New phosphine-functionalized N-heterocyclic carbene ligands for palladium-catalyzed hydroarylation reaction

Article abstract of DOI:10.1055/s-2006-939077

Novel triarylphosphine-functionalized imidazolinium salts have been prepared and successfully applied in palladium-catalyzed hydroarylation of bicyclic olefins. Under reductive conditions (HCOOH, Et₃N), the complexes generated in situ from imidazolinium salts and Pd(OAc)₂ catalyzed the hydroarylation of bicyclic alkenes with aryl iodides, providing the hydroarylation products with high turnover numbers (TON, up to 1.9-10 ⁵) and turnover frequencies (TOF, up to 6.3-10⁴). Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-939077

LETTER
1193
New Phosphine-Functionalized N-Heterocyclic Carbene Ligands for
Palladium-Catalyzed Hydroarylation Reaction
New
Phos
u
phine-Functi
n
onalizedN-Heter
o
Z
cyclic
C
arbene
h
L
igands ong, Jian-Hua Xie, Ai-E Wang, Wei Zhang, Qi-Lin Zhou*
State Key Laboratory and Institute of Elemento-organic Chemistry, Nankai University, Tianjin 300071, P. R. of China
Fax +86(22)23506177; E-mail: qlzhou@nankai.edu.cn
Received 6 December 2005
species6a which are similar to the palladacycles. There-
fore, we anticipate that the phosphine-functionalized
NHC–palladium complexes might be highly efficient cat-
alysts for the palladium-catalyzed Heck-type reactions.
Abstract: Novel triarylphosphine-functionalized imidazolinium
salts have been prepared and successfully applied in palladium-
catalyzed hydroarylation of bicyclic olefins. Under reductive condi-
tions (HCOOH, Et3N), the complexes generated in situ from imida-
zolinium salts and Pd(OAc)2 catalyzed the hydroarylation of
bicyclic alkenes with aryl iodides, providing the hydroarylation
products with high turnover numbers (TON, up to 1.9·105) and
turnover frequencies (TOF, up to 6.3·104).
Many functionalized NHC ligands have been synthesized
and successfully applied in transition-metal-catalyzed
transformations. Excellent activities were reported in
palladium-catalyzed Heck reaction, Suzuki coupling and
other important reactions.7 However, most of the func-
tionalized NHC ligands reported in literature have a N-do-
nor, such as pyridine, imine or oxazoline as pendant
group. In contrast, much less attention has been paid to the
phosphine-functionalized NHC ligands though a few of
them already showed excellent activities in some catalytic
reactions.8 Herein, we would like to describe the synthesis
of a new type of triarylphosphine-functionalized imidazo-
linium salts 2 and their application in palladium-catalyzed
hydroarylation of norbornene and other bicyclic alkenes.
Key words: bicyclic alkene, functionalized phosphine ligand,
hydroarylation, N-heterocyclic carbene, palladium
Palladium-catalyzed arylation and alkenylation of olefins,
known as the Heck reaction, is one of the most effective
catalytic methods for carbon–carbon bond formation in
organic synthesis.1 These reactions have been extensively
studied during the last few decades, and the phosphorus-2
and nitrogen-containing palladacycles3 were among the
most active catalysts reported to date. Recently, Brunel
and co-workers reported that the phosphorus-containing
palladacycle 14 (Figure 1) is a highly efficient catalyst for
the hydroarylation of norbornene under reductive condi-
tions developed by Larock and Johnson in 1989,5 with
turnover number (TON, mol product per mol catalyst) of
up to 1010. This excellent result showed that the carbon–
palladium bond in the palladacycles significantly stabi-
lized the catalysts and the combination of coordinating
carbon and phosphorus atoms in palladacycles is the key
factor for obtaining high turnover number and turnover
frequency in hydroarylation reaction. N-Heterocyclic car-
benes (NHCs), with a stronger s-donor electronic proper-
ty than bulky tertiary phosphines, have proven to be
effective ligands in numerous transition-metal-catalyzed
reactions.6 The strong ability of NHCs to coordinate to
transition metal allows the formation of stable metal
In the synthesis of triarylphosphine-functionalized imida-
zolinium salts 2, we chose o-fluoroaniline (3) as starting
material and the synthetic route was outlined in Scheme 1.
Nucleophilic substitution of 3 by potassium diphen-
ylphosphide (Ph2PK) provided (o-aminophenyl)diphen-
ylphosphine (4) in 55% yield. The amino group of (o-
aminophenyl)diphenylphosphine was protected by react-
ing with di-tert-butyl dicarbonate [(Boc)2O], giving
amide 5 in 57% yield.9 Amide 5 was treated with sodium
hydride in N,N-dimethylformamide, followed by treat-
ment with different N-(2-bromoethyl)arylamines at room
temperature for 1–3 days to give diamines 6 in 20–61%
yields.10 The diamines 6 were easily converted to the cor-
responding dihydrochlorides 7 in quantitative yield by
bubbling anhydrous hydrogen chloride into the methanol–
dichloromethane solution of 6 at –78 °C for 1 hour.11
Finally, the imidazolinium salts 2 were obtained by cy-
clization of dihydrochlorides 7 with HC(OEt)3 at 120 °C
for 3–5 hours in 49–64% yields. The 31P NMR spectra of
imidazolinium salts 2 have a single resonance at around
d = –18 ppm.12
Me2N NMe2
P
Ac
O
N
N
Pd
Pd
Aryl
O
Cl
Ac
P
Ph2P
To evaluate the efficiency of phosphine-functionalized
imidazolinium salts 2 as precursors of ligands in palladi-
um-catalyzed carbon–carbon bond forming reactions, we
investigated the hydroarylation of bicyclic alkenes, which
was successfully employed in the synthesis of natural
products such as epibatidine alkaloid and its analogues.13
Preliminary studies in the reaction of norbornene with io-
dobenzene under the reductive conditions (Et3N, HCO2H)
Me2N NMe2
2
1
Figure 1
SYNLETT 2006, No. 8, pp 1193–1196
1
5.
0
5.
2
0
0
6
Advanced online publication: 05.05.2006
DOI: 10.1055/s-2006-939077; Art ID: W32805ST
© Georg Thieme Verlag Stuttgart · New York

