Kinetic resolution of 1,1-biaryl-2,2-diols and amino alcohols through NHC-catalyzed atroposelective acylation

Article abstract of DOI:10.1002/anie.201406192

We present here a highly efficient NHC-catalyzed kinetic resolution of a wide range of 1,1-biaryl-2,2-diols and amino alcohols to provide them in uniformly ≥99% ee. This represents the first highly enantioselective catalytic acylation of axially chiral alcohols. The aldehyde backbone that is incorporated into the chiral acyl azolium intermediate was found to have a significant effect on the enantioselectivity of the process.

Full text of DOI:10.1002/anie.201406192

Angewandte
Chemie
DOI: 10.1002/anie.201406192
Asymmetric Catalysis
Kinetic Resolution of 1,1’-Biaryl-2,2’-Diols and Amino Alcohols
through NHC-Catalyzed Atroposelective Acylation**
Shenci Lu, Si Bei Poh, and Yu Zhao*
Abstract: We present here a highly efficient NHC-catalyzed
kinetic resolution of a wide range of 1,1’-biaryl-2,2’-diols and
amino alcohols to provide them in uniformly ꢀ 99% ee. This
represents the first highly enantioselective catalytic acylation of
axially chiral alcohols. The aldehyde backbone that is incor-
porated into the chiral acyl azolium intermediate was found to
have a significant effect on the enantioselectivity of the process.
Axially chiral biaryls are important structural motifs in
natural products, pharmaceuticals and materials,[1] and also
find wide application as chiral catalysts in organic synthesis.[2]
Accordingly, the development of efficient enantioselective
syntheses of them has attracted extensive attention and great
progress has been reported in recent years from the Tanaka
group,[3b,c] the Miller group,[3d,e] the Buchwald group,[3f] and
many others.[3] In particular, one class of axially chiral
alcohols including 1,1’-bi-2-naphthol (BINOL) and 2-amino-
2’-hydroxy-1,1’-binaphthyl (NOBIN) has proven to be priv-
ileged chiral backbones for asymmetric catalysis.[4,5] The
preparation of these axially chiral alcohols in enantiopure
form, however, still relies on conventional optical resolution,
which requires the stoichiometric use of chiral compounds.[6]
Whereas the oxidative coupling of 2-naphthols (or 2-naph-
thylamines) represents a straightforward way to prepare
BINOL and NOBIN analogues from achiral precursors, the
current state-of-the-art catalytic systems can only produce
binaphthols with certain specific substitution patterns in high
ee (and not biphenols at all; see (a) in Scheme 1).[7] The
catalytic kinetic resolution of these axially chiral diols and
amino alcohols has surprisingly been underdeveloped.[8] Only
a few highly enantioselective examples were reported on
orthogonally protected BINOL and NOBIN analogues, either
using asymmetric Pd-catalyzed alcoholysis by the Tsuji
group[8c] or using N-alkylation under phase transfer catalysis
by the Maruoka group[8d] (see (b) in Scheme 1). Although the
catalytic asymmetric acylation of alcohols (or other group
transfer reactions in general) has great potential to provide an
efficient, direct kinetic resolution of free BINOL and
NOBIN, no successful catalytic system along those lines has
Scheme 1. Catalytic approaches to enantioenriched BINOL and
NOBIN. s=selectivity factor.
been reported[9] despite the great success of asymmetric
acylation of alcohols that possess central chirality.[10,11] We
report here the first example of a highly efficient and
enantioselective acylative kinetic resolution of free BINOLs
and N-Boc-protected NOBINs to access a wide range of them
with ꢀ 99% ee (see (c) in Scheme 1).
