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Synlett 2009(18): 2896-2912  
DOI: 10.1055/s-0029-1218021
ACCOUNT
© Georg Thieme Verlag Stuttgart ˙ New York

Palladium-Catalyzed Alkynylation of Aryl and Hetaryl Halides: A Journey from Conventional Palladium Complexes or Salts to Palladium/Carbon

Manojit Pal*,
New Drug Discovery, Matrix Laboratories Limited, Anrich Industrial Estate, Bollaram, Jinnaram Mandal, Medak District, 502325 Andhra Pradesh, India
e-Mail: manojitpal@rediffmail.com;
Further Information

Publication History

Received 26 March 2009
Publication Date:
15 September 2009 (online)

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Abstract

Palladium-catalyzed alkynylation of aryl and hetaryl ­halides has found wide application in the areas of synthetic, heterocyclic, and medicinal chemistry. Attempts to introduce the stable and potentially recyclable palladium/carbon has provided an attractive alternative to the homogeneous palladium catalytic process. The present article provides a personal account of the outcome of the use of conventional palladium catalysts versus palladium/carbon, especially under Sonogashira conditions.

1 Introduction

1.1 The Focus on Palladium/Carbon

1.2 The Origin of the Research

2 Copper-Free Sonogashira Coupling: An Unusual Observation

3 Palladium-Mediated Synthesis of 3-Substituted (Thio)flavones: The Role of (S)-Prolinol and Copper

4 Palladium/Carbon in Water

4.1 Synthesis of Benzo[b]furans

4.2 2-Aminoethanol as an Alternative Base: Synthesis of Aryl- and Hetaryl-Substituted Alkynes

4.3 Synthesis of Indoles

5 Palladium/Carbon in Organic Solvents

5.1 Synthesis of Isocoumarins and Phthalides

5.2 Synthesis of Thieno[2,3-c]pyranones

5.3 Synthesis of Alkynylpyrimidines

5.4 Synthesis of Furoquinolines and Pyrroloquinolines

5.5 Synthesis of 2H-1,2-Benzothiazine 1,1-Dioxides

6 Alkynylation of b-Chloroacroleins

7 Synthesis of Substituted Benzenes Fused with Carbocycles/Heterocycles: Palladium Salts versus Palladium/Carbon

8 Palladium/Carbon in the Union of Organic Azide and Terminal Alkynes

9 Conclusions: Towards Fulfilling the Requirements for Commercialization

Key words

catalysis - palladium - palladium/carbon - alkynylation - aryl halides - Sonogashira reaction

