C O M M U N I C A T I O N S
Table 2
Supporting Information Available: Experimental procedures, as
1
13
well as H/ C NMR spectra and characterization data for all new
compounds (CIF, PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
References
(
1) For a review, see: Hsung, R. P.; Wei, L.-L.; Xiong, H. Acc. Chem. Res.
003, 36, 773.
2
(
2) For recent allenamide chemistry, see: (a) Achmatowicz, M.; Hegedus,
L. S. J. Org. Chem. 2004, 69, 2229. (b) Ranslow, P. D. B.; Hegedus, L.
S.; de los Rios, C. J. Org. Chem. 2004, 69, 105. (c) Gaul C.; Seebach, D.
HelV. Chim. Acta 2002, 85, 963. (b) Kozawa, Y.; Mori, M. Tetrahedron
Lett. 2002, 43, 1499. (c) Kozawa, Y.; Mori, M. Tetrahedron Lett. 2001,
4
2, 4869. (d) Grigg, R.; K o¨ ppen, I.; Rasparini, M.; Sridharan, V. Chem.
Commun. 2001, 964 and references therein.
(3) For our recent efforts, see: (a) Berry, C. R.; Hsung, R. P. Tetrahedron
004, 60, 7629. (b) Rameshkumar, C.; Hsung, R. P. Synlett 2003, 1241.
c) Berry, C. R.; Rameshkumar, C.; Tracey, M. R.; Wei, L.-L.; Hsung,
a
b
c
Isolated yields. HPLC determination for ees. ent-15b was used with
2
(
d
e
the ee not optimized. Ee was 24% without AgSbF6. Syn:anti ratios are in
brackets and were determined by H and/or C NMR. No Lewis acid was
used. Ees for syn regioisomers without AgSbF6 [entries 8 and 10] are 67
and 64%, respectively. Ees for anti regioisomers without AgSbF6 [entries
2-14] are 70, 80, and 63%, respectively. Ee for the syn regioisomers
was not determined.
1
13
f
R. P. Synlett 2003, 791. (d) Rameshkumar, C.; Xiong, H.; Tracey, M. R.;
Berry, C. R.; Yao, L. J.; Hsung, R. P. J. Org. Chem. 2002, 67, 1339. (e)
Xiong, H.; Hsung, R. P.; Wei, L.-L.; Berry, C. R.; Mulder, J. A.; Stockwell,
B. Org. Lett. 2000, 2, 2869.
g
h
i
1
(4) Xiong, H.; Hsung. R. P.; Berry, C. R.; Rameshkumar, C. J. Am. Chem.
Soc. 2001, 123, 7174.
Scheme 2
(5) (a) Rameshkumar, C.; Hsung, R. P. Angew. Chem., Int. Ed. 2004, 43,
6
15. (b) Xiong, H.; Huang, J.; Ghosh, S.; Hsung, R. P. J. Am. Chem. Soc.
2003, 125, 12694.
(
6) (a) Saez, J. A.; Arno, M.; Domingo, L. R. Org. Lett. 2003, 5, 4117. (b)
Funk, R. L.; Aungst, R. A. Org. Lett. 2001, 3, 3553. (c) Harmata, M.;
Sharma, U. Org. Lett. 2000, 2, 2703. (d) Masuya, K.; Domon, K.; Tanino,
K.; Kuwajima, I. J. Am. Chem. Soc. 1998, 120, 1724. (e) Lee, K.; Cha,
J. K. Org. Lett. 1999, 1, 523.
(
7) For recent reviews on [4 + 3] cycloadditions: (a) Harmata, M.;
Rashatasakhon, P. Tetrahedron 2003, 59, 2371. (b) Davies, H. M. L. In
AdVances in Cycloaddition; Harmata, M., Ed.; JAI Press: 1998; Vol. 5,
pp 119-164. (c) Harmata, M. In AdVances in Cycloaddition; Lautens,
M., Ed.; JAI: Grennwich, 1997; Vol. 4, pp 41-86. (d) West, F. G. In
AdVances in Cycloaddition; Lautens, M., Ed.; JAI: Grennwich, 1997; Vol.
2
5-27 with high ees but in favor the anti regioisomers instead of
4, pp 1-40.
syn regioisomers [entries 12-14]. Finally, we note that the
(8) Harmata, M. Rec. Res. DeV. Org. Chem. 1997, 1, 523-535.
16b,20
oxazolidinone ring could be cleaved using SmI
A working model can be proposed on the basis of a known
mechanistic analysis for asymmetric catalysis employing chiral C
2
.
(9) For an excellent review, see: Harmata, M. Acc. Chem. Res. 2001, 34,
595.
(
10) (a) Dennis, N.; Ibrahim, B.; Katritzky, A. R. J. Chem. Soc., Perkin Trans.
2
-
1
1976, 2307. (b) Walters, M. A.; Arcand, H. R. J. Org. Chem. 1996, 61,
symmetric ligands [Scheme 2].21 Use of this model allows the
observed enantioselectivity to be readily rationalized. Out of the
two productive front quadrants, the bottom endo-1 approach would
be sterically unfavorable due to the interaction between the furan-H
and bottom Ph ring, while the top endo-2 approach would pre-
dominate leading to the S-enantiomers [side view and top view-A].
