Synthesis 2015; 47(13): 1799-1856
DOI: 10.1055/s-0034-1378706
review
© Georg Thieme Verlag Stuttgart · New York

Enamide Derivatives: Versatile Building Blocks for Total Synthesis

Thibaut Courant
Centre de Recherche de Gif, Institut de Chimie des Substances Naturelles CNRS, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France   Email: Geraldine.Masson@cnrs.fr
,
Guillaume Dagousset
Centre de Recherche de Gif, Institut de Chimie des Substances Naturelles CNRS, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France   Email: Geraldine.Masson@cnrs.fr
,
Géraldine Masson*
Centre de Recherche de Gif, Institut de Chimie des Substances Naturelles CNRS, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France   Email: Geraldine.Masson@cnrs.fr
› Author Affiliations
Further Information

Publication History

Received: 30 January 2015

Accepted after revision: 16 March 2015

Publication Date:
27 May 2015 (online)


Abstract

Enamides and enecarbamates are versatile building blocks in organic synthesis. This review describes the development of enamide chemistry and the utility of the resulting products in the synthesis of a variety of important, biologically active molecules.

1 Introduction

2 Asymmetric Hydrogenation of Enamides

3 Monofunctionalization of Enamide Derivatives

3.1 Palladium-Catalyzed α-Functionalization of Enamide Derivatives

3.2 Ruthenium-Catalyzed β-Functionalization of Enamide Derivatives

4 Ionic Vicinal Difunctionalization of Enamide Derivatives

4.1 Tandem Difunctionalization of Enamide Derivatives

4.2 Cycloadditions

4.2.1 [4+2] Cycloadditions

4.2.2 [2+2] Cycloadditions

4.2.3 Cyclopropanation of Enamides

4.3 Other Pericyclic Reactions

4.3.1 Electrocyclization Reactions

4.3.2 Overman Rearrangement

4.4 Platinum-Catalyzed Vicinal Difunctionalization of Enamide Derivatives

5 Radical Vicinal Difunctionalization of Enamide Derivatives

6 Oxidative Vicinal Difunctionalization of Enamide Derivatives

7 N-Arylation of Enecarbamates

8 Conclusion

9 Ligand Glossary

 
  • References

    • 2a Hickmott PW. Tetrahedron 1982; 38: 1975
    • 2b Stork G. Med. Res. Rev. 1999; 19: 370
    • 2c Stork G. Tetrahedron 2011; 67: 9754

    • Also see:
    • 2d Seebach D, Beck AK, Badine DM, Limbach M, Eschenmoser A, Treasurywala AM, Hobi R, Prikoszovich W, Linder B. Helv. Chim. Acta 2007; 90: 425

    • For a review on electrophilic and nucleophilic substitution and addition reactions of enamines, see: 
    • 2e Hickmott PW In The Chemistry of Enamines, Part 1 . Rappoport Z. John Wiley & Sons; New York: 1994. Chap. 14, 727
    • 2f Enders D, Bettray W In Asymmetric Synthesis with Chemical and Biological Methods . Enders D, Jaeger K.-E. Wiley-VCH; Weinheim: 2007: 38
  • 3 Stork G, Dowd SR. J. Am. Chem. Soc. 1963; 85: 2178
  • 4 Mayr H. Chem. Eur. J. 2003; 9: 2209
    • 5a Èervinka O In The Chemistry of Enamines, Part 1 . Rappoport Z. John Wiley & Sons; New York: 1994. Chap. 9, 467
    • 5b Bélanger G, Doré M, Ménard F, Darsigny V. J. Org. Chem. 2006; 71: 7481

      For a review covering asymmetric organocatalysis, see:
    • 6a Dalko PI. Enantioselective Organocatalysis . Wiley–VCH; Weinheim: 2006
    • 6b Asymmetric Organocatalysis. In Topics in Current Chemistry. Vol. 291. List B. Springer; New York: 2009

