Syntheses of effectively-shielded N-heterocyclic carbene ligands

Article abstract of DOI:10.1016/j.tet.2012.12.036

A novel type of N-heterocyclic carbene ligand, with a bicyclic motif at the non-carbenic carbons of an imidazolin-2-ylidene core, has been developed. This type of ligand formed an air and moisture stable silver complex even with N,N′-dimethyl NHC. Allylic arylation with a Grignard reagent catalyzed by copper complexes of the NHC ligands proceeded preferentially at the γ-position, indicating the effective steric shielding ability of this framework.

Full text of DOI:10.1016/j.tet.2012.12.036

Tetrahedron 69 (2013) 1687e1693
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Syntheses of effectively-shielded N-heterocyclic carbene ligands
*
*
Shin Ando , Hirofumi Matsunaga, Tadao Ishizuka
Faculty of Life Sciences, Kumamoto University, 5-1 Oe-honmachi Chuo-ku, Kumamoto 862-0973, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel type of N-heterocyclic carbene ligand, with a bicyclic motif at the non-carbenic carbons of an
imidazolin-2-ylidene core, has been developed. This type of ligand formed an air and moisture stable
silver complex even with N,N0-dimethyl NHC. Allylic arylation with a Grignard reagent catalyzed by
Received 30 November 2012
Received in revised form 13 December 2012
Accepted 16 December 2012
Available online 21 December 2012
copper complexes of the NHC ligands proceeded preferentially at the
steric shielding ability of this framework.
g-position, indicating the effective
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
N-Heterocyclic carbene
Steric effect
Bicyclic system
Regioselective
Allylic arylation
1. Introduction
a different coupling activity toward transition metal. For example,
saturated NHC 2 is more active than unsaturated NHC 1 in the case
of Pd mediated amination reaction.6 On the other hand, from the
viewpoint of the stability, the unsaturated NHCs 1 are generally
more stable than the saturated NHCs 2 presumably by virtue of the
As a result of the pioneering work by Herrman et al.,1 in which
a N-heterocyclic carbene (NHC) was proposed as a promising al-
ternative to phosphines as a homogeneous organometallic catalyst,
extensive investigations to produce this type of novel ligand have
been pursued.2 The development of NHC ligands has generated as
much activity as that of phosphine ligands.3 This interest comes
p
-delocalization of the former.7 This trend also seems to be the case
in metal-NHC complexes.3a To stabilize the latter core, bulky sub-
stituents, such as an aryl group, are placed on the nitrogen(s), with
the intention of protecting the carbenic carbon via a steric shield.
This extra requirement from the saturated NHCs should make the
functionalization more difficult. Nonetheless, there has been a little
from the unique binding nature of NHC ligands,4 such as a strong
s-
donation to the bound transition metals, exceptionally strong
binding toward metals, and a resultant complex with good stability
against air and moisture. In addition to these remarkable proper-
ties, a more diverse structure than phosphines motivates the syn-
thetic and organometallic chemists. Among the numerous
heterocyclic core candidates that have been reported in the litera-
ture, imidazol-2-ylidene 1 (unsaturated NHC) and imidazolin-2-
ylidene 2 (saturated NHC) are frequently used with ligands.3
These heterocyclic cores have two nitrogens adjacent to a car-
benic carbon, which equates to easier substitution for the hetero-
atom than for carbon and leads to the drastic change at the
proximity of the bound transition metal. According to broad de-
rivatization studies, the electronic effects from the substituents are
relatively small,5 which allows a wider variety of substituents with
no negative impact to the binding nature.
The two cores, 1 and 2, are often compared to one another be-
cause of their structural similarity (Fig. 1a), and each has shown
* Corresponding authors. E-mail addresses: ando@gpo.kumamoto-u.ac.jp (S. Ando),
Fig. 1. (a) The opposing properties between unsaturated NHCs 1 and saturated NHCs 2.
tstone@gpo.kumamoto-u.ac.jp (T. Ishizuka).
(b) Substituents with a stronger effect on nitrogen than on non-carbenic carbon.
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.12.036

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S. Ando et al. / Tetrahedron 69 (2013) 1687e1693
use of the substituents on the non-carbenic carbons with this de-
mand, probably because the geometry seemed unlikely to produce
a strong effect toward an active site (Fig. 1b). If the stabilization
from the non-carbenic carbons is possible, the substituents on ni-
trogen could be designed to more flexibly functionalize the satu-
rated NHCs. Herein, we describe the synthesis and properties of
a novel NHC ligand with a bicyclic structure on the non-carbenic
carbons, which are effective in directly shielding the bound metal
center.
2.2. Syntheses of bicyclic saturated NHC
The synthesis of a new ligand with a bicyclic ring, summarized
in Scheme 1, commenced from the ‘roofed’ imidazolidinone 4 we
previously reported.9 A 2-naphthalenesulfonyl group (2-Nps) was
placed on the NeH functionality in a quantitative yield not only for
protection but also for activation of the carbonyl on the urea moi-
ety, which was needed to open the imidazolidinone ring. After the
methanolysis of the acetyl group in a yield of 98%, the imidazoli-
dinone ring was opened by reflux under basic condition to obtain
the free amine 7. Since the opened diamine 7 was unstable for
storage and poorly soluble in most organic solvents, a direct Boc
protection from the crude mixture was performed to afford the key
intermediate 8 in an 87% yield over two steps. After the depro-
tection of the 2-naphthalenesulfonyl group under reductive con-
2. Results and discussion
2.1. The design of a novel saturated NHC framework
Previously, we demonstrated the strong shielding effects of the
bicyclic architecture between anthracene and cis-diamine, and a Ru
complex using this diamine ligand 3 (Fig. 2) showed excellent
enantio control during the hydrogenation of ketones.8 Ideally, an
NHC with this bicyclic system, which could be derived from this
‘roofed’ diamine, would give us a rigid shield from the non-carbenic
carbon at the carbenic carbon, and the substituents on the nitro-
gens should be more finely tunable with less concern about sta-
bility. The asymmetric substitution on these two nitrogens provides
a chiral environment, but our objectives here were the de-
velopment of the synthetic strategy and an evaluation of the
shielding ability of this bicyclic NHC. Therefore, we started from
a synthesis of symmetric N,N0-dimethylated NHC, which should be
one of the least-stable of the derivatives.
