though high levels of selectivity can be achieved by
provide a much less active catalyst (5% vs 41% conversion).
Lowering the temperature to 40 °C increased the selectivity
to 91% ee (entry 5), which was found to be reproducible
8
employing stoichiometric amounts of chiral ligands, the
9
catalytic variants have not fared as well. In the best report,
Nakajima et al. employed chiral prolyldiamine ligands to
obtain 78% ee in the coupling of 7a to 8a (eq 1).
To survey the utility of the 1,5-diaza-cis-decalin structure
in this reaction, a number of catalysts were formed using
chiral 6a (Table 1, entries 1-3). In all cases homogeneous
3
over a number of trials. The use of CH CN, which stabilizes
the Cu(I) oxidation state, slightly enhanced the conversion
(60%) while maintaining the high selectivity (entry 6).
Derivatives of ligand 6a were prepared (eq 2) to assess
the impact of structure on reactivity and selectivity. N,N′-
Table 1. Metal-Catalyzed Biaryl Couplings Using Ligand 6
(eq 1)
3
Dialkyl derivatives were readily obtained from 6a through
1
reductive amination (R ) Me, 6c) or acylation followed by
ligand:
entry liganda metal metal source
yield
(%)b ee (%)c
1
reduction (R ) Bn, CH
2
3
CF ; 6d, 6e). The mono N-alkyl
solvent
MnCl2‚2H2O CH3CN
FeCl3‚6H2O CH3CN
derivative 6b was obtained in 31% yield by addition of 0.5
equiv of MeI to a dilute solution of heated 6a.
1
2
3
4
5
6
7
8
9
0
0
1
6a
6a
6a
6a
6a
6a
6b
6c
6d
6e
1:1
1:1
1:1
2:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
5
5
45 (R)
27 (R)
With 6b-6e in hand, these derivatives were examined as
ligands in the reaction in eq 1. For the purposes of
comparison, these reactions were run under the conditions
employed in entry 3 (Table 1, entries 7-10). All of the
derivatives displayed reactivity similar to that of the parent
with the exception of the N,N′-bis(trifluoroethyl) ligand 6e.
This diamine did not form a catalytically active complex,
indicating that an electron-poor ligand is not effective.
In general, substitution on the nitrogen was detrimental
with a decrease from 86% to 79% ee observed upon the
addition of one N-Me group and a further decrease to 3%
ee observed upon the addition of the two N-Me groups.
Interestingly, higher selectivity was observed for N,N′-
dibenzyl 6d (22% ee) compared to dimethyl 6c (3% ee).
Reasoning that the slow step in the catalytic cycle is
reduction of Cu(II) to Cu(I), parameters that favor the latter
became a focus (Table 2). In particular, the softer bromide,
iodide, and triflate anions were anticipated to stabilize Cu-
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
ClCH2CH2Cl
41 86 (R)
86 (R)
ClCH2CH2Cl
CH2Cl2
5
49 91 (R)
60 91 (R)
53 79 (R)
d
CH3CN
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
43
3 (R)
72 22 (R)
1
1
1
ClCH2CH2Cl NR
e,f
3
5
CH2Cl2
CH2Cl2
85 78 (S)
38 47 (S)
f
a
All reactions were performed on a 0.5 mmol scale and used the (S,S)-
b
c
diamines. Isolated yields. Enantiomeric excess determined by chiral
HPLC (Chiralpak AD). Absolute configuration assigned by comparison to
the literature. Performed at 40 °C. Reaction at rt. Reference 9d.
d
e
f
catalyst solutions could be obtained although MeCN was
required to solubilize the Mn and Fe derivatives. Under these
conditions, the reaction mixtures remained homogeneous
10
throughout the course of the transformation. Gratifyingly,
the Mn,11 Fe, and Cu catalysts all provided some level of
selectivity in the reaction, with the last generating 8a in 86%
ee. Only the CuCl catalyst turned over to any extent, but
the reactivity was low. A 1:1 ligand:CuCl catalyst stoichi-
ometry (entry 3) appears to be necessary for reactivity as
similar conditions but with a 2:1 stoichiometry (entry 4)
12
(
I) intermediates. In generating these new catalysts, their
(9) (a) Hamada, T.; Ishida, H.; Usui, S.; Watanabe, Y.; Tsumura, K.;
Ohkubo, K. J. Chem. Soc., Chem. Commun. 1993, 909-911. (b) Smrcina,
M.; Pol a´ kov a´ , J.; Vyskoil,.; Kocovsky, P. J. Org. Chem. 1993, 58, 4534-
4537. (c) Nakajima, M.; Kanayama, K.; Miyoshi, I.; Hashimoto, S.