    • For selected reviews on enamine catalysis, see:
    • 6c Mukherjee S, Yang JW, Hoffmann S, List B. Chem. Rev. 2007; 107: 5471
    • 6d Enders D, Grondal C, Hüttl MR. M. Angew. Chem. Int. Ed. 2007; 46: 1570
    • 6e MacMillan DW. C. Nature (London) 2008; 455: 304
    • 6f Melchiorre P, Marigo M, Carlone A, Bartoli G. Angew. Chem. Int. Ed. 2008; 47: 6138
    • 6g Bertelsen S, Jørgensen KA. Chem. Soc. Rev. 2009; 38: 2178
    • 6h Jensen KL, Dickmeiss G, Jiang H, Albrecht L, Jørgensen KA. Acc. Chem. Res. 2012; 45: 248
    • 6i Meninno S, Lattanzi A. Chem. Commun. 2013; 49: 3821
    • 7a Kuranaga T, Sesoko Y, Inoue M. Nat. Prod. Rep. 2014; 31: 514
    • 7b Yet L. Chem. Rev. 2003; 103: 4283

    • Selected examples, see:
    • 7c Okamoto K, Sakagami M, Feng F, Togame H, Takemoto H, Ichikawa S, Matsuda A. Org. Lett. 2011; 13: 5240
    • 7d Villa MV. J, Targett SM, Barnes JC, Whittingham WG, Marquez R. Org. Lett. 2007; 9: 1631
    • 7e Mathieson JE, Crawford JJ, Schmidtmann M, Marquez R. Org. Biomol. Chem. 2009; 7: 2170
    • 7f Wang X, Porco JA. J. Am. Chem. Soc. 2003; 125: 6040
    • 7g Kuranaga T, Sesoko Y, Sakata K, Maeda N, Hayata A, Inoue M. J. Am. Chem. Soc. 2013; 135: 5467
    • 7h Wang X, Porco JA. J. Org. Chem. 2001; 66: 8215; and reference cited
    • 8a Tracey MR, Hsung RP, Antoline J, Kurtz KC. M, Shen L, Slafer BW, Zhang Y In Science of Synthesis . Vol. 21. Georg Thieme Verlag; Stuttgart: 2005: 415
    • 8b Shen R, Porco JA. Org. Lett. 2000; 2: 1333
    • 9a Horner L, Siegel H, Büthe H. Angew. Chem., Int. Ed. Engl. 1968; 7: 942
    • 9b Knowles WS, Sabacky MJ. Chem. Commun. 1968; 1445
    • 10a Kagan HB, Langlois N, Dang TP. J. Organomet. Chem. 1975; 114: 325
    • 10b Sinou D, Kagan HB. Chem. Pharm. Bull. 1992; 40: 2894
  • 11 Vineyard BD, Knowles WS, Sabacky MJ, Bachman GL, Weinkauff DJ. J. Am. Chem. Soc. 1977; 99: 5946
  • 12 Gopalaiah K, Kagan HB. Chem. Rev. 2011; 111: 4599
  • 13 Storace L, Anzalone L, Confalone PN, Davis W, Fortunak JM, Giangiordano M, Haley JrJ. J, Kamholz K, Li H.-Y, Ma P, Nugent WA, Parsons Jr RL, Sheeran PJ, Silverman CE, Waltmire RE, Wood CC. Org. Process Res. Dev. 2002; 6: 54
    • 14a Burk MJ, Feaster JE, Harlow RL. Organometallics 1990; 9: 2653
    • 14b Burk MJ. J. Am. Chem. Soc. 1991; 113: 8518
    • 15a Crépy KV. L, Imamoto T. Adv. Synth. Catal. 2003; 345: 79
    • 15b Johnson NB, Lennon IC, Moran PH, Ramsden JA. Acc. Chem. Res. 2007; 40: 1291
    • 16a Harrison P, Meek G. Tetrahedron Lett. 2004; 45, 9277
    • 16b Mickel SJ. EP 543780, 1993 ; Chem. Abstr. 1993, 119, 203630.
  • 17 Zhu G, Zhang X. J. Org. Chem. 1998; 63: 9590
  • 18 Zhang G.-Y, Pai C.-C, Chan AS. C. J. Am. Chem. Soc. 1998; 120: 5808
  • 19 Kuwano R, Sato K, Kurokawa T, Karube D, Ito Y. J. Am. Chem. Soc. 2000; 122: 7614
  • 20 Xia D, Zhang Z, Zhang X. Org. Lett. 1999; 1: 1679
    • 21a Li W, Zhang X. J. Org. Chem. 2000; 65: 5871
    • 21b Yan Y, Rajanbabu TV. Org. Lett. 2000; 2: 4137
    • 22a Imamoto T, Watanabe J, Wada Y, Masuda H, Yamada H, Tsuruta H, Matsukawa S, Yamaguchi K. J. Am. Chem. Soc. 1998; 120: 1635
    • 22b Gridnev ID, Yamanoi Y, Higashi N, Tsuruta H, Yasutake M, Imamoto T. Adv. Synth. Catal. 2001; 343: 118
    • 22c Yamanoi Y, Imamoto T. J. Org. Chem. 1999; 64: 2988
    • 22d Gridnev ID, Imamoto T. Organometallics 2001; 20: 545
  • 23 Gridnev ID, Yasutake M, Higashi N, Imamoto T. J. Am. Chem. Soc. 2001; 123: 5268
  • 24 O’Shea PD, Gauvreau D, Gosselin F, Hughes G, Nadeau C, Roy A, Schultz CS. J. Org. Chem. 2009; 74: 4547
  • 25 Corey EJ, Gin DY, Kania RS. J. Am. Chem. Soc. 1996; 118: 9202
  • 26 Singh J, Kronenthal DR, Schwinden M, Godfrey JD, Fox R, Vawter EJ, Zhang B, Kissick TP, Patel B, Mneimne O, Humora M, Papaioannou CG, Szymanski W, Wong MK. Y, Chen CK, Heikes JE, DiMarco JD, Qiu J, Deshpande RP, Gougoutas JZ, Mueller RH. Org. Lett. 2003; 5: 3155
  • 27 Noyori R, Ohkuma T, Kitamura M, Takaya H, Sayo N, Kumobayashi H, Akutagawa S. J. Am. Chem. Soc. 1987; 109: 5856
  • 28 Tschaen DM, Abrahamson L, Cai D, Desmond R, Dolling U.-H, Frey L, Karady S, Shi Y.-J, Verhoeven TR. J. Org. Chem. 1995; 60: 4324
  • 29 Devocelle M, Morteux A, Agbossou F, Dormoy J.-R. Tetrahedron Lett. 1999; 40: 4551
  • 30 Lennon IC, Ramsden JA, Brear CJ, Broady SD, Muir JC. Tetrahedron Lett. 2007; 48: 4623

