Chloramine reactions with alkenes

Telturoxide elimination.2 Tellurides are converted to alkenes by reaction with chloramine-T, presumably via the adduct a (equation I). This elimination proceeds In low yield with r-butyl hydroperoxide. 

A-Tosylaziridines can be obtained directly from alkenes by reaction with Chloramine T, as shown below. ... 

The metal catalyst is not absolutely required for the aziridination reaction, and other positive nitrogen sources may also be used. After some years of optimization of the reactions of alkenes with positive nitrogen sources in the presence of bromine equivalents, Sharpless et al. reported the utility of chloramine-T in alkene aziridinations [24]. Electron-rich or electron-neutral alkenes react with the anhydrous chloramines and phenyltrimethylammonium tribromide in acetonitrile at ambient temperature, with allylic alcohols being particularly good substrates for the reaction (Schemes 4.18 and 4.19). 

A more practical, atom-economic and environmentally benign aziridination protocol is the use of chloramine-T or bromamine-T as nitrene source, which leads to NaCl or NaBr as the sole reaction by-product. In 2001, Gross reported an iron corrole catalyzed aziridination of styrenes with chloramine-T [83]. With iron corrole as catalyst, the aziridination can be performed rmder air atmosphere conditions, affording aziridines in moderate product yields (48-60%). In 2004, Zhang described an aziridination with bromamine-T as nitrene source and [Fe(TTP)Cl] as catalyst [84]. This catalytic system is effective for a variety of alkenes, including aromatic, aliphatic, cyclic, and acyclic alkenes, as well as cx,p-unsaturated esters (Scheme 28). Moderate to low stereoselectivities for 1,2-disubstituted alkenes were observed indicating the involvement of radical intermediate. 

V-(p-Toluenesulphonyl)sulphilimines have been prepared under solidtliquid phase-transfer catalytic conditions from the reaction of sulphides with Chloramine-T [25] (see Section 4.5). Osmium-catalysed oxyamination of alkenes by Chloramine-T under two-phase conditions is aided by the addition of benzyltriethylammonium chloride. p-Aminoalkanols are obtained in good yields (60-75%) [26]. 

Iodine was found to be an efficient catalyst for the aziridination of alkenes (Scheme 6) utilizing chloramine-T (A-chloro-A-sodio-p-toluenesulfonamide) as the nitrogen source. For example, when 2 equiv. of styrene (45a) were added to chloramine-T in the presence of a catalytic amount of iodine (10mol%) in a 1 1 solvent mixture of acetonitrile and neutral buffer, the corresponding aziridine (46) was obtained in 91% yield. The reaction proved to work with other acyclic and cyclic alkenes, such as oct-l-ene and cyclohexene. The aziridination of para-substituted styrene derivatives (45b-e) demonstrated that, as expected for an electrophilic addition, electron-rich alkenes reacted faster than electron-poor alkenes. However, with 1 equiv. of I2, mainly iodohydrin (47) was formed. A catalytic cycle has been proposed to account for the fact that only a catalytic amount of iodine is required (Scheme 1) ... 

The first reports on iron-catalyzed aziridinations date back to 1984, when Mansuy et al. reported that iron and manganese porphyrin catalysts were able to transfer a nitrene moiety on to alkenes [90]. They used iminoiodinanes PhIN=R (R = tosyl) as the nitrene source. However, yields remained low (up to 55% for styrene aziridination). It was suggested that the active intermediate formed during the reaction was an Fev=NTs complex and that this complex would transfer the NTs moiety to the alkene [91-93]. However, the catalytic performance was hampered by the rapid iron-catalyzed decomposition of PhI=NTs into iodobenzene and sulfonamide. Other reports on aziridination reactions with iron porphyrins or corroles and nitrene sources such as bromamine-T or chloramine-T have been published [94], An asymmetric variant was presented by Marchon and coworkers [95]. Biomimetic systems such as those mentioned above will be dealt with elsewhere. 

Isoxazolines.1 Reaction of aldoximes with chloramine-T generates nitrile oxides, which can be trapped by alkenes to give 2-isoxazolines. 

Tosylamination ofalkenes, The reaction of diphenyl disulfide with chloramine-T in acetone gives, in 91% yield, an adduct of the composition (C6HsSSC6H5)(NTs)2 shown to have the structure (1) by virtue of subsequent reactions with alkenes. Thus it reacts with cyclohexene to give (2), which was reduced by sodium borohydride to (3), whose structure was established by an independent synthesis. 

