Aziridine From alkene

Oxaziridines unsubstituted at nitrogen as well as some iV-acylated oxaziridines offer synthetic potentialities due to their ability to transfer their nitrogen function to nucleophiles (Section 5.08.3.1.4). The simplicity of preparation of some aziridines from alkenes and the Spiro oxaziridine (S2) equals the simplicity of epoxidation. Aziridine (299), for example, is obtained by simple heating of indene with (52) in toluene (74KGS1629). 

Scheme 33 N-Amino heterocycles which yield aziridines from alkenes and Pb(OAc)4...

NTs [17,18]. Simple copper(I) and copper(II) salts were found to be effective catalysts for the preparation of a wide range of racemic aziridines (Scheme 7). More recently, rhodium-based catalysts have been applied with success to the reaction of PhI=NNs with alkenes [19]. Along with Sharpless s recently-disclosed brom-onium ion-catalyzed reaction [3], the copper-catalyzed aziridination of olefins with PhI=NTs is probably the most general catalytic method devised thus far for the direct synthesis of racemic aziridines from alkenes. 

Scheme 6.10 Alternative mechanisms for the formation of aziridines from alkenes and organic azides ...

Some applications of the triazoline route to aziridines from alkenes and azides are described below. 

A straightforward synthesis of aziridines from electron-rich azide R-N3 (R = alkyl or aryl), electron-deficient alkene, and triflic acid in cold acetonitrile has been reported. The only byproduct was dinitrogen (N2).143... 

In addition to epoxides, three-membered nitrogen heterocycles, aziridines, can be obtained by means of catalytic asymmetric aziridinations (Eq. 30). To this aim, chiral ruthenium(salen) complexes 67 [56] and 68 [57] were useful (Fig. 1). The former phosphine complexes 67 gave the aziridine from two cy-cloalkenes with 19-83% ee [56]. On the other hand, terminal alkenes selectively underwent aziridination in the presence of the latter carbonyl complex 68 with 87-95% ee [57]. In these examples, N-tosyliminophenyliodinane or N-tosyl azide were used as nitrene sources. Quite recently, catalytic intramolecular ami-dation of saturated C-H bonds was achieved by the use of a ruthenium(por-phyrin) complex (Eq. 31) [58]. In the presence of the ruthenium catalyst and 2 equiv iodosobenzene diacetate, sulfamate esters 69 were converted into cyclic sulfamidates 70 in moderate-to-good yields. 

The nitrogen source for the aziridination of alkenes, a nitrene or nitrenoid, can be generated in various ways (1) oxidation of a primary amine (2) base-induced -elimination of HX from an amine or amide with an electronegative atom X (X = halogen, O) attached to the NH group or by -elimination of metal halides from metal A-arenesulfonyl-A-haloamides (3) metal-catalyzed reaction of [A-(alkane/arenesulfonyl)imino]aryliodanes (4) thermolytic or photolytic decomposition of organyl azides and (5) thermally induced cycloreversion reactions . 

Of the numerous other aziridine syntheses, there are several multistep procedures from alkenes. Though not strictly within the scope of this review, the practising chemist will wish to consider their merits alongside the rect syntheses, and the main possibilities are summarized in Scheme 8. There are several good recent reviews, - and two older compilations remain very useful. - Syntheses of those intermediates of Scheme 8 accessible from alkenes are described in later sections of tiie present review, and syntheses of epoxides (Volume 6, Chapter 1.1 and Volume 7, Chapters 3.1 and 3.2) and triazolines (Volume 5, Ch ter 3.1) are described elsewhere in Comprehensive Organic Synthesis . It is important to note that by careful choice of route one can either commence with alkene (14) and retain the cisitrans stereochemistry in the resulting aziridine (16), or start with alkene (13) and change the cisitrans relatitm-ships of the substituents. 

The oxidation by lead(IV) acetate of iV-aminophthalimide and of several IV-aminolactams leads to the foimation of intermediates which do not undergo fragmentation or rearrangement, but which can be intercepted by alkenes, alkynes, sulfoxides and other nucleophiles. The reactions have proved particularly useful for e synthesis of aziridines from a variety of alkenes. The mechanism of these reactions has commonly been assumed to require the intermediacy of aminonitrenes, but this is probably not the case. Atkinson and Kelly have shown that oxidation of the aminolactam (25) by lead(FV) acetate at -20 C leads to the formation of an unstable IV-acetoxy compound. This is the species which can form aziridines with alkenes. The mechanism shown in Scheme 18, which is analogous to that for the epoxida-tion of alkenes by peroxy acids, has been proposed for the aziridination process. 

The direct aziridination of alkenes can be accomplished by several methods which involve the in situ generation of the epiminating intermediate from a variety of precursors. 

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