In Pursuit of an Ideal Carbon-Carbon Bond-Forming Reaction: Development and Applications of the Hydrovinylation of Olefins

Abstract

Attempts to introduce the highly versatile vinyl group into other organic molecules in a chemo-, regio-, and stereoselective fashion via catalytic activation of ethylene provided challenging opportunities to explore new ligand and salt effects in homogeneous catalysis. This review provides a personal account of the development of enantioselective reactions involving ethylene.

1 Introduction

1.1 The Origins

1.2 Olefin Dimerization Reactions

2 Hydrovinylation Reactions

2.1 A Brief History of Hydrovinylation Reactions

2.2 Ruthenium- and Cobalt-Catalyzed Hydrovinylation Reactions

2.3 Best Practices prior to 1997: Nickel-Catalyzed Hydrovinyl-ation Reactions

2.4 Mechanism of the Nickel-Catalyzed Hydrovinylation of ­Vinylarenes

2.5 A New Protocol for Hydrovinylation Amenable to Asymmetric Catalysis

2.6 Heterodimerization of Vinylarenes with Other Olefins

2.7 Other Heterodimerization Reactions

2.8 Hydrovinylation of Norbornene

3 Enantioselective Hydrovinylation Reactions

3.1 Azaphospholene Ligands

3.2 Aminophosphine/Phosphinite Ligands

3.3 Use of Chelating Phosphines

4 Synergistic Relation between Hemilabile Ligands and Counterions

4.1 New Ligands for Asymmetric Hydrovinylation Reactions: 2-Alkoxy-2′-diphenylphosphino-1,1′-binaphthyl Derivatives

4.2 Effect of Hemilabile Groups

4.3 Solvent and Salt Effects

4.4 Electronic Effects

4.5 Other Protocols for Nickel-Catalyzed Hydrovinylation ­Reactions

4.6 A Model for Asymmetric Induction in Hydrovinylation ­Reactions

4.7 De Novo Design of an Asymmetric Ligand: Hemilabile Phospholanes

4.8 Diarylphosphinite Ligands

4.9 Phosphite Ligands

4.10 Phosphoramidite Ligands

5 Generation of All-Carbon Quaternary Centers

6 Asymmetric Hydrovinylation of 1,3-Dienes

7 Asymmetric Hydrovinylation of Norbornene

8 Applications of Asymmetric Hydrovinylation Reactions

8.1 (S)-2-Arylpropionic Acids

8.2 (R)-α-Curcumene and (R)-ar-Turmerone

8.3 Control of the Configuration of the Steroidal D-Ring Side Chain

8.4 Intramolecular Reactions: Synthesis of Carbocyclic and Heterocyclic Compounds

9 Large-Scale Synthesis

10 Summary and Future Prospects

carbon-carbon bond formation - hydrovinylations - asymmetric catalysis - ligand effects - transition metals

References

For a summary of early results, see:

1a RajanBabu TV. Chem. Rev.  2003,  103:  2845 

For other pertinent reviews, see:

1b Bogdanovic B. Adv. Organomet. Chem.  1979,  17:  105 

1c Jolly PW. Wilke G. In Applied Homogeneous Catalysis with Organometallic Compounds   Vol. 2:  Cornils B. Herrmann WA. VCH; New York: 1996.  p.1024-1048  

1d RajanBabu TV. Nomura N. Jin J. Radetich B. Park H. Nandi M. Chem. Eur. J.  1999,  5:  1963 

1e Gooßen LJ. Angew. Chem. Int. Ed.  2002,  41:  3775 

2 Wilke G. Angew. Chem., Int. Ed. Engl.  1988,  27:  185 

3 Chauvin Y. Olivier H. In Applied Homogeneous Catalysis with Organometallic Compounds   Vol. 1:  Cornils B. Herrmann WA. VCH; New York: 1996.  p.258-268  

4 Bogdanovic B. Spliethoff B. Wilke G. Angew. Chem., Int. Ed. Engl.  1980,  19:  622 

5a Rieu J.-P. Boucherle A. Cousse H. Mouzin G. Tetrahedron  1986,  42:  4095 

5b Sonawane HR. Bellur NS. Ahuja JR. Kulkarni DG. Tetrahedron: Asymmetry  1992,  3:  163 

