Preparation of benzothiophen compounds from bicyclic sulphides

Abstract 1. 1. Bicyclic sulphides of 2,3-dihydrobenzothiophen and thiochroman series readily undergo dehydrogenation and dehydro-isomerization to compounds of benzothiophen series in the presence of catalysts with aprotonic acidity (Al 2 O 3 ; 10, 20% ZnCl 2 /Al 2 O 3 ). Transformations of thiochroman take place with compression of the six-membered heterocycle. 2. 2. 20% ZnCl 2 /Al 2 O 3 is the optimum catalyst for aromatization of compounds of the 2,3-dihydrobenzothiophen series. Yields of benzothiophen compounds from mono-substituted bicyclic sulphides (2- and 3-methyl-2,3-dihydrobenzothiophens) reach 56–72% with a process selectivity of 85–96%. The yield of benzothiophen compounds from a di-substituted bicyclic sulphide (2,2-dimethyl-2,3-dihydrobenzothiophen) exceeds 50% with a process selectivity of 75%. 3. 3. 10% ZnCl 2 /Al 2 O 3 is the optimum catalyst in aromatization of thiochroman. Benzothiophen yield exceeds 50% with a process selectivity of 82%. 4. 4. The proposed catalytic method of obtaining benzothiophen compounds is simple and promising as bicyclic oil sulphides may be used as raw materials for this purpose.