Chemistry of the Podocarpaceae. XIX. Oxidation of some Podocarpa-8,11,13-trien-19-oic acid derivatives with lead tetraacetate

Abstract

A pathway involving the γ,δ-unsaturated acid (XIV) is suggested for the formation of lactones (IX) and (XII) from the oxidation of 12- methoxypodocarpa-8,11,13-trien-19-oic acid (I) with lead tetraacetate. Support for this suggestion has been obtained from an examination of the products from lead tetraacetate oxidations of 12-methoxypodocarpa- 6,8,11,13-tetraen-19-oic acid (XIV), methyl 12-methoxy-podocarpa- 8,11,13-trien-19-oate (II), methyl 12-methoxypodocarpa-6,8,11,13- tetraen-19-oate (XV), 12-methoxypodocarpa-8,11,13-trien-19-oic acid (XVIII), methyl 12-hydroxypodocarpa-8,11,13-trien-19-oate (III), methyl 12-acetoxypodocarpa-8,11,13-trien-19-oate (IV), 7-acetoxy-12- methoxypodocarpa-6,8,11,13-tetraen-19-oic acid (XVI), and methyl 7- acetoxy-12-methoxypodocarpa-6,8,11,13-tetraen-19-oate (XVII).     Evidence is presented confirming the assignment of a 7α- configuration for the acetoxy group of the acetoxy lactone (IX), and the preparation of some bromo 7-oxo- and 6,7,19-hydroxy derivatives of 12-methoxypodocarpa-8,11,13-trien-19-oic acid (I) is described.