Highly stereoselective aldol reactions of titanium enolates from lactate-derived chiral ketones

Organic Letters

Volumn 5, Issue 4, 2003, Pages 519-522

  Solsona, Joan G ^a   Romea, Pedro ^a   Urpí, Fèlix ^a   Vilarrasa, Jaume ^a  

^a UNIVERSITY OF BARCELONA   (Spain)

Author keywords

[No Author keywords available]

Indexed keywords

HYDROXYL GROUP; KETONE DERIVATIVE; LACTIC ACID; LEWIS ACID; TITANIUM DERIVATIVE; ALDEHYDE; KETONE; LACTIC ACID DERIVATIVE; TITANIUM;

ALDOL REACTION; ARTICLE; CHELATION; CHEMICAL MODIFICATION; CHEMICAL REACTION; CHIRALITY; DIASTEREOISOMER; ENOLIZATION; STEREOCHEMISTRY; CHEMISTRY; STEREOISOMERISM;

ALDEHYDES; KETONES; LACTATES; STEREOISOMERISM; TITANIUM;

EID: 0038158084     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol0274054     Document Type: Article

References (46)

1. See, for instance: (a) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 99. (b) Heathcock, C. H. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 133 and 181. (c) Kim, B. M.; Williams, S. F.; Masamune, S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 239. (d) Rathke, M. W.; Weipert, P. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 277. (e) Paterson, I. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 301. (f) Caine, D. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 3, p 1. (g) Braun, M. Houben-Weyl. Methods of Organic Chemistry. Stereoselective Synthesis; Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds.; Georg Thieme Verlag: Stuttgart, 1995; Vol. E21b, p 1603.
2. See, for instance: (a) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 99. (b) Heathcock, C. H. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 133 and 181. (c) Kim, B. M.; Williams, S. F.; Masamune, S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 239. (d) Rathke, M. W.; Weipert, P. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 277. (e) Paterson, I. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 301. (f) Caine, D. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 3, p 1. (g) Braun, M. Houben-Weyl. Methods of Organic Chemistry. Stereoselective Synthesis; Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds.; Georg Thieme Verlag: Stuttgart, 1995; Vol. E21b, p 1603.
3. See, for instance: (a) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 99. (b) Heathcock, C. H. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 133 and 181. (c) Kim, B. M.; Williams, S. F.; Masamune, S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 239. (d) Rathke, M. W.; Weipert, P. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 277. (e) Paterson, I. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 301. (f) Caine, D. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 3, p 1. (g) Braun, M. Houben-Weyl. Methods of Organic Chemistry. Stereoselective Synthesis; Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds.; Georg Thieme Verlag: Stuttgart, 1995; Vol. E21b, p 1603.
4. See, for instance: (a) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 99. (b) Heathcock, C. H. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 133 and 181. (c) Kim, B. M.; Williams, S. F.; Masamune, S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 239. (d) Rathke, M. W.; Weipert, P. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 277. (e) Paterson, I. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 301. (f) Caine, D. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 3, p 1. (g) Braun, M. Houben-Weyl. Methods of Organic Chemistry. Stereoselective Synthesis; Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds.; Georg Thieme Verlag: Stuttgart, 1995; Vol. E21b, p 1603.
