Anion radical coupling. Plan  methods for the formation of aryl-aryl bonds  anionic cyclohydrogenation  history  mechanism  applications.

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Presentation transcript:

Anion radical coupling

Plan  methods for the formation of aryl-aryl bonds  anionic cyclohydrogenation  history  mechanism  applications

Selective formation of aryl-aryl bonds between reaction partners (no functionality other than C-H bonds at the carbon atom):  transition metal catalyzed cross-coupling reactions  oxidative dimerization of electron-rich arenes (Scholl, Kovacic and others)  intramolecular oxidative dimerization (Müllen)  oxidative photocyclization of stilbenes to phenanthrenes (Mallory reaction)  thermal cyclodehydrogenations by flash vacuum pyrolysis  anionic cyclodehydrogenation of aromatic hydrocarbons

Classic example of anionic cyclodehydrogenation: Oxidative cyclization of 1,10-binaphthyl (1) to perylene (2 ) M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

Anion radical coupling as an unique method  the highest efficiency in conversion 1,1’-binaphthyl to perylene  alkali metals are used to induce oxidation

Classic example of anionic cyclodehydrogenation: Oxidative cyclization of 1,10-binaphthyl (1) to perylene (2 ) M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

History first isolated by Miller mechanism discovered by accident in 1967 by Solodovnikov et al. H.Gilman, C.G.Brennen, J. Am. Chem. Soc. 1949, 71, 657 M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

Definition Aromatic radical anion Ar + e - → Ar ●- Ar ●- + e - → Ar 2- N. L. Holy, Chem. Rev. 1974, 74, 243

General types of anion reactions

Reactivity of a radical anion Compound Electron affinity [eV] Naphthalene Triphenylene Phenantrhrene Anthracene 0,152 ± 0,016 0,284 ± 0,020 0,308 ± 0,024 0,552 ± 0,061 N. L. Holy, Chem. Rev. 1974, 74, 243

Mechanism M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358 The equilibrium constatnt depends on:  nature of the metal  hydrocarbon  solvent  temperature M + Ar → Ar ●- + M +

M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

Examined conditions K (in an excess), THF, at 80 º C gave 73% yield Other conditions examined (metal, solvent, temperature) gave yelds of 10% or less: a) K, 1,2-dimethoxyethane, 80 º C b) K, diglyme, 80 º C c) K, toluene, 80 º C d) Na, THF, 66 º C e) Na, diglyme, 80 º C f) Na, TMEDA, 120 º C g) Na, toluene, 110 º C M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

Oxidative agent  exposure to oxygene (small scale)  elemental iodine  Na 2 S 2 O 5  SO 2 S.H.Bossmann, H.Durr, M.R. Pokhrel, Synthesis 2005, 6, 907

SO 2 as an oxidative agent S. Hunig, I. Wehner, Synthesis 1989, 552

Applications P. Schlichting, U. Rohr, K. Müllen, J. Mater. Chem. 1998, 8, 2651

Applications

Reductive ring closure of helicenes A. Ayalon, M. Rabinovitz, Tetrahedron Lett. 1992, 33, 17, 2395

Applications Terrylene synthesis U.Scherf, K. Müllen, Synthesis 1992, 23

Summary formation of aryl-aryl bonds efficiency unique method oxidazing agent obscure mechanism

Thank you !!! Questions ???