SYNTHESIS AND STRUCTURE OF BETA-TELLUROVINYLCARBONYL COMPOUNDS

By coupling beta-chlorovinylcarbonyl compounds or beta-acylvinyltrieth ylammonium chlorides with arene (alkene) tellurolates and lithium tell uride beta-organyltellurovinyl aldehydes, ketones I and bis(beta-acylv inyl) tellurides II correspondingly have been prepared. beta-Methyltel lurovinyl aldehyde VI is readily oxidized by halogens, giving rise to previously undescribed beta-methyldihalogenotellurovinyl aldehydes IX, which convert to the respective beta-halogenotellurenylvinyl aldehyde s X via elimination of a molecule of methyl halogenide. Regardless of the initial configuration at the C-beta center of the beta-chlorovinyl carbonyl compounds, the nucleophilic vinylic substitution reaction res ults in the formation exclusively of Z-isomers of beta-organyltellurov inyl aldehydes and ketones. The stereochemical outcome of this reactio n is explained in terms of the addition-elimination mechanism of the n ucleophilic vinylic substitution reaction, as a consequence of strong stabilization of the intermediate carbanions XVIII by intramolecular c oordination of O --> Te bonds. For the same reason, nucleophilic addit ion of arenetellurolate anions to a triple bond of a-acetylenic aldehy des and ketones occurs stereospecifically, affording exclusively Z-(be ta-aryltellurovinylcarbonyl) diastereomers. The crystal and molecular structures of beta-(4-ethoxyphenyltelluro)-beta-phenylpropenal Ip and its N-(4-methylphenyl) imine V have been studied by X-ray. Both compou nds exist in the crystal as Z-diastereomers, the tellurium centers pos sessing a T-shaped configuration due to the formation of intramolecula r coordinationcorresponding to O --> Te (2.725 Angstrom) and N --> Te (2.771 Angstrom) bonds. (C) 1997 Elsevier Science S.A.