Dibromination, enantioselective

H2O2 in methanol. Aryl methyl ketones can be dibrominated (ArCOCHa ArCOCHBr2) in high yields with benzyltrimethylammonium tribromide. Active methylene compounds are chlorinated with NCS and Mg(C104)2. " Similar chlorination in the presence of a chiral copper catalyst led to cx-chlorination with modest enantioselectivity. 

Scheme 4.1 Palladium-catalyzed enantioselective chlorohydrin and dibromination reactions.

Scheme 16.43 Palladium(ll)-catalyzed enantioselective dibromination of alkenes.

An enantioselective dibromination of cinnamic alcohols (9) has been developed, which involves a combination of dibromomalonate as the bromonium source, a titanium bromide species as the bromide source, and a tartaric acid-derived diol (20 mol%). Ligand acceleration has been observed in this transformation, which affords the dibromides (11) with <85% ee transition state (10) has been proposed. ... 

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