1194
J. Zhong et al.
LETTER
Boc
N
H
N
i
iii
ii
Ar
Boc
NH2
NH2
PPh2
N
H
PPh2
6a–c
PPh2
F
3
4
5
Cl
H2
N
Cl
iv
v
N
N
Ar
Ar
a phenyl
Ar =
N
Cl
PPh2
2a–c
H2
b 2,4,6-trimethylphenyl
c 2,6-diisopropylphenyl
PPh2
7a–c
Scheme 1 Regents and conditions: (i) Ph2PK, DME, reflux, 4 d; (ii) (Boc)2O, THF, reflux, 2 d; (iii) N-(2-bromoethyl)arylamine, NaH, DMF,
r.t., 1–3 d; (iv) HCl, MeOH–CH2Cl2, –78 °C, 1 h; (v) HC(OEt)3, 120 °C, 3–5 h.
showed that the palladium complexes generated from tertiary amines or HCO2Na, instead of Et3N were used, the
Pd(OAc)2 and salts 2 in the presence of t-BuOK were ef- yields of arylation product became lower (entries 8–11).
ficient catalysts, providing exo-phenylnorbornane as a The activity of the palladium complex of triarylphos-
single product in high yields (Table 1, entries 1–3).14 Sol- phine-functionalized NHC 2b is remarkable. When the
vent screening revealed that DMSO was the choice for catalyst loading was lowered to 5·10–4 mol%, the reaction
gaining high yield albeit reaction can also be performed in was still complete in 3 hours, giving desired exo-phenyl-
other solvent. Base is another important parameter in pal- norbornane in 94% yield (entry 13). The high turnover
ladium-catalyzed hydroarylation reaction. When other numbers (TON: 1.9·105) and turnover frequencies (TOF:
6.3·104) of this catalyst shows that the activity of palladi-
um complexes of phosphine-functionalized NHCs are
higher than that of the Pd complexes with diphosphine,15
P–N ligands16 and dinitrogen ligands,17 however, lower
than that of palladacycle ligands.4
Table 1 Hydrophenylation of Norbornene with PhI Catalyzed by
Palladium Complexes of 2a
Pd(OAc)2/2/KOtBu
Ph
PhI
+
HCOOH, base
8
9a
Table 2 Hydroarylation of Norbornene with Aryl Iodidesa
Entry Ligand Solvent
Base
Time Yield
Pd(OAc)2/2b/KOtBu
Ar
(h)
(%)b
91
95
89
87
84
71
70
87
83
71
50
93
94
+
ArI
HCOOH, Et3N, DMSO, 120 °C
1
2
3
4
5
6
7c
8
9
2a
2b
2c
DMSO
DMSO
DMSO
DMF
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
i-Pr2NEt
2
9
8
2
Ar
Catalyst
Time
Productb Yield
(%)
TON
(mol% Pd) (h)
2
C6H5
5.0·10–4
2.5·10–3
2.5·10–3
2.5·10–3
5.0·10–3
2.5·10–3
5.0·10–3
2.5·10–3
3
4
9a
9b
9c
9d
9e
9f
94
92
79
91
83
82
57
48
1.9·105
3.7·104
3.1·104
3.6·104
1.7·104
3.2·104
1.1·104
1.9·104
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2
p-MeOC6H4
o-MeOC6H4
DMAc
Toluene
MeCN
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
2
7
2
m-MeOC6H4
p-MeC6H4
m-MeC6H4
p-O2NC6H4
o-FC6H4
4
24
2
12
15
12
20
Proton sponged
HCO2NH4
HCO2Na
Et3N
2
9g
9h
10
2
11
2
a Reaction conditions: Pd(OAc)2–2b–t-BuOK (1:1:1), ArI (1 mmol),
norbornene (3.4 mmol), formic acid (3 mmol), Et3N (3.8 mmol),
DMSO (5 mL).
12e
13f
2
Et3N
3
b No endo product was isolated.
a Reaction conditions: Pd(OAc)2 (0.5 mol%), 2 (0.5 mol%), t-BuOK
(0.5 mol%), PhI (1 mmol), norbornene (3.4 mmol), formic acid (3
mmol), base (3.8 mmol), solvent (5 mL) at 120 °C.
b Isolated yield.
Under the optimal reaction conditions, a range of aryl
iodides were reacted with norbornene at a low catalyst
loading, and the corresponding exo-arylnorbornane prod-
ucts were isolated in moderate to good yields. As shown
in Table 2, the introduction of a substituent, whether an
electron-donating or electron-withdrawing group, into
c At 80 °C.
d 1,8-Bis(dimethylamino)naphthalene.
e Pd(dba)2 as precatalyst.
f Catalyst loading is 5·10–4 mol%.
Synlett 2006, No. 8, 1193–1196 © Thieme Stuttgart · New York

