Parallel mechanisms for the cycloaromatization of enyne allenes †

Abstract

The Myers–Saito cycloaromatization of enyne allenes is proposed to consist of two parallel mechanisms, one involving a biradical and the other with dipolar character. MCSCF calculations suggest that a nonplanar cyclic allene could be fairly close in enthalpy to the biradical, while the planar zwitterion originally proposed as a possible second intermediate is in fact a transition state for the interconversion of the two enantiomeric cyclic allenes. Competitive trapping experiments rule out the presence of a single intermediate and are consistent with the participation of parallel pathways. The reaction of (Z )-hepta-1,2,4-trien-6-yne in cyclopentadiene gave an inseparable mixture of two tetracyclic products whose structures were elucidated with 2-D NMR.

References

1. A. G. Myers, Tetrahedron Lett., 1987, 28, 4493.
2. R. Nagata, H. Yamanaka, E. Okazaki and I. Saito, Tetrahedron Lett., 1989, 30, 4995.
3. A. G. Myers, E. Y. Kuo and N. S. Finney, J. Am. Chem. Soc., 1989, 111, 8057.
4. A. G. Myers, P. S. Dragovich and E. Y. Kuo, J. Am. Chem. Soc., 1992, 114, 9369.
5. A. G. Myers, P. J. Proteau and T. M. Handel, J. Am. Chem. Soc., 1988, 110, 7212; A. G. Myers and P. J. Proteau, J. Am. Chem. Soc., 1989, 111, 1146.
6. For representative examples: A. B. Padias and H. K. Hall, Jr., J. Org. Chem., 1987, 52, 4536; M. B. Zimmt, C. Doubleday, Jr. and N. J. Turro, Chem. Phys. Lett., 1987, 134, 549.
7. L. Salem and C. Rowland, Angew. Chem., Int. Ed. Engl., 1972, 11, 92.
8. B. Engels and M. Hanrath, J. Am. Chem. Soc., 1998, 120, 6356.
9. P. G. Wenthold, J. A. Paulino and R. R. Squires, J. Am. Chem. Soc., 1991, 113, 1845; P. G. Wenthold and R. R. Squires, J. Am. Chem. Soc., 1994, 116, 6961.
10. (a) P. G. Wenthold, S. G. Wierschke, J. J. Nash and R. R. Squires, J. Am. Chem. Soc., 1994, 116, 7378; (b) P. G. Wenthold, S. G. Wierschke, J. J. Nash and R. R. Squires, J. Am. Chem. Soc., 1993, 115, 12611.
11. M. Balci and W. M. Jones, J. Am. Chem. Soc., 1980, 102, 7607; M. Balci and W. M. Jones, J. Am. Chem. Soc., 1981, 103, 2874.
12. R. P. Johnson, Chem. Rev., 1989, 89, 1111; G. Wittig and P. Fritze, Angew. Chem., Int. Ed. Engl., 1966, 5, 846.
13. M. Christl, M. Braun and G. Müller, Angew. Chem., Int. Ed. Engl., 1992, 31, 473; H. Hopf, H. Berger, G. Zimmermann, U. Nüchter, P. G. Jones and I. Dix, Angew. Chem., Int. Ed. Engl., 1997, 36, 1187.
14. For an experimental estimate of the singlet–triplet gap, see: C. F. Logan, J. C. Ma and P. Chen, J. Am. Chem. Soc., 1994, 116, 2137.
15. R. O. Angus, Jr., M. W. Schmidt and R. P. Johnson, J. Am. Chem. Soc., 1985, 107, 532.
16. W. R. Moore and W. R. Moser, J. Org. Chem., 1970, 35, 908.
17. A. T. Bottini and L. L. Hilton, Tetrahedron, 1975, 31, 1997.
18. T. Tsuji, T. Shibata, Y. Hienuki and S. Nishida, J. Am. Chem. Soc., 1978, 100, 1806.
19. K.-L. Noble, H. Hopf and L. Ernst, Chem. Ber., 1984, 117, 455.
20. A. G. Myers and B. Zheng, J. Am. Chem. Soc., 1996, 118, 4492.
21. N. Koga and K. Morokuma, J. Am. Chem. Soc., 1990, 113, 1907.
22. P. G. Dopico and M. G. Finn, Tetrahedron, 1999, 55, 29.
23. GAUSSIAN98, Revision A.3, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon, E. S. ReplogleJ. A. Pople, GaussianInc., Pittsburgh PA, 1998.
24. MOLCAS Version 401. K. Andersson, M. R. A. Blomberg, M. P. Fülscher, G. Karlström, R. Lindh, P.-Å. Malmqvist, P. Neogrády, J. Olsen, B. O. Roos, A. J. Sadlej, M. Schütz, L. Seijo, L. Serrano-Andrés, P. E. M. SiegbahnP.-O. Widmark, Lund University, Sweden (1997).
25. GAMESS: M. W. Schmidt, K. K. Baldridge, J. A. Boatz, S. T. Elbert, M. S. Gordon, J. H. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S. J. Su, T. L. Windus, M. Dupuis and J. A. Montgomery, J. Comput. Chem., 1993, 14, 1347.
26. P. C. Hariharan and J. A. Pople, Theor. Chim. Acta, 1973, 28, 213.
27. M. W. Wong, M. J. Frisch and K. B. Wiberg, J. Am. Chem. Soc., 1991, 113, 4776.
28. PCModel: Serena Software, Box 3076, Bloomington, IN 47402-3076.
29. J. Suufert, E. Abraham, S. Raeppel and R. Brückner, Liebigs Ann., 1996, 447.
30. A. T. Dann and W. J. Davies, J. Chem. Soc., 1929, 1050.