Chemistry of the Podocarpaceae. XXIII. Preparation and reactions of some lactone derivatives of 12-Methoxypodocarpa-8,11,13-trien-19-oic acid

The parent lactone (V) of a series of 12-methoxypodocarpa-8,11,13- trien-19-oic acid derivatives has been prepared by successive dehydration and hydrogenation of the 7α- and 7β-hydroxy lactones (VII) and (VIII), and also by reduction of the 7-keto lactone (IV) with diborane. Attack by nucleophiles on the 7β-hydroxy lactone (VIII) is a convenient method for the preparation of less readily available 7α- substituted lactones. Treatment of the 7-keto lactone (IV) with sodium hydroxide in methanol effects a fragmentation reaction to give the diosphenol (XXIV), providing a potential method for the formation of hitherto inaccessible 6,7-diketones with a trans-fused A/B ring junction. Treatment of the diosphenol (XXV) with potassium hydroxide affords the cis-fused A/B ring junction diketo acid (XXXI) rather than the product of an expected benzilic acid rearrangement.