2 containing an oxazolidinone provides encouragingly high
ees for the epoxidation of cis-olefins and styrenes.8 Our
earlier studies suggest that electronic interactions play an
important role in stereodifferentiation. It appears that there
is an attractive interaction between the Rπ group and the
oxazolidinone moiety of the ketone catalyst in the transition
state (Scheme 2).9,10 As a result, groups with π systems (Rπ)
the enantioselectivity of the epoxidation.8c The influence of
the N-substituents on the enantioselectivity is believed to
be electronic rather than steric in nature.8c To further probe
the interaction, ketones 2a-e (Scheme 1) with substituents
on the phenyl group were prepared, and the effect of varying
the substituents on the enantioselectivity of the epoxidation
was studied. Herein, we report our preliminary efforts on
this subject.
The syntheses of ketones 2a-e are outlined in Schemes
3-5. Briefly, ketones 2a,b were prepared from D-glucose
Scheme 2
Scheme 3
could be significantly differentiated from those without π
electrons (R), leading to high enantioselectivity for the
reaction.
Our studies have also shown that the substituents on the
nitrogen of the ketone catalyst have a significant effect on
(6) For leading references on asymmetric epoxidation mediated in situ
by chiral ketones, see: (a) Curci, R.; Fiorentino, M.; Serio, M. R. J. Chem.
Soc., Chem. Commun. 1984, 155. (b) Curci, R.; D’Accolti, L.; Fiorentino,
M.; Rosa, A. Tetrahedron Lett. 1995, 36, 5831. (c) Denmark, S. E.; Forbes,
D. C.; Hays, D. S.; DePue, J. S.; Wilde, R. G. J. Org. Chem. 1995, 60,
1391. (d) Brown, D. S.; Marples, B. A.; Smith, P.; Walton, L Tetrahedron
1995, 51, 3587. (e) Yang, D.; Yip, Y. C.; Tang, M. W.; Wong, M. K.;
Zheng, J. H.; Cheung, K. K. J. Am. Chem. Soc. 1996, 118, 491. (f) Yang,
D.; Wang, X.-C.; Wong, M.-K.; Yip, Y.-C.; Tang, M.-W. J. Am. Chem.
Soc. 1996, 118, 11311. (g) Song, C. E.; Kim, Y. H.; Lee, K. C.; Lee, S. G.;
Jin, B. W. Tetrahedron: Asymmetry 1997, 8, 2921. (h) Adam, W.; Zhao,
C.-G. Tetrahedron: Asymmetry 1997, 8, 3995. (i) Denmark, S. E.; Wu, Z.;
Crudden, C. M.; Matsuhashi, H. J. Org. Chem. 1997, 62, 8288. (j) Wang,
Z.-X.; Shi, Y. J. Org. Chem. 1997, 62, 8622. (k) Adam, W.; Fell, R. T.;
Saha-Moller, C. R.; Zhao, C.-G. Tetrahedron: Asymmetry 1998, 9, 397.
(l) Armstrong, A.; Hayter, B. R. Chem. Commun. 1998, 621. (m) Yang,
D.; Wong, M.-K.; Yip, Y.-C.; Wang, X.-C.; Tang, M.-W.; Zheng, J.-H.;
Cheung, K.-K. J. Am. Chem. Soc. 1998, 120, 5943. (n) Yang, D.; Yip,
Y.-C.; Chen, J.; Cheung, K.-K. J. Am. Chem. Soc. 1998, 120, 7659. (o)
Adam, W.; Saha-Moller, C. R.; Zhao, C.-G. Tetrahedron: Asymmetry 1999,
10, 2749. (p) Carnell, A. J.; Johnstone, R. A. W.; Parsy, C. C.; Sanderson,
W. R. Tetrahedron Lett. 1999, 40, 8029. (q) Armstrong, A.; Hayter, B. R.
Tetrahedron 1999, 55, 11119. (r) Armstrong, A.; Hayter, B. R.; Moss, W.
O.; Reeves, J. R.; Wailes, J. S. Tetrahedron: Asymmetry 2000, 11, 2057.
(s) Solladie-Cavallo, A.; Bouerat, L. Org. Lett. 2000, 2, 3531. (t) Bortolini,
O.; Fogagnolo, M.; Fantin, G.; Maietti, S.; Medici, A. Tetrahedron:
Asymmetry 2001, 12, 1113. (u) Seki, M.; Furutani, T.; Imashiro, R.; Kuroda,
T.; Yamanaka, T.; Harada, N.; Arakawa, H.; Kusama, M.; Hashiyama, T.
Tetrahedron Lett. 2001, 42, 8201. (v) Armstrong, A.; Moss, W. O.; Reeves,
J. R. Tetrahedron: Asymmetry 2001, 12, 2779. (w) Matsumoto, K.;
Tomioka, K. Tetrahedron Lett. 2002, 43, 631. (x) Stearman, C. J.; Behar,
V. Tetrahedron Lett. 2002, 43, 1943. (y) Denmark, S. E.; Matsuhashi, H.
J. Org. Chem. 2002, 67, 3479. (z) Shing, T. K. M.; Leung, G. Y. C.
Tetrahedron 2002, 58, 7545.
by the Amadori rearrangement,11 ketalization, oxazolidinone
formation, and PDC oxidation in 13 and 31% overall yields,
respectively (Scheme 3). Ketone 2c was prepared in a manner
similar to 2a,b, except that the sulfide was oxidized to the
sulfone before the PDC oxidation of the alcohol (Scheme
4). Ketones 2d-e were prepared from compound 68c by a
Scheme 4
(7) For examples of asymmetric epoxidation mediated in situ by fructose-
derived ketones, see: (a) Tu, Y.; Wang, Z.-X.; Shi, Y. J. Am. Chem. Soc.
1996, 118, 9806. (b) Wang, Z.-X.; Tu, Y.; Frohn, M.; Zhang, J.-R.; Shi, Y.
J. Am. Chem. Soc. 1997, 119, 11224. (c) Shu, L.; Shi, Y. Tetrahedron 2001,
57, 5213.
(8) (a) Tian, H.; She, X.; Shu, L.; Yu, H.; Shi, Y. J. Am. Chem. Soc.
2000, 122, 11551. (b) Tian, H.; She, X.; Xu, J.; Shi, Y. Org. Lett. 2001, 3,
1929. (c) Tian, H.; She, X.; Yu, H.; Shu, L.; Shi, Y. J. Org. Chem. 2002,
67, 2435.
nucleophilic aromatic substitution, desilylation, and PDC
oxidation (Scheme 5). Among these ketones, crystal struc-
tures of 2a-b were obtained and showed that the phenyl
groups in these ketones are coplanar with the oxazolidinones.
The catalytic properties of ketones 2a-e were then
investigated using cis-â-methylstyrene, styrene, and 1-phen-
(9) Other nonbonding interactions such as hydrophobic interactions could
also contribute to the observed enantioselectivity.
(10) For an observation of electronic interaction in ketone-catalyzed
asymmetric epoxidation, see ref 6n.
(11) Hodge, J. E.; Fisher, B. E. Methods Carbohydr. Chem. 1963, 2, 99.
Org. Lett., Vol. 5, No. 3, 2003
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