Pd-Catalyzed Intramolecular C–N Bond Cleavage, 1,4-Migration, sp³ C–H Activation, and Heck Reaction: Four Controllable Diverse Pathways Depending on the Judicious Choice of the Base and Ligand

Abstract

Diverse and controllable pathways induced by palladium-catalyzed intramolecular Heck reaction of N-vinylacetamides for the synthesis of nitrogen-containing products in reasonable to high yields via tuning the phosphine ligands and bases are reported. Domino reactions including unique β-N-Pd elimination, 1,4-Pd migration, or direct acyl C-H bond functionalization were found to be involved forming different products, respectively. Given the ability of using the same starting material to generate diverse products via completely different chemoselective processes, these current methodologies offer straightforward access to valuable nitrogen-containing products under mild reaction conditions as well as inspire the discovery of novel reactions.

Transition-Metal-Catalyzed Cleavage of C–N Single Bonds

“…According to the proposed mechanism, the abstraction of the hydrogen radical from 268 by the tert-butyl alcohol radical, which is generated in situ by thermal homolysis of t-BuOOH, 219 Recently, Loh's group described an intramolecular Mizoroki−Heck reaction via a vinyl C−N bond cleavage (Scheme 80). 220 either electron-donating or electron-withdrawing groups could react smoothly with various olefins. The later stage of this reaction is suggested to be similar to the nature of the Heck reaction, in which an aryl−Pd complex is involved.…”

Substrate‐Controlled Diastereoselectivity Switch in the Formation of Dihydrothieno[3,4‐c]coumarins via [4+1] Annulations

“…The scope was substantial, and high yields were generally obtained for substrates having various substitutions. Only transproducts were observed in the [4 + 1] annulations (> 99:1 dr, entries [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. It appeared that the substitution patterns, regardless of the positions or electronic natures on the aromatic ring (R 1 , R 2 or Ar), had little effect on the reaction.…”

“…[8] In addition, chemoselective transformations open up a new avenue for the construction of complex molecules in synthetic organic and medicinal chemistry. [9][10] Among heteroaromatic compounds, thiophenes are unique sulfur-containing heterocycles that attract particular attention due to their special role as building blocks in natural products, pharmaceutical agents and materials. [11][12][13][14][15][16] Therefore, a variety of excellent protocols have been devoted to obtaining these valuable heterocycles, which include reactions between 1, 4-dithiane-2,5-diol and electron-deficient olefins (e. g., unsaturated aldehydes, [17a] trans-b-nitrostyrenes [17b] or chalcones [18] ) and domino reactions of other thiols to active alkenes.…”

σ‐Alkyl‐PdII Species for Remote C−H Functionalization

“…Remarkably,X u, Loh and co-workers [14] recently reported four possible Pd-catalyzedt ransformations for 2-Br-benzylimines substrates (Scheme 8). Interestingly,t he reactionp athway could be switchedf orm [1,4]-Pd shift to C(sp 3 )-H activation with the appropriate substrate design and control of the experimental conditions.…”