Tetrahedron Lett. 1995, 36, 9519-9520. (d) Nakajima, M.; Miyoshi, I.;
Kanayama, K.; Hashimoto, S.-I.; Noji, M.; Koga, K. J. Org. Chem. 1999,
6
4, 2264-2271. (e) Ireie, R.; Masutani, K.; Katsuki, T. Synlett 2000, 1453-
(
7) For non-oxidative methods of chiral binaphthyl synthesis, see: (a)
1436. (f) Hon, S.-W.; Li, C.-H.; Kuo, J.-H.; Barhate, N. B.; Liu, Y.-H.;
Wang, Y.; Chen, C.-T. Org. Lett. 2001, 3, 869-872.
Hayashi, T.; Hayashizaki, K.; Kiyoi, T.; Ito, Y. J. Am. Chem. Soc. 1988,
1
10, 8153-8156. (b) Shindo, M.; Koga, K.; Tomioka, K. J. Am. Chem.
(10) Homogeneous conditions were employed to preclude asymmetric
induction via diastereomieric recrystallization as has been reported for some
stoichiometric oxidative copper couplings. See refs 8a, 8e, and 9b.
(11) For Mn-promoted biaryl couplings, see: (a) Yamamoto, K.;
Fukushima, H.; Okamoto, Y.; Hatada, K.; Nakazaki, M. J. Chem. Soc.,
Chem. Commun. 1984, 1111-1112. (b) Dewar, M. J. S.; Nakaya, T. J.
Am. Chem. Soc. 1968, 90, 7134-7135.
Soc. 1992, 114, 8732-8733. (d) Cammidge, A. N.; Crepy, K. V. L. Chem.
Commun. 2000, 1723-1724. (e) Yin, J.; Buchwald, S. L. J. Am. Chem.
Soc. 2000, 122, 12051-12052.
(8) (a) Feringa, B.; Wynberg, H. Bioorg. Chem. 1978, 7, 397-408. (b)
Brussee, J.; Jansen, A. C. A. Tetrahedron Lett. 1983, 24, 3261-3262. (c)
Yamamoto, K.; Fukushima, H.; Nakazaki, M. J. Chem. Soc., Chem.
Commun. 1984, 1490-1491. (d) Brussee, J.; Groenendijk, J. L. G.; te
Koppele, J. M.; Jansen, A. C. A. Tetrahedron 1985, 41, 3313-3319. (e)
Smrcina, M.; Lorenc, M.; Hanus, V.; Sedmera, P.; Kocovsky, P. J. Org.
Chem. 1992, 57, 1917-1920. (f) Osa, T.; Kashiwagi, Y.; Yanagisawa, Y.;
Bobbitt, J. M. J. Chem. Soc., Chem. Commun. 1994, 2535-2537. (g) Saito,
S.; Kano, T.; Muto, H.; Nakadai, M.; Yamamoto, H. J. Am. Chem. Soc.
(12) For Fe-promoted biaryl couplings, see: (a) Ding, K.; Wang, Y.;
Zhang, L.; Wu, Y.; Matsuura, T. Tetrahedron 1996, 52, 1005-1010. (b)
Deussen, H.-J.; Frederiksen, P.; Bjrnholm, T.; Bechgaard, K. Org. Prep.
Proc. Int. 1996, 28, 484-486. (c) Toda, F.; Tanaka, K.; Iwata, S. J. Org.
Chem. 1989, 54, 3007-3009. (d) Feringa, B.; Wynberg, H. J. Org. Chem.
1981, 46, 2547-2557. (e) Pummerer, R.; Prell, E.; Rieche, A. Chem. Ber.
1926, 59, 2159-2161.
1
999, 121, 8943-8944.
1138
Org. Lett., Vol. 3, No. 8, 2001