Lactone-fused naphthopyran UV photoswitches with fast bleaching in the dark

Abstract The acid-catalyzed one-pot condensation of easily accessible ethyl 5-hydroxynaphtho[1,2-b]furan-3-carboxylate with 1,1-diarylbut-2-yne-1,4-diols provided lactone-fused naphthopyrans in moderate yields. UV irradiation of these colorless compounds in solution, for a few seconds, generates a red coloration that bleaches quickly and completely in the dark (t1/2 = 4.0 s at 20 °C).