Stereoselective reduction of chiral trans-3-acetyl 4-alkylpyrrolidin-2- ones

Tetrahedron Asymmetry

Volumn 10, Issue 3, 1999, Pages 587-605

  Galeazzi, Roberta ^a   Geremia, Silvano ^b   Mobbili, Giovanna ^a   Orena, Mario ^a  

^a UNIVERSITÀ POLITECNICA DELLE MARCHE   (Italy)

^b UNIVERSITY OF TRIESTE   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

CARBAPENEM DERIVATIVE; HYDROGEN; IODOBENZOIC ACID DERIVATIVE; PYRROLIDINE DERIVATIVE;

ARTICLE; CARBON NUCLEAR MAGNETIC RESONANCE; CHIRALITY; ENERGY; HYDROGEN BOND; MASS SPECTROMETRY; PRIORITY JOURNAL; PROTON NUCLEAR MAGNETIC RESONANCE; STEREOCHEMISTRY; X RAY DIFFRACTION;

EID: 0033548155     PISSN: 09574166     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0957-4166(99)00031-2     Document Type: Article

References (57)

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2. (b) Tsukada, N.; Shimada, T.; Gyoung, Y. S.; Asao, N. M; Yamamoto, Y. J. Org. Chem. 1995, 60, 143-148;
3. (c) Ishibashi, H.; Kodama, K.; Kameoka, C.; Kawanami, H.; Ikeda, M. Tetrahedron 1996, 52, 13867-13880;
4. (d) Ishibashi, H.; Kameoka, C.; Kodama, K.; Kawanami, H.; Hamada, M.; Ikeda, M. Tetrahedron 1997, 53, 9611-9622.
5. For recent reviews, see: (a) Nagahara, T.; Kametani, T. Heterocycles 1987, 25, 729-776; (b) Hart, D. J.; Ha, D. C. Chem. Rev. 1989, 89, 1447-1465; (c) Berks, A. H. Tetrahedron 1996, 52, 331-375.
6. For recent reviews, see: (a) Nagahara, T.; Kametani, T. Heterocycles 1987, 25, 729-776; (b) Hart, D. J.; Ha, D. C. Chem. Rev. 1989, 89, 1447-1465; (c) Berks, A. H. Tetrahedron 1996, 52, 331-375.
7. For recent reviews, see: (a) Nagahara, T.; Kametani, T. Heterocycles 1987, 25, 729-776; (b) Hart, D. J.; Ha, D. C. Chem. Rev. 1989, 89, 1447-1465; (c) Berks, A. H. Tetrahedron 1996, 52, 331-375.
8. (a) Hart, D. J.; Lee, C.-S. J. Am. Chem. Soc. 1986, 108, 6054-6056;
9. (b) Andreoli, P.; Cainelli, G.; Panunzio, M.; Bandini, E.; Martelli, G.; Spunta, G. J. Org. Chem. 1991, 56, 5984-5990;
10. (c) Tanner, D.; Somfai, P. Bioorg. Med. Chem. Lett. 1993, 3, 2415-2418.
11. (a) Georg, G. I. In Studies in Natural Product Chemistry; Atta-ur-Rahman, Ed. Elsevier Science: Amsterdam, 1989; Vol. 4, pp. 431-456.
12. (a) Fuentes, L. M.; Shinkai, I.; King, A.; Purick, R.; Reamer, R. A.; Schmitt, S. M.; Cama, L.; Christensen, B. G. J. Org. Chem. 1987, 52, 2563-2567;
13. (b) Yamanaka, T.; Seki, M.; Kuroda, T.; Ohmizu, H.; Iwasaki, T. Tetrahedron Lett. 1996, 37, 4967-4970;
14. (c) Nozaki, K.; Li, W.-G.; Horiuchi, T.; Takaya, H.; Saito, T.; Yoshida, A.; Matsumura, K.; Kato, Y; Imai, T.; Miura, T.; Kumobayashi, H. J. Org. Chem. 1996, 61, 7658-7659;
15. (d) Kume, M.; Ooka, H.; Ishitobi, H. Tetrahedron 1997, 53, 1635-1646.
