ortho-lithiation of benzene-1,2-dithiol: A methodology for ortho-functionalization of benzene-1,2-dithiol

The ortho-lithiation of benzene-1,2-dithiol with three equivalents of nBuLi afforded mono-as well as di-C-lithiated intermediates. The surprising kinetically controlled formation of di-C-lithiated species offers the opportunity to obtain dimercaptobenzoic and -terephthalic acid derivatives in a onepot synthesis in reasonable yields. Both compounds are versatile building blocks for the synthesis of macrocycles containing arylenedithiol units. Focusing on novel terephthalic acid derivatives, two preparation routes, via amide and via alkyl linkage, respectively, have been elaborated. The reaction sequence (i) sulfur protection using either isopropyl or benzyl groups, (ii) transformation of the carboxylic function into an an-tide or an alkyl group and (iii) subsequent removal of the protection groups afforded the terephthaldiamidedithiol 6 and the 1,2-bis(2,3-dimercaptophenyl)ethane 11.