The pivotal role of chelation as a stereochemical control element in non-evans anti aldol product formation

Organic Letters

Volumn 12, Issue 12, 2010, Pages 2868-2871

  Shinisha, C B ^a   Sunoj, Raghavan B ^a  

^a INDIAN INSTITUTE OF TECHNOLOGY BOMBAY   (India)

Author keywords

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Indexed keywords

EID: 77953557618     PISSN: 15237060     EISSN: 15237052     Source Type: Journal    
DOI: 10.1021/ol100969f     Document Type: Article

References (41)

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2. Evans, D. A.; Ennis, M. D.; Mathre, D. J. J. Am. Chem. Soc. 1982, 104, 1737
3. Evans, D. A.; Urpi, F.; Somers, T. D.; Clark, J. S.; Bilodeau, M. T. J. Am. Chem. Soc. 1990, 112, 8215
4. Evans, D. A.; Starr, J. T. Angew. Chem., Int. Ed. 2002, 41, 1787
5. Crimmins, M. T.; King, B. W. J. Am. Chem. Soc. 1998, 120, 9084
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8. Patel, J.; Clavé, G.; Renard, P.-Y.; Franck, X. Angew. Chem., Int. Ed. 2008, 47, 4224
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10. Evans, D. A. Aldrichim. Acta 1982, 15, 23
11. Evans, D. A.; Rieger, D. L.; Bilodeau, M. T.; Urpi, F. J. Am. Chem. Soc. 1991, 113, 1047
12. Crimmins, M. T.; King, B. W.; Tabet, E. A.; Chaudhary, K. J. Org. Chem. 2001, 66, 894
13. Details of the stereochemical descriptions and product nomenclature are provided in the Supporting Information.
14. Danda, H.; Hansen, M. M.; Heathcock, C. H. J. Org. Chem. 1990, 55, 173
15. Bonner, M. P.; Thornton, E. R. J. Am. Chem. Soc. 1991, 113, 1299
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22. Except for a rare account on oxazolidinone based stereoinduction by using boron enolates, see: Goodman, J. M.; Paton, R. S. Chem. Commun. 2007, 2124
23. Our efforts toward rationalizing the formation of Evans and non-Evans syn aldol products through chelated and nonchelated transition-state models to date is the only computational study on oxazolidinone mediated asymmetric aldol reaction between Ti-enolate and aldehydes. Shinisha, C. B.; Sunoj, R. B. Manuscript in preparation.
24. All the intermediates and TSs were respectively characterized as minima and first-order saddle points by using frequency calculations. Further, intrinsic reaction coordinate (IRC) calculations were performed to authenticate the TSs. Calculations on the critical TSs were further repeated at the mPW1K level of theory. See the Supporting Information for further details.
25. The solvent effects were incorporated with the continuum solvation model by using the SCRF-PCM framework. Dichloromethane was taken as the continuum solvent dielectric (ε = 8.93). The results are tabulated in Tables S1 and S2 in the Supporting Information.
26. Frisch, M. J. Gaussian 03, Revision C.02; Gaussian, Inc.: Wallingford, CT, 2004. See the full citation in the Supporting Information.
27. 2 correspond to Evans syn, non-Evans syn, Evans anti, and non-Evans anti products.
28. Qualitative models that are generally employed in rationalizing the stereoselectivity in oxazolidinone mediated aldol reaction are summarized in Scheme S1 in the Supporting Information.
29. A schematic representation of all these modes of addition are given in Scheme S2 in the Supporting Information.
30. Marrone, A.; Renzetti, A.; De Maria, P.; Gérard, S.; Sapi, J.; Fontana, A.; Re, N. Chem.-Eur. J. 2009, 15, 11537
31. Such a nonchelated working model has been documented: Nerz-Stormes, M.; Thornton, E. R. J. Org. Chem. 1991, 56, 2489
32. Siegel, C.; Thornton, E. R. J. Am. Chem. Soc. 1989, 111, 5722
33. Crimmins, M. T.; Shamszad, M. Org. Lett. 2007, 9, 149
34. See Scheme S1 in the Supporting Information.
35. Several key possibilities belonging to this category are presented in Scheme S2 of the Supporting Information.
36. Optimized TS geometries are given in Figure S1 in the Supporting Information.
37. The axial ligands are found to be tilted toward the substrate.
38. 4-promoted C-C bond formation reactions. See: Patel, C.; Sunoj, R. B. J. Org. Chem. 2010, 75, 359
39. The relative energies obtained from single-point calculations by using the PCM model at various levels of theory are provided in Table S2 of the Supporting Information.
40. See Figure S2 in the Supporting Information.
41. 2-4 appears to be more constrained (Figure S2, Supporting Information), leading to a higher degree of destabilization between the ester and the phenyl groups. It is to be noted that the computational methodology employed here, although adequate for the assessment of relative energies, may not provide an accurate description of van der Waals repulsions.