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Synlett 2011(14): 2075-2079  
DOI: 10.1055/s-0030-1260981
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Ir(III)-Catalyzed Room-Temperature Synthesis of Multisubstituted Benzofurans Initiated by C-H Activation of α-Aryloxy Ketones

Takanori Shibata*a, Yu-ki Hashimotoa, Maiko Otsukaa, Kyoji Tsuchikamaa, Kohei Endob
a Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, Okubo, Shinjuku, Tokyo, 169-8555, Japan
Fax: +81(3)52868098; e-Mail: tshibata@waseda.jp;
b Waseda Institute for Advanced Study, Shinjuku, Tokyo, 169-8050, Japan
Further Information

Publication History

Received 9 May 2011
Publication Date:
03 August 2011 (online)

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Abstract

Cyclodehydration of various α-aryloxy ketones proceeded to give various multisubstituted benzofurans by using an Ir(III) catalyst, which was prepared from [Cp*IrCl2]2, AgSbF6, and Cu(OAc)2. The use of the cationic iridium complex with a carboxylate salt realized the efficient transformation at ambient temperature.

Key words

C-H activation - benzofurans - cyclodehydration - iridium - room temperature

    Reference and Notes

  • For recent reviews, see:
  • 1a Handbook of C-H Transformations   Dyker G. Wiley-VCH; Weinheim: 2005. 
    Google Scholar
  • 1b Alberico D. Scott ME. Lautens M. Chem. Rev.  2007,  107:  174 
    Google Scholar
  • 1c Davies HML. Manning JR. Nature (London)  2008,  451:  417 
    Google Scholar
  • 1d Kakiuchi F. Kochi T. Synthesis  2008,  3013 
    Google Scholar
  • 1e Kitamura T. Eur. J. Org. Chem.  2009,  1111 
    Google Scholar
  • 1f Giri R. Shi B.-F. Engle KM. Maugel N. Yu J.-Q. Chem. Soc. Rev.  2009,  38:  3242 
    Google Scholar
  • 1g Colby DA. Bergman RG. Ellman JA. Chem. Rev.  2010,  110:  624 
    Google Scholar
  • 1h Lyons TM. Sanford MS. Chem. Rev.  2010,  110:  1147 
    Google Scholar
  • 1i C-H Activation   Yu J.-Q. Shi Z. Springer; Berlin: 2010. 
    Google Scholar
  • Rare examples of transition-metal-catalyzed C-H activation at or below room temperature:
  • 2a Fujii N. Kakiuchi F. Yamada A. Chatani N. Murai S. Bull. Chem. Soc. Jpn.  1998,  71:  285 
    Google Scholar
  • 2b Ishiyama T. Takagi J. Hartwig JF. Miyaura N. Angew. Chem. Int. Ed.  2002,  41:  3056 
    Google Scholar
  • 2c Boele MDK. van Strijdonck GPF. de Vries AHM. Kamer PCJ. de Vries JG. van Leeuwen PWNM. J. Am. Chem. Soc.  2002,  124:  1586 
    Google Scholar
  • 2d Zhang H.-B. Liu L. Chen Y.-J. Wang D. Li C.-J. Adv. Synth. Catal.  2006,  348:  229 
    Google Scholar
  • 2e Norinder J. Matsumoto A. Yoshikai N. Nakamura E. J. Am. Chem. Soc.  2008,  130:  5858 
    Google Scholar
  • 2f Nishikata T. Abela AR. Lipshutz BH. Angew. Chem. Int. Ed.  2010,  49:  781 
    Google Scholar
  • 2g Xiao B. Fu Y. Xu J. Gong T.-J. Dai J.-J. Yi J. Liu L. J. Am. Chem. Soc.  2010,  132:  468 
    Google Scholar
  • 2h Fumitoshi K. Kochi T. Mizushima E. Murai S. J. Am. Chem. Soc.  2010,  132:  17741 
    Google Scholar
  • 3a Tsuchikama K. Kasagawa M. Hashimoto Y. Endo K. Shibata T. J. Organomet. Chem.  2008,  693:  3939 
    Google Scholar
  • 3b Tsuchikama K. Kasagawa M. Endo K. Shibata T. Org. Lett.  2009,  11:  1821 
    Google Scholar