    References

  • 2a Sonogashira K. Tohda Y. Hagihara N. Tetrahedron Lett.  1975,  4467 
    Google Scholar
  • 2b Sonogashira K. Yatake T. Tohda Y. Takahashi S. Hagihara N. J. Chem. Soc., Chem. Commun.  1977,  291 
    Google Scholar
  • 2c Takahashi S. Kuroyama Y. Sonogashira K. Hagihara N. Synthesis  1980,  627 
    Google Scholar
  • 3 Dasgupta SK. Pal M. Mahanty JS. Kundu NG. Novel 5-Substituted Uracil Derivatives as Inhibitors of Thymidylate Synthesis Enzyme   Paper number CP22:  15th National Symposium on Organic Chemistry (NASOC-XV); Calcutta: March 22-23, 1994. 
    Google Scholar
  • 4 Kundu NG. Das B. Spears CP. Majumdar A. Kang SI. J. Med. Chem.  1990,  33:  1975 
    CrossrefGoogle Scholar
  • 5a Kundu NG. Dasgupta SK. J. Chem. Soc., Perkin Trans. 1  1993,  2657 
    Google Scholar
  • 5b Kundu NG. Pal M. Chowdhury C. J. Chem. Res., Synop.  1995,  4 
    Google Scholar
  • 6 Stephens RD. Castro CE. J. Org. Chem.  1963,  28:  3313 
    Google Scholar
  • 7 Robins MJ. Barr PJ. J. Org. Chem.  1983,  48:  1854 
    CrossrefGoogle Scholar
  • 8 Kundu NG. Pal M. Mahanty JS. Dasgupta SK. J. Chem. Soc., Chem. Commun.  1992,  41 
    Google Scholar
  • 9 Kundu NG. Pal M. Mahanty JS. De M. J. Chem. Soc., Perkin Trans. 1  1997,  2815 
    CrossrefGoogle Scholar
  • 10 Kundu NG. Pal M. J. Chem. Soc., Chem. Commun.  1993,  86 
    CrossrefGoogle Scholar
  • 11 Kundu NG. Pal M. Nandi B. J. Chem. Soc., Perkin Trans. 1  1998,  561 
    CrossrefGoogle Scholar
  • 12 Arcadi A. Cacchi S. Marinelli F. Synthesis  1986,   749 
    Google Scholar
  • 13 Kundu NG. Pal M. Chowdhury C. J. Chem. Res.  1993,  432 
    Google Scholar
  • 14 Rossi R. Carpita A. Bigelli C. Tetrahedron Lett.  1985,  26:  523 
    CrossrefGoogle Scholar
  • 15 Pal M. Kundu NG. J. Chem. Soc., Perkin Trans. 1  1996,  449 
    CrossrefGoogle Scholar
  • 16a Alonso F. Beletskaya IP. Yus M. Chem. Rev.  2004,  104:  3079 
    Google Scholar
  • 16b Krisch G. Hesse S. Comel A. Curr. Org. Synth.  2004,  1:  47 
    Google Scholar
  • 17 Zeni G. Larock RC. Chem. Rev.  2006,  106:  4644 
    CrossrefPubMedGoogle Scholar
  • 18 Patil NT. Yamamoto Y. Chem. Rev.  2008,  108:  3395 
    CrossrefPubMedGoogle Scholar
  • 19 Chinchilla R. Nájera C. Chem. Rev.  2007,  107:  874 
    Google Scholar
  • 20a De la Rosa MA. Velarde E. Guzman A. Synth. Commun.  1990,  20:  2059 
    Google Scholar
  • 20b Novak Z. Szabo A. Repasi J. Kotschy A. J. Org. Chem.  2003,  68:  3327 
    Google Scholar
  • For the use of Pd(OH)2/C as catalyst, see:
  • 20c Mori Y. Seki M. J. Org. Chem.  2003,  68:  1571 
    Google Scholar
  • 20d Heidenreich RG. Köhler K. Krauter JGE. Pietsch J. Synlett  2002,  1118 
    Google Scholar
  • 20e Felpin F.-X. Vo-Thanh G. Villiéras J. Lebreton J. Tetrahedron: Asymmetry  2001,  12:  1121 
    Google Scholar
  • 20f Bates RW. Boonsombat J. J. Chem. Soc., Perkin Trans. 1  2001,  654 
    Google Scholar
  • 20g Bleicher LS. Cosford NDP. Herbaut A. McCallum JS. McDonald IA. J. Org. Chem.  1998,  63:  1109 
    Google Scholar
  • 20h Bleicher L. Cosford NDP. Synlett  1995,  1115 
    Google Scholar
  • 20i Potts KT. Horwitz CP. Fessak A. Keshavarz KM. Nash KE. Toscano PJ. J. Am. Chem. Soc.  1993,  115:  10444 
