Diastereoselective intermolecular addition of the 1,3-dioxolanyl radical to N-acyl aldohydrazones. Asymmetric synthesis of α-amino acid derivatives

Organic Letters

Volumn 5, Issue 14, 2003, Pages 2461-2464

  Fernández, Marta ^a   Alonso, Ricardo ^a  

^a UNIVERSITY OF SANTIAGO DE COMPOSTELA   (Spain)

Author keywords

[No Author keywords available]

Indexed keywords

1,3 DIOXOLANE DERIVATIVE; AMINO ACID DERIVATIVE; HYDRAZONE DERIVATIVE; RADICAL;

ADDITION REACTION; ARTICLE; ASYMMETRIC SYNTHESIS; MOLECULAR INTERACTION; STEREOCHEMISTRY; SYNTHESIS; TEMPERATURE;

AMINO ACIDS; HYDRAZONES; STEREOISOMERISM;

EID: 0141854357     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol034696n     Document Type: Article

References (44)

1. Even fully carbon-substituted C=N double bonds intramolecularly trap alkyl and vinyl radicals in the 1,5-exo ((a) Noya, B.; Alonso, R. Tetrahedron Lett. 1997, 38, 2745-2748. (b) Noya, B.; Paredes, M. D.; Ozores, L.; Alonso, R. J. Org. Chem. 2000, 65, 5960-5968.) and 1,6-exo modes (unpublished).
2. Even fully carbon-substituted C=N double bonds intramolecularly trap alkyl and vinyl radicals in the 1,5-exo ((a) Noya, B.; Alonso, R. Tetrahedron Lett. 1997, 38, 2745-2748. (b) Noya, B.; Paredes, M. D.; Ozores, L.; Alonso, R. J. Org. Chem. 2000, 65, 5960-5968.) and 1,6-exo modes (unpublished).
3. For a review on free radical cyclizations involving nitrogen, including a compilation of cyclization and ring-opening rate constants for some representative cases, see: Fallis, A. G.; Brinza, I. M. Tetrahedron 1997, 53, 17543-17594.
4. For a review on the addition of carbon-centered radicals to imines and related compounds, see: Friestad, G. K. Tetrahedron 2001, 57, 5461-5496.
5. Although most examples apply to the addition at the C atom of the C=N bond, intramolecular addition at nitrogen is also known and synthetically useful; see: (a) Viswanathan, R.; Prabhakaran, E. N.; Plotkin, M. A.; Johnston, J. N. J. Am. Chem. Soc. 2003, 125, 163-168. (b) Falzon, C. T.; Ryu, I.; Schiesser, C. H. Chem. Commun. 2002, 2338-2339 and references therein. See also refs 2 and 3.
6. Although most examples apply to the addition at the C atom of the C=N bond, intramolecular addition at nitrogen is also known and synthetically useful; see: (a) Viswanathan, R.; Prabhakaran, E. N.; Plotkin, M. A.; Johnston, J. N. J. Am. Chem. Soc. 2003, 125, 163-168. (b) Falzon, C. T.; Ryu, I.; Schiesser, C. H. Chem. Commun. 2002, 2338-2339 and references therein. See also refs 2 and 3.
7. 2C=NOR): (a) Hart, D. J.; Seely, F. L. J. Am. Chem. Soc. 1988, 110, 1631-1633. (b) Hanamoto, T.; Inanaga, J. Tetrahedron Lett. 1991, 32, 3555-3556.
8. 2C=NOR): (a) Hart, D. J.; Seely, F. L. J. Am. Chem. Soc. 1988, 110, 1631-1633. (b) Hanamoto, T.; Inanaga, J. Tetrahedron Lett. 1991, 32, 3555-3556.
9. For a detailed account, see ref 3, pp 5481-5492. See also ref 7.
