Chiral bidentate bis(N-heterocyclic carbene)-based palladium complexes bearing carboxylate ligands: Highly effective catalysts for the enantioselective conjugate addition of arylboronic acids to cyclic enones

Article abstract of DOI:10.1002/chem.200701982

Axially chiral cis-chelated bidentate bis(N-heterocyclic carbene)-palladium(II) complexes with two weakly coordinating carboxylate ligands are effective catalysts for the asymmetric conjugate addition of arylboronic acids to cyclic enones, producing the corresponding adducts in moderate-to-high yields and with good-to-high enantioselectivities, in most cases under mild conditions.

Full text of DOI:10.1002/chem.200701982

FULL PAPER
DOI: 10.1002/chem.200701982
Chiral Bidentate Bis(N-Heterocyclic Carbene)-Based Palladium Complexes
Bearing Carboxylate Ligands: Highly Effective Catalysts for the
Enantio
A
C
H
T
R
E
U
N
G
selective Conjugate Addition of Arylboronic Acids to Cyclic Enones
A
H
R
U
G
[
a]
[a, b]
Tao Zhang and Min Shi*
Abstract: Axially chiral cis-chelated bidentate bis(N-heterocyclic carbene)–palla-
dium(II) complexes with two weakly coordinating carboxylate ligands are effective
catalysts for the asymmetric conjugate addition of arylboronic acids to cyclic
enones, producing the corresponding adducts in moderate-to-high yields and with
good-to-high enantioselectivities, in most cases under mild conditions.
Keywords: asymmetric catalysis
boronic acids · carbenes · Michael
addition · palladium
·
Introduction
gands in transition-metal catalysis, which provide more ef-
fective metal complexes owing to their stability to air and
moisture and their strong s-donor and poor p-acceptor
Catalytic asymmetric conjugate addition of organometallic
reagents to a,b-unsaturated carbonyl compounds is an effi-
cient method for the construction of chiral enantioenriched
compounds by using achiral precursors. Among the numer-
ous methods to achieve this, rhodium-catalyzed asymmetric
conjugate addition to enones with organoboron reagents
aryl- and alkenylboronic acids) has attracted much atten-
tion because of their stability towards air and moisture,
functional group tolerance, as well as easy availability and
[8]
properties.
Significantly, Pd–NHC complexes have
emerged as effective catalysts for a variety of coupling reac-
[1]
[9]
tions. Unfortunately, to date, the promise of a highly
active and enantioselective Pd–NHC catalyst has not been
fulfilled, even though many palladium-mediated transforma-
[
10]
[11]
(
tions, such as enolate arylation, p-allyl alkylation, and
[
12]
various ring-closing reactions with carbopalladation, have
opened up the possibility of the development of enantiose-
lective catalysis. Previously, we reported the synthesis of a
[2–4]
broad scope.
However, compared with asymmetric conju-
gate addition catalyzed by chiral rhodium complexes, suc-
cessful examples of chiral palladium-complex-catalyzed
asymmetric conjugate addition of aryl- and alkenylboronic
novel cis-chelated bidentate bis(NHC) ligand and its
A
T
E
N
[
13a]
rhodium
A
H
R
U
G
as well as its pallad-
[5,6]
acids to a,b-unsaturated ketones are rare.
Therefore, the
search for efficient chiral palladium complexes in asymmet-
ric conjugate addition is still a formidable challenge in asym-
metric catalysis.
[7]
N-Heterocyclic carbenes (NHCs) represent a growing
class of ligands that can be used in place of phosphine li-
[
a] T. Zhang, Prof. M. Shi
Laboratory for Advanced Materials and Institute of Fine Chemicals
East China University of Science and Technology
1
30 Mei Long Road, Shanghai, 200237 (China)
E-mail: mshi@mail.sioc.ac.cn
[
b] Prof. M. Shi
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
3
54 Fenglin Road, Shanghai, 200032 (China)
Fax : (+86)21-6416-6128
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
III
II
Scheme 1. Structures of NHC–Rh and NHC–Pd complexes 1, 2, and 3.
Chem. Eur. J. 2008, 14, 3759 – 3764
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3759

[13b]
A
C
H
T
R
E
U
N
G
ium(II) complex 1,
and their application in both Suzuki–
Miyaura and Heck coupling reactions as well as asymmetric
hydrosilylation of methyl ketones and aerobic oxidative ki-
[13c]
netic resolution of alcohols.
As chiral C -symmetric cis-
2
chelated bidentate NHC ligands remain scarce, we have
II
continued to seek out more efficient chiral NHC–Pd com-
[13,14]
plexes for asymmetric catalysis.
Herein, we report an in-
teresting first example of the asymmetric conjugate addition
of arylboronic acids to cyclic enones catalyzed by chiral cis-
chelated bidentate bis
and 3 with two weakly coordinating carboxylate ligands
Scheme 1).
A
H
R
U
G
(
Results and Discussion
II
Chiral NHC–Pd complex 1 was prepared from axially
chiral binaphthyl-2,2’-diamine (BINAM) according to a liter-
[13]
II
ature procedure. NHC–Pd complexes 2 and 3 were then
synthesized by treating 1 with AgO CCH and AgO CCF ,
Figure 1. X-ray structure of 3 with thermal ellipsoids drawn at the 30%
probability level. Hydrogen atoms and water have been omitted for clari-
ty.
