Microwave-promoted palladium-catalyzed coupling reactions

Journal of Organic Chemistry

Volumn 61, Issue 26, 1996, Pages 9582-9584

  Larhed, Mats ^a   Hallberg, Anders ^a  

^a UPPSALA UNIVERSITY   (Sweden)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000153468     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo9612990     Document Type: Article

References (83)

1. For reviews on the Heck reaction see: (a) Heck, R. F. Org. React. 1982, 27, 345.
2. (b) Trost, B. M.; Verhoeven, T. R. Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 8, pp 854.
3. (c) Heck, R. F. Palladium Reagents in Organic Synthesis; Academic Press: London, 1985; pp 276.
4. (d) Heck, R. F. Comprehensive Organic Synthesis; Trost, B. M., Flemming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 4, pp 833.
5. (e) de Meijere, A.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994, 33, 2379.
6. (f) Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2.
7. (g) Tsuji, J. Palladium Reagents and Catalysts: Innovations in Organic Chemistry; John Wiley & Sons: Chichester, 1995; pp 125.
8. For Heck arylation of heteroatom-substituted double bonds see: (h) Daves, G. D., Jr.; Hallberg, A. Chem. Rev. 1989, 89, 1433.
9. 4NCl, may have a favorable effect on the reaction temperature, (a) Jeffery, T. J. Chem. Soc., Chem. Commun. 1984, 1287. (b) Larock, R. C. Pure Appl. Chem. 1990, 62, 653. (c) Jeffery, T. Tetrahedron 1996, 52, 10113.
10. 4NCl, may have a favorable effect on the reaction temperature, (a) Jeffery, T. J. Chem. Soc., Chem. Commun. 1984, 1287. (b) Larock, R. C. Pure Appl. Chem. 1990, 62, 653. (c) Jeffery, T. Tetrahedron 1996, 52, 10113.
11. 4NCl, may have a favorable effect on the reaction temperature, (a) Jeffery, T. J. Chem. Soc., Chem. Commun. 1984, 1287. (b) Larock, R. C. Pure Appl. Chem. 1990, 62, 653. (c) Jeffery, T. Tetrahedron 1996, 52, 10113.
12. High pressure is known to accelerate the Heck reaction. (a) Voigt, K.; Schick, U.; Meyer, F. E.; de Meijere, A. Synlett 1994, 189. (b) Sugihara, T.; Takebayashi, M.; Kaneko, C. Tetrahedron Lett. 1995, 36, 5547.
13. High pressure is known to accelerate the Heck reaction. (a) Voigt, K.; Schick, U.; Meyer, F. E.; de Meijere, A. Synlett 1994, 189. (b) Sugihara, T.; Takebayashi, M.; Kaneko, C. Tetrahedron Lett. 1995, 36, 5547.
14. Arylation of electron-rich olefins employing bidentate nitrogen ligands were performed at 40 °C. (a) Cabri, W.; Candiani, I.; Bedeschi, A.; Santi, R. Synlett 1992, 871. (b) Cabri, W.; Candiani, I.; Bedeschi, A. J. Org. Chem. 1993, 58, 7421.
15. Arylation of electron-rich olefins employing bidentate nitrogen ligands were performed at 40 °C. (a) Cabri, W.; Candiani, I.; Bedeschi, A.; Santi, R. Synlett 1992, 871. (b) Cabri, W.; Candiani, I.; Bedeschi, A. J. Org. Chem. 1993, 58, 7421.
16. (a) Herrmann, W. A.; Brossmer, C.; Öfele, K.; Beller, M.; Fischer, H. J. Mol. Catal. A: Chem. 1995, 103 133.
17. 3P. Herrmann, W. A.; Brossmer, C.; Öfele, K.; Reisinger, C. P.; Priermeier, T.; Beller, M.; Fischer, H. Angew. Chem., Int. Ed. Engl. 1995, 34, 1844.
18. Heck reactions can be carried out with aryl chlorides at 140-160 °C when electron-rich chelating ligands are used. (a) Ben-David, Y.; Portnoy, M.; Gozin, M.; Milstein, D. Organometallics 1992, 11, 1995, (b) Portnoy, M.; Ben-David, Y.; Milstein, D. Organometallics 1993, 12, 4734, (c) Portnoy, M.; Ben-David, Y.; Rousso, I.; Milstein, D. Organometallics 1994, 13, 3465.
