Synthesis of model compounds related to the tetranortriterpenes / by M. Iqbal Tahirkheli

Abstract

In this thesis some preliminary studies have been described, which were aimed at the synthesis of compounds in which a 3-substituted furan is attached to a 6-lactone ring so as to yield structures of the type observed in the naturally occurring tetranortriterpenoids (e.g. see structures [8] till [13] on pp. 2 and 3). In an introductory literature survey various types of naturally occurring 3-substituted furan compounds have been described, and an outline has been given of some of the possible approaches to the synthesis of compounds containing a part structure [12] (p.3). Since 3-halofurans are essential starting materials for such a synthesis, the effectiveness of some preparations of 3-iodofuran and 3-bromofuran as reported in the literature has been studied. The reactions of 3-furyl^lithium and 3- thieny1-lithium with aldehydes and esters led to the isolation of coupling products, which were studied in some detail. Thus, oxidation of the alcohols obtained in this way gave information on the relative stabilities of this type of compounds under oxidising conditions. A mass spectrometric study of these model compounds led to the observation of some interesting fragmentation patterns which are discussed in detail. Finally, various reactions are discussed which were directed towards the preparation of derivatives of a-tetralone, which could be used in similar coupling reactions, in order to arrive at the desired 3-furyl-lactone structure. These modifications of the a-tetralone molecule were largely unsuccessful. Therefore, the discussion is concluded with an examination of the reasons for these difficulties, and some suggestions are made with respect to future studies in this area.