SYNTHESIS OF 2H-BENZO[b]THIETES BY TFA-MEDIATED CYCLIZATION OF O-tert-BUTYL S-(2-VINYLPHENYL) CARBONOTHIOATES VIA 4H-3,1-BENZOXATHIIN-2-ONE INTERMEDIATES

An efficient method for the preparation of 2H-benzo[b]thiete derivatives under mild conditions has been developed. The reaction of 2-(1-arylethenyl)phenyl bromides with butyllithium at -78 degrees C generates 2-(1-arylethenyl)phenyllithiums, which are successively treated with sulfur and Boc(2)O at the same temperature to afford S-[2-(1-arylethenyl)phenyl] O-tert-butyl carbonothioates. These compounds are then treated with TFA at 0 or 20 degrees C to yield 2-aryl-2-methyl-2H-benzo[b]thietes via formation of the 4-aryl-4-methyl-4H-3,1-benzoxathiin-2-ones followed by decarboxylation.