19. Heck reactions can be carried out with aryl chlorides at 140-160 °C when electron-rich chelating ligands are used. (a) Ben-David, Y.; Portnoy, M.; Gozin, M.; Milstein, D. Organometallics 1992, 11, 1995, (b) Portnoy, M.; Ben-David, Y.; Milstein, D. Organometallics 1993, 12, 4734, (c) Portnoy, M.; Ben-David, Y.; Rousso, I.; Milstein, D. Organometallics 1994, 13, 3465.
20. Heck reactions can be carried out with aryl chlorides at 140-160 °C when electron-rich chelating ligands are used. (a) Ben-David, Y.; Portnoy, M.; Gozin, M.; Milstein, D. Organometallics 1992, 11, 1995, (b) Portnoy, M.; Ben-David, Y.; Milstein, D. Organometallics 1993, 12, 4734, (c) Portnoy, M.; Ben-David, Y.; Rousso, I.; Milstein, D. Organometallics 1994, 13, 3465.
21. For recent reviews, see: (a) Hermkens, P. H. H.; Ottenheijm, H. C. J.; Rees, D. Tetrahedron 1996, 52, 4527. (b) Früchtel, J. S.; Jung, G. Angew. Chem., Int. Ed. Engl. 1996, 35, 17. (c) DeWitt, S. H.; Czarnik, A. W. Acc. Chem. Res. 1996, 29, 114. (d) Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.; Keating, T. A. Ibid. 1996, 29, 123. (e) Ellman, J. A. Ibid. 1996, 29, 132.
22. For recent reviews, see: (a) Hermkens, P. H. H.; Ottenheijm, H. C. J.; Rees, D. Tetrahedron 1996, 52, 4527. (b) Früchtel, J. S.; Jung, G. Angew. Chem., Int. Ed. Engl. 1996, 35, 17. (c) DeWitt, S. H.; Czarnik, A. W. Acc. Chem. Res. 1996, 29, 114. (d) Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.; Keating, T. A. Ibid. 1996, 29, 123. (e) Ellman, J. A. Ibid. 1996, 29, 132.
23. For recent reviews, see: (a) Hermkens, P. H. H.; Ottenheijm, H. C. J.; Rees, D. Tetrahedron 1996, 52, 4527. (b) Früchtel, J. S.; Jung, G. Angew. Chem., Int. Ed. Engl. 1996, 35, 17. (c) DeWitt, S. H.; Czarnik, A. W. Acc. Chem. Res. 1996, 29, 114. (d) Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.; Keating, T. A. Ibid. 1996, 29, 123. (e) Ellman, J. A. Ibid. 1996, 29, 132.
24. For recent reviews, see: (a) Hermkens, P. H. H.; Ottenheijm, H. C. J.; Rees, D. Tetrahedron 1996, 52, 4527. (b) Früchtel, J. S.; Jung, G. Angew. Chem., Int. Ed. Engl. 1996, 35, 17. (c) DeWitt, S. H.; Czarnik, A. W. Acc. Chem. Res. 1996, 29, 114. (d) Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.; Keating, T. A. Ibid. 1996, 29, 123. (e) Ellman, J. A. Ibid. 1996, 29, 132.
25. For recent reviews, see: (a) Hermkens, P. H. H.; Ottenheijm, H. C. J.; Rees, D. Tetrahedron 1996, 52, 4527. (b) Früchtel, J. S.; Jung, G. Angew. Chem., Int. Ed. Engl. 1996, 35, 17. (c) DeWitt, S. H.; Czarnik, A. W. Acc. Chem. Res. 1996, 29, 114. (d) Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.; Keating, T. A. Ibid. 1996, 29, 123. (e) Ellman, J. A. Ibid. 1996, 29, 132.
26. (f) Gordon, E. M.; Gallop, M. A.; Patel, D. V. Ibid. 1996, 29, 144.
27. (g) Thompson, L. A.; Ellman, J. A. Chem. Rev. 1996, 96, 555.
28. (a) Mingos, D. M. P.; Baghurst, D. R. Chem. Soc. Rev. 1991, 20, 1.
