Asymmetric induction via an intramolecular haloetherification reaction of chiral ene acetals: A novel approach to optically active 1,4- and 1,5-diols

Journal of Organic Chemistry

Volumn 61, Issue 21, 1996, Pages 7309-7315

  Fujioka, Hiromichi ^a   Kitagawa, Hidetoshi ^a   Nagatomi, Yasushi ^a   Kita, Yasuyuki ^a  

^a OSAKA UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0001445098     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo960714l     Document Type: Article

References (42)

1. For examples, see: (a) Kotsuki, H. Synlett 1992, 97. (b) Mukaiyama, T.; Murakami, M. Synthesis 1987, 1043. (c) Mukaiyama, T. Org. React. 1982, 28, 203.
2. For examples, see: (a) Kotsuki, H. Synlett 1992, 97. (b) Mukaiyama, T.; Murakami, M. Synthesis 1987, 1043. (c) Mukaiyama, T. Org. React. 1982, 28, 203.
3. For examples, see: (a) Kotsuki, H. Synlett 1992, 97. (b) Mukaiyama, T.; Murakami, M. Synthesis 1987, 1043. (c) Mukaiyama, T. Org. React. 1982, 28, 203.
4. For studies of halonium ion mediated neighboring group activation of acetal cleavage, see: (a) Robert, M.; Udodong, U. E.; Roberts, C.; Mootoo, D. R.; Konradsson, P.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1554. (b) Roberts, C.; Madsen, R.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1546. (c) Madsen, R.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 111. (d) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, J.; Merritt, J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (e) Zhang, H.; Wilson, P.; Shan, W.; Ruan, Z.; Mootoo, D. R. Tetrahedron Lett. 1995, 36, 649. (f) Wilson, P.; Shan, W. F.; Mootoo, D. R. J. Carbohydr. Chem. 1994, 13, 133. (g) Elvey, S. P.; Mootoo, D. R. J. Am. Chem. Soc. 1992, 60, 9685. (h) Mootoo, D. R.; Date, V.; Fraser-Reid, B. J. Chem. Soc., Chem. Commun. 1987, 1462. References e-h include the reactions of remote stereocontrol.
5. For studies of halonium ion mediated neighboring group activation of acetal cleavage, see: (a) Robert, M.; Udodong, U. E.; Roberts, C.; Mootoo, D. R.; Konradsson, P.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1554. (b) Roberts, C.; Madsen, R.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1546. (c) Madsen, R.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 111. (d) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, J.; Merritt, J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (e) Zhang, H.; Wilson, P.; Shan, W.; Ruan, Z.; Mootoo, D. R. Tetrahedron Lett. 1995, 36, 649. (f) Wilson, P.; Shan, W. F.; Mootoo, D. R. J. Carbohydr. Chem. 1994, 13, 133. (g) Elvey, S. P.; Mootoo, D. R. J. Am. Chem. Soc. 1992, 60, 9685. (h) Mootoo, D. R.; Date, V.; Fraser-Reid, B. J. Chem. Soc., Chem. Commun. 1987, 1462. References e-h include the reactions of remote stereocontrol.
6. For studies of halonium ion mediated neighboring group activation of acetal cleavage, see: (a) Robert, M.; Udodong, U. E.; Roberts, C.; Mootoo, D. R.; Konradsson, P.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1554. (b) Roberts, C.; Madsen, R.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1546. (c) Madsen, R.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 111. (d) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, J.; Merritt, J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (e) Zhang, H.; Wilson, P.; Shan, W.; Ruan, Z.; Mootoo, D. R. Tetrahedron Lett. 1995, 36, 649. (f) Wilson, P.; Shan, W. F.; Mootoo, D. R. J. Carbohydr. Chem. 1994, 13, 133. (g) Elvey, S. P.; Mootoo, D. R. J. Am. Chem. Soc. 1992, 60, 9685. (h) Mootoo, D. R.; Date, V.; Fraser-Reid, B. J. Chem. Soc., Chem. Commun. 1987, 1462. References e-h include the reactions of remote stereocontrol.
