thesis is concerned with the utilisation of the natural product, abieta-8,11,13-trien-18-oic acid* (dehydroabietic acid) (1) for the synthesis of optically active steroids and diterpenoids. The work has been divided into three sections which describe transformations of rings A, B and C of abieta-8,11,13-trien-18-oic acid (1).
Selective epoxidation of the alkene mixture (3-5) derived from oxidative decarboxylation of abieta-8,11,13-trien-18-oic acid (1) with lead tetraacetate has given the epoxides (64), (65), a low yield of the epoxide (66), and the pure exocyclic alkene (3). The alkene (3) was oxidised to the ketone (6) which has been previously employed as an intermediate for the synthesis of the ?,?-unsaturated ketone (10). The epoxides (64) and (65) have been converted to the unsaturated ketones (89), (107), and (67), and the saturated ketones (13), (99) and (100). A study of the boron triflouride rearrangements of the three epoxides (64), (65) and (66) has been made using benzene and dimethyl suplhoxide as solvents, and pathways for the formation of the products are suggested.
Peracid oxidation of the enol acetate (155) derived from the C 7-ketone (18) provided a facile introduction of oxygen substituents into the hindered C 6 position of abieta-8,11,13-trien-18-oic acid (1). By hydrogenolysis of the C 7-hydroxy substituent of the compound (162), the C 6-acetate (172) was obtained. Hydrolysis of the latter compound, and methylation of the acid formed gave the C 6-alcohol (175) which was oxidised to the C 6-ketone (176).
The literature pertaining to the intramolecular functionalisation of aromatic alkyl groups has been surveyed, and, with the ultimate aim of synthesizing the aromatic steroids (237) and (249), the C 13-isopropyl group of abieta-8,11-13-trien-18-oic acid (1) has been functionalised by the application of two of the published procedure, viz. the lead tetraacetate oxidation of aromatic acids, and the thermolysis of diaxomethyl ketones.
Nitration of methyl 12-acetylabieta-8,11,13-trien-18-oate (227) has given products of nitrodeacylation (44) and nitrodealkylation (266). The product of nitrodealkylation (266) has been converted to methyl 13-hydroxy-podocarpa-8,11,13-trien-18-oate (59) in 36% yield. Methylation of the phenol (59), and Birch reduction of the methyl ether (276) has given podocarp-8(14)-en-18-ol-13-one (281). Annelation of the ?,?-unsaturated ketone (281) with bromoacetone was attempted in order to synthesize the steroid (284), but the only product identified was the furan (286).
* The numbering system used throughout this thesis is that proposed by J.W. Rose (personal communication to Professor R. C. Cambie) in “The Common and Systematic Nomenclature of Cyclic Diterpenes” 3rd revision, Oct 1968, to be submitted to the IUPAC Commission on Organic Nomenclature.