Stereoselectivity of superacid-catalyzed Pictet-Spengler cyclization reactions

Organic Letters

Volumn 5, Issue 12, 2003, Pages 2087-2090

  Nakamura, Satoshi ^a   Tanaka, Masaru ^b   Taniguchi, Tooru ^b   Uchiyama, Masanobu ^a   Ohwada, Tomohiko ^a  

^a UNIVERSITY OF TOKYO   (Japan)

^b NAGOYA CITY UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

PHENETHYLAMINE DERIVATIVE;

ACIDITY; ARTICLE; CATALYSIS; CATALYST; CHEMICAL REACTION; CYCLIZATION; ELECTRON; REACTION ANALYSIS; STEREOCHEMISTRY;

EID: 0141742516     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol034526a     Document Type: Article

References (37)

1. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
2. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
3. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
4. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
5. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
6. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
7. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
8. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
9. For reviews, see: (a) Czerwinski, K. M.; Cook, J. M. Adv. Heterocycl. Nat. Prod. Synth. 1996, 3, 217-277. (b) Cox, E. D.; Cook, J. M. Chem. Rev. 1995, 5 (6), 1797-1842. (c) Waldmann, H. Synlett 1995, 133-141. (d) Rozwadowska, M. D. Heterocycles 1994, 39 (2), 903-931. (e) Badia, D.; Dominguez, E.; Lete, E.; Villa, M. J. Trends Heterocycl. Chem. 1991, 2, 1-11. (f) Ungemach, F.; Cook, J. M. Heterocycles 1978, 9, 1089-1119. (g) Claret, P. A. In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Ed.; Pergamon: Oxford, 1979; Vol. 4, pp 209-211. (h) Gensler, W. J. In Heterocyclic Compounds; Elderfield, R. C., Ed.; Wiley: New York, 1952; Vol. 4, pp 353-361. (i) Whaley, W. M.; Govindachari, T. R. Org. React. 1951, 6, 151-190.
10. (a) Pictet, A.; Spengler, T. Ber. Dtsch. Chem. Ges. 1911, 44, 2030-2036.
11. Decker, H.; Becker, P. Justus Liebigs Ann. Chem. 1913, 395, 342-362.
12. Relevance of unsubstituted 1,2,3,4-tetrahydroisoquinoline derivatives to Parkinson's disease: (a) Tasaki, Y.; Makino, Y.; Ohta, S.; Hirobe, M. J. Neurochem. 1991, 57, 1940-1943. (b) Manini, P.; d'Ischia, M.; Prota, G. J. Org. Chem. 2001, 66, 5048-5053. (c) Ishiwata, K.; Koyanagi, Y.; Abe, K.; Kawamura, K.; Taguchi, K.; Saitoh, T.; Toda, J.; Senda, M.; Sano, T. J. Neurochem. 2001, 79, 868-876. (d) Absi, E.; Parrado, J.; Ayala, A.; Machado, A. Brain Res. 2002, 955, 161-163. Pharmaceutical interests on the stereoisomers of substituents of the 1,2,3,4-tetrahydroisoquinoline derivatives: (e) Gray, N. M.; Cheng, B. K.; Mick, S. J.; Lair, C. M.; Contrras, P. C. J. Med. Chem. 1989, 32, 1242-1248. (f) Ohkubo, M.; Kuno, A.; Katsuta, K.; Ueda, Y.; Shirakawa, K.; Nakanishi, H.; Nakanishi, I.; Kinoshita, T.; Takasugi, H. Chem. Pharm. Bull. 1996, 44, 95-102. (g) Anan, H.; Tanaka, A.; Tsuzuki, R.; Yokota, M.; Yatsu, T.; Fujiwara, T. Chem. Pharm. Bull. 1996, 44, 1865-1870.
13. Relevance of unsubstituted 1,2,3,4-tetrahydroisoquinoline derivatives to Parkinson's disease: (a) Tasaki, Y.; Makino, Y.; Ohta, S.; Hirobe, M. J. Neurochem. 1991, 57, 1940-1943. (b) Manini, P.; d'Ischia, M.; Prota, G. J. Org. Chem. 2001, 66, 5048-5053. (c) Ishiwata, K.; Koyanagi, Y.; Abe, K.; Kawamura, K.; Taguchi, K.; Saitoh, T.; Toda, J.; Senda, M.; Sano, T. J. Neurochem. 2001, 79, 868-876. (d) Absi, E.; Parrado, J.; Ayala, A.; Machado, A. Brain Res. 2002, 955, 161-163. Pharmaceutical interests on the stereoisomers of substituents of the 1,2,3,4-tetrahydroisoquinoline derivatives: (e) Gray, N. M.; Cheng, B. K.; Mick, S. J.; Lair, C. M.; Contrras, P. C. J. Med. Chem. 1989, 32, 1242-1248. (f) Ohkubo, M.; Kuno, A.; Katsuta, K.; Ueda, Y.; Shirakawa, K.; Nakanishi, H.; Nakanishi, I.; Kinoshita, T.; Takasugi, H. Chem. Pharm. Bull. 1996, 44, 95-102. (g) Anan, H.; Tanaka, A.; Tsuzuki, R.; Yokota, M.; Yatsu, T.; Fujiwara, T. Chem. Pharm. Bull. 1996, 44, 1865-1870.
