Regio- and Stereoselective Fe(III)- and Pd(0)-Mediated Ring Openings of 3-Aza-2-oxabicyclo[2.2.1]hept-5-ene Systems

Journal of Organic Chemistry

Volumn 63, Issue 15, 1998, Pages 4874-4875

  Mulvihill, Mark J ^a   Surman, Matthew D ^a   Miller, Marvin J ^a  

^a UNIVERSITY OF NOTRE DAME   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0001364588     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo980950r     Document Type: Article

References (45)

1. For accounts of the synthesis and biological importance of related N-hydroxyamino acids, see: (a) Ottenheijm, H. C. J.; Herscheid, J. D. M. Chem. Rev. 1986, 86, 697.
2. (b) Chimiak, A.; Mitewska, M. J. Prog. Chem. Org. Nat. Prod. 1988, 53, 203.
3. (c) Coutts, R. T. Can. J. Pharm. Sci. 1967, 27, 1.
4. (d) Kehl, H., Ed. Chemistry and Biology of Hydroxamic Acids; Karger: Basel, 1982.
5. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
6. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
7. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
8. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
9. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
10. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
11. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
12. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
13. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
14. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
15. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
16. As antibacterial agents, see: (e) Miller, M. J. Acc. Chem. Res. 1986, 19, 49. (f) Neilands, J. B.; Valenta, J. R. In Metal Ions in Biological Systems; Sigel, H., Ed.; Marcel Dekker: New York, 1985; Vol. 19, Chapter 11. (g) Rogers, H. J. In Iron Transport in Microbes, Plants and Animals; Winkelmann, G., van der Helm, D., Neilands, J. B., Eds.; VCH: Weinheim, New York, 1987; Chapter 13. (h) Griffiths, E. In Iron and Infection; Bullen, J. J., Griffiths, E., Eds.; Wiley: New York, 1987; Chapter 3. As antifungal agents, see: (i) Kaczka, E. A.; Gitterman, C. O.; Dulaney, E. L.; Falkers, K. Biochemistry 1962, 1, 340. (j) Young, C. W.; Schachetman, C. S.; Hodas, S.; Bolis, M. C. Cancer Res. 1967, 27, 535. As anticancer agents, see: (k) Neilands, J. B. Bacteriol. Rev. 1957, 21, 101. As specific enzyme inhibitors, see: (1) Umezawa, H.; Aoyagi, T.; Ogawa, K.; Obata, T.; Iinuma, H.; Naganawa, H.; Hamada, M.; Takekuchi, T. J. Antibiot. 1985, 38, 1815. Stewart, A. O.; Martin, J. G. J. Org. Chem. 1989, 54, 1221. (n) Staszak, M. A.; Doecke, C. W. Tetrahedron Lett. 1994, 35, 6021. (o) Currid, P.; Wightman, R. H. Nucleosides Nucleotides 1997, 16, 115. As constituents in siderophores, see: (p) Miller, M. J. Chem. Rev. 1989, 89, 1563.
17. (a) Vogt, P. F.; Miller, M. J. Tetrahedron 1998, 54, 1317.
18. (b) Kirby, G. W. Chem. Soc. Rev. 1977, 6, 1.
19. (c) Kirby, G. W.; Nazeer, M. Tetrahedron Lett. 1988, 29, 6173.
20. (d) Miller, A.; McC. Patterson, T.; Procter G. Synlett 1989, 1, 32.
21. (e) Miller, A.; Procter, G. Tetrahedron Lett. 1990, 30, 1041.
22. (a) Ritter, A. R.; Miller, M. J. J. Org. Chem. 1994, 59, 4602.
23. (b) Zhang, D.; Miller, M. J. J. Org. Chem. 1998, 63, 755.
24. (a) Trost, B. M.; Van Vranken, D. L. J. Am. Chem. Soc. 1993, 115, 444.
25. (b) King, S. B.; Ganem, B. J. Am. Chem. Soc. 1991, 113, 5089.
26. (c) Ledford, B. E.; Carreira, E. M. J. Am. Chem. Soc. 1995, 117, 11811.
27. Keck, G. E.; Fleming, S.; Nickell, D.; Weider, P. Synth. Commun. 1979, 9, 281.
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29. (b) Muxworthy, J. P.; Wilkinson, J. A.; Procter, G. Tetrahedron Lett. 1995, 36, 7535.
30. (c) Muxworthy, J. P.; Wilkinson, J. A.; Procter, G. Tetrahedron Lett. 1995, 36, 7541.
31. Ritter, A. R.; Miller, M. J. Tetrahedron Lett. 1994, 35, 9379.
32. (a) Ghosh, A.; Miller, M. J. Tetrahedron Lett. 1995, 36, 6399.
33. (b) Vogt, P. F.; Hansel, J. G.; Miller, M. J. Tetrahedron Lett. 1997, 38, 2803.
34. (c) Hansel, J. G.; O'Hogan, S.; Lensky, S.; Ritter, A. R.; Miller, M. J. Tetrahedron Lett. 1995, 36, 2913.
35. 2O in 0.5 N HCl), stain dark purple, typical of free hydroxamic acid chelation to Fe(III).
36. For the synthesis of phenylacetohydroxamic acid 1, see: Defoin A.; Fritz, H.; Schmidlin, C.; Streith, J. Helv. Chim. Acta 1987, 70, 554. For the synthesis of cycloadduct 3, see the Supporting Information.
37. See Scheme 2, hydroxamic acid 14, for an example of a 1,2-disubstituted cyclopentene.
38. 1H NMR pattern: δ 1.62 (overlapping ddd, J = 6.6, 6.6, 12.6 Hz, 1H) and 2.38 (overlapping ddd, J = 7.2, 7.2, 12.6 Hz, 1H), clearly displaying cis-coupling.
39. 2;
40. 3-CN, -43°C;
41. 2;
42. HCl, EtOAc.
43. 3 in order to provide a milder, less acidic form of Fe(III).
44. (a) Trost, B. Acc. Chem. Res. 1996, 29, 9 (8), 355.
45. (b) Bäckvall, J. E.; Gatti, R.; Schink, H. E. Synthesis 1993, 51, 727.