N-sulfonyl imine

Saito has recently reported high yields and enantioselectivities in aziridine synthesis through reactions between aryl- or vinyl-substituted N-sulfonyl imines and aryl bromides in the presence of base and mediated by a chiral sulfide 122 (Scheme 1.41) [66]. Aryl substituents with electron-withdrawing and -donating groups gave modest transxis selectivities (around 3 1) with high enantioselectiv-... 

Warwel S, Sojka M, R6sch M (1993) Synthesis of Dicarboxylic Acids by Transition-Metal Catalyzed Oxidative Cleavage of Terminal-Unsaturated Fatty Acids. 164 79-98 Weinreb SM (1997) N-Sulfonyl Imines - Useful Synthons in Stereoselective Organic Synthesis. 190 131-184... 

In the N-sulfonyl imine-catalyzed sulfoxidation, aqueous hydrogen peroxide serves as the final oxidizing agent, which is clearly of practical advantage. In principle it can be assumed that either an oxaziridine (F, Scheme 10.17) or a hydroper-oxy hemiaminal (H, Scheme 10.17) can result as the active species from the reaction of the N-sulfonyl imine E with hydrogen peroxide (Scheme 10.17). For imine 79 the idea of an intermediate oxaziridine is supported by the experimental finding that oxidation by the isolated oxaziridine and in the catalytic reaction (using 79 and... 

Similar to the addition to HFIPA, the /MCD-mediated addition of methyl, phenyl, and naphthyl acrylates to N-sulfonyl imines afforded the (S)-adduct, which is opposite to that observed with aldehydes (Table 5.12) [95]. The best conditions were found using either dichloromethane or acetonitrile as solvent. 

Further studies concerning aza Diels-Alder reactions of N-sulfonyl imines have been carried out by Holmes et al. [200] and Whiting et al. [201,202], and the utility of glyoxylato imines for the synthesis of cyclic amino acids has been investigated by Stella s group [203, 204]. An extensive study concerning intramole-... 

In contrast to the hydrazones mentioned above, a,/ -unsaturated N -sulfonyl imines react as electron-deficient diene component in aza Diels-Alder reactions. In addition to several investigations dealing with their intermolecular cycloadditions under thermal and under high pressure conditions [231-234], Boger s... 

N-Sulfonyl Imines - Useful Synthons in Stereoselective Organic Synthesis... 

Furthermore, its Ir-complexes have performed successfully in the reductive coupling of alkynes with N-sulfonyl imines (08CAJ1384). The general synthetic route to SOLPHOS derivatives of type 59 is depicted in Scheme 13. 

The addition of arylboronic acids to imines in an aqueous solvent gave a mixture of amine (Eq. 6) and alcohol (Eq. 4) because the imines were partially hydrolyzed to the aldehyde during the reaction. The use of Ph4BNa in place of phenylboronic acid allowed the catalytic addition to various N-sulfonyl imines in the absence of water (Eq. 6). The representative results are summarized in Table 5. The cationic rhodium complexes such as [Rh(cod)(MeCN)2]BF4 was found to be the most efficient catalyst for both aromatic and aliphatic N-sulfonyl imines whereas no reactions were observed for N-alkyl and N-aryl imine derivatives. 

Related chiral ligands have been developed for the copper catalyzed addition to N sulfonyl imines, but the enantioselectivities are usually lower and/or the scope is more limited (Figure 1.6) [73]. 

Catalytic Asymmetric Nucleophilic Addition to Achiral Imines 33 Table 1.17 Iridium catalyzed vinylation of N sulfonyl imines. 

Finally, a chiral N linked C2 symmetric bidentate phosphoramidite was developed by Miyaura for the arylation of N sulfonyl imines [115]. Over 38 different chiral N tosyl amines were prepared in high yields and enantiomeric excesses using this novel ligand. These conditions were also quite effective (72 99% yield and 93 98% ee) for the arylation of N p nitrobenzenesulfonyl imines, which can be cleaved under mild conditions to liberate the free amine. 

