Au/Ag-Catalyzed Synthesis of 3-Fluorofurans

Significance

The synthesis of 2,5-disubstituted 3-fluorofurans from alk(ar)-3-yn-1-ones is reported. The starting ynone requires conversion into its TBDMS enol ether for the monofluorination (step 1). Without this, bisfluorination occurs. Non-halogenated ynones may be cyclized to furans by ­simple Lewis acid catalysis, but the fluorinated substrates are found to be unreactive under these conditions (step 2). After optimization, the cyclization was found to occur under gold/silver catalysis within short reaction times. Lowering both catalyst loadings to 1 mol% reduced the yield significantly. Although the yields are modest to excellent, the substrate scope was inadequately studied. The starting alk(ar)-3-yn-1-ones are synthesized from the reaction of the corresponding propargyl bromides with aldehydes followed by oxidation.