Synthesis of bicyclic dioxetanes bearing a 3-hydroxy-4-isoxazolylphenyl moiety: new CIEEL-active dioxetanes emitting light with remarkable high-efficiency in aqueous medium

Bicyclic dioxetanes bearing a 3-hydroxy-4-isoxazolylphenyl moiety (3a–c) were synthesized. All these dioxetanes (3a–c) underwent base-induced CIEEL-decay to afford light with high efficiency in an NaOH/H2O system as well as in a TBAF (tetrabutylammonium fluoride)/acetonitrile system. Among them, a dioxetane bearing a 3-hydroxy-4-[5-(trifluoromethyl)isoxazol-3-yl]phenyl moiety (3a) emitted light in the aqueous system with the highest efficiency which parallels that attained in an aprotic solvent system. Fluorescence study and the AM1 calculations for 3a and the parent CIEEL-active dioxetanes (1) suggested that one important factor affecting chemiluminescence efficiency in an aqueous system should be the hydrogen-bonding at the carbonyl oxygen site of an oxyanion of hydroxyarenecarboxylate as the emitter produced by the CIEEL-decay.