Thompson, Mary C. (1937)
The configuration of heterocyclic compounds.
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A new cause of molecular dissymmetry was discovered in 1934 by Lesslie and Turner who showed that 10-methylphenox-arsine-2-carboxylic acid (I) could exist in stable dextro and laevo forms. The dissymmetry was ascribed to the folding of the molecule about the oxygen-arsenic axis, but an alternative explanation was that compound (I) contained the first known example of an asymmetric tervalent arsenic atom. If the cause of the activity in (I) is due to the folding of the molecule, it should be possible to detect similar activity in a number of other types. I have therefore investigated the possibility of obtaining and resolving the phe-noxselenine-carboxylieacid (II). The optical properties of the cinchonidiner 1- and d-a-phenylethylamine and brucine salts were examined and the latter gave some indication that the acid is a racemate. During, crystallisation the specific rotation decreased, and the crop with the lowest rotation when decomposed, gave a free acid which was dextro-rotatory, since no successful resolution of a selenoxide has been recorded, salts of the selenoxide-carboxylic acid (III) were investigated. Only the no r-d-epliedrine salt was found to be suitable for the examination of its optical properties and its specific rotation was found to remain constant during repeated fractional crystallisation. Resolution experiments were conducted upon the salts of selenoxanthone-4-car-boxylic acid, but this substance does not appear to be a racemate. The nitration of phenoxselenine-2-carboxylic acid was investigated, but I failed to get a single mono-nitrated product. An unsuccessful attempt was made to prepare 1:3-dimethylphenoxselenine-8-carboxylic acid, but 2;4-diehlorphenoxselenine-8-earboxylie acid has been prepared with a view to examining its optical properties.
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Institution: University of London, Bedford College (United Kingdom).