1,2-Asymmetric induction in a new tandem of (33)-sigmatropic rearrangement of chiral thiocyanates and intramolecular amine addition to N=C=S group

Tetrahedron Letters

Volumn 38, Issue 5, 1997, Pages 875-878

  Martinková, Miroslava ^a   Gonda, Jozef ^a  

^a P J AFÁRIK UNIVERSITY   (Slovakia)

Author keywords

[No Author keywords available]

Indexed keywords

2 IMIDAZOLIDINE 2 THIONE DERIVATIVE; IMIDAZOLIDINE DERIVATIVE; UNCLASSIFIED DRUG;

ARTICLE; CALCULATION; DRUG SYNTHESIS; MOLECULAR DYNAMICS; QUANTUM CHEMISTRY; REACTION ANALYSIS; STEREOCHEMISTRY;

EID: 0031034271     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(96)02429-X     Document Type: Article

References (34)

1. Oishi, T.: Hirama, M. J. Org. Chem. 1989, 54, 5834. Tokles, M.; Snider, J. K. Tetrahedron Lett. 1986, 27, 3951. Corey, E. J.; DaSilva Jardine, P.; Virgil, S.; Yuen, P.-W.; Connel, R.D. J. Am. Chem. Soc. 1989, 111, 9243.
2. Oishi, T.: Hirama, M. J. Org. Chem. 1989, 54, 5834. Tokles, M.; Snider, J. K. Tetrahedron Lett. 1986, 27, 3951. Corey, E. J.; DaSilva Jardine, P.; Virgil, S.; Yuen, P.-W.; Connel, R.D. J. Am. Chem. Soc. 1989, 111, 9243.
3. Oishi, T.: Hirama, M. J. Org. Chem. 1989, 54, 5834. Tokles, M.; Snider, J. K. Tetrahedron Lett. 1986, 27, 3951. Corey, E. J.; DaSilva Jardine, P.; Virgil, S.; Yuen, P.-W.; Connel, R.D. J. Am. Chem. Soc. 1989, 111, 9243.
4. Alexakis, A.; Serdrani, R.; Mangeney, P.; Normant, J. F. Tetrahedron Lett. 1988, 29, 4411.
5. Hanessian, S.; Delorme, D.; Beaudoin, S.; Leblanc, Y. J. Am. Chem. Soc. 1984, 106, 5754.
6. Corey, E. J.; Yu, C.-M.; Kim, S. S. J. Am. Chem. Soc. 1989, 111, 5495.
7. Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N. J. Am. Chem. Soc. 1990, 112, 2801.
8. Corey, E. J.; Kim, S. S. J. Am. Chem. Soc. 1990, 112, 4976.
9. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
10. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
11. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
12. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
13. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
14. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
15. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
16. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
17. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152. Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
18. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
19. Kano, S., Yokomatsu, T.; Iwasawa, H.; Shibuya, S.; Chem. Pharm. Bul. 1988, 57, 6653. Nantz, M.H.; Lee, D. A.; Bender, D. M.; Roohi, A.H. J. Org. Chem. 1992, 57, 6653. Dieter, R.K.; Deo, N.; Lagu, B.; Dieter, J.W. J. Org. Chem. 1992, 57, 1663. Phammatter, E., Seebach, D. Liebigs Ann. Chem. 1991, 1323. Yoda, H.; Shirai, T.; Kawasaki, T.; Katagiri, T.; Takabe, K.; Kimata, K.; Hosoya, K. Cem. Lett. 1991, 793. Dunn, P.J.; Hänner, R.; Rappoport, H. J. Org. Chem. 1990, 55, 5017. Shigematsu, N.; Setoi, H.; Uchida, I.; Shibata, t; Terano, H.; Hashimoto, M. Tetrahedron Lett. 1988, 29, 5147. Mangerey, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant, J. Synthesis 1988, 255. Roskamp, E.J.; Pedersen, S.F. J. Am. Chem. Soc. 1987, 109, 3152 Arrowsmith, R.J.; Carter, K.; Dann, J.G.; Davies, D.E.; Harris, C.J.; Morton, J.A.; Lister, P.; Robinson, J.A; Williams, D.J. J. Chem. Soc., Chem. Commun. 1986, 755. Natsugari, H.; Whittle, R.R.; Weinreb, S.M. J. Am. Chem. Soc. 1984, 106, 7867.
20. Gonda, J.; Helland, A.-Ch.; Ernst, B.; Belluš, D. Synthesis 1993, 729.
21. 13C, IR, HRMS spectra consistent with the reported structures.
22. Moriwake, T.; Hamano, S.; Miki, D.; Saito, S. Chem. Lett. 1986, 815.
23. 2O=55:45).
24. 1H NMR data are supported by HPLC analysis (ref.11 ) of the reaction mixtures, which indicates the presence of a trace amounts (≥ 1%) of the second isomers 8a-e.
25. This indicates that the diastereosetectivity of the reaction may be explained by proton transfer in the transition state of the rate determining step. 2-Hydroxypyridine probably works as proton transfer catalysator: The protic nucleophilles react with isothiocyanates substantially slower as their anionic counterparts: Drobnica, L.; Kristian, P.; Augustin, J. in The Chemistry of Cyanates and their Thio Derivatives (Patai S., Ed.), p. 1007. Wiley, New York 1977.
26. 2. The solvent was then removed under vacuum. The crude product was chromatographed (20% ethyl acetate in hexane) and afforded 0.089g (89%) of 7a as a white solid.
27. 13C NMR spectral data of 10a are identical with literature data (ref.8).
