Facile synthesis of aromatic unsymmetrical fluorine-containing acyloins through the reductive trifluoroacetylation of benzaldehyde and transposition of the carbonyl group

The reductive coupling reaction between benzaldehyde and ethyl trifluoroacetate in the presence of magnesium and chlorotrimethylsilane in N-methyl-2-pyrrolidinone gave the acetal of the corresponding coupling compound in good yields. The yield of the coupling product largely depended on the benzaldehyde concentration in the solution and it was essential to avoid the formation of pinacol type compounds in order to obtain the coupling product in high yields. The subsequent desilylation of the acetal using tetrabutylammonium fluoride easily yielded an acyloin compound as the sole product after the transposition of the carbonyl group through keto-enol tautomerism.