ditions, which gave
9 together with inseparable impurities,
temporal aminal formation by refluxing in acetone enabled the
mono alkylation of the deprotected amine. The subsequent cleav-
age of this aminal, and the simultaneous removal of the Boc group
on the other amine, gave the mono methylated diamine as an HCl
salt 10 in a 74% yield overall. The same sequential mono alkylation
of the free amine resulted in N,N0-dimethylated diamine 12 in a 76%
yield (over two steps). This HCl salt was treated with refluxed
triethyl orthoformate to achieve the synthesis of the carbene pre-
cursor 14 in 99% yield. Dibenzylated derivative 15 was also pre-
pared under the similar conditions with use of BnBr for alkylations.
Although the imidazolidinone 4 used for these syntheses was
a racemic mixture, it should be noted that we have the synthetic
methodology for the optically active form, which will allow us to
synthesize chiral NHC ligands in the future.9
2.3. Synthesis and properties of N,N0-dimethylated bicyclic
NHCeAg complex
The dimethylated carbene precursor 14 was applied to the
syntheses of an Agecarbene complex under the condition reported
by Lin et al.10a NHCeAg complexes are generally accepted as good
NHC transfer agents, and a transmetalation to another transition
metal is easily accomplished by a simple mix in a reaction solution
Fig. 2. The design of bicyclic saturated NHC.
Ac
Ba(OH)2•8H2O
DMSO/EtOH/H2O
O
Cs2CO3
(Boc)2O
N
NH
NHBoc
NH2
MeOH
98%
N
N
NH
2-Nps
O
NH
2-Nps
87%
(for 2 steps)
R
2-Nps
( )-4: R = H
2-Nps-Cl
( )-6
( )-7
( )-8
(quant.)
( )-5: R = 2-Nps
NaH
1) acetone, Δ ;
2M HCl aq.
acetone, Δ ;
Na,
Boc
N
NH2
NH
naphthalene
2) (MeO)2SO2 or
BnBr, K2CO3
NHBoc
NH2
•HCl
N
R
R
( )-10: R = Me (74%)
( )-11: R = Bn (84%)
( )-9
R = Me or Bn
1) (MeO)2SO2 or
Ag2O,
(EtO)3CH
BnBr, K2CO3
2) 2M HCl aq.
;
R
R
N
N
NH
NH
R
CH2Cl2
N
Ag
N
R
NH
N
Cl
R
•HCl
Cl
R
R
16: R = Me (92%);
DHASIMeAgCl
17: R = Bn (83%);
DHASIBnAgCl
R = Me or Bn
12: R = Me (76%)
13: R = Bn (88%)
14: R = Me (99%)
15: R = Bn (77%)
Scheme 1. The syntheses of bicyclic NHC precursors and NHCeAg complexes; 2-Nps¼2-naphthalenesulfonyl.

S. Ando et al. / Tetrahedron 69 (2013) 1687e1693
1689
prior to use as a catalyst.10 Gratifyingly, bicyclic imidazolinium salt
14 reacted smoothly with Ag2O in CH2Cl2, and we obtained carbene
complex 16 wherein the 1H NMR showed a disappearance of the
imidazolinium proton signal. This complex was isolated as a color-
less solid and was stable enough to store on a bench at ambient
temperature. We named this bicyclic NHC motif DHASI (4,5-(9,10-
dihydroanthraceno)-imidazolin-2-ylidene. Based on the abbrevia-
tion on the past reports about NHCs,3 the imidazolin-2-ylidene core
was named SI). The dibenzylated precursor 15 was also reacted
with Ag2O in CH2Cl2 and gave the stable complex 17 as a colorless
solid. It was somewhat surprising that there were no signals in-
dicating the carbenic carbon on the 13C NMR spectrum, which also
was the case in reports by other groups.11 The MS spectrum (FABþ)
showed the m/z L2Agþ as the parent peak (the structures of
NHCeAg complexes in the gas phase are often inaccurate10b). Be-
cause the structures of NHCesilver complexes with a halogen
counter anion are varied,10b,c finally, the X-ray studies of the crystal
were accepted as confirmation of their structure.12
shown in Table 1. As the comparison with DHASIMe (entries 3 and
5) obviously indicates, our rigid framework overcame the electron
deficiency of the unsaturated NHC (ligand 18, entry 2) and the steric
effect of the DPEN framework (ligand 19, entry 4), which has been
the most widely used of chiral NHC ligands.3 In the case of the
reaction catalyzed by the copper complex with DHASIBn (entry 6),
which is more bulky ligand than DHASIMe, the substitution with
the resultant copper complex gave a product that was almost
completely
on non-carbenic carbons induces the appropriate shielding effect
for the metal center. Despite the fact that the buried volume (%Vbur
g-selective. These results suggest that our bicyclic motif
)
of complex 16, which is the quantity of the steric demand of the
NHC ligands represented by Nolan and Cavallo et al.,15 was only
26.1%,16 the rigidity of the bicyclic framework seemed to amplify
the ‘steric bulkiness’.
Table 1
Copper-catalyzed allylic arylation with PhMgBr
Single crystals of complex 16 were grown by the slow vapor
diffusion of Et2O into a CH2Cl2 solution. The silver complex of N,N0-
dimethylated NHC 16 was a 1:1 complex between NHC and Ag
(Fig. 3), which is relatively rare among the saturated NHC ligands.
