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 1H NMR spectroscopy. “Smart UV” for macrocyclic products: Photochemical rearrangement of 19‐membered azoxybenzocrown (19‐AZB‐O) in a one‐pot reaction results in formation of macrocyclic compounds, including three hydroxyazobenzocrowns. Macrocycles can be obtained, depending on conditions, with high, even over 70 %, yield. The structures of two atypical products 21‐o′‐OH and 19‐al were determined in the solid state (X‐ray) and in solution (NMR). The tautomeric equilibrium of hydroxyazobenzocrowns and its change depending on acidity/basicity of the environment and metal cation complexation were studied using spectroscopic methods.