    • For reviews see:
    • 31a Dounay AB, Overman LE. Chem. Rev. 2003; 103: 2963
    • 31b Zhou F, Liu Y.-L, Zhou J. Chem. Rev. 2010; 352: 1381
    • 31c Steven A, Overman LE. Angew. Chem. Int. Ed. 2007; 46: 5488
    • 31d Nicolaou KC, Bulger PG, Sarlah D. Angew. Chem. Int. Ed. 2005; 44: 4442
  • 32 Grigg R, Sridharan V, Stevenson P, Worakun T. J. Chem. Soc., Chem. Commun. 1984; 1697
  • 33 Abelman MM, Oh T, Overman LE. J. Org. Chem. 1987; 52: 4133
  • 34 Comins D, Baevsky M, Hong H. J. Am. Chem. Soc. 1992; 114: 10971
  • 35 Grigg R, Sridharan V, Stevenson P, Sukirthalingam S, Worakun T. Tetrahedron 1990; 46: 4003
  • 36 Yoneda R, Sakamoto Y, Oketo Y, Minami K, Harusawa S, Kurihara T. Tetrahedron Lett. 1994; 35: 3749
  • 37 Grigg R, Loganathan V, Santhakumar V, Sridharan V, Teasdale A. Tetrahedron Lett. 1991; 32: 687
  • 38 Nukui S, Sodeoka M, Shibasaki M. Tetrahedron Lett. 1993; 34: 4965
    • 39a Sato Y, Nukui S, Sodeoka M, Shibasaki M. Tetrahedron 1994; 50: 371
    • 39b Nukui S, Sodeoka M, Sasai H, Shibasaki M. J. Org. Chem. 1995; 60: 398
  • 40 Kiewel K, Tallant M, Sulikowski GA. Tetrahedron Lett. 2001; 42: 6621
  • 41 Endo A, Yanagisawa A, Abe M, Tohma S, Kan T, Fukuyama T. J. Am. Chem. Soc. 2002; 124: 6552
  • 42 Kawagishi F, Toma T, Inui T, Yokoshima S, Fukuyama T. J. Am. Chem. Soc. 2013; 135: 13684
  • 43 Vallin KS. A, Zhang Q, Larhed M, Curran DP, Hallberg A. J. Org. Chem. 2003; 68: 6639
  • 44 Tsukano C, Zhao L, Takemoto Y, Hirama M. Eur. J. Org. Chem. 2010; 4198
  • 45 Ding R, Sung B.-F, Lin G.-Q. Org. Lett. 2012; 14: 4446

