Synthesis and reactions of heterocyclic sulphur compounds

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Spreadbury, A.C., 1981. Synthesis and reactions of heterocyclic sulphur compounds. PhD, Nottingham Trent University.

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Abstract

This thesis describes the synthesis of substituted m-dithiins by the reaction of acetylenic esters with aromatic aldehydes and hydrogen sulphide in the presence of boron trifluoride etherate, and their thermal rearrangement to the corresponding 3,4-dihydro-o-dithiins. Chemical evidence is presented for the proposed mechanism of formation of the 3,4- dihydro-o-dithiins, and the stereochemistry and reactions of the m- and o-dithiins are discussed.

The preparation of several new m-dithiin analogues and their thermal rearrangement was carried out. Treatment of dimethyl 2,4-diphenyl-4H-m-dithiin-5,6-dicarboxylate with n-butyllithium followed by water resulted in a prototropic shift and the formation of a tautomeric m-dithiin. Reaction of the deprotonated species with appropriate electrophiles afforded deutero-, methyl- and acetyl-substituted m-dithiins. The two tautomeric m-dithiins were the subject of X-ray crystallographic determinations, which furnished information regarding their configuration and conformation.

Oxidation of dimethyl 2,4-diphenyl-4H-m-dithiin- 5,6-dicarboxylate gave a mixture of monosulphoxide isomers which were separated and their configuration assigned. The same m-dithiin, when treated with aqueous base, suffered an unusual sulphur extrusion yielding a thiophen; the mechanism of this transformation is considered.

Cis and trans isomers of dimethyl 3,4-dihydro-3,4- diphenyl-o-dithiin-5,6-dicarboxylate were isolated, and their configurations were assigned by spectroscopic and chemical means. Attempts were made to form anhydro-o-dithiins, first by direct dehydrogenation, then by other routes involving oxidation followed by halogenation.

Desulphurisation of 3 ,4-dihydro-io-dithiins with trivalent phosphorus reagents gave stereospecific conversion to a series of new and previously inaccessible 2,3- dihydrothiophens; these were converted by dehydrogenation into thiophens.

Initial attempts to hydrolyse vicinal dicarboxylic ester groups in both m- and o-dithiins were unsuccessful, as were attempts to form the required diacids by the protection, cyclisation and deprotection of acetylenedicarb- oxylic acid. Reaction of the diesters, however, with boron trifluoride etherate in the presence of water, led to the isolation in high yield of the corresponding carboxylic anhydrides. The required diacids were prepared from these by standard methods.

Item Type:

Thesis

Creators:

Spreadbury, A.C.

Date:

1981

ISBN:

9781369315967

Identifiers: