Synthesis of monoacylated derivatives of 1,2- cyclohexanediamine. Evaluation of their catalytic activity in the preparation of Wieland-Miescher ketone

Article abstract of DOI:10.1021/jo101723v

Ureas, carbamoyl derivatives, amides, and sulfonamides can be easily prepared from the strained (R,R)-cylohexanediamine urea (1) in high yield, leaving a free amino group that shows good catalytic activity in intramolecular aldol condensations. The preparation of Wieland-Miescher ketone has been studied with these catalysts.

Full text of DOI:10.1021/jo101723v

pubs.acs.org/joc
trans-Cyclohexanediamine is widely exploited as a source
Synthesis of Monoacylated Derivatives of
1,2- Cyclohexanediamine. Evaluation of their
Catalytic Activity in the Preparation of
Wieland-Miescher Ketone†
of chirality in many organic chemistry processes,5 and numer-
ous derived bifunctional catalysts have been prepared. Many
of these organocatalysts combine the presence of the chiral
primary amine group with another functionality (thiourea, urea,
sulfonamide, etc.), so selective monoacylation is desired.6
Monoacylation of cyclohexanediamine can be achieved
following the procedure of Kim et al.,4 protecting both amines
as their benzyloxycarbonyl derivatives, followed by reaction
with Boc2O and hydrogenolysis. Here, we develop an alter-
native procedure for monoacylation based on the reactivity
of urea 1 (Scheme 1).
‡
Angel L. Fuentes de Arriba, David G. Seisdedos,
‡
ꢀ
‡
Luis Simon, Victoria Alcazar, Cesar Raposo, and
§
ꢀ
ꢀ
ꢀ
,‡
ꢀ
Joaquın R. Moran*
´
‡
´
Organic Chemistry Department, Plaza de los Caıdos 1-5,
Universidad de Salamanca, Salamanca 37008, Spain,
§Industrial Chemistry and Environmental Engineering
ꢀ
Department, Jose Gutierrez Abascal 2, Universidad
Politeꢀcnica de Madrid, Madrid 28006, Spain, and
´
Mass Spectrometry Service, Plaza de los Caıdos, 1-5,
Universidad de Salamanca, Salamanca 37008, Spain
ꢀ
SCHEME 1. Preparation of Ureas Starting from (R,R)-Cyclo-
hexanediamine
romoran@usal.es
Received September 1, 2010
Cyclic urea 1 can be obtained when cyclohexanediamine is
reacted with the gaseous and toxic carbonyl sulfide.7 A simple
and high-yield alternative synthesis is based on the use of
diphenylcarbonate, which can also be employed when the
starting material is the straightforwardly obtained enantio-
pure (R,R)-cyclohexanediamine tartrate salt.8
Owing to the trans-fused rings, under acidic conditions
urea 1 shows suitable reactivity with nucleophiles.9 Thus,
aromatic amines can open the urea 1 ring in the presence of
methanesulfonic acid to afford the corresponding aminoureas
2-6 after basic workup (Scheme 1). The reaction seems to
be general for all anilines, including electron-poor (3 and 4)
Ureas, carbamoyl derivatives, amides, and sulfonamides
can be easily prepared from the strained (R,R)-cylohexane-
diamine urea (1) in high yield, leaving a free amino group
that shows good catalytic activity in intramolecular aldol
condensations. The preparation of Wieland-Miescher
ketone has been studied with these catalysts.
Although the formation of amide bonds by reaction of amines
with acid chlorides is a common procedure in organic syn-
thesis, high-yield monoacylation of symmetrical diamines
may be, in some cases, a difficult process. Several hypotheses
have been proposed to explain these findings, such as an
inefficient mixture of reagents or intramolecular catalysis by
the first-formed amide group.1 However, monoacylation has
been shown to be possible by working with low reactivity
compounds like esters,2 by employing aggregation effects,3
or by making use of steric hindrance.4
(5) (a) Xue, F.; Zhang, S.; Duan, W.; Wang, W. Adv. Synth. Catal. 2008,
350, 2194. (b) Lalonde, M. P.; Chen, Y.; Jacobsen, E. N. Angew. Chem., Int.
Ed. 2006, 45, 6366. (c) Uehara, H.; Barbas, C. F., III. Angew. Chem., Int. Ed.
