Reactivity of [1]benzothieno[3,2-b][1]benzothiophene -: Electrophilic and metallation reactions

Electrophilic nitration, formylation and acetylation of the title heterocycle 1 were studied. Monosubstitution proceeds preferentially in position 2 and to a lesser extent in position 4. Lowering the reaction temperature substantially increases regioselectivity of nitration and acetylation. Substitution reactions of the 2-substituted derivatives of 1 led to the corresponding 2,7-disubstituted derivatives as major products. Formation of other regioisomers was also observed. Metallation of 1 with butyllithium preferably proceeds in position 1; subsequent reaction with N,N-dimethylformamide, carbon dioxide or iodine gives rise to corresponding 1-substituted derivatives. Long-chain 2,7-disubstitued derivatives exhibit liquid-crystalline properties.