16. Cardillo, B.; Galeazzi, R.; Mobbili, G.; Orena, M.; Rossetti, M. Heterocycles 1994, 38, 2663-2676.
17. (a) Cardillo, B.; Galeazzi, R.; Mobbili, G.; Orena, M. Synlett 1995, 1159-1160;
18. (b) Galeazzi, R.; Mobbili, G.; Orena, M. Tetrahedron 1996, 52, 1069-1084;
19. (c) Galeazzi, R.; Mobbili, G.; Orena, M. Tetrahedron: Asymmetry 1997, 8, 133-137;
20. (d) Galeazzi, R.; Mobbili, G.; Orena, M. In Targets in Heterocyclic Systems - Chemistry and Properties; Attanasi, O. A.; Spinelli, D., Eds. Italian Society of Chemistry: Rome, 1997; Vol. 1, pp. 355-400.
21. Galeazzi, R.; Geremia, S.; Mobbili, G.; Orena, M. Tetrahedron: Asymmetry 1996, 7, 79-88.
22. For syntheses of 4-substituted cis-3-hydroxyethylpyrrolidin-2-ones, see: (a) Zuger, M.; Weller, T.; Seebach, D. Helv. Chim. Acta 1980, 63, 2005-2022; (b) Bartels, A.; Jones, P. G.; Liebscher, J. Tetrahedron: Asymmetry 1997, 8, 1545-1549.
23. For syntheses of 4-substituted cis-3-hydroxyethylpyrrolidin-2-ones, see: (a) Zuger, M.; Weller, T.; Seebach, D. Helv. Chim. Acta 1980, 63, 2005-2022; (b) Bartels, A.; Jones, P. G.; Liebscher, J. Tetrahedron: Asymmetry 1997, 8, 1545-1549.
24. For a recent review, see: Berks, A. H. Tetrahedron 1996, 52, 331-375.
25. For some recent examples concerning stereoselective intramolecular conjugate additions leading to pyrrolidine or piperidine ring formation, see also: (a) Barco, A.; Benetti, S.; Casolari, A.; Pollini, G. P.; Spalluto, G. Tetrahedron Lett. 1990, 31, 4917-4920; (b) Barco, A.; Benetti, S.; Spalluto, G.; Casolari, A.; Pollini, G. P.; Zanirato, V. J. Org. Chem. 1992, 57, 6279-6286; (c) Hirai, Y.; Terada, T.; Yamazaki, T. J. Am. Chem. Soc. 1988, 110, 958-960; (d) Hirai, Y.; Terada, T.; Yamazaki, T.; Momose, T. J. Chem. Soc., Perkin Trans. 1 1992, 509-516.
26. For some recent examples concerning stereoselective intramolecular conjugate additions leading to pyrrolidine or piperidine ring formation, see also: (a) Barco, A.; Benetti, S.; Casolari, A.; Pollini, G. P.; Spalluto, G. Tetrahedron Lett. 1990, 31, 4917-4920; (b) Barco, A.; Benetti, S.; Spalluto, G.; Casolari, A.; Pollini, G. P.; Zanirato, V. J. Org. Chem. 1992, 57, 6279-6286; (c) Hirai, Y.; Terada, T.; Yamazaki, T. J. Am. Chem. Soc. 1988, 110, 958-960; (d) Hirai, Y.; Terada, T.; Yamazaki, T.; Momose, T. J. Chem. Soc., Perkin Trans. 1 1992, 509-516.
