Electrochemical trifluoromethylation of 3-sulpholene. Synthesis of meso- and DL-3,4-bis(trifluoromethyl)sulpholanes

Electrochemical trifluoromethylation of 3-sulpholene (1) in a CF3COOH/CH3COONa/CH3CN/H2O system gives a complex mixture consisting of meso- and DL-3,4-bis(trifluoromethyl)sulpholanes (2a) and (2b) as the major components and isomeric trifluoromethylsulpholenes 3a and 3b, 3,4-bis( trifluoromethyl) sulpholenes 4a and 4b, 3-trifluoromethylsulpholane 5 and 2,3,4-tris( trifluoromethyl) sulpholanes 6a-c as the minor components with a 40-50% total yield. Compounds 2a and 2b were efficiently isolated from the crude reaction mixture and fully identified by spectral methods. The reaction conducted in a CF3COOH/CF3COONa/H2O system, without acetonitrile, gave 4-trifluoromethyl-2-sulpholene (3a) as the main product, albeit total yield was low. (C) 1998 Elsevier Science S.A.