Subsequently, Shi and Li synthesized a more nucleophilic chiral phosphine 19i and subjected it to the aza MBH reaction of N sulfonyl imines with 2 cyclohexen 1 one or 2 cyclopenten 1 one [28]. The resulting adducts could be obtained in good yields, but with moderate enantiomeric excess (Scheme 13.16). 

Until recently, N-sulfonyl imines had found only limited and sporadic use in organic synthesis. During the past decade, however, it has become increasingly clear that these species are valuable synthons and are capable of undergoing many unique transformations. A comprehensive review of the chemistry of these compounds is presented here with particular emphasis on their applications in stereoselective processes. Methods for preparing N -sulfonyl imines are outlined, along with a survey of their uses in a wide range of addition, pericyclic and cycloaddition reactions. 

This article outlines the methodology currently available for producing N-sulfonyl imines. In addition, a survey of the applications of this functionality... 

Kresze and coworkers have reported that simply heating a neat mixture of an aryl sulfonamide and an ethyl or methyl acetal from an aromatic aldehyde affords the N-sulfonyl imine in good yields [6] [Eq. (5)]. However, with the diethyl acetal of ethyl glyoxylate, only the bis-sulfonamido acetal was produced. No indication was given if this procedure was attempted with acetals of aliphatic aldehydes. 

The reaction probably involves an initial [2+2]-cycloaddition of the aldehyde and the N-sulfinyl compound to produce an adduct 2 [10] which loses sulfur dioxide to yield the N-sulfonyl imine. Isolated yields of the sulfonyl imines shown in Scheme 1 were generally quite good. In the case of the enolizable aldehyde dichloroacetaldehyde, only a low yield of N-sulfonyl imine was produced. An attempt was also made using these same reaction conditions to convert butyraldehyde to the corresponding Af-tosyl imine [6]. However, all that could be isolated here was the bis-sulfonamido acetal. 

More recently, in a series of papers Weinreb and coworkers have found that N-sulfonyl aldimines can in fact be rapidly produced in situ from aliphatic aldehydes using N-sulfinyl sulfonamides and boron trifluoride etherate as catalyst at low temperature [11-15] [Eq. (6)]. Similarly, aliphatic aldehydes can be converted to the N-sulfonyl imines in the absence of a Lewis acid at room temperature or above, but more slowly. The former procedure also works well for aromatic aldehydes, whereas the reaction is too slow to be useful if a Lewis acid is not used. The N-sulfonyl imines generated in this manner can be utilized in a number of transformations (vide infra). However, except in rare cases [16], AT-sul-fonyl ketimines cannot be formed by this methodology. 

Studies by Hudson and coworkers have demonstrated that both N-sulfonyl al-dimines and ketimines can be prepared from the corresponding aldoxime or ketoxime [18]. Thus, treatment of the oxime with a sulfinyl chloride initially affords the O-sulfinylated oxime 6 (Scheme 3). If 6 is warmed, it rearranges via a free radical process into an N-sulfonyl imine. This transformation appears to provide one of the best and most general routes to N-sulfonyl imines and has been extensively exploited recently by Boger and coworkers [19] in hetero Diels-Alder reactions (see Section 5.2). 

The direct iV-sulfonylation of simple NH imines has not been studied to any significant degree despite the availability [22] of these precursors. In a rare use of this approach, Hudson and coworkers [18] have reported two examples of N-sul-fonylation of ditolyl imine (10) to afford the N-sulfonyl imines [Eq. (7)] in reasonable yields. 

More recently, Georg et al. [23] have found that N -trimethylsilyl imines 11 of aromatic non-enolizable aldehydes and ketones, prepared by the methodology of Hart [24], can be converted to the corresponding IST-sulfonyl imines using aryl or alkyl sulfonyl chlorides (Scheme 5). Unfortunately, the procedure is not applicable to forming N-sulfonyl imines from enolizable aldehydes and ketones. 

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