Enamines oxidation, oxaziridine

A -Arylimincs (21a) can be oxidatively rearranged to fonnamides (21b) with sodium perborate.42 The reaction works best for secondary or aryl R groups. An oxaziridine intermediate is proposed. Results with chiral secondary R groups indicate epimeriza-tion, suggested to occur via equilibration of (21a) with its enamine tautomer. 

The vast majority of organocatalytic reactions proceeds via covalent formation of the catalyst-substrate adduct to form an activated complex. Amine-based reactions are typical examples, in which amino acids, peptides, alkaloids and synthetic nitrogen-containing molecules are used as chiral catalysts. The main body of reactions includes reactions of the so-called generalized enamine cycle and charge accelerated reactions via the formation of iminium intermediates (see Chapters 2 and 3). Also, Morita-Baylis-Hillman reactions (see Chapter 5), carbene-mediated reactions (see Chapter 9), as well as asymmetric ylide reactions including epoxidation, cyclopropanation, and aziridination (see Chapter 10), and oxidation with the in situ generation of chiral dioxirane or oxaziridine catalysts (see Chapter 12), are typical examples. 

Oxidation of Enamines. Enamines are rapidly oxidized by (+)-(camphorylsulfonyl)oxaziridine (1). Disubstituted enamines give rise to racemic ot-amino ketones, while trisubstituted enamines afford, after hydrolysis, ot-hydroxy ketones (eq 2). A mechanism involving initial oxidation of the enamine to an a-amino epoxide is suggested to account for these products. 

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