Regioselectivity of biradical cyclizations of enyne-allenes: Influence of substituents on the switch from the Myers-Saito to the novel C2-C6 cyclization

Angewandte Chemie - International Edition

Volumn 37, Issue 13-14, 1998, Pages 1960-1963

  Engels, Bernd ^a   Lennartz, Christian ^a   Hanrath, Michael ^a   Schmittel, Michael ^b   Strittmatter, Marc ^b  

^a UNIVERSITY OF BONN   (Germany)

^b UNIVERSITY OF WÜRZBURG   (Germany)

Author keywords

Ab initio calculations; Cycloaromatizations; Diradicals; Enyne allenes; Reaction mechanisms

Indexed keywords

EID: 0032479752     PISSN: 14337851     EISSN: None     Source Type: Journal    
DOI: 10.1002/(SICI)1521-3773(19980803)37:13/14<1960::AID-ANIE1960>3.0.CO;2-3     Document Type: Article

References (30)

1. A. G. Myers, E. Y. Kuo, N. S. Finney, J. Am. Chem. Soc. 1989, 111, 8057; R. Nagata, H. Yamanaka, E. Okazaki, I. Saito, Tetrahedron Lett. 1989, 30, 4995.
2. A. G. Myers, E. Y. Kuo, N. S. Finney, J. Am. Chem. Soc. 1989, 111, 8057; R. Nagata, H. Yamanaka, E. Okazaki, I. Saito, Tetrahedron Lett. 1989, 30, 4995.
3. M. E. Maier, Synlett 1995, 13.
4. J. W. Grissom, G. U. Gunawardena, D. Klingberg, D. Huang, Tetrahedron 1996, 52, 6453; K. K. Wang, Chem. Rev. 1996, 96, 207.
5. J. W. Grissom, G. U. Gunawardena, D. Klingberg, D. Huang, Tetrahedron 1996, 52, 6453; K. K. Wang, Chem. Rev. 1996, 96, 207.
6. M. Schmittel, M. Strittmatter, S. Kiau, Tetrahedron Lett. 1995, 36, 4975; M. Schmittel, S. Kiau, Liebigs Ann. 1997, 733; M. Schmittel, M. Keller, S. Kiau, M. Strittmatter Chem. Eur. J. 1997, 3, 807, and references therein.
7. M. Schmittel, M. Strittmatter, S. Kiau, Tetrahedron Lett. 1995, 36, 4975; M. Schmittel, S. Kiau, Liebigs Ann. 1997, 733; M. Schmittel, M. Keller, S. Kiau, M. Strittmatter Chem. Eur. J. 1997, 3, 807, and references therein.
8. M. Schmittel, M. Strittmatter, S. Kiau, Tetrahedron Lett. 1995, 36, 4975; M. Schmittel, S. Kiau, Liebigs Ann. 1997, 733; M. Schmittel, M. Keller, S. Kiau, M. Strittmatter Chem. Eur. J. 1997, 3, 807, and references therein.
9. T. Gillmann, T. Hülsen, W. Massa, S. Wocadlo, Synlett 1995, 1257.
10. J. G. Garcia, B. Ramos, L. M. Pratt, A. Rodriguez Tetrahedron Lett. 1995, 36, 7391.
11. M. Schmittel, M. Strittmatter, S. Kiau, Angew. Chem. 1996, 108, 1952; Angew. Chem. Int. Ed. Engl. 1996, 35, 1843.
12. M. Schmittel, M. Strittmatter, S. Kiau, Angew. Chem. 1996, 108, 1952; Angew. Chem. Int. Ed. Engl. 1996, 35, 1843.
13. M. Schmittel, M. Maywald, M. Strittmatter, Synlett 1997, 165.
14. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
15. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
16. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
17. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
18. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
19. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
20. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
21. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
22. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
23. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
24. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
25. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
26. 6 CSFs. The influence of the neglected CSFs was estimated by the Buenker-Peyerimhoff extrapolation (R. J. Buenker, S. D. Peyerimhoff, Theor. Chim. Acta 1975, 39, 217; R. J. Buenker, S. D. Peyerimhoff, W. Butscher, Mol. Phys. 1978, 35, 771; R. J. Buenker, R. A. Phillips, J. Mol. Struct. THEOCHEM 1985, 123, 291, and references therein). The influence of higher excitations are estimated by the normalized form of the Davidson correction (J. E. Del Bene, E. A. Stahlberg, I. Shaviatt, Int. J. Quantum. Chem. Symp. 1990, 24, 455). In these calculations, abbreviated in the following as MR-CI + Q, all valence electrons were correlated. The calculations were performed with the DIESEL-MR-CI program package (B. Engels, M. Hanrath, DIESEL-MR-CI (direct internal external separated individually selecting MR-CI) program package, Universität Bonn, Germany, 1997; M. Hanrath, B. Engels, Chem. Phys. 1997, 225, 197). The transition states were optimized and characterized by frequency calculations. As discussed above, the DFT (B33LYP) approach was used (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785). These calculations were performed with the Gaussian 94 program package (M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995) and the TurboMol program package (R. Ahlrichs, M. Baer, M. Haeser, H. Horn, C. Koelmel, Chem. Phys. Lett. 1989, 162, 165; O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346).
27. -1.
28. M. Schmittel, S. Kiau, T Siebert, M. Strittmatter, Tetrahedron Lett. 1996, 37, 7691.
29. S. Heckhoff, W. Dolle, D. Spickermann, T. Gillmann, unpublished results.
30. Our calculations for R = H and R = Ph identify both biradical intermediates as minimum structures on the potential surface. A zwitterionic mechanism could be ruled out, because the first excited singlet state of the biradical intermediate, which has a zwitterionic structure, lies above the singlet ground state.