Synthesis of Novel Bis(benzoxazole) Derivatives by Tandem Claisen Rearrangement and Their Fluorescence Behavior

Novel bis(benzoxazole) derivatives were easily synthesized from isobutenyl bis(amide−ether)s by tandem Claisen rearrangement and subsequent intramolecular cyclization of the amide−phenol intermediates. The yields of the bis(benzoxazole)s depended on whether the reaction was carried out with or without solvent, as well as on the substituents on the aryl group and the carbonyl group. The solvent effect was dramatic. No significant difference in the overall reaction rate constant with variation of the substituents on the carbonyl group was observed, but the nature of the aryl group on the ether had a large effect on the tandem Claisen rearrangement. The corresponding amide−phenol derivatives were confirmed as intermediates in this rearrangement. The fluorescence quantum yields of the obtained bis(benzoxazole)s were high, but the yields were lower than those of the corresponding monobenzoxazoles. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)