10. Compounds where a C=N bond activated by electron-withdrawing substituents successfully traps carbon radicals intermolecularly include the following. α-Sulfonyl oxime ethers: (a) Kim, S.; Song, H.-J.; Choi, T.-L. ; Yoon, J.-Y. Angew. Chem., Int. Ed. 2001, 40, 2524-2526. (b) Kim, S.; Yoon, J.-Y. J. Am. Chem. Soc. 1997, 119, 5982-5983. (c) Kim, S.; Lee, I. Y.; Yoon, J.-Y.; Oh, D. H. J. Am. Chem. Soc. 1996, 118, 5138-5139. Glyoxylic aldoxime ethers: (d) Miyabe, H.; Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454-1455. (e) Miyabe, H.; Ushiro, C.; Ueda, M.; Yamakawa, K.; Naito, T. J. Org. Chem. 2000, 65, 176-185. Glyoxylic aldimines: (f) Bertrand, M. P.; Coantic, S. ; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951-3961 and references therein. Glyoxylic aldonitrones: (g) Ueda, M.; Miyabe, H.; Teramachi, M.; Miyata, O.; Naito, T. Chem. Commun. 2003, 426-427. N-Sulfonylimines: (h) Miyabe, H.; Ueda, M.; Naito, T. Chem. Commun. 2000, 2059-2060.
11. Compounds where a C=N bond activated by electron-withdrawing substituents successfully traps carbon radicals intermolecularly include the following. α-Sulfonyl oxime ethers: (a) Kim, S.; Song, H.-J.; Choi, T.-L. ; Yoon, J.-Y. Angew. Chem., Int. Ed. 2001, 40, 2524-2526. (b) Kim, S.; Yoon, J.-Y. J. Am. Chem. Soc. 1997, 119, 5982-5983. (c) Kim, S.; Lee, I. Y.; Yoon, J.-Y.; Oh, D. H. J. Am. Chem. Soc. 1996, 118, 5138-5139. Glyoxylic aldoxime ethers: (d) Miyabe, H.; Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454-1455. (e) Miyabe, H.; Ushiro, C.; Ueda, M.; Yamakawa, K.; Naito, T. J. Org. Chem. 2000, 65, 176-185. Glyoxylic aldimines: (f) Bertrand, M. P.; Coantic, S. ; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951-3961 and references therein. Glyoxylic aldonitrones: (g) Ueda, M.; Miyabe, H.; Teramachi, M.; Miyata, O.; Naito, T. Chem. Commun. 2003, 426-427. N-Sulfonylimines: (h) Miyabe, H.; Ueda, M.; Naito, T. Chem. Commun. 2000, 2059-2060.
12. Compounds where a C=N bond activated by electron-withdrawing substituents successfully traps carbon radicals intermolecularly include the following. α-Sulfonyl oxime ethers: (a) Kim, S.; Song, H.-J.; Choi, T.-L. ; Yoon, J.-Y. Angew. Chem., Int. Ed. 2001, 40, 2524-2526. (b) Kim, S.; Yoon, J.-Y. J. Am. Chem. Soc. 1997, 119, 5982-5983. (c) Kim, S.; Lee, I. Y.; Yoon, J.-Y.; Oh, D. H. J. Am. Chem. Soc. 1996, 118, 5138-5139. Glyoxylic aldoxime ethers: (d) Miyabe, H.; Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454-1455. (e) Miyabe, H.; Ushiro, C.; Ueda, M.; Yamakawa, K.; Naito, T. J. Org. Chem. 2000, 65, 176-185. Glyoxylic aldimines: (f) Bertrand, M. P.; Coantic, S. ; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951-3961 and references therein. Glyoxylic aldonitrones: (g) Ueda, M.; Miyabe, H.; Teramachi, M.; Miyata, O.; Naito, T. Chem. Commun. 2003, 426-427. N-Sulfonylimines: (h) Miyabe, H.; Ueda, M.; Naito, T. Chem. Commun. 2000, 2059-2060.