    Google Scholar
  • 21 Yin LX. Liebscher J. Chem. Rev.  2007,  107:  133 
    CrossrefPubMedGoogle Scholar
  • 22 Seki M. Synthesis  2006,  2975 
    Article in Thieme ConnectGoogle Scholar
  • 23a Pal M. Parasuraman K. Gupta S. Yeleswarapu KR. Synlett  2002,  1976 
    Google Scholar
  • For a review, see:
  • 23b Pal M. Tetrahedron  2009,  65:  433 
    Google Scholar
  • 24 Rao YK, Pal M, Sharma VM, Venkateswarlu A, and Pillaresetti R. inventors; Patent Application  US 2005/0119269 A1.  June 2
  • 25 Pal M. Subramanian V. Parasuraman K. Yeleswarapu KR. Tetrahedron  2003,  59:  9563 
    CrossrefGoogle Scholar
  • 26 Kalai T. Kulcsar G. Osz E. Jeko J. Sumegi B. Hideg K. Arkivoc  2004,  (vii):  266 
    Google Scholar
  • 27 Pal M. Dakarapu R. Parasuraman K. Subramanian V. Yeleswarapu KR. J. Org. Chem.  2005,  70:  7179 
    CrossrefGoogle Scholar
  • 28 Pal M. Parasuraman K. Subramanian V. Dakarapu R. Yeleswarapu KR. Tetrahedron Lett.  2004,  45:  2305 
    CrossrefGoogle Scholar
  • 29 Li C.-J. Chem. Rev.  2005,  105:  3095 
    CrossrefPubMedGoogle Scholar
  • 30 Bhattacharya S. Sengupta S. Tetrahedron Lett.  2004,  45:  8733 
    CrossrefGoogle Scholar
  • 31 Cacchi S. Fabrizi G. Goggiamani A. Curr. Org. Chem.  2006,  10:  1423 
    CrossrefGoogle Scholar
  • 32 Dai W.-M. Lai KW. Tetrahedron Lett.  2002,  43:  9377 
    CrossrefGoogle Scholar
  • 33a Pal M. Subramanian V. Yeleswarapu KR. Tetrahedron Lett.  2003,  44:  8221 
    Google Scholar
  • 33b Xu G. Searle LL. Hughes TV. Beck AK. Connolly PJ. Abad MC. Neeper MP. Struble GT. Springer BA. Emanuel SL. Gruninger RH. Pandey N. Adams M. Moreno-Mazza S. Fuentes-Pesquera AR. Middleton SA. Greenberger LM. Bioorg. Med. Chem. Lett.   2008,  18:  3495 
    Google Scholar
  • 34a Heidenreich R.-G. Krauter JGE. Pietsch J. Köheler K. J. Mol. Catal. A: Chem.  2002,  182-183:  499 
    Google Scholar
  • 34b Tagata T. Nishida M. J. Org. Chem.  2003,  68:  9412 
    Google Scholar
  • 35a Pal M. Batchu VR. Subramanian V. Parasuraman K. Swamy NK. Kumar S. Tetrahedron  2005,  61:  9869 
    Google Scholar
  • 35b Subramanian V. Batchu VR. Pal M. An Improved Synthesis of 2-Substituted Benzo[b]furans in Water under Pd/C-Cu Catalysis   Paper number P15:  Indo-US Conference on Recent Advances in Organometallic Catalysis and Olefin Polymerization; IIT Madras / Chennai / India: December 10-12, 2003. 
    Google Scholar
  • 35c Bong DT. Ghadiri MR. Org. Lett.  2001,  3:  2509 
    Google Scholar
  • 35d Raju S. Kumar PR. Mukkanti K. Annamalai P. Pal M. Bioorg. Med. Chem. Lett.  2006,  6185 
    Google Scholar
  • 36a Reddy EA. Barange DK. Islam A. Mukkanti K. Pal M. Tetrahedron  2008,  64:  7143 
    Google Scholar
  • 36b Reddy EA. Islam A. Mukkanti K. Bandameedi V. Bhownik DR. Pal M. Beilstein J. Org. Chem.  2009,  5: No32 (DOI: 10.3762/bjoc.5.32)
    Google Scholar
  • 37a Nolan JM. Comins DL. J. Org. Chem.  2003,  68:  3736 
    Google Scholar
  • 37b Elangoven A. Chen T.-Y. Chen C.-Y. Ho T.-I. Chem. Commun.  2003,  2146 
    Google Scholar
  • 37c Seck M. Franck X. Hocquemiller R. Figadère B. Peyrat J.-F. Provot O. Brion J.-D. Alami M. Tetrahedron Lett.  2004,  45:  1881 
