Huisgen reaction tetrazole acylation with

An attempt to ringclose the free acid 8 to the benzoxazinone 3 with the help of acetic anhydride led to an unexpected result If 8 (or preferable 3) is heated in acetic anhydride the oxadiazolyl benzoxazine 12 is obtained. However, the outcome of this reaction is not surprising since R. Huisgen [68AG359] and others, have shown, that the acylation of tetrazoles give 1,3,4-oxadiazoles via N-acylnitrilimines (such as 11) by 1,5-dipolar electrocyclic ringclosure. 

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