Hydrogen peroxide oxidation of polysubstituted pyrylium salts: formation of enol esters and furans

摘要: Abstract 2,4,6-Trialkylsubstituted pyrylium salts 1 have been known to afford 2-acyl-3,5-dialkyl-furans 2 in moderate yields (30 – 45%). Oxidation of these buffer solutions (pH = 3 4.5) increased the acylfurans 75%. In contrast, tetra- and penta-substituted are mainly converted into enol esters with a δ-keto group furans all originating presumably by CO bond cleavages common intermediate. This intermediate may result acyl shift as inferred from analogous compounds deuterium labelling.