27. For some recent examples concerning stereoselective intramolecular conjugate additions leading to pyrrolidine or piperidine ring formation, see also: (a) Barco, A.; Benetti, S.; Casolari, A.; Pollini, G. P.; Spalluto, G. Tetrahedron Lett. 1990, 31, 4917-4920; (b) Barco, A.; Benetti, S.; Spalluto, G.; Casolari, A.; Pollini, G. P.; Zanirato, V. J. Org. Chem. 1992, 57, 6279-6286; (c) Hirai, Y.; Terada, T.; Yamazaki, T. J. Am. Chem. Soc. 1988, 110, 958-960; (d) Hirai, Y.; Terada, T.; Yamazaki, T.; Momose, T. J. Chem. Soc., Perkin Trans. 1 1992, 509-516.
28. For some recent examples concerning stereoselective intramolecular conjugate additions leading to pyrrolidine or piperidine ring formation, see also: (a) Barco, A.; Benetti, S.; Casolari, A.; Pollini, G. P.; Spalluto, G. Tetrahedron Lett. 1990, 31, 4917-4920; (b) Barco, A.; Benetti, S.; Spalluto, G.; Casolari, A.; Pollini, G. P.; Zanirato, V. J. Org. Chem. 1992, 57, 6279-6286; (c) Hirai, Y.; Terada, T.; Yamazaki, T. J. Am. Chem. Soc. 1988, 110, 958-960; (d) Hirai, Y.; Terada, T.; Yamazaki, T.; Momose, T. J. Chem. Soc., Perkin Trans. 1 1992, 509-516.
29. According to Ref. 5a, a R,S mixture of the corresponding azetidinone can be easily converted into the 1β-methyl derivative, exclusively.
30. 4) and removal of the solvent under reduced pressure, the residue was purified by silica gel chromatography (ethyl acetate) to give products 13a-d and 14a-d as colourless oils in d.r. 60:40.
31. 4 a 3-acetyl azetidinone afforded a 1:1 diastereomeric mixture: Ponsford, R. J.; Southgate, R. J. Chem. Soc., Chem. Commun. 1979, 846-847.
32. + force field, an extension of MM2 which was developed by Allinger and co-workers. For references see: (a) Allinger, N. L. J. Am. Chem. Soc. 1977, 99, 8127-8134, and subsequent versions, e.g. MM2-87, MM2-89, MM2-91; (b) Allinger, N. L.; Yuh, Y. H. Quantum Chemistry Program Exchange, Bloomington, Indiana, Program #395, Molecular Mechanics; Burkert, U.; Allinger, N. L. ed. ACS Monograph 177, American Chemical Society: Washington, DC, 1982; (c) Lii, J.; Gallion, S.; Bender, C.; Wikstrom, H.; Allinger, N. L., Flurchick, K. M.; Teeter, M. M. J. Comput. Chem. 1989, 10, 503-511; (d) Lipkowitz, K. B., QCPE Bulletin, Indiana University 12, 1 (Feb. 1982). The program is enclosed in Hyperchem package, release 5.01, available from Hypercube, Gainesville, Florida, USA.
33. + force field, an extension of MM2 which was developed by Allinger and co-workers. For references see: (a) Allinger, N. L. J. Am. Chem. Soc. 1977, 99, 8127-8134, and subsequent versions, e.g. MM2-87, MM2-89, MM2-91; (b) Allinger, N. L.; Yuh, Y. H. Quantum Chemistry Program Exchange, Bloomington, Indiana, Program #395, Molecular Mechanics; Burkert, U.; Allinger, N. L. ed. ACS Monograph 177, American Chemical Society: Washington, DC, 1982; (c) Lii, J.; Gallion, S.; Bender, C.; Wikstrom, H.; Allinger, N. L., Flurchick, K. M.; Teeter, M. M. J. Comput. Chem. 1989, 10, 503-511; (d) Lipkowitz, K. B., QCPE Bulletin, Indiana University 12, 1 (Feb. 1982). The program is enclosed in Hyperchem package, release 5.01, available from Hypercube, Gainesville, Florida, USA.
