Stereochemistry of the electrophilic addition of bromine to dibenzo[b,f]thiepin and its 5,5-dioxide

Abstract

The dibromide formed by kinetically controlled bromine addition to dibenzo[b,f]thiepin (3) is the trans-isomer (5). Treatment of this product with methanolic sodium methoxide gives the bromo-ene (1) together with products resulting from substitution and rearrangement reactions, but the reaction with potassium t-butoxide in t-butyl alcohol gives only the bromo-ene (1). Bromine addition to the sulphone (2) in carbon tetrachloride gives the cis-dibromide whereas in acetic acid the trans-dibromide is obtained. The acid-catalysed dehydration and rearrangement of 9-hydroxymethylthioxanthen (18) proceeds abnormally under anhydrous conditions in toluene giving 10,11-dihydro-10-p-tolyldibenzo[b,f]theipin (19).