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‐membered o , o′ ‐azoxybenzocrown are presented. In photochemical rearrangement, besides the expected product i. e. 19‐membered o ‐hydroxy‐ o , o′ ‐azobenzocrown ( 19‐ o ‐OH) obtained under defined conditions with 75 % yield, also other macrocyclic products were isolated and identified, namely: 19‐membered p ‐hydroxy‐ o , o′ ‐azobenzocrown ( 19‐ p ‐OH) , 21‐membered o′ ‐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′ ‐OH and 19‐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.