C O M M U N I C A T I O N S
Table 1. Quinone Diels-Alder Reaction Scope
a Absolute stereochemistry was determined by selective Luche reduction of the less sterically hindered ketone, followed by Mosher ester analysis. The
remaining product configurations were assigned by analogy. b Isolated yields of a mixture of regioisomers 5:1 and 15:1 for entries 7 and 8, respectively.c Ee
of major diastereomer was determined after selective Luche reduction of the less sterically hindered ketone.
Supporting Information Available: Experimental details and
characterization data for all new compounds (PDF). This material is
References
(1) (a) Evans, D. A.; Chapman, K. T.; Bisaha, J. J. Am. Chem. Soc. 1988,
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(2) (a) Kobayashi, S.; Ishitani, H. J. Am. Chem. Soc. 1994, 116, 4083-4084.
For a recent review on catalytic, enantioselective Diels-Alder reactions,
see: (b) Corey, E. J. Angew. Chem., Int. Ed. 2002, 41, 1650-1667. (c)
Evans, D. A.; Johnson J. S. In ComprehensiVe Asymmetric Catalysis;
Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer-Verlag:
Heidelberg, 1999; Vol III, pp 1178-1235. (d) Morita, T.; Arai, T.; Sasai,
H.; Shibasaki, M. Tetrahedron: Asymmetry 1998, 9, 1445-1450.
(3) (a) Mikami, K.; Motoyama, Y. T.; Terada, M. J. Am. Chem. Soc. 1994,
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125, 6388-6390.
(4) For related studies, see: (a) White, J. D.; Choi, Y. Org. Lett. 2000, 2,
Figure 1. Plot of percent ee of 4a vs ee of complex 1a-(Sm).
2373-2376. (b) Moharram, S.; Hirai, G.; Koyama, K.; Oguri, H.; Hirama,
M. Tetrahedron Lett. 2000, 41, 6669-6673. (c) Brimble, M. A.; McEwan,
J. F. Tetrahedron: Asymmetry 1997, 8, 4069-4078. (d) Engler, T. A.;
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59, 1179-1183. (e) Engler, T. A.; Letavic, M. A.; Takusagawa, F.
Tetrahedron Lett. 1992, 33, 6731-6734.
Preliminary mechanistic studies with the 1a-(Sm) catalyst indicate
the absence of a nonlinear effect (Figure 1).11 The enantioselec-
tivities of cycloadduct 4a were monitored as a function of catalyst
enantiomeric composition. The illustrated linear relationship be-
tween ee (ligand) and ee (product) suggests that neither catalyst
aggregation nor dimer formation is occurring.
This investigation has highlighted three new lanthanide pybox
complexes, 1a-(Sm), 1a-(Gd), and 1b-(Gd) that might have broader
applications in enantioselective Lewis acid-catalyzed reactions.
(5) Breuning, M.; Corey, E. J. Org. Lett. 2001, 3, 1559-1562.
(6) (a) Evans, D. A.; Masse, C. E.; Wu, J. Org. Lett. 2002, 4, 3375-3378.
(b) Evans, D. A.; Wu, J.; Masse, C. E.; MacMillan, D. W. C. Org. Lett.
2002, 4, 3379-3382. (c) Evans, D. A.; Sweeney, Z. K.; Rovis, T.; Tedrow,
J. J. Am. Chem. Soc. 2001, 123, 12095-12096.
(7) Nakazaki, M.; Naemura, K. J. Org. Chem. 1981, 46, 106-111.
(8) See the Supporting Information for a list of reaction solvent effects.
(9) On the basis of chiral HPLC analysis, it was determined that (S,S)-1a-
(Sm) and (S,S)-1a-(Gd) complexes furnished products possessing the same
(illustrated) absolute stereochemistry.
(10) The rate of reaction using piperylene was at least 7.4 and 10.0 times greater
than with 13 when catalyzed by complexes 1a-(Sm) and 1a-(Gd),
respectively, as determined by chiral HPLC analysis.
Acknowledgment. Support is provided by the NSF (CHE-
9907094) and Merck Research Laboratories. J.W. thanks the ASEE
for a NDSEG predoctoral Fellowship.
(11) (a) Kagan, H. B. AdV. Synth. Catal. 2001, 343, 227-233. (b) Kagan, H.
B. Synlett 2001, 888-899.
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