Iron(III) and BF3·OEt2-Promoted O-Transfer Reaction of N-Aryl-α,ß-Unsaturated Nitrones to Prepare Difluoroboron ß-Ketoiminates.

We described an iron(III) and BF3·OEt2-promoted oxygen transfer reaction of N-aryl-α,ß-unsaturated nitrones to prepare various N,O-difluoroboron ß-ketoiminates in good yields ranging from 24% to 87%. Control experiments revealed that the enaminone was the vital intermediate for the formation of N,O-difluoroboron ß-ketoiminates, and iron(III) combined with BF3·OEt2 played as cocatalyst to promote the oxygen transfer reaction through intramolecular cyclization and N-O bond cleavage. More importantly, an estrone-derived N,O-difluoroboron ß-ketoiminate was easily prepared in 40% yield from estrone in four steps.