28. 2=), 5.80 (m, 1H, CH=), 6.20 (bs, 1H, NH), 6.10 (bs, 1H, NH).
29. DeWolfe, R.; Young, W.G. in: The chemistry of alkenes (Patai S., Ed), p. 681. Wiley, Ney York 1964.
30. Theoretical calculations were carried out at the semiempirical RHF AM1 method, as implemented in the MOPAC 6.0 program (Stewart, J. P. P. J. Comput. Chem. 1989, 10, 209; Stewart, J. P. P. ibid. 1988, 44, 5597; Stewart, J. P. P. QCPE 1989, program 455). The transition states for intramolecular cyclization 5a->7a and 6a->8a were located using the SADDLE routine implemented in MOPAC. Further refinements of these approximate transition state geometries were carried out by minimizing the norm of energy (Baker, J. J. Comput. Chem. 1986, 7, 385) using the eigenvector-following (EF) method. The resulting geometries have a one negative vibration frequency (Mclver, J. W.; Komornicky, A. J. Am. Chem. Soc. 1972, 94, 2625) and verification using intrinsic reaction coordinate calculations for modes 1 and -1 leads to the reactants and products of the reactions.
31. Theoretical calculations were carried out at the semiempirical RHF AM1 method, as implemented in the MOPAC 6.0 program (Stewart, J. P. P. J. Comput. Chem. 1989, 10, 209; Stewart, J. P. P. ibid. 1988, 44, 5597; Stewart, J. P. P. QCPE 1989, program 455). The transition states for intramolecular cyclization 5a->7a and 6a->8a were located using the SADDLE routine implemented in MOPAC. Further refinements of these approximate transition state geometries were carried out by minimizing the norm of energy (Baker, J. J. Comput. Chem. 1986, 7, 385) using the eigenvector-following (EF) method. The resulting geometries have a one negative vibration frequency (Mclver, J. W.; Komornicky, A. J. Am. Chem. Soc. 1972, 94, 2625) and verification using intrinsic reaction coordinate calculations for modes 1 and -1 leads to the reactants and products of the reactions.
32. Theoretical calculations were carried out at the semiempirical RHF AM1 method, as implemented in the MOPAC 6.0 program (Stewart, J. P. P. J. Comput. Chem. 1989, 10, 209; Stewart, J. P. P. ibid. 1988, 44, 5597; Stewart, J. P. P. QCPE 1989, program 455). The transition states for intramolecular cyclization 5a->7a and 6a->8a were located using the SADDLE routine implemented in MOPAC. Further refinements of these approximate transition state geometries were carried out by minimizing the norm of energy (Baker, J. J. Comput. Chem. 1986, 7, 385) using the eigenvector-following (EF) method. The resulting geometries have a one negative vibration frequency (Mclver, J. W.; Komornicky, A. J. Am. Chem. Soc. 1972, 94, 2625) and verification using intrinsic reaction coordinate calculations for modes 1 and -1 leads to the reactants and products of the reactions.
33. Theoretical calculations were carried out at the semiempirical RHF AM1 method, as implemented in the MOPAC 6.0 program (Stewart, J. P. P. J. Comput. Chem. 1989, 10, 209; Stewart, J. P. P. ibid. 1988, 44, 5597; Stewart, J. P. P. QCPE 1989, program 455). The transition states for intramolecular cyclization 5a->7a and 6a->8a were located using the SADDLE routine implemented in MOPAC. Further refinements of these approximate transition state geometries were carried out by minimizing the norm of energy (Baker, J. J. Comput. Chem. 1986, 7, 385) using the eigenvector-following (EF) method. The resulting geometries have a one negative vibration frequency (Mclver, J. W.; Komornicky, A. J. Am. Chem. Soc. 1972, 94, 2625) and verification using intrinsic reaction coordinate calculations for modes 1 and -1 leads to the reactants and products of the reactions.
34. Theoretical calculations were carried out at the semiempirical RHF AM1 method, as implemented in the MOPAC 6.0 program (Stewart, J. P. P. J. Comput. Chem. 1989, 10, 209; Stewart, J. P. P. ibid. 1988, 44, 5597; Stewart, J. P. P. QCPE 1989, program 455). The transition states for intramolecular cyclization 5a->7a and 6a->8a were located using the SADDLE routine implemented in MOPAC. Further refinements of these approximate transition state geometries were carried out by minimizing the norm of energy (Baker, J. J. Comput. Chem. 1986, 7, 385) using the eigenvector-following (EF) method. The resulting geometries have a one negative vibration frequency (Mclver, J. W.; Komornicky, A. J. Am. Chem. Soc. 1972, 94, 2625) and verification using intrinsic reaction coordinate calculations for modes 1 and -1 leads to the reactants and products of the reactions.