Application of oxidative aryl migration in organo-selenium and -tellurium compounds to the synthesis of 2-arylpropanoic acids

Abstract

The ethylene acetals of aryl α-phenylseleno- and α-phenyltelluro-ethyl ketones [aryl =p-XC₆H₄(X = H, Me, Buⁱ, Ph, Br) and 5-bromo-6-methoxy-2-naphthyl] have been prepared in 12–83% yields by treating the corresponding α-bromo compounds with diphenyl diselenide–sodium or diphenyl ditelluride–sodium, respectively, in tetrahydrofuran–dimethylformamide under reflux for 6–20 h, during which the bromine is substituted by the PhSe or PhTe group. This substitution is not observed when the (PhM)₂–NaBH₄–EtOH (M = Se, Te) system which is known as a source of PhM^– anion is used. Oxidation of the acetals thus formed with an excess of meta-chloroperbenzoic acid at 20–25 °C for 1 h affords hydroxyethyl 2-arylpropanoates in 56–86% yields via aryl group migration which are hydrolysed to 2-arylpropanoic acids, some of which are pharmaceutically important compounds. Overall isolated yields of 2-arylpropanoic acids are around 30–42% based on the starting propiophenones over 5 steps.