Olefin aziridine intermediate

After successful application of the silver catalyst shown in olefin aziridination (Section 6.1.1), He and coworkers showed that intramolecular amidation was possible with both hydrocarbon-tethered carbamates and sulfamate esters.24 They found that only the Bu3tpy silver complex could catalyze efficient intramolecular amidation, while other pyridine ligands gave either dramatically lower yields or complicated product mixtures. In an interesting control study, both copper and gold were also tested in this reaction. Both the copper and gold Bu tpy complexes can mediate olefin aziridination, but only silver can catalyze intramolecular C-H amidation, indicating that the silver catalyst forms a more reactive metal nitrene intermediate. 

It is worth mentioning that mechanistic studies on the olefin aziridination reaction with TffML complexes have shown that this transformation occurs throughout a complex pathway (Scheme 20) that involves metallonitrene intermediates in the triplet state as well as both singlet and triplet reaction pathways, which intercross several times along the... 

Flowever, Mansuy el al. reported that treatment of olefins with [A-(p-toluenesulfonyl)imino]-phenyliodinane, PhI=NTs, in the presence of a Mn or Fe porphyrin, provided the corresponding aziridine or allylic sulfonamide, depending on the substrate and the catalyst used (Scheme 33).145-147 The reaction has been considered to proceed through a metal-A-toluenesulfonylnitrenoid species. Similarly to epoxidation via the oxo-Mn species, this aziridination is nonstereospecific, and the participation of a radical intermediate has been suggested.146... 

Recently, Scott et al. have reported that a Cu complex bearing an axially chiral ligand (49) is an excellent catalyst for aziridination of 2,2-dimethylchromene and cinnamate esters (Scheme 36), though it is also less efficient for the reactions of simple olefins.157,158 On the basis of DFT investigation of the nitrenoid intermediate (50), one of the oxygen atoms of the A -sulfonyl group has been proposed to be interacting with the nitrene N-atom.158... 

It has been found that A-tosyl aziridines undergo oxidative addition to palladium complexes to form azapalladacyclobutanes <06JA15415>. Reaction of aziridine 95 with Pd2(dba)3 and 1,10-phenanthroline provides the palladacycle 96 in 45% isolated yield. This compound is an air stable solid. Treatment the palladacycle 96 with catalytic Cul is believed to open the palladacycle to form a copper intermediate, which cyclizes to cyclopentyl alkylpalladium intermediate 97. Loss of Cul then provides the product palladacycle 97 as an air stable solid. Several different aziridines were examined in this reaction. Only a limited set of olefin substituted aziridines provided the azapalladacyclobutanes (e.g. 96). 

Various approaches to epoxide also show promise for the preparation of chiral aziridines. Identification of the Cu(I) complex as the most effective catalyst for this process has raised the possibility that aziridination might share fundamental mechanistic features with olefin cyclopropanation.115 Similar to cyclo-propanation, in which the generally accepted mechanism involves a discrete Cu-carbenoid intermediate, copper-catalyzed aziridation might proceed via a discrete Cu-nitrenoid intermediate as well. 

The procedure reported here, which is that of Hassner and Heathcock,3 is more convenient than the Wenker synthesis of aziridines4 and appears to be more general.5 It represents a simple route from olefins to aziridines (via 8-iodo carbamates).356 Aziridines are also useful as intermediates in the synthesis of amino alcohols and heterocyclic systems.5,7-9... 

Sulfitation and Bisulfitation of Unsaturated Hydrocarbons. Sulfites and bisulfites react with compounds such as olefins, epoxides, aldehydes, ketones, alkynes, aziridines, and episulfides to give aliphatic sulfonates or hydroxysulfonates. These compounds can be used as intermediates in the synthesis of a variety of organic compounds. 

Episulfides, which can be generated in situ in various ways, react similarly to give p-amino thiols,835 and aziridines give 1,2-diamines.836 Triphenylphosphine similarly reacts with epoxides to give an intermediate that undergoes elimination to give olefins (see the Wittig reaction, 6-47). 

Aziridines not substituted on the nitrogen atom react with nitrous acid to produce olefins.324 An N-nitroso compound is an intermediate (2-51) other reagents that produce such intermediates also give olefins. The reaction is stereospecific cis aziridines give cis olefins and trans aziridines give trans olefins.325 Aziridines carrying N-alkyl substituents can be converted to olefins by treatment with ferrous iodide326 or with m-chloroperbenzoic acid.327 An N-oxide intermediate (9-28) is presumably involved in the latter case. 

Arylation, olefins, 187, 190 Arylketimines, iridium hydrogenation, 83 Arylpropanoic acid, Grignard coupling, 190 Aspartame, 8, 27 Asymmetric catalysis characteristics, 11 chiral metal complexes, 122 covalently bound intermediates, 323 electrochemistry, 342 hydrogen-bonded associates, 328 industrial applications, 8, 357 optically active compounds, 2 phase-transfer reactions, 333 photochemistry, 341 polymerization, 174, 332 purely organic compounds, 323 see also specific complexes Asymmetric induction, 71, 155 Attractive interaction, 196, 216 Autoinduction, 330 Axial chirality, 18 Aza-Diels-Alder reaction, 220 Azetidinone, 44, 80 Aziridination, olefins, 207... 