The degree (171.64ꢀ) of the angle of C(1)eAg(1)eCl(1) and the
packing system indicated that there was a weak interaction be-
tween the two silver atoms, however, the distances between
0
0
ꢀ
ꢀ
Ag(1)eAg(1) (3.650 A) and Ag(1)eCl(1) (3.717 A) were longer than
the sum of van der Waals radii. The selected bond lengths and
angles are shown in the caption of Fig. 3. These geometric charac-
ters around the carbenic carbon were within the range of the
general NHC species, and the distances between the silver and the
ꢀ
a
Entry
L (mol %)
Combined yielda (%)
Ratio (a:g)
carbons on the bicyclic motif ranged from 5.0 to 5.5 A, which was
three times longer than the van der Waals radius for silver.
1
2
3
4
5
6
None
95
98
98
99
98
95
96:4
18 (2.5)b
49:51
20:80
80:20
21:79
5:95
DHASIMe 16 (5.0)b
19 (5.0)c
14 (5.0)c
DHASIBn 17 (5.0)b
a
Determined by 1H NMR.
NHCeAg complex was used as NHC transfer agent.
Carbene was generated in situ.
b
c
3. Conclusion
In conclusion, we synthesized NHC ligands with a bicyclic
framework on the non-carbenic carbons, and used them to con-
struct silver complexes. The structure of the silver complex was
confirmed by X-ray crystallographic analysis. This novel type of
NHC ligand has successfully been applied to a copper-catalyzed
regioselective allylic arylation with a Grignard reagent, and the
selectivity suggested that the bound copper was effectively shiel-
ded from the backbone framework of these NHC ligands. Further
investigation into the synthesis of chiral and functionalized NHC
ligands with this bicyclic motif and their applications to stereo-
selective reactions are underway in our laboratory.
Fig. 3. ORTEP diagram of complex 16, thermal ellipsoids are shown at 50% probability
ꢀ
ꢀ
level. Selected bond length (A) and angles ( ): Cl(1)eAg(1), 2.326; Ag(1)eC(1), 2.100;
C(1)eN(1), 1.323; C(1)eN(2), 1.328; Cl(1)eAg(1)eC(1), 171.64; Ag(1)eC(1)eN(1),
125.14; Ag(1)eC(1)eN(2), 126.00; N(1)eC(1)eN(2), 108.86.
2.4. The application to a copper-catalyzed allylic arylation
with PhMgBr
4. Experimental section
4.1. General remarks
With these bicyclic NHC ligands in hand, we tested the regio-
selective allylic arylation for proof of our concept. Copper-catalyzed
g-selective allylic substitution with a Grignard reagent is one of the
most well-established reactions and a synthetic chemist would be
expected to design a ligand theoretically on the basis of two im-
portant factors: steric bulkiness and electron deficiency.13 More
bulky and electron-deficient ligands accelerate the reductive
All reactions were carried out under an argon atmosphere with
freshly distilled solvents under anhydrous conditions, unless oth-
erwise noted. Anhydrous CH2Cl2 and THF were purchased from
KANTO CHEMICAL CO. INC. and used without further distillation.
Dimethoxyethane (DME) was distilled from Na. Reagents were used
without further purification. Yields refer to chromatography
and spectroscopically (1H NMR) homogeneous materials, unless
elimination step, which produces the g-substituted product pref-
erentially.14 To test the efficiency of the steric shielding by the
framework, we set the ligands 18 and 19 for the comparisons

1690
S. Ando et al. / Tetrahedron 69 (2013) 1687e1693
otherwise stated. All reactions were monitored by thin-layer
chromatography (TLC) carried out on 0.25-mm E. Merck silica gel
plates (60Fꢁ254) using UV-light (254 nm) for visualization or using
5% ninhydrin in n-BuOH for developing agents and heat for visu-
alization. Fuji silysia silica gel (PSQ60B) was used for flash chro-
matography. Melting points were measured using Yanako micro
melting point apparatus and are uncorrected. NMR spectra were
recorded on JEOL JNM-AL300 (300 MHz) or JEOL JNM-ECX-400
(400 MHz) instruments and calibrated using solvent and TMS
peaks as internal references. The following abbreviations are used
to indicate the multiplicities; s¼singlet, d¼doublet, t¼triplet,
q¼quartet, m¼multiplet, br¼broad, app¼apparent. MS and HRMS
(EI or FAB) were obtained with a JEOL JMS-700 mass spectrometer.
High-resolution mass spectra were obtained using EBE geometry.
IR spectra were recorded on a JEOL JIR-6500W FT-IR spectrometer.
Optical rotation was measured at 27 ꢀC in a 5.0 cm cell on JASCO
Rf¼0.26 (CH2Cl2); IR (KBr pellet): nmax¼3356, 3054, 2927, 1743 (C]
O), 1470, 1348, 1246, 1169, 1134, 1076, 1032, 931, 860, 818, 748 cmꢁ1
1H NMR (300 MHz, DMSO-d6, 298 K):
;
d
¼8.59 (s, 1H), 8.01e7.90 (m,
4H), 7.68e7.58 (m, 2H), 7.46e7.43 (m, 1H), 7.29e7.21 (m, 4H),
7.20e7.07 (m, 1H), 6.97e6.90 (m, 2H), 4.98 (d, J¼3.1 Hz,1H), 4.65 (dd,
J¼9.5, 3.1 Hz, 1H), 4.32 (d, J¼3.1 Hz, 1H), 4.01 (dd, J¼9.5, 3.1 Hz, 1H)
ppm; 13C NMR (75 MHz, DMSO-d6, 298 K):
d
¼154.1, 140.4, 139.6,
139.0, 138.4, 136.1, 134.7, 131.5, 129.5, 129.3, 129.0, 129.0, 127.8, 127.6,
126.8, 126.7, 126.3, 126.20, 126.16, 126.0, 125.2, 124.9, 122.8, 59.4,
52.5, 48.3, 47.8 ppm; HRMS (FABþ) calcd for C27H21N2O3S [MþH]þ
453.1273, found 453.1289.