29. (b) Abramovitch, R. A. Org. Prep. Proc. Int. 1991, 23, 683.
30. (c) Loupy, A.; Bram, G.; Sansoulet, J. New J. Chem. 1992, 16, 233.
31. (d) Strauss, C. R.; Trainer, R. W. Aust. J. Chem. 1995, 48, 1665.
32. (e) Caddick, S. Tetrahedron 1995, 51, 10403. For a theoretical background see also:
33. (f) Neas, E. D.; Collins, M. J. Introduction to Microwave Sample Preparation; Kingston, H. M., Jassie, L. B., Eds.; American Chemical Society: Washington, DC, 1988; p 7.
34. (a) Bose, A. K.; Banik, B. K.; Barakat, K. J.; Manhas, M. S. Synlett 1993, 575.
35. (b) Leskovsek, S.; Smidovnik, A.; Koloini, T. J. Org. Chem. 1994, 59, 7433.
36. Abramovitch, R. A.; Abramovitch, D. A.; Iyanar, K.; Tamareselvy, K. Tetrahedron Lett. 1991, 32, 5251.
37. Adámek, F.; Hájek, M. Tetrahedron Lett. 1992, 33, 2039.
38. Kundu, M. K.; Mukherjee, S. B.; Balu, N.; Padmakumar, R.; Bhat, S. V. Synlett 1994, 444. See also ref 8d.
39. For reviews on the Suzuki reaction see: (a) Martin, A. R.; Yang, Y. Acta Chem., Scand. 1993, 47, 221. (b) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
40. For reviews on the Suzuki reaction see: (a) Martin, A. R.; Yang, Y. Acta Chem., Scand. 1993, 47, 221. (b) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
41. For reviews on the Stille reaction see; (a) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (b) Michell, T. N. Synthesis 1992, 803. (c) Ritter, K. Synthesis 1993, 735. (d) Farina, V. Pure Appl. Chem. 1996, 68, 73.
42. For reviews on the Stille reaction see; (a) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (b) Michell, T. N. Synthesis 1992, 803. (c) Ritter, K. Synthesis 1993, 735. (d) Farina, V. Pure Appl. Chem. 1996, 68, 73.
43. For reviews on the Stille reaction see; (a) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (b) Michell, T. N. Synthesis 1992, 803. (c) Ritter, K. Synthesis 1993, 735. (d) Farina, V. Pure Appl. Chem. 1996, 68, 73.
44. For reviews on the Stille reaction see; (a) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (b) Michell, T. N. Synthesis 1992, 803. (c) Ritter, K. Synthesis 1993, 735. (d) Farina, V. Pure Appl. Chem. 1996, 68, 73.
45. A solvent with a high dipole moment (more correctly; a high dielectric loss tangent) is beneficial for efficient absorption of microwave energy. Trialkylamines are known to couple less effectively with microwave radiation than DMF. Gedye, R. N.; Smith, F. E.; Westaway, K. C. Can. J. Chem. 1988, 66, 17. See also ref 8.
46. Heck, R. F.; Nolley, J. P., Jr. J. Org. Chem. 1972, 37, 2320.
47. Patel, B. A.; Ziegler, C. B.; Cortese, N. A.; Plevyak, J. E.; Zebovitz, T. C.; Terpko, M.; Heck, R. F. J. Org. Chem. 1977, 42, 3903.
48. Melpolder, J. B.; Heck, R. F. J. Org. Chem. 1976, 41, 265.
49. Plevyak, J. E.; Dickerson, J. E.; Heck, R. F. J. Org. Chem. 1979, 44, 4078.
50. (a) Cabri, W.; Candiani, I.; Bedeschi, A.; Santi, R. J. Org. Chem. 1990, 55, 3654.
51. (b) Cabri, W.; Candiani, I.; Bedeschi, A.; Penco, S.; Santi, R. J. Org. Chem. 1992, 57, 1481.
52. (a) Andersson, C.-M.; Larsson, J.; Hallberg, A. J. Org. Chem. 1990, 55, 5757.
53. (b) Larhed, M.; Andersson, C.-M.; Hallberg, A. Acta. Chem. Scand. 1993, 47, 212.