14. Relevance of unsubstituted 1,2,3,4-tetrahydroisoquinoline derivatives to Parkinson's disease: (a) Tasaki, Y.; Makino, Y.; Ohta, S.; Hirobe, M. J. Neurochem. 1991, 57, 1940-1943. (b) Manini, P.; d'Ischia, M.; Prota, G. J. Org. Chem. 2001, 66, 5048-5053. (c) Ishiwata, K.; Koyanagi, Y.; Abe, K.; Kawamura, K.; Taguchi, K.; Saitoh, T.; Toda, J.; Senda, M.; Sano, T. J. Neurochem. 2001, 79, 868-876. (d) Absi, E.; Parrado, J.; Ayala, A.; Machado, A. Brain Res. 2002, 955, 161-163. Pharmaceutical interests on the stereoisomers of substituents of the 1,2,3,4-tetrahydroisoquinoline derivatives: (e) Gray, N. M.; Cheng, B. K.; Mick, S. J.; Lair, C. M.; Contrras, P. C. J. Med. Chem. 1989, 32, 1242-1248. (f) Ohkubo, M.; Kuno, A.; Katsuta, K.; Ueda, Y.; Shirakawa, K.; Nakanishi, H.; Nakanishi, I.; Kinoshita, T.; Takasugi, H. Chem. Pharm. Bull. 1996, 44, 95-102. (g) Anan, H.; Tanaka, A.; Tsuzuki, R.; Yokota, M.; Yatsu, T.; Fujiwara, T. Chem. Pharm. Bull. 1996, 44, 1865-1870.
15. Relevance of unsubstituted 1,2,3,4-tetrahydroisoquinoline derivatives to Parkinson's disease: (a) Tasaki, Y.; Makino, Y.; Ohta, S.; Hirobe, M. J. Neurochem. 1991, 57, 1940-1943. (b) Manini, P.; d'Ischia, M.; Prota, G. J. Org. Chem. 2001, 66, 5048-5053. (c) Ishiwata, K.; Koyanagi, Y.; Abe, K.; Kawamura, K.; Taguchi, K.; Saitoh, T.; Toda, J.; Senda, M.; Sano, T. J. Neurochem. 2001, 79, 868-876. (d) Absi, E.; Parrado, J.; Ayala, A.; Machado, A. Brain Res. 2002, 955, 161-163. Pharmaceutical interests on the stereoisomers of substituents of the 1,2,3,4-tetrahydroisoquinoline derivatives: (e) Gray, N. M.; Cheng, B. K.; Mick, S. J.; Lair, C. M.; Contrras, P. C. J. Med. Chem. 1989, 32, 1242-1248. (f) Ohkubo, M.; Kuno, A.; Katsuta, K.; Ueda, Y.; Shirakawa, K.; Nakanishi, H.; Nakanishi, I.; Kinoshita, T.; Takasugi, H. Chem. Pharm. Bull. 1996, 44, 95-102. (g) Anan, H.; Tanaka, A.; Tsuzuki, R.; Yokota, M.; Yatsu, T.; Fujiwara, T. Chem. Pharm. Bull. 1996, 44, 1865-1870.
16. Relevance of unsubstituted 1,2,3,4-tetrahydroisoquinoline derivatives to Parkinson's disease: (a) Tasaki, Y.; Makino, Y.; Ohta, S.; Hirobe, M. J. Neurochem. 1991, 57, 1940-1943. (b) Manini, P.; d'Ischia, M.; Prota, G. J. Org. Chem. 2001, 66, 5048-5053. (c) Ishiwata, K.; Koyanagi, Y.; Abe, K.; Kawamura, K.; Taguchi, K.; Saitoh, T.; Toda, J.; Senda, M.; Sano, T. J. Neurochem. 2001, 79, 868-876. (d) Absi, E.; Parrado, J.; Ayala, A.; Machado, A. Brain Res. 2002, 955, 161-163. Pharmaceutical interests on the stereoisomers of substituents of the 1,2,3,4-tetrahydroisoquinoline derivatives: (e) Gray, N. M.; Cheng, B. K.; Mick, S. J.; Lair, C. M.; Contrras, P. C. J. Med. Chem. 1989, 32, 1242-1248. (f) Ohkubo, M.; Kuno, A.; Katsuta, K.; Ueda, Y.; Shirakawa, K.; Nakanishi, H.; Nakanishi, I.; Kinoshita, T.; Takasugi, H. Chem. Pharm. Bull. 1996, 44, 95-102. (g) Anan, H.; Tanaka, A.; Tsuzuki, R.; Yokota, M.; Yatsu, T.; Fujiwara, T. Chem. Pharm. Bull. 1996, 44, 1865-1870.