    Google Scholar
  • 37d Rodriguez JG. de los Rios C. Lafuente A. Tetrahedron  2005,  61:  9042 
    Google Scholar
  • 37e Toyota M. Komori C. Ihara M. J. Org. Chem.  2000,  65:  7110 
    Google Scholar
  • 37f Ciufolini MA. Mitchell JW. Roschangar F. Tetrahedron Lett.  1996,  37:  8281 
    Google Scholar
  • 37g Yamanaka H. Shiraiwa M. Edo K. Sakamoto T. Chem. Pharm. Bull.  1979,  27:  270 
    Google Scholar
  • 37h Belmont P. Andrez J.-C. Allan CSM. Tetrahedron Lett.  2004,  45:  2783 
    Google Scholar
  • 38 Cacchi S. Fabrizi G. Chem. Rev.  2005,  105:  2873 
    CrossrefPubMedGoogle Scholar
  • 39 Patil S. Buolamwini JK. Curr. Org. Synth.  2006,  3:   477 
    Google Scholar
  • 40 Pal M. Subramanian V. Batchu VR. Dager I. Synlett  2004,  1965 
    Article in Thieme ConnectGoogle Scholar
  • 41 Sakamoto T. Kondo Y. Iwashita S. Nagano T. Yamanaka H. Chem. Pharm. Bull.  1988,  36:  1305 
    Google Scholar
  • 42 Amjad M. Knight DW. Tetrahedron Lett.  2004,  45:  539 
    CrossrefGoogle Scholar
  • 43 Mackman RL. Katz BA. Breitenbucher JG. Hui HC. Verner E. Luong C. Liu L. Sprengeler PA. J. Med. Chem.  2001,  44:  3856 
    CrossrefGoogle Scholar
  • 44 Kundu NG. Mahanty JS. Das P. Das B. Tetrahedron Lett.  1993,  34:  1625 
    CrossrefGoogle Scholar
  • 45 Takeda A. Kamijo S. Yamamoto Y. J. Am. Chem. Soc.  2000,  122:  5662 
    CrossrefGoogle Scholar
  • 46 Liao H.-Y. Cheng C.-H. J. Org. Chem.  1995,  60:  3711 
    CrossrefGoogle Scholar
  • 47 Kanazawa C. Terada M. Tetrahedron Lett.   2007,  48:  933 
    Google Scholar
  • 48 Uchiyama M. Ozawa H. Takuma K. Matsumoto Y. Yonehara M. Hiroya K. Sakamoto T. Org. Lett.  2006,  8:  5517 
    CrossrefPubMedGoogle Scholar
  • 49a Barange DK. Batchu VR. Pal M. First Pd/C-Mediated Synthesis of (Z)-3-Alkynylidene Phthalides   Joint International Conference on Building Bridges Forging Bonds (ACS-CSIR OCCB); Pune / India: January 7-9, 2006. 
    Google Scholar
  • 49b Zhou L. Jiang H.-F. Tetrahedron Lett.  2007,  48:  8449 
    Google Scholar
  • 50 Raju S. Batchu VR. Swamy NK. Dev RV. Babu JM. Kumar PR. Mukkanti K. Pal M. Tetrahedron Lett.  2006,  47:  83 
    CrossrefGoogle Scholar
  • 51a Raju S. Batchu VR. Swamy NK. Dev RV. Sreekanth BR. Babu JM. Vyas K. Kumar PR. Mukkanti K. Annamalai P. Pal M. Tetrahedron  2006,  62:  9554 
    Google Scholar
  • 51b Queiroz M.-JRP. Calhelha RC. Vale-Silva LA. Pinto E. Nascimento MS.-J. Eur. J. Med. Chem.  2009,  44:  1893 
    Google Scholar
  • 52a Pal M, Kalleda S, Padakanti S, Kumara Swamy N, Yeleswarapu KR, Alexander CW, Khanna I, Iqbal J, Pillarisetti S, and Barange D. inventors; Patent Application US 2006/0084645  A1.  April 20,
  • 52b Pal M. Batchu VR. Swamy NK. Padakanti S. Tetrahedron Lett.  2006,  47:  3923 
    Google Scholar
  • 53a McGuigan C. Barucki H. Blewett S. Carangio A. Erichsen JT. Andrei G. Snoeck R. De Clercq E. Balzarini J. J. Med. Chem.  2000,  43:  4993 
    Google Scholar
  • 53b McGuigan C. Brancale A. Andrei G. Snoeck R. De Clercq E. Balzarini J. Bioorg. Med. Chem. Lett.  2000,  10:  1215 
    Google Scholar