5. See, for instance: (a) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 99. (b) Heathcock, C. H. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 133 and 181. (c) Kim, B. M.; Williams, S. F.; Masamune, S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 239. (d) Rathke, M. W.; Weipert, P. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 277. (e) Paterson, I. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 301. (f) Caine, D. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 3, p 1. (g) Braun, M. Houben-Weyl. Methods of Organic Chemistry. Stereoselective Synthesis; Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds.; Georg Thieme Verlag: Stuttgart, 1995; Vol. E21b, p 1603.
6. See, for instance: (a) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 99. (b) Heathcock, C. H. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 133 and 181. (c) Kim, B. M.; Williams, S. F.; Masamune, S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 239. (d) Rathke, M. W.; Weipert, P. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 277. (e) Paterson, I. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 301. (f) Caine, D. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 3, p 1. (g) Braun, M. Houben-Weyl. Methods of Organic Chemistry. Stereoselective Synthesis; Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds.; Georg Thieme Verlag: Stuttgart, 1995; Vol. E21b, p 1603.
7. See, for instance: (a) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 99. (b) Heathcock, C. H. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 133 and 181. (c) Kim, B. M.; Williams, S. F.; Masamune, S. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 239. (d) Rathke, M. W.; Weipert, P. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 277. (e) Paterson, I. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 301. (f) Caine, D. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 3, p 1. (g) Braun, M. Houben-Weyl. Methods of Organic Chemistry. Stereoselective Synthesis; Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds.; Georg Thieme Verlag: Stuttgart, 1995; Vol. E21b, p 1603.
8. For reviews dealing with titanium complexes, see: (a) Duthaler, R. O.; Hafner, A. Chem. Rev. 1992, 92, 807. (b) Cozzi, P. G.; Solari, E.; Floriani, C. ; Chiesi-Villa, A.; Rizzoli, C. Chem. Ber. 1996, 129, 1361.
9. For reviews dealing with titanium complexes, see: (a) Duthaler, R. O.; Hafner, A. Chem. Rev. 1992, 92, 807. (b) Cozzi, P. G.; Solari, E.; Floriani, C. ; Chiesi-Villa, A.; Rizzoli, C. Chem. Ber. 1996, 129, 1361.
10. (a) Evans, D. A.; Clark, J. S.; Metternich, R.; Novack, V. J.; Sheppard, G. S. J. Am. Chem. Soc. 1990, 112, 866.
11. (b) Evans, D. A.; Rieger, D. L.; Bilodeau, M. T.; Urpí, F. J. Am. Chem. Soc. 1991, 113, 1047.
12. (c) Annunziata, R.; Cinquini, M.; Cozzi, F.; Borgia, A. L. J. Org. Chem. 1992, 57, 6339.
13. (d) Yan, T.-H.; Tan, C.-W.; Lee, H.-C.; Lo, H. C.; Huang, T.-Y. J. Am. Chem. Soc. 1993, 115, 2613.
14. (e) Luke, G. P.; Morris, J. J. Org. Chem. 1995, 60, 3013.
15. (f) Ghosh, A. K.; Onishi, M. J. Am. Chem. Soc. 1996, 118, 2527.
16. (g) Matsumura, Y.; Nishimura, M.; Hiu, H.; Watanabe, M.; Kise, N. J. Org. Chem. 1996, 61, 2809.
17. (h) González, A.; Aiguadé, J.; Urpí, F.; Vilarrasa, J. Tetrahedron Lett. 1996, 37, 8949.
18. (i) Yoshida, Y.; Hayashi, R.; Sumihara, H.; Tanabe, Y. Tetrahedron Lett. 1997, 38, 8727. Crimmins, M. T.; King, B. W.; Tabet, E. A. J. Am. Chem. Soc. 1997, 119, 7883.
19. (i) Yoshida, Y.; Hayashi, R.; Sumihara, H.; Tanabe, Y. Tetrahedron Lett. 1997, 38, 8727. Crimmins, M. T.; King, B. W.; Tabet, E. A. J. Am. Chem. Soc. 1997, 119, 7883.
20. (k) Adrian, J. C., Jr.; Barkin, J. L.; Fox, R. J.; Chuck, J. L.; Hunter, A. D.; Nicklow, R. A. J. Org. Chem. 2000, 65, 6264.
21. (l) Crimmins, M. T.; King, B. W.; Tabet, E. A.; Chaudhury, K. J. Org. Chem. 2001, 66, 894.
22. (m) Guz, N. R.; Phillips, A. J. Org. Lett. 2002, 4, 2253.
23. (a) Figueras, S.; Martín, R.; Romea, P.; Urpí, F.; Vilarrasa, J. Tetrahedron Lett. 1997, 38, 1637.