Recent advances in N-heterocyclic carbene (NHC) catal-
ysis have led to the catalytic generation of activated
carboxylates either through internal redox reaction of func-
tionalized aldehydes (such as a,b-unsaturated aldehydes or a-
halo aldehydes) or from simple aldehydes under oxidative
conditions.[12] The chiral acyl azolium species generated in this
À
way has been employed for enantioselective C C bond
formation as well as acylation of the alcohol counterpart.[13,14]
Following the early proof-of-principle reports from the
groups of Rovis, Scheidt, and Studer,[13a–d] we have recently
disclosed a highly enantioselective acylative kinetic resolution
of oxindole-derived tertiary alcohols, in which oxidative NHC
catalysis with the aid of a Lewis acid proved essential to
obtain high enantioselectivity.[13e–f] Takasu, Yamada, and co-
workers also reported a NHC-catalyzed asymmetric acylation
of cyclic trans-diols and amino alcohols with high levels of
stereoselectivity, in which a carboxylate salt was identified as
a basic cocatalyst for an enhanced rate and selectivity.[13g]
Recognizing the lack of efficient acylation reactions for
axially chiral alcohols, we decided to examine NHC catalysis
for the kinetic resolution of free BINOL.
[*] Dr. S. Lu, S. B. Poh, Prof. Y. Zhao
Department of Chemistry, National University of Singapore
3 Science Drive 3, Singapore 117543 (Singapore)
E-mail: zhaoyu@nus.edu.sg
Homepage: http://zhaoyu.science.nus.edu.sg
[**] We are grateful for the financial support from the Singapore
National Research Foundation (NRF Fellowship) and the National
University of Singapore.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201406192.
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The original conditions were adopted from our previous
studies[13e] using oxidative NHC catalysis and provided very
poor selectivity for the resolution of BINOL (selectivity
factor s = 1.2; Scheme 2).[15] We reasoned that the strong
proved to be too bulky for an efficient reaction to take place,
b-substituted aldehydes 2l (+ MnO2) yielded a good s factor
of 20, albeit with low reactivity. Finally, inspired by the
pioneering work of the Scheidt group[16a,b] and Smith
group[16c,d] on the use of a-aryloxy aldehyde in NHC catalysis
as well as previous kinetic resolution experiments from the
Takasu and Yamada group,[13g] we examined the use of 2m,
which resulted in a higher conversion with the same
selectivity. With this promising lead, further reaction con-
ditions were systematically screened, from which the choice
of DCM as solvent and a lower concentration of 0.1m led to
further improvement. Under the optimal conditions, an
excellent selectivity of 52 was obtained for the resolution of
BINOL, which was recovered in 99% ee with 44% yield
(entry 1, Table 1).
Scheme 2. Initial catalyst and base optimization.
acidity of the phenol functionality in BINOL may require the
use of a weak base. Indeed, DIPEA proved optimal after
extensive screening, which, in combination with azolium 5,
led to an improved but still poor selectivity factor of 3.5.
The breakthrough was achieved by screening different
aldehydes (Scheme 3). Compounds 2b and 2c were tested
with the hope that they might provide the same acyl azolium
intermediate Awithout the need for MnO2 and hopefully lead
to a different outcome. The results turned out to be similar to
those observed in the reaction with 2a in terms of selectivity.
Using 2a in the absence of MnO2 (leading to a different acyl
azolium ion B), however, resulted in a significantly improved
s factor of 13 with reasonable conversion. Again, the use of
different aldehydes (2d + MnO2, 2e, and 2 f) that lead to the
same intermediate B resulted in similar selectivities (s ranges
from 10–13). It was clear at this point that the selectivity of
this system was largely influenced by the substituent of the
aldehyde; a wider range of aldehydes was then examined.