  • 53c McGuigan C. Yarnold CJ. Jones G. Velazquez S. Barucki H. Brancale A. Andrei G. Snoeck R. De Clercq E. Balzarini J. J. Med. Chem.  1999,  42:  4479 
    Google Scholar
  • 53d Janeba Z. Balzarini J. Andrei G. Snoeck R. De Clercq E. Robins MJ. J. Med. Chem.  2005,  48:  4690 
    Google Scholar
  • 54a Venkataraman S. Barange DK. Pal M. Tetrahedron Lett.  2006,  47:  7317 
    Google Scholar
  • 54b Layek M. Gajare V. Kalita D. Islam A. Mukanti K. Pal M. Tetrahedron Lett.  2009,  50:  3867 
    Google Scholar
  • See also
  • 54c Layek M. Rao A. VD. Gajare V. Kalita D. Barenge DK. Islam A. Mukkanti K. Pal M. Tetrahedron Lett.  2009,  50:  4878 
    Google Scholar
  • 55 Harmata M. Rayanil K.-o. Gomes MG. Zheng P. Calkins NL. Kim S.-Y. Fan Y. Bumbu V. Lee DR. Wacharasindhu S. Hong X. Org. Lett.  2005,  7:  143 
    CrossrefGoogle Scholar
  • For benzo[b]furans, see:
  • 56a Banwell MG. Flynn BL. Willis AC. Hamel E. Aust. J. Chem.  1999,  52:  767 
    Google Scholar
  • 56b Arcadi A. Cacchi S. Fabrizi G. Marinelli F. Moro L. Synlett  1999,  1432 
    Google Scholar
  • 56c Colobert F. Castanet A.-S. Abillard O. Eur. J. Org. Chem.  2005,  3334 
    Google Scholar
  • 56d Yue D. Yao T. Larock RC. J. Org. Chem.  2005,  70:  10292 
    Google Scholar
  • For benzo[b]thiophenes, see:
  • 56e Yue D. Larock RC. J. Org. Chem.  2002,  67:  1905 
    Google Scholar
  • 56f Hessian KO. Flynn BL. Org. Lett.  2003,  5:  4377 
    Google Scholar
  • For furopyridines, see:
  • 57a Arcadi A. Cacchi S. Di Giuseppe S. Fabrizi G. Marinelli F. Org. Lett.  2002,  4:  2409 
    Google Scholar
  • For furoquinolines, see:
  • 57b Aillaud I. Bossharth E. Conreaux D. Desbordes P. Monteiro N. Balme G. Org. Lett.  2006,  8:  1113 
    Google Scholar
  • 58 For furopyrimidines, see: Rao MS. Esho N. Sergeant C. Roman D. J. Org. Chem.  2003,  68:  6788 
    CrossrefGoogle Scholar
  • For indoles, see:
  • 59a Yue D. Larock RC. Org. Lett.  2004,  6:  1037 
    Google Scholar
  • 59b Barluenga J. Trincado M. Rubio E. Gonzalez JM. Angew. Chem. Int. Ed.  2003,  42:  2406 
    Google Scholar
  • 59c Yao D. Yue D. Larock RC. J. Comb. Chem.  2005,  7:  809 
    Google Scholar
  • For isoquinolines and naphthyridines, see:
  • 59d Huang Q. Hunter JA. Larock RC. J. Org. Chem.  2002,  67:  3437 
    Google Scholar
  • 60 For isoindolinones, see: Yao T. Larock RC. J. Org. Chem.  2005,  70:  1432 
    CrossrefPubMedGoogle Scholar
  • For isochromenes, see:
  • 61a Barluenga J. Vazquez-Villa H. Ballesteros A. Gonzalez JM. J. Am. Chem. Soc.  2003,  125:  9028 
    Google Scholar
  • 61b Yue D. Della Ca N. Larock RC. Org. Lett.  2004,  6:  1581 
    Google Scholar
  • For isocoumarins, see:
  • 62a Yao T. Larock RC. J. Org. Chem.  2003,  68:  5936 
    Google Scholar
  • 62b Rossi R. Carpita A. Bellina F. Stabile P. Mannina L. Tetrahedron  2003,  59:  2067 
    Google Scholar
  • For phosphaisocoumarins, see:
  • 62c Peng A.-Y. Ding Y.-X. Org. Lett.  2004,  6:  1119 
    Google Scholar
  • 63 For coumestans, see: Yao T. Yue D. Larock RC. J. Org. Chem.  2005,  70:  9985 
    CrossrefGoogle Scholar
  • For other examples of iodonium-promoted heterocyclizations of acetylenic compounds, see:
