Reagent control of geometric selectivity and enantiotopic group preference in asymmetric Horner-Wadsworth-Emmons reactions with meso- dialdehydes

Journal of Organic Chemistry

Volumn 63, Issue 23, 1998, Pages 8284-8294

  Tullis, Joshua S ^a,b,c   Vares, Lauri ^a,b   Kann, Nina ^b,e   Norrby, Per Ola ^d   Rein, Tobias ^a,b  

^a TECHNICAL UNIVERSITY OF DENMARK   (Denmark)

^b ROYAL INSTITUTE OF TECHNOLOGY   (Sweden)

^c UNIVERSITY OF NOTRE DAME   (United States)

^d UNIVERSITY OF COPENHAGEN   (Denmark)

^e CHALMERS UNIVERSITY OF TECHNOLOGY   (Sweden)

Author keywords

[No Author keywords available]

Indexed keywords

ALDEHYDE DERIVATIVE; ALKENE DERIVATIVE; PHOSPHONIC ACID DERIVATIVE; REAGENT;

ARTICLE; CHEMICAL STRUCTURE; CHIRALITY; REACTION ANALYSIS; STEREOCHEMISTRY;

EID: 0032514973     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo981102z     Document Type: Article

References (78)

1. For reviews on the use of bifunctional substrates in two-directional synthesis, see: (a) Poss, C. S.; Schreiber, S. L. Acc. Chem. Res. 1994, 27, 9-17, and references therein. (b) Magnuson, S. R. Tetrahedron 1995, 51, 2167-2213. (c) Maier, M. In Organic Synthesis Highlights II; Waldmann, H., Ed.; VCH: Weinheim, 1995; pp 203-222.
2. For reviews on the use of bifunctional substrates in two-directional synthesis, see: (a) Poss, C. S.; Schreiber, S. L. Acc. Chem. Res. 1994, 27, 9-17, and references therein. (b) Magnuson, S. R. Tetrahedron 1995, 51, 2167-2213. (c) Maier, M. In Organic Synthesis Highlights II; Waldmann, H., Ed.; VCH: Weinheim, 1995; pp 203-222.
3. For reviews on the use of bifunctional substrates in two-directional synthesis, see: (a) Poss, C. S.; Schreiber, S. L. Acc. Chem. Res. 1994, 27, 9-17, and references therein. (b) Magnuson, S. R. Tetrahedron 1995, 51, 2167-2213. (c) Maier, M. In Organic Synthesis Highlights II; Waldmann, H., Ed.; VCH: Weinheim, 1995; pp 203-222.
4. For an excellent recent review, see: Schoffers, E.; Golebiowski, A.; Johnson, C. R. Tetrahedron 1996, 52, 3769-3826.
5. (a) Eder, U.; Sauer, G.; Wiechert, R. Angew. Chem. 1971, 83, 492-493.
6. (b) Hajos, Z. G.; Parrish, D. R. J. Org. Chem. 1974, 39, 1615-1621.
7. For reviews, see: (c) Ward, R. S. Chem. Soc. Rev. 1990, 19, 1-19. (d) Gais, H.-J. In Houben-Weyl, Stereoselective Synthesis; Helmchen, G., Hoffman, R. W., Mulzer, J., Schaumann, E., Eds.; Thieme: Stuttgart, 1996; Vol. 1, pp 589-643.
8. For reviews, see: (c) Ward, R. S. Chem. Soc. Rev. 1990, 19, 1-19. (d) Gais, H.-J. In Houben-Weyl, Stereoselective Synthesis; Helmchen, G., Hoffman, R. W., Mulzer, J., Schaumann, E., Eds.; Thieme: Stuttgart, 1996; Vol. 1, pp 589-643.
9. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
10. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
11. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
12. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
13. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
14. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
15. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
16. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
17. For examples of the use of meso-dialdehydes as substrates for other types of asymmetric transformations, see: (a) Yamazaki, Y.; Hosono, K. Tetrahedron Lett. 1988, 29, 5769-5770. (b) Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707-4710. (c) Wang, Z.; Deschênes, D. J. Am. Chem. Soc. 1992, 114, 1090-1091. (d) Ward, D. E.; Liu, Y.; Rhee, C. K. Synlett 1993, 561-563. (e) Ward, D. E.; Liu, Y. D.; Rhee, C. K. Can. J. Chem. 1994, 72, 1429-1446. (f) Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151-2152. (g) Oppolzer, W.; De Brabander, J.; Walther, E., Bernardinelli, G. Tetrahedron Lett. 1995, 36, 4413-4416. (h) De Brabander, J.; Oppolzer, W. Tetrahedron 1997, 53, 9169-9202. (i) Oppolzer, W.; Walther, E.; Balado, C. P.; De Brabander, J. Tetrahedron Lett. 1997, 38, 809-812.