2009, 48, 9848. (d) Tsogoeva, S. B.; Wei, S. Chem. Commun. 2006, 1451.
(e) Sohtome, Y.; Tanatani, A.; Hashimoto, Y.; Nagasawa, K. Chem. Pharm.
Bull. 2004, 52, 477. (f) Rasappan, R.; Reiser, O. Eur. J. Org. Chem. 2009,
1305. (g) Peng, F.; Shao, Z. J. Mol. Catal. A: Chem. 2008, 285, 1. (h) Luo, S.;
Xu, H.; Li, J.; Zhang, L.; Cheng, J.-P. J. Am. Chem. Soc. 2007, 129, 3074.
(i) Mei, K.; Jin, M.; Zhang, S.; Li, P.; Liu, W.; Chen, X.; Xue, F.; Duan, W.;
Wang, W. Org. Lett. 2009, 11, 2864. (j) Wang, J.; Wang, X.; Ge, Z.; Cheng,
T.; Li, R. Chem. Commun. 2010, 1751. (k) Ma, H.; Liu, K.; Zhang, F.- G.;
Zhu, C.- L.; Nie, J.; Ma, J.- A. J. Org. Chem. 2010, 75, 1402. (l) Huang, H.;
Jacobsen, E. N. J. Am. Chem. Soc. 2006, 128, 7170. (m) Liu, K.; Cui, H.-F.;
Nie, J.; Dong, K.-Y.; Li, X.-J.; Ma, J.-A. Org. Lett. 2007, 9, 923. (n) He, T.;
Gu, Q.; Wu, X.-Y. Tetrahedron 2010, 66, 3195.
†
ꢀ
Dedicated to Professor Carmen Najera on the occasion of her 60th birthday.
(1) Jacobson, A. R.; Makris, A. N.; Sayre, L. M. J. Org. Chem. 1987, 52,
(6) Mitchell, J. M.; Finney, N. S. Tetrahedron Lett. 2000, 41, 8431.
(7) Davies, S. G.; Mortlock, A. A. Tetrahedron 1993, 49, 4419.
2592.
(2) Tang, W.; Fang, S. Tetrahedron Lett. 2008, 49, 6003.
(8) Schanz, H.-J.; Linseis, M. A.; Gilheany, D. G. Tetrahedron: Asymmetry
2003, 14, 2763.
~
ꢀ
ꢀ
ꢀ
(3) Muniz, F. M.; Simon, L.; Saez, S.; Raposo, C.; Moran, J. R. Tetra-
ꢀ
(9) Hutchby, M.; Houlden, C. E.; Ford, J. G.; Tyler, S. N. G.; Gagne,
hedron Lett. 2008, 49, 790.
(4) Kim, Y. K.; Lee, S. J.; Ahn, K. H. J. Org. Chem. 2000, 65, 7807.
M. R.; Lloyd-Jones, G. C.; Booker-Milburn, K. I. Angew. Chem., Int. Ed.
2009, 48, 8721.
DOI: 10.1021/jo101723v
r
Published on Web 11/08/2010
J. Org. Chem. 2010, 75, 8303–8306 8303
2010 American Chemical Society

Fuentes de Arriba et al.
JOCNote
SCHEME 2. Monoprotection of Cyclohexanediamine as
Carbamoyl (Carbamothioyl) Derivatives
SCHEME 4. One-Pot Synthesis of Carbamate 9 and Preparation
of Amides and Sulfonamides
SCHEME 3. Transformation of the Carbamoyl Derivatives
into Sulfonamides
and electron-rich systems (5) and hindered amines (6). Ring
opening can also be carried out without methanesulfonic acid
when the hydrochloride salt of the aromatic amine is employed.
In this case, the reaction also works well and the isolation
of the corresponding ureas may be easily accomplished by
precipitation upon addition of a proper solvent to the reac-
tion medium (see the Supporting Information). By contrast,
aliphatic amines failed to produce the desired ring opening
under the above conditions.
SCHEME 5. Preparation of Catalyst 18
Monoamides and sulfonamides are other target compounds
whose synthesis is achieved through the monocarbamoyl
derivatives (see Schemes 3 and 4). Hence, the first step in
the synthesis comprises the reaction of urea 1 with alcohols
yielding the monocarbamates (Scheme 2). Compound 7 was
obtained by reacting the cyclic urea 1 with MeOH/HCl,
and the carbamoyl derivatives 8 and 9 were prepared by
treatment with the corresponding alcohols and MeSO3H.
