Nitrenoid sources

According to the original protocol [3] alkenes can be converted to racemic iV-tosyl protected 9-amino alcohols in the presence of catalytic amounts of osmium tetroxide using N-chloramine-T as the nitrenoid source and water as the hydroxyl source. However, unlike the AD-process, the aminohydroxylation of unsymmetrical alkenes can lead to two regio-isomeric products which was a drawback in... 

The transition metal-catalysed amination of C-H bonds via reactive metal-imide intermediates (i.e., nitrenoids) remains a powerful taetie for C-N bond formation. In that context, the intramolecular C(ip )-H amination of biaryl azides as nitrenoid sources has been computationally explored regarding the nature of the transition metal that plays the catalytic role. Four common transition metals (Ir, Rh, Ru and Zn) have thus been considered, and while the calculations have revealed similar energy profiles regardless of the nature of the metal, catalytically active Ru speeies have nevertheless been shown to be the more efficient from a kinetic viewpoint. 

Asymmetric Ru((II)-catalysed aziridination of terminal olefins has been achieved using Ru(CO)(salen) complex as chiral catalyst and sulfonyl azide (173) as nitrenoid source. " Under such reaction conditions, the desired aziridines have been obtained in high yields and excellent enantioselectivities (up to 99% ee). 

The oxyamidation of cyclic enamides, enecarbamates, and enesulfonamides has been successfully performed under Rh(II) catalysis using trichloroethylsulfamate (174) as nitrenoid source and PhI(OAc)2 as oxidant. The oxyamidated products (175) have 0 been formed with excellent efficiency (up to 98% yield), moderate to good diastereose-lectivity, and complete regioselectivity. 

Two mechanisms are possible for the Cu-mediated aziridination using PhI=NTs as a nitrogen source (i) aziridination via Cu-nitrenoid species (L Cu=NTs) and (ii) aziridination via a L (Cu—PhI=NTs) adduct, in which the Cu complex functions as a Lewis acid catalyst. Jacobsen et al. demonstrated that the enantioselectivity of the aziridination using (48) as the chiral auxiliary did not depend on the nitrogen precursors.1 5 This supports the intermediacy of the Cu-nitrenoid... 

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 . 

In the arena of alternative nitrene sources, a flurry of activity has centered around the use of the readily available chloramine-T 469. Komatsu and co-workers have reported on the successful aziridination of alkenes using 469, catalyzed either by substoichiometric amounts of iodine (e.g., 470—>471) <1998T13485> or a combination of 5% cuprous chloride and 5 A powdered molecular sieves (e.g., 472 —> 473) < 1998TL309>. In certain cases, better yields are obtained using the bromo analog, presumably due to the more facile formation of the copper nitrenoid complex (Scheme 122) <1998TL4715>. 

To expand the utility of the direct use of sulfonamide as a nitrogen source, several effective catalyst systems have been reported. Chang and coworkers developed the alkene aziridination using 5-methyl-2-pyridinesulfonamide and Phi (OAc)2 catalyzed by Cu(tfac)2 (tfac = trifluoroacetylaceto-nate) without external ligands or bases (Scheme 2.26) [39]. It was postulated that the coordination of pyridyl N atom to the copper center was the driving force for the formation of copper nitrenoid 20. Indeed, replacement of the pyridyl N atom to CH suppressed the reaction. 

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