Base- and Phosphine-Free Palladium-Catalyzed Homocoupling of ­Arylboronic Acid Derivatives under Air

Abstract

In the presence of a catalytic amount of Pd(OAc)₂, ­various arylboronic acids underwent homocoupling in MeOH at ambient temperature under air to give rise to symmetrical biaryls. The homocoupling of arylboronic acids was also carried out using polyurea-encapsulated Pd(OAc)₂ as a recyclable catalyst.

Key words

biaryls - boron - catalysis - coupling - palladium

References and Notes

• 1a Bringmann G. Menche D. Acc. Chem. Res.  2001,  34:  615 
• 1b Lloyd-Williams P. Giralt E. Chem. Soc. Rev.  2001,  30:  145 
• 2a Meier H. Angew. Chem. Int. Ed.  2005,  44:  2482 
• 2b Tian H. Yang S. Chem. Soc. Rev.  2004,  33:  85 
• 2c Lemieux RP. Acc. Chem. Res.  2001,  34:  845 
• 3 Shimizu H. Nagasaki I. Saito T. Tetrahedron  2005,  61:  5405 
• 4a Hassan J. Sévignon M. Gozzi C. Schulz E. Lemaire M. Chem. Rev.  2002,  102:  1359 
• 4b Stanforth SP. Tetrahedron  1998,  54:  263 
• 5a Suzuki A. J. Organomet. Chem.  1999,  576:  147 
• 5b Miyaura N. Suzuki A. Chem. Rev.  1995,  95:  2457 
• For selected examples, see:
• 6a Cravotto G. Beggiato M. Penoni A. Palmisano G. Tollari S. Lévêque J.-M. Bonrath W. Tetrahedron Lett.  2005,  46:  2267 
• 6b Punna S. Díaz DD. Finn MG. Synlett  2004,  2351 
• 6c Yoshida H. Yamaryo Y. Ohshita J. Kunai A. Tetrahedron Lett.  2003,  44:  1541 
• 6d Parrish JP. Jung YC. Floyd RJ. Jung KW. Tetrahedron Lett.  2002,  43:  7899 
• 6e Kabalka GW. Wang L. Tetrahedron Lett.  2002,  43:  3067 
• 6f Lei A. Zhang X. Tetrahedron Lett.  2002,  43:  2525 
• 6g Wong MS. Zhang XL. Tetrahedron Lett.  2001,  42:  4087 
• Recently, Au-catalyzed homocouplings were reported, see:
• 7a Carrettin S. Guzman J. Corma A. Angew. Chem. Int. Ed.  2005,  44:  2242 
• 7b González-Arellano C. Corma A. Iglesias M. Sánchez F. Chem. Commun.  2005,  1990 
• 7c Tsunoyama H. Sakurai H. Ichikuni N. Negishi Y. Tsukuda T. Langmuir  2004,  20:  11293 
• 8a Yamamoto Y. Ishii J. Nishiyama H. Itoh K. J. Am. Chem. Soc.  2005,  127:  9625 
• 8b Yamamoto Y. Hattori K. Ishii J. Nishiyama H. Itoh K. Chem. Commun.  2005,  4438 
• 9 Goodson FE. Wallow TI. Novak BM. J. Am. Chem. Soc.  1997,  119:  12441 
• 10 Nishimura T. Kakiuchi N. Onoue T. Ohe K. Uemura S. J. Chem. Soc., Perkin Trans. 1  2000,  1915 
• 12a Lee CKY. Holmes AB. Ley SV. McConvey IF. Al-Duri B. Leeke GA. Santos RCD. Seville JPK. Chem. Commun.  2005,  2175 
• 12b Vikerstaffe E. Warrington BH. Ladlow M. Ley SV. Org. Biomol. Chem.  2003,  1:  2419 
• 12c Ley SV. Mitchell C. Pears D. Ramarao C. Yu J.-Q. Zhou W. Org. Lett.  2003,  5:  4665 
• 12d Yu J.-Q. Wu H.-C. Ramarao C. Spencer JB. Ley SV. Chem. Commun.  2003,  678 
• 12e Ley SV. Ramarao C. Gordon RS. Holmes AB. Morrison AJ. McConvey IF. Shirley IM. Smith SC. Smith MD. Chem. Commun.  2002,  1134 
• 12f Ramarao C. Ley SV. Smith SC. Shirley IM. DeAlmeida N. Chem. Commun.  2002,  1132 
• 13 Pears DA. Smith SC. Aldrichimica Acta  2005,  38:  23 

11

Typical Procedure for the Synthesis of 2a.
Method i: To a solution of p-tolylboronic acid (1a, 115.7 mg, 0.85 mmol) in MeOH (17 mL) was added Pd(OAc)₂ (5.7 mg, 0.026 mmol), and the reaction mixture was stirred for 5 h at r.t. under air. The reaction mixture was concentrated in vacuo and the residue was diluted with EtOAc (15 mL). After filtration of insoluble materials, the filtrate was concentrated in vacuo and the residue was purified by silica gel column flush chromatography (eluent: hexane) to afford 2a (72.6 mg, 94%) as colorless solids.
Method ii: To a solution of p-tolylboronic acid (1a, 68.0 mg, 0.50 mmol) in MeOH (10 mL) was added PdEnCat 30 (ca. 0.4 mmol/g, 37.5 mg, 0.015 mmol), and the reaction mixture was stirred for 24 h at r.t. under air. After filtration of the catalyst, the filtrate was concentrated in vacuo and the residue was purified by silica gel column flush chromato-graphy (eluent: hexane) to afford 2a (29.2 mg, 64%) as colorless solids. All starting materials and products are known compounds.