2
3
2
3
respectively, in a mixed solvent system of CH Cl and
2
2
II
CH CN at room temperature. These two NHC–Pd com-
3
plexes were isolated as white solids in 88 and 90% yields,
respectively (Scheme 2). They are fairly stable towards air
and moisture in solution and in the solid state.
[
a]
Table 1. Optimization of the reaction conditions.
[
b]
[c]
Entry
Catalyst
Solvent
Base (equiv
to 4a)
Yield
[%]
ee
[%]
[
d]
1
2
3
4
5
6
7
8
9
1
2
3
3
3
3
3
3
3
3
3
3
3
3
3
THF
THF
THF
THF
THF
THF
THF
IPA
MeCN
toluene/THF
THF
THF
THF
KOH (0.4)
KOH (0.4)
KOH (0.4)
KOH (0.07)
KOH (0.5)
KOH (1.0)
<5
95
97
46
85
22
94
99
8
96
97
39
32
65
97
n.d.
93 (S)
94 (S)
80 (S)
90 (S)
78 (S)
91 (S)
74 (S)
2 3
K CO (0.4)
KOH (0.4)
KOH (0.4)
KOH (0.4)
KOH (0.4)
KOH (0.4)
KOH (0.4)
KOH (0.4)
KOH (0.4)
Scheme 2. Preparation of 2 and 3.
[d]
n.d.
[
[
[
[
[
e]
10
11
12
13
14
15
80 (S)
96 (S)
94 (S)
96 (S)
94 (S)
96 (S)
f]
f,g]
f,h]
f,i]
Single crystals of 2 and 3 that were suitable for X-ray dif-
fraction studies were grown from a mixed solvent system of
hexane/CH Cl . The molecular structure of 3 is shown in
THF
THF
2
2
[f,j]
[15]
Figure 1.
As can be seen from Figure 1, the palladium
[
a] All reactions were conducted with 4a (0.25 mmol), 5a (0.75 mmol),
center is coordinated by the two carbene moieties of the ax-
ially chiral bidentate bis(NHC) ligand and two trifluoroace-
tate counterions in this interesting NHC–Pd complex.
Initial examination of the asymmetric addition of phenyl-
boronic acid (5a) to 2-cyclohexenone (4a) in the presence
of 1, 2, or 3 (3 mol%) failed to give the desired product
KOH (0.1 mmol), and catalyst 1, 2, or 3 (0.0075 mmol) in THF/H
2
O
A
H
R
U
G
(10:1, 1.1 mL) at 208C for 36 h. [b] Yield of isolated product. [c] Deter-
mined by HPLC analysis using chiral stationary phase columns. The ab-
solute configuration of 6aa was determined by comparing the optical ro-
tation [a]
[
II
D
with the data in the literature. [d] n.d.=not determined.
e] Toluene/THF 1:1. [f] The reaction was conducted with 0.375 mmol of
a. [g] The reaction was carried out at 508C for 10 h. [h] The reaction
5
after 48 h at room temperature (208C) in THF/H O (10:1).
was carried out at room temperature (208C) for 10 h. [i] The reaction was
carried out at 508C for 20 h. [j] The reaction was carried out at room
temperature (208C) for 20 h.
2
Premixing 2 or 3 with KOH (40 mol% of 5a) followed by
the addition of 4a and 5a afforded the desired product 6aa
in 95% yield along with 93% enantiomeric excess (ee) and
97% yield along with 94% ee, respectively, after 36 h at
room temperature (208C) (Table 1, entries 2 and 3). Howev-
er, complex 1 was ineffective as the catalyst under identical
conditions (Table 1, entry 1). These results suggest that the
two weakly coordinating carboxylate ligands play a very im-
portant role in this reaction. Interestingly, this asymmetric
II
conjugate addition reaction catalyzed by (R)-bis(NHC)–Pd
A
H
R
U
G
3760
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3759 – 3764

Carbene-Based Palladium Complexes
FULL PAPER
complex 2 or 3 gave 6aa with an S configuration, which is a
different outcome to that observed for the asymmetric con-
jugate addition reaction catalyzed by (S)-BINAP-rhodium
By using 2-cycloheptenone (4b) as the substrate with aryl-
boronic acids 5a, 5b, 5d, and 5 f, the corresponding adducts
6ba, 6bb, 6bd, and 6bf were produced in good yields and
high enantiomeric excesses in the presence of catalyst 2 or 3
under the standard conditions (Table 3, entries 1–6). The
[3]
in which 6aa was also obtained with an S configuration.
We next attempted to optimize further the reaction condi-
tions and the results of these experiments are summarized
in Table 1 (entries 4–11). Decreasing or increasing the
amount of KOH lowered the yield and ee of 6aa (Table 1,
entries 4–6). Potassium carbonate (0.4 equiv K CO ) is also
Table 3. Asymmetric conjugate addition of arylboronic acids to cyclic
[
a]
enones.
