Nitrenes diazirines

Finally, in some cases diradical negative ions can even be generated directly npon ionization of appropriate precnrsors. For example, nitrene and carbene anions can be formed by El of organic azides, diazo-compounds, and diazirines, whereas Branman and co-workers have reported the formation of oxyallyl anions by El of flnorinated acetyl componnds (Eq. 5.12). ... 

The great majority of matrix isolation studies of carbenes and nitrenes have employed their formal adducts with molecular nitrogen, that is, diazo compounds or diazirines in the case of carbenes, azides in the case of nitrenes, as precursors for their in situ generation. Usually, these compounds will readily release N2 on irradiation with a low-pressure mercury lamp (254 nm), and this fragment has the advantage that it will usually not react with or perturb the targeted reactive intermediate (see Scheme 17.2). 

Figure 32 Structures of three common photocross-linking moieties. Benzophenone is photoactivated to a reactive diradical that can relax back to the starting material. Aryl azides and diazirines both irreversibly lose N2 to react through nitrene and carbene species, respectively.

As it is known that in the flash thermolysis of tetrazole (5.80) in the vapor, cyanamide, diazomethane, and dinitrogen are formed, Guimon et al. (1989) calculated with ab initio (3-21G ) and with MNDO methods the potential energy surface including the compounds mentioned and diazirine (5.59), carbodiimide (5.77), isodiazirine (5.78), and the nitrene 5.82. Tetrazole is calculated slightly more stable than its isomer 5.81. 

Finally, the ferrocenyl complexes were decomposed photochemically and thermally. Thermolyses can be performed in this case because the decomposition temperature of the azide (96) (80 °C) is much lower than those employed for other diazirines and azides. The results obtained from photolyses and thermolyses do not differ significantly. Here again, a-CD causes the most drastic changes because of the complete encapsulation of the guest in a 1 2 complex (Scheme 10.27). In accord with the other reactions performed in a-CD, the main reaction pathway is hydrogen abstraction from the host. Upon thermolysis ferrocenyl amine (112) is obtained in a yield up to 60%. More remailcably, ferrocenyl nitrene (111) seems to react in very low yields with a-CD. However, the structure of the reaction product 113 has not been fully established yet and is quite unexpected because 113 is the result of a glucopyranose-furanose conversion. In contrast, the products obtained by thermolysis of ferrocenyl nitrene in the soUd state, namely... 

The nitrenic potential of l//-diazirines (165) has been further expanded. After the generation of various l//-diazirine (165)/imidoylnitrene (166) hybrids by simply reacting the corresponding 3-bromo-3//-diazirines (167) with diverse nucleophiles, their nitrenic behaviour has been demonstrated thanks to their observed reactivity towards phenylmagnesium bromide and tetrabutylammonium cyanide. Noteworthily, the first example of an imidoylnitrene C-H insertion has been aehieved in the course of this work. 

A mechanism involving nitrene formation by fragmentation of an intermediate N-substituted diazirine has been suggested to account for production of benzonitrile on reaction of aryl halodiazirines with potassium ethyl xanthate. ... 

---