13. Compounds where a C=N bond activated by electron-withdrawing substituents successfully traps carbon radicals intermolecularly include the following. α-Sulfonyl oxime ethers: (a) Kim, S.; Song, H.-J.; Choi, T.-L. ; Yoon, J.-Y. Angew. Chem., Int. Ed. 2001, 40, 2524-2526. (b) Kim, S.; Yoon, J.-Y. J. Am. Chem. Soc. 1997, 119, 5982-5983. (c) Kim, S.; Lee, I. Y.; Yoon, J.-Y.; Oh, D. H. J. Am. Chem. Soc. 1996, 118, 5138-5139. Glyoxylic aldoxime ethers: (d) Miyabe, H.; Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454-1455. (e) Miyabe, H.; Ushiro, C.; Ueda, M.; Yamakawa, K.; Naito, T. J. Org. Chem. 2000, 65, 176-185. Glyoxylic aldimines: (f) Bertrand, M. P.; Coantic, S. ; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951-3961 and references therein. Glyoxylic aldonitrones: (g) Ueda, M.; Miyabe, H.; Teramachi, M.; Miyata, O.; Naito, T. Chem. Commun. 2003, 426-427. N-Sulfonylimines: (h) Miyabe, H.; Ueda, M.; Naito, T. Chem. Commun. 2000, 2059-2060.
14. Compounds where a C=N bond activated by electron-withdrawing substituents successfully traps carbon radicals intermolecularly include the following. α-Sulfonyl oxime ethers: (a) Kim, S.; Song, H.-J.; Choi, T.-L. ; Yoon, J.-Y. Angew. Chem., Int. Ed. 2001, 40, 2524-2526. (b) Kim, S.; Yoon, J.-Y. J. Am. Chem. Soc. 1997, 119, 5982-5983. (c) Kim, S.; Lee, I. Y.; Yoon, J.-Y.; Oh, D. H. J. Am. Chem. Soc. 1996, 118, 5138-5139. Glyoxylic aldoxime ethers: (d) Miyabe, H.; Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454-1455. (e) Miyabe, H.; Ushiro, C.; Ueda, M.; Yamakawa, K.; Naito, T. J. Org. Chem. 2000, 65, 176-185. Glyoxylic aldimines: (f) Bertrand, M. P.; Coantic, S. ; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951-3961 and references therein. Glyoxylic aldonitrones: (g) Ueda, M.; Miyabe, H.; Teramachi, M.; Miyata, O.; Naito, T. Chem. Commun. 2003, 426-427. N-Sulfonylimines: (h) Miyabe, H.; Ueda, M.; Naito, T. Chem. Commun. 2000, 2059-2060.
15. Compounds where a C=N bond activated by electron-withdrawing substituents successfully traps carbon radicals intermolecularly include the following. α-Sulfonyl oxime ethers: (a) Kim, S.; Song, H.-J.; Choi, T.-L. ; Yoon, J.-Y. Angew. Chem., Int. Ed. 2001, 40, 2524-2526. (b) Kim, S.; Yoon, J.-Y. J. Am. Chem. Soc. 1997, 119, 5982-5983. (c) Kim, S.; Lee, I. Y.; Yoon, J.-Y.; Oh, D. H. J. Am. Chem. Soc. 1996, 118, 5138-5139. Glyoxylic aldoxime ethers: (d) Miyabe, H.; Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454-1455. (e) Miyabe, H.; Ushiro, C.; Ueda, M.; Yamakawa, K.; Naito, T. J. Org. Chem. 2000, 65, 176-185. Glyoxylic aldimines: (f) Bertrand, M. P.; Coantic, S. ; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951-3961 and references therein. Glyoxylic aldonitrones: (g) Ueda, M.; Miyabe, H.; Teramachi, M.; Miyata, O.; Naito, T. Chem. Commun. 2003, 426-427. N-Sulfonylimines: (h) Miyabe, H.; Ueda, M.; Naito, T. Chem. Commun. 2000, 2059-2060.
