In order to acquire data on this particular point, some experiments using CCll as a depolarizer, ie the carbene precursor, have been performed. CH2C12 and CHCl3 were the reaction media in which: CC12 was generated. Under these conditions, where: CC12 reacts with the undissociated substrate, it is possible to assume that only CHCl3, if present, is able to transfer a proton to the zwitterionic intermediate 2 (Scheme 1). CHC13 is assumed to be ...