Under the same conditions, dodecanethiol afforded the mono-
carbamothioyl derivative 10.
Preparation of sulfonamides 11 and 12 was carried out in two
steps, starting from the related carbamoyl derivatives. For the
obtention of sulfonamides, compounds 7 and 8, respectively,
were reacted with tosyl chloride. These sulfonamides may be
deprotected yielding the primary amine 13 (Scheme 3). Depro-
tection can be carried out under basic conditions, nucleophilic
displacement in the case of the methyl group,10 or hydrogeno-
lysis for the benzyl group. Additionally, the tosyl derivative 11
was converted to the corresponding methylamine 14 through
reduction of the carbamoyl group with LiAlH4.
monocarbamoylated compound 9. This compound is highly
water-soluble as its methanesulfonate salt but readily crystallizes
as the hydroiodide. Tosylation or benzoylation, for example,
can be carried out in chloroform in the presence of triethylamine
to yield compounds 15 and 16. Hydrolysis of the phenylcar-
bamoyl group can be readily achieved under mild basic condi-
tions to yield the sulfonamide 13 and the amide 17 (Scheme 4).
The “oxyanion hole” properties of isophthalic derivatives11
inspired us to prepare compound 18, which incorporates an
extra amide functionality. This cyclohexanediamine derivative
is obtained starting from the isophthalic acid monobutyl amide,12
according to the synthetic procedure depicted in Scheme 5
(see the Supporting Information).
Chiral amines derived from diaminocyclohexane have proved
to be efficient organocatalysts for the aldol reaction.13 Due to
(11) (a) Dixon, R. P.; Geib, S. J.; Hamilton, A. D. J. Am. Chem. Soc. 1992,
~
114, 365. (b) Gale, P. A. Coord. Chem. Rev. 2003, 240, 191. (c) Muniz, F. M.;
Montero, V. A.; Fuentes de Arriba, A. L.; Simon, L.; Raposo, C.; Moran,
The one-pot synthesis of the monocarbamate 9 starting
from the cyclohexanediamine tartrate salt offers an attrac-
tive possibility to achieve the monoprotected compounds
(Scheme 4). Since urea 1 can be obtained from diphenyl carbo-
nate, generating two phenol equivalents in situ, the addition of
methanesulfonic acid led to ring opening, directly affording the
ꢀ
ꢀ
J. R. Tetrahedron Lett. 2008, 49, 5050.
ꢀ
~
ꢀ
(12) Oliva, A. I.; Simon, L.; Muniz, F. M.; Sanz, F.; Moran, J. R.
Tetrahedron 2004, 60, 3755.
(13) (a) Raj, M.; Parashari, G. S.; Singh, V. K. Adv. Synth. Catal. 2009,
351, 1284. (b) Nakayama, K.; Maruoka, K. J. Am. Chem. Soc. 2008, 130,
17666. (c) Luo, S.; Xu, H.; Chen, L.; Cheng, J.-P. Org. Lett. 2008, 10, 1775.
(d) Luo, S. Z.; Xu, H.; Li, J. Y.; Zhang, L.; Cheng, J. P. J. Am. Chem. Soc.
2007, 129, 3074. (e) Mei, K.; Zhang, S.; He, S.; Li, P.; Jin, M.; Xue, F.; Luo,
G.; Zhang, H.; Song, L.; Duan, W.; Wang, W. Tetrahedron Lett. 2008, 49,
2681. (f) Liu, J.; Yang, Z.; Wang, Z.; Wang, F.; Chen, X.; Liu, X.; Feng, X.;
Su, Z.; Hu, C. J. Am. Chem. Soc. 2008, 130, 5654.
(10) Elsinger, F.; Schreiber, J.; Eschenmoser, A. Helv. Chim. Acta 1960,
43, 113.
8304 J. Org. Chem. Vol. 75, No. 23, 2010

Fuentes de Arriba et al.
JOCNote
TABLE 1. Preparation of the Wieland-Miescher Ketone in CDCl3
(1.0 M) with 10 mol % of Catalyst at 20 °C
the preparation of the Hajos-Wiechert ketone; however, in
this case, the reaction was much slower (only 20% conver-
sion to the ketone after 94 h and 81% ee), which limits its use
for preparative purposes.
