Singlet aryl nitrenes

Table 2 Kinetic parameters of para-substituted singlet aryl nitrenes (X— in pentane.

In the early 1990s, singlet aryl nitrenes had never been detected and the influence of structure on reactivity was only dimly appreciated. Laser flash photolysis studies in combination with theory has provided insight and has led to a comprehensive theory of substituent effects. We have been proud to be part of this process. 

Table 5.7 Kinetic Parameters of Para-Substituted Singlet Aryl Nitrenes (X-C6H4-N) in Pentane...

Aryl Azides in Nonacidic Media The Chemistry of Singlet Aryl Nitrenes 44-5... 

Photolysis of aryl azides in acidic media represents a special case. At low pH, singlet aryl nitrenes may be N-protonated, rapidly yielding singlet nitrenium ions. These ionic reactive intermediates undergo reactions different from those of singlet nitrenes. 

The development of highly correlated methods of ab initio theory has provided us with insight into the properties of singlet aryl nitrenes. Time-resolved laser flash photolysis (LFP) with picosecond time-... 

TABLE 44.1 Spectroscopic and Kinetic Parameters of Singlet Aryl Nitrenes... 

The effect of substituents placed para to the nitrene center was investigated in a series of matrix isolation, laser flash photolysis, and product studies. Table 44.1 Ksts a number of rate constants (k,sc for intersystem crossing to the triplet ground-state and for rearrangement to the didehydroazepine). For comparison, the kinetic parameters of several other singlet aryl nitrenes are also given. 

Photolysis of aryl azides in amine solution, with a tertiary amine as cosolvent to promote stabilization of the singlet nitrene, has met with some success. For example, the yield of 2-piperidino-3 W-azepme. obtained by the photolysis of phenyl azide in piperidine, is increased from 35 to 58% in the presence of A A /V. /V -tetramethylethylenediamine (TMLDA).180 Also, an improved yield (36 to 60 %) of A,(V-diethyl-3W-azepin-2-amine (38, R = Et) can be obtained by irradiating phenyl azide in triethylamine, rather than in dicthylaminc, solution.181 Photolysis (or thermolysis) of phenyl azide in TMEDA produces, in each case, 38 (R = Et) in 40% yield.181 In contrast, irradiation of phenyl azide in aniline with trimethylamine as cosolvent furnishes jV-phenyl-377-azepin-2-amine (32, R = Ph) in only low yield (2%).35... 

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