Photoinduced Direct C-H Arylation of (Hetero)Arenes with Halo and Dihaloarenes without Transition Metals or Ligands as Catalysts

BUDÉN, MARÍA E.; GUASTAVINO, JAVIER F.; ROSSI, ROBERTO A.

Foz do Iguazú

Congreso; 12th Latin American Conference on Physical Organic Chemistry; 2013

Universidade Federal de Santa Catarina

The synthesis of biaryl has been known for more of a century using different transition metal catalyses. These reactions typically involve either the coupling of an aryl halide or pseudohalide with an organometallic reagent, or the homocoupling of two aryl halides or two organometallic reagents.[1] These methodologies often require a ligand, base and high temperature. New cheap, efficient and non-contaminant methodologies to prepare these motifs are great interest. Recently, an attractive alternative to the C–H arylation of arenes using base-promoted Homolytic Aromatic Substitution (HAS) reactions has been reported, which avoids the use of stoichiometric amounts of tin or silicon reagents, initiators, or transition metals. This proposed mechanism is a chain process with radicals and radical anions as intermediates (Scheme 1, A),[2] similar to Substitution Radical Nucleophilic Unimolecular (SRN1), Scheme 1, B.[3] As t-BuOK can form [ArX]-. by ET in photostimulated (SRN1) reactions, we speculated that the C-H arylation of benzene could only be achieved with t-BuOK and light. In this work we present a conceptually different approach toward biaryl syntheses by photoinduced direct C-H arylation at room temperature without the addition of transition metals or ligands (Eq. 1). This environmentally friendly methodology promotes effectively the arylation of unactivated arenes, such as benzene and thiophene, with a broad range of aryl and heteroaryl halides, including aryl iodides, aryl bromides and even aryl chloride. Moreover, double C-H bond arylation were successfully achieved to construct extended p–electron systems (Eq. 2). On the basis of our results a plausible chain mechanism with radical and radical anion as intermediates for this photoinduced reaction is proposed [1] A. de Meijere, F. Diederich, Metal-Catalyzed Cross-Coupling Reactions, 2nd Ed, WILEY-VCH Verlag, 2004. [2] A. Studer, D. P. Curran, Angew. Chem. Int. Ed. Engl. 2011, 50, 5018-5022. [3] R. A. Rossi, A. B. Pierini, A. B. Peñéñory, Chem. Rev. 2003, 103, 71-168.