4.2.3. (ꢂ)-N-Boc, N0-2-naphthalenesulfonyl-1,2-(9,10-dihydroanth-
raceno)-ethylenediamine 8. Ba2(OH)2$8H2O (31.5 g, 100 mmol) was
added to a suspension of imidazolidinone (ꢂ)-6 (9.05 g, 20 mmol) in
EtOH/DMSO/H2O (280 mL, 5:1:1 mixture) at 25 ꢀC. The reaction
solution was heated at reflux until TLC monitoring showed the ac-
complishment of the reaction (normally 24e48 h). The reaction was
cooled to 25 ꢀC and then poured to H2O (1.0 L) at the same tem-
perature to precipitate the diamine product (ꢂ)-7. The white pre-
cipitate was filtered and suspended into CH2Cl2 (200 mL). (Boc)2O
(5.52 mL, 24 mmol) was added to the resulting mixture and stirred at
25 ꢀC for 17 h. The reaction mixture was filtered through CeliteÒ pad,
washed with CH2Cl2. The combined filtrate and washings were
washed with brine (1ꢃ200 mL), dried over Na2SO4, filtered, and
concentrated under reduced pressure. The crude residue was puri-
fied by chromatography (0e10% EtOAc in CH2Cl2) on silica gel
(600 mL) to afford the titled compound (ꢂ)-8 (9.14 g, 87%) as a pale
yellow foam; Rf¼0.30 (30% EtOAc in n-hexane); IR (KBr pellet):
nmax¼3381, 3184, 2976, 2943, 1693 (C]O), 1468, 1361, 1331, 1169,
1099, 1072, 1022, 957, 818, 760 cmꢁ1; 1H NMR (300 MHz, CDCl3þ1%
DIP-360; [a]
value was given in 10ꢁ1 deg cm2 gꢁ1 (concentration
D
given as g/100 mL). X-ray crystallography was recorded on a Rigaku
AFC/RASA7R single-crystal diffractometer with sealed-tube Mo-
lybdenum radiation.
4.2. Syntheses of the bicyclic NHC ligand precursors and
NHCeAg complexes
4.2.1. (ꢂ)-N-Ac, N0-2-Naphthalenesulfonyl-4,5-(9,10-dihydroanthr-
aceno)-imidazolidinone 5. A solution of imidazolidinone 49 (61 mg,
0.2 mmol) in THF (2.0 mL) was cooled to 0 ꢀC in an ice bath. NaH (60%
in mineral oil, 16 mg, 0.4 mmol) was added to the solution at 0 ꢀC,
followed by 2-naphthalenesulfonyl chloride (68 mg, 0.3 mmol). The
resulting reaction mixture was warmed to 25 ꢀC by a removal of the
ice bath and stirred at the same temperature for 1 h. After the con-
firmation of the accomplishment of the reaction by TLC monitoring,
the reaction mixture was cooled in an ice bath and then quenched by
addition of saturated NH4Cl aq (4.0 mL) at 0 ꢀC. The resulting solution
was extracted with EtOAc (3ꢃ4.0 mL), and the combined organic
extracts were washed with brine (1ꢃ2.0 mL), dried over Na2SO4,
filtered, and concentrated under reduced pressure. The crude residue
was purified by flash chromatography (10e30% EtOAc in n-hexane)
on silica gel (10 mL) to afford the titled compound 5 (97 mg, quan-
titative) as a colorless amorphous solid; mp >200 ꢀC; Rf¼0.33 (30%
EtOAc in n-hexane); IR (KBr pellet): nmax¼3035, 2962, 1753 (C]O),
1701 (C]O), 1470, 1369, 1288, 1236, 1171, 1132, 1099, 1072, 860,
CD3OD, 323 K):
d
¼8.43 (s, 1H), 7.98 (d, J¼8.80 Hz, 2H), 7.91 (d,
J¼7.3 Hz, 1H), 7.79 (d, J¼8.80 Hz, 1H), 7.67e7.61 (m, 2H), 7.30e7.20
(m, 5H), 7.10e7.08 (m, 3H), 4.28 (d, J¼2.2 Hz, 1H), 4.14 (br s, 1H), 4.11
(dd, J¼9.2, 2.2 Hz, 1H), 3.90 (dd, J¼9.2, 2.2 Hz, 1H), 1.34 (s, 9H) ppm;
13C NMR (75 MHz, CDCl3, 323 K):
d¼155.1, 140.5, 139.9, 139.1, 138.6,
135.0, 132.3, 129.5, 129.3, 128.8, 128.3, 127.9, 127.6, 127.1, 126.8, 126.7,
126.5, 125.9, 124.4, 122.4, 80.1, 53.4, 51.2, 50.0, 49.4, 28.2 ppm; HRMS
(FABþ) calcd for C31H30N2O4SNa [MþNa]þ 549.1824, found 549.1843.
4.2.4. (ꢂ)-NeH, N0-Methyl-1,2-(9,10-dihydroanthraceno)-ethylenedi-
amine hydrochloride 10. Na metal (1.29 g, 56 mmol) was added to
a solution of naphthalene (1.54 g, 24 mmol) in DME (40 mL) at 25 ꢀC.
