Highly regioselective and metal-free γ-addition of β-keto esters to isatins, catalyzed by DABCO: direct access to novel class of diversely functionalized 3-hydroxy-2-oxindole scaffolds

DABCO catalyzed, highly regioselective γ-addition of β-keto esters has been achieved in the aldol reaction with isatins to afford γ-(3-hydroxy-2-oxindole)-β-keto ester structural framework under metal-free condition. The generality of the method has been demonstrated by screening series of isatin electrophiles as well as linear and cyclic β-keto esters. Compare to the dianion method, the present method is very simple and handy, which provides straightforward access for the new diversely functionalized 3-β-keto ester substituted-3-hydroxy-2-oxindole structural scaffolds in very good yields from readily available starting materials.