Tetrakis(alkylthio)thieno[3,4-c]thiophene: Synthesis,stability, and reactivity

The synthesis of tetrakis(alkylthio)thieno3,4-c]thiophenes la-e by the dimerization reaction of bis(alkylthio)cyclopropenethiones is described. The remarkable thermodynamic and kinetic stability suggests the significant electron-accepting conjugation of the alkylthio substituents to the carbanionic 1, 3, 4, and 6 carbons in the framework. The isopropylthio- and ethylthio-substituted thienothiophenes 1d and 1e undergo cycloaddition reactions with dienophiles such as N-phenylmaleimide and dimethyl acetylenedicarboxylate to give the cycloadducts in moderate yields.