Vilsmeier formylation of para-substituted tert-anilines results in dibenzo[1,5]diazocines or quinazolinium salts: a remarkable example of the ‘t-amino effect’

Abstract

Formylation of para-substituted tert-anilines with various N-formylated sec-anilines†; in phosphoryl chloride results in ortho-formylation followed by cyclisation of the iminium salt to the adjacent tert-amino α-position by way of the ‘t-amino effect’ giving dibenzo[b,f][1,5]diazocines; in a similar manner, with N-formylated sec-aliphatic amines, quinazolinium salts are formed while bulky formanilides give the expected ortho-formylated tert-aniline.