Whereas substituted cinnamaldehydes (2g, 2h) or a-substi-
tuted aldehydes (2i, 2j) led to either reduced selectivity or
The scope of this catalytic system turned out to be very
broad. Various binaphthyl (entries 1–6) and biphenyl diols
(entries 7–12) with different substitution patterns were
Table 1: Scope of axially chiral diols.[a]
Entry
1
Yield1
[%][b]
ee1
6
Yield6
[%][b]
ee6
Conv.
s
[%][c]
[%][c] [%]
1
1a 44
1b 42
1c 44
1d 43
1e 42
1 f 42
1g 41
1h 43
1i 40
1j 38
99
99
99
99
99.4
99
99.1
99
99.4
99.3
99.5
99
6a 53
6b 54
6c 53
6d 55
6e 55
6 f 53
6g 56
6h 55
6i 57
6j 58
6k 61
6l 50
82
77
81
77
76
76
72
76
68
66
60
92
55
56
55
56
57
56
58
56
59
60
62
52
52
38
49
40
41
37
31
37
30
26
22
2[d]
3
4
5
6[e]
7
8
9
10
11[d] 1k 37
12
1l 47
116
[a] The reactions were carried out at ambient temperature with 0.7–
0.8 equiv 2m. See the Supporting Information for details. [b] Yields of
isolated products. [c] Determined by HPLC. [d] 1.5 equiv of 2m was
used. [e] A mixture of two esters with a ratio of 2:3 was produced with the
same ee.
Scheme 3. Effect of the aldehyde on the resolution of 1a.
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resolved with similarly high selectivity; all substrates exam-
ined were recovered in ꢀ 99% ee with 37–47% isolated yield.
For biphenyl diols, the substituents at the 6,6’-positions
showed some influence on the selectivity. Whereas 1k bearing
small methoxy groups showed a relatively low selectivity of
22, the widely used VANOL 1l[17] with phenyl substituents
was resolved with an excellent selectivity of > 100. The non-
C2 symmetrical diols such as 1 f could be resolved efficiently
as well (entry 6), for which two ester products were formed
with the same ee and the same axial configuration.
It is also noteworthy that this catalytic procedure is very
simple to perform with readily available catalysts at ambient
temperature. The reaction can also be easily scaled up. A test
reaction with BINOL worked similarly well at gram scale to
yield enantiopure BINOL (> 99% ee) in 40% yield
(Scheme 4).
Scheme 5. Resolution of the NOBIN analogue and Boc removal.
enantiomeric BINOL and NOBIN, which was then resolved
under similar conditions using the enantiomeric catalyst ent-5
to yield enantiomeric BINOL and NOBIN in > 99% ee and
high yield (Scheme 6). In this way, the racemic starting
materials could be converted to two enantiomers of BINOL
or NOBIN in ꢀ 99% ee with an overall yield of > 84%
(Tables 1 and 2, Scheme 6).
Scheme 4. Gram-scale resolution of 1a.
In an effort to extend the scope to axially chiral amino
alcohols, it was discovered that the kinetic resolution of
unprotected NOBIN using this catalytic system was problem-
atic due to side reaction pathways. To our excitement, the
acyl- or Boc-protected NOBIN worked out well with s = 15
(entries 1 and 2, Table 2). A new catalyst 7 with a bromo
substituent proved superior and an excellent selectivity was
obtained at 08C (s = 34; entry 4); enantiopure 8b could be
isolated with 41% yield. The extension of the method to other
NOBIN analogues proved successful (Scheme 5a); 8c was
recovered in 36% yield and, again, in 99% ee. As expected,
the removal of the Boc group worked out cleanly to yield free
NOBIN in a high yield (Scheme 5b). Our method thus
represents one of the most straightforward syntheses of
NOBIN and its analogues in their enantiopure form.
Scheme 6. Recycling of the esters to enantiopure BINOL and NOBIN.
During our studies, it was found that an intramolecular
H bond interaction between the two phenols (or with aniline)
presumably serves as a key element that may increase the
nucleophilicity of the substrate and/or help to organize the
substrate conformation leading to a better enantioselectivity.
When methyl ether 11a or dimethyl amino derived 11b was
tested, a much lower selectivity as well as lower reactivity was
observed (Scheme 7). The spirocyclic diol 13 was also tested,
whose rigid structure does not allow H bond interaction
between its two phenols. Indeed, a low selectivity (s = 3.4) was
observed using the current catalytic system. Further optimi-
To increase the overall efficiency of the process, the ester
products generated in these studies were hydrolyzed to the
Table 2: Optimization of NOBIN resolution.[a]
Entry
8
T [8C] Azolium Yield8;[b]
Yield9;[b]
ee9
Conv. [%]
s
[c]
[c]
ee8
1
2
3
4
8a 24
8b 24
8b 24
5
5
7
7
38;95
40;93
41;94
41;99
57;63
53;64
56;70
56;74
60
58
57
57
15
15
19
34
8b
0
[a–c] See Table 1.