7. For studies of halonium ion mediated neighboring group activation of acetal cleavage, see: (a) Robert, M.; Udodong, U. E.; Roberts, C.; Mootoo, D. R.; Konradsson, P.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1554. (b) Roberts, C.; Madsen, R.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1546. (c) Madsen, R.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 111. (d) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, J.; Merritt, J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (e) Zhang, H.; Wilson, P.; Shan, W.; Ruan, Z.; Mootoo, D. R. Tetrahedron Lett. 1995, 36, 649. (f) Wilson, P.; Shan, W. F.; Mootoo, D. R. J. Carbohydr. Chem. 1994, 13, 133. (g) Elvey, S. P.; Mootoo, D. R. J. Am. Chem. Soc. 1992, 60, 9685. (h) Mootoo, D. R.; Date, V.; Fraser-Reid, B. J. Chem. Soc., Chem. Commun. 1987, 1462. References e-h include the reactions of remote stereocontrol.
8. For studies of halonium ion mediated neighboring group activation of acetal cleavage, see: (a) Robert, M.; Udodong, U. E.; Roberts, C.; Mootoo, D. R.; Konradsson, P.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1554. (b) Roberts, C.; Madsen, R.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1546. (c) Madsen, R.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 111. (d) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, J.; Merritt, J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (e) Zhang, H.; Wilson, P.; Shan, W.; Ruan, Z.; Mootoo, D. R. Tetrahedron Lett. 1995, 36, 649. (f) Wilson, P.; Shan, W. F.; Mootoo, D. R. J. Carbohydr. Chem. 1994, 13, 133. (g) Elvey, S. P.; Mootoo, D. R. J. Am. Chem. Soc. 1992, 60, 9685. (h) Mootoo, D. R.; Date, V.; Fraser-Reid, B. J. Chem. Soc., Chem. Commun. 1987, 1462. References e-h include the reactions of remote stereocontrol.
9. For studies of halonium ion mediated neighboring group activation of acetal cleavage, see: (a) Robert, M.; Udodong, U. E.; Roberts, C.; Mootoo, D. R.; Konradsson, P.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1554. (b) Roberts, C.; Madsen, R.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1546. (c) Madsen, R.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 111. (d) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, J.; Merritt, J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (e) Zhang, H.; Wilson, P.; Shan, W.; Ruan, Z.; Mootoo, D. R. Tetrahedron Lett. 1995, 36, 649. (f) Wilson, P.; Shan, W. F.; Mootoo, D. R. J. Carbohydr. Chem. 1994, 13, 133. (g) Elvey, S. P.; Mootoo, D. R. J. Am. Chem. Soc. 1992, 60, 9685. (h) Mootoo, D. R.; Date, V.; Fraser-Reid, B. J. Chem. Soc., Chem. Commun. 1987, 1462. References e-h include the reactions of remote stereocontrol.
10. For studies of halonium ion mediated neighboring group activation of acetal cleavage, see: (a) Robert, M.; Udodong, U. E.; Roberts, C.; Mootoo, D. R.; Konradsson, P.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1554. (b) Roberts, C.; Madsen, R.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1546. (c) Madsen, R.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 111. (d) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, J.; Merritt, J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (e) Zhang, H.; Wilson, P.; Shan, W.; Ruan, Z.; Mootoo, D. R. Tetrahedron Lett. 1995, 36, 649. (f) Wilson, P.; Shan, W. F.; Mootoo, D. R. J. Carbohydr. Chem. 1994, 13, 133. (g) Elvey, S. P.; Mootoo, D. R. J. Am. Chem. Soc. 1992, 60, 9685. (h) Mootoo, D. R.; Date, V.; Fraser-Reid, B. J. Chem. Soc., Chem. Commun. 1987, 1462. References e-h include the reactions of remote stereocontrol.
11. For studies of halonium ion mediated neighboring group activation of acetal cleavage, see: (a) Robert, M.; Udodong, U. E.; Roberts, C.; Mootoo, D. R.; Konradsson, P.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1554. (b) Roberts, C.; Madsen, R.; Fraser-Reid, B. J. Am. Chem. Soc. 1995, 117, 1546. (c) Madsen, R.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 111. (d) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, J.; Merritt, J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (e) Zhang, H.; Wilson, P.; Shan, W.; Ruan, Z.; Mootoo, D. R. Tetrahedron Lett. 1995, 36, 649. (f) Wilson, P.; Shan, W. F.; Mootoo, D. R. J. Carbohydr. Chem. 1994, 13, 133. (g) Elvey, S. P.; Mootoo, D. R. J. Am. Chem. Soc. 1992, 60, 9685. (h) Mootoo, D. R.; Date, V.; Fraser-Reid, B. J. Chem. Soc., Chem. Commun. 1987, 1462. References e-h include the reactions of remote stereocontrol.