LETTER
New Phosphine-Functionalized N-Heterocyclic Carbene Ligands
1195
phenyl iodide had a negative influence on the yield of
hydroarylation products. The substrates with an electron-
withdrawing group such as p-NO2C6H4I and o-FC6H4I
gave very low yields. Phenyl bromide and triflate were
also tested under the same reaction conditions, and were
found to be inert in the reaction with norbornene.
References and Notes
(1) (a) Heck, R. F. Acc. Chem. Res. 1979, 12, 146. (b) Heck, R.
F. Palladium Reagents in Organic Synthesis; Academic
Press: New York, 1985. (c) Shibasaki, M.; Vogl, E. M.;
Ohshima, T. Adv. Synth. Catal. 2004, 346, 1533. (d)Farina,
V. Adv. Synth. Catal. 2004, 346, 1553.
(2) (a) Herrmann, W. A.; Böhm, V. P. W.; Reisenger, C.-P. J.
Organomet. Chem. 1999, 576, 23. (b) Herrmann, W. A.;
Öfele, K.; Preysing, D. V.; Schneider, S. K. J. Organomet.
Chem. 2003, 687, 229.
(3) (a) Tulloch, A. A. D.; Danopoulos, A. A.; Tooze, R. P.;
Cafferkey, S. M.; Kleinhenz, S.; Hursthouse, M. B. Chem.
Commun. 2000, 1247. (b) Dupont, J.; Pfeffer, M.; Spencer,
J. Eur. J. Inorg. Chem. 2001, 8, 1917. (c) Peris, E.; Loch, J.
A.; Mata, J.; Crabtree, R. H. Chem. Commun. 2001, 201.
(4) (a) Brunel, J. M.; Heumann, A.; Buono, G. Angew. Chem.
Int. Ed. 2000, 39, 1946. For highly efficient hydroarylation
using nitrogen-containing palladacycle catalysts, see:
(b) Bravo, J.; Cativiela, C.; Navarro, R.; Urriolabeitia, E. P.
J. