REACTION OF DIAZOMETHANE WITH SELENOESTERS PREPARATION OF α-(ALKYL- OR ARYLSELENO)METHYL KETONES AND METHYL KETONES

Article abstract of DOI:10.1016/S0040-4020(01)96714-6

The reaction of diazomethane with a series of selenoesters 1 in the presence of CuI, CuSePh or Cu powder produced α-(alkyl- or arylseleno)methyl ketones 2 in yield of 41-65percent.Methyl ketones 3 and bis(arylseleno)methanes 9 or 14 were formed as by-products.The direct conversion of selenoesters to methyl ketones was accomplished in high yield by the usual reaction with diazomethane, followed by workup with HBr solution.The simultaneous copper-catalyzed reactions of selenoesters 1c and 1i with diazomethane resulted in crossover, with the formation of all four possible α-seleno ketones 2b, 2c, 2h and 2i.A non-concerted mechanism involving attack by the diazo compound upon the acyl carbon atom of an activated selenoester with the formation of a tetrahedral intermediate 11 has been suggested.The reaction of the selenothiocarbamate 4 with diazomethane resulted in 1,3-dipolar cycloaddition to afford 5 instead of insertion into the acyl-selenium bond.