Unusual thiophilic ring-opening of fused oligothiophenes with organolithium reagents

Organolithium reagents attack the sulfur atoms of fused oligothiophenes producing ring-opened organolithium intermediates that can be trapped with a suitable electrophile. The reaction was found to be general for fused thieno[2,3-b]-thiophenes and some [3,2-b]-fused oligothiophenes. Thermodynamic (organilithiums basicity) and mechanistic (RLi coordination by neighboring sulfur) aspects control the substrate scope and regioselectivity of the reaction. When competitive deprotonation of the substrate is possible, high selectivity toward ring-opening was observed with n-BuLi when compared with the other tested organolithiums. The recently discovered octathio[8]circulene produces multifold ring-opening products.