The resulting mixture was sonicated at 25 ꢀC for 10 min and then
cooled to ꢁ30 ꢀC. A solution of protected-diamine (ꢂ)-8 (2.11 g,
4.0 mmol) in DME (15 mL) was dropwise to the reaction mixture, and
an additional DME (5.0 mL) was used to rinse the vessel and com-
plete the addition of the compound (ꢂ)-8. The reaction solution was
stirred at the same temperature until TLC monitoring showed the
accomplishment of the reaction (normally 1.5e2 h). The reaction
mixture was then poured to H2O (500 mL), which had been pre-
chilled in an ice bath, by pipette (CAUTION!! Extra amount of Na
still be in the reaction mixture. Pour the supernatant carefully and
kill the residual Na appropriately). Brine (100 mL) was added to the
resulting mixture, and the resulting mixture was extracted with Et2O
(3ꢃ200 mL). The combined organic extracts were washed with brine
(1 ꢃ200 mL), dried over Na2SO4, filtered, and concentrated under
reduced pressure. The crude residue was purified by flash chroma-
tography (50e100% EtOAc in CH2Cl2) on silica gel (50 mL) to afford N-
Boc, N0eH diamine product (ꢂ)-9 (1.18 g; Rf¼0.29 (EtOAc)) together
with inseparable impurities. The deprotected diamine (ꢂ)-9 was
dissolved in acetone (20 mL) and heated at reflux until TLC moni-
toring indicated the complete formation of aminal protected com-
pound (normally ca. 2 h). The reaction solution was cooled to 25 ꢀC,
and K2CO3 (1.66 g,12 mmol) and (MeO)2SO2 (0.38 mL, 6 mmol) were
added. The resulting mixture was then heated at reflux for 12 h. The
731 cmꢁ1
;
1H NMR (300 MHz, CDCl3, 298 K):
d
¼8.63 (s, 1H),
8.02e7.90 (m, 4H), 7.70e7.60 (m, 2H), 7.46e7.37 (m, 2H), 7.24e7.04
(m, 4H), 6.95e6.90 (m, 2H), 5.05 (d, J¼2.9 Hz, 1H), 5.03 (d, J¼2.9 Hz,
1H), 4.58 (dd, J¼9.9, 2.9 Hz, 1H), 4.47 (dd, J¼9.9, 2.9 Hz, 1H), 2.25 (s,
3H) ppm; 13C NMR (75 MHz, CDCl3, 298 K):
d¼170.4, 150.8, 139.1,
138.9, 138.0, 137.1, 135.3, 131.8, 130.2, 129.6, 129.3, 127.9, 127.8, 127.3,
127.2, 127.1, 126.5, 125.5, 125.3, 125.2, 122.7, 57.0, 55.8, 48.1, 45.1,
24.4 ppm; HRMS (FABþ) calcd for C29H23N2O4S [MþH]þ 495.1379,
found 495.1404.
4.2.2. (ꢂ)-NeH, N0-2-Naphthalenesulfonyl-4,5-(9,10-dihydroanthr-
aceno)-imidazolidinone 6. Cs2CO3 (652 mg, 2.0 mmol) was added to
a solution of imidazolidinone (ꢂ)-5 (9.89 g, 20 mmol) in MeOH/
CH2Cl2 (130 mL, 1:1 mixture) at 25 ꢀC. The reaction solution was
stirred at the same temperature until TLC monitoring showed the
accomplishment of the reaction (normally within 30 min). The re-
action was quenched by an addition of citric acid (4.0 g) and sub-
sequent 15 min stirring at 25 ꢀC. The resulting mixture was
concentrated under reduced pressure, and the residue was dissolved
in CH2Cl2 (200 mL). The mixture was then washed with brine
(1ꢃ200 mL), dried over Na2SO4, filtered, and concentrated under
reduced pressure. The crude residue was purified by chromatogra-
phy (0e5% EtOAc in CH2Cl2) on silica gel (600 mL) to afford the
titled compound (ꢂ)-6 (8.86 g, 98%) as a white powder; mp >200 ꢀC;

S. Ando et al. / Tetrahedron 69 (2013) 1687e1693
1691
mixture was cooled to 25 ꢀC, diluted with EtOAc (20 mL), and filtered
through CeliteÒ pad. The filtrate was concentrated under reduced
pressure to afford the methylated aminal product as a crude mixture.
Because of its instability against light, this crude mixture was used
for the next step directly. The crude residue was dissolved in MeOH
(10 mL), and 2 M HCl aq (10 mL) was added to the solution. The
reaction mixture was then heated at reflux until TLC monitoring
indicated the complete consumption of methylated aminal com-
pound (normally 2e3 h). The resulting solution was concentrated
under reduced pressure, and the residue was dissolved in EtOH.
CH2Cl2 was added to the solution to precipitate the product as HCl
salt. The salt was filtered and washed with CH2Cl2 to afford the titled
compound (ꢂ)-10 (849 mg, 74% over three steps) as a white powder;
mp >200 ꢀC; IR (KBr pellet): nmax¼3570, 3496, 2841, 1430, 2050,
1556,1508,1470,1174,1149,1028, 769, 744 cmꢁ1; 1H NMR (300 MHz,
7.27 (dd, J¼5.5, 3.3 Hz, 2H), 7.17 (dd, J¼5.5, 3.3 Hz, 2H), 4.91 (s, 2H),
3.89 (s, 2H), 2.90 (s, 6H) ppm; 13C NMR (75 MHz, D2Oþ10% DMSO-
d6, 298 K):
d
¼140.5, 138.3, 129.3, 128.4, 126.5, 60.3, 45.1, 34.6 ppm;
HRMS (FABþ) calcd for C18H21N2 [MþH]þ 265.1705, found 265.1709.
4.2.7. N,N0-Dibenzyl-1,2-(9,10-dihydroanthraceno)-ethylenediamine
hydrochloride 13. The preparation of N,N0-dibenzylated diamine 13
was accomplished by the same procedure as the method used for
N,N0-dimethylated diamine 12 except for the following differences.
