Oxidative dimerization of diethyl 3-thienylmalonate by high valent metal salts. Synthesis of benzo[1,2-b:4,5-b']dithiophene derivatives

Article abstract of DOI:10.1016/0040-4020(96)00797-1

The oxidation of diethyl 3-thienylmalonate (1) by metal oxidants (Fe(ClO₄)₃, Mn(OAc)₃, MnO₂ and CuO) in various solvents at 60 °C affords dimerization products arising from side-chain and nuclear coupling of the intermediate delocalized malonyl radicals 6. Metal to sulphur binding is suggested to play a role in controlling the distribution of dimers 2-5. The higher thermodynamic stability of unsymmetric dimer 3, along with its oxidative intramolecular 1,6-cyclization to 4, allows to develop a new simple synthesis of benzo[1,2-b:4,5-b']dithiophene derivatives 15-18.