34. + force field, an extension of MM2 which was developed by Allinger and co-workers. For references see: (a) Allinger, N. L. J. Am. Chem. Soc. 1977, 99, 8127-8134, and subsequent versions, e.g. MM2-87, MM2-89, MM2-91; (b) Allinger, N. L.; Yuh, Y. H. Quantum Chemistry Program Exchange, Bloomington, Indiana, Program #395, Molecular Mechanics; Burkert, U.; Allinger, N. L. ed. ACS Monograph 177, American Chemical Society: Washington, DC, 1982; (c) Lii, J.; Gallion, S.; Bender, C.; Wikstrom, H.; Allinger, N. L., Flurchick, K. M.; Teeter, M. M. J. Comput. Chem. 1989, 10, 503-511; (d) Lipkowitz, K. B., QCPE Bulletin, Indiana University 12, 1 (Feb. 1982). The program is enclosed in Hyperchem package, release 5.01, available from Hypercube, Gainesville, Florida, USA.
35. + force field, an extension of MM2 which was developed by Allinger and co-workers. For references see: (a) Allinger, N. L. J. Am. Chem. Soc. 1977, 99, 8127-8134, and subsequent versions, e.g. MM2-87, MM2-89, MM2-91; (b) Allinger, N. L.; Yuh, Y. H. Quantum Chemistry Program Exchange, Bloomington, Indiana, Program #395, Molecular Mechanics; Burkert, U.; Allinger, N. L. ed. ACS Monograph 177, American Chemical Society: Washington, DC, 1982; (c) Lii, J.; Gallion, S.; Bender, C.; Wikstrom, H.; Allinger, N. L., Flurchick, K. M.; Teeter, M. M. J. Comput. Chem. 1989, 10, 503-511; (d) Lipkowitz, K. B., QCPE Bulletin, Indiana University 12, 1 (Feb. 1982). The program is enclosed in Hyperchem package, release 5.01, available from Hypercube, Gainesville, Florida, USA.
36. The search for low energy conformations was run using a BATCHMIN program included in MacroModel, Version 5.5. All calculations were carried out on a Silicon Graphics Indigo 2 R10000 workstation. For a reference, see: Mohamadi, F.; Richards, N. G. J.; Guida, W. C.; Liskamp, R.; Lipton, M.; Canfield, C.; Chang, G.; Hendrickson, T.; Still, W. C. J. Comput. Chem. 1990, 11, 440-448.
37. Whereas conformer I of 13a is practically missing (ΔE=2.44 kcal/mol with respect to A), conformer II of 14a is significantly present (ΔE=0.64 kcal/mol with respect to B). (equation presented)
38. A number of stereoselective reductions of 3-acetyl azetidinones are reported in the literature. For examples see: (a) Bouffard, F. A.; Christensen, B. G. J. Org. Chem. 1981, 46, 2208-2212; (b) Reider, P. J.; Grabowski, E. J. J. Tetrahedron Lett. 1982, 23, 2293-2296; (c) Chiba, T.; Nakai, T. Chemistry Lett. 1985, 651-654; (d) Chiba, T.; Nagatsuma, M.; Nakai, T. Chemistry Lett. 1985, 1343-1346; (e) Chiba, T.; Nakai, T. Tetrahedron Lett. 1985, 26, 4647-4648; (f) Ito, Y.; Kobayashi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron 1989, 45, 5767-5790; (g) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron Lett. 1986, 27, 6241-6244; (h) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron 1988, 44, 2149-2165.
39. A number of stereoselective reductions of 3-acetyl azetidinones are reported in the literature. For examples see: (a) Bouffard, F. A.; Christensen, B. G. J. Org. Chem. 1981, 46, 2208-2212; (b) Reider, P. J.; Grabowski, E. J. J. Tetrahedron Lett. 1982, 23, 2293-2296; (c) Chiba, T.; Nakai, T. Chemistry Lett. 1985, 651-654; (d) Chiba, T.; Nagatsuma, M.; Nakai, T. Chemistry Lett. 1985, 1343-1346; (e) Chiba, T.; Nakai, T. Tetrahedron Lett. 1985, 26, 4647-4648; (f) Ito, Y.; Kobayashi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron 1989, 45, 5767-5790; (g) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron Lett. 1986, 27, 6241-6244; (h) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron 1988, 44, 2149-2165.