2
3
an effective base in this reaction. Examination of solvent ef-
fects, reaction temperature, and the amount of 5a employed
revealed that the best reaction conditions involve the use of
3
(3 mol%) and KOH (40 mol%) with 5a (1.5 equiv) in
THF at room temperature, which gives 6aa in high yield
and high ee (Table 1, entry 11). Note, adduct 6aa was ob-
tained in a lower yield and with a high ee after 10 h at room
temperature (208C) and also when the reaction was carried
out at 508C for 10 h (Table 1, entries 12 and 13). After 20 h,
[b]
[c]
Entry Substrate Ar
Catalyst Yield [%]
ee [%]
1
2
3
4
5
6
7
8
9
4b
4b
4b
4b
4b
4b
4c
4d
4e
C
C
6
H
H
5
5
(5a)
(5a)
3
2
3
3
3
2
3
3
3
88 (6ba)
85 (6ba)
90 (6bb)
86 (6bd)
99 (6bf)
84 (6bf)
53 (6ca)
62 (6df)
58 (6ea)
91 (À)
94 (À)
91 (À)
96 (À)
97 (À)
96 (À)
81 (À)
38 (+)
32 (+)
6
4-MeC H (5b)
3-MeOC
2-naphthyl (5 f)
2-naphthyl (5 f)
6
4
6
H
4
(5d)
6
aa was obtained in good yield and high ee at room temper-
ature (208C) and in moderate yield and high ee at 508C
Table 1, entries 14 and 15), which suggests that this asym-
[d]
d]
C
6
H
5
(5a)
2-naphthyl (5 f)
(5a)
[
(
metric conjugate addition reaction is facilitated at room
temperature.
6 5
C H
[a] All reactions were conducted with 4a (0.25 mmol), 5 (0.375 mmol),
KOH (0.1 mmol), and NHC–Pd catalyst 2 or 3 (0.0075 mmol) in THF/
H O (10:1, 1.1 mL) at room temperature (20–258C) for 36 h. [b] Yield of
2
isolated product. [c] Determined by HPLC analysis with chiral stationary
phase columns (Daicel Chiralcel OD-H, AD-H or AS-H). The signs of
the optical rotations are indicated in parentheses. [d] The reaction was
carried out at 508C.
II
With these optimized reaction conditions identified, by
using 3 mol% of catalyst 2 or 3, the generality of this inter-
esting asymmetric conjugate addition reaction with various
other arylboronic acids was examined and the results are
shown in Table 2. We found that the adducts were obtained
in high yields (78–99%) and excellent enantiomeric excesses
(
88–97% ee) with electron-rich arylboronic acids, which in-
cluded easily hydrolyzed p-anisylboronic acid (Table 2,
conjugate addition of 5a to benzyl 2,3-dihydro-4-oxo-1H-
pyridinecaboxylate (4c) and of 5 f to 5,6-dihydropyran-2-one
(4d) afforded the corresponding products 6ca in moderate
yield along with good ee and 6df in good yield along with a
lower ee in the presence of 3 at 508C, respectively (Table 3,
entries 7 and 8). The asymmetric conjugate addition reaction
of 2-cyclopentenone (4e) with 5a afforded the correspond-
ing adduct 6ea in moderate yield and low ee under the stan-
dard conditions (Table 3, entry 9).
[6d,16]
entry 5).
acid, the corresponding adduct (6ah) was produced in a
slightly lower yield and lower enantiomeric excess
Table 2, entry 9).
With electron-poor m-chlorophenylboronic
a
(
[
a]
Table 2. Asymmetric conjugate addition of arylboronic acids to 4a.
On the basis of previous mechanistic studies by Hayashi
[3,4]
and co-workers,
a plausible catalytic cycle is outlined in
Scheme 3. First, catalyst 3 reacts with KOH to afford the
corresponding hydroxopalladium complex 7, which readily
[
b]
[c]
Entry
Ar
Catalyst
Yield [%]
ee [%]
[5a,6b,d,17]
undergoes transmetalation with 5a
to produce a phe-
1
2
3
4
5
6
7
8
9
3-MeC
4-MeC
3-MeOC
3-MeOC
4-MeOC
2-naphthyl (5 f)
2-naphthyl (5 f)
4-C
3-ClC
3,5-Me
6
6
H
H
4
4
(5b)
(5c)
3
3
3
2
3
3
2
3
3
3
97 (6ab)
89 (6ac)
90 (6ad)
92 (6ad)
82 (6ae)
99 (6af)
98 (6af)
97 (6ag)
78 (6ah)
90 (6ai)
97 (À)
92 (À)
97 (À)
94 (À)
94 (À)
97 (À)
96 (À)
93 (À)
88 (À)
92 (À)
nylpalladium species 8. Insertion of the CÀPd bond of 8 into
the C=C double bond of the cyclic enone substrate takes
place to give p-oxaallylpalladium species 9 or the palladium
enolate species 9’. The resulting species is hydrolyzed by
water to give product 6aa and regenerate 7.
6
6
6
H
H
H
4
4
4
(5d)
(5d)
(5e)
6
H
5
C
6
H
4
(5g)
(5h)
(5i)
6
H
4
1
0
2
C
6
H
3
Conclusion
[
a] All reactions were conducted with 4a (0.25 mmol), 5 (0.375 mmol),
KOH (0.1 mmol), and NHC–Pd catalyst 2 or 3 (0.0075 mmol) in THF/
O (10:1, 1.1 mL) at room temperature (20–258C) for 36 h. [b] Yield of
isolated product. [c] Determined by HPLC analysis with chiral stationary
phase columns (Daicel Chiralcel OD-H, AD-H or AS-H). The signs of
the optical rotations are indicated in parentheses.