In summary, an alternative approach to the synthesis
of monofunctionalized 1,2-cyclohexanediamines has been
described, starting from the readily available (R,R)-cyclo-
hexanediamine urea and taking advantage of the reactivity
provided by the trans ring junction. In addition, we have
explored the possibilities of these compounds as catalysts in
the intramolecular aldol condensation yielding the Wieland-
Miescher ketone, with the best results being obtained for ureas
and amides, reaching up to 95% ee.
entry catalyst conversiona (%) yieldb (%) time (h) eec (%)
1
2
3
4
5
6
7
8
2d
3
4
8
13
14
17
18d
95
94
81
76
3
24
94
100
76
82
63
59
n.d.
n.d.
77
22
30
85
89
75
65
61
-11
91
117
117
161
161
44
85
16
95
Experimental Section
aDetermined by integration of the corresponding signals in the 1H
(3aR,7aR)-Hexahydro-1H-benzo[d]imidazol-2(3H)-one (1).
Enantiopure (R,R)-cyclohexanediamine tartrate salt was readily
obtained starting from the racemic trans-cyclohexane-1,2-diamine
and L-tartaric acid.8 This tartrate salt (40.0 g, 150.8 mmol) and
KOH (17.0 g, 303.6 mmol) were dissolved in H2O (30 mL) to
generate the free diamine. The reaction mixture was heated until all
of the solid was dissolved. Then, 2-propanol (100 mL) was added,
and the solution was stirred and cooled (ice bath) to yield a
potassium tartrate precipitate. To complete the precipitation and
remove the water, powdered sodium sulfate (40.0 g) was added and
the precipitate was filtered off. The solid was washed with more
2-propanol (2Â20 mL), diphenyl carbonate (35.0 g, 163 mmol) was
added to the filtrate, and the mixture was refluxed for 30 min. Steam
distillation and water evaporation allowed us to obtain a crude urea
which could be further purified by recrystallization from EtOH/
H2O (1:1) to yield 18.8 g (90% yield) of a compound with the same
physical properties as those described in the literature.16
General Procedure for the Preparation of Monoureas (2-6)
with Methanesulfonic Acid (Procedure A). To a mixture of the
urea 1 (2.2 mmol) and the aromatic amine (2.2 mmol) in diglyme
(2 mL) was added methanesulfonic acid (0.15 mL) was added,
and the reaction mixture was heated at 120 °C for ∼1 h with
stirring under argon atmosphere. After the mixture was cooled to
room temperature, H2O (10 mL) and Na2CO3 (2.0 g, 19 mmol)
were added, and a crystalline solid precipitated that was filtered to
afford the desired compound. If the urea did not crystallize
spontaneously, diethyl ether (2 mL) was added to assist the precipi-
tation. This procedure has been carried out on a 2-15 mmol scale.
(1R,2R)-1,2-Diaminocyclohexane 3,5-bis(trifluoromethyl) phenyl-
urea (3). Urea 1 (2.0 g, 14.2 mmol), 3,5-bis(trifluoromethyl)aniline
(3.4 g, 14.8 mmol), and methanesulfonic acid (1 mL) were dissolved
in diglyme (2 mL), and the mixture was heated at 120 °C for 30 min.
Then, H2O (30 mL) and Na2CO3 (7 g, 66 mmol) were added. The
product was extracted with ethyl acetate (2 Â 20 mL), and the
solvent was evaporated. The crude residue was purified by recrys-
tallization from ether-hexane at 0 °C to afford 3.5 g (66% yield)
of compound 3, whose properties are in agreement with those
published.5e
b
c
NMR spectra. Isolated yield after silica gel chromatography. Deter-
mined by chiral HPLC (Daicel Chiralpak IC column). d2.0 M concen-
tration of the ketone, 10 mol % catalyst. Higher concentrations of the
ketone yielded reduced enantioselectivities.
our interest in this reaction,14 we decided to explore the ability of
these compounds in the preparation of the Wieland-Miescher
ketone.15 Ureas 2-4 are good organocatalysts for this reaction,
showing high enantioselectivities (Table 1, entries 1-3). The
catalytic activity of the carbamoyl derivative 8 was also eval-
uated (entry 4, Table 1), but enantioselectivity was reduced in
comparison with that obtained with the urea compounds.
