Multi-step radical spiro-cyclization of an alkynylaryl isothiocyanate

Arkivoc

Volumn 2006, Issue 6, 2006, Pages 6-14

  Minozzi, Matteo ^a   Nanni, Daniele ^a   Zanardi, Giuseppe ^a   Calestani, Gianluca ^b  

^a UNIVERSITY OF BOLOGNA   (Italy)

^b UNIVERSITY OF PARMA   (Italy)

Author keywords

Cyclizations; Isonitriles; Isothiocyanates; Radicals; Rearrangements

Indexed keywords

EID: 31544472852     PISSN: 14246376     EISSN: None     Source Type: Journal    
DOI: None     Document Type: Article

References (43)

1. (a) Leardini, R.; Pedulli, G. F.; Tundo, A.; Zanardi, G. J. Chem. Soc., Chem. Commun. 1984, 1320.
2. (b) Leardini, R.; Nanni, D.; Pedulli, G. F.; Tundo, A.; Zanardi, G. J. Chem. Soc., Perkin Trans. 1 1986, 1591.
3. (c) Leardini, R.; Nanni, D.; Tundo, A.; Zanardi, G. J. Chem. Soc., Chem. Commun. 1989, 757.
4. (d) Leardini, R.; Nanni, D.; Tundo, A.; Zanardi, G. Gazz. Chim. It. 1989, 119, 637.
5. (e) Curran, D. P.; Liu, H. J. Am. Chem. Soc. 1991, 113, 2127.
6. (f) Ryu, I.; Sonoda, N.; Curran, D. P. Chem. Rev. 1996, 96, 177.
7. (g) Josien, H.; Ko, S. -B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67.
8. Other processes involving imidoyl radicals: (a) Nanni, D.; Pareschi, P.; Rizzoli, C.; Sgarabotto, P.; Tundo, A. Tetrahedron 1995, 51, 9045.
9. (b) Nanni, D.; Pareschi, P.; Tundo, A. Tetrahedron Lett. 1996, 37, 9337.
10. (c) Camaggi, C. M.; Leardini, R.; Nanni, D.; Zanardi, G. Tetrahedron 1998, 54, 5587.
11. (d) Leardini, R.; Nanni, D.; Zanardi, G. J. Org. Chem. 2000, 65, 2763.
12. For a review on radical addition to isonitriles see: Nanni, D. in Radicals in Organic Synthesis, Vol. 2 (Renaud, P.; Sibi, M. P., Eds.), Wiley-VCH, Weinheim, 2001, ch 1.3.1, pp. 44-61.
13. (a) Bachi, M. D.; Balanov, A.; Bar-Ner, N. J. Org. Chem. 1994, 59, 7752.
14. (b) Bachi, M. D.; Melman, A. Synlett. 1996, 60.
15. (c) Bachi, M. D.; Melman, A. J. Org. Chem. 1997, 62, 1896.
16. (d) Bachi, M. D.; Melman, A. Pure Appl. Chem. 1998, 70, 259.
17. (a) Leardini, R.; Nanni, D.; Pareschi, P.; Tundo, A.; Zanardi, G. J. Org. Chem. 1997, 62, 8394.
18. (b) Benati, L.; Leardini, R.; Minozzi, M.; Nanni, D.; Spagnolo, P.; Zanardi, G. J. Org. Chem. 2000, 65, 8669.
19. (c) Benati, L.; Calestani, G.; Leardini, R.; Minozzi, M.; Nanni, D.; Spagnolo, P.; Strazzari, S.; Zanardi, G. J. Org. Chem., 2003, 68, 3454.
20. Benati, L.; Leardini, R.; Minozzi, M.; Nanni, D.; Scialpi, R.; Spagnolo, P.; Strazzari, S.; Zanardi, G. Angew. Chem. Int. Ed. 2004, 43, 3598.
21. (a) Minozzi, M.; Nanni, D.; Walton, J. C. Org. Lett. 2003, 5, 901.
22. (b) Minozzi, M.; Nanni, D.; Walton, J. C. J. Org. Chem. 2004, 69, 2056.
23. 1-Substituted vinyl radicals can be linear-π, or bent, rapidly inverting ó-radicals, depending on the substituent. Whereas a TMS group is commonly accepted to give rise to linear radicals, the structure of the 1-phenyl congeners is more debatable - see: (a) Ito, O.; Omuri, R.; Matsuda, M. J. Am. Chem. Soc. 1982, 104, 3934.
24. (b) Benati, L.; Montevecchi, P. C.; Spagnolo, P. J. Chem. Soc., Perkin Trans 1 1991, 2103.
25. (c) Guerra, M. Res. Chem. Intermediat. 1996, 22, 369. This is the reason for a wavy bond being used for the C•Ph connection in radical 5.
