The Oxidation of Acetophenones to Arylglyoxals with Aqueous Hydrobromic Acid in Dimethyl Sulfoxide

Article abstract of DOI:10.1021/jo00225a004

The reaction of acetophenones with aqueous hydrobromic acid (HBr) in dimethyl sulfoxide (Me2SO) leads to the formation of arylglyoxals in good yield.Evidence has been obtained which suggests that this oxidation is mediated by a low concentration of molecular bromine, with the consecutive intermediacy of the α-bromo- and α-hydroxyacetophenones.The reaction of α-bromoacetophenone 2 with Me2SO alone provides the arylglyoxal 4 with the glyoxylic acid 6 as the major products.The α-hydroxyacetophenone 3 and thiol ester 5 are intermediates leading to 4 and 6, respectively, and may be isolated as minor products.The presence of water in the medium suppresses the formation of 5 and 6 and results in a cleaner conversion to 4.Treatment of aryl aldehyde 13 with 14 followed by reaction of the resulting 15 with aqueous HBr in Me2SO gave arylglyoxal 4 in good yield.