The reaction of disulfides and diselenides with chloramine-T affords N-SR or N —SeR species which are able to undergo addition to alkenes, for example, cyclohexene by an ionic mechanism. After reduction of the cyclohexene adducts, traiw-jS-functionalized amines 1 and 2 were obtained in low yield89. 

Oxyamination of Alkenes and Oxidation of Other Functional Groups. Osmium tetroxide catalyzes the vicinal oxyamination of alkenes to give c/s-vicinal hydroxyamides with Chloramine-T (eq 23) and alkyl Ai-chloro-M-argentocarbamate, generated in situ by the reaction of alkyl Ai-chlorosodiocarbamate (such as ethyl or f-butyl iV-chlorosodiocarbamate) with Silver(I) Nitrate (eq 24). ... 

After hydroboration, oxidation of radioiodide is performed with Chloramine-T, forming HO-I, which then adds to the C-B bond. The reactivity of the C-B bonds depends on the position of boron, which can either be formed from a terminal double bond or from an internal alkene. While the former case produces two radioiodinated compounds, the latter forms only one. Therefore, dicyclohexylborane is used for the hydroboration step. Both reactions, hydroboration of the alkene and radioiodination can be performed in one sequence without isolating the intermediately formed trialkylborane. 

In contrast with the great wealth of information on both cationic and free-radical additions to alkenes and alkynes, not too much is known about analogous cation radical reactions. The most commonly known among these are additions of aminium radicals. The overall reaction is that of, say, an N-chloramine or N-nitros-amine in acid solution, brought about photochemically or by reaction with ferrous ion (eq. 23) ( ). A chain reaction occurs in... 

Heteropoly acids (HPAs) such as 12-phosphomolybdic acid (PMA) and 12-phosphotungstic acid (PWA) function as a catalyst in the aziridination of alkenes with chloramine-T (Scheme 2.37) [56]. PMA catalyzed the reaction most efficiently in the presence of a quaternary ammonium cocatalyst and molecular sieves, affording aziridine products in good yields. The low stereospecificity of the reaction indicates the stepwise mechanism. The authors proposed the involvement of metallo-oxaziridine 22 as an intermediate. 

Organoboranes react with a mixture of aqueous NH3 and NaOCl to produce primary amines. It is likely that the actual reagent is chloramine NH2CI. Chloramine itself,hydroxylamine-O-sulfonic acid in diglyme, and trimethyl-silyl azide " also give the reaction. Since the boranes can be prepared by the hydroboration of alkenes (15-16), this is an indirect method for the addition of NH3 to a double bond with anti-Markovnikov orientation. Secondary amines can be prepared by the treatment of alkyl- or aryldichloroboranes or dialkylchlorobor-anes with alkyl or aryl azides. 

N-Tosylated P-hydroxy alkylamines (which can be easily hydrolyzed to P-hydroxyamines" ) can be prepared " by treatment of alkenes with the trihydrate of Chloramine-T and a catalytic amount of OSO4. In some cases yields can be improved by the use of phase-transfer catalysis." The reaction has been carried out enantioselectively." In another procedure, certain P-hydroxy secondary alkylamines can be prepared by treatment of alkenes with the osmium compounds... 

The same researchers found that imino derivatives of Os04 react with alkenes to produce cis-jS-amino alcohols (equation 124).346,347 This oxyamination reaction can be made catalytic in the presence of chloramine salts, e.g. ArS02NClNa or ROCONClAg.348,349... 

Sharpless and co-workers first reported the aminohydroxyIation of alkenes in 1975 and have subsequently extended the reaction into an efficient one-step catalytic asymmetric aminohydroxylation. This reaction uses an osmium catalyst [K20s02(OH)4], chloramine salt (such as chloramine T see Chapter 7, section 7.6) as the oxidant and cinchona alkaloid 1.71 or 1.72 as the chiral ligand. For example, asymmetric aminohydroxylation of styrene (1.73) could produce two regioisomeric amino alcohols 1.74 and 1.75. Using Sharpless asymmetric aminohydroxylation, (IR)-N-ethoxycarbonyl-l-phenyl-2-hydroxyethylamine (1.74) was obtained by O Brien et al as the major product and with high enantiomeric excess than its regioisomeric counterpart (R)-N-ethoxycarbonyl-2-phenyl-2-hydroxyethylamine (1.75). The corresponding free amino alcohols were obtained by deprotection of ethyl carbamate (urethane) derivatives. 

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