Rhodium(ii)-mediated reactions of thiobenzoylketene S,N-acetals with α-diazo carbonyl compounds: synthesis of 2-substituted 3-alkylamino-5-phenylthiophenes

Abstract

Treatment of 3-methylamino-3-methylsulfanyl-1-phenylpropenethione 1 with excess (2.5 equiv.) α-diazo carbonyl compounds such as α-diazoketones and α-diazoesters in the presence of a catalytic amount of Rh(II) acetate in CH₂Cl₂ at rt gave 2-acyl- or 2-aroyl-3-methylamino-5-phenylthiophenes and alkyl 3-methylamino-5-phenylthiophene-2-carboxylates, respectively, as major products along with 1-phenyl-2-methylsulfanylethanones. The formation of the major products indicates that the carbenes or carbenoids generated interact initially with the thione sulfur of 1.