Enantioselective H-atom transfer reaction: A strategy to synthesize formaldehyde aldol products

Organic Letters

Volumn 7, Issue 8, 2005, Pages 1453-1456

  Sibi, Mukund P ^a   Patil, Kalyani ^a  

^a NORTH DAKOTA STATE UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ESTER; FORMALDEHYDE; HYDROGEN;

ALDOL REACTION; ALKYLATION; ARTICLE; ATOM; BAYLIS HILLMAN REACTION; CHEMICAL BOND; ENANTIOSELECTIVITY; HYDROGENATION; REACTION ANALYSIS; STRUCTURE ANALYSIS; SYNTHESIS;

ALDEHYDES; ALKYLATION; CATALYSIS; FORMALDEHYDE; MOLECULAR STRUCTURE; PROTONS; STEREOISOMERISM;

EID: 17844392836     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol047347h     Document Type: Article

References (56)

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28. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
29. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
30. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
31. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
32. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
33. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
34. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
35. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
36. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
37. For examples of H-atom transfer reactions mediated by chiral Lewis acids, see: (a) Sugimoto, H.; Nakamura, S.; Watanabe, Y.; Toru, T. Tetrahedron: Asymmetry 2003, 14, 3043. (b) Sibi, M. P.; Sausker, J. B. J. Am. Chem. Soc. 2002, 124, 984. (c) Sibi, M. P.; Asano, Y.; Sausker, J. B. Angew. Chem., Int. Ed. 2001, 40, 1293. (d) Murakata, M.; Tsutsui, H.; Takeuchi, N.; Hoshino, O. Tetrahedron 1999, 55, 10295. (e) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576. For selected examples of enantioselective reductions with chiral H-atom transfer reagents, see: (f) Zeng, L.; Perchyonok, T.; Schiesser, C. H. Tetrahedron: Asymmetry 2004, 15, 995. (g) Dakterniecks, D.; Perchyonok, V. T.; Schiesser, C. H. Tetrahedron: Asymmetry 2003, 14, 3057. (h) Blumenstein, M.; Lemmler, M.; Hayen, A.; Metzger, J. O. Tetrahedron: Asymmetry 2003, 14, 3069. (i) Dakternieks, D.; Dunn, K.; Perchyonok, V. T.; Schiesser, C. H. Chem. Commun. 1999, 1665. (j) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235. (k) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
38. For a review on enantioselective protonations see: Eames, J.; Weerasooriya, N. Tetrahedron: Asymmetry 2001, 12, 1. For non free radical methods involving reductive alkylation of acrylates with enantioselective protonation see: (a) Reetz, M. T.; Moulin, D.; Gosburg, A. Org. Lett. 2001, 3, 4083. (b) Chapman, C. J.; Wadsworth, K. J.; Frost, C. G. J. Organomet. Chem. 2003, 680, 206. (c) Chapman C. J.; Frost, C. G. Adv. Synth. Catal. 2003, 345, 353. (d) Huang, T.-S.; Li, C.-J. Org. Lett. 2001, 3, 2037. (e) Moss, R. J.; Wadsworth, K. J.; Chapman, C. J.; Frost, C. G. Chem. Commun. 2004, 1984. For Co-mediated reduction/protonation, see: Ohtsuka, Y.; Ikeno, T.; Yamada, T. Tetrahedron: Asymmetry 2003, 14, 967.
39. For a review on enantioselective protonations see: Eames, J.; Weerasooriya, N. Tetrahedron: Asymmetry 2001, 12, 1. For non free radical methods involving reductive alkylation of acrylates with enantioselective protonation see: (a) Reetz, M. T.; Moulin, D.; Gosburg, A. Org. Lett. 2001, 3, 4083. (b) Chapman, C. J.; Wadsworth, K. J.; Frost, C. G. J. Organomet. Chem. 2003, 680, 206. (c) Chapman C. J.; Frost, C. G. Adv. Synth. Catal. 2003, 345, 353. (d) Huang, T.-S.; Li, C.-J. Org. Lett. 2001, 3, 2037. (e) Moss, R. J.; Wadsworth, K. J.; Chapman, C. J.; Frost, C. G. Chem. Commun. 2004, 1984. For Co-mediated reduction/protonation, see: Ohtsuka, Y.; Ikeno, T.; Yamada, T. Tetrahedron: Asymmetry 2003, 14, 967.
40. For a review on enantioselective protonations see: Eames, J.; Weerasooriya, N. Tetrahedron: Asymmetry 2001, 12, 1. For non free radical methods involving reductive alkylation of acrylates with enantioselective protonation see: (a) Reetz, M. T.; Moulin, D.; Gosburg, A. Org. Lett. 2001, 3, 4083. (b) Chapman, C. J.; Wadsworth, K. J.; Frost, C. G. J. Organomet. Chem. 2003, 680, 206. (c) Chapman C. J.; Frost, C. G. Adv. Synth. Catal. 2003, 345, 353. (d) Huang, T.-S.; Li, C.-J. Org. Lett. 2001, 3, 2037. (e) Moss, R. J.; Wadsworth, K. J.; Chapman, C. J.; Frost, C. G. Chem. Commun. 2004, 1984. For Co-mediated reduction/protonation, see: Ohtsuka, Y.; Ikeno, T.; Yamada, T. Tetrahedron: Asymmetry 2003, 14, 967.
