Synthesis and photochromic behaviour of new methyl induced linear and angular thieno-2H-chromenes

New methyl induced linear and angular thieno-2H-chromenes , and were prepared by reaction of new methylated 6-hydroxybenzo[b]thiophenes (a, b and c) and propargylic alcohols and , using acidic Alumina Brockmann I as catalyst and drying agent. Compounds were prepared in good to excellent yields in a ‘one pot’ three step reaction from the corresponding bromo compounds . The photochromic behaviour of compounds , and was evaluated with the aid of a classical set of spectrokinetic parameters, and compared to reference compounds that are benzoannellated in the 5,6 and 6,7 positions of the chromene (naphthopyrans) and also to thieno-2H-chromenes and , previously prepared, which are analogues of . The resistance to fatigue (photodegradation) under continuous irradiation was also evaluated.