Tautomerism of hydroxyazo compounds of the series of sterically hindered phenols

First Evidence for Wheland Intermediates in Azo‐Coupling Reactions − Reactions between 1,3,5‐Tris(dialkylamino)benzene and Arenediazonium Salts

“…[9] In particular, σ complexes in azocoupling reactions [10] have not been directly observed so far, although in the literature [11] complexes arising from azo coupling between p-benzoquinone diazide and 2,6-dialkylphenols were not isolated, but only hypothesized on the basis of kinetic data. Now we report the direct observation (in 1 H NMR spectroscopy) of Wheland complexes in the reactions of 1,3,5-tris(1-piperidyl)benzene and 1,3,5-tris(4-morpholinyl)benzene and arenediazonium tetrafluoroborate salts, and their transformation into the corresponding azo dyes, as reported in Scheme 2.…”