5c Stahly GP. Starrett RM. In Chirality in Industry II   Collins AN. Sheldrake GN. Crosby J. Wiley; Chichester: 1997.  p.19 

6a Alderson T. Jenner EL. Lindsey RV. J. Am. Chem. Soc.  1965,  87:  5638 

6b Umezaki H. Fujiwara Y. Sawara K. Teranishi S. Bull. Chem. Soc. Jpn.  1973,  46:  2230 

7 Dzhemilev UM. Gubaidullin LY. Tolstikov GA. Bull. Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.)  1976,  25:  2009 

For the early use of Co, see:

8a Pu LS. Yamamoto A. Ikeda S. J. Am. Chem. Soc.  1968,  90:  7170 

8b Pillai SM. Tembe GL. Ravindranathan M. J. Mol. Catal.  1993,  84:  77 

For early studies with Pd catalysts, see:

9a Barlow MG. Bryant MJ. Haszeldine RN. Mackie AG. J. Organomet. Chem.  1970,  21:  215 

9b Kawamoto K. Tatani A. Imanaka T. Teranishi S. Bull. Chem. Soc. Jpn.  1971,  44:  1239 

For related studies, see:

9c Drent E. inventors; US Patent  5227561.  ; Chem. Abstr. 1994, 120, 31520

9d Nozima H. Kawata N. Nakamura Y. Maruya K. Mizoroki T. Ozaki A. Chem. Lett.  1973,  1163 

10a Kawata N. Maruya K. Mizoroki T. Ozaki A. Bull. Chem. Soc. Jpn.  1971,  44:  3217 

10b Kawata N. Maruya K. Mizoroki T. Ozaki A. Bull. Chem. Soc. Jpn.  1974,  47:  413 

10c Kawakami K. Kawata N. Maruya K. Mizoroki T. Ozaki A. J. Catal.  1975,  39:  134 

10d

See also ref. 7.

10e Azizov AG. Mamedaliev GA. Aliev SM. Aliev VS. Azerb. Khim. Zh.  1978,  3 ; Chem. Abstr. 1979, 90, 6002

10f Azizov AG. Mamedaliev GA. Aliev SM. Aliev VS. Azerb. Khim. Zh.  1979,  3 ; Chem. Abstr. 1980, 93, 203573

10g Mamedaliev GA. Azizov AG. Yu G. Polym. J. (Tokyo, Jpn.)  1985,  17:  1075;   Chem. Abstr.  1986,  104:  34390 

11a Bogdanovic B. Henc B. Meister B. Pauling H. Wilke G. Angew. Chem., Int. Ed. Engl.  1972,  11:  1023 

11b Bogdanovic B. Henc B. Lösler A. Meister B. Pauling H. Wilke G. Angew. Chem., Int. Ed. Engl.  1973,  12:  954 

Among asymmetric metal-catalyzed carbon-carbon bond-forming reactions, only Nozaki’s Cu(II)-catalyzed cyclopropanation of styrene with ethyl diazo-acetate predates this discovery, see:

11c Nozaki H. Moriuti S. Takaya H. Noyori R. Tetrahedron Lett.  1966,  5239 

12a Britovsek GJP. Keim W. Mecking S. Sainz D. Wagner T. J. Chem. Soc., Chem. Commun.  1993,  1632 

12b Britovsek GJP. Cavell KJ. Keim W. J. Mol. Catal. A: Chem.  1996,  110:  77 

For a related dendrimeric Pd catalyst, see:

12c Hovestad NJ. Eggeling EB. Heidbüchel HJ. Jastrzebski JTBH. Kragl U. Keim W. Vogt D. van Koten G. Angew. Chem. Int. Ed.  1999,  38:  1655 

For a full report on dendrimeric Pd catalysts, see:

12d Eggeling EB. Hovestad NJ. Jastrzebski TBH. Vogt D. van Koten G. J. Org. Chem.  2000,  65:  8857 

12e Shi W.-J. Xie J.-H. Zhou Q.-L. Tetrahedron: Asymmetry  2005,  16:  705 

13 Bayersdörfer R. Ganter B. Englert U. Keim W. Vogt D. J. Organomet. Chem.  1998,  552:  187 

14a Albert J. Cadena M. Granell J. Muller G. Ordinas JI. Panyella D. Puerta C. Sanudo C. Valerga P. Organometallics  1999,  18:  3511 

