Rhodium-Catalyzed Selective Oxidative (Spiro)annulation of 2-Arylindoles by Using Benzoquinone as a C2 or C1 Synthon

Abstract

Rhodium-catalyzed substrate-tunable oxidative annulation and spiroannulation reactions of 2-arylindoles with benzoquinone leading to 9H-dibenzo­[a,c]­carbazol-3-ols and new spirocyclic products are reported. Intriguingly, with 2-aryl-substituted indoles, benzoquinone could act as a C2 synthon to afford dibenzo­[a,c]­carbazoles. On the contrary, when 2-aryl-3-substituted indoles were used, benzoquinone switched to act as a C1 synthon to furnish spirocyclic compounds. In addition, further transformations of the obtained products demonstrate the synthetic utility of the present protocol.

The Different Facets of Metal‐Catalyzed C−H Functionalization Involving Quinone Compounds

“…Guo et al . reported a indole‐directed Rh(III)‐catalysed arylation of quinones in 2019 [73] . The quinone substrate acted as either a C1 or C2 synthon depending on whether the 2‐arylindole substrates had a substituent at C‐3 (Scheme 40).…”

Recent advances in rhodium-catalysed cross-dehydrogenative-coupling between two C(sp2)–H bonds

“…Fan, Zhang and Guo accomplished a Rh-catalysed CDC reaction of 2-arylindoles with benzoquinone for the synthesis of 9 H -dibenzo[ a,c ]carbazol-3-ol derivatives (Scheme 35). 51 Very recently, a similar reaction protocol was developed by Wang's group using the same Rh catalyst yet different bases and solvents for the same transformation. 52…”

“…Fan, Zhang and Guo accomplished a Rh-catalysed CDC reaction of 2-arylindoles with benzoquinone for the synthesis of 9H-dibenzo[a,c]carbazol-3-ol derivatives (Scheme 35). 51 Very recently, a similar reaction protocol was developed by Wang's group using the same Rh catalyst yet different bases and solvents for the same transformation. 52 Fan and Zhang further achieved the dehydrogenative reaction of 2-arylindazoles with maleimides for affording the indazolo[2,3-a]pyrrolo[3,4-c]quinolinones with a C-C double bond formation (Scheme 36a).…”

Formations of aryl or pyrrole ring via palladium‐catalyzed CH functionalization on amido‐substituted quinones in the presence of amines or phosphines

“…Benzoquinone is a six‐membered ring organic compound that exhibits many interesting characters. [ 7 ] The moiety of quinone could be found in many organic compounds and could display diverse functions such as oxidant, [ 8 ] ligand, [ 9 ] promoter, [ 10 ] carbon synthon, [ 11 ] dienophile, [ 12 ] bioactivity [ 13 ] in various circumstances. Our previous works had shown that the reactions of an amido‐substituted 1,4‐quinone, N ‐(3,6‐dioxocyclohexa‐1,4‐dien‐1‐yl)acetamide ( 1a_BQ ), or N ‐(3,6‐dioxocyclohexa‐1,4‐dien‐1‐yl)propionamide ( 1b_BQ ), with NR 3 (R = Et, Pr, Bu, i‐Pentyl) in the presence of palladium salts had yielded some products with unexpected structural features (Scheme 2).…”