41. For a review on enantioselective protonations see: Eames, J.; Weerasooriya, N. Tetrahedron: Asymmetry 2001, 12, 1. For non free radical methods involving reductive alkylation of acrylates with enantioselective protonation see: (a) Reetz, M. T.; Moulin, D.; Gosburg, A. Org. Lett. 2001, 3, 4083. (b) Chapman, C. J.; Wadsworth, K. J.; Frost, C. G. J. Organomet. Chem. 2003, 680, 206. (c) Chapman C. J.; Frost, C. G. Adv. Synth. Catal. 2003, 345, 353. (d) Huang, T.-S.; Li, C.-J. Org. Lett. 2001, 3, 2037. (e) Moss, R. J.; Wadsworth, K. J.; Chapman, C. J.; Frost, C. G. Chem. Commun. 2004, 1984. For Co-mediated reduction/protonation, see: Ohtsuka, Y.; Ikeno, T.; Yamada, T. Tetrahedron: Asymmetry 2003, 14, 967.
42. For a review on enantioselective protonations see: Eames, J.; Weerasooriya, N. Tetrahedron: Asymmetry 2001, 12, 1. For non free radical methods involving reductive alkylation of acrylates with enantioselective protonation see: (a) Reetz, M. T.; Moulin, D.; Gosburg, A. Org. Lett. 2001, 3, 4083. (b) Chapman, C. J.; Wadsworth, K. J.; Frost, C. G. J. Organomet. Chem. 2003, 680, 206. (c) Chapman C. J.; Frost, C. G. Adv. Synth. Catal. 2003, 345, 353. (d) Huang, T.-S.; Li, C.-J. Org. Lett. 2001, 3, 2037. (e) Moss, R. J.; Wadsworth, K. J.; Chapman, C. J.; Frost, C. G. Chem. Commun. 2004, 1984. For Co-mediated reduction/protonation, see: Ohtsuka, Y.; Ikeno, T.; Yamada, T. Tetrahedron: Asymmetry 2003, 14, 967.
43. For a review on enantioselective protonations see: Eames, J.; Weerasooriya, N. Tetrahedron: Asymmetry 2001, 12, 1. For non free radical methods involving reductive alkylation of acrylates with enantioselective protonation see: (a) Reetz, M. T.; Moulin, D.; Gosburg, A. Org. Lett. 2001, 3, 4083. (b) Chapman, C. J.; Wadsworth, K. J.; Frost, C. G. J. Organomet. Chem. 2003, 680, 206. (c) Chapman C. J.; Frost, C. G. Adv. Synth. Catal. 2003, 345, 353. (d) Huang, T.-S.; Li, C.-J. Org. Lett. 2001, 3, 2037. (e) Moss, R. J.; Wadsworth, K. J.; Chapman, C. J.; Frost, C. G. Chem. Commun. 2004, 1984. For Co-mediated reduction/protonation, see: Ohtsuka, Y.; Ikeno, T.; Yamada, T. Tetrahedron: Asymmetry 2003, 14, 967.
44. For a review on enantioselective protonations see: Eames, J.; Weerasooriya, N. Tetrahedron: Asymmetry 2001, 12, 1. For non free radical methods involving reductive alkylation of acrylates with enantioselective protonation see: (a) Reetz, M. T.; Moulin, D.; Gosburg, A. Org. Lett. 2001, 3, 4083. (b) Chapman, C. J.; Wadsworth, K. J.; Frost, C. G. J. Organomet. Chem. 2003, 680, 206. (c) Chapman C. J.; Frost, C. G. Adv. Synth. Catal. 2003, 345, 353. (d) Huang, T.-S.; Li, C.-J. Org. Lett. 2001, 3, 2037. (e) Moss, R. J.; Wadsworth, K. J.; Chapman, C. J.; Frost, C. G. Chem. Commun. 2004, 1984. For Co-mediated reduction/protonation, see: Ohtsuka, Y.; Ikeno, T.; Yamada, T. Tetrahedron: Asymmetry 2003, 14, 967.
45. For recent reviews on Baylis-Hillman reaction, see: (a) Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. Rev. 2003, 103, 811. (b) Langer, P. Angew. Chem., Int. Ed. 2000, 39, 3049. (c) Ciganek, E. Org. React. 1997, 51, 201.
46. For recent reviews on Baylis-Hillman reaction, see: (a) Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. Rev. 2003, 103, 811. (b) Langer, P. Angew. Chem., Int. Ed. 2000, 39, 3049. (c) Ciganek, E. Org. React. 1997, 51, 201.
47. For recent reviews on Baylis-Hillman reaction, see: (a) Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. Rev. 2003, 103, 811. (b) Langer, P. Angew. Chem., Int. Ed. 2000, 39, 3049. (c) Ciganek, E. Org. React. 1997, 51, 201.
48. For the synthesis of substrates, see the Supporting Information. For benzyl substituent, see: O'Leary, B. M.; Szabo, T.; Svenstrup, N.; Schalley, C. A.; Lutzen, A.; Schafer, M.; Rebek J., Jr. J. Am. Chem. Soc. 2001, 123, 11519.
49. Reaction of 6 with different radicals at -78°C in the absence of any Lewis acid gave products in good yields; EtI (78%), i-Pr-I (51%), cyclopentyl-I (79%), cyclohexyl-I (74%), t-Bu-I (62%). Compound 5 showed similar results.
50. 2 for synthesizing β-amino acids, the same Lewis acid has been used for obtaining the aldol products.
51. Various other chiral Lewis acids were investigated and the best results are shown here. Chiral Lewis acid reactions were also performed on methyl ester. Since the results were similar, they are not shown here.
52. Sibi, M. P.; Manyem, S. Org. Lett. 2002, 4, 2929.
53. 3SiH (TMS = trimethylsilyl) were not clean.
54. 30 mol % chiral Lewis acid-catalyzed reactions provided ee values in the range of 20-25% for most of the substrates with the radical precursors shown.
55. Imogai, H.; Larcheveque, M. Tetrahedron: Asymmetry 1997, 8, 965. Also see the Supporting Information.
56. Reactions of methyl ester substituted acetate provided polymerized products.