16. Compounds where a C=N bond activated by electron-withdrawing substituents successfully traps carbon radicals intermolecularly include the following. α-Sulfonyl oxime ethers: (a) Kim, S.; Song, H.-J.; Choi, T.-L. ; Yoon, J.-Y. Angew. Chem., Int. Ed. 2001, 40, 2524-2526. (b) Kim, S.; Yoon, J.-Y. J. Am. Chem. Soc. 1997, 119, 5982-5983. (c) Kim, S.; Lee, I. Y.; Yoon, J.-Y.; Oh, D. H. J. Am. Chem. Soc. 1996, 118, 5138-5139. Glyoxylic aldoxime ethers: (d) Miyabe, H.; Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454-1455. (e) Miyabe, H.; Ushiro, C.; Ueda, M.; Yamakawa, K.; Naito, T. J. Org. Chem. 2000, 65, 176-185. Glyoxylic aldimines: (f) Bertrand, M. P.; Coantic, S. ; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951-3961 and references therein. Glyoxylic aldonitrones: (g) Ueda, M.; Miyabe, H.; Teramachi, M.; Miyata, O.; Naito, T. Chem. Commun. 2003, 426-427. N-Sulfonylimines: (h) Miyabe, H.; Ueda, M.; Naito, T. Chem. Commun. 2000, 2059-2060.
17. Compounds where a C=N bond activated by electron-withdrawing substituents successfully traps carbon radicals intermolecularly include the following. α-Sulfonyl oxime ethers: (a) Kim, S.; Song, H.-J.; Choi, T.-L. ; Yoon, J.-Y. Angew. Chem., Int. Ed. 2001, 40, 2524-2526. (b) Kim, S.; Yoon, J.-Y. J. Am. Chem. Soc. 1997, 119, 5982-5983. (c) Kim, S.; Lee, I. Y.; Yoon, J.-Y.; Oh, D. H. J. Am. Chem. Soc. 1996, 118, 5138-5139. Glyoxylic aldoxime ethers: (d) Miyabe, H.; Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454-1455. (e) Miyabe, H.; Ushiro, C.; Ueda, M.; Yamakawa, K.; Naito, T. J. Org. Chem. 2000, 65, 176-185. Glyoxylic aldimines: (f) Bertrand, M. P.; Coantic, S. ; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951-3961 and references therein. Glyoxylic aldonitrones: (g) Ueda, M.; Miyabe, H.; Teramachi, M.; Miyata, O.; Naito, T. Chem. Commun. 2003, 426-427. N-Sulfonylimines: (h) Miyabe, H.; Ueda, M.; Naito, T. Chem. Commun. 2000, 2059-2060.
18. Friestad recently introduced 2-oxazolidinones as auxiliaries for the asymmetric synthesis of amines: (a) Friestad, G. K.; Qin, J. J. Am. Chem. Soc. 2001, 123, 9922-9923. (b) Friestad, G. K.; Qin, J. J. Am. Chem. Soc. 2000, 122, 8329-8330.
19. Friestad recently introduced 2-oxazolidinones as auxiliaries for the asymmetric synthesis of amines: (a) Friestad, G. K.; Qin, J. J. Am. Chem. Soc. 2001, 123, 9922-9923. (b) Friestad, G. K.; Qin, J. J. Am. Chem. Soc. 2000, 122, 8329-8330.
20. We have recently demonstrated that the use of α-oxygenated carbon radicals in intermolecular radical addition is particularly convenient, so that even fully carbon-substituted ketoxime ethers efficiently trap them: Torrente, S.; Alonso, R. Org. Lett. 2001, 3, 1985-1987. In these cases, and as an additional synthetic advantage, the addition results in higher functionalized adducts. See also: (a) Yamada, K.; Fujihara, H.; Yamamoto, Y.; Miwa, Y.; Taga, T.; Tomioka, K. Org. Lett. 2002, 4, 3509-3511. (b) Kim, S.; Kim, N.; Chung, W.; Cho, C. H. Synlett 2001, 937-940.
