Addition nitrenes

Aziridines are important compounds due to their versatility as synthetic intermediates. In addition, aziridine rings are present in innumerable natural products and biologically active compounds. Nitrene addition to alkenes is one of the most well established methods for the synthesis of aziridines. Photolysis or thermolysis of azides are good ways to generate nitrenes. Nitrenes can also be prepared in situ from iodosobenzene diacetate and sulfonamides or the ethoxycarbonylnitrene from the A-sulfonyloxy precursor. 

Nitrene addition to alkenes can be aided by the nse of a transition metal, such as copper, rhodium, ruthenium, iron, cobalt, etc. NHC-Cu catalysts have been used in nitrene addition. For example [Cu(DBM)(IPr)] 147 (DBM = dibenzoyl-methane) was successfully employed in the aziridination of aliphatic alkenes 144 in presence of trichloroethylsulfamate ester 145 and iodosobenzene 146 (Scheme 5.38) [43]. 

Copper(I) complexes containing NHC-phenoxyimine 153 or NHC-phenoxyamine 154 were shown to be good catalyst systems for nitrene addition to alkenes 144 (Scheme 5.40) [45]. The catalyst systems showed to be highly efficient as only 1 mol% catalyst loading was required to afford aziridines 155 in moderate to good yields. 

Scheme 5.40 Nitrene addition to alkenes catalysed by NHC-Cu complex...

Sonderheit CH-Bindungen —, oder Produkte der Nitren-Addition an Doppelbindungen. Solche Produkte beobachteten beispielsweise Lwowski und Mattingly beim Zerfall von Azidoameisensaureathylester und schlos-sen daraus auf das Auftreten von Nitrenen (58). 

Aziridine synthesis can be achieved via nitrene addition to alkenes making use of a sulfonoxycarbamate [112]. Treatment of this reagent vith potassium carbonate in the presence of an alkene together with a PTC leads to the aziridine (Eq. 3.20). The reaction time is reduced from 2-3 h to 15 min when sonication is applied. 

Cycloadditions to [6,6]-double bonds of Cjq are among the most important reactions in fullerene chemistry. For a second attack to a [6,6]-bond of a C q monoadduct nine different sites are available (Figure 10.1). For bisadducts with different but symmetrical addends nine regioisomeric bisadducts are, in principle, possible. If only one type of symmetrical addends is allowed, eight different regioisomers can be considered, since attack to both e - and e"-positions leads to the same product. Two successive cycloadditions mostly represent the fundamental case and form the basis for the regioselectivity of multiple additions. In a comprehensive study of bisadduct formations with two identical as well as with two different addends, nucleophilic cyclopropanations, Bamford-Stevens reactions with dimethoxybenzo-phenone-tosylhydrazone and nitrene additions have been analyzed in detail (Scheme 10.1) [3, 9, 10]. 

Die Umlagerung eines intermediaren Aziridins ist der zentrale Schritt der Nitren-Addition an die 0-Silyl-keten-0,0-acetale verschiedener Alkansaure-ester zu a-Acylamino-car-bonsaure-estern5 (vgl. a. S. 614, 620ff.) ... 

In contrast, nitrene addition under the same conditions (80JCS(P2)385) is non-selective, affording the diastereomeric sulfimides in 1 1 mixture (equation 13). Again the dominant factors may be steric as reaction of the same nitrenes with mixed acyclic sulfides shows little selectivity. Sulfimines are also formed by the action of N- chloroarenesulfonamide sodium salts on the sulfide, and an extensive kinetic investigation (76T2763) has sliown the minor influence of steric factors in this reaction as well. Equation (14) sets out the proposed course of the reaction. 

This nitrene-addition approach was used by Knight to synthesize vinyl aziridines from 1,3-dienes using PhI=NTs and a copper catalyst. The more electron-rich double bond is selectively transformed in most cases. When the electronic difference is negligible the regioselectivity is then determined by steric hindrance. A mixture of cis and tram isomers is usually obtained [95SL949],... 

Nitrene additions led to a considerable increase in solubility in organic solvents the highest solubility of 1.2 mg mL4 in DMSO and TCE was found for SWCNT ethylene glycol-crown ether adducts. AFM and TEM revealed that the formation... 

The outcome of the nitrene addition reaction depends on the type of 7i-bond involved. In contrast to electron deficient olefins [26] and nonpolar olefins forming aziridines, electron rich olefins react with alkoxycarbonyl nitrenes to give oxazolines (Sch. 14) [22]. The same type of cycloaddition reaction leading to the production of five-membered rings has also been observed with nitriles [27] (such as compound 35 in Sch. 14) and isocyanates [28] as illustrated in Sch. 15. 

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