For the use of other highly basic phosphines, see:

14b Albert J. Bosque R. Cadena JM. Delgado S. Granell J. Muller G. Ordinas JI. Bardia MF. Solans X. Chem. Eur. J.  2002,  8:  2279 

14c Englert U. Haerter R. Vasen D. Salzer A. Eggeling EB. Vogt D. Organometallics  1999,  18:  4390 

15a Ceder R. Muller G. Ordinas JI. J. Mol. Catal.  1994,  92:  127 

15b Muller G. Ordinas JI. J. Mol. Catal. A: Chem.  1997,  125:  97 

16a Monteiro AL. Seferin M. Dupont J. Souza RF. Tetrahedron Lett.  1996,  37:  1157 

16b Fassina V. Ramminger C. Seferin M. Monteiro AL. Tetrahedron  2000,  56:  7403 

17a Yi CS. He Z. Lee DW. Organometallics  2001,  20:  802 

17b RajanBabu TV. Nomura N. Jin J. Nandi M. Park H. Sun X. J. Org. Chem.  2003,  68:  8431 

These results have since been confirmed in another more recent publication, see:

17c Sanchez RP. Connell BT. Organometallics  2008,  27:  2902 

18a Grutters MMP. Müller C. Vogt D. J. Am. Chem. Soc.  2006,  128:  7414 

For a related reaction, see:

18b Hilt G. Lüers S. Synthesis  2002,  609 

19 Wilke G, Monkiewicz J, and Kuhn H. inventors; US Patent  4912274.  ; Chem. Abstr. 1991, 114, 43172

Use of the Wilke catalyst system in supercritical carbon dioxide has since been reported, see:

20a Wegner A. Leitner W. Chem. Commun.  1999,  1583 

20b Bösmann A. Franciò G. Janssen E. Solinas M. Leitner W. Wasserscheid P. Angew. Chem. Int. Ed.  2001,  40:  2697 

21 Angermund K. Eckerle A. Lutz F. Z. Naturforsch., B  1995,  50:  488 

22 Nomura N. Jin J. Park H. RajanBabu TV. J. Am. Chem. Soc.  1998,  120:  459 

23 Müller U. Keim W. Krüger C. Betz P. Angew. Chem. Int. Ed.  1989,  28:  1011 

24 We thank Professor Brookhart and Dr. DiRenzo for a copy of the following dissertation: Mechanistic Studies of Catalytic Olefin Dimerization Reactions Using Electrophilic η3-allyl-Palladium(II) Complexes: DiRenzo GM. Ph.D. Thesis   University of North Carolina; USA: 1997. 

25 Brandes H. Goddard R. Jolly PW. Krüger C. Mynott R. Wilke G. Z. Naturforsch. B  1984,  39:  1139 

26 Barnett BL. Krüger C. J. Organomet. Chem.  1974,  77:  407 

27 Jin J. RajanBabu TV. Tetrahedron  2000,  56:  2145 

28a Kumareswaran R. Nandi N. RajanBabu TV. Org. Lett.  2003,  5:  4345 

28b Park H. Kumareswaran R. RajanBabu TV. Tetrahedron Symposia-in-Print  2005,  61:  6352 

29 Buono G. Siv C. Peiffer G. Triantaphylides C. Denis P. Mortreux A. Petit F. J. Org. Chem.  1985,  50:  1781 

30 Nandi M. Jin J. RajanBabu TV. J. Am. Chem. Soc.  1999,  121:  9899 

For a discussion of hemilabile ligands, see:

31a Jeffrey JC. Rauchfuss TB. Inorg. Chem.  1979,  18:  2658 

31b Bader A. Lindner E. Coord. Chem. Rev.  1991,  108:  27 

31c Slone CS. Weinberger DA. Mirkin CA. In Progress in Inorganic Chemistry   Vol. 48:  Karlin KD. Wiley; New York: 1999.  p.233-350  

32a Mecking S. Keim W. Organometallics  1996,  15:  2650 

32b Keim W. Angew. Chem., Int. Ed. Engl.  1990,  29:  235 

32c Bonnet MC. Dahan F. Ecke A. Keim W. Schulz RP. Tkatchenko I. J. Chem. Soc., Chem. Commun.  1994,  615 

32d Keim W. Maas H. Mecking S. Z. Naturforsch., B  1995,  50:  430 

32e

See also ref. 12a

32f

See also ref. 12b

33 Uozumi Y. Tanahashi A. Lee S.-Y. Hayashi T. J. Org. Chem.  1993,  58:  1945 

34

For a structurally related, unreactive neutral Pd complex, see ref. 12b.