Scheme 7. Importance of intramolecular H bond.
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126, 3758 – 3761; m) A. Link, C. Sparr, Angew. Chem. Int. Ed.
2014, 53, 5458 – 5461; Angew. Chem. 2014, 126, 5562 – 5565.
[4] For selected general reviews on BINOL, see: a) Y. Chen, S.
Yekta, A. K. Yudin, Chem. Rev. 2003, 103, 3155 – 3212; b) J. M.
Brunel, Chem. Rev. 2007, 107, PR1 – PR45; c) M. Shibasaki, S.
Matsunaga in Privileged Chiral Ligands and Catalysts (Ed.: Q.-
L. Zhou), Wiley, Hoboken, 2011, pp. 295 – 332; For selected
review and reports on NOBIN, see: d) K. Ding, H. Guo, X. Li, Y.
Yuan, Y. Wang, Top. Catal. 2005, 35, 105 – 116; e) E. M. Carreira,
R. A. Singer, W. Lee, J. Am. Chem. Soc. 1994, 116, 8837 – 8838;
f) J. J. Van Veldhuizen, S. B. Garber, J. S. Kingsbury, A. H.
Hoveyda, J. Am. Chem. Soc. 2002, 124, 4954 – 4955.
zation is ongoing for the resolution of this unique and highly
useful class of compounds.[18]
In conclusion, we have developed a highly efficient NHC-
catalyzed atroposelective kinetic resolution of a wide range of
BINOL and NOBIN derivatives that gives them in constantly
high eeꢀs of ꢀ 99%, representing the first highly enantiose-
lective catalytic acylation of axially chiral alcohols.[19] Mech-
anistic and computational studies will be performed to better
understand the basis for asymmetric induction in this catalytic
system.
[5] BINAP (2,2’-Bis(diphenylphosphino)-1,1’-binaphthyl), a privi-
leged chiral ligand in asymmetric catalysis, is prepared from
BINOL. For a recent review, see: T. Ohkuma, N. Kurono in
Privileged Chiral Ligands and Catalysts (Ed.: Q.-L. Zhou),
Wiley, Hoboken, 2011, pp. 1 – 53.
[6] a) D. Cai, D. L. Hughes, T. R. Verhoeven, P. J. Reider, Org.
Synth. 1999, 76, 1 – 3; For other selected examples using HPLC
separation or an interesting mechanochemical approach, see:
b) W. H. Pirkle, J. L. Schreiner, J. Org. Chem. 1981, 46, 4988 –
4991; c) K. M. Wiggins, C. W. Bielawski, Angew. Chem. Int. Ed.
2012, 51, 1640 – 1643; Angew. Chem. 2012, 124, 1672 – 1675.
[7] For a recent review, see: a) H. Wang, Chirality 2010, 22, 827 –
Experimental Section
To
a 4 mL vial the racemic BINOL derivative (0.075 mmol),
triazolium salt 5 (0.0075 mmol), and 4 ꢁ MS (25 mg) was added.
The mixture was transferred into the glovebox, where aldehyde 2m
(9 mL, 0.052 mmol), anhydrous DCM (0.75 mL), and DIPEA (18 mL,
0.075 mmol) were added and the reaction mixture was removed from
the glovebox. The vial was then sealed and the reaction mixture was
allowed to stir at ambient temperature for 24 h. The crude reaction
mixture was directly purified by silica gel column chromatography
with hexanes/ethyl acetate (10:1 v/v) as eluent to afford the ester
product and the recovered starting material in pure form.
