Synthesis of Fused or Spiro Polyheterocyclic Compounds via the Dehydrogenative Annulation Reactions of 2-Arylindazoles with Maleimides

Abstract

A dehydrogenative annulation of 2-arylindazoles with maleimides for the switchable synthesis of indazolo­[2,3-a]­pyrrolo­[3,4-c]­quinolinones or spiroindolo­[1,2-b]­indazole-11,3′-pyrrolidinones is presented. Mechanistically, the formation of the title compounds involves a Rh­(III)-catalyzed C–H metalation of 2-arylindazole, followed by maleimide insertion and intramolecular cyclization. Interestingly, the selectivity to form the fused or spiro compounds could be switched by resorting to different additives. The notable features of this protocol include simple substrates and excellent atom economy and regioselectivity.

Rhodium(III)‐Catalyzed Annulation of 2‐Arylimidazo[1,2‐a]pyridines with Maleimides: Synthesis of 1H‐Benzo[e]pyrido[1′,2′:1,2]imidazo[4,5‐g]isoindole‐1,3(2H)‐Diones and their Photophysical Studies

“…Based on the control experimental results, our own understanding, and previous studies, [8a,9,13c,16] a putative mechanism for the annulation reaction is depicted in Scheme 4. Initially, 1 coordinates with in situ formed active [Cp*RhX 2 ] species to give intermediate A which subsequently undergoes C−H metalation via C−H activation to generates rhodacycle B .…”

Rhodium(III)‐Catalyzed Dehydrogenative Annulation of 2‐Arylindazoles with Cyclic Enones

“…[7] In particular, 2-arylindazoles have successfully been functionalized with α-diazocarbonyl compounds, [8] 2alkynylanilines, [9] alkynyl triazenes, [10] 1,2-disubstituted alkynes [11] dioxazolone [12] and maleimides etc. [13] However, this is the first report using 2-arylindazoles with cyclic enones.…”

Direct Catalytic Functionalization of Indazole Derivatives

“…In 2019, Fan et al showed a Rh(III)-catalyzed dehydrogenative annulation of 2-arylindazoles (85 a) with maleimides (85 b) for preparation of indazolo [2,3a]pyrrolo [3,4-c]quinolinones (85 c) (Scheme 85). [141] In…”