Oxidative carbon-carbon coupling. II. Effect of ring substituents on the oxidative carbon-carbon coupling of arylmalonic esters, arylmalodinitriles, and arylcyanoacetic esters

Abstract

Arylmalonic esters and arylmalonodinitriles can be coupled oxidatively to the corresponding bibenzyls. Good yields of dimers are obtained when a para substituent (CH3, Cl) is introduced, which inhibits the formation of higher oligomers through benzylic C-para C coupling. Substitution at both ortho positions and the para position (CH3) in phenylcyanoacetic esters completely inhibits C-C coupling by steric crowding. Ketene imines are formed instead by C-N coupling. Substitution at one ortho position (CHa) partially gives the usual C-C coupling together with benzylic C-para C coupling (oligomer formation) in case of a free para position and C-N coupling (ketene imine formation) in case of a CHs-substituted para position. The thermal dissociation of the dimers into radicals is confirmed by esr analysis. From nmr line width measurements kinetic parameters for the dissociation reaction are obtained.

N‐Substituted Dicyanomethylphenyl Radicals: Dynamic Covalent Properties and Formation of Stimuli‐Responsive Cyclophanes by Self‐Assembly

“…It was also reported that the introduction of a substituent such as a Me, Cl, and NO 2 group at the paraposition of the dicyanomethyl group prohibited such an isomerization reaction. [6][7][8] However, the equilibrium strongly favored the dimeric form for such cases at room temperature. To realize the selective formation of thermodynamic products by DCC, a sufficiently fast equilibration is required.…”

“…[1][2][3][4] As a motif of DCC, organic radicals are promising compounds because of the simplicity of the reaction equilibrium, that is, it does not involve catalysts or byproducts. [5][6][7][8][9][10][11][12][13][14] We have focused on aryldicyanomethyl radicals because of their symmetric and sterically unhindered structures, which do not give diastereomers upon dimerization. In 1966, Hartzler reported that 1,2-diphenyl-1,1,2,2tetracyanoethane (A 2 ), which is regarded as the dimer of the phenyldicyanomethyl radical (AC), is in equilibrium with AC in solution.…”

Aerobic Copper-Catalyzed Organic Reactions

“…561 More recently, a copper TMEDA catalyst with molecular oxygen has been shown to be highly efficient in the oxidative dimerization of α-cyanoesters (Scheme 277). 562 The reaction is proposed to proceed through deprotonation followed by the transfer of an electron to the copper catalyst to generate the resonance-stabilized radical that subsequently dimerizes. The para -substitution of the substrate is required, as unsubstituted compounds tend to polymerize due contribution of the para radical to the resonance form.…”

N‐Substituted Dicyanomethylphenyl Radicals: Dynamic Covalent Properties and Formation of Stimuli‐Responsive Cyclophanes by Self‐Assembly

“…[1][2][3][4] As am otif of DCC,o rganic radicals are promising compounds because of the simplicity of the reaction equilibrium, that is,i td oes not involve catalysts or byproducts. [5][6][7][8][9][10][11][12][13][14] We have focused on aryldicyanomethyl radicals because of their symmetric and sterically unhindered structures,w hich do not give diastereomers upon dimerization. In 1966, Hartzler reported that 1,2-diphenyl-1,1,2,2tetracyanoethane (A 2 ), which is regarded as the dimer of the phenyldicyanomethyl radical (AC), is in equilibrium with AC in solution.…”

“…[5][6][7][8][9][10][11][12][13][14] We have focused on aryldicyanomethyl radicals because of their symmetric and sterically unhindered structures,w hich do not give diastereomers upon dimerization. [6][7][8] However,the equilibrium strongly favored the dimeric form for such cases at room temperature. [5] However, AC was easily decomposed irreversibly to form B because of the high reactivity at its para-position (Scheme 1a).…”