Organoselenium Chemistry. Alkylation of Acid, Ester, Amide, and Ketone Enolates with Bromomethyl Benzyl Selenide and Sulfide: Preparation of Selenocysteine Derivatives

Article abstract of DOI:10.1021/jo00365a025

Bromomethyl benzyl selenide has been prepared and used for the alkylation of several carboxylic acid and amide dianions and certain ketones and ester enolates.Clean reaction could not be achieved for ketones and esters whose alkylation products were subject to selenolate elimination.The selenide reacted 18 times more slowly than bromomethyl benzyl sulfide, which alkylated ketones in fair yield even in some cases where the selenide failed.The bromomethyl benzyl sulfide alkylation products gave α-methylene ketones upon oxidation to sulfoxide and thermolysis.Several protected amino acid enolates (valine, alanine, and glycine) were alkylated with bromomethyl benzyl selenide.The product from glycine, 5b, was converted to the protected dehydroalanine 11 by oxidation and to the protected selenocysteine 10 by using bromine cleavage of the benzyl selenide.Halogen reagents (Br2, SO2Cl2) were shown to very efficiently and generally convert benzyl selenides to selenenyl halides, which were converted to diselenides or selenides by reduction or alkylation.