18. Part of this work has been described in an earlier communication; see ref 4m.
19. (a) Horner, L.; Huffman, H.; Wippel, H. G. Chem. Ber. 1958, 91, 61-63.
20. (b) Horner, L.; Hoffman, H.; Wippel, H. G.; Klahre, G. Chem. Ber. 1959, 92, 2499-2505.
21. (c) Wadsworth, W. S.; Emmons, W. D. J. Am. Chem. Soc. 1961, 83, 1733-1738.
22. For reviews discussing general aspects of the HWE reaction, see: (d) Boutagy, J.; Thomas, R. Chem. Rev. 1974, 74, 87-99. (e) Wadsworth, W. S., Jr. Org. React. 1977, 25, 73-253. (f) Walker, B. J. In Organophosphorus Reagents in Organic Synthesis; Cadogan, J. I. G., Ed.; Academic Press: New York, 1979; pp 155-205.
23. For reviews discussing general aspects of the HWE reaction, see: (d) Boutagy, J.; Thomas, R. Chem. Rev. 1974, 74, 87-99. (e) Wadsworth, W. S., Jr. Org. React. 1977, 25, 73-253. (f) Walker, B. J. In Organophosphorus Reagents in Organic Synthesis; Cadogan, J. I. G., Ed.; Academic Press: New York, 1979; pp 155-205.
24. For reviews discussing general aspects of the HWE reaction, see: (d) Boutagy, J.; Thomas, R. Chem. Rev. 1974, 74, 87-99. (e) Wadsworth, W. S., Jr. Org. React. 1977, 25, 73-253. (f) Walker, B. J. In Organophosphorus Reagents in Organic Synthesis; Cadogan, J. I. G., Ed.; Academic Press: New York, 1979; pp 155-205.
25. (g) Maryanoff, B. E.; Reitz, A. B. Chem. Rev. 1989, 89, 863-927.
26. (h) Kelly, S. E. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 1, pp 730-817. See also ref 4d.
27. Hatakeyama, S.; Satoh, K.; Sakurai, K.; Takano, S. Tetrahedron Lett. 1987, 28, 2713-2716. In our hands, stoichiometric amounts of DMAP were in some cases required for the reactions to give good yields.
28. Compound 1b is commercially available. Phosphonate 1d was prepared according to the procedure of Still: Still, W. C.; Gennari, C. Tetrahedron Lett. 1983, 24, 4405-4408.
29. After our initial report on asymmetric HWE reactions with 6, this dialdehyde has also been used as substrate in group-selective asymmetric aldol reactions; see refs 5g and 5h.
30. Norcross, R. D.; Paterson, I. Chem. Rev. 1995, 95, 2041-2114.
31. Rychnovsky, S. D. Chem. Rev. 1995, 95, 2021-2040.
32. For experimental details regarding the preparation of 4 and 5, see Supporting Information.
33. (a) Harada, T.; Matsuda, Y.; Uchimura, J.; Oku, A. J. Chem. Soc., Chem. Commun. 1990, 21-22.
34. (b) Harada, T.; Inoue, A.; Wada, I.; Uchimura, J.; Tanaka, S.; Oku, A. J. Am. Chem. Soc. 1993, 115, 7665-7674. For an enzyme-catalyzed desymmetrization of 5 by group-selective esterification, see: Chenevert, R.; Courchesne, G. Tetrahedron: Asymmetry 1995, 6, 2093-2096.
35. (b) Harada, T.; Inoue, A.; Wada, I.; Uchimura, J.; Tanaka, S.; Oku, A. J. Am. Chem. Soc. 1993, 115, 7665-7674. For an enzyme-catalyzed desymmetrization of 5 by group-selective esterification, see: Chenevert, R.; Courchesne, G. Tetrahedron: Asymmetry 1995, 6, 2093-2096.
36. Mancuso, A.; Huang, S.-L.; Swern, D. J. Org. Chem. 1978, 43, 2480-2482.
37. Harada, T.; Kagamihara, Y.; Tanaka, S.; Sakamoto, K.; Oku, A. J. Org. Chem. 1992, 57, 1637-1639.
38. Schink, H. E.; Petterson, H.; Bäckvall, J.-E. J. Org. Chem. 1991, 56, 2769-2774.
39. Bäckvall, J.-E.; Byström, S. E.; Nordberg, R. E. J. Org. Chem. 1984, 49, 4619-4631.