21. We have recently demonstrated that the use of α-oxygenated carbon radicals in intermolecular radical addition is particularly convenient, so that even fully carbon-substituted ketoxime ethers efficiently trap them: Torrente, S.; Alonso, R. Org. Lett. 2001, 3, 1985-1987. In these cases, and as an additional synthetic advantage, the addition results in higher functionalized adducts. See also: (a) Yamada, K.; Fujihara, H.; Yamamoto, Y.; Miwa, Y.; Taga, T.; Tomioka, K. Org. Lett. 2002, 4, 3509-3511. (b) Kim, S.; Kim, N.; Chung, W.; Cho, C. H. Synlett 2001, 937-940.
22. We have recently demonstrated that the use of α-oxygenated carbon radicals in intermolecular radical addition is particularly convenient, so that even fully carbon-substituted ketoxime ethers efficiently trap them: Torrente, S.; Alonso, R. Org. Lett. 2001, 3, 1985-1987. In these cases, and as an additional synthetic advantage, the addition results in higher functionalized adducts. See also: (a) Yamada, K.; Fujihara, H.; Yamamoto, Y.; Miwa, Y.; Taga, T.; Tomioka, K. Org. Lett. 2002, 4, 3509-3511. (b) Kim, S.; Kim, N.; Chung, W.; Cho, C. H. Synlett 2001, 937-940.
23. For details see Supporting Information.
24. Use of an external activating agent was found to be mandatory for the intermolecular addition of plain carbon radicals to inactivated N-acylhydrazones: see ref 8.
25. For the nonasymmetric one-pot intermolecular radical addition to aldimines derived from aromatic aldehydes, see: Yamada, K.; Yamamoto, Y.; Tomioka, K. Org. Lett. 2003, 5, 1797-1799.
26. S)-3-Amino-4-benzyl-1,3-oxazolan-2-one (7S) was prepared from commercial (S)-4-benzyl-1,3-oxazolan-2-one (Supporting Information). For a recent work on the comparison of electrophilic amination reagents for N-amination of 2-oxazolidinones, see: Shen, Y.; Friestad, G. K. J. Org. Chem. 2002, 67, 6236-6239.
27. Numerous methods have been reported for the reductive cleavage of N-N bonds; see: Enders, D.; Lochtman, R.; Meiers, M.; Müller, S.; Lazny, R. Synlett 1998, 1182-1184 and references therein.
28. Deslongchamps and Moreau first reported that aldehyde acetals reacted with ozone to give esters in high yield: Deslongchamps, P.; Moreau, C. Can. J. Chem. 1971, 49, 2465-2467. For additional methods, see: Curini, M.; Epifano, F. ; Marcotullio, M. C.; Rosati, O. Synlett 1999, 777-779 and references therein.
29. Deslongchamps and Moreau first reported that aldehyde acetals reacted with ozone to give esters in high yield: Deslongchamps, P.; Moreau, C. Can. J. Chem. 1971, 49, 2465-2467. For additional methods, see: Curini, M.; Epifano, F. ; Marcotullio, M. C.; Rosati, O. Synlett 1999, 777-779 and references therein.
30. Commercially available (R)-2-aminobutanoic acid was converted to 10 according to: Nosho, Y.; Seki, T.; Kondo, M.; Ohfuji, T.; Tamura, M.; Okai, H. J. Agric. Food Chem. 1990, 38, 1368-1373.
31. Access to the enantiomer of 10 would be possible starting with 7R, accessible in turn from (R)-4-benzyl-1,3-oxazolan-2-one (see ref 13), which is also commercially available at approximately the same price as its enantiomer.
32. First stereocontrolled synthesis of (S)-cleonin and related cyclopropyl-substituted amino acids has been recently published: Esposito, A.; Piras, P. P.; Ramazzotti, D.; Taddei, M. Org. Lett. 2001, 3, 3273-3275.
