MgBr2-PROMOTED ELECTROSYNTHESIS OF SULFENIMINES (THIOOXIMES) FROM α-AMINOALKANOATES AND DIARYL/DIALKYL DISULFIDES IN A CH2Cl2–H2O TWO-PHASE SYSTEM. A STRAIGHTFORWARD PREPARATION OF C(6)/C(7)-SULFENIMINE DERIVATIVES OF PENICILLIN AND CEPHALOSPORIN