II
We have developed a novel type of effective axially chiral
H
2
cis-chelated bidentate bis(NHC)–palladium(II) catalyst for
A
H
E
N
the asymmetric conjugate addition of arylboronic acids to
cyclic enones, which affords the corresponding adducts in
Chem. Eur. J. 2008, 14, 3759 – 3764
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3761

M. Shi and T. Zhang
2
D
0
1
2
688C (decomp); [a] =52.0 (c=0.12 in DMSO); H NMR (300 MHz,
CDCl
H; ArH), 6.83–6.92 (m, 10H; ArH), 7.20–7.26 (m, 2H; ArH), 7.71 (d,
J=8.4 Hz, 2H; ArH), 8.05 (d, J=8.4 Hz, 2H; ArH), 8.15 ppm (d, J=
3 3 3
, TMS): d=1.88 (brs, 6H; CH ), 3.90 (s, 6H; CH ), 6.70–6.73 (m,
2
1
3
8
1
1
2
3
.4 Hz, 2H; ArH); C NMR (75 MHz, CDCl , TMS): d=23.7, 35.0,
09.1, 112.4, 123.1, 123.4, 124.9, 126.4, 126.9, 127.5, 130.1, 131.2, 132.5,
32.7, 133.1, 135.1, 135.8, 171.6, 177.3 ppm; IR (KBr): n˜ =3408, 3053,
À1
+
924, 2847, 1580, 1510, 1385, 751 cm ; MS (MALDI): m/z: 620.2.0 [M
CCH ]; elemental analysis calcd (%) for C40 Pd·1.5H O re-
quires: C 62.71, H 4.60, N 7.31; found: C 62.75, H 4.62, N 7.30%.
Synthesis of 3: Complex 1 (174 mg, 0.20 mmol) was suspended in a mix-
ture of CH Cl (15 mL) and CH CN (5 mL). AgOCOCF (93 mg,
.42 mmol) was added and the reaction mixture was stirred at room tem-
À2O
2
3
H
32
N
4
O
4
2
2
2
3
3
0
perature for 3 h. The resulting suspension was filtered from the precipi-
tated AgI through Celite and the solvent was removed under reduced
pressure to give 3 as a white powder (153 mg, 90%). Crystals that were
2 2
suitable for diffraction study were grown from solutions in CH Cl /
2
0
hexane (1:1). M.p. 2488C (decomp); [a] =49.0 (c=0.55 in DMSO);
D
1
H NMR (300 MHz, CDCl
3 3
, TMS): d=3.88 (s, 6H; CH ), 6.75–6.78 (m,
2
H; ArH), 6.83–6.97 (m, 10H; ArH), 7.22–7.27 (m, 2H; ArH), 7.73 (d,
1
3
J=8.1 Hz, 2H; ArH), 8.09 ppm (s, 4H; ArH); C NMR (75 MHz,
CDCl , TMS): d=34.9, 109.4, 112.6, 115.9 (q, J=287.9 Hz, CF ), 123.8,
24.0, 124.4, 126.8, 127.3, 127.7, 130.5, 131.1, 132.5, 132.8, 133.0, 134.6,
3
3
1
1
9
Scheme 3. Proposed catalytic cycle for the conjugate addition of 5a to 4a
by catalysis with 3.
135.7, 161.7 (q, J=36.7 Hz, CO), 166.7 ppm; F NMR (282 MHz, CDCl
CFCl
): d=À74.9 ppm; IR (KBr): n˜ =3558, 2924, 1680, 1510, 1393,
45 cm ; MS (MALDI): m/z: 515.2 [M À2OCOCF ÀPd]; elemental
analysis calcd (%) for C40 Pd·H O requires: C 55.54, H 3.26, N
.48; found: C 55.64, H 3.11, N 6.27%.
3
,
3
À1
+
7
3
H
26
F
6
N
4
O
4
2
6
moderate-to-high yields and with good-to-high enantioselec-
tivities, in most cases under mild conditions. To the best of
our knowledge, this is the first example of the use of chiral
General procedure for the palladium-catalyzed asymmetric conjugate ad-
dition of arylboronic acids to cyclic enones: The NHC–Pd catalyst
II
(3 mol%, 7.5 mol) and KOH (40 mol%, 0.1 mmol, 5.6 mg) were dis-
solved in dry THF (1.0 mL) in a flame-dried Schlenk tube equipped with
a septum and stirring bar and the mixture was stirred under argon at
room temperature for 10 min. Arylboronic acid 5 (1.5 equiv, 0.375 mmol)
was added followed by the addition of enone 4 (0.25 mmol). After the
cis-chelated bidentate bis(NHC)–palladium(II) catalysts in
A
H
R
U
G
the asymmetric conjugate addition of arylboronic acids to
cyclic enones. Further studies on substrate scope, the mecha-
nistic details of the catalytic system, and the use of palladi-
um complexes 2 and 3 as catalysts in other asymmetric CÀC
addition of H O (0.1 mL), the reaction mixture was stirred at room tem-
2
perature for 36 h. Saturated aqueous solution of NaHCO
added. The organic phase was separated and the resulting aqueous layer
was extracted with Et O. The combined organic phases were filtered
through a plug of silica, dried over anhydrous Na SO , concentrated
3
was then
bond-forming reactions are in progress.