54. (c) Larhed, M.; Andersson, C.-M.; Hallberg, A. Tetrahedron 1994, 50, 285.
55. Many Heck arylations are known to proceed smoothly in water or in water/organic solvent mixtures. Leading references. (a) Bumagin, N. A.; More, P. G.; Beletskaya I. P. J. Organomet. Chem. 1989, 371, 397. (b) Genet, J. P.; Blart, E.; Savignac, M. Synlett 1992, 715. (c) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499. (d) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051. (e) Reardon, P.; Metts, S.; Crittendon, C.; Daugherity, P.; Parsons, E. J. Organometallics 1995, 14, 3810. (f) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A: Chem. 1995, 97, 73. See also: (g) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Catal. 1984, 22, 349. (h) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112, 4324.
56. Many Heck arylations are known to proceed smoothly in water or in water/organic solvent mixtures. Leading references. (a) Bumagin, N. A.; More, P. G.; Beletskaya I. P. J. Organomet. Chem. 1989, 371, 397. (b) Genet, J. P.; Blart, E.; Savignac, M. Synlett 1992, 715. (c) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499. (d) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051. (e) Reardon, P.; Metts, S.; Crittendon, C.; Daugherity, P.; Parsons, E. J. Organometallics 1995, 14, 3810. (f) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A: Chem. 1995, 97, 73. See also: (g) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Catal. 1984, 22, 349. (h) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112, 4324.
57. Many Heck arylations are known to proceed smoothly in water or in water/organic solvent mixtures. Leading references. (a) Bumagin, N. A.; More, P. G.; Beletskaya I. P. J. Organomet. Chem. 1989, 371, 397. (b) Genet, J. P.; Blart, E.; Savignac, M. Synlett 1992, 715. (c) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499. (d) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051. (e) Reardon, P.; Metts, S.; Crittendon, C.; Daugherity, P.; Parsons, E. J. Organometallics 1995, 14, 3810. (f) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A: Chem. 1995, 97, 73. See also: (g) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Catal. 1984, 22, 349. (h) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112, 4324.
58. Many Heck arylations are known to proceed smoothly in water or in water/organic solvent mixtures. Leading references. (a) Bumagin, N. A.; More, P. G.; Beletskaya I. P. J. Organomet. Chem. 1989, 371, 397. (b) Genet, J. P.; Blart, E.; Savignac, M. Synlett 1992, 715. (c) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499. (d) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051. (e) Reardon, P.; Metts, S.; Crittendon, C.; Daugherity, P.; Parsons, E. J. Organometallics 1995, 14, 3810. (f) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A: Chem. 1995, 97, 73. See also: (g) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Catal. 1984, 22, 349. (h) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112, 4324.
59. Many Heck arylations are known to proceed smoothly in water or in water/organic solvent mixtures. Leading references. (a) Bumagin, N. A.; More, P. G.; Beletskaya I. P. J. Organomet. Chem. 1989, 371, 397. (b) Genet, J. P.; Blart, E.; Savignac, M. Synlett 1992, 715. (c) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499. (d) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051. (e) Reardon, P.; Metts, S.; Crittendon, C.; Daugherity, P.; Parsons, E. J. Organometallics 1995, 14, 3810. (f) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A: Chem. 1995, 97, 73. See also: (g) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Catal. 1984, 22, 349. (h) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112, 4324.
60. Many Heck arylations are known to proceed smoothly in water or in water/organic solvent mixtures. Leading references. (a) Bumagin, N. A.; More, P. G.; Beletskaya I. P. J. Organomet. Chem. 1989, 371, 397. (b) Genet, J. P.; Blart, E.; Savignac, M. Synlett 1992, 715. (c) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499. (d) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051. (e) Reardon, P.; Metts, S.; Crittendon, C.; Daugherity, P.; Parsons, E. J. Organometallics 1995, 14, 3810. (f) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A: Chem. 1995, 97, 73. See also: (g) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Catal. 1984, 22, 349. (h) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112, 4324.