35a Nishida H. Takada N. Yoshimura M. Sonoda T. Kobayashi H. Bull. Chem. Soc. Jpn.  1984,  57:  2600 

35b Brookhart M. Grant B. Volpe A. Organometallics  1992,  11:  3920 

For the use of BARF^- in related reactions, see:

35c DiRenzo GM. White PS. Brookhart M. J. Am. Chem. Soc.  1996,  118:  6225 

36 Braunstein P. Chauvin Y. Nähring J. DeCian A. Fischer J. Tiripicchio A. Ugozzoli F. Organometallics  1996,  15:  5551 

37 Saha B. RajanBabu TV. J. Org. Chem.  2007,  72:  2357 

Examination of electronic effects has become common practice in asymmetric catalysis. For some early examples of the electronic tuning of asymmetric catalysts, see:

38a Inoguchi K. Sakuraba S. Achiwa K. Synlett  1992,  169 

38b Jacobsen EN. Zhang W. Guler ML. J. Am. Chem. Soc.  1991,  113:  6703 

38c RajanBabu TV. Casalnuovo AL. J. Am. Chem. Soc.  1992,  114:  6265 

38d RajanBabu TV. Ayers TA. Casalnuovo AL. J. Am. Chem. Soc.  1994,  116:  4101 

38e Schnyder A. Hintermann L. Togni A. Angew. Chem., Int. Ed. Engl.  1995,  34:  931 

For other examples from our work, see:

38f Casalnuovo AL. RajanBabu TV. Ayers TA. Warren TH. J. Am. Chem. Soc.  1994,  116:  9869 

38g RajanBabu TV. Casalnuovo AL. J. Am. Chem. Soc.  1996,  118:  6325 

38h RajanBabu TV. Ayers TA. Halliday GA. You KK. Calabrese JC. J. Org. Chem.  1997,  62:  6012 

38i RajanBabu TV. Radetich B. You KK. Ayers TA. Casalnuovo AL. Calabrese JC. J. Org. Chem.  1999,  64:  3429 

38j Clyne DS. Mermet-Bouvier YC. Nomura N. RajanBabu TV. J. Org. Chem.  1999,  64:  7601 

38k Yan Y. RajanBabu TV. Org. Lett.  2000,  2:  4137 

39 Komon ZJA. Bu X. Bazan GC. J. Am. Chem. Soc.  2000,  122:  1830 

40 Zhang A. RajanBabu TV. Org. Lett.  2004,  6:  1515 

41 Park H. RajanBabu TV. J. Am. Chem. Soc.  2002,  124:  734 

42

For a report on the use of a phosphinite ligand in a Pd-catalyzed hydrovinylation, see ref. 13.

43 Feringa BL. Acc. Chem. Res.  2000,  33:  346 

44 Arnold LA. Imbos R. Mandoli A. de Vries AHM. Naasz R. Feringa BL. Tetrahedron  2000,  56:  2865 

For representative examples of the use of finely tuned phosphoramidites from various research groups, see:

45a Alexakis A. Polet D. Rosset S. March S. J. Org. Chem.  2004,  69:  5660 

45b Bernsmann H. van den Berg M. Hoen R. Minnaard AJ. Mehler G. Reetz MT. De Vries JG. Feringa BL. J. Org. Chem.  2005,  70:  943 

45c Streiff S. Welter C. Schelwies M. Lipowsky G. Miller N. Helmchen G. Chem. Commun.  2005,  2957 

45d Leitner A. Shekhar S. Pouy MJ. Hartwig JF. J. Am. Chem. Soc.  2005,  127:  15506 

