Catalytic enantioselective chlorination and bromination of beta-keto esters

The Ti(TADDOLato) complexes dichloro[(4R,5R)-2,2-dimethyl-alpha,alpha,alpha ',alpha'-tetraphenyl-1,3-dioxolane-4,5-dimethanolato(2- )-O,O']titanium ((R )-1a) and dichloro[(4R,5R)-2,2-dimethyl-alpha,alpha,alpha',alpha'yl)-1,3-di oxolane-4,5-dimethanolato(2 -)-O,O']titanium ((R)-1b) are efficient catalys ts for the electrophilic enantioselective chlorination and bromination of b eta-keto esters with N-chlorosuccinimide (NCS) and N-bromosuccinimide (NBS) ,respectively. With 5 mol-% of catalyst at room temperature an enantioselec tivity of up to 88% ee could be obtained for the chlorination reaction. Und er comparable conditions, bromination reactions are slower and less stereos elective.