Organocatalyzed Asymmetric α‑Thiocyanation of Oxindoles: Synthesis of Chiral Tertiary 3‑Thiocyanatoxindoles

An enantioselective thiocyanation
of oxindoles has been developed
for the first time using a bifunctional cinchona-derived organo-catalyst
and N-thiocyanatophthalimide as the electrophilic
thiocyanation source in the presence of 2-naphthol as the additive.
Various enantioenriched 3,3′-disubstituted oxindoles with SCN-containing
quaternary carbon stereocenters were synthesized under mild conditions
in high yields (up to 99%) and good enantioselectivities (up to 6:94
er).