Synthesis of 4-Isoxazolines through Gold(I)-Catalyzed Cyclization of Propargylic <i>N</i>-Hydroxylamines
作者:B. Chandrasekhar、Sewon Ahn、Jae-Sang Ryu
DOI:10.1021/acs.joc.6b01499
日期:2016.8.5
New catalytic methods for the synthesis of 4-isoxazolines have been developed via catalytic intramolecularcyclizations of propargylic N-hydroxylamines. The reactions proceed rapidly in less than 1 h at room temperature in the presence of 5 mol % (PPh3)AuCl/5 mol % AgOTf or 5 mol % (PPh3)AuNTf2. This process features an efficient route to 4-isoxazolines with high yields, short reaction times, and mild
One pot synthesis of optically active 4-isoxazolines was achieved by asymmetric addition of alkynylzinc reagents to nitrones utilizing di(t-butyl) (R,R)-tartrate as a chiral auxiliary followed by cyclization. By addition of dimethylzinc, the cyclization step was accelerated to afford the corresponding 4-isoxazolines with up to 93% ee. Furthermore, a cyclized zinc intermediate could be trapped with formaldehyde to give the corresponding 2,3,4,5-tetrasubstituted 4-isoxazoline with 85% ee.