12. 2-symmetric acetals, see: (a) Alexakis, A.; Mangeny, P. Tetrahedron: Asymmetry 1990, 1, 477. (b) Fujioka, H.; Kita, Y. Studies in Natural Product Chemistry; Atta-ur-Rahman, Elsevier, Ed.; Amsterdam: 1994; Vol. 14, p 469.
13. 2-symmetric acetals, see: (a) Alexakis, A.; Mangeny, P. Tetrahedron: Asymmetry 1990, 1, 477. (b) Fujioka, H.; Kita, Y. Studies in Natural Product Chemistry; Atta-ur-Rahman, Elsevier, Ed.; Amsterdam: 1994; Vol. 14, p 469.
14. 2-symmetric acetals, see: (a) Fujioka, H.; Kitagawa, H.; Yamanaka, T.; Kita, Y. Chem. Pharm. Bull. 1992, 40, 3118. (b) Fujioka, H.; Annoura, H.; Murano, K.; Kita, Y.; Tamura, Y. Chem. Pharm. Bull. 1989, 37, 2047. (c) Tamura, Y. Annoura, H.; Yamamoto, H.; Kondo, H.; Kita, Y. Fujioka, H. Tetrahedron Lett. 1987, 28, 5709. (d) Tamura, Y. Annoura, Fujioka, H. Tetrahedron Lett. 1987, 28, 5681. (e) Tamura, Y.; Ko, T.; Kondo, H.; Annoura, H.; Fuji, M.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 2117. (f) Tamura, Y.; Kondo, H.; Annoura, H.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 81.
15. 2-symmetric acetals, see: (a) Fujioka, H.; Kitagawa, H.; Yamanaka, T.; Kita, Y. Chem. Pharm. Bull. 1992, 40, 3118. (b) Fujioka, H.; Annoura, H.; Murano, K.; Kita, Y.; Tamura, Y. Chem. Pharm. Bull. 1989, 37, 2047. (c) Tamura, Y. Annoura, H.; Yamamoto, H.; Kondo, H.; Kita, Y. Fujioka, H. Tetrahedron Lett. 1987, 28, 5709. (d) Tamura, Y. Annoura, Fujioka, H. Tetrahedron Lett. 1987, 28, 5681. (e) Tamura, Y.; Ko, T.; Kondo, H.; Annoura, H.; Fuji, M.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 2117. (f) Tamura, Y.; Kondo, H.; Annoura, H.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 81.
16. 2-symmetric acetals, see: (a) Fujioka, H.; Kitagawa, H.; Yamanaka, T.; Kita, Y. Chem. Pharm. Bull. 1992, 40, 3118. (b) Fujioka, H.; Annoura, H.; Murano, K.; Kita, Y.; Tamura, Y. Chem. Pharm. Bull. 1989, 37, 2047. (c) Tamura, Y. Annoura, H.; Yamamoto, H.; Kondo, H.; Kita, Y. Fujioka, H. Tetrahedron Lett. 1987, 28, 5709. (d) Tamura, Y. Annoura, Fujioka, H. Tetrahedron Lett. 1987, 28, 5681. (e) Tamura, Y.; Ko, T.; Kondo, H.; Annoura, H.; Fuji, M.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 2117. (f) Tamura, Y.; Kondo, H.; Annoura, H.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 81.
17. 2-symmetric acetals, see: (a) Fujioka, H.; Kitagawa, H.; Yamanaka, T.; Kita, Y. Chem. Pharm. Bull. 1992, 40, 3118. (b) Fujioka, H.; Annoura, H.; Murano, K.; Kita, Y.; Tamura, Y. Chem. Pharm. Bull. 1989, 37, 2047. (c) Tamura, Y. Annoura, H.; Yamamoto, H.; Kondo, H.; Kita, Y. Fujioka, H. Tetrahedron Lett. 1987, 28, 5709. (d) Tamura, Y. Annoura, Fujioka, H. Tetrahedron Lett. 1987, 28, 5681. (e) Tamura, Y.; Ko, T.; Kondo, H.; Annoura, H.; Fuji, M.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 2117. (f) Tamura, Y.; Kondo, H.; Annoura, H.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 81.
