Formal (2+2) ring expansion prevails over (4+2) cycloaddition of a kinetically stabilized benzoborirene with reactive cycloaddends

Abstract

Benzoborirene carrying a bulky Trip₂C₆H₃ (Trip = 2,4,6-tri-iso-Pr₃C₆H₂) group at boron reacts with the dienophile 4-phenyl-1,2,4-triazoline-3,5-dione and the diene 3,6-di(4-pyridyl)-1,2,4,5-tetrazine by opening of the borirene ring rather than undergoing the typical Diels–Alder reactions. The formal insertion results in diazaborole and azaborolo[1,5-b][1,2,4,5]tetrazine derivatives, respectively.