Pd-Catalyzed C-7 Arylation of Indolines with Aryltriazenes under Mild Conditions

Abstract

A palladium-catalyzed direct C−H arylation of indolines at C-7 position has been achieved at near-ambient temperature. The reaction was carried out with aryltriazene as a stable aryl source and electron shuttle to sustainably release aryl radical in situ under the action of promoter, and pyrimidine as a detachable directing group for the synthesis of 7-arylindolines under oxidant-and ligand-free conditions. Notably, this catalytic system can also be applied to the direct and site-selective arylation of tetrahydroquinolines (C-8) and carbazoles (C-1).

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part A: the C(sp2)−C(sp2), C(sp2)−C(sp3) and C(sp3)−C(sp3) Bonds

“…The Pd II -catalyzed C7-arylation of 1-(pyrimidin-2-yl)indoline with p-tolyldiazenylpyrrolidine using HPF 6 as a promoter has been recently disclosed by Liu, Zhang and co-workers (Scheme 2m). [27] Pd-(OCOCF 3 ) 2 provides a better yield than Pd(OAc) 2 . The rather unclear proposed catalytic cycle [27] summarized in Scheme 2n involves Pd II -mediated C7-activation of the substrate leading to 2nA which gives rise to Pd IV complex 2nB via addition of aryl radical and hexafluorophosphoric anion produced through a set of reactions involving acid-activation of the aryltriazene, single electron transfer and possibly a Pd III intermediate.…”

“…The Pd II ‐catalyzed C7‐arylation of 1‐(pyrimidin‐2‐yl)indoline with p ‐tolyldiazenylpyrrolidine using HPF 6 as a promoter has been recently disclosed by Liu, Zhang and co‐workers (Scheme 2m) [27] . Pd(OCOCF 3 ) 2 provides a better yield than Pd(OAc) 2 .…”

“…Pd(OCOCF 3 ) 2 provides a better yield than Pd(OAc) 2 . The rather unclear proposed catalytic cycle [27] summarized in Scheme 2n involves Pd II ‐mediated C7‐activation of the substrate leading to 2nA which gives rise to Pd IV complex 2nB via addition of aryl radical and hexafluorophosphoric anion produced through a set of reactions involving acid‐activation of the aryltriazene, single electron transfer and possibly a Pd III intermediate. Finally, reductive elimination releases the product and the catalyst.…”

Pd-Catalyzed Direct C7 Trifluoromethylation of Indolines with Umemoto’s Reagent

“…Recently, TM-catalyzed C–H functionalization of indole derivatives has witnessed major advances . In particular, a great deal of contribution has been devoted by synthetic organic researchers to get a synthetic protocol to access C-7 functionalized indolines or indoles, which include arylation, alkylation, ammoniation, carbonylation, allylation reaction, and so on. , Hence, the alternative approaches for the synthesis of C-7 decorated indoles can be achieved via TM-catalyzed C(7)–H bond activation/oxidation sequential reaction of indolines (Scheme b). , However, as far as we know, the direct C-7 trifluoromethylation of indolines by using Umemoto’s reagent has not yet been realized. To continue on our interest in development of an efficient method to access functionalized heterocyclic compound, herein, we report the Pd-catalyzed C7 trifluoromethylation of indolines by using Umemoto’s reagent as a trifluoromethylating reagent (Scheme c).…”