One was the usage of BnBr instead of (MeO)2SO2 as an alkylating
reagent, and the other one was the usage of Et2O instead of CH2Cl2
to precipitate the HCl salt. The titled compound 13 was obtained in
88% (547 mg from 499 mg, 1.1 mmol of (ꢂ)-11) yield over two steps
as a white powder; mp 143e145 ꢀC; IR (KBr pellet): nmax¼3421,
2964, 2696, 1585, 1460, 1209, 1174, 1014, 962, 920, 748, 698 cmꢁ1
;
DMSO-d6, 333 K):
d
¼7.57e7.40 (m, 4H), 7.27e7.19 (m, 4H), 5.05 (d,
1H NMR (300 MHz, DMSO-d6, 353 K):
d¼7.57e7.51 (m, 6H),
J¼2.4 Hz, 1H), 4.89 (d, J¼2.4 Hz, 1H), 3.96 (dd, J¼8.8, 2.4 Hz, 1H), 3.84
7.39e7.32 (m, 8H), 7.25e7.16 (m, 4H), 5.01 (br s, 2H), 4.40 (d,
J¼13.0 Hz, 2H), 4.23 (d, J¼13.0 Hz, 2H), 3.69 (br s, 2H) ppm; 13C NMR
(dd, J¼8.8, 2.4 Hz,1H), 2.80 (s, 3H) ppm; 13C NMR (75 MHz, DMSO-d6,
333 K):
d
¼139.7, 139.4, 137.2, 136.9, 127.42, 127.38, 126.9, 126.8, 126.4,
(75 MHz, DMSO-d6, 353 K):
d
¼140.1, 137.8, 129.3, 128.0, 127.9, 126.8,
126.2, 124.5, 124.3, 58.1, 50.2, 46.1, 43.8, 31.6 ppm; HRMS (FABþ)
126.4, 126.1, 124.0, 56.7, 50.2, 44.3 ppm; HRMS (FABþ) calcd for
calcd for C17H19N2 [MþH]þ 251.1548, found 251.1546.
C30H29N2 [MþH]þ 417.2331, found 417.2322.
4.2.5. (ꢂ)-NeH, N0-Benzyl-1,2-(9,10-dihydroanthraceno)-ethylenedi-
amine hydrochloride 11. The preparation of NeH, N0-Bn diamine 11
was accomplished by the same procedure as the method used for
NeH, N0-Me diamine 10 except for the following differences. One
was the usage of BnBr instead of (MeO)2SO2 as an alkylating reagent,
and the other one was the usage of Et2O instead of CH2Cl2 to pre-
cipitate the HCl salt. The titled compound 11 was obtained in 70%
yield (455 mg from 603 mg of 8) over three steps as a white powder;
mp >200 ꢀC; IR (KBr pellet): nmax¼3442, 2740, 2428, 1620, 1556,
4.2.8. N,N0-Dimethyl-4,5-(9,10-dihydroanthraceno)-imidazolinium
chloride 14. (EtO)3CH (6.8 mL) was added to a flask charged with
N,N0-dimethyldiamine hydrochloride 12 (460 mg, 1.38 mmol), and
the resulting suspension was heated at 100 ꢀC in an oil bath for 16 h.
The white precipitate was filtered and washed with Et2O to afford
the titled compound 14 (420 mg, 99%) as a white powder; mp
>200 ꢀC; IR (KBr pellet): nmax¼3020, 2954, 1659, 1529, 1458, 1311,
1279, 1153, 1034, 771 cmꢁ1 1H NMR (300 MHz, DMSO-d6, 298 K):
;
d
¼8.23 (s, 1H), 7.55 (dd, J¼5.3, 3.3 Hz, 2H), 7.45 (dd, J¼5.3, 3.3 Hz,
1516, 1500, 1460, 1427, 1201, 1171, 1024, 746 cmꢁ1
;
1H NMR
2H), 7.24 (dd, J¼5.3, 3.3 Hz, 4H), 5.06 (s, 2H), 4.65 (s, 2H), 3.06 (s,
(300 MHz, DMSO-d6, 353 K):
d
¼7.57e7.55 (m, 3H), 7.45e7.33 (m,
6H) ppm; 13C NMR (75 MHz, DMSO-d6, 298 K):
d
¼158.1, 139.1, 137.8,
6H), 7.26e7.17 (m, 4H), 4.94 (br s, 1H), 4.76 (d, J¼2.6 Hz, 1H), 4.28 (d,
J¼13.4 Hz, 1H), 4.20 (d, J¼13.4 Hz, 1H), 3.81 (dd, J¼8.8, 2.6 Hz, 1H),
3.62 (br d, J¼8.8 Hz, 1H) ppm; 13C NMR (75 MHz, DMSO-d6, 353 K):
127.0, 126.9, 125.7, 125.2, 66.1, 43.2, 31.8 ppm; HRMS (FABþ) calcd
for C19H19N2 [M]þ 275.1548, found 275.1534.
d
¼139.8, 139.7, 137.4, 129.6, 128.5, 128.3, 127.4, 127.3, 126.8, 126.5,
4.2.9. N,N0-Dibenzyl-4,5-(9,10-dihydroanthraceno)-imidazolinium
chloride 15. (EtO)3CH (3.0 mL) was added to a flask charged with
N,N0-dibenzylated diamine hydrochloride 13 (136 mg, 0.30 mmol),
and the resulting suspension was heated to a 100 ꢀC in an oil bath
for 16 h. The white precipitate was filtered and washed with Et2O to
afford the titled compound 15 (107 mg, 77%) as a white powder; mp
>200 ꢀC; IR (KBr pellet): nmax¼3039, 2999, 2881, 2837, 1633, 1458,
126.2, 124.42, 124.36, 56.6, 50.3, 49.8, 46.2, 43.8, ppm; HRMS (FABþ)
calcd for C23H23N2 [MþH]þ 327.1861, found 327.1884.