ˇ
837; For selected examples, see: b) M. Smrcina, J. Polꢆkovꢆ, S.
ˇ
ˇ
Vyskocil, P. Kocovsky, J. Org. Chem. 1993, 58, 4534 – 4538; c) M.
Nakajima, I. Miyoshi, K. Kanayama, S.-i. Hashimoto, J. Org.
Chem. 1999, 64, 2264 – 2271; d) S.-W. Hon, C.-H. Li, J.-H. Kuo,
N. B. Barhate, Y.-H. Liu, Y. Wang, C.-T. Chen, Org. Lett. 2001, 3,
869 – 872; e) Q.-X. Guo, Z.-J. Wu, Z.-B. Luo, Q.-Z. Liu, J.-L. Ye,
S.-W. Luo, L.-F. Cun, L.-Z. Gong, J. Am. Chem. Soc. 2007, 129,
13927 – 13938; f) J. B. Hewgley, S. S. Stahl, M. C. Kozlowski, J.
Am. Chem. Soc. 2008, 130, 12232 – 12233; g) H. Egami, T.
Katsuki, J. Am. Chem. Soc. 2009, 131, 6082 – 6083.
Received: June 13, 2014
Revised: July 2, 2014
Published online: August 21, 2014
Keywords: acylation · axial chirality · enantioselectivity ·
.
kinetic resolution · N-heterocyclic carbene
[8] For enzymatic kinetic resolution of BINOL, see: a) F. Toda, K.
Tanaka, J. Org. Chem. 1988, 53, 3607 – 3609; b) R. J. Kazlauskas,
J. Am. Chem. Soc. 1989, 111, 4953 – 4959; For catalytic asym-
metric methods, see: c) H. Aoyama, M. Tokunaga, J. Kiyosu, T.
Iwasawa, Y. Obora, Y. Tsuji, J. Am. Chem. Soc. 2005, 127,
10474 – 10475; d) S. Shirakawa, X. Wu, K. Maruoka, Angew.
Chem. Int. Ed. 2013, 52, 14200 – 14203; Angew. Chem. 2013, 125,
14450 – 14453.
[9] For an N-acylative kinetic resolution of NOBIN with modest
selectivity, see: S. Arseniyadis, M. Mahesh, P. McDaid, T.
Hampel, S. G. Davey, A. C. Spivey, Collect. Czech. Chem.
Commun. 2011, 76, 1239 – 1253.
[10] For selected reviews, see: a) S. France, D. J. Guerin, S. J. Miller,
T. Lectka, Chem. Rev. 2003, 103, 2985 – 3012; b) G. C. Fu, Acc.
Chem. Res. 2004, 37, 542 – 547; c) E. R. Jarvo, S. J. Miller in
Comprehensive Asymmetric Catalysis, Supplement 1 (Eds.: E. N.
Jacobsen, A. Pfaltz, H. Yamamoto), Springer, Berlin, 2004,
chap. 43, pp. 189 – 206.
[11] For examples of other group transfer reactions, see: a) B. R.
Sculimbrene, A. J. Morgan, S. J. Miller, J. Am. Chem. Soc. 2002,
124, 11653 – 11656; b) K. W. Fiori, A. L. A. Puchlopek, M. J.
Miller, Nat. Chem. 2009, 1, 630 – 634; c) Y. Zhao, J. Rodrigo,
A. H. Hoveyda, M. L. Snapper, Nature 2006, 443, 67 – 70; d) Y.
Zhao, A. W. Mitra, A. H. Hoveyda, M. L. Snapper, Angew.
Chem. Int. Ed. 2007, 46, 8471 – 8474; Angew. Chem. 2007, 119,
8623 – 8626; e) N. Mannville, H. Alite, F. Haeffner, A. H.
Hoveyda, M. L. Snapper, Nat. Chem. 2013, 5, 768 – 774.
