Sulfenimine

Increasing interest is expressed in diastereoselective addition of organometallic reagents to the ON bond of chiral imines or their derivatives, as well as chiral catalyst-facilitated enantioselective addition of nucleophiles to pro-chiral imines.98 The imines frequently selected for investigation include N-masked imines such as oxime ethers, sulfenimines, and /V-trimcthylsilylimines (150-153). A variety of chiral modifiers, including chiral boron compounds, chiral diols, chiral hydroxy acids, A-sull onyl amino acids, and /V-sulfonyl amido alcohols 141-149, have been evaluated for their efficiency in enantioselective allylboration reactions.680... 

Sulfenimines are versatile building blocks for the preparation of secondary and tertiary amines. Therefore, fluoroalkylated sulfenimines should be promising building blocks for the preparation of N-fluoroalkylamino compounds. In fact, very recently, trifluoromethylated sulfenimines have been easily prepared in... 

The sulfenimines have been shown to be highly useful building blocks for the preparation of trifluoromethylated amines, aminoketones, and aminoalkano-ates as illustrated in Scheme 6.19. 

Attempted direct extension of the two foregoing methodologies to synthesis of the 3-C-methyl analogs of 17, 18, 23 and 24 starting from the diastereoisomeric methyl ketones 10 and 12 was ineffective, as ammonia does not add across the triply substituted double bond of the 3-C-methyl analogs of the esters 19 and 20. However, the phenyl-sulfenimines 25 and 26 add allylmagnesium bromide and diallylzinc with different stereochemistry (8), so that it is possible to have eventual access to the four configurational isomers of 3-amino-2,3,6-trideoxy--3-C-methyl-3-L-hexose. 

Bromide and iodide ions are not only effective as redox catalyst in the indirect electrochemical formation of carbon-hetero atom bonds but also of hetero-hetero atom bonds. Thus, the nitrogen-sulfur bond in sulfenimides (Eq. (53) Table 4, No. 33) and sulfenimines (Eq. (54) Table 4, No. 34) can be generated. The electrogenerated active bromine species forms a positively polarized sulfenyl intermediate from disulfides. 

Direct transformation of a/p/w-aminoalkanoates 27 to the corresponding sulfenimines 29 by electrolysis with disulfide 28 in a CHjCyHjO—MgBr2—(Pt) system has been developed (Scheme 2-9)22). The procedure can be applied to the sulfenylation of C-6/C-7 amino groups of penicillins and cephalosporins 30 (Scheme 2-10). 

Chemoselective oxidation of sulfenimines 2 is a useful method for the preparation of sulfinimines 3.10-12 The oxidation was usually carried out with m-CPBA (3-chlo-roperbenzoic acid) in a biphasic mixture of chloroform and aqueous sodium bicarbonate and a variety of sulfinimines have been prepared in this way. Sulfinimines 3 were usually obtained as a single -isomer despite the fact that their precursors 2 may exist as mixtures of E- and Z-isomers.10 Other oxidants which have been demonstrated to be effective for oxidation include MMPP (magnesium monoperoxyphthalate)13 and chlorine.14,15... 

Various sulfinimines with other oxidizable groups in the molecules can also be obtained in good yields by this method.16,17 For example, chemoselective oxidation of sulfenimine 4 with m-CPBA gave sulfinimine 5 in 95% yield.16 Gordon et al. 

Optically active sulfinimines were prepared by Yang and co-workers by oxidation of nonracemic sulfenimines.20 Thus, treatment of 11 with m-CPBA or MMPP afforded sulfinimines 12 in 83-99% yield. The diastereoselectivity, however, was highly dependent on the R group in the chiral auxiliary. When R = H, diastereopure sulfinimine (/ s)-12 was obtained. 

Another approach to the enantiomerically enriched sulfinimines reported by Davis and co-workers is the enantioselective oxidation of sulfenimines with an asymmetric oxidizing reagent, (-)-jV-(phenylsulfonyl)(3,3-dichlorocamphoryl)-... 

Although no report has appeared on the direct oxidation of sulfinimines, studies have indicated that sulfonimines 106 were probably obtained on oxidation of sulfenimines 104 with excess m-CPBA via the intermediate sulfinimines 105.70,71... 

N-Sulfonyloxaziridines are an important class of selective, neutral, and aprotic oxidizing reagents.11 Enantiopure N-sulfonyloxaziridines have been used in the asymmetric hydroxylation of enolates to enantiomerically enriched a-hydroxy carbonyl compounds,9 11-13 the asymmetric oxidation of sulfides to sulfoxides,14 1S selenides to selenoxides,16 sulfenimines to sulfinimines,17 and the epoxidation of alkenes.18... 

Trifluoromethylated sulfenimines which are useful starting materials for the preparation of A(-fluoroalkylamines, aminoketones and aminoalkanoates, have been prepared by the anodic oxidation of 2,2,2-trifluoroethylamine and diaryl sulfides in MeCN/Et4NC104 with MgBr2 as the redox mediator (Scheme 49) [276]. 

When mixtures of a-aminoalkanoates and disulfides are electrolyzed in CH2CI2-H20-MgBr2 using Pt electrodes, they are transformed directly into sulfenimines [Eq. (24)] [54]. Amino groups of penicillin and cephalosporin are conveniently sulfanylated by this procedure. 

The formation of nitrogen-sulfur bonds, as in the synthesis of sulfenimides and sulfenimines [173], and phosphorous-sulfur bonds [174] is achieved by electrolyses of activated N-H and P-H compounds in the presence of an RSSR/Br mixture ... 

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