Synthesis of fluorescent trisubstituted oxazoles via a facile tandem Staudinger/aza-Wittig/isomerization reaction

A new facile synthesis of trisubstituted oxazoles starting from azides was developed. The reactions of azides with triphenyl phosphine afforded the corresponding 2,4,5-trisubstituted oxazole derivatives via tandem Staudinger, aza-Wittig and isomerization reaction either thermally or under basic conditions. Properties of the oxazole derivatives were surveyed and some of the examples showed reasonable fluorescence. The greatest fluorescence intensity was observed when the 2- and the 5- substituents on the oxazole ring were aromatic groups (with epsilon = 23-3.0 x 10(4) mol(-1) dm(3) cm(-1) and Phi = 0.25-0.29 relative to quinine sulphate). However, the fluorescence intensity was diminished when either the 2- or the 5-substituent was H or alkyl. (C) 2016 Elsevier Ltd. All rights reserved.