24. (b) Esteve, C.; Ferreró, M.; Romea, P.; Urpí, F.; Vilarrasa, J. Tetrahedron Lett. 1999, 40, 5083.
25. For stereoselective aldol reactions based on chiral hydroxy ketones involving chelated transition states, see: (a) Van Draanen, N. A.; Arseniyadis, S.; Crimmins, M. T.; Heathcock, C. H. J. Org. Chem. 1991, 56, 2499. (b) Paterson, I.; Tillyer, R. D. Tetrahedron Lett. 1992, 33, 4233. (c) Choudhury, A.; Thornton, E. R. Tetrahedron Lett. 1993, 34, 2221. (d) Palomo, C.; González, A.; García, J. M.; Landa, C.; Oiarbide, M.; Rodríguez, S.; Linden, A. Angew. Chem., Int. Ed. 1998, 37, 180. (e) Perkins, M. V.; Sampson, R. A. Org. Lett. 2001, 3 123. (f) Paterson, I.; Temal-Laïb, T. Org. Lett. 2002, 4, 2473.
26. For stereoselective aldol reactions based on chiral hydroxy ketones involving chelated transition states, see: (a) Van Draanen, N. A.; Arseniyadis, S.; Crimmins, M. T.; Heathcock, C. H. J. Org. Chem. 1991, 56, 2499. (b) Paterson, I.; Tillyer, R. D. Tetrahedron Lett. 1992, 33, 4233. (c) Choudhury, A.; Thornton, E. R. Tetrahedron Lett. 1993, 34, 2221. (d) Palomo, C.; González, A.; García, J. M.; Landa, C.; Oiarbide, M.; Rodríguez, S.; Linden, A. Angew. Chem., Int. Ed. 1998, 37, 180. (e) Perkins, M. V.; Sampson, R. A. Org. Lett. 2001, 3 123. (f) Paterson, I.; Temal-Laïb, T. Org. Lett. 2002, 4, 2473.
27. For stereoselective aldol reactions based on chiral hydroxy ketones involving chelated transition states, see: (a) Van Draanen, N. A.; Arseniyadis, S.; Crimmins, M. T.; Heathcock, C. H. J. Org. Chem. 1991, 56, 2499. (b) Paterson, I.; Tillyer, R. D. Tetrahedron Lett. 1992, 33, 4233. (c) Choudhury, A.; Thornton, E. R. Tetrahedron Lett. 1993, 34, 2221. (d) Palomo, C.; González, A.; García, J. M.; Landa, C.; Oiarbide, M.; Rodríguez, S.; Linden, A. Angew. Chem., Int. Ed. 1998, 37, 180. (e) Perkins, M. V.; Sampson, R. A. Org. Lett. 2001, 3 123. (f) Paterson, I.; Temal-Laïb, T. Org. Lett. 2002, 4, 2473.
28. For stereoselective aldol reactions based on chiral hydroxy ketones involving chelated transition states, see: (a) Van Draanen, N. A.; Arseniyadis, S.; Crimmins, M. T.; Heathcock, C. H. J. Org. Chem. 1991, 56, 2499. (b) Paterson, I.; Tillyer, R. D. Tetrahedron Lett. 1992, 33, 4233. (c) Choudhury, A.; Thornton, E. R. Tetrahedron Lett. 1993, 34, 2221. (d) Palomo, C.; González, A.; García, J. M.; Landa, C.; Oiarbide, M.; Rodríguez, S.; Linden, A. Angew. Chem., Int. Ed. 1998, 37, 180. (e) Perkins, M. V.; Sampson, R. A. Org. Lett. 2001, 3 123. (f) Paterson, I.; Temal-Laïb, T. Org. Lett. 2002, 4, 2473.
29. For stereoselective aldol reactions based on chiral hydroxy ketones involving chelated transition states, see: (a) Van Draanen, N. A.; Arseniyadis, S.; Crimmins, M. T.; Heathcock, C. H. J. Org. Chem. 1991, 56, 2499. (b) Paterson, I.; Tillyer, R. D. Tetrahedron Lett. 1992, 33, 4233. (c) Choudhury, A.; Thornton, E. R. Tetrahedron Lett. 1993, 34, 2221. (d) Palomo, C.; González, A.; García, J. M.; Landa, C.; Oiarbide, M.; Rodríguez, S.; Linden, A. Angew. Chem., Int. Ed. 1998, 37, 180. (e) Perkins, M. V.; Sampson, R. A. Org. Lett. 2001, 3 123. (f) Paterson, I.; Temal-Laïb, T. Org. Lett. 2002, 4, 2473.
30. For stereoselective aldol reactions based on chiral hydroxy ketones involving chelated transition states, see: (a) Van Draanen, N. A.; Arseniyadis, S.; Crimmins, M. T.; Heathcock, C. H. J. Org. Chem. 1991, 56, 2499. (b) Paterson, I.; Tillyer, R. D. Tetrahedron Lett. 1992, 33, 4233. (c) Choudhury, A.; Thornton, E. R. Tetrahedron Lett. 1993, 34, 2221. (d) Palomo, C.; González, A.; García, J. M.; Landa, C.; Oiarbide, M.; Rodríguez, S.; Linden, A. Angew. Chem., Int. Ed. 1998, 37, 180. (e) Perkins, M. V.; Sampson, R. A. Org. Lett. 2001, 3 123. (f) Paterson, I.; Temal-Laïb, T. Org. Lett. 2002, 4, 2473.
31. Ferreró, M.; Galobardes, M.; Martín, R.; Montes, T.; Romea, P.; Rovira, R. Urpí, F.; Vilarrasa, J. Synthesis 2000, 1608.