61. Many Heck arylations are known to proceed smoothly in water or in water/organic solvent mixtures. Leading references. (a) Bumagin, N. A.; More, P. G.; Beletskaya I. P. J. Organomet. Chem. 1989, 371, 397. (b) Genet, J. P.; Blart, E.; Savignac, M. Synlett 1992, 715. (c) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499. (d) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051. (e) Reardon, P.; Metts, S.; Crittendon, C.; Daugherity, P.; Parsons, E. J. Organometallics 1995, 14, 3810. (f) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A: Chem. 1995, 97, 73. See also: (g) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Catal. 1984, 22, 349. (h) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112, 4324.
62. Many Heck arylations are known to proceed smoothly in water or in water/organic solvent mixtures. Leading references. (a) Bumagin, N. A.; More, P. G.; Beletskaya I. P. J. Organomet. Chem. 1989, 371, 397. (b) Genet, J. P.; Blart, E.; Savignac, M. Synlett 1992, 715. (c) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499. (d) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051. (e) Reardon, P.; Metts, S.; Crittendon, C.; Daugherity, P.; Parsons, E. J. Organometallics 1995, 14, 3810. (f) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A: Chem. 1995, 97, 73. See also: (g) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Catal. 1984, 22, 349. (h) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112, 4324.
63. Larock, R. C.; Gong, W. H.; Baker, B. E. Tetrahedron Lett. 1989, 30, 2603.
64. To minimize the undesired diarylation, an olefin/iodobenzene ratio of 10/1 was employed.
65. (a) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth.Commun. 1981, 11, 513. DME was introduced as solvent in the Suzuki reaction by Gronowitz.
66. (b) Gronowitz, S.; Bobosik, V.; Lawitz, K. Chem. Scripta 1984, 23, 120.
67. Farina, V.; Krishnan, B.; Marshall, D. R.; Roth, G. P. J. Org. Chem. 1993, 58, 5434.
68. The ratio of phenyl vs. butyl transfer in the crude product was 93/7 according to GC-MS.
69. Coulson, D. R. Inorg. Synth. 1972, 13, 121.
70. Generously supplied by Mr. Tero Linnanen. (a) Eaborn, C.; Kornfeld, H. L.; Walton, D. R. M. J. Organomet. Chem. 1967, 10, 529. (b) Kozyrod, R. P.; Morgan, J.; Pinhey, J. T. Aust. J. Chem. 1986, 38, 1147.
71. Generously supplied by Mr. Tero Linnanen. (a) Eaborn, C.; Kornfeld, H. L.; Walton, D. R. M. J. Organomet. Chem. 1967, 10, 529. (b) Kozyrod, R. P.; Morgan, J.; Pinhey, J. T. Aust. J. Chem. 1986, 38, 1147.
72. Saá, J. M.; Dopico, M.; Martorell, G.; García-Raso, A. J. Org. Chem. 1990, 55, 991.
73. (a) Effenberger, F.; Mack, K. E. Tetrahedron Lett. 1970, 3947.
74. (b) Hendrickson, J. B.; Bergeron, R. Tetrahedron Lett. 1973, 4607.
75. Echavarren, A. M.; Stille, J. K. J. Am. Chem. Soc. 1987, 109, 5478.
76. Bohlmann, F.; Jacob, J. Chem. Ber. 1974, 107, 2578.
77. (a) Wagner, G.; Garbe, C.; Richter, P. Pharmazie 1973, 28, 724.
78. (b) Happer, D. A. R.; Steenson, B. E. J. Chem. Soc., Perkin Trans. 2 1988, 19.
79. Cabri, W.; Candiani, I.; Bedeschi, A.; Santi, R. J. Org. Chem. 1992, 57, 3558.
80. Pouchert, C. J.; Campbell, J. R. The Aldrich Library of NMR Spectra; Aldrich Chemical Co.: Milwaukee, 1974.
81. (a) Scribe, P.; Wiemann, J. Bull. Soc. Chim. Fr. 1971, 2268.
82. (b) Ozawa, F.; Kubo, A.; Matsumoto, Y.; Hayashi, T.; Nishioka, E.; Yanagi, K.; Moriguchi, K. Organometallics 1993, 12, 4188.
83. For a discussion of safety precautions in microwave systems see; Raner, K. D.; Strauss, C. R.; Trainor, R. W.; Thorn, J. S. J. Org. Chem. 1995, 60, 2456 and references cited therein.