Azides, ethoxycarbonyl nitrenes from

Ketenimines also react as dipolarophiles in their reactions with ethoxycarbonyl nitrene, generated from the corresponding azide at 100 °C to give 109 . 

The base-catalyzed condensation of a-azido esters and ketones with aromatic aldehydes has recently been developed as a new vinyl azide synthesis.42,43 The yields range from moderate to excellent in some cases. The thermal decomposition of ethyl a-azidocinnamate (87) in xylene gives only 2-ethoxycarbonylindole (88).44 The unstable 2-ethoxycarbonyl-3-phenyl-l-azirine could be detected if the thermolysis was carried out at a lower temperature. This fact indicates that the 1-azirine is probably an intermediate leading to the indole, although the intermediacy of the vinyl nitrene could not be established. This result is similar to that observed by Isomura et al. on the pyrolysis of terminal vinyl azides.27,28... 

Better yields, but lower enantiomeric excesses, were obtained by an alternative method, the cycloaddition of ethoxycarbonyl azide, followed by irradiation to give the aziridine64. Interestingly, the opposite configuration at the stereogenic center was formed by the two methods. The enantiomeric excess of the product was determined by ketalization with (2/, 3/ )-2,3-butanediol and GC or l3C-NMR analyses of the reaction mixture. The choice of the chiral auxiliary is crucial unfortunately, the enamine derived from //ww-2,5-dimethyl pyrrolidine does not react with either the nitrene or the azide. 

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