American Chemical Society
ol6b00493_si_004.pdf (9.75 MB)

Dihydrooxazine N‑Oxide Intermediates as Resting States in Organocatalytic Kinetic Resolution of Functionalized Nitroallylic Amines with Aldehydes

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journal contribution
posted on 2016-06-09, 15:37 authored by Ramani Gurubrahamam, Yan ming Chen, Wan-Yun Huang, Yu-Te Chan, Hsiang-Kai Chang, Ming-Kang Tsai, Kwunmin Chen
Kinetic resolution of nitroallylic amines was established using chiral α,α-l-diphenylprolinol silyl ether auxiliary through isolation of the dihydrooxazine N-oxide intermediates. Further hydrolyzing the resting states provided tetrahydropyridines in high chemical yields and high to excellent stereoselectivities (up to >20:1 dr and 98% ee). A detailed mechanistic explanation for stereoselective protonation in the dihydrooxazine was probed computationally. In addition, the probable intermediates in α-halogenation of aldehydes (masked with enamines) were isolated to provide crystallographic evidence.