    • For reviews on RCM in total synthesis see:
    • 46a Fürstner A. Angew. Chem. Int. Ed. 2000; 39: 3012
    • 46b Trnka TM, Grubbs RH. Acc. Chem. Res. 2001; 34: 18
    • 46c Connon SJ, Blechert SA. H. Angew. Chem. Int. Ed. 2003; 42: 1900
    • 46d Schrock RE, Hoveyda AH. Angew. Chem. Int. Ed. 2003; 42: 4592
    • 46e Grubbs RH. Tetrahedron 2004; 60: 7117
    • 46f Schrodi Y, Pederson RL. Aldrichimica Acta 2007; 40: 45
    • 47a Kinderman SS, van Maarseveen JH, Schoemaker HE, Hiemstra H, Rutjes FP. J. T. Org. Lett. 2001; 3: 2045
    • 47b Arisawa M, Terada Y, Nakagawa M, Nishida A. Angew. Chem. Int. Ed. 2002; 41: 4732
    • 47c Chen Y, Zhang H, Nan F. J. Comb. Chem. 2004; 6: 684
    • 47d Manzoni L, Colombo M, Scolastico C. Tetrahedron Lett. 2004; 45: 2623
    • 47e Benasar ML, Roca T, Monerris M, Garcia-Diaz D. J. Org. Chem. 2006; 71: 7028
    • 48a Toumi M, Couty F, Evano G. J. Org. Chem. 2008; 73: 1270

    • For a review see:
    • 48b Evano G, Blanchard N, Toumi M. Chem. Rev. 2008; 108: 3054
  • 49 Hoye TR, Jeffrey CS, Tannakoon MA, Wang J, Zhao H. J. Am. Chem. Soc. 2004; 126: 10210
  • 50 Katz JD, Overman LE. Tetrahedron 2004; 60: 9559
    • 51a Madin A, O’Donnell CJ, Oh T, Old DW, Overman LE, Sharp MJ. Angew. Chem. Int. Ed. 1999; 38: 2934
    • 51b Earley WG, Jacobsen JE, Madin A, Meier GP, O’Donnell CJ, Oh T, Old DW, Overman LE, Sharp MJ. J. Am. Chem. Soc. 2005; 127: 18046
    • 52a Padwa A, Danca MD. Org. Lett. 2002; 4: 715
    • 52b Padwa A, Danca MD, Hardcastle KI, McClure MS. J. Org. Chem. 2003; 68: 929
  • 53 Ahmad VU, Iqbal S. Phytochemistry 1993; 3: 735
    • 54a Nilson MG, Funk RL. Org. Lett. 2006; 8: 3833
    • 54b Nilson MG, Funk RL. Org. Lett. 2010; 12: 4912
    • 55a Deng H, Yang X, Tong Z, Li Z, Zhai H. Org. Lett. 2008; 10: 1791
    • 55b Cheng B, Wu F, Yang X, Zhou Y, Wan X, Zhai H. Chem. Eur. J. 2011; 17: 12569
  • 56 Movassaghi M, Siegel DS, Han S. Chem. Sci. 2010; 1: 561
  • 57 Reyes JC. P, Romo D. Angew. Chem. Int. Ed. 2012; 51: 6870
  • 58 Zöllinger M, Mayer P, Lindel T. J. Org. Chem. 2006; 71: 9431
    • 59a Witherup KM, Ransom RW, Graham AC, Bernard AM, Salvatore MJ, Lumma WC, Anderson PS, Pitzenberger SM, Varga SL. J. Am. Chem. Soc. 1995; 117: 6682
    • 59b Xia Y, Yang Z.-Y, Xia P, Bastow KF, Tachibana Y, Kuo S.-C, Hamel E, Hackl T, Lee K.-H. J. Med. Chem. 1998; 41: 1155
    • 59c Di Fabio R, Tranquillini E, Bertani B, Alvaro G, Micheli F, Sabbatini F, Domenica Pizzi M, Pentassuglia G, Pasquarello A, Messeri T, Donati D, Ratti E, Arban R, Dal Forno G, Reggiani A, Barnaby RJ. Bioorg. Med. Chem. Lett. 2003; 13: 3863
    • 59d Guinó M, Phua PH, Caille J.-C, Hii KK. J. Org. Chem. 2007; 72: 6290
    • 60a Povarov LS, Mikhailov BM. Izv. Akad. Nauk. SSSR, Ser. Khim. 1963; 953
    • 60b Povarov LS. Russ. Chem. Rev. 1967; 36: 656