4.2.6. N,N0-Dimethyl-1,2-(9,10-dihydroanthraceno)-ethylenediamine
hydrochloride 12. Excess amount of Et3N was added to the sus-
pension of mono methylated-diamine hydrochloride (ꢂ)-10
(143 mg, 0.5 mmol) in CH2Cl2, and the resulting solution was
concentrated under reduced pressure to desalt. The desalted di-
amine was dissolved in acetone (20 mL) and heated at reflux until
TLC monitoring indicated the complete formation of the aminal
protected compound (normally ca. 2 h). The reaction solution was
cooled to 25 ꢀC, and K2CO3 (207 mg, 1.5 mmol) and (MeO)2SO2
1435, 1362, 1308, 1279, 1215, 1173, 1105, 1043, 758, 704 cmꢁ1 1H
;
NMR (300 MHz, DMSO-d6, 298 K):
d
¼8.36 (s, 1H), 7.46e7.34 (m,
14H), 7.23e7.17 (m, 4H), 5.05 (s, 2H), 4.71 (d, J¼14.8 Hz, 2H), 4.59 (d,
J¼14.8 Hz, 2H), 4.55 (s, 2H) ppm; 13C NMR (100 MHz, DMSO-d6,
298 K):
d
¼158.7, 139.6, 138.4, 133.8, 129.7, 129.5, 129.2, 127.6, 127.4,
126.4, 125.8, 65.5, 49.2, 43.9 ppm; HRMS (FABþ) calcd for C31H27N2
[M]þ 427.2174, found 427.2193.
(71
mL, 750 mmol) were added. The resulting mixture was then
heated at reflux for 12 h. The mixture was cooled to 25 ꢀC, diluted
with EtOAc (20 mL), and filtered through CeliteÒ pad. The filtrate
was concentrated under reduced pressure to afford the methylated
aminal product as crude mixture. This crude mixture was used for
the next step directly. The crude residue was dissolved in MeOH
(1 mL), and 2 M HCl aq (1 mL) was added to the solution. The re-
action mixture was then heated at reflux until TLC monitoring in-
dicated the complete consumption of methylated aminal
compound (normally 2e3 h). The resulting solution was concen-
trated under reduced pressure, and the residue was dissolved in
EtOH. CH2Cl2 was added to the solution to precipitate the product
as HCl salt. The salt was filtered and washed with CH2Cl2 to afford
the titled compound 12 (115 mg, 76% over two steps) as a white
powder; mp >200 ꢀC; IR (KBr pellet): nmax¼3442, 2725, 2428, 1628,
4.2.10. N,N0-Dimethyl-4,5-(9,10-dihydroanthraceno)-imidazolin-2-
ylidene silver chloride (DHASIMeAgCl) 16. Ag2O (25.3 mg,
0.11 mmol) was added to a suspension of N,N0-dimethyl imidazo-
linium salt 14 (62 mg, 0.2 mmol) in CH2Cl2 (2.0 mL), and the re-
action mixture was stirred for 1 h with cover of aluminum foil to
darken. The resulting mixture was filtered through CeliteÒ pad,
washed with CH2Cl2. The combined filtrate and washings were
concentrated under reduced pressure to make the total volume ca.
2.0 mL. Hexane (ca. 4 mL) was added to the resulting solution to
precipitate the titled complex 16 (77 mg, 92%) as a white powder.
The single crystalline for X-ray diffraction analysis was grown by
the slow vapor diffusion of Et2O into a CH2Cl2 solution; mp
179e182 ꢀC (decomp.); IR (KBr pellet): nmax¼3039, 2914, 2860,
1562, 1460, 1161, 1022, 768, 748 cmꢁ1
;
1H NMR (300 MHz, D2O,
2789, 1520, 1468, 1400, 1315, 1273, 1207, 1034, 960, 926, 758 cmꢁ1
1H NMR (300 MHz, CD2Cl2, 298 K):
¼7.37 (dd, J¼5.5, 3.3 Hz, 2H),
;
298 K):
d
¼7.50 (dd, J¼5.5, 3.3 Hz, 2H), 7.37 (dd, J¼5.5, 3.3 Hz, 2H),
d

1692
S. Ando et al. / Tetrahedron 69 (2013) 1687e1693
7.35 (dd, J¼5.5, 3.3 Hz, 2H), 7.24e7.19 (m, 4H), 4.68 (s, 2H), 4.32 (dd,
J¼1.5, 1.5 Hz, 2H), 3.09 (s, 6H) ppm; 13C NMR (75 MHz, CD2Cl2,
stirred for another 1 h at the same temperature. The reaction
mixture was then diluted with Et2O (2.0 mL) and quenched with
2 M HCl aq (2.0 mL) at ꢁ78 ꢀC. The resulting mixture was allowed to
warm to 25 ꢀC and extracted with Et2O (3ꢃ4 mL). The combined
organic extracts were dried over Na2SO4, filtered, and concentrated
under reduced pressure. The crude residue was dissolved in CH2Cl2,
and anthracene (89 mg, 0.5 mmol) was added to the solution as an
external standard to calculate the yield based on the crude 1H NMR.
After the removal of the solvent, the ratios of the products were
calculated based on the crude 1H NMR.
298 K):
d
¼139.6, 138.0, 127.3, 127.2, 125.6, 125.1, 68.8, 45.7,
35.8 ppm; LRMS (FABþ) m/z 655 ½ðC19H18N2Þ2107Agꢄþ, 657
½ðC19H18N2Þ2109Agꢄþ.
Anal.
Calcd
for
C19H18AgClN2$H2O
(434.0315): C, 52.38; H, 4.63; N, 6.43. Found: C, 52.32; H, 4.28; N,
6.19. (Removal of H2O could not be accomplished by a heating
under reduced pressure.)