  • 3c Tsuchikama K. Kasagawa M. Endo K. Shibata T. Synlett  2010,  97 
    Google Scholar
  • 4 Tsuchikama K. Hashimoto Y. Endo K. Shibata T. Adv. Synth. Catal.  2009,  351:  2850 
    CrossrefGoogle Scholar
  • C-H bond activation along with 1,2-addition to imines:
  • 5a Kuninobu Y. Kawata A. Takai K. J. Am. Chem. Soc.  2005,  127:  13498 
    Google Scholar
  • 5b Kuninobu Y. Tokunaga Y. Kawata A. Takai K. J. Am. Chem. Soc.  2006,  128:  202 
    Google Scholar
  • 7 Dicationic Pd complex as an efficient catalyst for C-H bond activation: Nishikata T. Abela AR. Huang S. Lipshutz BH. J. Am. Chem. Soc.  2010,  132:  4978 
    CrossrefGoogle Scholar
  • Preparation and characterization of dicationic Cp*Ir complex:
  • 8a White C. Thompson SJ. Maitlis PM. J. Organomet. Chem.  1977,  127:  415 
    Google Scholar
  • 8b Amouri H. Guyard-Duhayon C. Vaissermann J. Rager MN. Inorg. Chem.  2002,  41:  1397 
    Google Scholar
  • Base suppressed dehydration from benzofuranols to benzofurans:
  • 9a Liu G. Lu X. J. Am. Chem. Soc.  2006,  128:  16504 
    Google Scholar
  • 9b Liu G. Lu X. Tetrahedron  2008,  64:  7324 
    Google Scholar
  • 10 The effect of inorganic salts for the ratio of benzofuran 2a and benzofuranol 3a is unclear
  • In recent years, a stoichiometric or more amounts of Cu(OAc)2 was often used as an oxidant in C-H activation using Rh catalyst prepared from [Cp*RhCl2]2 and AgSbF6:
  • 11a Stuart DR. Bertrand-Laperle M. Burgess KMN. Fagnou K. J. Am. Chem. Soc.  2008,  130:  16474 
    Google Scholar
  • 11b Guinond N. Fagnou K. J. Am. Chem. Soc.  2009,  131:  12050 
    Google Scholar
  • 11c Rakshit S. Patureau FW. Glorius F. J. Am. Chem. Soc.  2010,  132:  9585 
    Google Scholar
  • 11d Patureau FW. Glorius F. J. Am. Chem. Soc.  2010,  132:  9982 
    Google Scholar
  • 11e Stuart DR. Alsabeh P. Kuhn M. Fagnou K. J. Am. Chem. Soc.  2010,  132:  18326 
    Google Scholar
  • 11f Patureau FW. Besset T. Glorius F. Angew. Chem. Int. Ed.  2011,  50:  1064 
    Google Scholar
  • 11g Tsai AS. Brasse M. Bergman RG. Ellman JA. Org. Lett.  2011,  13:  540 
    Google Scholar
  • 14a Davies DL. Al-Duaji O. Fawcett J. Giardiello M. Hilton ST. Russell DR. Dalton Trans.  2003,  4132 
    Google Scholar
  • 14b Davies DL. Donald SMA. Al-Duaij O. Macgregor SA. Polleth M. J. Am. Chem. Soc.  2006,  128:  4210 
    Google Scholar
  • 14c Li L. Brennessel WW. Jones WD. J. Am. Chem. Soc.  2008,  130:  12414 
    Google Scholar
  • 14d Li L. Brennessel WW. Jones WD. Organometallics  2009,  28:  3492 
    Google Scholar
  • 14e Boutadla Y. Davies DL. Macgregor SA. Poblador-Bahamonde AI. Dalton Trans.  2009,  5887 
    Google Scholar
6

We already excluded a Friedel-Crafts mechanism by competitive experiment of 4-(3-acetylphenyl)butan-2-one (1a) and 4-(3-methoxyphenyl)butan-2-one, see Supporting Information of ref. 4 in detail.

12

Other silver salts, such as AgOTf and AgBF4, gave poorer results than AgSbF6.

13

Iridium dicarboxylate complex, which was prepared from [Cp*IrCl2]2 (5 mol% Ir), AgSbF6 (10 mol%), and KOPiv (10 mol%), had almost no catalytic activity.

15

The reaction of 4-(3-acetylphenyl)butan-2-one or
1-(3-acetyl­phenylamino)propan-2-one did not proceed under the same reaction conditions.