  • 64a Sniady A. Wheeler KA. Dembinski R. Org. Lett.  2005,  7:  1769 
    Google Scholar
  • 64b Liu Y. Song F. Cong L. J. Org. Chem.  2005,  70:  6999 
    Google Scholar
  • 64c Yao T. Zhang X. Larock RC. J. Org. Chem.  2005,  70:  7679 
    Google Scholar
  • 64d Liu Y. Zhou S. Org. Lett.  2005,  7:  4609 
    Google Scholar
  • 64e Waldo JP. Larock RC. Org. Lett.  2005,  7:  5203 
    Google Scholar
  • For iodocyclization of sulfonamide derivatives of o-(alk-1-ynyl)anilines leading to 3-iodoindoles, see:
  • 64f Amjad M. Knight DW. Tetrahedron Lett.  2004,  45:  539 
    Google Scholar
  • 65 Barange DK. Batchu VR. Gorja D. Pattabiraman VR. Tatini LK. Babu JM. Pal M. Tetrahedron  2007,  63:  1775 
    CrossrefGoogle Scholar
  • 66 Barange DK. Nishad TC. Swamy NK. Bandameedi V. Kumar D. Sreekanth BR. Vyas K. Pal M. J. Org. Chem.  2007,  72:  8547 
    CrossrefPubMedGoogle Scholar
  • 67a Hesse S. Kirsch G. Synthesis  2001,  755 
    Google Scholar
  • 67b Hesse S. Kirsch G. Tetrahedron Lett.  2002,  43:  1213 
    Google Scholar
  • 67c Hesse S. Kirsch G. Synthesis  2003,  717 
    Google Scholar
  • 68 Bera R. Swamy NK. Dhananjaya G. Babu JM. Kumar PR. Mukkanti K. Pal M. Tetrahedron  2007,  63:  13018 
    CrossrefGoogle Scholar
  • 69a Snieckus V. Chem. Rev.  1990,  90:  879 
    Google Scholar
  • 69b Lautens M. Klute W. Tam W. Chem. Rev.  1996,  96:  49 
    Google Scholar
  • 69c Saito S. Yamamoto Y. Chem. Rev.  2000,  100:  2901 
    Google Scholar
  • 69d Yamamoto Y. Ishii J.-I. Nishiyama H. Itoh K. J. Am. Chem. Soc.  2004,  126:  3712 
    Google Scholar
  • 70a Saito S. Chounan Y. Nogami T. Fukushi T. Tsuboya N. Yamada Y. Kitahara H. Yamamoto Y. J. Org. Chem.  2000,  65:  5350 
    Google Scholar
  • 70b Gevorgyan V. Tsuboya N. Yamamoto Y. J. Org. Chem.  2001,  66:  2743 
    Google Scholar
  • 70c Saito S. Salter MM. Gevorgyan V. Tsuboya N. Tando K. Yamamoto Y. J. Am. Chem. Soc.  1996,  118:  3970 ; and references cited therein
    Google Scholar
  • 70d Gevorgyan V. Takeda A. Homma M. Sadayori N. Radhakrishnan U. Yamamoto Y. J. Am. Chem. Soc.  1999,  121:  6391 
    Google Scholar
  • For a sequential one-pot procedure involving Sonogashira coupling and homo-benzannulation for the synthesis of 6H-dibenzo[b,d]pyran-6-ones, see:
  • 71a Kawasaki T. Yamamoto Y. J. Org. Chem.  2002,  67:  5138 
    Google Scholar
  • 71b Xi C. Chen C. Lin J. Hong X. Org. Lett.  2005,  7:  347 
    Google Scholar
  • 72 Swamy NK. Tatini LK. Babu JM. Annamalai P. Pal M. Chem. Commun.  2007,  1035 
    CrossrefGoogle Scholar
  • 73 Batchu VR. Barange DK. Kumar D. Sreekanth BR. Vyas K. Reddy EA. Pal M. Chem. Commun.  2007,  1966 
    CrossrefGoogle Scholar
  • 74a Rostovtsev VV. Green LG. Fokin VV. Sharpless KB. Angew. Chem. Int. Ed.  2002,  41:  2596 
    Google Scholar
  • 74b Tornøe CW. Christensen C. Meldal M. J. Org. Chem.  2002,  67:  3057 
    Google Scholar
  • 74c Kamijo S. Jin T. Huo Z. Yamamoto Y. J. Am. Chem. Soc.  2003,  125:  7786 
    Google Scholar
  • 75 Chowdhury C. Mandal SB. Achari B. Tetrahedron Lett.  2005,  46:  8531 
    CrossrefGoogle Scholar
1

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