Journal of the American Chemical Society
COMMUNICATION
’ AUTHOR INFORMATION
Corresponding Author
’ ACKNOWLEDGMENT
Support by the NIGMS (GM-64451) and the NSF (DBI-
0619576, BC Mass Spec. Center; CHE-0923264, BC X-ray
Facility) is gratefully acknowledged. We thank AllyChem for a
donation of B2(pin)2 and BASF for pinBH, both of which are
used in the construction of allylboronates. We thank Dr. Bo Li of
Boston College for crystallography.
Figure 1. X-ray structure of (R)-methoxy(furyl)biphep PdCl2. Elip-
soids are shown at 50% probability level.
3
’ REFERENCES
(1) Review: Hill, R. K. Comp. Org. Syn. 1991, 5, 785.
(2) Review on catalysis of the Cope rearrangement: (a) Overman,
L. E. Angew. Chem., Int. Ed. Engl. 1984, 23, 579. Selected primary
references, Pd(II) catalysis: (b) Overman, L. E.; Knoll, F. M. J. Am.
Chem. Soc. 1980, 102, 865. (c) Hamilton, R.; Mitchell, T. R. B.; Rooney,
J. J. Chem. Commun. 1981, 456. (d) Bluthe, N.; Malacria, M.; Gore, J.
Tetrahedron Lett. 1983, 24, 1157. (e) Overman, L. E.; Renaldo, A. F.
Tetrahedron Lett. 1983, 24, 3757. (f) Overman, L. E.; Renaldo, A. F.
J. Am. Chem. Soc. 1990, 112, 3945. (g) Overman, L. E.; Jacobsen, E. J.
J. Am. Chem. Soc. 1982, 104, 7225. Pd(0) catalysis: (h) Nakamura, H.;
Iwama, H.; Ito, M.; Yamamoto, Y. J. Am. Chem. Soc. 1999, 121, 10850.
Alumina catalysis: (i) Lutz, R. P.; Berg, H. A.; Wang, P. J. J. Org. Chem.
1976, 41, 2048.
Figure 2. Model for stereochemical outcome in allylꢀallyl couplings.
allyl fragment is able to undergo isomerization (minimizing steric
effects to give G) prior to stereochemistry-determining reductive
elimination to give H.
(3) (a) Zhang, P.; Brozek, L. A.; Morken, J. P. J. Am. Chem. Soc. 2010,
132, 10686. (b) Zhang, P. A.; Le, H.; Kyne, R. E.; Morken, J. P. J. Am.
Chem. Soc. 2011, 133, 9716.
To gain a sense for the stereocontrol mechanisms that under-
lie this and other allylꢀallyl coupling reactions, the crystal struc-
ture of (R)-methoxy(furyl)biphep complexed to PdCl2 was de-
termined. As depicted in Figure 1, the R configuration of the
biaryl ligand causes the cyclic chelate involving Pd to adopt the
λ skew conformation, with the furyl rings adopting pseudoaxial
and pseudoequatorial postions about the seven-membered ring.
The pseudoequatorial furyl rings impinge on the Pd square plane
in a manner that causes the chlorine atoms to cant above and
below the plane, and this is an important feature with respect to
stereoinduction in allylꢀallyl couplings (vide infra).
(4) For linear selective allylꢀallyl couplings, see the following.
Allylstannanes: (a) Trost, B. M.; Keinan, E. Tetrahedron Lett. 1980,
21, 2595. (b) Godschalx, J.; Stille, J. K. Tetrahedron Lett. 1980, 21, 2599.
(c) Keinan, E.; Peretz, M. J. Org. Chem. 1983, 48, 5302. (d) Trost, B. M.;
Pietrusiewicz, K. M. Tetrahedron Lett. 1985, 26, 4039. (e) Goliaszewski,
A.; Schwartz, J. Tetrahedron 1985, 41, 5779. (f) Goliaszewski, A.;
Schwartz, J. Organometallics 1985, 4, 417. (g) Keinan, E.; Bosch, E.
