Regioselective and Chemodivergent Synthesis of 1,3-Indandione-Fused Spirocyclopentenes and Spiropyrrolidines.

Herein, we report a divergent cyclization strategy for the synthesis of 1,3-indandione-fused five-membered carbocyclic and heterocyclic scaffolds. The reaction between 2-arylidene-1,3-indandiones and β-keto enamines gives Michael adducts─1,3-indandione-substituted β-keto enamines─which were used as reaction precursors. Subsequent reaction of these precursors with Cu(OAc)2 leads to the formation of 1,3-indandione-fused spirocyclopentenes via C-C bond formation. In contrast, treatment with N-iodosuccinimide yields diastereoselective spiropyrrolidine derivatives via C-N bond formation. Both reaction pathways proceed with high chemoselectivity, exhibit excellent functional group tolerance, and afford good to excellent yields of the desired products. An ionic mechanism is proposed for the formation of these two classes of spiro-compounds, as supported by radical scavenging experiments.