Alkyl 2-azidocinnamates

Scheme 6.6 Conversion of alkyl 2-azidocinnamates into indole-2-carboxylic esters ...

For example, 2-arylazirines 13 can rearrange to indoles 14 when heated in xylene (Scheme 6.6) and the direct thermal conversion of alkyl 2-azidocinnamates into indoles has been exploited as a route to indole-2-carboxylic acid esters. The temperature has to be controlled when these vinyl azides were decomposed in solution in order to isolate 2H-azirines. ° Dilute solutions are also usually preferable in order to avoid bimolecular reactions. Photolysis is sometimes preferable to thermolysis for the generation of thermally unstable azirines. ... 

A simple intramolecular nucleophilic addition is illustrated in Scheme 6.30. °° Normally alkyl 2-azidocinnamates are converted into aUcyl indole-2-carboxylates when they are heated in solution (Scheme 6.6). The azidoester 72 gave the corresponding indole in very low yield, however. The major product was the aziridine 74 which is formed by interception of the intermediate 2 f-azirine 73 by the internal nucleophile. 

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