Spectroscopic and Computational Study of Organocatalytic Umpolung of Bromocations: An Accelerated Stereoselective Dibromination Protocol

Herein, the reversal of polarity of cationic bromine, organocatalytically, is presented. NBS, a proven bromocation source was converted to a superior bromoanion reagent by H/Br exchange with a secondary amine, substantiated with spectroscopic and computational evidences. The concept has further been used in a successful accelerated organocatalyzed dibromination of olefins, in a non-hazardous, commercially viable process with a wide substrate scope. The reactivity of key entities has been observed through NMR kinetics and reaction acceleration using 10 mol% of catalyst loading accounts for its major success. The nucleophilicity of the bromoanion was found to be superior in comparison to other nucleophiles such as MeOH, H2O etc. and the protocol dominates over competing allylic bromination reaction.