Enolate generation under hydrogenation conditions: Catalytic aldol cycloreduction of keto-enones

Organic Letters

Volumn 5, Issue 7, 2003, Pages 1143-1146

  Huddleston, Ryan R ^a   Krische, Michael J ^a  

^a UNIVERSITY OF TEXAS AT AUSTIN   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALDEHYDE; CARBONYL DERIVATIVE; ENOLATE; KETONE DERIVATIVE; UNCLASSIFIED DRUG; HETEROCYCLIC COMPOUND; HYDROGEN; KETONE;

ALDOL REACTION; ARTICLE; CATALYSIS; CHEMICAL BOND; HYDROGENATION; PROTON NUCLEAR MAGNETIC RESONANCE; REDUCTION; X RAY DIFFRACTION; CHEMICAL STRUCTURE; CHEMISTRY; CYCLIZATION; SYNTHESIS;

ALDEHYDES; CATALYSIS; CYCLIZATION; HETEROCYCLIC COMPOUNDS; HYDROGEN; HYDROGENATION; KETONES; MOLECULAR STRUCTURE;

EID: 0038537593     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol0300219     Document Type: Article

References (35)

1. For selected reviews on the generation and utilization of enolates, see: (a) Arya, P.; Qin, H. Tetrahedron 2000, 56, 917. (b) Hughes, D. L. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. III, p 1273. (c) Evans, D. A. Asymmetric Synth. 1984, 3, 1. (d) Jackman, L. M.; Lange, B. C. Tetrahedron 1977, 33, 2737. (e) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. II, p 99.
2. For selected reviews on the generation and utilization of enolates, see: (a) Arya, P.; Qin, H. Tetrahedron 2000, 56, 917. (b) Hughes, D. L. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. III, p 1273. (c) Evans, D. A. Asymmetric Synth. 1984, 3, 1. (d) Jackman, L. M.; Lange, B. C. Tetrahedron 1977, 33, 2737. (e) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. II, p 99.
3. For selected reviews on the generation and utilization of enolates, see: (a) Arya, P.; Qin, H. Tetrahedron 2000, 56, 917. (b) Hughes, D. L. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. III, p 1273. (c) Evans, D. A. Asymmetric Synth. 1984, 3, 1. (d) Jackman, L. M.; Lange, B. C. Tetrahedron 1977, 33, 2737. (e) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. II, p 99.
4. For selected reviews on the generation and utilization of enolates, see: (a) Arya, P.; Qin, H. Tetrahedron 2000, 56, 917. (b) Hughes, D. L. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. III, p 1273. (c) Evans, D. A. Asymmetric Synth. 1984, 3, 1. (d) Jackman, L. M.; Lange, B. C. Tetrahedron 1977, 33, 2737. (e) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. II, p 99.
5. For selected reviews on the generation and utilization of enolates, see: (a) Arya, P.; Qin, H. Tetrahedron 2000, 56, 917. (b) Hughes, D. L. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. III, p 1273. (c) Evans, D. A. Asymmetric Synth. 1984, 3, 1. (d) Jackman, L. M.; Lange, B. C. Tetrahedron 1977, 33, 2737. (e) Mekelburger, H. B.; Wilcox, C. S. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. II, p 99.
6. Jang, H.-Y.; Huddleston, R. R.; Krische, M. J. J. Am. Chem. Soc. 2002, 124, 15156.
7. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
8. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
9. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
10. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
11. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
12. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
13. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
14. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
15. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
