Unraveling the mechanism of epoxide formation from sulfur ylides and aldehydes

被引:135
作者
Aggarwal, VK [1 ]
Harvey, JN [1 ]
Richardson, J [1 ]
机构
[1] Univ Bristol, Sch Chem, Bristol BS8 1TS, Avon, England
关键词
D O I
10.1021/ja025633n
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Sulfur ylides R2S+-C-HR' react with aldehydes R"-CHO to form epoxides, predominantly as the trans isomers, in a synthetically useful reaction which is increasingly used in its asymmetric variant with chiral sulfides. The mechanisms of the "model" reaction (R = Me, R' = R" = H) and the reaction forming stilbene oxide (R = Me, R' = R" = Ph) have been studied in detail using density functional theory, the B3LYP density functional, and flexible basis sets. It has been shown that for this reaction involving highly polar intermediates, continuum solvation models need to be used throughout to obtain reasonable results. For the reaction of benzaldehyde with dimethylsulfonium benzylide, the key steps are shown to be quasi [2 + 2] addition of the ylide to the aldehyde to form a betaine R'-CH(S+Me2)-CH(O-)-R" in which the charged groups are gauche to one another, and torsional rotation around the C-C single bond of the betaine to form its rotamer with the two charged groups anti. The final step, elimination of sulfide from this second rotamer of the betaine, is found to be facile. In the case of the anti pathway, leading to trans-stilbene epoxide, the initial addition is found to be rate-determining, whereas for the diastereomeric syn pathway, leading to the cis-epoxide, it is instead the torsional rotation which is slowest. These results are in excellent agreement with experiment, unlike previous computational work. The unexpected and apparently unprecedented (for C-C bond-forming reactions) importance of the torsional rotation step, especially in the syn case, is due to the fact that all the barriers involved are low-lying. This novel picture of the mechanism provides a sound basis for the future development of chiral sulfides for enantioselective epoxide synthesis.
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页码:5747 / 5756
页数:10
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共 52 条
  • [1] Aggarwal V.K., 1999, Comprehensive Asymmetric Catalysis II, P679
  • [2] Synthesis and evaluation of a broad range of chiral sulfides for asymmetric sulfur ylide epoxidation of aldehydes
    Aggarwal, VK
    Angelaud, R
    Bihan, D
    Blackburn, P
    Fieldhouse, R
    Fonquerna, SJ
    Ford, GD
    Hynd, G
    Jones, E
    Jones, RVH
    Jubault, P
    Palmer, MJ
    Ratcliffe, PD
    Adams, H
    [J]. JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1, 2001, (20): : 2604 - 2622
  • [3] Catalytic asymmetric epoxidation of aldehydes. Optimization, mechanism, and discovery of stereoelectronic control involving a combination of anomeric and Cieplak effects in sulfur ylide epoxidations with chiral 1,3-oxathianes
    Aggarwal, VK
    Ford, JG
    Fonquerna, S
    Adams, H
    Jones, RVH
    Fieldhouse, R
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1998, 120 (33) : 8328 - 8339
  • [4] Direct asymmetric epoxidation of aldehydes using catalytic amounts of enatiomerically pure sulfides
    Aggarwal, VK
    Ford, JG
    Thompson, A
    Jones, RVH
    Standen, MCH
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1996, 118 (29) : 7004 - 7005
  • [5] Additions of benzylsulfonium ylides to aldehydes and ketones: Are they under kinetic or thermodynamic control?
    Aggarwal, VK
    Calamai, S
    Ford, JG
    [J]. JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1, 1997, (05): : 593 - 599
  • [6] Aggarwal VK, 2001, ANGEW CHEM INT EDIT, V40, P1430, DOI 10.1002/1521-3773(20010417)40:8<1430::AID-ANIE1430>3.0.CO
  • [7] 2-W
  • [8] [Anonymous], CATALYTIC ASYMMETRIC
  • [9] Asymmetric epoxidation of enones employing polymeric alpha-amino acids in non-aqueous media
    Bentley, PA
    Bergeron, S
    Cappi, MW
    Hibbs, DE
    Hursthouse, MB
    Nugent, TC
    Pulido, R
    Roberts, SM
    Wu, LE
    [J]. CHEMICAL COMMUNICATIONS, 1997, (08) : 739 - 740
  • [10] A quantum chemical exploration of the Horner-Wadsworth-Emmons reaction
    Brandt, P
    Norrby, PO
    Martin, I
    Rein, T
    [J]. JOURNAL OF ORGANIC CHEMISTRY, 1998, 63 (04) : 1280 - 1289