2
2
4
under reduced pressure, and purified by flash chromatography (eluent:
EtOAc/petroleum ether) to yield the corresponding product 6.
Experimental Section
[
3]
3
-Phenylcyclohexanone (6aa): Ketone 6aa was obtained after purifica-
tion by flash chromatography (eluent: petroleum ether/Et OAc 25:1;
2
General methods: Melting points are uncorrected (Yanagimoto micro
1
13
97% yield, 96% ee). The ee was determined by HPLC analysis (Chiral-
pak AD column, hexane/iPrOH 100:1, detection at 209 nm, retention
melting apparatus). H and C NMR spectra were recorded by using a
Varian Mercury vx 300 MHz spectrometer in CDCl with tetramethylsi-
3
2
D
5
times: 19.5 (major)/23.6 min (minor)). [a] =À20.4 (c=1.0 in CHCl
3
)
lane (TMS) as an internal standard at 300 and 75 MHz, respectively.
Mass spectra were recorded by using an HP-5989 instrument by EI/ESI/
MALDI methods. Organic solvents used were dried by standard methods
when necessary. Satisfactory CHN microanalyses were obtained by using
a Carlo Erba 1106 analyzer. X-ray diffraction analysis was performed by
using a Bruker Smart-1000 X-ray diffractometer. Optical rotations were
determined at 589 nm (sodium D line) by using a Perkin–Elmer 341 MC
1
(
for 96% ee); H NMR (300 MHz, CDCl
3
, TMS): d=1.70–1.92 (m, 2H),
2
.06–2.18 (m, 2H;), 2.32–2.63 (m, 4H), 2.96–3.05 (m, 1H), 7.21–7.36 ppm
1
3
(
m, 5H); C NMR (75 MHz, CDCl
3
, TMS): d=25.5, 32.7, 41.1, 44.7,
4
8.9, 126.5, 126.6, 128.6, 144.3, 211.0 ppm.
[
3]
3-(3-Methylphenyl)cyclohexanone (6ab): Ketone 6ab was obtained
after purification by flash chromatography (eluent: petroleum ether/
2
À1 À1
digital polarimeter; [a]
D
values are given with units of 10 cm deg
g
.
Et
2
OAc 25:1; 97% yield, 97% ee). The ee was determined by chiral
Chiral HPLC was performed by using a SHIMADZU SPD-10A vp series
instrument with chiral columns (Chiralpak AS-H, OD-H, and AD-H col-
umns, 4.6”250 mm, Daicel Chemical). Commercially obtained reagents
were used without further purification. All reactions were monitored by
TLC by using Huanghai GF254 silica gel coated plates. Flash column
chromatography was carried out by using 300–400 mesh silica gel at in-
creased pressure.
HPLC analysis (Chiralpak OD column, hexane/iPrOH 100:1, detection
2
5
at 210 nm, retention times: 14.65 (major)/17.83 min (minor)). [a] =
D
1
À20.8 (c=1.0 in CHCl
3 3
) (for 97% ee); H NMR (300 MHz, CDCl ,
TMS): d=1.78–1.87 (m, 2H), 2.04–2.16 (m, 2H), 2.34 (s, 3H), 2.35–2.55
(m, 4H), 2.95–2.96 (m, 1H), 7.00–7.06 (m, 3H), 7.19–7.24 ppm (m, 1H);
1
3
C NMR (75 MHz, CDCl
3
, TMS): d=21.4, 25.5, 32.7, 41.1, 44.7, 48.9,
123.5, 127.32, 127.34, 128.2, 138.2, 144.3, 211.1 ppm.
[
3]
Synthesis of 2: Complex 1 (174 mg, 0.20 mmol) was suspended in a mix-
3-(4-Methylphenyl)cyclohexanone (6ac): Ketone 6ac was obtained
ture of CH
2
Cl
2
(15 mL) and CH
3
CN (5 mL). AgOAc (70 mg, 0.42 mmol)
after purification by flash chromatography (eluent: petroleum ether/
was added and the mixture was stirred at room temperature for 3 h. The
resulting suspension was filtered from the precipitated AgI through
Celite and the solvent was removed under reduced pressure to give 2 as
a white powder (131 mg, 88%). Crystals that were suitable for X-ray dif-
Et
2
OAc 25:1; 89% yield, 92% ee). The ee was determined by chiral
HPLC analysis (Chiralpak AD column, hexane/iPrOH 150:1, detection
2
5
at 209 nm, retention times: 8.11 (major)/8.77 min (minor)). [a] =À16.4
D
1
(c=0.5 in CHCl
3
) (for 92% ee); H NMR (300 MHz, CDCl
3
, TMS): d=
fraction study were grown from solutions in CH
2
Cl
2
/hexane (2:1). M.p.
1.73–1.90 (m, 2H), 2.04–2.18 (m, 2H), 2.33 (s, 3H), 2.36–2.62 (m, 4H),
3762
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3759 – 3764

Carbene-Based Palladium Complexes
FULL PAPER
1
3
1
2
.93–3.02 (m, 1H), 7.10–7.16 ppm (m, 4H); C NMR (75 MHz, CDCl
3
,
CHCl
3 3
) (for 91% ee); H NMR (300 MHz, CDCl , TMS): d=1.41–1.48
TMS): d=20.90, 25.5, 32.8, 41.1, 44.3, 49.0, 126.3, 129.2, 136.2, 141.3,
(m, 1H), 1.64–1.80 (m, 2H), 1.96–2.10 (m, 3H), 2.57–2.66 (m, 3H), 2.85–
2.96 (m, 2H), 7.16–7.32 ppm (m, 5H); C NMR (75 MHz, CDCl , TMS):
3
1
3
2
11.2 ppm.
