C2-symmetric copper(II) complexes as chiral Lewis acids.: Scope and mechanism of the catalytic enantioselective aldol additions of enolsilanes to pyruvate esters

被引:253
作者
Evans, DA [1 ]
Burgey, CS [1 ]
Kozlowski, MC [1 ]
Tregay, SW [1 ]
机构
[1] Harvard Univ, Dept Chem & Biol Chem, Cambridge, MA 02138 USA
关键词
D O I
10.1021/ja982983u
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The C-2-symmetric (S,S)-tert-butyl-bis(oxazolinyl)Cu(OTf)(2) complex (1a) has been shown to catalyze the enantioselective aldol reaction between cr-keto esters and silylketene acetals or enolsilanes with enantioselectivities ranging from 93 to 99%. With substituted silylketene acetals, syn reaction diastereoselection ranging from 90:10 to 98:2 and enantioselectivities ranging from 93 to 98% are observed. High levels of carbonyl regioselectivity (98:2),diastereoselectivity (93:7), and enantioselectivity (97% ee) are also observed in the aldol addition to 2,3-pentanedione. In all instances, the aldol adducts are generated in high yield and in excellent enantiomeric excess using as little as 1 mol % of the chiral complex la. Mechanistic insight: into the pyruvate aldol reaction has also been gained. Silyl crossover experiments demonstrate that the silyl-transfer step is intermolecular. Based upon these results, TMSOTf has been identified as an addend to accelerate these reactions. Furthermore, solvent was shown to have a dramatic impact on the rates of addition and catalyst turnover in the pyruvate aldol reaction. Crystallographic structures and semiempirical calculations provide insight into the mode of asymmetric induction, allowing the construction of a model in which chelation of the pyruvate ester through a square planar Cu(II) complex accounts for the observed sense of asymmetric induction. Two other Cu(II) complexes, [Cu(S,S-i-Pr-pybox)](SbF6)(2) and bis(imine) complex 26, have also been evaluated asenantioselective catalysts for the pyruvate aldol reaction; however, the scope of the process with these systems is more limited.
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页码:686 / 699
页数:14
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  • [41] HIGHLY ENANTIOSELECTIVE HYDROSILYLATION OF KETONES WITH CHIRAL AND C2-SYMMETRICAL BIS(OXAZOLINYL)PYRIDINE-RHODIUM CATALYSTS
    NISHIYAMA, H
    KONDO, M
    NAKAMURA, T
    ITOH, K
    [J]. ORGANOMETALLICS, 1991, 10 (02) : 500 - 508
  • [42] ASYMMETRIC CROSS ALDOL SYNTHESIS - ASYMMETRIC ADDITION OF SILYL ENOL ETHER AND KETENE SILYL ACETAL TO ALPHA-KETO ESTERS
    OJIMA, I
    YOSHIDA, K
    INABA, S
    [J]. CHEMISTRY LETTERS, 1977, (04) : 429 - 432
  • [43] OTERA J, 1994, SYNLETT, P213
  • [44] Robins D J, 1982, Fortschr Chem Org Naturst, V41, P115
  • [45] Schwartz M A, 1992, Prog Med Chem, V29, P271, DOI 10.1016/S0079-6468(08)70011-0
  • [46] EFFICIENT ASYMMETRIC INDUCTION VIA COORDINATION OF CHIRAL DIAMINE TO TIN(II) ENOLATE - A HIGHLY ENANTIOSELECTIVE SYNTHESIS OF 2-SUBSTITUTED MALATES
    STEVENS, RW
    MUKAIYAMA, T
    [J]. CHEMISTRY LETTERS, 1983, (11) : 1799 - 1802
  • [47] Ester-type cephalotaxus alkaloids from Cephalotaxus harringtonia var drupacea
    Takano, I
    Yasuda, I
    Nishijima, M
    Yanagi, Y
    Takeya, K
    Itokawa, H
    [J]. PHYTOCHEMISTRY, 1997, 44 (04) : 735 - 738
  • [48] SUBSTRATE-ANALOG BINDING TO THE COUPLED BINUCLEAR COPPER ACTIVE-SITE IN TYROSINASE
    WILCOX, DE
    PORRAS, AG
    HWANG, YT
    LERCH, K
    WINKLER, ME
    SOLOMON, EI
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1985, 107 (13) : 4015 - 4027
  • [49] ZARAGOZIC ACID A, A POTENT INHIBITOR OF SQUALENE SYNTHASE - INITIAL CHEMISTRY AND ABSOLUTE STEREOCHEMISTRY
    WILSON, KE
    BURK, RM
    BIFTU, T
    BALL, RG
    HOOGSTEEN, K
    [J]. JOURNAL OF ORGANIC CHEMISTRY, 1992, 57 (26) : 7151 - 7158
  • [50] TOTAL SYNTHESIS OF (+)-K252A AND (-)-K252A
    WOOD, JL
    STOLTZ, BM
    DIETRICH, HJ
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1995, 117 (41) : 10413 - 10414