Asymmetric Hydrogenation of Isoxazolium Triflates with a Chiral Iridium Catalyst
作者:Ryuhei Ikeda、Ryoichi Kuwano
DOI:10.1002/chem.201600732
日期:2016.6.13
enantiomeric ratio (e.r.). Chiral cis‐isoxazolidines were obtained in up to 89:11 e.r., with no formation of their trans isomers, when the substrates had a primary alkyl substituent at the 5‐position. The mechanistic studies indicate that the hydridoiridium(III) species prefers to deliver its hydride to the C5 atom of the isoxazole ring. The hydride attack leads to the formation of the chiral isoxazolidine via
Thirteen N-substituted 4-isoxazoline derivatives were obtained by reaction of 3-unsubstituted and 3, 5-disubstituted isoxazolium salts with Grignard reagents. Similarly, 3-benzyl-2-methyl-2, 3, 4, 5-tetrahydronaphth [2, 1-d] isoxazoles and 3-benzyl-2-ethyl-2, 3-dihydrobenzisoxazole were produced by reaction of the corresponding quaternary salts with benzylmagnesium chloride. Thermal reactions of some 4-isoxazoline derivatives and 3-benzyl-2, 3, 4, 5-tetrahydronaphth [2, 1-d] isoxazole derivatives leading to substituted pyrrole derivatives and 3H-benz [e] indole derivatives were investigated. A tentative mechanism for the formation of pyrrole from 4-isoxazoline is also presented.