Download PDF
Synlett 2003(7): 1028-1030
DOI: 10.1055/s-2003-39316
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

An Efficient Synthesis of Optically Active trans-2-Aryl-2,3-dihydrobenzofuran-3-carboxylic Acid Esters via C-H Insertion Reaction

Wataru Kurosawa, Toshiyuki Kan, Tohru Fukuyama*
Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Fax: +81(3)58028694; e-Mail: fukuyama@mol.f.u-tokyo.ac.jp;
Further Information

Publication History

Received 24 March 2003
Publication Date:
20 May 2003 (online)

    Permissions and Reprints All articles of this category

Abstract

Optically active trans-2-Aryl-2,3-dihydrobenzofuran-3-carboxylic acid esters were synthesized by intramolecular C-H insertion reaction. Upon treatment with a catalytic amount of Rh2(R-DOSP)4, aryldiazoester 8c possessing a chiral auxiliary underwent C-H insertion reaction to give 9c in high yield and in high selectivity (84% yield, 86% de).

Key words

dihydrobenzofuran - C-H insertion - Rh2(R-DOSP)4 - chiral auxiliary - pyrrolidinyl lactamide

    References

  • 1 For a review on neolignans, see: Ward RS. Nat. Prod. Rep.  1999,  16:  75 
    CrossrefGoogle Scholar
  • 2 Sato H. Kawagishi H. Nishimura T. Yoneyama S. Yoshimoto Y. Sakamura S. Furusaki A. Katsuragi S. Matsumoto T. Agric. Biol. Chem.  1985,  49:  2969 
    Google Scholar
  • 3 Tamada M. Endo K. Hikino H. Kabuto C. Tetrahedron Lett.  1979,  873 
    CrossrefGoogle Scholar
  • For construction of dihydrobenzofuran rings by oxidative dimerisation, see:
  • 4a Rummakko P. Brunow G. Orlandi M. Rindone B. Synlett  1999,  333 
    Google Scholar
  • 4b Bolzacchini E. Brunow G. Meinardi S. Orlandi M. Rindone B. Rummakko P. Setala H. Tetrahedron Lett.  1998,  39:  3291 
    Google Scholar
  • 4c Maeda S. Masuda H. Tokoroyama T. Chem. Pharm. Bull.  1994,  42:  2536 
    Google Scholar
  • 4d Maeda S. Masuda H. Tokoroyama T. Chem. Pharm. Bull.  1994,  42:  2500 
    Google Scholar
  • 4e Antus S. Gottsegen A. Kolonits P. Wagner H. Liebigs Ann. Chem.  1989,  593 
    Google Scholar
  • 4f Antus S. Bauer R. Gottsegen A. Seligmann O. Wagner H. Liebigs Ann. Chem.  1987,  357 
    Google Scholar
  • For other methods for constructing dihydrobenzofuran rings, see:
  • 5a Russell MGN. Baker R. Ball RG. Thomas SR. Tsou NN. Castro JL. J. Chem. Soc., Perkin Trans. 1  2000,  893 
    CrossrefGoogle Scholar
  • 5b Russell MGN. Baker R. Castro JL. Tetrahedron Lett.  1999,  40:  8667 
    CrossrefGoogle Scholar
  • 5c Prakash O. Tanwar MP. Bull. Chem. Soc. Jpn.  1995,  68:  1168 
    CrossrefGoogle Scholar
  • 5d Baker R. Cooke NG. Humphrey GR. Wright SHB. Hirshfield J. J. Chem. Soc., Chem. Commun.  1987,  1102 
    CrossrefGoogle Scholar
  • 6 For a review on asymmetric intermolecular C-H activation, see: Davies HML. Antoulinakis EG. J. Organomet. Chem.  2001,  617:  47 
    CrossrefGoogle Scholar
  • 7 Davies HML. Grazini MVA. Aouad E. Org. Lett.  2001,  3:  1475 
    CrossrefGoogle Scholar
  • 8 Davies HML. Hansen T. Churchill MR. J. Am. Chem. Soc.  2000,  122:  3063 
    CrossrefGoogle Scholar
  • 10 Recently, Hashimoto reported a similar C-H insertion reaction with his Rh(II)-catalyst, which proceeded in high enantio- and diastereoselectivity: Treatment of a similar aryldiazoacetate with 1 mol% of the catalyst in toluene at-78 °C provided the cis-benzofuran in 94% ee, see:
    Saito     H. Oishi H. Kitagaki S. Nakamura S. Anada M. Hashimoto S. Org. Lett.  2002,  4:  3887 
    Google Scholar
  • 11 Davies HML. Huby NJS. Cantrell WR. Olive JL. J. Am. Chem. Soc.  1993,  115:  9468 
    CrossrefGoogle Scholar
  • 13 High diastereoinduction with pyrrolidinyl (S)-lactamide as a chiral auxiliary has been reported by Tschaen in the SN2 reaction of α-haloester derivatives, see: Devine PN. Dolling U.-H. Heid RM. Tschaen DM. Tetrahedron Lett.  1996,  37:  2683 
    CrossrefGoogle Scholar
  • 14 For double asymmetric induction in intramolecular C-H insertion reactions, see: Hashimoto S. Watanabe N. Kawano K. Ikegami S. Synth. Commun.  1994,  24:  3277 
    Google Scholar
  • 15 The absolute configuration of the major carboxylic acid was determined as (2R,3R) by comparison of the optical rotation of the corresponding methyl ester 9a with the related compound reported in ref. 5a. Furthermore, the dihydro-benzofuran 9a was independently synthesized by utilizing Evans’ asymmetric aldol reaction and subsequent acidic cyclization to confirm the stereochemistry. For Evans’ enantioselective aldol reaction, see: Evans DA. Bartroli J. Shih TL. J. Am. Chem. Soc.  1981,  103:  2127 
    CrossrefGoogle Scholar
9

The 2,3-cis-benzofuran was readily converted to the thermodynamically more stable trans-isomer as shown in Scheme [4] . After removal of the benzyl group, treatment of 11 with TFA resulted in the predominant formation of the trans isomer 12. The α-position of the ester 11 was unaffected during the transformation based on the fact that no deuterium incorporation was observed in 12 when 11 was treated with CF3CO2D in CD2Cl2.

12

The high diastereoselectivities observed with 8b and 8c indicate that the carbenoid intermediate might have strong interaction with the carbonyl group of the chiral auxiliary as illustrated in Scheme [5] . The similar interaction was reported in ref. 10.

16

We have recently completed the total synthesis of
(-)-ephedradine A (4). Full details of the total synthesis of 4 will be reported in due course.