      For reviews, see:
    • 61a Glushkov VA, Tolstikov AG. Russ. Chem. Rev. 2008; 77: 137
    • 61b Kouznetsov VV. Tetrahedron 2009; 65: 2721
    • 61c Masson G, Lalli C, Benohoud M, Dagousset G. Chem. Soc. Rev. 2013; 42: 902
    • 61d Fochi M, Caruana L, Bernardi L. Synthesis 2014; 46: 135
    • 62a Hadden M, Stevenson PJ. Tetrahedron Lett. 1999; 40: 1215
    • 62b Hadden M, Nieuwenhuyzen M, Potts D, Stevenson PJ, Thompson N. Tetrahedron 2001; 57: 5615
    • 62c Hadden M, Nieuwenhuyzen M, Osborne D, Stevenson PJ, Thompson N. Tetrahedron Lett. 2001; 42: 6417
    • 62d Hadden M, Nieuwenhuyzen M, Osborne D, Stevenson PJ, Thompson N, Walker AD. Tetrahedron 2006; 62: 3977
    • 63a Batey AR, Simoncic DP, Lin D, Smyj PR, Lough JA. Chem. Commun. 1999; 651
    • 63b Batey RA, Powell DA. Chem. Commun. 2001; 2362
  • 64 Dagousset G, Retailleau P, Masson G, Zhu J. Chem. Eur. J. 2012; 18: 5869
  • 65 Xia C, Heng L, Ma D. Tetrahedron Lett. 2002; 43: 9405
  • 66 Powell DA, Batey RA. Org. Lett. 2002; 4: 2913
  • 67 Xu AH, Zuend SJ, Woll MG, Tao Y, Jacobsen EN. Science (Washington, D.C.) 2010; 327: 986
    • 68a Liu H, Dagousset G, Masson G, Retailleau P, Zhu J. J. Am. Chem. Soc. 2009; 131: 4598
    • 68b Dagousset G, Zhu J, Masson G. J. Am. Chem. Soc. 2011; 133: 14804
  • 69 Movassaghi M, Hunt DK, Tjandra M. J. Am. Chem. Soc. 2006; 128: 8126
  • 70 Omura S, Murata M, Imamura N, Iwai Y, Tanaka H, Furusaki A, Matsumoto T. J. Antibiot. 1984; 37: 1324
  • 71 Bach T, Schröder J. Liebigs Ann./Recl. 1997; 2265
    • 72a de Faria AR, Matos CR. R, Correia CR. D. Tetrahedron Lett. 1993; 34: 37
    • 72b Correia CR. D, de Faria AR, Carvahlo ES. Tetrahedron Lett. 1995; 36: 5109
    • 72c de Faria AR, Salvador EL, Correia CR. D. J. Org. Chem. 2002; 67: 3651
    • 72d Ambrosio JC. L, Santos RH. de A, Correia CR. D. J. Braz. Chem. Soc. 2003; 14: 27
    • 73a Geissman TA, Waiss Jr AC. J. Org. Chem. 1962; 27: 139
    • 73b Buchanan JG, Jigajinni VB, Singh G, Wightman RH. J. Chem. Soc., Perkin Trans. 1 1987; 2377
  • 74 Gross U, Nieger M, Bräse S. Org. Lett. 2009; 11: 4740
    • 75a Feltenberger JB, Hayashi R, Tang Y, Babiash ES. C, Hsung RP. Org. Lett. 2009; 11: 3666
    • 75b Ma Z.-X, Feltenberger JB, Hsung RP. Org. Lett. 2012; 14: 2742
    • 76a Csuk R, von Scholz Y. Tetrahedron 1994; 50: 10431
    • 76b Lee MG, Du JF, Chun MW, Chu CK. J. Org. Chem. 1997; 62: 1991
  • 77 Song Z, Lu T, Hsung RP, Al-Rashid Z, Ko C, Tang Y. Angew. Chem. Int. Ed. 2007; 46: 4069