40. A number of stereoselective reductions of 3-acetyl azetidinones are reported in the literature. For examples see: (a) Bouffard, F. A.; Christensen, B. G. J. Org. Chem. 1981, 46, 2208-2212; (b) Reider, P. J.; Grabowski, E. J. J. Tetrahedron Lett. 1982, 23, 2293-2296; (c) Chiba, T.; Nakai, T. Chemistry Lett. 1985, 651-654; (d) Chiba, T.; Nagatsuma, M.; Nakai, T. Chemistry Lett. 1985, 1343-1346; (e) Chiba, T.; Nakai, T. Tetrahedron Lett. 1985, 26, 4647-4648; (f) Ito, Y.; Kobayashi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron 1989, 45, 5767-5790; (g) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron Lett. 1986, 27, 6241-6244; (h) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron 1988, 44, 2149-2165.
41. A number of stereoselective reductions of 3-acetyl azetidinones are reported in the literature. For examples see: (a) Bouffard, F. A.; Christensen, B. G. J. Org. Chem. 1981, 46, 2208-2212; (b) Reider, P. J.; Grabowski, E. J. J. Tetrahedron Lett. 1982, 23, 2293-2296; (c) Chiba, T.; Nakai, T. Chemistry Lett. 1985, 651-654; (d) Chiba, T.; Nagatsuma, M.; Nakai, T. Chemistry Lett. 1985, 1343-1346; (e) Chiba, T.; Nakai, T. Tetrahedron Lett. 1985, 26, 4647-4648; (f) Ito, Y.; Kobayashi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron 1989, 45, 5767-5790; (g) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron Lett. 1986, 27, 6241-6244; (h) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron 1988, 44, 2149-2165.
42. A number of stereoselective reductions of 3-acetyl azetidinones are reported in the literature. For examples see: (a) Bouffard, F. A.; Christensen, B. G. J. Org. Chem. 1981, 46, 2208-2212; (b) Reider, P. J.; Grabowski, E. J. J. Tetrahedron Lett. 1982, 23, 2293-2296; (c) Chiba, T.; Nakai, T. Chemistry Lett. 1985, 651-654; (d) Chiba, T.; Nagatsuma, M.; Nakai, T. Chemistry Lett. 1985, 1343-1346; (e) Chiba, T.; Nakai, T. Tetrahedron Lett. 1985, 26, 4647-4648; (f) Ito, Y.; Kobayashi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron 1989, 45, 5767-5790; (g) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron Lett. 1986, 27, 6241-6244; (h) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron 1988, 44, 2149-2165.
43. A number of stereoselective reductions of 3-acetyl azetidinones are reported in the literature. For examples see: (a) Bouffard, F. A.; Christensen, B. G. J. Org. Chem. 1981, 46, 2208-2212; (b) Reider, P. J.; Grabowski, E. J. J. Tetrahedron Lett. 1982, 23, 2293-2296; (c) Chiba, T.; Nakai, T. Chemistry Lett. 1985, 651-654; (d) Chiba, T.; Nagatsuma, M.; Nakai, T. Chemistry Lett. 1985, 1343-1346; (e) Chiba, T.; Nakai, T. Tetrahedron Lett. 1985, 26, 4647-4648; (f) Ito, Y.; Kobayashi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron 1989, 45, 5767-5790; (g) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron Lett. 1986, 27, 6241-6244; (h) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron 1988, 44, 2149-2165.
