Regioselective TEMPO oxidation of 2-alkylidene-1,3-propanediols to (E)-2-hydroxymethyl-2-alkenals and application to 4-alkylidene-2-penten-5-olide synthesis

The oxidation system comprised of TEMPO and (diacetoxyiodo)benzene (stoichiometric) is enhanced during the conversion of primary alcohols to aldehydes by adding a catalytic amount of acids, p-TsOH and PPTS. 2-Alkylidene-1,3-propanediols, available from 1,3-dihydroxyacetone, are oxidized under the stated conditions to the corresponding (E)-2-hydroxymethyl-2-alkenals, which are utilized as an intermediate for the expeditious synthesis of 4-alkylidene-2-penten-5-olides.