The biphenacyl benzotriazolium salts 12 give a tautomeric equilibrium 13[Formula: see text]14 in the presence of triethylamine (TEA) or NaOH. The evaluation of this tautomeric equilibrium has been studied using a dynamic NMR analysis and a new synthetic procedure of disubstituted benzotriazolium ylides 15 and 16, which have in their structures a picryl fragment. This study also includes a theoretical analysis on the reactivity of salts 12a–c and the thermodynamical stability of tautomeric forms 13 and 14 by AM1 and PM3 procedure methods.Key words: synthesis, salts, ylides, semiempirical calculations, kinetics.

The paper presents the synthesis of cyclo (bis-paraquat p-phenylene p-phenylene-carbonyl) tetrakis (hexafluorophosphate), named �CETOBOX�, and the closely related structural determinations. This compound exists in three tautomeric forms. These forms were evidentiated by NMR-data (1H-NMR, TOCSY, COSY, NOESY), UV-Vis spectra coupled with pH measurements and by synthesis. As the �CETOBOX� gives �in situ� only the corresponding monoylide, the synthesis of a new fluorescent indolizine cyclophane has been performed by a 3+2 cycloaddition. All structures of the new compounds presented herein have been established by NMR spectroscopy. Also, theoretical methods (MM3, AM1, AM1-COSMO and B88LYPDFT) have been used to determine the most stable conformer structures.