32. Greene, T. W.; Wuts, R. G. M. In Protective Groups in Organic Synthesis; Wiley & Sons: New York, 1999.
33. Isolated yield of 3a and 4a (see Scheme 2) = 55%. Diastereomeric ratio (3a:4a) = 84:16.
34. 2NEt were added to ketone 1 at -90 °C, and the enolization and the further aldol reaction with isobutyraldehyde were carried out at -78 °C, the cleavage of the PMB was reduced to less than 5%.
35. 4) and concentrated. The resulting oil was analyzed by HPLC and purified by flash chromatography (hexanes/EtOAc).
36. Stereochemistry of 3f was established by X-ray diffraction analysis; see Supporting Information. The stereochemistry of 3a was confirmed by chemical correlation.
37. Stereochemistry of 5f was established by X-ray diffraction analysis; see Supporting Information. The stereochemistry of 5a and 6a was confirmed by chemical correlation.
38. 4-mediated aldol reaction of 1 with benzaldehyde (e) afforded a mixture of 3e and 4e (see Scheme 2) in low yield (58%) and with a poor diastereomeric ratio (3e:4e = 25:75), the syn-syn aldol being the major diastereomer. This result is opposite to that obtained with (i-OPr)TiC13 (compare with entry 5 in Table 1), which proves the crucial role played by the Lewis acid on the stereochemical outcome of these reactions.
39. 3) used in the enolization. These results suggest that the fickle behavior observed in the titanium-mediated aldol reactions of 1 and 2 is related to the formation of a chelated enolate, whose more rigid architecture has a crucial influence on the stereodetermining step of the process.
40. Gau, H.-M.; Lee, C.-S.; Lin, C.-C.; Jiang, M.-K.; Ho, Y.-C.; Kuo, C.-N. J. Am. Chem. Soc. 1996, 118, 2936.
41. 4-mediated aldol reactions of 2 cannot be linked to the carbon-carbon bond formation step.
42. For related discussions on the structure of titanium complexes involved in stereoselective Diels-Alder reactions, see: (a) Seebach, D.; Dahinden, R.; Marti, R. E.; Beck, A. K.; Plattner, D. A.; Kühnle, F. N. M. J. Org. Chem. 1995, 60, 1788. (b) Haase, C.; Sarko, C. R.; DiMare, M. J. Org. Chem. 1995, 60, 1777. (c) Gothelf, K. V.; Jorgensen, K. A. J. Org. Chem. 1995, 60, 6847. (d) García, J. I.; Martínez-Merino, V.; Mayoral, J. A. J. Org. Chem. 1998, 63, 2321.
43. For related discussions on the structure of titanium complexes involved in stereoselective Diels-Alder reactions, see: (a) Seebach, D.; Dahinden, R.; Marti, R. E.; Beck, A. K.; Plattner, D. A.; Kühnle, F. N. M. J. Org. Chem. 1995, 60, 1788. (b) Haase, C.; Sarko, C. R.; DiMare, M. J. Org. Chem. 1995, 60, 1777. (c) Gothelf, K. V.; Jorgensen, K. A. J. Org. Chem. 1995, 60, 6847. (d) García, J. I.; Martínez-Merino, V.; Mayoral, J. A. J. Org. Chem. 1998, 63, 2321.
44. For related discussions on the structure of titanium complexes involved in stereoselective Diels-Alder reactions, see: (a) Seebach, D.; Dahinden, R.; Marti, R. E.; Beck, A. K.; Plattner, D. A.; Kühnle, F. N. M. J. Org. Chem. 1995, 60, 1788. (b) Haase, C.; Sarko, C. R.; DiMare, M. J. Org. Chem. 1995, 60, 1777. (c) Gothelf, K. V.; Jorgensen, K. A. J. Org. Chem. 1995, 60, 6847. (d) García, J. I.; Martínez-Merino, V.; Mayoral, J. A. J. Org. Chem. 1998, 63, 2321.
45. For related discussions on the structure of titanium complexes involved in stereoselective Diels-Alder reactions, see: (a) Seebach, D.; Dahinden, R.; Marti, R. E.; Beck, A. K.; Plattner, D. A.; Kühnle, F. N. M. J. Org. Chem. 1995, 60, 1788. (b) Haase, C.; Sarko, C. R.; DiMare, M. J. Org. Chem. 1995, 60, 1777. (c) Gothelf, K. V.; Jorgensen, K. A. J. Org. Chem. 1995, 60, 6847. (d) García, J. I.; Martínez-Merino, V.; Mayoral, J. A. J. Org. Chem. 1998, 63, 2321.
46. For related examples on the impact of additives on titanium-mediated aldol reactions, see for instance, refs 3k-m and: Nakamura, S.; Hayakawa, T.; Nishi, T.; Watanabe, Y.; Toru, T. Tetrahedron 2001, 57, 6703.