26. The 5-endo-trig radical cyclization mode is very uncommon, but in our case it could be thermodynamically favored by the high delocalization of the resulting radical 7. A few bona fide examples of 5-endo-trig radical cyclizations have however been reported; see: (a) Mendenhall, G. D.; Protasiewicz, J. D.; Brown, C. E.; Ingold, K. U.; Lusztyk, J. J. Am. Chem. Soc. 1994, 116, 1718.
27. (b) Sato, T.; Machigashira, N.; Ishibashi, H.; Ikeda, M. Heterocycles 1992, 33, 139.
28. (c) Ishibashi, H.; Nakamura, N.; Sato, T.; Takeuchi, M.; Ikeda, M. Tetrahedron Lett. 1991, 32, 1725.
29. (d) Sato, T.; Nakamura, N.; Ikeda, K.; Okada, M.; Ishibashi, H.; Ikeda, M. J. Chem. Soc., Perkin Trans. 1 1992, 2399.
30. For recent examples of hydrogen translocation to vinyl radicals, see: (a) Capella, L.; Montevecchi, P. C.; Navacchia, M. L. J. Org. Chem. 1996, 61, 6783.
31. (b) Montevecchi, P. C.; Navacchia, M. L. J. Org. Chem. 1997, 62, 5600.
32. (c) Kunishima, M.; Hioki, K.; Kono, K.; Kato, A.; Tani, S. J. Org. Chem. 1997, 62, 7542.
33. (d) Sha, C. -K.; Ho, W. -Y.; Mohanakrishnan, A. K.; Lin, C. -L.; Chu, S. -Y. C. R. Acad. Sci. Paris 2001, 4, 439.
34. -1; for theoretical studies, see: Huang, X. L.; Dannenberg, J. J. J. Org. Chem. 1991, 56, 5421.
35. Viskolcz, B.; Lendvay, G.; Seres, L. J. Phys. Chem. A 1997, 101, 7119.
36. •--- H distances (1.311 and 1.415 Å, respectively) and the C-H---C angle (160.5° ) are consistent with other calculated transition states for 1,5-H rearrangements of alkyl radicals (ref. 11): see also the Supporting Information.
37. When the thiol was all added to the starting reaction mixture the results reported in the text were obtained; when the thiol was added slowly in two hours by a syringe pump, the quinoline 10 and compound 2 were the only reaction products. The formation of the quinoline 10 has not been rationalized yet. The ability of isonitriles to behave like hydrogen-atom abstractors (see ref. 2a) suggests that 9 could abstract a hydrogen from radical 7 to afford the final spiro-compound 2 and, concomitantly, an imidoyl radical that might cyclize onto the C-C triple bond to give 10. This explanation, however, can only partially explain our result, since it should involve the formation of comparable amounts of 10 and 2, that is not our case. Quinoline 10 is not in any case the result of an electrocyclization process of isonitrile 9, since no trace of 10 was obtained when 9 was refluxed in benzene for several hours in the absence of other reagents.
38. (a) Feray, L.; Kuznetsov, N.; Renaud, P. in Radicals in Organic Synthesis, Vol. 2 (Renaud, P. and Sibi, M. P. Eds.), Wiley-VCH, Weinheim, 2001, pp. 246-278.
39. (b) Bertrand, M. P.; Ferreri, C. in Radicals in Organic Synthesis, Vol. 2 (Renaud, P. and Sibi, M. P. Eds.), Wiley-VCH, Weinheim, 2001, pp. 485-504.
40. Castro, C. E.; Gaughan, E. J.; Owsley, D. C. J. Org. Chem. 1966, 31, 4071.
41. (a) Suginome, M.; Fukuda, T.; Ito, Y. Org. Lett. 1999, 1, 1977.
42. (b) Rainier, J. D.; Kennedy, A. R.; Chase, E. Tetrahedron Lett. 1999, 40, 6325.
43. Mongin, F.; Mojovic, L.; Guillamet, B.; Trécourt, F.; Quéguiner, G. J. Org. Chem. 2002, 67, 8991.