Benzoxazoles, 2-amino-, tautomerism

Unlike the products of condensation of 1,2-diaminoethane and 1-amino-2-hydroxyethane with aminobutynones, which exist almost exclusively in the enole form, benzoxazoles 359,361 and benzothiazoles 360,362 are present in the solution as a tautomeric mixture of the ketone (359, 360) and enole (361,362) forms. This seems to be related to weakening of the imine nitrogen basicity due to adjacent oxygen and sulfur atoms. 

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