NOVEL METAL- AND MINERAL-ACID FREE SYNTHESIS OF ORGANIC AMMONIUM TRIBROMIDES AND APPLICATION OF ETHYLENEPHENANTHROLIUM BISTRIBROMIDE FOR BROMINATION OF ACTIVE METHYLENE GROUP OF 1,3-DIKETONES AND beta-KETOESTERS

摘要

A novel procedure for the preparation of organic ammonium tribromides (OATBs) is described from their corresponding bromides. Quaternary ammonium bromides (QABs) and a N,N-heterocyclic dibromide are efficiently oxidized to their corresponding monotribromides and bistribromide by m-chloroperbenzoic acid (MCPBA) in the presence of 2 and 4 equiv of KBr, respectively. The reactions are carried out in an aqueous medium without the use of any mineral acid or metal catalyst/promoters. A variety of tribromides are synthesized in very good yields including a hitherto unknown reagent, 1,10-(ethane-1, 2-diyl)phenanthrolinediium bistribromide (EPDBT). EPDBT is investigated as brominating agent and found to be highly effective for selective bromination of active methylene groups of a variety of 1,3-diketones and -ketoesters.