Synthesis of α-aminooxy amides through [3 + 3] cycloaddition and Sc(OTf)_3-catalyzed double C-N bond cleavage in a one-pot reaction

摘要

Various a-aminooxy amides bearing a quaternary carbon at the a-position were prepared in good to excellent yields under mild reaction conditions from N-vinyl nitrones and a-bromohydroxamates. The N-vinyl nitrones tolerate a wide range of N-vinyl fluorenone nitrones and N-vinyl isatin nitrones. Mechanistic studies show that the reaction initially proceeds through [3 + 3] cycloaddition between N-vinyl nitrones and aza-oxyallyl cations generated from a-bromohydroxamates to afford six-membered N.O-heterocycles, followed by double C-N bond cleavage in the presence of the Sc(OTf)_3 catalyst. A selective N-O bond cleavage of the obtained a-aminooxy amides is also realized under Fe/NH_4Cl conditions. Furthermore, gram-scalable preparations of a-aminooxy amides are easily achieved.