Rh(?)-catalyzed [3+2] Cycloaddition To Synthesize 1,2-dihydropyrrolo[3,4-b]indol-3-ones

1,2-Dihydropyrrolo[3,4-b]indol-3-ones are a kind of important nitrogen-containing heterocycles,which are widely found in many compounds with biological activities and medicinal value.Therefore,many chemists have focused on the synthesis of these compounds.Herein,we mainly introduce the efficient synthesis of 1,2-dihydropyrrolo[3,4-b]indol-3-ones through the tandem cyclization reaction.We designed and synthesized a kind of indoles with electron-deficient alkenes at the C3 position of the indole moiety and pyridine groups at the N1 position of the indole moiety.We used Rh(?)as the catalyst to promote tandem cyclization reaction between the above indoles and isocyanates.This tandem cyclization reaction involved coupling reaction between above indoles and isocyanates initiated by C-H activation and subsequent intramolecular aza-Michael addition of electron-deficient alkenes.The reaction could be considered as formal [3+2] cycloaddition reaction between1-pyridinyl-3-alkenyl indoles and isocyanates affording a series of1,2-dihydropyrrolo[3,4-b]indol-3-ones.After that,We tested the applicability of the reaction by extending the substrates.A series of1,2-dihydropyrrolo[3,4-b]indol-3-ones were afforded in moderate to good yields no matter indole with electron-donating or electron-withdrawing substituents.The tandem cyclization we provided has the advantages of high bonding efficiency,high atom utilization,simple operation,and environmental friendliness.It provides a more efficient,convenient,economical and green method for the synthesis of 1,2-dihydropyrrolo[3,4-b]indol-3-ones.