40. 18 compound meso-(3R,5s,7S)-5-methoxy-3,7-diacetoxycyclohept-1-ene. As evidenced by NMR on the crude product, the Pd-catalyzed diacetoxylation was not completely stereoselective. However, the other product isomers could be cleanly removed by use of the MPLC system described by Baeckstrom: Baeckström, P.; Stridh, K.; Li, L.; Norin, T. Acta Chem. Scand., Ser. B 1987, 41, 442-447.
41. 6, excellent yields of isomerically pure dialdehyde 14b were reproducibly obtained. Oxidative cleavage of the alkenes 12 by ozonolysis was also attempted, but in our hands the two-step osmylation/periodic acid protocol gave much cleaner products.
42. Thompson, S. K.; Heathcock, C. H. J. Org. Chem. 1990, 55, 3386-3388, and references therein.
43. For details regarding how structure assignments for the HWE product isomers have been made, and how isomer ratios have been determined, see Supporting Information.
44. In general, the (E)- and (Z)-monoaddition products could be separated by flash chromatography. It also proved possible to separate the (E)-diastereomers 23a and 24a (Scheme 6, vide infra) by chromatography, if Amicon silica (see Experimental Section) was used; however, we have not yet found conditions which enable complete separation of other diastereomeric products (i.e., 19/20, 23b/24b, 25a/26a). Some of the HWE products showed tendencies to undergo slight epimerization during chromatography, but this could be suppressed by use of appropriate conditions: compounds 19 and 21 could be chromatographed on Merck silica (see Experimental Section) if the silica was deactivated by elution with EtOAc or EtOAc/MeOH prior to chromatography; compounds 23b and 25b could be chromatographed on Amicon silica without detectable epimerization, whereas use of the Merck silica caused some epimerization. The silyl-protected products 23a and 25a did not undergo observable epimerization on either type of silica.
45. (a) Dale, J. A.; Mosher, H. S. J. Am. Chem. Soc. 1973, 95, 512-519.
46. (b) Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H. J. Am. Chem. Soc. 1991, 113, 4092-4096, and references therein. For further details regarding the preparation and NMR analyses of compounds 27 and 30, see Supporting Information.
47. We have found the same general trend to be valid also in kinetic/dynamic resolutions of racemic monoaldehydes by reaction with phosphonates 3a-d; see refs 4o, 4s, and 4t.
48. A topic worthy of future investigation is whether the use of another protecting group would enable a change in the mechanism by which the α-stereocenter in the substrate influences the reaction stereochemistry (see mechanistic discussion below, and also ref 4cc); such a change could, in turn, enable complementary preparation of other product diastereomers.
49. Schreiber, S. S.; Schreiber, T. S.; Smith, D. B. J. Am. Chem. Soc. 1987, 109, 1525-1529, and references therein.
50. This expectation rests on the assumption that the unreacted aldehyde carbonyl groups in the monoaddition diastereomers show relative reactivities similar to the corresponding enantiotopic carbonyl groups in the dialdehyde substrate.
51. Brandt, P.; Norrby, P.-O.; Martin, I.; Rein, T. J. Org. Chem. 1998, 63, 1280-1289.
52. (a) Norrby, P.-O. In Transition State Modelling for Catalysis; Truhlar, D., Morokuma, K., Eds.; ACS Symposium Series, in press.
53. (b) Norrby, P.-O.; Brandt, P.; Rein, T., manuscript in preparation. At present, modeling tools are available for reactions involving phosphonates containing simple alkyl groups (e.g., 3a-c). Work toward the design of parameter sets which will allow modeling of trifluoroethyl reagents is in progress.
54. Note that the designation of the geometry of enolate 34 as (E) or (Z) depends on whether a counterion is considered as being bonded to the anionic oxygen or not, and if so, on the CIP priority of that counterion relative to carbon.
