Highly regioselective palladium-catalyzed direct arylation of oxazole at C-2 or C-5 with aryl bromides, chlorides, and triflates

Organic Letters

Volumn 12, Issue 16, 2010, Pages 3578-3581

  Strotman, Neil A ^a   Chobanian, Harry R ^a   Guo, Yan ^a   He, Jiafang ^a   Wilson, Jonathan E ^a  

^a MERCK RESEARCH LABORATORIES   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

BROMINATED HYDROCARBON; CHLORINATED HYDROCARBON; MESYLIC ACID DERIVATIVE; OXAZOLE DERIVATIVE; PALLADIUM;

ARTICLE; CATALYSIS; CHEMICAL STRUCTURE; CHEMISTRY; COMBINATORIAL CHEMISTRY; STEREOISOMERISM; SYNTHESIS;

CATALYSIS; COMBINATORIAL CHEMISTRY TECHNIQUES; HYDROCARBONS, BROMINATED; HYDROCARBONS, CHLORINATED; MESYLATES; MOLECULAR STRUCTURE; OXAZOLES; PALLADIUM; STEREOISOMERISM;

EID: 77955667491     PISSN: 15237060     EISSN: 15237052     Source Type: Journal    
DOI: 10.1021/ol1011778     Document Type: Article

References (42)

1. For review articles of oxazole-containing natural products, see
2. Yeh, V. S. C. Tetrahedron 2004, 60, 11995-12042
3. Jin, Z. Nat. Prod. Rep. 2003, 20, 584-605
4. Also known as virginiamycin M1
5. Delpierre, G. R.; Eastwood, F. W.; Cream, G. E.; Kingston, D. G. I.; Sarin, P. S.; Todd, L.; Williams, D. H. Tetrahedron Lett. 1966, 36, 9-372
6. Delpierre, G. R.; Eastwood, F. W.; Gream, G. E.; Kingston, D. G. I.; Sarin, P. S.; Todd, L.; Williams, D. H. J. Chem. Soc. C 1966, 165, 3-1669
7. Looker, A. R.; Littler, B. J.; Blythe, T. A.; Snoonian, J. R.; Ansell, G. K.; Jones, A. D.; Nyce, P.; Chen, M.; Neubert, B. J. Org. Process Res. Dev. 2008, 12, 666-673
8. Strotman, N. A.; Chobanian, H. R.; He, J.; Guo, Y.; Dormer, P. G.; Jones, C. M.; Steves, J. E. J. Org. Chem. 2010, 75, 1733-1739
9. For recent examples of benzoxazole arylation with Cu, Ni, and Pd, respectively, see
10. Do, H.-Q.; Daugulis, O. J. Am. Chem. Soc. 2007, 129, 12404-12405
11. Hachiya, H.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2009, 11, 1737-1740
12. Ackerman, L.; Barfüsser, S.; Pospech, J. Org. Lett. 2010, 12, 724-726
13. Aoyagi, Y.; Inoue, A.; Koizumi, I.; Hashimoto, K. T.; Gohma, K.; Komatsu, J.; Sekine, K.; Miyafuji, A.; Kunoh, J.; Honma, R.; Akita, Y.; Ohta, A. Heterocycles 1992, 33, 257-272
14. C-5 arylation when C-2 is substituted
15. Ohnmacht, S. A.; Mamone, P.; Culshaw, A. J.; Greaney, M. F. Chem. Commun. 2008, 124, 1-1243
16. Pivsa-Art, S.; Satoh, T.; Kawamura, Y.; Miura, M.; Nomura, M. Bull. Chem. Soc. Jpn. 1998, 71, 467-473
17. C-4 arylation when both C-2 and C-5 are substituted: Liegault, B.; Lapointe, D.; Caron, L.; Vlassova, A.; Fagnou, K. J. Org. Chem. 2009, 74, 1826-1834
18. There are several examples of selective C-2 arylation of oxazoles even when C-5 is not substituted, for example
19. Flegeau, E. F.; Popkin, M. E.; Greaney, M. F. Org. Lett. 2008, 10, 2717-2720
20. Verrier, C.; Martin, T.; Hoarau, C.; Marsais, F. J. Org. Chem. 2008, 73, 7383-7386
21. Derridj, F.; Djebbar, S.; Benali-Baitich, O.; Doucet, H. J. Organomet. Chem. 2008, 693, 135-144
22. Hoarau, C.; Du Fou de Kerdaniel, A.; Bracq, N.; Grandclaudon, P.; Couture, A.; Marsais, F. Tetrahedron Lett. 2005, 46, 8573-8577
23. For a general review of direct arylation including C-2/C-5 selective arylation of thiazole and N-alkylimidazoles, see
24. Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107, 174-238
25. Bellina, F.; Rossi, R. Tetrahedron 2009, 65, 10269-10310
26. For related solvent effects with a 3-carboalkoxy furan and thiophene, see: Glover, B.; Harvey, K. A.; Liu, B.; Sharp, M. J.; Tymoschenko, M. F. Org. Lett. 2003, 5, 301-304
27. Except for CataCXium A, every other ligand that we examined showed much lower C-5/C-2 selectivity when arylated with chlorobenzene rather than with bromobenzene.
28. 3.
29. Phenyl tosylate was very poorly reactive.
30. 2-Bromotoluene, 2-bromomesitylene, and 4-bromoanisole all showed incomplete conversion with method B but full conversion with method A.
31. Gorelsky, S. I.; Lapointe, D.; Fagnou, K. J. Am. Chem. Soc. 2008, 130, 10848-10849
32. 1/2 of 17 min: Brown, D. J.; Ghosh, P. B. J. Chem. Soc. B 1969, 270-276
33. The formation of Cu-2-thiazoyl and Cu-2-N-arylimidazoyl intermediates has been implicated in the C-2-selective direct arylation of thiazole and imidazoles
34. Bellina, F.; Cauteruccio, S.; Mannina, L.; Rossi, R.; Viel, S. Eur. J. Org. Chem. 2006, 693
35. Mori, A.; Sekiguchi, A.; Masui, K.; Shimada, T.; Horie, M.; Osakada, K.; Kawamoto, M.; Ikeda, T. J. Am. Chem. Soc. 2003, 125, 1700
36. It has been shown through trapping experiments and spectroscopically that 2-lithiooxazoles and 2-oxazole magnesiates exist predominantly in the ring-opened form
37. Hodges, J. C.; Patt, W. C.; Connolly, C. J. J. Org. Chem. 1991, 56, 449-452
38. Whitney, S. E.; Rickborn, B. J. Org. Chem. 1991, 56, 3058-3063
39. Bayh, O.; Awad, H.; Mongin, F.; Hoarau, C.; Bischoff, L.; Trécourt, F.; Quéguiner, G.; Marsais, F.; Blanco, F.; Abarca, B.; Ballesteros, R. J. Org. Chem. 2005, 70, 5190-5196
40. 3.
41. 2 intermediate followed by reductive elimination. In reactions that are C-5 selective, we have isolated 5,5′-bis-oxazole.
42. Formation of an ArPd(2-oxazole) intermediate may also involve coordination of oxazole to Pd through N or O and subsequent deprotonation.