16. For related catalytic reductive aldol processes, see: (a) Revis, A.; Hilty, T. K. Tetrahedron Lett. 1987, 28, 4809. (b) Matsuda, I.; Takahashi, K.; Sato, S. Tetrahedron Lett. 1990, 31, 5331. (c) Isayama, S.; Mukaiyama, T. Chem. Lett. 1989, 2005. (d) Kiyooka, S.; Shimizu, A.; Torii, S. Tetrahedron Lett. 1998, 39, 5237. (e) Ooi, T.; Doda, K.; Sakai, D.; Maruoka, K. Tetrahedron Lett. 1999, 40, 2133. (f) Taylor, S. J.; Morken, J. P. J. Am. Chem. Soc. 1999, 121, 12202. (g) Taylor, S. J.; Duffey, M. O.; Morken, J. P. J. Am. Chem. Soc. 2000, 122, 4528. (h) Zhao, C.-X.; Duffey, M. O.; Taylor, S. J.; Morken, J. P. Org. Lett. 2001, 3, 1829. (i) Baik, T.-G.; Luiz, A. L.; Wang, L.-C.; Krische, M. J. J. Am. Chem. Soc. 2001, 123, 5112. (j) Emiabata-Smith, D.; McKillop, A.; Mills, C.; Motherwell, W. B.; Whitehead, A. J. Synlett 2001, 1302.
17. For a review on the use of enones as latent enolates in catalysis, see: Huddleston, R. R.; Krische, M. J. Synlett 2003, 12.
18. Borane-mediated aldol cycloreduction of keto-enones was recently reported by our lab: Huddleston, R. R.; Cauble, D. F.; Krische, M. J. J. Org. Chem. 2003, 68, 11.
19. For selected reviews on the conjugate reduction of enones via catalytic hydrogenation, see: (a) Keinan, E.; Greenspoon, N. Partial Reduction of Enones, Styrenes and Related Systems. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. III, p 523. (b) House, H. O. Modern Synthetic Reactions, 2nd ed.; Benjamin: Menlo Park, CA, 1972. (c) James, B. R. Homogeneous Hydrogenation; Wiley-Interscience: New York, 1973. (d) Rylander, P. N. Hydrogenation Methods; Academic Press: London, 1985. (e) Rylander, P. N. Catalytic Hydrogenation in Organic Synthesis; Academic Press: New York, 1979. (f) Freifelder, M. Catalytic Hydrogenation in Organic Synthesis; Wiley-Interscience: New York, 1978.
20. For selected reviews on the conjugate reduction of enones via catalytic hydrogenation, see: (a) Keinan, E.; Greenspoon, N. Partial Reduction of Enones, Styrenes and Related Systems. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. III, p 523. (b) House, H. O. Modern Synthetic Reactions, 2nd ed.; Benjamin: Menlo Park, CA, 1972. (c) James, B. R. Homogeneous Hydrogenation; Wiley-Interscience: New York, 1973. (d) Rylander, P. N. Hydrogenation Methods; Academic Press: London, 1985. (e) Rylander, P. N. Catalytic Hydrogenation in Organic Synthesis; Academic Press: New York, 1979. (f) Freifelder, M. Catalytic Hydrogenation in Organic Synthesis; Wiley-Interscience: New York, 1978.
21. For selected reviews on the conjugate reduction of enones via catalytic hydrogenation, see: (a) Keinan, E.; Greenspoon, N. Partial Reduction of Enones, Styrenes and Related Systems. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. III, p 523. (b) House, H. O. Modern Synthetic Reactions, 2nd ed.; Benjamin: Menlo Park, CA, 1972. (c) James, B. R. Homogeneous Hydrogenation; Wiley-Interscience: New York, 1973. (d) Rylander, P. N. Hydrogenation Methods; Academic Press: London, 1985. (e) Rylander, P. N. Catalytic Hydrogenation in Organic Synthesis; Academic Press: New York, 1979. (f) Freifelder, M. Catalytic Hydrogenation in Organic Synthesis; Wiley-Interscience: New York, 1978.
22. For selected reviews on the conjugate reduction of enones via catalytic hydrogenation, see: (a) Keinan, E.; Greenspoon, N. Partial Reduction of Enones, Styrenes and Related Systems. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. III, p 523. (b) House, H. O. Modern Synthetic Reactions, 2nd ed.; Benjamin: Menlo Park, CA, 1972. (c) James, B. R. Homogeneous Hydrogenation; Wiley-Interscience: New York, 1973. (d) Rylander, P. N. Hydrogenation Methods; Academic Press: London, 1985. (e) Rylander, P. N. Catalytic Hydrogenation in Organic Synthesis; Academic Press: New York, 1979. (f) Freifelder, M. Catalytic Hydrogenation in Organic Synthesis; Wiley-Interscience: New York, 1978.