This model provides a rationale for C3-substituted furans in
which anti isomers were found [top view-A]. To approach from
the favored endo-2 face, the substituent at C3 would prefer to be
1478. (c) Myers, A. G.; Barbay, J. K. Org. Lett. 2001, 3, 425.
(11) For the sole account, see: Harmata, M.; Ghosh, S. K.; Hong, X.;
Wacharasindu, S.; Kirchhoefer, P. J. Am. Chem. Soc. 2003, 125, 2058.
(
12) For recent stereoselective attempts: (a) Grainger, R. S.; Owoare, R. B.;
Tisselli, P.; Steed, J. W. J. Org. Chem. 2003, 68, 7899. (b) Montan a˜ , A.
M.; Grima, P. M. Tetrahedron 2002, 58, 4769.
(
13) (a) Beck, H.; Stark, C. B. W.; Hoffman, H. M. R. Org. Lett. 2000, 2, 883
and ref 11 cited therein. (b) Harmata, M.; Jones, D. E.; Kahraman, M.;
Sharma, U.; Barnes, C. L. Tetrahedron Lett. 1999, 40, 1831. (c) Cho, S.
Y.; Lee, J. C.; Cha, J. K. J. Org. Chem. 1999, 64, 3394. (d) Davis, H. M.
L.; Stafford, D. G.; Doan, B. D.; Houser, J. H. J. Am. Chem. Soc. 1998,
120, 3326.
3L
3R
(14) For an elegant example of achiral template-based asymmetric catalysis,
see: Sibi, M. P.; Zhang, R.; Manyem, S. J. Am. Chem. Soc. 2003, 125,
9306.
on the left side [see R ], for being on the right side [see R ] would
lead to steric interaction with the top Ph ring. The ees of the anti
regioisomer should also be high, for the bottom endo-1 approach
would experience additional steric interaction between the R3L and
the bottom Ph ring.
(15) For ligand 11, see: (a) Huang, Y.; Iwama, T.; Rawal, V. H. J. Am. Chem.
Soc. 2002, 124, 5950. (b) Jacobsen, E. N. Acc. Chem. Res. 2000, 33, 421.
1
2: (c) Corey, E. J.; Shibata, T.; Lee, T. W. J. Am. Chem. Soc. 2002,
124, 3808. 13a-c, 14: (d) Johnson, J. S.; Evans, D. A. Acc. Chem. Res.
000, 33, 325. (e) Nishiyama, H.; Kondo, M.; Nakamura, T.; Itoh, K.
2
Reactions of 2-substituted furans and 2,5-dimethyl furan led to
a reduced ee from that of the parent furan. This is likely due to an
Organometallics 1991, 10, 500. (f) Nishiyama, H.; Sakaguchi, H.;
Nakamura, T.; Horlhata, M.; Kondo, M.; Itoh, K. Organometallics 1989,
8, 846. 15a: (g) Φstergaard, N.; Jensen, J. F.; Tanner, D. Tetrahedron
2L
enhanced steric interaction between the C2-substituent(s) [R and/
2
001, 57, 6083. 15b: (h) Ji, J.; Barnes, D. M.; Zhang, J.; King, S. A.;
2R
or R : top view-B] and the oxyallyl cation moiety. To alleviate
this interaction, 2-substituted furans and 2,5-dimethyl furan would
have to “slide over,” thereby diminishing the critical interaction
between the furan-H and bottom Ph ring [see the boxed area],
especially for 2,5-dimethyl furan.
Wittenberger, S. J.; Morton, H. E. J. Am. Chem. Soc. 1999, 121, 10215.
6: (i) Evans, D. A.; Seidel, D.; Rueping, M.; Lam, H. W.; Shaw, J. T.;
1
Downey, C. W. J. Am. Chem. Soc. 2003, 125, 12692. For a review on
Lewis acids, see: (j) Yamamoto, H. In Lewis Acids in Organic Synthesis;
Wiley-VCH: Weinheim, 2000.
(
16) (a) Absolute configuration of 8-S was assigned via the single-crystal X-ray
structure of a chiral ester derivative. (b) See Supporting Information for
the cleavage of the oxazolidinone auxiliary and also see ref 20.
We have described here chiral Lewis acid-catalyzed highly
enantioselective [4 + 3] cycloadditions using nitrogen-stabilized
chiral oxyallyl cations derived from allenamides. Efforts in ap-
plications in natural product syntheses and further mechanistic
exploration are underway.
(
17) For a key reference, see: Evans, D. A.; Murry, J. A.; von Matt, P.;
Norcross, R. D.; Miller, S. J. Angew. Chem., Int. Ed. Engl. 1995, 34,
798.
(18) Syn or anti isomer could be readily assigned using COSY.
(
(
(
19) Harmata, M.; Rashatasakhon, R. Synlett 2000, 1419.
20) Honda, T.; Ishikawa, F. Chem. Commun. 1999, 1065.
21) For a recent review on C
2
-symmetric ligands in asymmetric catalysis,
Acknowledgment. Authors thank NSF [CHE-0094005] for
support and Dr. Victor Young for X-ray analysis. We thank
Professor Jeffrey S. Johnson for valuable discussions.
see: Rosini, C.; Franzini, L.; Raffaelli, A.; Salvadori, P. Synthesis 1992,
503.
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J. AM. CHEM. SOC.
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