Studies in the synthesis of the higher terpenes

• Main Author: Whiteley, J. M.
• Published: University of Oxford 1963
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.734622

In the introduction to this Thesis recent progress in the biogenesis of triterpenes is discussed with particular reference to the dammarene diols (XI a and b). This example is also taken to illustrate the techniques now used in the elucidation and determination of such complex structures. There follows a survey of the methods used in the total synthesis of pentacyclic triterpenes. Because of difficulties presented by both the structure and the stereochemistry of such molecules the approaches have necessarily been limited to three main courses of attack, the acid-catalysed cyclisation of aqualene (XII), the combination of two decalin derivatives to provide rings AB and DE of the pentacyclic system, and the combination of a of a tricyclic ABC moiety with a monocyclic unit to provide ring E. The main body of this Thesis is divided into two sections (A and B). In the first a detailed investigation is made into a previously reported route from elemadienolic acid (I) to a possible ABC tricyclic intermediate (I→IX) with particular emphasis being placed on yields and reproducibility. It is shown that the route has several undesirable features and a superior alternative is offered (X→XI→IX). In connection with this work two potential monocyclic ring E precursors have been synthesised (XIIIa and XIVa) and an attempted electrolytic coupling of (XIIIa) and (IX) has been carried out. The second section represents a continuation of the work of Littlehailes and is devoted to the synthesis of a hydroxylated bicyclic AB unit (XV) which could be utilised in alkylating the decalone (XVI) with the aim of constructing a pentacyclic triterpene of the amyrin series.