nitrogen source. The bright-blue reagent 1, readily accessible by chlorination of cyclohexanone oxime [4], can safely be stored for a least 1 year at -30" but is preferably distilled in vacuo before use. In contrast to infamous N-nitroso derivatives, C-nitroso compound 1 proved not to be mutagenic in the Ames test'). Nitroso compound 1 and its analogues are well known dieno-and enophiles [5] which also form nitrone products with methyl-and phenylmagnesium halides or Me,A1 [6]. Their reactivity towards enolates, however, remained totally unexplored.
Chiral 'enolates', derived from sultam 2, react with a broad range of electrophiles in a highly stereoface-selective manner [7] and, thus, were expected to undergo asymmetric C-N-bond formation on exposure to 1.
Preparation of (2R)-and (2s)-a-Amino Acids and N-Hydroxyamino Acids by Asymmetric, Electrophilic Amination. ~ Sultam 2 as well as its antipode ent-2, which are readily available on a kg scale [812) were routinely transformed into their N-acyl derivatives [gal [lo] (Scheme 2). Deprotonation of acyl sultam 3a with sodium hexamethyldisi-Scheme 2 1) NaN(SiMe& 1) NaH 2)RCH2COCI