[
5a,18]
d=24.1, 29.2, 39.2, 42.7, 43.9, 51.2, 126.3, 126.4, 128.6, 146.9, 213.5 ppm.
3
-(3-Methoxylphenyl)cyclohexanone (3ad):
Ketone 3ad was ob-
tained after purification by flash chromatography (eluent: petroleum
ether/Et OAc 25:1; 90% yield, 97% ee). The ee was determined by chiral
HPLC analysis (Chiralpak OD column, hexane/iPrOH 50:1, detection at
3-(4-Methylphenyl)cycloheptanone (6bb): Ketone 6bb was obtained
after purification by flash chromatography (eluent: petroleum ether/
Et OAc 25:1; 90% yield, 91% ee). The ee was determined by chiral
2
2
2
5
2
10 nm, retention times: 42.95 (major)/49.80 min (minor)). [a] =À11.8
HPLC analysis (Chiralpak OD column, hexane/iPrOH 50:1, detection at
D
1
25
(
c=1.1 in CHCl
3
) (for 97% ee); H NMR (300 MHz, CDCl
3
, TMS): d=
210 nm, retention times: 12.71 (major)/14.59 min (minor)). [a] =À51.4
D
1
1
1
.73–1.88 (m, 2H), 2.06–2.18 (m, 2H), 2.34–2.63 (m, 4H), 2.95–3.02 (m,
(c=0.5 in CHCl
3
) (for 91% ee); H NMR (300 MHz, CDCl
3
, TMS): d=
1
3
H), 3.80 (s, 3H), 6.77–6.83 (m, 3H), 7.22–7.28 ppm (m, 1H); C NMR
, TMS): d=25.5, 32.6, 41.2, 44.7, 48.9, 55.1, 111.7, 112.6,
18.8, 129.6, 145.9, 159.7, 211.1 ppm.
-(4-Methoxylphenyl)cyclohexanone (6ae): Ketone 6ae was obtained
1.47–1.51 (m, 1H), 1.67–1.76 (m, 2H), 1.98–2.09 (m, 3H), 2.33 (s, 3H),
1
3
(
75 MHz, CDCl
3
2.57–2.65 (m, 3H), 2.87–2.98 (m, 2H), 7.06–7.14 ppm (m, 4H); C NMR
(75 MHz, CDCl , TMS): d=20.9, 24.1, 29.1, 39.2, 42.2, 43.9, 51.3, 126.2,
1
3
[
16]
129.2, 135.7, 143.9, 213.6 ppm.
3
after purification by flash chromatography (eluent: petroleum ether/
Et OAc 20:1) in 82% yield and 94% ee. The ee was determined by chiral
HPLC analysis (Chiralpak OD column, hexane/iPrOH 100:1, detection
3-(3-Methoxylphenyl)cycloheptanone (6bd): Ketone 6bd was obtained
after purification by flash chromatography (eluent: petroleum ether/
Et OAc 25:1; 86% yield, 96% ee. The ee was determined by chiral
2
2
2
5
at 210 nm, retention times: 30.50 (minor)/32.11 min (major)). [a]
=
HPLC analysis (Chiralpak AD column, hexane/iPrOH 50:1, detection at
D
1
25
À19.1 (c=0.35 in CHCl
TMS): d=1.72–1.88 (m, 2H), 2.03–2.17 (m, 2H), 2.31–2.60 (m, 4H),
.91–3.01 (m, 1H), 3.79 (s, 3H), 6.87 (d, J=10.2 Hz, 2H), 7.18 ppm (d,
3
) (for 94% ee); H NMR (300 MHz, CDCl
3
,
210 nm, retention times: 28.67 (major)/32.28 min (minor)). [a] =À15.9
D
1
(c=0.4 in CHCl
3
) (for 96% ee); H NMR (300 MHz, CDCl
3
, TMS): d=
2
1.42–1.56 (m, 1H), 1.64–1.79 (m, 2H), 1.96–2.07 (m, 3H), 2.57–2.70 (m,
1
3
J=10.2 Hz, 2H). C NMR (75 MHz, CDCl
3
, TMS): d=25.5, 33.0, 41.2,
3H), 2.82–2.97 (m, 2H), 2.80 (s, 3H), 6.73–6.78 (m, 3H), 7.22 ppm (t, J=
1
3
4
3.9, 49.2, 55.2, 114.0, 127.5, 136.5, 158.2, 211.3 ppm.
3
7.8 Hz, 1H); C NMR (75 MHz, CDCl , TMS): d=24.1, 29.2, 39.0, 42.7,
[
3]
43.9, 51.1, 55.1, 111.3, 112.3, 118.7, 129.6, 148.6, 159.6, 213.5 ppm.