33. For the first asymmetric synthesis of (R)- and (S)-2-amino-3,3-dimethoxypropanoic acid (α-formylgycine dimethylacetal), including references for its previous use in synthesis, see: DeMong, D. E.; Williams, R. M. Tetrahedron Lett. 2002, 43, 2355-2357.
34. Although still not tested, controlled oxidation of 5c should only affect the dioxolane ring, as acyclic dialkoxy acetals react much more slowly than cyclic ones due to stereoelectronic control: (a) Deslongchamps, P.; Atlani, P.; Frehel, D.; Malaval, A.; Moreau, C. Can. J. Chem. 1974, 52, 3651-3664. See also: (b) Li, S.; Deslongchamps, P. Tetrahedron Lett. 1993, 34, 7759-7762, (c) Sueda, T.; Fukuda, S.; Ochiai, M. Org. Lett. 2001, 3, 2387-2390. (d) Plesničar, B.; Cerkovnik, J.; Tuttle, T.; Kraka, E.; Cremer, D. J. Am. Chem. Soc. 2002, 124, 11260-11261 and references therein. See also ref 15.
35. Although still not tested, controlled oxidation of 5c should only affect the dioxolane ring, as acyclic dialkoxy acetals react much more slowly than cyclic ones due to stereoelectronic control: (a) Deslongchamps, P.; Atlani, P.; Frehel, D.; Malaval, A.; Moreau, C. Can. J. Chem. 1974, 52, 3651-3664. See also: (b) Li, S.; Deslongchamps, P. Tetrahedron Lett. 1993, 34, 7759-7762, (c) Sueda, T.; Fukuda, S.; Ochiai, M. Org. Lett. 2001, 3, 2387-2390. (d) Plesničar, B.; Cerkovnik, J.; Tuttle, T.; Kraka, E.; Cremer, D. J. Am. Chem. Soc. 2002, 124, 11260-11261 and references therein. See also ref 15.
36. Although still not tested, controlled oxidation of 5c should only affect the dioxolane ring, as acyclic dialkoxy acetals react much more slowly than cyclic ones due to stereoelectronic control: (a) Deslongchamps, P.; Atlani, P.; Frehel, D.; Malaval, A.; Moreau, C. Can. J. Chem. 1974, 52, 3651-3664. See also: (b) Li, S.; Deslongchamps, P. Tetrahedron Lett. 1993, 34, 7759-7762, (c) Sueda, T.; Fukuda, S.; Ochiai, M. Org. Lett. 2001, 3, 2387-2390. (d) Plesničar, B.; Cerkovnik, J.; Tuttle, T.; Kraka, E.; Cremer, D. J. Am. Chem. Soc. 2002, 124, 11260-11261 and references therein. See also ref 15.
37. Although still not tested, controlled oxidation of 5c should only affect the dioxolane ring, as acyclic dialkoxy acetals react much more slowly than cyclic ones due to stereoelectronic control: (a) Deslongchamps, P.; Atlani, P.; Frehel, D.; Malaval, A.; Moreau, C. Can. J. Chem. 1974, 52, 3651-3664. See also: (b) Li, S.; Deslongchamps, P. Tetrahedron Lett. 1993, 34, 7759-7762, (c) Sueda, T.; Fukuda, S.; Ochiai, M. Org. Lett. 2001, 3, 2387-2390. (d) Plesničar, B.; Cerkovnik, J.; Tuttle, T.; Kraka, E.; Cremer, D. J. Am. Chem. Soc. 2002, 124, 11260-11261 and references therein. See also ref 15.
38. Aldehydes 6d and 6e were selected as potential precursors of aromatic and heteroaromatic α-amino acids, preparation of which in enantiomerically pure form is complicated because of their comparatively easier base-catalyzed epimerization of the acidic α-methine proton. For a recent contribution, see: Saaby, S.; Bayón, P.; Aburel, P. S.; Jørgensen, K. A. J. Org. Chem. 2002, 67, 4352-4361.
