1 Synthesis and photochromic behaviour of new methyl induced linear and angular thieno-2H-chromenes Maria-João R. P. Queiroz, a * Paula M. S. Plasencia, a Roger Dubest, b Jean Aubard b and Robert Guglielmetti c a Departamento de Química, Universidade do Minho, 4710-057 Braga, Portugal b ITODYS, UMR 7086 CNRS, Université Denis Diderot Paris 7, 75005 Paris, France c LCMOM, UMR 6114 CNRS, Université de la Méditerranée, 13288 Marseille cedex 9, France ______________________________________________________________________ Abstract: New methyl induced linear and angular thieno-2H-chromenes 4, 5 and 6 were prepared by reaction of new methylated 6-hydroxybenzo[b]thiophenes 2 (a, b and c) and propargylic alcohols 3a and 3b, using acidic Alumina Brockmann I as catalyst and drying agent. Compounds 2 were prepared in good to excellent yields in a “one pot” three step reaction from the corresponding bromo compounds 1. The photochromic behaviour of compounds 4, 5 and 6b 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 7 and 8, previously prepared, which are analogues of 5a. The resistance to fatigue (photodegradation) under continuous irradiation was also evaluated. ______________________________________________________________________ 1. Introduction Since the discovery of the photochromic behaviour of the 2H-chromenes (2H-1- benzopyrans) 1 much research has been devoted to this important class of oxygenated heterocyclic compounds. 2 They exhibit their photochromic properties by a reversible pyran ring opening, induced by light, that converts a colourless form (closed form) in a set of photoisomers where the pyran ring is open (open forms). Among the structural Keywords: Thieno-2H-chromenes, hydroxybenzo[b]thiophenes, photochromism, flash photolysis * Corresponding author. Tel.+351253604378; fax. +351253678983