Comparative studies on the enantioselective fluorination of oxindoles with structurally modified N-fluorobenzenesulfonimides

Structurally modified N-fluorobenzenesulfonimides (NFSIs) have been used to study the enantioselective fluorination of oxindoles in the presence of a bis-cinchona alkaloid, (DHQD)2PHAL, as the catalyst. We observe that the NFSI analogues bearing two tert-butyl groups at the para-position of the symmetric phenyl rings led to an enhanced enantioselectivity in most cases (up to 96% ee) compared with the unmodified NFSIs (less than 69% ee).