17. Relevance of unsubstituted 1,2,3,4-tetrahydroisoquinoline derivatives to Parkinson's disease: (a) Tasaki, Y.; Makino, Y.; Ohta, S.; Hirobe, M. J. Neurochem. 1991, 57, 1940-1943. (b) Manini, P.; d'Ischia, M.; Prota, G. J. Org. Chem. 2001, 66, 5048-5053. (c) Ishiwata, K.; Koyanagi, Y.; Abe, K.; Kawamura, K.; Taguchi, K.; Saitoh, T.; Toda, J.; Senda, M.; Sano, T. J. Neurochem. 2001, 79, 868-876. (d) Absi, E.; Parrado, J.; Ayala, A.; Machado, A. Brain Res. 2002, 955, 161-163. Pharmaceutical interests on the stereoisomers of substituents of the 1,2,3,4-tetrahydroisoquinoline derivatives: (e) Gray, N. M.; Cheng, B. K.; Mick, S. J.; Lair, C. M.; Contrras, P. C. J. Med. Chem. 1989, 32, 1242-1248. (f) Ohkubo, M.; Kuno, A.; Katsuta, K.; Ueda, Y.; Shirakawa, K.; Nakanishi, H.; Nakanishi, I.; Kinoshita, T.; Takasugi, H. Chem. Pharm. Bull. 1996, 44, 95-102. (g) Anan, H.; Tanaka, A.; Tsuzuki, R.; Yokota, M.; Yatsu, T.; Fujiwara, T. Chem. Pharm. Bull. 1996, 44, 1865-1870.
18. Relevance of unsubstituted 1,2,3,4-tetrahydroisoquinoline derivatives to Parkinson's disease: (a) Tasaki, Y.; Makino, Y.; Ohta, S.; Hirobe, M. J. Neurochem. 1991, 57, 1940-1943. (b) Manini, P.; d'Ischia, M.; Prota, G. J. Org. Chem. 2001, 66, 5048-5053. (c) Ishiwata, K.; Koyanagi, Y.; Abe, K.; Kawamura, K.; Taguchi, K.; Saitoh, T.; Toda, J.; Senda, M.; Sano, T. J. Neurochem. 2001, 79, 868-876. (d) Absi, E.; Parrado, J.; Ayala, A.; Machado, A. Brain Res. 2002, 955, 161-163. Pharmaceutical interests on the stereoisomers of substituents of the 1,2,3,4-tetrahydroisoquinoline derivatives: (e) Gray, N. M.; Cheng, B. K.; Mick, S. J.; Lair, C. M.; Contrras, P. C. J. Med. Chem. 1989, 32, 1242-1248. (f) Ohkubo, M.; Kuno, A.; Katsuta, K.; Ueda, Y.; Shirakawa, K.; Nakanishi, H.; Nakanishi, I.; Kinoshita, T.; Takasugi, H. Chem. Pharm. Bull. 1996, 44, 95-102. (g) Anan, H.; Tanaka, A.; Tsuzuki, R.; Yokota, M.; Yatsu, T.; Fujiwara, T. Chem. Pharm. Bull. 1996, 44, 1865-1870.
19. Bringmann, G.; Ewers, C. T.; Walter, R. Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 6, Chapter 4.2.
20. Yokoyama, A.; Ohwada, T.; Shudo, K. J. Org. Chem. 1999, 64, 611-617.
21. (a) Olah, G. A. Angew. Chem., Int. Ed. Engl. 1993, 32, 767-788.
22. (b) Ohwada, T.; Yamagata, N.; Shudo, K. J. Am. Chem. Soc. 1991, 113, 1364-1373.
23. (a) Zucker, L.; Hammett, L. P. J. Am. Chem. Soc. 1939, 61, 2791-2798.
24. (b) Bonner, T. G.; Thorne, M. P.; Wilkins, J. M. J. Chem. Soc. 1955, 2351-2358.
25. (c) Bonner, T. G.; Barnard, M. J. Chem. Soc. 1958, 4181-4186.
26. (d) Long, F. A.; Paul, M. A. Chem. Rev. 1957, 57, 935-1010.
27. (e) Sato, Y.; Yato, M.; Ohwada, T.; Saito, S.; Shudo, K. J. Am. Chem. Soc. 1995, 117, 3037-3043.
28. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Salvador, P.; Dannenberg, J. J.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J. ; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, Revision A.11; Gaussian, Inc.: Pittsburgh, PA, 2001.
29. This value is the sum of electronic and thermal enthalpies (at 298.15 K) with a scaled thermal correction (a scale factor 0.8929, on the basis of the RHF/6-31G* frequency calculation): (a) Pople, J. A.; Scott, A. P.; Wong, M. W.; Radom, L. Isr. J. Chem. 1993, 33, 345. (b) Scott, A.; Radom, L. J. Phys. Chem. 1996, 100, 16502. (c) Foresman, J. B.; Frish, Æ. Exploring Chemistry with Electronic Structure Methods, 2nd ed.; Gaussian, Inc.: Pittsburgh, 1996.
30. This value is the sum of electronic and thermal enthalpies (at 298.15 K) with a scaled thermal correction (a scale factor 0.8929, on the basis of the RHF/6-31G* frequency calculation): (a) Pople, J. A.; Scott, A. P.; Wong, M. W.; Radom, L. Isr. J. Chem. 1993, 33, 345. (b) Scott, A.; Radom, L. J. Phys. Chem. 1996, 100, 16502. (c) Foresman, J. B.; Frish, Æ. Exploring Chemistry with Electronic Structure Methods, 2nd ed.; Gaussian, Inc.: Pittsburgh, 1996.
