Nickel(II)-Catalyzed Oxygen Transfer Reaction of N-Vinyl Nitrones to Prepare 2-(Pyridin-2-yl)ethanols

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

We described an iron(III) and BF3·OEt2-promoted oxygen transfer reaction of N-aryl-α,β-unsaturated nitrones to prepare various N,O-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 N,O-difluoroboron β-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 β-ketoiminate was easily prepared in 40% yield from estrone in four steps.

Synthesis of 1,2,4-Oxadiazolines through Deoxygenative Cyclization of N-Vinyl-α,β-Unsaturated Nitrones with in Situ Generated Nitrile Oxides from Hydroxamoyl Chlorides

A variety of 1,2,4-oxadiazoline derivatives were synthesized in moderate to good yields through a deoxygenative cyclization cascade reaction of N-vinyl-α,β-unsaturated nitrones and hydroxamoyl chlorides. Mechanistic studies revealed that the reaction underwent double additions of nitrile oxides to N-vinyl-α,β-unsaturated nitrones, sequential elimination, and intramolecular cyclization to afford 1,2,4-oxadiazolines. Alternatively, 1,2,5-oxadiazolines were also obtained as major products in i-PrOH solvent through [3 + 3] cycloaddition and selective [3,3]-rearrangement. Moreover, the prepared 1,2,4-oxadiazolines were easily converted to polysubstituted pyrroles under thermal conditions.

Synthesis of α-substituted indolylacetamide using acetonitriles as acetamide enolate equivalents through O-transfer reactions

We introduce readily available ammonium hemiaminals as O-transfer reagents and commercially available acetonitriles as a primary amide enolate precursor. The combination serves as an amide enolate equivalent, thereby providing one-pot access to α-substituted indolylacetamides. A broad substrate scope and good functional group tolerance as well as gram-scale synthesis make this protocol highly attractive. Mechanistic experiments suggest that the cyano group is trapped by a hydroxy group of hemiaminals en route to the desired primary amides under metal-free conditions.