Pd(ii)/Lewis acid catalyzed regioselective olefination of indole with dioxygen

Abstract

Transition metal ions catalyzed indole olefination through C-H activation has offered a convenient protocol to synthesize versatile bioactive vinylindole compounds, however, in most cases, stoichiometric oxidants were employed to achieve...

Pd(II)/Lewis Acid Catalyzed Intramolecular Annulation of Indolecarboxamides with Dioxygen through Dual C–H Activation

“…The UV–vis spectrum of the Pd­(OAc) 2 /Sc­(OTf) 3 catalyst also disclosed the formation of a new Pd­(II) species by adding Sc­(OTf) 3 to the TFE solution of Pd­(OAc) 2 (see Figure ). These phenomena are very similar to Pd­(II)/LA catalysis for other organic syntheses in CH 3 CN or dimethyl sulfoxide (DMSO) solvent in our previous study . Particularly, similar acetate bridged heterobimetallic Pd­(II) structures were even isolated with X-ray characterizations in the literature .…”

Pd(II)/Lewis Acid Catalyzed Intramolecular Oxidative C−H Amination to Construct Carbazoles with Dioxygen

“…In 1 H NMR characterizations (Figure 3), adding Sc(OTf) 3 to the DMF solution of Pd(OAc) 2 significantly downshifted the chemical shift of the methyl group in acetate from 1.95 to 2.14 ppm, indicating the occurrence of a more electron‐deficient environment surrounding the methyl group. These phenomena are very similar to the Pd(II)/LA catalysts in our previous studies for other organic syntheses, [5,6a,e,f,h,k] in which a diacetate bridged heterometallic Pd(II)/LA core was proposed as the active species for the catalysis. Similar acetate‐bridged heterometallic Pd(II) structures have even been reported in the literature with X‐ray characterizations [18] .…”

“…As evidence, a carbonyl moiety of the − N Ac group ligated palladacycle compound was even isolated with X‐ray characterizations in Pd(II)/Sc(III)‐catalyzed C−H activation of acetanilides in our previous studies [9] . Unexpectedly, the H/D exchange was also observed at the meta position of this aniline ring, giving a 4 % deuteration ratio, which may be attributed to the remote C−H activation of the aniline ring [6f,23] . This phenomenon was much clearer by using 1 w as the substrate, which gave a 64 % deuteration ratio at the ortho position with a 36 % deuteration ratio at the meta position of the aniline ring (Scheme S1).…”

Distinguishing the Internal/External Base-Assisted Deprotonation Mechanisms in Aromatic C–H Activation with the Pd(II)/LA Catalyst

“…54−60 Herein, due to the solubility limit, 1 equiv of K 2 CO 3 or 2 equiv of Cs 2 CO 3 was also tested as the external base, and no palladacycle compound 4 formation was observed as well as those by adding other tested external bases (Figure 4k,l). Notably, unlike adding 6 equiv of sodium (fluoro-or chlorosubstituted)acetate, adding either K 2 CO 3 or Cs 2 CO 3 also did not break up the dichloro bridged Pd(II)/Sc(III) core in long-time treatment as well as that by adding NaTFA (Figures S43 and S44 Finally, Pd(MeCN) 2 Cl 2 /Sc(OTf) 3 -catalyzed C−H activation and functionalization reactions were investigated in the absence/presence of different external bases to distinguish the internal/external base-assisted deprotonation in catalysis with previously reported Pd(II)/LA-catalyzed reactions, 37,[41][42][43][44]46 which were compared with using Pd(OAc) 2 /Sc(OTf) 3 as the catalyst. As shown in Scheme 2 and Table 1, six reported Pd(OAc) 2 /Sc(OTf) 3 -catalyzed C−H activation and functionalization reactions were applied in the present study including olefination of 3,4-dimethoxyacetanilide (reaction 1), olefination of indole (reaction 2), olefination/annulation of Nmethoxybenzamide (reaction 3), olefination of 2-phenylacetamide (reaction 4), intramolecular annulation of 1methyl-N-phenyl-1H-indole-3-carboxamide (reaction 5), and regioselective olefination of N,N-dimethyl-1H-indole-1-carboxamide (reaction 6).…”