Synthesis and structure of β-tellurovinylcarbonyl compounds

Abstract

By coupling β-chlorovinylcarbonyl compounds or β-acylvinyltriethylammonium chlorides with arene (alkene) tellurolates and lithium telluride β-organyltellurovinyl aldehydes, ketones I and bis(β-acylvinyl) tellurides II correspondingly have been prepared. β-Methyltellurovinyl aldehyde VI is readily oxidized by halogens, giving rise to previously undescribed β-methyldihalogenotellurovinyl aldehydes IX, which convert to the respective β-halogenotellurenylvinyl aldehydes X via elimination of a molecule of methyl halogenide. Regardless of the initial configuration at the Cβ center of the β-chlorovinylcarbonyl compounds, the nucleophilic vinylic substitution reaction results in the formation exclusively of Z-isomers of β-organyltellurovinyl aldehydes and ketones. The stereochemical outcome of this reaction is explained in terms of the addition—elimination mechanism of the nucleophilic vinylic substitution reaction, as a consequence of strong stabilization of the intermediate carbanions XVIII by intramolecular coordination of O ș Te bonds. For the same reason, nucleophilic addition of arenetellurolate anions to a triple bond of α-acetylenic aldehydes and ketones occurs stereospecifically, affording exclusively Z-(β-aryltellurovinylcarbonyl) diastereomers. The crystal and molecular structures of β-(4-ethoxyphenyltelluro)-β-phenylpropenal Ip and its N-(4-methylphenyl) imine V have been studied by X-ray. Both compounds exist in the crystal as Z-diastereomers, the tellurium centers possessing a T-shaped configuration due to the formation of intramolecular coordination corresponding to O ș Te (2.725 Å) and N ș Te (2.771 Å) bonds.