Quantitative Gas‐Solid Diazotization of 3‐Aminopyrazolo[3,4‐b]pyridine Derivatives and Azo Dye Syntheses by Means of Solid‐Solid Reactions

Abstract

AbstractGas‐solid and solid‐solid techniques allow for waste‐free quantitative syntheses and coupling reactions of the heterocyclic diazonium salts 2. The solid‐state diazotization of 1a with gaseous NO2 has been mechanistically investigated by atomic force microscopy (AFM). Azo couplings are achieved in quantitative yields by cautious co‐grinding of the solid diazonium salt 2a with five (thio)barbituric acids, six acetoacetanilides (these couplings are followed by internal cyclization in solid‐state cascades), β‐naphthol, and 2,6‐dimethylphenol. The solid diazonium salt 2a is quantitatively coupled with three solid anilines to give the tautomeric triazenes 16. The structures of the products were established with IR, NMR and mass spectroscopy, while the tautomeric properties of the compounds were judged by density functional calculations at the B3LYP/6−31G* and BLYP/6−31G** levels. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)