Products of Photo- and Thermochemical Rearrangement of 19-Membered di-tert-Butyl-Azoxybenzocrown

Abstract

The preparation and characterization of products of the photochemical and thermochemical rearrangements of 19-membered azoxybenzocrowns with two, bulky, tert-butyl substituents in benzene rings in the para positions to oligooxyethylene fragments (meta positions to azoxy group, i.e., t-Bu-19-Azo-O have been presented. In photochemical rearrangement, two colored typical products were expected, i.e., 19-membered o-hydroxy-m,m′-di-tert-butyl-azobenzocrown (t-Bu-19-o-OH) and 19-membered p-hydroxy-m,m′-di-tert-butyl-azobenzocrown (t-Bu-19-p-OH). In experiments, two colored atypical macrocyclic derivatives, one 6-membered and one 5-membered ring, bearing an aldehyde group (t-Bu-19-al) or intramolecular ester group (t-Bu-20-ester), were obtained. Photochemical rearrangement led to one more macrocyclic product being isolated and identified: a 17-membered colorless compound, without an azo moiety, t-Bu-17-p-OH. The yield of the individual compounds was significantly influenced by the reaction conditions. Thermochemical rearrangement led to t-Bu-20-ester as the main product. The structures of the four crystalline products of the rearrangement—t-Bu-19-o-OH, t-Bu-19-p-OH, t-Bu-20-ester and t-Bu-17-p-OH—were determined by the X-ray method. Structures in solution of atypical derivatives (t-Bu-19-al and t-Bu-20-ester) and t-Bu-19-p-OH were defined using NMR spectroscopy. For the newly obtained hydroxyazobenzocrowns, the azo–phenol⇄quinone–hydrazone tautomeric equilibrium was investigated using spectroscopic methods. Complexation studies of alkali and alkaline earth metal cations were studied using UV-Vis absorption spectroscopy. 1H NMR spectroscopy was additionally used to study the cation recognition of metal cations. Cation binding studies in acetonitrile have shown high selectivity towards calcium over magnesium for t-Bu-19-o-OH.

Do Phenyl Substituents Affect the Properties of Azobenzocrown Derivatives?

“…Similar results were obtained for the photo-and thermal rearrangement of t-Bu-19-Azo-O. [39] Under analogous conditions 19-Azo-O does not undergo rearrangement. 20-membered esters (Table 1) were found in reaction mixtures only in case of transformations of para-substituted azoxybenzocrowns Ph-19-Azo-O and t-Bu-19-Azo-O.…”

“…Tautomeric equilibrium of hydroxyazobenzocrowns of different macrocycle size has been studied by us to different degrees [27,[38][39][40][41] (Scheme 2).…”

“…19-Azo-O [38] t-Bu-19-Azo-O [39] Ph- Scheme 2. General presentation of azophenol !quinone-hydrazone tautomeric equilibrium of hydroxyazobenzocrowns.…”

“…General presentation of azophenol !quinone-hydrazone tautomeric equilibrium of hydroxyazobenzocrowns. [27,[38][39][40][41] ChemPlusChem environment such as solvent type, pH, the presence of ionic species (e. g. metal salts) or temperature. For 19-membered phydroxyazobenzocrowns we have recently postulated [38,39] that in polar solvents such as acetonitrile and DMSO, differing in hydrogen-bonding affinity, the contribution of tautomers seems to be also connected with the presence of substituents in benzene rings.…”

“…Among them are hydroxyazomacrocycles as well as compounds of rather unexpected structure. [38,39] The main aim of the present work was the investigation of the direction of the rearrangements of sterically hindered azoxymacrocycle and character-ization of the formed products. In this attempt we have used 19-membered azoxybenzocrown with two phenyl substituents in benzene rings in para positions to the oligooxyethylene fragment (meta positions to azoxy group), labeled as Ph-19-Azo-O.…”