Aziridinations alkenes, -phenyliodinane

Aziridination of alkenes can be carried out using N-(p- to I ucncsu I I o n y I i m i n o) phenyliodinane and copper triflate or other copper salts.257 These reactions are mechanistically analogous to metal-catalyzed cyclopropanation. Rhodium acetate also acts as a catalyst.258 Other arenesulfonyliminoiodinanes can be used,259 as can chloroamine T260 and bromoamine T.261 The range of substituted alkenes that react includes acrylate esters.262... 

Decomposition of sulfonyl azides was shown to be catalyzed by copper in 1967 (72, 73). In the presence of alkenes, the reaction provides both aziridines and the C-H insertion products, albeit in low yields (73). In 1991, Evans et al. (74, 75) illustrated that both Cu(I) and Cu(II) salts were effective catalysts for nitrenoid transfer from [A-(/Moluenesulfonyl)imino]phenyliodinane (PhI=NTs) to a variety of acceptor alkenes. In the absence of ancillary ligands, reactions proceed best in polar aprotic solvents such as acetonitrile. Similar results are observed using both Cu(MeCN)4C104 and Cu(acac)2 as precatalysts, Eq. 53. 

The first catalytic, asymmetric aziridination of an alkene in good yield and high enantioselectivity was recently reported56. Thus styrene (63) was treated with [N-(p-toluenesulphonyl)imino]phenyliodinane (64) and an asymmetric copper catalyst to yield (/ )-Ar-(p-toluenesulphonyl)-2-phenylaziridine [(/ )-65] in 97% yield with an ee of 61%, the catalyst being the complex formed in situ in chloroform from the chiral bis[(5 ) 4-ferf-butyloxazoline] [(S,S)-66] and copper triflate (CuOTf)56, the reaction proceeding by way of a nitrene transfer57. 

The preparation of A-methoxyaziridincs by generation of methoxynitrenium ion from dimethoxyamine and boron trifluoride is described in Section 7.2.5.9. Finally, the transition metal catalyzed aziridination of alkenes with /V-(4-methylphenylsulfonylimino)phenyliodinane, involving the in situ generation of transition metal imido species, is described in Section 7.2.7.6. 

The transition metal-mediated nitrenoid transfer to olefins represents a very concise route to the aziridine structure very often, however, an excess of the olefinic substrate is required for preparatively useful yields. In this arena, Andersson and co-workers have studied the copper-catalyzed aziridination of olefins using [A -(arenesulfonyl)imino]phenyliodinanes 446 as nitrene precursors, and have reported on conditions which give good to excellent yields of aziridines 447 without the constraint of having to use an excess of alkene (Scheme 116). 

Enantioselective Aziridination of Alkenes. Copper complexes with neutral methylenebis(oxazoline) ligands (1) and (2) have also been employed as enantioselective catalysts for the reaction of alkenes with (Al-tosylimino)phenyliodinane, leading to A-tosylaziridines. The best results have been reported for cinna-mate esters as substrates, using 5 mol % of catalyst prepared from CuOTf and the phenyl-substituted ligand (2) (eq 6). The highest enantiomeric excesses are obtained in benzene, whereas in more polar and Lewis basic solvents, such as acetonitrile, the selectiv-ities are markedly lower. The chemical yield can be substantially improved by addition of 4X molecular sieves. Both Cu - and Cu"-bisoxazoline complexes, prepared from Cu or Cu triflate, respectively, are active catalysts, giving similar results. In contrast to the Cu-catalyzed cyclopropanation reactions discussed above, in which only Cu complexes are catalytically active, here Cu complexes are postulated as the actual catalysts. ... 

The nitrogen equivalent of the epoxidation reaction is the aziridination reaction. Cu(acac)2 was used as a catalyst for the aziridination of alkenes with [N-(p-tolylsiilfonyl)imino]phenyliodinane (PhI=NTs) in [BMIM][PF6] [277] and is shown in Scheme 5.2-127. 

Direct preparation of an aziridine from an alkene is possible by reaction of the alkene with a nitrene or metal nitrenoid species. Nitrenes can be generated thermally or photochemically from azides, although their reaction with alkenes to give aziridines is often low yielding and is complicated by side reactions. Oxidation of iV-amino-phthalimide or related hydrazine compounds (e.g. with Pb(OAc>4 or by electrolysis) and reaction with an alkene has found some generality. The metal-catalysed reaction of nitrenes with alkenes has received considerable study. A variety of metal catalysts can be used, with copper(II) salts being the most popular. For example, styrene was converted to its A-tosyl aziridine 72 by reaction with [A-(tosyl)imino]phenyliodinane (PhI=NTs) and copper(II) triflate (5.75). ... 

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