18. 2-symmetric acetals, see: (a) Fujioka, H.; Kitagawa, H.; Yamanaka, T.; Kita, Y. Chem. Pharm. Bull. 1992, 40, 3118. (b) Fujioka, H.; Annoura, H.; Murano, K.; Kita, Y.; Tamura, Y. Chem. Pharm. Bull. 1989, 37, 2047. (c) Tamura, Y. Annoura, H.; Yamamoto, H.; Kondo, H.; Kita, Y. Fujioka, H. Tetrahedron Lett. 1987, 28, 5709. (d) Tamura, Y. Annoura, Fujioka, H. Tetrahedron Lett. 1987, 28, 5681. (e) Tamura, Y.; Ko, T.; Kondo, H.; Annoura, H.; Fuji, M.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 2117. (f) Tamura, Y.; Kondo, H.; Annoura, H.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 81.
19. 2-symmetric acetals, see: (a) Fujioka, H.; Kitagawa, H.; Yamanaka, T.; Kita, Y. Chem. Pharm. Bull. 1992, 40, 3118. (b) Fujioka, H.; Annoura, H.; Murano, K.; Kita, Y.; Tamura, Y. Chem. Pharm. Bull. 1989, 37, 2047. (c) Tamura, Y. Annoura, H.; Yamamoto, H.; Kondo, H.; Kita, Y. Fujioka, H. Tetrahedron Lett. 1987, 28, 5709. (d) Tamura, Y. Annoura, Fujioka, H. Tetrahedron Lett. 1987, 28, 5681. (e) Tamura, Y.; Ko, T.; Kondo, H.; Annoura, H.; Fuji, M.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 2117. (f) Tamura, Y.; Kondo, H.; Annoura, H.; Takeuchi, R.; Fujioka, H. Tetrahedron Lett. 1986, 27, 81.
20. The preliminary stereoseiective synthesis of optically active 1,4-diols has been recently communicated: Fujioka, H.; Kitagawa, H.; Matsunaga, N.; Nagatomi, Y.; Kita, Y. Tetrahedron Lett. 1996, 37, 2245.
21. Solladié, G.; Huser, N. Recl. Trav. Chim. Pays-Bas 1995, 114, 153 and references therein.
22. For previous synthesis of the optically active natural product, see: (a) Keinan, E.; Seth, K. K.; Lamed, R. J. Am. Chem. Soc. 1986, 108, 3474. (b) Seebach, D.; Pohmakotr, M. Helv. Chim. Acta 1979, 62, 1096. (c) Lichtenthaler, F. W.; Klingler, F. D.; Jarglis, P. Carbohydr. Res. 1984, 132, C1.
23. For previous synthesis of the optically active natural product, see: (a) Keinan, E.; Seth, K. K.; Lamed, R. J. Am. Chem. Soc. 1986, 108, 3474. (b) Seebach, D.; Pohmakotr, M. Helv. Chim. Acta 1979, 62, 1096. (c) Lichtenthaler, F. W.; Klingler, F. D.; Jarglis, P. Carbohydr. Res. 1984, 132, C1.
24. For previous synthesis of the optically active natural product, see: (a) Keinan, E.; Seth, K. K.; Lamed, R. J. Am. Chem. Soc. 1986, 108, 3474. (b) Seebach, D.; Pohmakotr, M. Helv. Chim. Acta 1979, 62, 1096. (c) Lichtenthaler, F. W.; Klingler, F. D.; Jarglis, P. Carbohydr. Res. 1984, 132, C1.
25. Chiral hydrobenzoin is readily available in both enantiomeric forms by asymmetric synthesis or resolution; for asymmetric synthesis, see, Wang et al. (Wang, Z. -M.; Sharpless, K. B. J. Org. Chem. 1994, 59, 8302) and for resolution of dl-hydrobenzoin, see Optical Resolution Procedures for Chemical Compounds; Mewman, P., Optical Information Center: Manhattan College, Riverdale, NY 1984; Vol. 3, p 353.
26. Chiral hydrobenzoin is readily available in both enantiomeric forms by asymmetric synthesis or resolution; for asymmetric synthesis, see, Wang et al. (Wang, Z. -M.; Sharpless, K. B. J. Org. Chem. 1994, 59, 8302) and for resolution of dl-hydrobenzoin, see Optical Resolution Procedures for Chemical Compounds; Mewman, P., Optical Information Center: Manhattan College, Riverdale, NY 1984; Vol. 3, p 353.
