Nitrene transfer reaction

Three different side reactions are found in [Fe(TTP)Cl]-catalyzed nitrene transfer reaction including... 

Metal-oxenoid (oxo metal) species and metal-nitrenoid (imino metal) species are isoelectronic and show similar reactivity both species can add to olefins and be inserted into C—H bonds. Naturally, the study of nitrene transfer reactions began with metalloporphyrins, which were originally used as the catalysts for oxene transfer reactions. 

Reaction of metal nitrosyls with azide ion proceeds with formation of N2 and N20 (56). This can be viewed as the result of a nitrene transfer reaction in analogy with the Curtius rearrangement (62) and its organome-tallic counterpart (63). 

Catalytic methods are suitable for nitrene transfer," and many of those found to be effective for carbene transfer are also effective for these reactions. However, 5- to 10-times more catalyst is commonly required to take these reactions to completion, and catalysts that are sluggish in metal carbene reactions are unreactive in nitrene transfer reactions. An exception is the copper(ll) complex of a 1,4,7-triaza-cyclononane for which aziridination of styrene occurred in high yield, even with 0.5 mol% of catalyst. Both addition and insertion reactions have been developed. 

As discussed above, iodosylbenzene (Phl=0) oxidizes various transition-metal ions (Mn+) such as manganese, iron, ruthenium, and chromium ions to the corresponding oxo-metal species (0=Mtransfer agents. Likewise, fM-(p-toluenesulfonyl)imino]-phenyliodinane(PhI=NTs) also oxidizes these metal ions to give the corresponding tosylimino-metal species (TsN=M(n+2)+) that undergo nitrene-transfer reaction such as aziridination (Scheme 6B.28) [73],... 

In 1991, Evans et al. reported that cationic Cu(I) ions catalyzed the nitrene-transfer reaction smoothly (Scheme 6B.29) [74]. Since then, many studies on asymmetric aziridination have been carried out with chiral copper(I) complexes as catalysts. 

A carbene or nitrene transfer reaction to a carbon-carbon or carbon-heteroatom double bond system leads to the formation of three-membered rings, such as a cyclopropane, an aziridine or an epoxide. These processes can be catalyzed by applying iron catalysts and the different cyclic systems are discussed here. 

The aziridination of olefins, which forms a three-membered nitrogen heterocycle, is one important nitrene transfer reaction. Aziridination shows an advantage over the more classic olefin hydroamination reaction in some syntheses because the three-membered ring that is formed can be further modified. More recently, intramolecular amidation and intermolecular amination of C-H bonds into new C-N bonds has been developed with various metal catalysts. When compared with conventional substitution or nucleophilic addition routes, the direct formation of C-N bonds from C-H bonds reduces the number of synthetic steps and improves overall efficiency.2 After early work on iron, manganese, and copper,6 Muller, Dauban, Dodd, Du Bois, and others developed different dirhodium carboxylate catalyst systems that catalyze C-N bond formation starting from nitrene precursors,7 while Che studied a ruthenium porphyrin catalyst system extensively.8 The rhodium and ruthenium systems are... 

In addition to rhodium and ruthenium, silver catalysts have also been investigated, and this chapter discusses these silver-based nitrene transfer reactions.2 1 In discussing the work chronologically, we hope that the readers can get an idea of the evolution of thinking in the research process. 

As stated in the introduction, chloramine-T (where T denotes three crystalline water molecules) is a commonly used nitrene precursor, which is commercially available and costs less than do most other nitrene sources. The benefit of a silver salt in nitrene transfer reactions with chloramine-T is surprisingly simple. Because silver chloride is insoluble in most solvents, substoichiometric amounts of silver salts (like silver nitrate) can be used to remove the chloride from chloramine to facilitate the release of a free nitrene radical, which can aziridinate olefins. Since the amount of silver is near stoichiometric, it should not be called silver-based catalysis, although turnover numbers (TONs) higher than 1 have been observed in some cases. 

Zraras-aziridine products were still detected from r/.v-olefin substrates, and sometimes as the predominant product. Current results on silver-catalyzed nitrene transfer reactions, indicate that silver probably can interact with iminoiodanes to generate a silver nitrene precursor. This precursor can lead to reactions via either a concerted metal nitrene or a stepwise radical pathway, depending on the substrate and reaction conditions (Scheme 6.8). 

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). 

Another related zirconium complex 32 containing redox active tridentate NNN pincer ligand catalyzes nitrene transfer reactions from organic azides to f rf-butyl isocyanide to form non-symmetrical carbodiimides where the metal maintains the Zr(IV)... 

Scheme 17 The catalytic nitrene transfer reaction to olefins and C—H bonds...

N-halosuccinimide (NBS or NCS) [42] as the oxidant. The complex TpBr3Cu(NCMe) displays high activity towards nitrene-transfer reactions (Equation 11.17) [43]. Various substrates can be used under the same catalytic conditions. 

Ruthenium catalysts can also be used in nitrene transfer reactions. The intramolecular amidation reactions of saturated C—H bonds have been developed with mthenium catalysts (Equation 11.23) [54]. In addition, the Ru-catalyzed asymmetric animation of benzylic and allylic C—H bonds has also been reported [55],... 

Similarly, the nitrene transfer reaction from 128 is facilitated by a variety of catalysts, including MTO (136) <01JCS(CC)235>, the lri(pyrazolyl)borate-coppcr(l) complex 137 <01OL1423>, and tetrakis(acetonitrile)copper(I) hexafluorophosphate (138) <01JA7707>. In the latter case, the reaction can be carried out using a sulfonamide and the primary oxidant, iodosylbenzene, whereby the actual nitrene transfer reagent 128 is presumed to be formed in situ. In all cases, acetonitrile appears to be the solvent of choice. 

Nitrene-Transfer Reaction. Pd(PhCN)2Cl2 catalyzes the nitrene-transfer reaction of methyl azidoformate with vinyl ethers, affording methyl iV-methoxycarbonylpropionimidate derivatives (eq 137). ... 

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