45e Yu RT. Rovis T. J. Am. Chem. Soc.  2006,  128:  12370 

45f Du H. Yuan W. Zhao B. Shi Y. J. Am. Chem. Soc.  2007,  129:  11688 

46a Franció G. Faraone F. Leitner W. J. Am. Chem. Soc.  2002,  124:  736 

For a computational study of the phosphoramidite ligand system, see:

46b Hölscher M. Franció G. Leitner W. Organometallics  2004,  23:  5606 

47a Smith CR. RajanBabu TV. Org. Lett.  2008,  10:  1657 

For a scalable procedure for the synthesis of phosphoramidites, see:

47b Smith CR. Mans DJ. RajanBabu TV. Org. Synth.  2008,  85:  238 

48

To the best of our knowledge, ligand 87 has not been described in the literature. For a complete list of the phosphoramidites used in this study and its corresponding supporting information, see ref. 47.

49

Only naproxen is currently sold in an enantiomerically pure form. For a review of the practical aspects of the synthesis of 2-arylpropionic acids, see ref. 5a.

For reviews and a history of the problem, see:

50a Douglas CJ. Overman LE. Proc. Natl. Acad. Sci. U.S.A.  2004,  101:  5363 ; and references cited therein

50b Denissova I. Barriault L. Tetrahedron  2003,  59:  10105 

50c Corey EJ. Guzman-Perez A. Angew. Chem. Int. Ed.  1998,  37:  388 

50d Romo D. Meyers AI. Tetrahedron  1991,  47:  9503 

50e Martin SF. Tetrahedron  1980,  36:  419 

51 Takemoto T. Sodeoka M. Sasai H. Shibasaki M. J. Am. Chem. Soc.  1993,  115:  8477 ; corrigendum: J. Am. Chem. Soc. 1994, 116, 11207

52 For a leading reference, see: Edwards DJ. Gerwick WH. J. Am. Chem. Soc.  2004,  126:  11432 

53 Huang A. Kodanko JJ. Overman LE. J. Am. Chem. Soc.  2004,  126:  14043 

54 Denmark SE. Fu J. Org. Lett.  2002,  4:  1951 

55a Zhang A. RajanBabu TV. J. Am. Chem. Soc.  2006,  128:  5620 

For the use of another phosphoramidite, see:

55b Shi W.-J. Zhang Q. Xie J.-H. Zhu S.-F. Hou G.-H. Zhou Q.-L. J. Am. Chem. Soc.  2006,  128:  2780 

56a Zhang A. RajanBabu TV. J. Am. Chem. Soc.  2006,  128:  54 

56b

Dan Mans in our group has since completed the synthesis of a number of pseudopterosin aglycones by applying back-to-back enantioselective hydrovinylations of vinylarenes and dienes. This work will be reported in due course.

57 For a detailed procedure of this and other related hydrovinylation reactions, see: Smith CR. Zhang A. Mans DJ. RajanBabu TV. Org. Synth.  2008,  85:  248 

58a Hulme AN. Henry SS. Meyers AI. J. Org. Chem.  1995,  60:  1265 

58b Fadel A. Arzel P. Tetrahedron: Asymmetry  1997,  8:  371 

For an early example (non-asymmetric) of the co-dimerization of ethylene and dienes, see:

59a Su ACL. Adv. Organomet. Chem.  1979,  17:  269 

59b Peiffer G. Cochet X. Petit F. Bull. Soc. Chim. Fr. II  1979,  415 

60 He Z. Yi CS. Donaldson WA. Org. Lett.  2003,  5:  1567 

61 He Z. Yi CS. Donaldson WA. Synlett  2004,  1312 

Apart from Diels-Alder reactions, the asymmetric catalyzed carbon-carbon bond-forming reactions of acyclic 1,3-dienes give only moderate regio- and enantioselectivities. See the following examples. Cyclopropanation:

62a Doyle M. In Catalytic Asymmetric Synthesis   Ojima I. Wiley-VCH; New York: 2000.  p.191-228  

Ene reaction:

62b Terada M. Mikami K. J. Chem. Soc., Chem. Commun.  1995,  2391 

Hydroformylation:

62c Horiuchi T. Ohta T. Shirakawa E. Nozaki K. Takaya H. Tetrahedron  1997,  53:  7795 

Hydrocyanation:

62d Saha B. RajanBabu TV. Org. Lett.  2006,  8:  4657 

63

For an extensive list of related references, see ref. 56.