Evans et al. proposed that an imino-copper species in the 3+ oxidation state (Cu3+=NTs) should be the key intermediate in copper-catalyzed aziridinations [75b]. This proposal was supported by Jacobsen s study on the dependence of enantioselectivity on the nitrene precursors and/or the substrate structures with two iminoiodoarenes, PhI=NTs and 2,3,4-Me3-6-(r-Bu)C6HI=NTs), in the presence of CuPF6-33a complex and four olefins [80b]. This study disclosed that enantioselectivity did not depend on the iminoiodoarene, but on the olefins used, that is, the finding excludes the possibility that a Cu-Arl=NTs adduct is a key intermediate. It has also been observed that the photochemical aziridination with tosyl azide (TsN3) catalyzed... 

Alkenylsilanes react with silyl azide and other organic azides to give bissilylenamines and silylaziridines, respectively, via unstable triazoline intermediates.78 Heating trimethylsilyl azide with cyclohexene or vinyltrieth-ylsilane for 10 days affords a modest yield of the respective aziridine,178 but with carefully purified trimethylsilyl azide, even after 2 weeks of reflux, no olefin consumption is indicated.104 Unstable triazoline intermediates are also formed from the reaction of cyanogen azide,808 picryl azide,29 and arylsulfonyl azides808 with unactivated olefinic bonds. 

Based on results presented in Scheme 37, Logothetis suggested that the thermal decomposition products from the olefinic azides in the scheme are derived from triazoline intermediates formed by an intramolecular cycloaddition reaction and not by fragmentation of the azido group to a nitrene.100 However, allyl azide and 4-azido-l-pentene do not undergo internal cycloaddition because of the strain in the corresponding triazoline they fail to give aziridines and imines upon thermolysis.100... 

The aziridination works for both aromatic and aliphatic olefins, including less active linear terminal olefins. Most reactions proceed in good yield at room temperature. The use of ci.v-stilbene at 0°C gives predominately cis aziridine product in about 90 10 cis trails ratio (Table 6.1). The conservation of cis structure suggests that a discrete silver nitrene intermediate is involved in the reaction path. Because of the unique disilver structure and unlikely formation of a silver(III) species, the authors suspect that a bridged nitrene intermediate between the two silver atoms may be responsible for this transformation in which each silver atom donates one electron to the nitrenoid. However, further research is necessary to prove this hypothesis and a fast radical reaction mechanism cannot be eliminated on the basis of current evidence. 

The most impressive methodology utilizing CT, which has been developed by the group of Sharpless, is the vicinal aminohydroxylation of olefins catalyzed by osmium tetroxide [15]. The method has been elegantly extended to a practical asymmetric synthesis [16]. The reaction system was employed to the achiral aminohydroxylation of a,P-unsaturated amides to afford two hydroxysulfonamide regio-isomers. The crude mixtures were cyclized to the aziridines in a one-pot procedure, without the need for purification of the intermediates [17] (Scheme 10). 

The reaction of A -[A -(benzoylimino)-A -phenylsulfonyl]amide 429 with iodosylbenzene 426 leads efficiently to nitrene intermediates that convert olefins 411 into aziridines 430 in good yields, through a copper(ll)-mediated (Cu(OTf)2) reaction. Owing to the stereogenic sulfur atom present in the molecules, the reactions proceed with some degree of diastereoselectivity (Scheme 111) <2004OL3573>. 

Methyltrioxorhenium has been found to be a universal catalyst for a number of [2-1-1] cycloaddition reactions, including nitrene, carbene, or oxo-atom addition to olefins <2001GC235>. Typically, to increase the chemical yield of the reaction, at least 5 equiv of an olefin is required. As with most nitrene transfer reactions, simple cyclic olefins such as cyclohexene produce a low chemical yield of aziridine. The authors assume that the intermediate of the reaction is a reactive rhenoxaziridine intermediate. 1,2-Dihydronaphthalene provides aziridine 28 in 43% chemical yield under these reaction conditions (Equation 11). 

Fused-ring aziridines such as 56 are common intermediates for the synthesis of azinomycin and related anticancer agents. The presence of the exocyclic olefin/vinylogous amide greatly increases the reactivity of such aziridines. 

The azido olefins 117 and 120 were cyclized to the triazolines 118 and 119 in excellent yields <2001TL9175>. This is an interesting process in that the intermediate triazolines are isolated and then photolytically decomposed to aziridines 119 and 122 in very good yields (Scheme 19). All of these aziridines were reported to be stable compounds especially to acidic conditions. This is significant in that previous examples of silyl-substituted monocyclic aziridines were quite unstable undergoing acid-catalyzed rearrangements. 

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