Photochemical Rearrangement of a 19-Membered Azoxybenzocrown: Products and their Properties

The preparation and characterization of products of the chemical and photochemical rearrangements of a 19-memberedo,o '-azoxybenzocrown are presented. In photochemical rearrangement, besides the expected product i. e. 19-memberedo-hydroxy-o,o '-azobenzocrown (19-o-OH)obtained under defined conditions with 75 % yield, also other macrocyclic products were isolated and identified, namely: 19-memberedp-hydroxy-o,o '-azobenzocrown (19-p-OH), 21-memberedo '-hydroxy-o,p '-azobenzocrown (21-o '-OH)and 19-membered macrocycle containing a 5-membered ring bearing an aldehyde group (19-al). The structures of two atypical products of the photochemical rearrangement -21-o '-OHand19-al- were determined in the solid state by X-ray analysis and in solution using NMR spectroscopy. Tautomeric equilibrium of the formed hydroxyazobenzocrowns and its change depending on acidity/basicity of the environment and alkali and alkaline earth metal cations complexation were studied using UV-Vis spectrophotometry, spectrofluorimetry and(1)H NMR spectroscopy.