44. A number of stereoselective reductions of 3-acetyl azetidinones are reported in the literature. For examples see: (a) Bouffard, F. A.; Christensen, B. G. J. Org. Chem. 1981, 46, 2208-2212; (b) Reider, P. J.; Grabowski, E. J. J. Tetrahedron Lett. 1982, 23, 2293-2296; (c) Chiba, T.; Nakai, T. Chemistry Lett. 1985, 651-654; (d) Chiba, T.; Nagatsuma, M.; Nakai, T. Chemistry Lett. 1985, 1343-1346; (e) Chiba, T.; Nakai, T. Tetrahedron Lett. 1985, 26, 4647-4648; (f) Ito, Y.; Kobayashi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron 1989, 45, 5767-5790; (g) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron Lett. 1986, 27, 6241-6244; (h) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron 1988, 44, 2149-2165.
45. A number of stereoselective reductions of 3-acetyl azetidinones are reported in the literature. For examples see: (a) Bouffard, F. A.; Christensen, B. G. J. Org. Chem. 1981, 46, 2208-2212; (b) Reider, P. J.; Grabowski, E. J. J. Tetrahedron Lett. 1982, 23, 2293-2296; (c) Chiba, T.; Nakai, T. Chemistry Lett. 1985, 651-654; (d) Chiba, T.; Nagatsuma, M.; Nakai, T. Chemistry Lett. 1985, 1343-1346; (e) Chiba, T.; Nakai, T. Tetrahedron Lett. 1985, 26, 4647-4648; (f) Ito, Y.; Kobayashi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron 1989, 45, 5767-5790; (g) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron Lett. 1986, 27, 6241-6244; (h) Kawabata, T.; Kimura, Y.; Ito, Y.; Terashima, S.; Sasaki, A.; Sunagawa, M. Tetrahedron 1988, 44, 2149-2165.
46. It is worth mentioning that for 3-hydroxyethyl azetidinones neither coupling constants or chemical shifts are useful tools for determining the configuration of the stereogenic centre in every case at the hydroxyethyl chain. See Ref. 18a.
47. All calculations were carried out on a VAX 2000 by using the program package Molen, An Interactive Structure Solution Procedure, Enraf-Nonius, Delft, The Netherlands, 1990.
48. Atom coordinates, anisotropic thermal parameters and tables of bond lengths and angles are deposited at the Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge CB2 1EW, UK.
49. Only in conformer III of compound 15 does H-1″ lie on the plane of the carbonyl group, but this conformer is not significantly present (ΔE=6.23 kcal/mol with respect to A′). (equation presented)
50. The low chelating effect of the potassium ion, further diminished by the high cation solvating ability of methanol, could explain the absence of the chelation effect.
51. Tanner, D.; Somfai, P. Bioorg. Med. Chem. Lett. 1993, 3, 2415-2418.
52. Schmitt, S. M.; Johnston, D. B. R.; Christensen, B. G. J. Org. Chem. 1980, 45, 1142-1148.
53. Grynkiewicz, G.; Burzynska, H. Tetrahedron 1976, 32, 2109-2111.
54. Cardillo, G.; Orena, M.; Sandri, S.; Tomasini C. J. Org. Chem. 1984, 49, 3951-3954.
55. The functionalisation at the C-5 of the pyrrolidin-2-one ring is currently studied according reported methods: (a) Murahashi, S. I.; Naota, T.; Kuwabara, T.; Saito, T.; Kumobayashi, H.; Akutagawa, S. J. Am. Chem. Soc. 1990, 112, 7820-7822; (b) Cainelli, G.; Da Col, M.; Galletti, P.; Giacomini, D. Synlett. 1997, 923-924.
56. The functionalisation at the C-5 of the pyrrolidin-2-one ring is currently studied according reported methods: (a) Murahashi, S. I.; Naota, T.; Kuwabara, T.; Saito, T.; Kumobayashi, H.; Akutagawa, S. J. Am. Chem. Soc. 1990, 112, 7820-7822; (b) Cainelli, G.; Da Col, M.; Galletti, P.; Giacomini, D. Synlett. 1997, 923-924.
57. Johnson, C. K. ORTEP Report ORNL-3794 Oak Ridge National Laboratory, Tennessee, USA, 1965.