Considering enantioselectivity, sulfonamide 13 proved to
be a similar catalyst to the carbamoyl derivative 8 (entries 4
and 5, Table 1), although the conversion rate was consider-
ably reduced. To test the influence of a secondary amine in
the conversion and enantioselectivity, we prepared the sulfon-
amide 14 with a methylamino group (entry 6, Table 1). This
catalyst showed the lowest enantioselectivity with the opposite
enantiomer as the major product.
When amide 17 was used, enantioselectivity was increased
up to 91% ee (entry 7, Table 1). The isophthalic derivative 18,
which resembles the oxyanion hole geometry, gave the best
enantioselectivity (95% ee) with a complete conversion with-
in 16 h (entry 8, Table 1). This catalyst has also been tested in
ꢀ
(14) (a) Fuentes de Arriba, A. L.; Simon, L.; Raposo, C.; Alcazar, V.;
ꢀ
Moran, J. R. Tetrahedron 2009, 65, 4841. (b) Fuentes de Arriba, A. L.;
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
~
ꢀ
Simon, L.; Raposo, C.; Alcazar, V.; Sanz, F.; Muniz, F. M.; Moran, J. R.
Org. Biomol. Chem. 2010, 8, 2979.
(15) (a) Almasi, D.; Alonso, D. A.; Balaguer, A.-N.; Najera, C. Adv.
ꢀ
ꢀ
Synth. Catal. 2009, 351, 1123. (b) Almasi, D.; Alonso, D. A.; Najera, C. Adv.
Synth. Catal. 2008, 350, 2467. (c) Bradshaw, B.; Etxebarrıa-Jardi, G.;
´
ꢀ
ꢀ
Bonjoch, J.; Viozquez, S. F.; Guillena, G.; Najera, C. Adv. Synth. Catal.
2009, 351, 2482. (d) Davies, S. G.; Sheppard, R. L.; Smith, A. D.; Thomson,
J. E. Chem. Commun. 2005, 3802. (e) Lacoste, E.; Vaique, E.; Berlande, M.;
Pianet, I.; Vincent, J.-M.; Landais, Y. Eur. J. Org. Chem. 2007, 167. (f) He, L.
Hecheng Huaxue (Chin. J. Synth. Chem.) 2007, 15, 231. (g) Akahane, Y.;
Inage, N.; Nagamine, T.; Inomata, K.; Endo, Y. Heterocycles 2007, 74, 637.
(h) Akahane, Y.; Inomata, K.; Endo, Y. Heterocycles 2009, 77, 1065.
(i) D’Elia, V.; Zwicknagl, H.; Reiser, O. J. Org. Chem. 2008, 73, 3262.
General Procedure for the Preparation of Monoureas (2-6)
Starting from the Hydrochloride Salts of the Amines (Procedure B).
Urea 1 (3.5 mmol) and the amine hydrochloride (3.5 mmol) were
heated in diglyme (2 mL) at 120 °C. After the mixture was heated
for ∼1 h, a solid precipitated from the reaction medium. NMR
1H analysis of an aliquot confirmed that the reaction had finished.
The mixture was cooled to room temperature, and diethyl ether
(10 mL) was added. The solid was filtered and dried under vacuum
(0.1 mmHg) heating at 90 °C to remove completely the traces of
diglyme, affording the monoureas as their hydrochloride salts.
This procedure has been carried out on a 1-5 mmol scale.
ꢀ
ꢀ
(j) Guillena, G.; Hita, M. d. C.; Najera, C.; Viozquez, S. F. J. Org. Chem.
2008, 73, 5933. (k) Kanger, T.; Kriis, K.; Laars, M.; Kailas, T.; Muurisepp,
A.-M.; Pehk, T.; Lopp, M. J. Org. Chem. 2007, 72, 5168. (l) Davies, S. G.;
Russell, A. J.; Sheppard, R. L.; Smith, A. D.; Thomson, J. E. Org. Biomol.
ꢀ
ꢀ
Chem. 2007, 5, 3190. (m) Guillena, G.; Najera, C.; Viozquez, S. F. Synlett
2008, 19, 3031. (n) Kriis, K.; Kanger, T.; Laars, M.; Kailas, T.; Muurisepp,
A.-M.; Pehk, T.; Lopp, M. Synlett 2006, 11, 1699. (o) Nozawa, M.; Akita, T.;
Hoshi, T.; Suzuki, T.; Hagiwara, H. Synlett 2007, 4, 661. (p) Zhang, X.-M.;
Wang, M.; Tu, Y.-Q.; Fan, C.-A.; Jiang, Y.-J.; Zhang, S.-Y.; Zhang, F.-M.