39. For a report on the properties of 1,3-dioxolane, including toxicological and environmental issues, see: http://www.epa.gov/chemrtk/dioxlne/c12846.pdf.
40. For a treatise, see: (a) Giese, B. Radicals in Organic Synthesis: Formation of Carbon-Carbon Bonds; Pergamon Press: Oxford, 1986; pp 69-77. Recent work in this field includes: (b) Yoshimitsu, T.; Arano, Y.; Nagaoka, H. J. Org. Chem. 2003, 68, 625-627. (c) Mosca, R.; Fagnoni, M.; Mella, M.; Albini, A. Tetrahedron 2001, 57, 10319-10328. (d) Hirano, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. Chem. Commun. 2000, 2457-2458. (e) Manfrotto, C.; Mella, M.; Freccero, M.; Fagnoni, M.; Albini, A. J. Org. Chem. 1999, 64, 5024-5028.
41. For a treatise, see: (a) Giese, B. Radicals in Organic Synthesis: Formation of Carbon-Carbon Bonds; Pergamon Press: Oxford, 1986; pp 69-77. Recent work in this field includes: (b) Yoshimitsu, T.; Arano, Y.; Nagaoka, H. J. Org. Chem. 2003, 68, 625-627. (c) Mosca, R.; Fagnoni, M.; Mella, M.; Albini, A. Tetrahedron 2001, 57, 10319-10328. (d) Hirano, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. Chem. Commun. 2000, 2457-2458. (e) Manfrotto, C.; Mella, M.; Freccero, M.; Fagnoni, M.; Albini, A. J. Org. Chem. 1999, 64, 5024-5028.
42. For a treatise, see: (a) Giese, B. Radicals in Organic Synthesis: Formation of Carbon-Carbon Bonds; Pergamon Press: Oxford, 1986; pp 69-77. Recent work in this field includes: (b) Yoshimitsu, T.; Arano, Y.; Nagaoka, H. J. Org. Chem. 2003, 68, 625-627. (c) Mosca, R.; Fagnoni, M.; Mella, M.; Albini, A. Tetrahedron 2001, 57, 10319-10328. (d) Hirano, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. Chem. Commun. 2000, 2457-2458. (e) Manfrotto, C.; Mella, M.; Freccero, M.; Fagnoni, M.; Albini, A. J. Org. Chem. 1999, 64, 5024-5028.
43. For a treatise, see: (a) Giese, B. Radicals in Organic Synthesis: Formation of Carbon-Carbon Bonds; Pergamon Press: Oxford, 1986; pp 69-77. Recent work in this field includes: (b) Yoshimitsu, T.; Arano, Y.; Nagaoka, H. J. Org. Chem. 2003, 68, 625-627. (c) Mosca, R.; Fagnoni, M.; Mella, M.; Albini, A. Tetrahedron 2001, 57, 10319-10328. (d) Hirano, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. Chem. Commun. 2000, 2457-2458. (e) Manfrotto, C.; Mella, M.; Freccero, M.; Fagnoni, M.; Albini, A. J. Org. Chem. 1999, 64, 5024-5028.
44. For a treatise, see: (a) Giese, B. Radicals in Organic Synthesis: Formation of Carbon-Carbon Bonds; Pergamon Press: Oxford, 1986; pp 69-77. Recent work in this field includes: (b) Yoshimitsu, T.; Arano, Y.; Nagaoka, H. J. Org. Chem. 2003, 68, 625-627. (c) Mosca, R.; Fagnoni, M.; Mella, M.; Albini, A. Tetrahedron 2001, 57, 10319-10328. (d) Hirano, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. Chem. Commun. 2000, 2457-2458. (e) Manfrotto, C.; Mella, M.; Freccero, M.; Fagnoni, M.; Albini, A. J. Org. Chem. 1999, 64, 5024-5028.