Transformations and rearrangements of diterpenoids

Abstract

Chapter I Ozonolysis of a hydroquinone derived from podocarpic acid gave the biologically active natural product, winterin. Treatment of a quinone with ozone gave a ring contracted spirofuranone, a mechanism for formation of which is proposed. Chapter II Totarol has been converted into a type A nagilactone analogue by oxidative decarboxylation of an acid. The acid was formed from a benzyl ester after removal of the protecting group by hydrogenolysis, thereby circumventing a difficult hydrolysis step encountered in a previous conversion of a methyl ester into the acid. Chapter III Treatment of totary1 methyl ether under Friedel-Crafts acetylation conditions gave three products of rearrangement in addition to the expected acetyl compound. The structures of these side products were investigated and a mechanism is proposed for their formation. Chapter IV Podocarpic acid and totarol have been converted into five diterpenoids reported to have been isolated from the neem tree. The synthetic diterpenoids have been compared with the natural diterpenoids but only the structure of nimbidiol has been confirmed. The structure for margosolone has been revised after synthesis of both its reported and actual structures. Chapter V Derivatives of totarol and podocarpic acid have been oxygenated in ring C via their corresponding aryl bromides, to form catechol derivatives. These oxygenations have been accomplished by the use of copper (I) in catalytic quantities. Chapter VI The two intermediates postulated in the rearrangement of a naphthopyranone into a naphthofuranone have been synthesised and coupled. This provides some support for a previously proposed rearrangement mechanism. Chapter VII 7-Oxototaryl acetate has undergone a perchloric acid catalysed acetylation at the 6α position. 7-Oxototaryl acetate has also undergone a Baeyer-Villiger reaction which another worker had previously been unable to achieve.