[12] For selected recent reviews, see: a) E. M. Phillips, A. Chan,
K. A. Scheidt, Aldrichimica Acta 2009, 42, 55 – 66; b) A. T. Biju,
N. Kuhl, F. Glorius, Acc. Chem. Res. 2011, 44, 1182 – 1195; c) V.
Nair, R. S. Menon, A. T. Biju, C. R. Sinu, R. R. Paul, A. Jose, V.
Sreekumar, Chem. Soc. Rev. 2011, 40, 5336 – 5346; d) P. C.
Chiang, J. W. Bode in N-Heterocyclic Carbenes: From Labora-
[1] For selected general reviews, see: a) G. Bringmann, C. Gꢂnther,
M. Ochse, O. Schupp, S. Tasler in Progress in the Chemistry of
Organic Natural Products, Vol. 82 (Eds.: W. Herz, H. Falk, G. W.
Kirby, R. E. Moore), Springer, Berlin, 2001, pp. 1 – 249; b) G.
Bringmann, M. Breuning, S. Tasler, Synthesis 1999, 525 – 558.
[2] For selected general reviews, see: a) M. McCarthy, P. J. Guiry,
Tetrahedron 2001, 57, 3809 – 3844; b) S. G. Telfer, R. Kuroda,
Coord. Chem. Rev. 2003, 242, 33 – 46.
[3] For an excellent general review on atroposelective synthesis of
axially chiral biaryls, see: a) G. Bringmann, A. J. P. Mortimer,
P. A. Keller, M. J. Gresser, J. Garner, M. Breuning, Angew.
Chem. Int. Ed. 2005, 44, 5384 – 5427; Angew. Chem. 2005, 117,
5518 – 5563; For selected recent examples, see: b) G. Nishida, K.
Noguchi, M. Hirano, K. Tanaka, Angew. Chem. Int. Ed. 2007, 46,
3951 – 3954; Angew. Chem. 2007, 119, 4025 – 4028; c) K. Tanaka,
Chem. Asian J. 2009, 4, 508 – 518; d) J. L. Gustafson, D. Lim, S. J.
Miller, Science 2010, 328, 1251 – 1255; e) J. L. Gustafson, D. Lim,
K. T. Barrett, S. J. Miller, Angew. Chem. Int. Ed. 2011, 50, 5125 –
5129; Angew. Chem. 2011, 123, 5231 – 5235; f) X. Shen, G. O.
Jones, D. A. Watson, B. Bhayana, S. L. Buchwald, J. Am. Chem.
Soc. 2010, 132, 11278 – 11287; g) K. Mori, Y. Ichikawa, M.
Kobayashi, Y. Shibata, M. Yamanaka, T. Akiyama, J. Am. Chem.
Soc. 2013, 135, 3964 – 3970; h) G.-Q. Li, H. Gao, G. Keene, M.
Devonas, D. H. Ess, L. Kꢂrti, J. Am. Chem. Soc. 2013, 135, 7414 –
7417; i) C. K. De, F. Pesciaioli, B. List, Angew. Chem. Int. Ed.
2013, 52, 9293 – 9295; Angew. Chem. 2013, 125, 9463 – 9465; j) A.
Ros, B. Estepa, P. Ramꢃrez-Lꢄpez, E. ꢅlvarez, R. Fernꢆndez,
J. M. Lassaletta, J. Am. Chem. Soc. 2013, 135, 15730 – 15733;
k) V. Bhat, S. Wang, B. M. Stoltz, S. C. Virgil, J. Am. Chem. Soc.
2013, 135, 16829 – 16832; l) D.-J. Cheng, L. Yan, S.-K. Tian, M.-Y.
Wu, L.-X. Wang, Z.-L. Fan, S.-C. Zheng, X.-Y. Liu, B. Tan,
Angew. Chem. Int. Ed. 2014, 53, 3684 – 3687; Angew. Chem. 2014,
11044 www.angewandte.org
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tory Curiosities to Efficient Synthetic Tools (Ed.: S. Dꢃez-
Gonzꢆlez), 2011, pp. 399 – 435; e) H. U. Vora, P. Wheeler, T.