64 Hodgson M. Parker D. Taylor RJ. Ferguson G. Organometallics  1988,  7:  1761 

65

For reviews of the synthesis of 2-arylpropionic acids, see ref. 5.

See the following for the best asymmetric routes to date [no useful catalytic asymmetric methods are known for other (S)-2-arylpropionic acid precursors]. Naproxen via Ru-catalyzed asymmetric hydrogenation of 2-arylacrylic acids (98% ee):

66a Ohta T. Takaya H. Kitamura M. Nagai K. Noyori R. J. Org. Chem.  1987,  52:  3174 

Ni-catalyzed asymmetric hydrocyanation (95% ee):

66b

See also ref. 38g; and references cited therein. Ibuprofen via Ru-catalyzed hydrogenation (97% ee):

66c Uemura T. Zhang X. Matsumura K. Sayo N. Kumobayashi H. Ohta T. Nozaki K. Takaya H. J. Org. Chem.  1996,  61:  5510 

Rh-catalyzed asymmetric hydroformylation (92% ee):

66d Nozaki K. Sakai N. Nanno T. Higashijima T. Mano S. Horiuchi T. Takaya H. J. Am. Chem. Soc.  1997,  119:  4413 

Hydrovinylation (91% ee):

66e

See ref. 40. Flurbiprofen via dynamic kinetic resolution:

66f Norinder J. Bogár K. Kaupp L. Backvall J.-E. Org. Lett.  2007,  9:  5095 

67

Smith, C. R.; RajanBabu, T. V. J. Org. Chem. 2009, 74, in press.

For publications, see the following and references cited therein. Bisabolanes:

68a Hagiwara H. Okabe T. Ono H. Kamat VP. Hoshi T. Suzuki T. Ando M. J. Chem. Soc., Perkin Trans. 1  2002,  895 

68b Vyvyan JR. Loitz C. Looper RE. Mattingly CS. Peterson EA. Staben ST. J. Org. Chem.  2004,  69:  2461 

Heliannanes:

68c Kishuku H. Shindo M. Shishido K. Chem. Commun.  2003,  350 

Pseudopterosins:

68d Look SA. Fenical W. Jacobs RS. Clardy J. Proc. Natl. Acad. Sci. U.S.A.  1986,  83:  6238 

68e Johnson TW. Corey EJ. J. Am. Chem. Soc.  2003,  125:  13486 

68f Harrowven DC. Tyte MJ. Tetrahedron Lett.  2004,  45:  2089 

Serrulatanes:

68g Rodriguez A. Ramirez C. J. Nat. Prod.  2001,  64:  100 

68h Dehmel F. Lex J. Schmalz H.-G. Org. Lett.  2002,  4:  3915 

69

For a comparison of the various methods for the synthesis of curcumene, see ref. 71.

70 Hagiwara H. Okabe T. Ono H. Kamat VP. Hoshi T. Suzuki T. Ando M. J. Chem. Soc., Perkin Trans. 1  2002,  895 

71 Zhang A. RajanBabu TV. Org. Lett.  2004,  6:  3159 

For a leading reference and discussion and citations of earlier work, see:

72a Guevel A.-C. Hart DJ. J. Org. Chem.  1996,  61:  465 ; and references cited therein

For a pedagogical view of this problem and a historical account of the syntheses of erythro- and threo-juvabiones, see:

72b Carey FA. Sundberg RJ. Advanced Organic Chemistry   2nd ed., Vol. 2:  Kluwer; New York: 2001.  p.848-859  

72c Trost BM. Verhoeven TR. J. Am. Chem. Soc.  1976,  98:  630 

72d Snider BB. Acc. Chem. Res.  1980,  13:  426 

72e Snider BB. Deutsch EA. J. Org. Chem.  1983,  48:  1823 

72f Wulkovich PM. Barcelos A. Sereno JF. Baggiolini EG. Hennesey BM. Uskokovic MR. Tetrahedron  1984,  40:  2283 