23. For selected reviews on the conjugate reduction of enones via catalytic hydrogenation, see: (a) Keinan, E.; Greenspoon, N. Partial Reduction of Enones, Styrenes and Related Systems. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. III, p 523. (b) House, H. O. Modern Synthetic Reactions, 2nd ed.; Benjamin: Menlo Park, CA, 1972. (c) James, B. R. Homogeneous Hydrogenation; Wiley-Interscience: New York, 1973. (d) Rylander, P. N. Hydrogenation Methods; Academic Press: London, 1985. (e) Rylander, P. N. Catalytic Hydrogenation in Organic Synthesis; Academic Press: New York, 1979. (f) Freifelder, M. Catalytic Hydrogenation in Organic Synthesis; Wiley-Interscience: New York, 1978.
24. For selected reviews on the conjugate reduction of enones via catalytic hydrogenation, see: (a) Keinan, E.; Greenspoon, N. Partial Reduction of Enones, Styrenes and Related Systems. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon: New York, 1991; Vol. III, p 523. (b) House, H. O. Modern Synthetic Reactions, 2nd ed.; Benjamin: Menlo Park, CA, 1972. (c) James, B. R. Homogeneous Hydrogenation; Wiley-Interscience: New York, 1973. (d) Rylander, P. N. Hydrogenation Methods; Academic Press: London, 1985. (e) Rylander, P. N. Catalytic Hydrogenation in Organic Synthesis; Academic Press: New York, 1979. (f) Freifelder, M. Catalytic Hydrogenation in Organic Synthesis; Wiley-Interscience: New York, 1978.
25. For a review on the heterolytic activation of elemental hydrogen, see: Brothers, P. J. Prog. Inorg. Chem. 1981, 28, 1.
26. (a) Tolman, C. A.; Meakin, P. Z.; Lindner, D. L.; Jesson, J. P. J. Am. Chem. Soc. 1974, 96, 2762.
27. (b) Halpern, J.; Okamoto, T.; Zakhariev, A. J. Mol. Catal. 1976, 2, 65.
28. For a review, see: Marko, L. Pure Appl. Chem. 1979, 51, 2211.
29. Monohydride formation by deprotonation of a dihydride intermediate is known for cationic Rh complexes: (a) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 2134. (b) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 2143. (c) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 4450.
30. Monohydride formation by deprotonation of a dihydride intermediate is known for cationic Rh complexes: (a) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 2134. (b) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 2143. (c) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 4450.
31. Monohydride formation by deprotonation of a dihydride intermediate is known for cationic Rh complexes: (a) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 2134. (b) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 2143. (c) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 4450.
32. 2 has been suggested, but the mechanism likely involves an intermediate dihydride: Evans, D.; Osborn, J. A.; Wilkinson, G. J. Chem. Soc., A 1968, 3133.
33. For a review, see: Norton, J. R. In Transition Metal Hydrides; Dedieu, A. Ed.; New York, 1992, Chapter 9.
34. For a review, see: Burkhardt, E. R.; Doney, J. J.; Slough, G. A.; Stack, J. M.; Heathcock, C. H.; Bergman, R. G. Pure Appl. Chem. 1988, 60, 1.
35. 3 (0.37 mmol, 80 mol %) were added. The system was purged with hydrogen gas for 3 min, and the reaction was allowed to stir at 80°C under 1 atm of hydrogen until complete consumption of the substrate. Yields represent averages of three runs. Cycloreductions to produce compounds 6b, 12b, and 13b-18b were conducted at 25°C.