Issue 13, 2021

Mild reductive rearrangement of oximes and oxime ethers to secondary amines with hydrosilanes catalyzed by B(C6F5)3

Abstract

The strong boron Lewis acid tris(pentafluorophenyl)borane, B(C6F5)3, has been found to catalyze the reductive rearrangement of oximes and their ether derivatives at room temperature with hydrosilanes as the reducing agents. Cyclic substrates undergo ring enlargement, and the secondary amine products are generally formed in good yields. Control experiments combined with a DFT computational analysis of the reaction mechanism suggest that there are three energetically accessible reaction pathways (paths A–C), either or not involving hydroxylamine derivatives. Paths A and B proceed through the intermediacy of a common N,O-bissilylated hydroxylamine, and the ring-expanding rearrangement yields an iminium ion. With no intermediate at the hydroxylamine oxidation level (path C), the reaction mechanism resembles that of the Beckmann rearrangement where an O-silylated oxime converts into a nitrilium ion. The reduction–rearrangement sequence (paths A and B) is slightly preferred over the rearrangement–reduction order of events (path C), especially at ambient temperature.

Graphical abstract: Mild reductive rearrangement of oximes and oxime ethers to secondary amines with hydrosilanes catalyzed by B(C6F5)3

Supplementary files

Article information

Article type
Research Article
Submitted
11 Nah 2021
Accepted
31 Cig 2021
First published
01 Agd 2021
This article is Open Access
Creative Commons BY license

Org. Chem. Front., 2021,8, 3280-3285

Mild reductive rearrangement of oximes and oxime ethers to secondary amines with hydrosilanes catalyzed by B(C6F5)3

H. Fang, G. Wang and M. Oestreich, Org. Chem. Front., 2021, 8, 3280 DOI: 10.1039/D1QO00251A

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