Iron(III) and BF·OEt-Promoted O-Transfer Reaction of -Aryl-α,β-Unsaturated Nitrones to Prepare Difluoroboron β-Ketoiminates.

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