3
-(2-Naphthyl)cyclohexanone (6af): Ketone 6af was obtained after pu-
OAc
5:1; 99% yield, 97% ee). The ee was determined by chiral HPLC analy-
sis (Chiralpak OD column, hexane/iPrOH 50:1, detection at 210 nm, re-
rification by flash chromatography (eluent: petroleum ether/Et
2
3-(2-Naphthyl)cycloheptanone (6bf): Ketone 6bf was obtained after pu-
rification by flash chromatography (eluent: petroleum ether/Et OAc
2
20:1; 99% yield, 97% ee). The ee was determined by chiral HPLC analy-
2
2
5
tention times: 40.42 (major)/49.07 min (minor)). [a] =À8.4 (c=1.0 in
sis (Chiralpak AD column, hexane/iPrOH 100:1, detection at 210 nm, re-
D
1
25
CHCl
(
3
) (for 97% ee); H NMR (300 MHz, CDCl
3
, TMS): d=1.80–1.98
tention times: 31.10 (major)/35.80 min (minor)). [a] =À35.3 (c=0.8 in
D
1
m, 2H), 2.15–2.22 (m, 2H), 2.41–2.47 (m, 2H), 2.64–2.68 (m, 2H), 3.17–
CHCl
3
) (for 97% ee); H NMR (300 MHz, CDCl
3
, TMS): d=1.70–1.81
3
7
4
1
.20 (m, 1H), 7.36 (d, J=8.7 Hz, 1H), 7.43–7.51 (m, 2H), 7.65 (s, 1H),
(m, 2H), 2.00–2.13 (m, 2H), 2.29 (s, 3H), 2.30–2.55 (m, 4H), 2.89–2.96
(m, 1H), 7.06–7.22 ppm (m, 4H); C NMR (75 MHz, CDCl , TMS): d=
3
20.96, 25.6, 32.9, 41.2, 44.4, 49.1, 126.4, 129.3, 136.2, 141.4, 211.05 ppm.
1
3
13
.80–7.84 ppm (s, 3H); C NMR (75 MHz, CDCl
3
, TMS): d=25.5, 32.7,
1.2, 44.8, 48.8, 124.7, 125.3, 125.6, 126.2, 127.57, 127.64, 128.3, 132.3,
33.5, 141.7, 211.0 ppm.
[5a]
4
-Oxo-2-phenylpiperidine-1-carboxylic acid benzyl ester (6ca): Ketone
[
3]
3
-Biphenyl-4-ylcyclohexanone (6ag): Ketone 6ag was obtained after
OAc
0:1; 97% yield, 93% ee). The ee was determined by chiral HPLC analy-
sis (Chiralpak OD column, hexane/iPrOH 50:1, detection at 209 nm, re-
6ca was obtained after purification by flash chromatography (eluent: pe-
troleum ether/Et OAc 4:1; 53% yield, 81% ee). The ee was determined
purification by flash chromatography (eluent: petroleum ether/Et
2
2
2
by chiral HPLC analysis (Chiralpak OD column, hexane/iPrOH 90:10,
detection at 210 nm, retention times: 29.24 (major)/34.59 min (minor)).
2
5
25
1
tention times: 25.25 (minor)/34.62 min (major)). [a] =À5.5 (c=0.5 in
[a]D =À30.5 (c=0.9 in CHCl
3
) (for 81% ee). H NMR (300 MHz,
D
1
CHCl
3
) (for 93% ee); H NMR (300 MHz, CDCl
3
, TMS): d=1.77–1.92
3
CDCl , TMS): d=2.37 (d, J=15.9 Hz, 1H), 2.49–2.60 (m, 1H), 2.86 (dd,
(
7
m, 2H), 2.11–2.21 (m, 2H), 2.37–2.67 (m, 4H), 3.03–3.10 (m, 1H), 7.26–
1 2
J =15.6 Hz, J =6.6 Hz, 1H), 3.00 (d, J=15.6 Hz, 1H), 3.19 (t, J=
11.1 Hz, 1H), 4.28 (brs, 1H), 5.19 (d, J=12.6 Hz, 1H), 5.25 (d, J=
12.6 Hz, 1H), 5.84 (brs, 1H), 7.23–7.35 ppm (m, 10H).
1
3
.37 (m, 3H), 7.44 (t, J=7.2 Hz, 2H), 7.55–7.60 ppm (m, 4H); C NMR
, TMS): d=25.5, 32.7, 41.2, 44.4, 48.9, 126.98, 126.99,
27.2, 127.4, 128.7, 139.6, 140.7, 143.4, 211.1 ppm.
(
75 MHz, CDCl
3
1
[16]
4
-(2-Naphthyl)tetrahydropyran-2-one (6df). Ketone 6df was obtained
[
3]
3
-(3-Chlorophenyl)cyclohexanone (6ah): Ketone 6ah was obtained
after purification by flash chromatography (eluent: petroleum ether/
Et OAc 4:1; 62% yield, 38% ee). The ee was determined by chiral
HPLC analysis (Chiralpak AS column, hexane/iPrOH 90:10, detection at
after purification by flash chromatography (eluent: petroleum ether/
Et OAc 25:1; 78% yield, 88% ee). The ee was determined by chiral
HPLC analysis (Chiralpak AD column, hexane/iPrOH 50:1, detection at
2
(
1
1
2
2
2
2
5
210 nm, retention times: 49.85 (minor)/54.42 min (major). [a] =+12.9
D
2
5
1
10 nm, retention times: 16.06 (major)/18.28 min (minor)). [a] =À5.4
(c=0.4 in CHCl
2.14–2.32 (m, 2H), 2.76 (dd, J
11.4 Hz, J =6.3 Hz, 1H), 3.36–3.47 (m, 1H), 4.40–4.57 (m, 2H), 7.34 (d,
3
) (for 38% ee); H NMR (300 MHz, CDCl
3
, TMS): d=
D
1
c=1.0 in CHCl
3
) (for 88% ee); H NMR (300 MHz, CDCl
3
, TMS): d=
1
=17.7 Hz, J
2
=10.5 Hz, 1H), 3.03 (dd, J
1
=
.74–1.91 (m, 2H), 2.07–2.19 (m, 2H), 2.34–2.62 (m, 4H), 2.95–3.03 (m,
2
1
3
H), 7.09–7.29 ppm (m, 4H); C NMR (75 MHz, CDCl
3
, TMS): d=
J=8.7 Hz, 1H), 7.47–7.53 (m, 2H), 7.64 (s, 1H), 7.80–7.87 ppm (m, 3H).