J. Org. Chem. 1986, 51, 4006. (h) Cuerva, J. M.; Goꢀmez-Bengoa, E.;
Mꢀendez, M.; Echavarren, A. M. J. Org. Chem. 1997, 62, 7540. (i) van
Heerden, F. R.; Huyser, J. J.; Williams, D. B. G.; Holzapfel, C. W.
Tetrahedron Lett. 1998, 39, 5281. (j) Nakamura, H.; Bao, M.; Yamamoto,
Y. Angew. Chem., Int. Ed. 2001, 40, 3208. (k) Mꢀendez, M.; Cuerva, J. M.;
Gꢀomez-Bengoa, E.; Cꢀardenas, D. J.; Echavarren, A. M. Chem.—Eur. J.
2002, 8, 3620. Homoallylic alcohols: (l) Sumida, Y.; Hayashi, S.;
Hirano, K.; Yorimitsu, H.; Oshima, K. Org. Lett. 2008, 10, 1629. Allyl
boronates: (m) Flegeau, E. F.; Schneider, U.; Kobayashi, S. Chem.—Eur.
J. 2009, 15, 12247. (n) Jimꢀenez-Aquino, A.; Flegeau, E. F.; Schneider, U.;
Kobayashi, S. Chem. Commun. 2011, 47, 9456.
(5) For an alternate catalytic enantioselective construction of vicinal
alkene structures, see: (a) Davies, H. M. L.; Jin, Q. J. Am. Chem. Soc.
2004, 126, 10862. (b) Davies, H. M. L.; Jin, Q. Proc. Nat. Acad. Sci. U.S.A.
2004, 101, 5472. (c) Hansen, J. H.; Gregg, T. M.; Ovalles, S. R.; Lian, Y.;
Autschbach, J.; Davies, H. M. L. J. Am. Chem. Soc. 2011, 133, 5076.
(6) (a) Mꢀendez, M.; Cuerva, J. M.; Gꢀomez-Bengoa, E.; Cꢀardenas,
D. J.; Echavarren, A. M. Chem.—Eur. J. 2002, 8, 3620. (b) Cꢀardenas,
D. J.; Echavarren, A. M. New J. Chem. 2004, 28, 338. (c) Perez-Rodrguez,
M.; Braga, A. A. C; de Lera, A. R.; Maseras, F.; Alvarez, R.; Espinet, P.
Organometallics 2010, 29, 4983. For a related experimentally observable
η1-allyl-η1-carboxylate, see: (d) Sherden, N. H.; Behenna, D. C.; Virgil,
S. C.; Stoltz, B. M. Angew. Chem., Int. Ed. 2009, 48, 6840.
In accord with the experiments described above, we proposed
that reductive elimination from bis(trans-η1-allyl)Pd complex
G (Scheme 3) is the stereochemistry-determining step and that
this elimination occurs in a 3,30 mode. Computational studies by
Echavarren6b concluded that such reactions occur through chair-
like transition structures. Collectively, these data suggest that a
favored reaction path is that depicted in Figure 2. In this model,
the η1-allyl ligands are each canted in a manner that minimizes
interaction with the pseudoequatorial furyl rings of the ligand.
This causes one chair conformer to be favored (shown) over the
other and leads to high asymmetric induction.
In conclusion, we have described a simple but highly effective
method for establishing vicinal stereocenters in a catalytic asymmetric
fashion. Analysis of ligandꢀmetal structures allows for straightfor-
ward predictions of the stereochemical outcome of these reactions.
’ ASSOCIATED CONTENT
(7) For related inner-sphere reductive elimination of bis(allyls) or
their equivalents, see ref 3 and the following: (a) Goliaszewski, A.;
Schwartz, J. J. Am. Chem. Soc. 1984, 106, 5028. (b) Keith, J. A.; Behenna,
D. C.; Mohr, J. T.; Ma, S.; Marinescu, S. C.; Oxgaard, J.; Stoltz, B. M.;
Goddard, W. A., III J. Am. Chem. Soc. 2007, 129, 11876. (c) Sieber, J. D.;
S
Supporting Information. Characterization and proce-
b
dures. This material is available free of charge via the Internet
16780
dx.doi.org/10.1021/ja2075967 |J. Am. Chem. Soc. 2011, 133, 16778–16781