The biosynthesis of alkaloids derived from tyrosine is reviewed, on the basis of recent tracer studies in the field. Evidence for the most widely accepted concept for the biosynthesis of the Amaryllidaceae alkaloids has been accumulated by a series of tracer experiments. Hypothetical phenolic precursors were synthesised containing a labelled carbon atom, and their incorporation into alkaloids of the family investigated. Various degradations to establish the labelling pattern have been carried out, and in the light of available evidence a plausible biosynthetic route to two of the alkaloids has been proposed. Unambiguous proof is presented for the derivation of the methylenedioxy group of haemanthamine from the methoxyl group of one of the precursors synthesized. A series of experiments to establish the obligatory nature of various precursors has been carried out, in particular, one phenolic precursor has been shown to be a necessary intermediate in alkaloid biosynthesis.

Investigations are described of the slow combustion of six aliphatic esters, ethyl acetate, ethyl formate, methyl acetate, n—propyl acetate, isopropyl acetate and ethyl propionate. The main purpose of the work was to elucidate the reaction mechanism with a particular view to discovering whether or not high yields of single oxidation products could be obtained. In the Introduction (Section 1) the mechanism of gaseous oxidation of organic compounds is reviewed. Possible means of controlling such reactions are discussed, particular attention being paid to the selectivity of attack arising from the presence of certain groups in the fuel molecule. The experimental methods employed are discussed in Section 2. The combustion experiments were carried out in a flow system. Chemical methods of analysis were adopted for estimation and determination of the acids, aldehydes, ketones and peroxides formed during combustion. Wherever possible the absence or presence of certain products was confirmed by spot tests and by gas liquid chromatographic analysis. Liquid chromatography was used for separation and estimation of individual carboxylic acids. In Section 3 are given the results of a detailed study of the oxidation of ethyl acetate. Determination of the effects of temperature and reactant ratio on the formation of acids, aldehydes, ketones and peroxides has elucidated the pattern of the product formation, a mechanism consistent with this pattern is proposed in Section 4. In Section 5 an account is given of the effect of temperature on the oxidation of the other esters studied. The results obtained show that these compounds in their behaviour on oxidation exhibit distinct similarities to ethyl acetate. The extent to which the mechanism postulated for ethyl acetate oxidation is a general one is discussed in Seution 6. It appears that a primary chain cycle common to the oxidation of each ester involves initially abstraction of hydrogen from the carbon atom in the -position to the 'ethereal' oxygen leading to hydroperoxylation. The hydroperoxides formed may break down by several routes, furnishing a variety of combustion products, and an attempt is made to explain the important differences between the results obtained with the various esters in terms of structural influences. It is concluded that a mechanism of slow combustion common to many esters has been elucidated. Despite the specificity of initial attack, however, the large number of possible modes of breakdown of a given hydroperoxide makes it unlikely that high yields of specific products can be obtained by the controlled oxidation of esters.

This thesis, which is divided into three main sections, deals mainly with the transannular cyclisation reactions of some alicyclic dienes. In the first part of the thesis, the synthesis and cyclisation reactions of germacrene, a possible intermediate in the biosynthesis of certain classes of sesquiterpene, are described. Germacrene, a cyclodecane sesquiterpene, can be converted to sesquiterpenes of the selinane and elemane types. The second section is concerned with the related medium-ring sesquiterpenes, humulene and caryophyllene. The mechanisms of the formation and decyclisation of some tricyclic humulene derivatives are discussed. Also described are the reduction reactions of two brominated humulene derivatives, and some attempts to convert caryophyllene to humulene. Finally, a new method for the preparation of 1,4-dienes by the lithium in liquid ammonia reduction of suitable acetoxy-dienes is described. 1,4-Dienes fulfilling certain geometrical requirements give the product of honoconjugate 1,5-addition on treatment with bromine or hypobromous acid.

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