27. Preparation: Lemieux, R. U.; Morgan, A. R. Can. J. Chem. 1965, 43, 2190.
28. 4 reduction, and (3) hydrogenolysis. (Matrix Presented)
29. The structures of b, c, and d were postulated from consideration of the reaction mechanism and the assignment is tentative.
30. A similar result was reported by B. Fraser-Reid et al. They suggested that the formation of the 6-membered oxonium ion was slower than that of the 5-membered one (see ref 2d).
31. Optically active 1,3-diphenyl-1,3-propanediol is available in both enantiomeric forms by asymmetric synthesis or microbial resolution; for asymmetric synthesis, see, Wang et al. (Wang, Z. -M.; Ito, K.; Harada, T.; Tai, A. Bull. Chem. Soc. Jpn. 1980, 53, 3367) and for microbial resolution, see: Yamamoto, K.; Ando, H.; Chikamatsu, H. J. Chem. Soc., Chem. Commun. 1994, 334.
32. Optically active 1,3-diphenyl-1,3-propanediol is available in both enantiomeric forms by asymmetric synthesis or microbial resolution; for asymmetric synthesis, see, Wang et al. (Wang, Z. -M.; Ito, K.; Harada, T.; Tai, A. Bull. Chem. Soc. Jpn. 1980, 53, 3367) and for microbial resolution, see: Yamamoto, K.; Ando, H.; Chikamatsu, H. J. Chem. Soc., Chem. Commun. 1994, 334.
33. There is another possible 6,5-membered bicyclic intermediate from reaction of the acetal derived from 4-pentenal and 1,3-diphenyl-1,3-propanediol. We did not feel it necessary to examine its reaction in order to develop the asymmetric synthesis of 1,4-diols.
34. 6) is also used during halolactonization, see: Simonot, B.; Rousseau, G. J. Org. Chem. 1994, 59, 5912.
35. We performed MO calculations for all of possible 6,6-membered bicyclic oxonium ions by SPARTAN (version 3.1.2) using the AM1 Hamiltonian. The results showed that the cis-decalin form intermediate C is the most stable among the others involving trans-decalin form intermediates. (The heat of formation of C was 145.71 kcal/mol. The others were 146.80 kcal/mol for another cis-decalin form intermediate and 148.79, 151.16 kcal/mol for trans ones.) These calculational results were consistent with our experimental results. We think that the stability of bicyclic intermediates has a large influence on the reaction of 1c. We also performed MO calculations on 5,5-membered bicyclic intermediates. In these cases, the intermediate A′ was more stable than A. (The heat of formation of A was 159.30 kcal/mol, and of A′ was 157.18 kcal/mol.) This calculational result did not fit with our experimental results. It is probable that the repulsion between the halomethyl substituent and anion species, which should exist on the convex side of the cation, has a large influence on the reaction of 1a and makes the formation of A′ undesirable.
36. For the reaction of a Grignard reagent and an acetal, see: Yuan, T.-M.; Yeh, S.-M.; Hsieh, Y.-T.; Luh, T.-Y. J. Org. Chem. 1994, 59, 8192 and references therein.
37. The stereochemistry of compounds 9a-h were determined by X-ray crystallography of the p-nitrobenzoate derivative 16 derived from 9d by hydroboration-oxidation followed by p-nitrobenzoylation. The author has deposited atomic coordinates for this structure with the Cambridge Crystallographic Data Centre. The coordinates can be obtained, on request, from the Director, Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, U.K.
38. (a) van Dorp, D. A.; Word, J. P. Experientia 1981, 37, 917.
39. (b) Maurer, B.; Tohmmen, W. Ibid. 1979, 62, 1096.
40. (c) Maurer, B.; Grieder, A.; Tohmmen, W. Helv. Chim. Acta 1979, 62, 44.
41. (a) Fujioka, H.; Kitagawa, H.; Kondo, M.; Kita, Y. Heterocydes 1994, 37, 743.
42. (b) Fujioka, H.; Kitagawa, H.; Kondo, M.; Matsunaga, N.; Kitagaki, S.; Kita, Y. Heterocycles 1993, 35, 665.