Transformations of bicyclic diterpenoids

Abstract

Chapter one of this thesis reports the synthesis of two naturally occurring furanoterpenoids from manoyl oxide. The most difficult step was the construction of the furan ring system and a new reaction was developed in order to achieve this. The absolute configurations of the natural products were then related to that of manoyl oxide. Chapter two describes several attempted furan syntheses that finally led to the method that was used in chapter one. The mechanism of this new reaction was investigated and found to proceed via a cyclopropyl intermediate. Useful yields of pyrroles are also formed when ammonia or amines are included in the reaction mixture. The third chapter reports the synthesis of an analogue of the natural occurring antibiotic pisiferic acid via lead tetraacetate oxidation of 2β-hydroxymanoyl oxide resulting in functionalization at C 20. Antimicrobial testing of the analogue gave negative results. The synthesis of a naturally occurring labdane, 12β-hydroxymanoyl oxide, from manoyl oxide is described in chapter four. The functionalization of the 12-position of manoyl oxide was achieved by another lead tetraacetate long range oxidation. The corresponding 12α-isomer could not be synthesized using the same reaction sequence. Chapter five describes the attempted synthesis of the spongiane skeleton via a Diels-Alder cycloaddition. However, the diene proved to be too unreactive due to steric problems. The sixth chapter reports the isolation and characterization of two new labdanes from Lagarostrobos colensoi, namely 8,13-epoxy-3β-hydroxylabd-14-en-2-one and 8,13-epoxy-2-hydroxylabda-1,4-dien-3-one.