PIFA-mediated oxidative cycloisomerization of 2-propargyl-1,3-dicarbonyl compounds: divergent synthesis of furfuryl alcohols and furfurals

PhI(OCOCF3)2 (PIFA) in the presence of trifluoroacetic acid (TFA) in CH2Cl2 efficiently promotes the oxidative cycloisomerization of 2-propargyl 1,3-dicarbonyl compounds to give 4,5-disubstituted furfuryl alcohols. PIFA in hexafluoroisopropanol (HFIP) or PIFA-BF3·OEt2 in CH2Cl2 bring about the direct formation of furfurals from 2-propargyl 1,3-dicarbonyl compounds. In a few cases, PhIO is suitable for the direct formation of furfurals.