Nitrenes generation

On the other hand, poly(ethoxycarbonylimino-4-vi-nylpyridinium ylide) (Scheme 13) was prepared essentially by the same method from 1-ethoxycarbonylimino-pyridinium ylide, as described by Hafner [15] from the reaction of poly (4-vinylpyridine) with nitrene, generated from the pyrolysis of ethyl azidoformate. 

Trifluoroethanol has been shown to promote the addition of nitrenes, generated by the reaction of nitroso-compounds with phosphites, to aromatic hydrocarbons, e.g. (57), (58), and (59) are formed from the reaction... 

The [l,2,3]triazolo[2,l- ]benzotriazole (74 2,3-benzo-l,3a,4,6a-tetraazapentalene) heterocyclic ring system is obtained by an electrophilic attack of singlet nitrene, generated by heating the corresponding nitrophenyl triazole 251 in trialkyl phosphite, on the triazole nitrogen (Equation 39) <1998JOC3352>. 

Fuostifoline (47), a furo[3,2-a]carbazole, was isolated from Murraya euchrestifolia. Timdri s total synthesis of 47 commenced with alkylation of bromocresol 43 with bromoacetaldehyde diethyl acetal and P4Oio-promoted cyclization to furnish 5-bromo-7-methylbenzofuran (44) [47]. The Suzuki coupling of boronic acid 45, derived from 44, with o-bromonitrobenzene yielded biaryl 46. Nitrene generation, achieved via deoxygenation of nitro compound 46 using triethyl phosphite, was followed by cyclization to fuostifoline (47). 

This indicates that the prebaking temperature higher than the melting point of the azide decomposes the azide (50%) and it totally decomposes upto 100 mJ/cm2 irradiation. It is possible that subsequent reactions of the nitrene, generated from the azide thermolysis and photolysis, with the styrene resin could be responsible for solubility modulation of this type resist (16). 

Padwa has shown that rhodium-catalyzed oxidation of indolyl carbamate 67 employing either Phl(OAc)2 or Phl=0 follows a path similar to that of the D-aUal carbamate (Scheme 17.26) [95]. In principle, indole attack of the putative rhodium-nitrene generates zwitterion 68, which is trapped subsequently by an exogenous nucleophile. Spiro-oxazolidinone products (for example, 69) are isolated as single diastereomers in yields ranging from 50 to 85%. As an intriguing aside, Padwa has found that certain carbamates react with Phl=0 in the absence of any metal catalyst to furnish oxazoHdinone products. This result may have implications for the mechanism of the rhodium-catalyzed process, although it should be noted that control experiments by Espino and Du Bois confirm the essential role of the metal catalyst for C-H amination [57]. 

The nitrenes generated by reduction of 2-(2-nitrophenyl)furan with triethyl phosphite or by thermolysis of 2-(2-azidophenyl)furan in 1,2-dichlorobenzene undergo insertion into... 

Efficient nitrene generation and insertion into the CHf bonds of the solvent (cyclohexane) was observed for a series of perfluoroarylazides linked to metal-ligating systems (63).70... 

A nitrene generated from the reaction of A-aminophthalimide (101) and PhI(OAc)2 was key to the metal-free ring expansion of alkylidenecyclopropanes (102) and an alkylidenecyclobutane.85 The authors propose two plausible mechanisms for these ring-expansion reactions either an aziridine is formed which undergoes facile rearrangement to form the final 2,2-disubstituted cyclobutylidene hydrazine product (103), or reaction of the alkylidenecyclopropane with the nitrene generates an ionic or diradical species which rearranges. 

Nitrenes generated from PhINTs and copper acetoacetate react with thietanes to form isothiazolidines.86 The initially formed S-N donor-acceptor complex undergoes ring expansion with retention of stereochemistry. Yields range from 56 to 76%. 

The photochemistry152 of Rh(NH3)5N + also seems to have a component of a nitrene generation pathway as in reaction (61), but at higher excitation energies CT states are populated which decay to give azido radicals and presumably Rh(NH3)f+ species. A comparison of quantum yields for the M(NH3)SN3+ (M = Co, Rh, Ir) complexes are given in Table 25.151 153 The Co(NH3)5N3+ gives no... 

Sidewall functionalization of SWCNTs was achieved via the addition of reactive alkyloxycarbonyl nitrenes obtained from alkoxycarbonyl azides. The driving force for this reaction is the thermally-induced N2 extrusion. The nitrenes generated attack nanotube sidewalls in a [2+l]-cycloaddition forming an aziridine ring at the tubes sidewalls (Scheme 1.19). 

The high-temperature reaction occurs via elimination of molecular nitrogen on nitrene generation (78JOC1346). 

The typical reactions of nitrenes generated from aliphatic azide precursors are shown below and include isomerization to imines (a), intramolecular insertion into C—H bonds (b) has been questioned (see 1. c. n> p. 57) and intermolecular hydrogen abstraction (c). 

Suitable enamines can react with (ethoxycarbonyl)nitrene, generated from ethyl 7V-(4-nitrophenylsulphoxy)carbamate, giving relatively unstable aziridines103. Diaster-eoselective attack of this nitrene on the double bond of chiral enamine 98 and opening of the intermediate aziridine (197) afforded enantiomerically enriched 2-ethoxycarbony-laminocyclohexanone 198104,105 (equation 42). 

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