  • 78 De Simone F, Gertsch J, Waser J. Angew. Chem. Int. Ed. 2010; 49: 5767
  • 79 Wenkert E, Hudlicky T. J. Org. Chem. 1988; 53: 1953
    • 80a The Chemistry of Heterocyclic Compounds . Vol. 25. Taylor EC, Saxton JE. Wiley-Interscience; New York: 1983: 1994
    • 80b Sundberg RJ. In Indoles. Academic Press; New York: 1996
    • 81a Greshock TJ, Funk RL. J. Am. Chem. Soc. 2006; 128: 4946
    • 81b Huntley RJ, Funk RL. Org. Lett. 2006; 8: 3403
    • 82a Greshock TJ, Funk RL. Org. Lett. 2006; 8: 2643
    • 82b Huntley RL, Funk RL. Org. Lett. 2006; 8: 4775
  • 83 Overman LE. J. Am. Chem. Soc. 1974; 96: 597
    • 84a Imaoka T, Iwamoto O, Noguchi K, Nagasawa K. Angew. Chem. Int. Ed. 2009; 48: 3799
    • 84b Imaoka T, Akimoto T, Iwamoto O, Nagasawa K. Chem. Asian J. 2010; 5: 1810
  • 85 Harrison TJ, Patrick BO, Dake GR. Org. Lett. 2007; 9: 367
  • 86 Kozak JA, Dake GR. Angew. Chem. Int. Ed. 2008; 47: 4221
    • 87a Ishibashi H, Kato I, Takeda Y, Tamura O. Tetrahedron Lett. 2001; 42: 931
    • 87b Kato I, Higashimoto M, Tamura O, Ishibashi H. J. Org. Chem. 2003; 68: 7983
  • 88 Taniguchi T, Iwasaki K, Uchiyama M, Tamura O, Ishibashi H. Org. Lett. 2005; 7: 4389
  • 89 Valencia E, Freyer AJ, Shamma M, Fajardo V. Tetrahedron Lett. 1984; 25: 599
  • 90 Taniguchi T, Tanabe G, Muraoka O, Ishibashi H. Org. Lett. 2008; 10: 197
  • 91 Kuehne MK, Bornmann WG, Parsons WH, Spitzer TD, Blount JF, Zubieta J. J. Org. Chem. 1988; 53: 3439
    • 92a Pouységu L, Deffieux D, Quideau S. Tetrahedron 2010; 66: 2235
    • 92b Roche SP, Porco JA. Angew. Chem. Int. Ed. 2011; 50: 4068
    • 92c Silva LF, Olofsson B. Nat. Prod. Rep. 2011; 28: 1722
    • 92d Quideau S, Pouységu L, Duffieux D. Synlett 2008; 467
  • 93 Honda T, Shigehisa H. Org. Lett. 2006; 8: 657
  • 94 Shigehisa H, Takayama J, Honda T. Tetrahedron Lett. 2006; 47: 7301
  • 95 Huang X, Shao N, Palani A, Aslanian R, Buevich A. Org. Lett. 2007; 9: 2597
    • 96a Chavan SP, Subbarao YT. Tetrahedron Lett. 1999; 40: 5073
    • 96b Norton Matos MR. P, Afonso CA. M, Batey RA. Tetrahedron Lett. 2001; 42: 7007
  • 97 Le Corre L, Kizirian J.-C, Levraud C, Boucher J.-L, Bonnet V, Dhimane H. Org. Biomol. Chem. 2008; 6: 3388
  • 98 Li Q, Li G, Ma S, Feng P, Shi Y. Org. Lett. 2013; 15: 2601
  • 99 Ren W, Wang Q, Zhu J. Angew. Chem. Int. Ed. 2014; 53: 1818
  • 100 Okano K, Tokuyama H, Fukuyama T. J. Am. Chem. Soc. 2006; 128: 7136