Anhydrides with azirines

Sato et al. observed that the reaction of 2-phenyl-1-azirine with acid chlorides and anhydrides in the presence of triethylamine gives the oxazole directly.57 They have reported that azirines also react with carboxylic anhydrides to give oxazoles (136).57 Aziridine (135) is suggested as a likely intermediate in the reaction of acetic anhydride with azirine (42a), since carrying out the reaction at lower temperature and for a shorter reaction time gave a compound to which they assigned structure 135. 

A 2-azirine structure has been assigned to a by-product of Umi reactitai of acetic anhydride with the triazoledicarbo lic add obtained from the treatmenti of acetylenedicarboxylic acid with, hydi-azoic acid (Eq. 80). 

Treatment of triazole (7) with acetic anhydride was reported to give the 2-azirine (8),3 but further investigation of this reaction by Rees ef al. has shown that the correct structure is the oxazole (9).4... 

The reaction of azirine (42a) with phthalic anhydride does not lead to the oxazole,67 Rather, the ketoamide (138) is produced, presumably through hydrolysis of intermediate 137. 

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