SYNTHESIS OF ALPHA-PHENYLCHALCOGENO ACETIC-ACIDS, ETHYL-ALPHA-PHENYLCHALCOGENO ACETATES AND ETHYL-ALPHA-HALO-ALPHA-PHENYLCHALCOGENO ACETATES

Reaction of phenyltellurolate or phenylselenolate anion with alpha-bro moacetic acid under phase transfer conditions using a liquid-solid sys tem affords the alpha-phenyltelluro acetic acid and the alpha-phenylse leno acetic acid in 44 and 50% yields respectively. Under similar reac tion conditions, phenyl chalcogenate anions react with ethyl alpha-bro moacetate to give the corresponding ethyl-alpha-phenyltelluro acetate in 52% and ethyl-alpha-phenylseleno acetate in 47% yield. Reaction of phenylselenenyl chloride with ethyl diazoacetate in THF at 0-degrees-C yields exclusively the ethyl-alpha-chloro-alpha-phenylseleno acetate in 88% yield. Similar reactions performed by addition of phenylselenen yl bromide in THF or benzene to the ethyl diazoacetate at different te mperatures result in mixtures of ethyl-alpha-bromo-alpha-phenylseleno acetate and ethyl-alpha,alpha-bis(phenylseleno) acetate in different r atios. However, when the ethyl diazoacetate was slowly added to a solu tion of phenylselenenyl bromide in benzene under reflux, the ethyl-alp ha-bromo-alpha-phenylseleno acetate was obtained in 84% yield as the o nly product. Reaction of ethyl diazoacetate with phenyltellurenyl brom ide in benzene at room temperature results in formation of ethyl-alpha -bromo-alpha-phenyltelluro acetate that decomposes rapidly into the co rresponding tellurone. Addition of ethyl diazoacetate to a mixture of diphenyldiselenide and copper sulfate in benzene under reflux results in a mixture of ethyl-alpha-phenylseleno acetate: ethyl-alpha,alpha-bi s(phenylseleno) acetate (10:1). Using an alternative route, the ethyl- alpha-phenylseleno acetate was obtained in 74% yield by esterification of alpha-phenylseleno acetic acid in benzene with ethanol/sulfuric ac id. The ethyl-alpha-phenylseleno acetate was transformed into the ethy l-alpha-bromo-alpha-phenylseleno acetate in 41% yield by treatment wit h N-bromosuccinimide. On the other hand, the copper-catalyzed thermal reaction of ethyl diazoacetate with diphenyl ditelluride in benzene af forded the corresponding ethyl-alpha-phenyltelluro acetate as the only product.