0.96, 25.6, 32.9, 41.2, 44.4, 49.1, 126.4, 129.3, 136.2, 141.4, 211.05 ppm.
[3]
3
-Phenylcyclopentanone (6ea): Ketone 6ea was obtained after purifica-
3
-(3,5-Dimethylphenyl)cyclohexanone (6ai): Ketone 6ai was obtained
2
tion by flash chromatography (eluent: petroleum ether/Et OAc 20:1;
after purification by flash chromatography (eluent: petroleum ether/
Et OAc 25:1; 90% yield, 92% ee). The ee was determined by chiral
HPLC analysis (Chiralpak OD column, hexane/iPrOH 50:1, detection at
58% yield, 32% ee). The ee was determined by chiral HPLC analysis
(Chiralpak OB column, hexane/iPrOH 99.5:0.5, detection at 210 nm, re-
tention times: 39.93 (major)/42.78 min (minor)). H NMR (300 MHz,
2
1
2
5
2
10 nm, retention times: 13.08 (major)/20.12 min (minor)). [a] =À4.2
CDCl
3
, TMS): d=1.94–2.02 (m, 1H), 2.26–2.48 (m, 4H), 2.62–2.71 (dd,
D
1
(
c=0.8 in CHCl
3
) (for 92% ee); H NMR (300 MHz, CDCl
3
, TMS): d=
J
1
=7.8 Hz, J
2
=18.0 Hz, 1H), 3.38–3.44 (m, 1H), 7.22–7.37 ppm (m, 5H).
1
2
.72–1.89 (m, 2H), 2.03–2.18 (m, 2H), 2.30 (s, 6H), 2.33–2.59 (m, 4H),
1
3
.87–2.96 (m, 1H), 6.83 (s, 2H), 6.88 ppm (s, 1H); C NMR (75 MHz,
, TMS): d=21.3, 25.6, 32.8, 41.2, 44.7, 49.0, 124.3, 128.3, 138.1,
44.3, 211.2 ppm.
-Phenylcycloheptanone (6ba): Ketone 6ba was obtained after purifica-
OAc 25:1;
8% yield, 91% ee). The ee was determined by chiral HPLC analysis
Chiralpak OD column, hexane/iPrOH 50/1, detection at 210 nm, reten-
CDCl
1
3
Acknowledgements
[
3]
3
tion by flash chromatography (eluent: petroleum ether/Et
8
(
tion times: 12.68 (major)/13.66 min (minor)). [a] =À50.8 (c=1.0 in
2
Financial support from the Shanghai Municipal Committee of Science
and Technology (04JC14083 and 06XD14005) and the National Natural
Science Foundation of China (20472096, 203900502, 20672127 and
20732008) are gratefully acknowledged.
2
5
D
Chem. Eur. J. 2008, 14, 3759 – 3764
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3763

M. Shi and T. Zhang
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7
0, 9651–9653.
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[
H
34
N
4
O
5
r
prismatic; crystal dimensions=0.503”0.387”0.050 mm; orthorhom-
bic; primitive; a=9.5879(12), b=16.684(2), c=22.540(3) Š; a=90,
b=90, g=90 ; V=3605.4(8) Š ; space group=P2
1
309; b) W. Kirmse, Angew. Chem. 2004, 116, 1799—1801; Angew.
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o
3
1
2
1
2
1
;
Z=4;
À3
1
calcd =1.395 gcm ; F000 =1552; diffractometer: Rigaku AFC7R; re-
siduals: R;
R
w
:
0.0556, 0.1079. Crystal data for 3: formula=
Pd; M : 865.06; colorless; prismatic; crystal dimen-
sions=0.234”0.168”0.109 mm; orthorhombic; primitive; a=
C
40
H
28
F
6
N
4
O
5
r
2
007, 119, 2824–2870; Angew. Chem. Int. Ed. 2007, 46, 2768–2813.
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9
.6346(7), b=17.2104(13), c=22.7713(18) Š; a=90, b=90, g=90 ;
3
À3
V=3775.8(5) Š ; space group=P2
F
0
supplementary crystallographic data for this paper. These data can
be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
1
2
1
2
1
; Z=4; 1calcd =1.522 gcm
;
:
000 =1744; diffractometer: Rigaku AFC7R; residuals: R;
R
w
.0536, 0.1018. CCDC-605041 (2) and CCDC-633231 (3) contain the
1
2–22.
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Published online: February 28, 2008
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