The synthesis of some odorous compounds

Lane, Roger Michael (1976) The synthesis of some odorous compounds. University of Southampton, Doctoral Thesis.

Abstract

The synthesis of fragrant compounds is an important aspect of organic chemistry on account of their intrinsic value and the opportunities they present for the application of new synthetic methodology.Cyclic 2-hydroxy-2-enones make an important contribution to the odour and flavour of a wide variety of foodstuffs. A new general synthetic route to these compounds was developed, based upon the cyclisation of dialdehydes to cyclic acyloins under the catalytic influence of thiazolium salts and subsequent oxidation to the enolised a=diketones. The catalysis of the cyclisation by thiazolium salts mimics in vitro the role playedd by the coenzyme thiamine pyrophosphate in biological systems. A number of both. naturally occurring and novel cyclic enolones was prepared including 2-hydroxy-3-methylcyclopent-2en-i-one, an important industrial caramel flavouring. The ability of thiazolium salts to catalyse the intramolecular addition of aldehyde groups to a variety of other functional groups was investigated. A competing intermolecular reaction to give dimeric acyloins was. found to restrict the general, applicability of these reactions. Attempts were made to synthesise substitutes for methyl jasmonate, a valuable material in perfumery, and -6-lactones by the intramolecular conjugate addition of an aldehyde group to an acrylic function.A synthesis of,4-(2,6,6-trimethyl cyclohex-3-enyl)but- 3-en-2-one,a fragrant member of the ionone family, utilised an acid catalysed Diels-Alder reaction to construct a suitably substituted cyclohexene ring which was then further elaborated. A similar route was applied,less successfully, to the synthesis of 4-(2,6,6-trimethlcyclohexa1,3-dienyl)but-3-en-2-one, a naturally occurring synthetic precursor..to the plant growth hormone abscisic acid. Several approaches to the conversion of ionones into the isomeric damascones through epoxide intermediates are also described.

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