Synthesis of photochromic thieno-2H-chromene derivatives

Syntheses of photochromic thieno-2H-chromenes from hydroxybenzo[b]thiophene s and 1,1-diphenyl-2-propyn-1-ol using an acid catalyst are described. The hydroxybenzo[b]thiophenes were prepared by demethylation of methoxybenzo[b] thiophenes with pyridinium chloride or boron tribromide. The precursors wer e synthesized in two steps, which involved the reaction of methoxythiopheno ls with 3-bromobutan-2-one in an alkaline medium, to give ketoarysulfides, followed by cyclization using phosphorus pentoxide or polyphosphoric acid. The photochromic behaviour of the target compounds was evaluated with the a id of the usual spectrokinetic parameters, and the results were compared to data from reference compounds that are benzoannellated in the 5,6 and 7,8 positions of the 2H-chromene system. (C) 2000 Elsevier Science Ltd. All rig hts reserved.