Asymmetric Neber-rearrangement

The Neber rearrangement of oxime sulfonates has been considered to proceed via a nitrene pathway or an anion pathway. If the latter mechanism is operative, the use of a certain chiral base might result in the discrimination of two enantiotropic a-protons to furnish optically active a-amino ketones. Verification of this hypothesis was provided by realizing the asymmetric Neber rearrangement of simple oxime sulfonate 83,... 

Scheme 11.24 Asymmetric Neber rearrangement of oxime sulfonate 90...

Asymmetric induction in the Neber rearrangement was also obtained under phase-transfer conditions with chiral quaternary ammonium bromides 544 as catalysts (equation 243). Moderate enantioselectivities (30-70% ee, 60-95% yield) were observed, but there is still an opportunity for extending the full synthetic utility of this classical rearrangement. 

Ooi, T., Takahashi, M., Doda, K., Maruoka, K. Asymmetric Induction in the Neber Rearrangement of Simple Ketoxime Sulfonates under Phase-Transfer Conditions Experimental Evidence for the Participation of an Anionic Pathway. J. Am. Chem. Soc. 2002, 124, 7640-7641. 

In addition to the above-mentioned asymmetric transformations, some novel phase-transfer catalytic reactions, such as dihydroxylation [143], Neber-rearrangement [144], ring-opening reaction [145], and hydrolysis [146], have emerged in recent years. Under mild PTC conditions, these asymmetric transformations involve... 

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