31. This value is the sum of electronic and thermal enthalpies (at 298.15 K) with a scaled thermal correction (a scale factor 0.8929, on the basis of the RHF/6-31G* frequency calculation): (a) Pople, J. A.; Scott, A. P.; Wong, M. W.; Radom, L. Isr. J. Chem. 1993, 33, 345. (b) Scott, A.; Radom, L. J. Phys. Chem. 1996, 100, 16502. (c) Foresman, J. B.; Frish, Æ. Exploring Chemistry with Electronic Structure Methods, 2nd ed.; Gaussian, Inc.: Pittsburgh, 1996.
32. The most stable conformer with respect to the conformations of the dimethoxy groups of 5a was used. Another structure, e.g., with anti and all-in-plane conformation of the methoxy groups of 5a, is higher in energy than the present conformer (in Figure 1) by 2.2 kcal/mol (RHF/6-31G*, after scaled ZPE correction).
33. Single-point energy calculations with B3LYP/6-31G* levels on the basis of the RHF/6-31G*-optimized geometries were carried out. The enthalpies of activation (at 298.15 K, after the scaled thermal correction, based on RHF/6-31G* frequency calculations) are as follows: TS1 (monocationic cyclization), 21.1 kcal/mol; TS2 (dicationic cyclization), -0.3 kcal/mol; TS3 (monocationic cyclization), 16.0 kcal/mol, respectively. The energy differences of the enthalpies of activation through these relevant TS structures are of similar magnitude as in the RHF calculations, while the dicationic cycliztion through TS2 became a nonactivation barrier process. This might be partially because of the incomplete estimation of electron correlations in this type of reactions (see ref 10c).
34. The dihedral angle between the bending aromatic C-H bond and the neighoring aromatic C-H bond is also a descriptor of the strurural distortion (in the reactant cations, these values are less than 0.9°): TS1, 23.3°; TS2, 13.5°; TS3, 28.1°.
35. Cox, E. D.; Li, J.; Hamaker, L. K.; Yu, P.; Cook, J. M. Chem. Commun 1996 2477-2478.
36. Our preliminary calculations suggested that the enhanced stereoselectivity in the cases of 2-alkyl-substituted imines under superacid conditions can be rationalized in terms of the difference in the structures and energies of the TSs of the cyclizations. The TSs for trans and cis cyclization of the N-monoprotonated cation (7c) of 2-ethyl-N-benzylidene-2-(3′ ,4′-dimethoxy)phenethylamine (5c) were obtained (TS4 and TS5, Scheme S1, Supporting Information). The structural features are similar to those of TS3. The TSs for the trans and cis cyclization of the N,N-diprotonated imine (4c) of 2-ethyl-N-benzylidene-2-phenethylamine (1c) were also obtained (TS6 and TS7, Scheme S1, Supporting Information). The structural features are similar to those of TS2. The activation energies for cyclization are 25.6 kcal/mol (for trans cyclization through TS4) and 25.8 kcal/mol (for cis cyclization through TS5), respectively. The TS for the trans cyclization of the monocation 3c is lower in energy than that for the cis cyclization by 0.25 kcal/mol. The energy difference between the TSs for trans (TS5) and cis (TS6) cyclizations of the dication 4c is increased 0.37 kcal/mol. Thus, the gap is larger than that of the monocationic cyclization of the dimethoxyphenyl substrate (5c). This increased gap between the energies of the TSs for the trans and cis cyclizations seems to be consistent with the enhanced stereoselection.
37. b-benzyltryptophan methyl ester. See ref 14.