55. 4y that the lithium enolate formed from 3a has (E)-geometry. We are presently studying the stuctures of enolates derived from reagents 3b-d, as well as the dependence of the enolate ratios on the reaction conditions; these studies will be reported upon separately.
56. (a) Bottin-Strzalko, T.; Corset, J.; Froment, F.; Pouet, M.-J.; Seyden-Penne, J.; Simmonin, M.-P. J. Org. Chem. 1980, 45, 1270-1276.
57. (b) Seyden-Penne, J. Bull. Soc. Chim. France 1988 (II), 238-242, and references therein.
58. (a) Chérest, M.; Felkin, H. Tetrahedron Lett. 1968, 2205-2208.
59. (b) Anh, N. T.; Eisenstein, O.; Lefour, J.-M.; Trân Huu Dâu, M. E. J. Am. Chem. Soc. 1973, 95, 6146-6147.
60. (c) Anh, N. T.; Eisenstein, O. Nouv. J. Chem. 1977, 1, 61-70.
61. (d) Anh, N. T. Top. Curr. Chem. 1980, 88, 145-162.
62. (e) Lodge, E. P.; Heathcock, C. H. J. Am. Chem. Soc. 1987, 109, 2819-2820.
63. (f) Lodge, E. P.; Heathcock, C. H. J. Am. Chem. Soc. 1987, 709, 3353-3361.
64. For excellent discussions of different models for diastereoselection in nucleophilic additions to carbonyl compounds, see: (g) Roush, W. R. J. Org. Chem. 1991, 56, 4151-4157. (h) Evans, D. A.; Dart, M. J.; Duffy, J. L.; Yang, M. G. J. Am. Chem. Soc. 1996, 118, 4322-4343. (i) Gung, B. W. Tetrahedron 1996, 52, 5263-5301.
65. For excellent discussions of different models for diastereoselection in nucleophilic additions to carbonyl compounds, see: (g) Roush, W. R. J. Org. Chem. 1991, 56, 4151-4157. (h) Evans, D. A.; Dart, M. J.; Duffy, J. L.; Yang, M. G. J. Am. Chem. Soc. 1996, 118, 4322-4343. (i) Gung, B. W. Tetrahedron 1996, 52, 5263-5301.
66. For excellent discussions of different models for diastereoselection in nucleophilic additions to carbonyl compounds, see: (g) Roush, W. R. J. Org. Chem. 1991, 56, 4151-4157. (h) Evans, D. A.; Dart, M. J.; Duffy, J. L.; Yang, M. G. J. Am. Chem. Soc. 1996, 118, 4322-4343. (i) Gung, B. W. Tetrahedron 1996, 52, 5263-5301.
67. 34h a stereoehemical model which rationalizes the merged influence of α- and β-substituents in aldol-type additions to substituted aldehydes, including α-methyl-β-alkoxy-aldehydes. However, from substrates containing α- and β-substituents in an anti relationship (as in dialdehyde 6), the Evans model also predicts formation of FAE-type products.
68. We have observed the same general trend in all asymmetric HWE reactions studied by us to date. A similar argumentation is used by Fuji and co-workers when analyzing the results of asymmetric HWE reactions between a chiral phosphonate and a group of meso-diketones; see ref 4bb.
69. Ireland, R. E.; Meissner, R. S. J. Org. Chem. 1991, 56, 4566-4568.
70. Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923-2925.
71. Ort, O. Org. Synth. 1987, 65, 203-214.
72. Dahnke, K. R.; Paquette, L. A. Org. Synth. 1992, 71, 181-188.
73. Schuster, D. I.; Palmer, J. M.; Dickerman, S. C. J. Org. Chem. 1966, 31, 4281-4282.
74. Helmchen, G. In Houben-Weyl, Stereoselective Synthesis; Helmchen, G., Hoffman, R. W., Mulzer, J., Schaumann, E., Eds.; Thieme: Stuttgart, 1996; Vol. 1, pp 1-74.
75. The opposite mode of addition (i.e., adding a precooled solution of the aldehyde to the phosphonate enolate) gave identical results, if the transfer was performed rapidly.
76. The sample also contained 3% of an isomer tentatively assigned as being epimeric at the carbon α to the aldehyde carbonyl; see Supporting Information for details.
77. 4 reduction of the HWE product.
78. 4 reduction, were fully characterized, however; see Supporting Information for details.