Synlett 2008, 18, 2831. (q) Agami, C.; Meynier, F.; Puchot, C.; Guilhem, J.;
Pascard, C. Tetrahedron 1984, 40, 1031. (r) Bui, T.; Barbas, C. F. Tetrahedron
Lett. 2000, 41, 6951.
(16) Davies, S. G.; Mortlock, A. A. Tetrahedron 1993, 49, 4419.
J. Org. Chem. Vol. 75, No. 23, 2010 8305

Fuentes de Arriba et al.
JOCNote
(1R,2R)-1,2-Diaminocyclohexane Phenylurea (2). Urea 1(495mg,
3.5 mmol) and aniline hydrochloride (460 mg, 3.5 mmol) were
heated in diglyme (2 mL) at 120 °C. After the mixture was heated
for ∼1 h, a solid precipitated from the reaction medium. 1H NMR
analysis of an aliquot confirmed that the reaction had finished. The
mixture was cooled to room temperature, and diethyl ether (10 mL)
was added. The solid was filtered and dried under vacuum
(0.1 mmHg) heating at 90 °C to remove completely the traces of
diglyme. The urea 2 as its hydrochloride salt (621 mg, 66%) was
obtained. Spectral and physical data of the free amine (liberated
with aqueous KOH (3.3 mL, 6 mM) and extracted with diethyl
ether) were in agreement with those published.17
was added, and the phenol was extracted with ethyl acetate
(2Â 30 mL). To the aqueous layer, cooled to 0 °C, was added KI
(7.0 g, 42 mmol), and a precipitate of the hydroiodide salt of
compound 9 (12 g, 87% yield) was obtained: mp 187-189 °C;
[R]20 -6.33 (c 0.6, CH3OH); 1H NMR (200 MHz, CDCl3/
D
CD3OD) δ 7.22-7.15 (2H, m), 7.06-6.97 (3H, m), 3.38 (1H, m),
3.03 (1H, m), 1.94-1.84 (2H, m), 1.65-1.55 (2H, m), 1.30-1.16
(4H, m); 13C NMR (50 MHz, CDCl3/CD3OD) δ 155.9 (C), 150.9
(C), 129.3 (CH), 125.6 (CH), 121.8 (CH), 54.6 (CH), 53.1 (CH),
31.7 (CH2), 29.9 (CH2), 24.4 (CH2), 23.7 (CH2); IR (film) 3565,
3318, 1729, 1599, 1462 cm-1. Anal. Calcd for C13H19IN2O2: C,
43.11; H, 5.29; N, 7.73. Found: C, 42.89; H, 5.38; N, 7.83.
Phenyl (1R,2R)-2-Aminocyclohexylcarbamate 9. Initially, (R,R)-
cyclohexane-1,2-diamine tartrate salt (10.02 g, 37.9 mmol) was
reacted under the same conditions described for the preparation of
urea 1. After the mixture was refluxed with diphenyl carbonate
(8.11 g, 37.9 mmol) in 2-propanol, the solvent was evaporated
under reduced pressure, and the crude residue was dried through
azeotropic destillation with benzene (100 mL). To this mixture of
phenol and the urea 1 was added 1 equiv of methanesulfonic acid
(2.5 mL), and the reaction was heated at 110 °C with stirring for 1 h
under Ar atmosphere. Then the solution was cooled, water (30 mL)
Acknowledgment. This work was supported by the Spanish
ꢀ
(DGICYT) (CTQ-2008-01771/BQU), and the UE (European
Reintegration Grant PERG04-GA-2008-239244). A.L.F.A.
ꢀ
Direccion General de Investigacion, Ciencia y Tecnologıa
´
ꢀ
thanks the Ministerio de Educacion y Ciencia for a FPU Grant
and Angelica del Castillo for working with us.
ꢀ
Supporting Information Available: Synthesis of catalysts,
characterization data (including 1H and 13C spectra of the new
compounds), and HPLC chromatograms. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
(17) Bied, C.; Moreau, J. J. E.; Wong Chi Man, M. Tetrahedron:
Asymmetry 2001, 12, 329.
8306 J. Org. Chem. Vol. 75, No. 23, 2010