N nitrene

Asymmetric aziridination of a,P-unsaturated esters by use of N-nitrenes was studied in great detail by Atkinson and co-workers [34, 35]. Here, lead tetraacetate-mediated oxidative addition of N-aminoquinazolone 30 (Scheme 3.10) to a-methy-lene-y-butyrolactone 32 was reported to proceed with complete asymmetric indue-... 

For monographs, sec Scriven Azides and Nitrenes-, Academic Press New York, 1984 Lwowski Nitrenes. Wiley New York. 1970. For reviews, see Scriven React. Interned. (Plenum) 1962,2, 1-54 Lwowski React. Interned. (Wiley) 1985, 3. 305-332.1981, 2, 315-334. 1978, 1. 197-227, Angew. Chem. Ini. Ed. Engl. 1967, 6. 897-906 [Angew. Chem. 79. 922-931) Abramovitch, in McManus. Ref. 1. pp. 127-192 Hiinig Helv. Chim. Acta 1971, 54, 1721-1747 Belloli J. Chem. Educ. 1971, 48, 422-426 Kuznetsov Ioffe Russ. Chem. Rev. 1989, 58, 732-746 (N- and O-nitrenes) Mcth-Cohn Acc. Chem. Res. 1987,20,18-27 (oxycarbonylnitrenes) Abramovitch Sutherland Fortsch. Chem. Forsch. 1970, 16. 1-33 (sulfonyl nitrenes) Ioffe Kuznetsov Russ. Chem. Rev. 1972, 41, 131-146 (N-nitrenes). 

Oxidation of the 1-aminoquinazolinones (44) with lead tetraacetate culminated in the intramolecular addition of the resulting N-nitrene intermediate to the triple bond to give the pyrrolo[2, l-b]quinazoline (45) [85CC544 86JCS(P1)1215]. The pyrrole ring of 47 was also formed by cyclization of 2-methyl-3-phenacylquinazolin-4-one (46) with dilute aqueous alkali followed by fusion (86T4481). 

N(nitrene) coupling leading to the metal-tetraazadiene species (73).191,195 Reactions which can be considered as models for the conversions of the intermediates (70)-(72) have been found. 

Another way to introduce substituents at the A -atnino group is via oxidation to an N-nitrene. Such reactions are discussed in Section IV,D. 

Other evidence to support nitrene formation is the identity of the reaction products obtained when nitrenes are generated by independent methods. For instance, N-nitrenes of 1,2,3-triazoles can be generated by oxidation of 1-amino-u-triazoles (88M1041), on photolysis of their potassium tosylates (134) (64AG144), or by decomposition of unstable lithium salts of l-(l,2,3-triazole-l-yl)-4-p-tolylsulfonyl-tetrazenes[72JCS(Pl)1315] [Eq. 

In all three cases, the corresponding acetylenes are formed in good yield as the result of N-nitrene fragmentation. 

Boulton and co-workers [86JCS(P1)1249] suggested three distinct classes of N-nitrenes ... 

Clearly, in many cases where the formation of N-nitrenes has been postulated as intermediates, the process really proceeds by an alternate non-nitrene pathway. For example, the mechanism of such an apparently simple reaction as the formation of )V,N -diazoles may be presented as (1) the result of dimerization of two nitrene particles (2) interaction of the (V-nitrene with the starting amine affording a tetrazane followed by its... 

Compounds of type 303 were isolated by Atkinson and Kelly on cautious oxidation of 3-amino-2-ethylquinazolone-4 [Eq. (87)] (87CC1362). N-Acetoxyamino derivative 305 is stable only at temperatures below 0 C, and at -40°C it reacts with styrene to give aziridine 307, supposedly via intermediate 306. These data were interpreted as a proof of the possibility of forming aziridines without N-nitrene participation. Notice, however, that in principal there is no great difference between the nitrene mechanism and mechanisms presented in Eqs. (86) and (87), since if elimination of X from 304 and of MeCOj from 305 is a little ahead of the following reaction, then, in fact, the masked nitrene mechanism is described. 

Nltrenes (s. a. Sulfonylnitrenes) N-heterocyclics via review 18,338 suppl. 27 review 26, 630 N-Nitrenes, review 23, 381 suppl. 27... 

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