72g Andersen NH. Hadley SW. Kelly JD. Bacon ER. J. Org. Chem.  1985,  50:  4144 

72h Mikami K. Kawamoto K. Nakai T. Tetrahedron Lett.  1985,  26:  5799 

72i Mikami K. Loh T.-P. Nakai T. J. Chem. Soc., Chem. Commun.  1988,  1430 

72j Houston TA. Tonaka Y. Koreeda M. J. Org. Chem.  1993,  58:  4287 

For recent references dealing with the side chain of the anticancer natural product OSW-1, see:

72k Yu W. Jin Z. J. Am. Chem. Soc.  2002,  124:  6576 

73a Honzawa S. Suhara Y. Nihei K. Saito N. Kishimoto S. Fujishima T. Kurihara M. Sugiura T. Waku K. Takayama H. Kittaka A. Bioorg. Med. Chem. Lett.  2003,  13:  3503 ; and references cited therein

For leading references, see:

73b Kabat MM. Garofalo LM. Daniewski AJ. Hutchings SD. Liu W. Okabe M. Radinov R. Zhou Y. J. Org. Chem.  2001,  66:  6141 

74a Fujishima T. Konno K. Nakagawa K. Kurobe M. Okano T. Takayama H. Bioorg. Med. Chem.  2000,  8:  123 

74b Fernández B. Martinez Pérez JA. Granja JR. Castedo L. Mourino A. J. Org. Chem.  1992,  57:  3173 

See also:

74c Fernández C. Gómez G. Lago C. Momán E. Fall Y. Synlett  2005,  2163 

74d Hijikuro I. Doi T. Takahashi T. J. Am. Chem. Soc.  2001,  123:  3716 

For a review of vitamin D chemistry, see:

74e Dai H. Posner GH. Synthesis  1994,  1383 

74f Posner GH. Lee JK. White MC. Hutchings RH. Dai H. Kachinski JL. Dolan P. Kensler TW. J. Org. Chem.  1997,  62:  3299 

75 Saha B. Smith CR. RajanBabu TV. J. Am. Chem. Soc.  2008,  130:  9000 

76 Trost BM. Acc. Chem. Res.  1990,  23:  34 ; and references cited therein

For the use of early transition metals, see:

77a Nugent WA. Taber DF. J. Am. Chem. Soc.  1989,  111:  6435 

77b Piers WE. Shapiro PJ. Bunel EE. Bercaw JE. Synlett  1990,  74 

77c Knight KS. Waymouth RM. J. Am. Chem. Soc.  1991,  113:  6268 

77d Molander GA. Hoberg JO. J. Am. Chem. Soc.  1992,  114:  3123 

77e Negishi E. Takahashi T. Acc. Chem. Res.  1994,  27:  124 

77f Dzhemilev UM. Tetrahedron  1995,  51:  4333 

77g Christoffers J. Bergman RG. J. Am. Chem. Soc.  1996,  118:  4715 

77h Thiele S. Erker G. Chem. Ber./Recl.  1997,  130:  201 

77i Yamaura Y. Hyakutake M. Mori M. J. Am. Chem. Soc.  1997,  119:  7615 ; and references cited therein

78a Bright A. Malone JF. Nicholson JK. Powell J. Shaw BL. J. Chem. Soc., Chem. Commun.  1971,  712 

78b

See also ref. 1b

78c Grigg R. Malone JF. Mitchell TRB. Ramasubbu A. Scott RM. J. Chem. Soc., Perkin Trans. 1  1984,  1745 

78d Behr A. Freudenberg U. Keim W. J. Mol. Catal.  1986,  35:  9 

79 Radetich B. RajanBabu TV. J. Am. Chem. Soc.  1998,  120:  8007 

α,ω-Diene cyclization and related reactions have since received a lot of attention. For example, see:

80a Böing C. Franciò G. Leitner W. Chem. Commun.  2005,  1456 

80b Lloyd-Jones GC. Org. Biomol. Chem.  2003,  1:  215 

80c Bothe U. Rudbeck HC. Tanner D. Johannsen M. J. Chem. Soc., Perkin Trans. 1  2001,  3305 

80d Perch NS. Pei T. Widenhoefer RA. J. Org. Chem.  2000,  65:  3836