4.2.11. N,N0-Dibenzyl-4,5-(9,10-dihydroanthraceno)-imidazolin-2-
ylidene silver chloride (DHASIBnAgCl) 17. Ag2O (18.7 mg, 81
was added to a suspension of N,N0-dibenzyl imidazolinium salt 15
(62 mg, 134 mol) in CH2Cl2 (2.6 mL), and the reaction mixture was
mmol)
4.3.3. The preparation of the comparison, (4R),(5R)-N,N0-dimethyl-
4,5-diphenyl-4,5-dihydro-imidazolinium iodide 19. CH2Cl2 (3.9 mL)
was added to a flask charged with (R),(R)-4,5-diphenyl-4,5-dihydro-
1-H-imidazoline17 (172 mg, 0.77 mmol), K2CO3 (107 mg, 0.77 mmol),
m
stirred for 17 h with cover of aluminum foil to darken. The resulting
mixture was filtered through CeliteÒ pad, washed with CH2Cl2. The
combined filtrate and washings were concentrated under reduced
pressure. The residue was treated with a mixture of CH2Cl2 and
Et2O (ca. 1: 10) and sonicated for 5 min. The filtration of the white
precipitate yielded the titled complex 17 (63 mg, 83%) as a white
powder; mp 168e171 ꢀC (decomp.); IR (KBr pellet): nmax¼3026,
2914, 1485, 1452, 1354, 1311, 1248, 1169, 1047, 1028, 945, 928, 754,
and magnetic stir bar at 25 ꢀC. MeI (145
mL, 2.33 mmol) was added to
the resulting mixture, and the reaction mixture was stirred at 25 ꢀC
for 21 h. The resulting mixture was then filtered through CeliteÒ
pad, washed with CH2Cl2. The combined filtrate and washings were
concentrated under reduced pressure, and the residue was washed
with Et2O to afford the titled compound 19 (102 mg, quantitative) as
a white powder; mp 185e187 ꢀC (decomp.); IR (KBr pellet):
nmax¼3487, 3444, 3008, 2941, 1641, 1495, 1458, 1284, 1223, 1151,
706 cmꢁ1
;
1H NMR (300 MHz, CD2Cl2, 298 K):
d
¼7.46e7.22 (m,
16H), 7.12e7.09 (m, 2H), 4.93 (d, J¼15.2 Hz, 2H), 4.63 (s, 2H), 4.44 (d,
J¼15.2 Hz, 2H), 4.19 (dd, J¼1.6, 1.6 Hz, 2H) ppm; 13C NMR
1101, 978, 827, 758, 700 cmꢁ1 1H NMR (300 MHz, CDCl3, 293 K):
;
(75 MHz, CD2Cl2, 298 K):
d¼139.5, 138.1, 135.0, 129.2, 128.6, 128.2,
d
¼7.47e7.45 (m, 6H), 7.40e7.38 (m, 4H), 4.91 (s, 2H), 3.23 (s, 3H)
ppm; 13C NMR (75 MHz, CDCl3, 293 K):
¼159.4, 133.9, 130.0, 129.8,
127.8, 75.8, 33.9 ppm; HRMS (FABþ) calcd for C17H19N2 [M]þ
127.3, 127.2, 125.7, 125.1, 65.9, 53.1, 45.4 ppm; LRMS (FABþ) 959
½ðC31H26N2Þ2107Agꢄþ, 961 ½ðC31H26N2Þ2109Agꢄþ. Anal. Calcd for
C31H26AgCl N2$H2O (586.0941): C, 63.33; H, 4.80; N, 4.77. Found: C,
63.41; H, 4.45; N, 4.63. (Removal of H2O could not be accomplished
by a heating under reduced pressure.)
d
251.1548, found 251.1553. [a]
27 210.4 (c 0.10, CHCl3).
D
Acknowledgements
4.3. Copper-catalyzed allylic arylation with PhMgBr
This research was financially supported in part by JSPS KAKENHI
(NO. 23590011 to H.M.) and by the Hoansha Foundation (to T.I.). We
greatly thank Dr. Akihito Yamano (Rigaku Corporation) for assis-
tance with the X-ray analysis.
4.3.1. General procedure for an allylic arylation via a transmetalation
process. CH2Cl2 (0.50 mL) was added to a flask charged with CuCl
(2.5 mg, 25
mmol), silverecarbene complex (25 mmol for 16 or 17,
12.5
m
mol for [Ag(IMe)2][AgI2]18), and magnetic stir bar at 25 ꢀC.
Supplementary data
The resulting suspension was stirred at the same temperature for
10 min, and a solution of cinnamyl bromide (99 mg, 0.50 mmol) in
CH2Cl2 (0.50 mL) was added to the resulting mixture, followed by
cooling in a dry-ice/EtOH bath. A solution of PhMgBr (0.20 mL of
3.0 M solution in Et2O diluted with 0.25 mL of CH2Cl2) was added to
the reaction mixture by a syringe pump over 15 min. Once the
addition was complete, the resulting mixture was stirred for an-
other 1 h at the same temperature. The reaction mixture was then
diluted with Et2O (2.0 mL) and quenched with 2 M HCl aq (2.0 mL)
at ꢁ78 ꢀC. The resulting mixture was allowed to warm to 25 ꢀC and
extracted with Et2O (3ꢃ4 mL). The combined organic extracts were
dried over Na2SO4, filtered, and concentrated under reduced pres-
sure. The crude residue was dissolved in CH2Cl2, and anthracene
(89 mg, 0.5 mmol) was added to the solution as an external stan-
dard to calculate the yield based on the crude 1H NMR. After the
removal of the solvent, the ratios of the products were calculated
based on the crude 1H NMR.
Supplementary data related to this article can be found online at
http://dx.doi.org/10.1016/j.tet.2012.12.036.
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added to the mixture. After being stirred at the same temperature
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CH2Cl2 (0.50 mL) was added to the resulting mixture. A solution of
PhMgBr (0.20 mL of 3.0 M solution in Et2O diluted with 0.25 mL of
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15 min. Once the addition was complete, the resulting mixture was

S. Ando et al. / Tetrahedron 69 (2013) 1687e1693
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ꢀ
ꢀ
16. A radius of 3.5 A for the sphere, a distance of 2.1 A between the metal and
ꢀ
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imidazolinylidene ligand without substituents on non-carbenic carbons, in-
dicating that almost no effect of our framework was detected based on this
calculation.
€
ꢂ
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