Ethyl azide, photolysis

The photolysis of ethyl azide in various organic solvents gives N2 and ethyl-ideneimine as major products 0 2 = 1, independent of azide concentration. 

Internal nitrenes normally react at the adjacent position. Reduction of 2-(2-nitrophenyl)furan by ethyl phosphite yields furoindole derivatives in fair yield (34%) only, whereas much better results attend the pyrolysis of 2-(2-azidophenyl)furan.280 Furopyrazoles are obtained similarly.281 Azidofurans yield nitrenes that insert into adjacent CH links to form furo-pyrroles.282 Quite different results attend either the pyrolysis or the photolysis of azide 107a for the expected insertion into the side chain occurs giving the related indole but it is accompanied by the surprising replacement of furan oxygen by nitrogen producing 107b and similar products.283... 

One-pot synthesis of aziridinyl ketones including the initial dipolar addition of azides to the ethylene bond with subsequent elimination of the nitrogen by photolysis is also possible [55, 56]. For example, in the case of azidocarboxylic acid ethyl ester 35,2-oxo-7-azabicyclo[4.1.0]heptane-7-carboxylic acid ethyl ester 37 was synthesized via the formation of the cycloadduct 36 [55] (Scheme 1.10). 

Ethoxycarbonyl nitrene is readily formed by thermolysis or photolysis of cthoxycarbonyl azide (ethyl azidoformate), as well as by the base-induced a-elimination of (4-nitrophenylsulfonyloxy)-carbamate9 13> 158> 159. 

Similar results were obtained in the photolysis of ethyl azidofor-mate and in the decomposition of sulphonyl azides, which yielded sulphonamides . ... 

In the photolysis of neat ethyl azidoformate (66) diethyl azodiformate (76) is produced in the early stages of the process, to be later replaced by the triethyl nitrilotriformate (77) which is produced in 58% yield A detailed investigation showed that the nitrilo compound (77) is apparently not formed by the action of a nitrene, and the reaction between an azide and an excited azodiformate was suggested as a possible pathway. Hancock has proposed an alternative mechanism which involves triazacyclopropene (see, however, Huisgen ). 

Sheinker has studied the u.v. and i.r. spectra of azidoformates. The 285 nm band, seen in alkyl azides, was not found perhaps it disappears into the short wavelength band due to a blue shift. The u.v. spectrum of ethyl azidoformate extends to nearly 300 nm (see Table 2) but its photolysis is most conveniently carried out with the mercury resonance line near 254 nm, for which efficient lamps are available . Ethyl azidoformate shows i.r. absorption bands at 2185 and 2137 cm"i (Ng), 1759 and 1730 (C=0) and 1242 (0-0) cm i 235 -pjje y spectrum is given in Table 2. The i.r. and... 

The second new synthesis of 7-methoxymitosene (3) was published by Wender and Cooper [34]. Based on a novel triazole photolysis, it affords the product in 8.3% yield after 12 steps. It is more efficient than the original synthesis of 3, but it requires more steps than the synthesis reported by Luly and Rapoport in 1984. As illustrated in Scheme 12, it began with 2,6-dimethoxytol-uene (91), which was converted into azido derivative 92 by the sequence of nitration, catalytic reduction, diazotization, and treatment with sodium azide. Dimroth condensation of 92 with ethyl 6-triisopropylsiloxy-3-oxohexanoate in... 

The insertion of nitrenes, generated via the photolysis or thermolysis of azides, into C-H bonds is well known, although the yields are generally poor. However, when ethyl azidoformate is thermolyzed in the presence of 1-chlorocyclohexene, the allylic insertion product is formed in 49% 3deld (eq 10). In this case it is not clear if the product is formed through direct insertion or by the ring opening of an aziridine intermediate. 

The synthesis of 4,5-difluoroimidazole has also been described by Kirk using a photochemical Schiemann reaction (Scheme 59) [74]. Curtius rearrangement of the acyl azide, prepared in two steps from ethyl 4-fluoroimidazole-5-carboxylate via hydrazide, afforded the key intermediate Boc-protected 5-fluoroimidazol-4-carboxylate. In situ Boc deprotection followed by diazotization of the amine and photolysis of the diazonium tetrafluoroborate afforded 4,5-difluoroimidazole. 

Azido-l-ethyl-3-carboxylate-6,8-difluoroquinolone was proposed for photoaffinity labeling [113], Photolysis of this azide with diethyl amine gave 7-hydrazino-derivative as the major product. This compound was generated by singlet nitrene N-H insertion. In addition, 7-amino-l-ethyl-3-carboxylate-6,8-difluoroquinolone was also obtained. 

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