Nickel-Catalyzed Ring-Opening of Benzofurans for the Divergent Synthesis of ortho-Functionalized Phenol Derivatives

Abstract

The ring-opening reaction of benzofuran is a highly desirable, yet underdeveloped transformation for the construction of valuable phenol derivatives. Herein, we report a nickel-catalyzed ring-opening transformation of benzofuran with silanes, giving ortho-alkene-, branched/linear alkyl silane-, and alkenyl silanesubstituted phenol derivatives selectively. Control experiments and DFT calculations supported Ni−H insertion and β−O elimination to achieve the formal C−O bond activation of benzofuran but not through the direct oxidative addition of nickel (0) into the C−O bond of benzofurans. Further regioselective hydrosilylation or dehydrogenative silylation occurs via Ni(I)−H or Ni(I)−[Si] intermediates to form ortho-branched/linear alkyl silane-or alkenyl silane-substituted phenol derivatives.

Dearomatization Silylation of Benzofurans and Furopyridines via Silyl Radical Addition and Endocyclic C–O Bond Scission

“…13 15 (s, 1H), 1.01 (t, J = 7.9 Hz, 9H), 0.70 (q, J = 7.9 Hz, 6H). 19 F NMR (376 MHz, CDCl 3 ) δ −116.51. 13 1H), 1.02 (t, J = 7.9 Hz, 9H), 0.70 (q, J = 7.9 Hz, 6H), 0.31 (s, 9H).…”

“…1 H NMR (400 MHz, CDCl 3 ) δ 7.60 (d, J = 2.3 Hz, 1H), 7.56 (d, J = 8.7 Hz, 2H), 7.33 (dd, J = 8.3, 2.4 Hz, 1H), 7.27 (s, 1H), 7.25 (s, 1H), 7.18 (d, J = 19.5 Hz, 1H), 6.87 (d, J = 8.3 Hz, 1H), 6.45 (d, J = 19.5 Hz, 1H), 5.07 (s, 1H), 1.00 (t, J = 7.9 Hz, 9H), 0.69 (q, J = 7.9 Hz, 6H). 19 F NMR (376 MHz, CDCl 3 ) δ −57.81 (s, 3F). 13…”

“…1 H NMR (400 MHz, CDCl 3 ) δ 7.18−7.06 (m, 2H), 6.86−6.78 (m, 1H), 6.72 (dd, J = 8.8, 4.7 Hz, 1H), 6.38 (d, J = 19.0 Hz, 1H), 0.99 (t, J = 8.0 Hz, 9H), 0.67 (q, J = 7.9 Hz, 6H). 19 F NMR (376 MHz, CDCl 3 ) δ −115.80. 13 (…”

“…Then, the formation of oxaheterocycles and azaborins was elegantly achieved by transition-metal-catalyzed or lithium-mediated multivalent heteroatom insertion into the C(2)–O bond of benzofurans . Huang’s group developed the nickel-catalyzed ring-opening reaction of benzofuran using silane as the reducing reagent . Despite significant progress in this field, these tactics generally required transition-metal catalysts, inconvenient organometallic reagents, and in some cases harsh reaction conditions.…”

“…18 Huang's group developed the nickel-catalyzed ring-opening reaction of benzofuran using silane as the reducing reagent. 19 Despite significant progress in this field, these tactics generally required transition-metal catalysts, inconvenient organometallic reagents, and in some cases harsh reaction conditions. As part of our ongoing interest in inert bond activation, 20 we report a novel method for the dearomatization silylation of benzofurans and furopyridines via silyl radical addition and subsequent β-elimination (Scheme 1c).…”