Rovis, Adv. Synth. Catal. 2012, 354, 1617 – 1639; f) J. Izquierdo,
G. E. Hutson, D. T. Cohen, K. A. Scheidt, Angew. Chem. Int. Ed.
2012, 51, 11686 – 11698; Angew. Chem. 2012, 124, 11854 – 11866;
g) J. Mahatthananchai, J. W. Bode, Acc. Chem. Res. 2014, 47,
696 – 707.
hydroxamic acids, see: c) M. Binanzer, S.-Y. Hsieh, J. W. Bode, J.
Am. Chem. Soc. 2011, 133, 19698 – 19701.
[15] Conversions and s factor values were calculated by the methods
of Kagan: Conv. = ee1a/(ee1a+ee3a); s = ln[(1Àconv.)(1Àee1a)]/ln-
[(1Àconv.)(1+ee1a)]. See: H. B. Kagan, J. C. Fiaud, Top. Stereo-
chem. 1988, 18, 249 – 330.
[16] a) E. M. Phillips, M. Wadamoto, H. S. Roth, A. W. Ott, K. A.
Scheidt, Org. Lett. 2009, 11, 105 – 108; b) Y. Kawanaka, E. M.
Phillips, K. A. Scheidt, J. Am. Chem. Soc. 2009, 131, 18028 –
18029; c) K. B. Ling, A. D. Smith, Chem. Commun. 2011, 47,
373 – 375; d) J. E. Taylor, D. S. B. Daniels, A. D. Smith, Org. Lett.
2013, 15, 6058 – 6061.
[17] J. Bao, W. D. Wulff, J. B. Dominy, M. J. Fumo, E. B. Grant, A. C.
Rob, M. C. Whitcomb, S.-M. Yeung, R. L. Ostrander, A. L.
Rheingold, J. Am. Chem. Soc. 1996, 118, 3392 – 3405.
[18] For a recent review, see: S.-F. Zhu, Q.-L. Zhou in Privileged
Chiral Ligands and Catalysts (Ed.: Q.-L. Zhou), Wiley, Hobo-
ken, 2011, pp. 137 – 170.
[19] We have become aware of a related study of the resolution of
axially chiral biaryls by the Sibi group from personal commu-
nication, see: G. Ma, J. Deng, M. P. Sibi, Angew. Chem. Int. Ed.,
DOI: 10.1002/anie.201406684; Angew. Chem., DOI: 10.1002/
ange.201406684.
[13] a) N. T. Reynolds, J. Read deAlaniz, T. Rovis, J. Am. Chem. Soc.
2004, 126, 9518 – 9519; b) A. Chan, K. A. Scheidt, Org. Lett.
2005, 7, 905 – 908; c) B. E. Maki, A. Chan, E. M. Phillips, K. A.
Scheidt, Org. Lett. 2007, 9, 371 – 374; d) S. De Sarkar, A. Biswas,
C. H. Song, A. Studer, Synthesis 2011, 1974 – 1983; e) S. Lu, S. B.
Poh, W.-Y. Siau, Y. Zhao, Angew. Chem. Int. Ed. 2013, 52, 1731 –
1734; Angew. Chem. 2013, 125, 1775 – 1778; f) S. Lu, S. B. Poh,
W.-Y. Siau, Y. Zhao, Synlett 2013, 1165 – 1169; g) S. Kuwano, S.
Harada, B. Kang, R. Oriez, Y. Yamaoka, K. Takasu, K.-i.
Yamada, J. Am. Chem. Soc. 2013, 135, 11485 – 11488.
[14] For NHC-catalyzed kinetic resolution of secondary alcohols
through an alternative asymmetric transesterification approach,
see: a) Y. Suzuki, K. Yamauchi, K. Muramatsu, M. Sato, Chem.
Commun. 2004, 2770 – 2771; b) T. Kano, K. Sasaki, K. Maruoka,
Org. Lett. 2005, 7, 1347 – 1349; For kinetic resolution of cyclic
secondary amines using an achiral NHC catalyst and a chiral
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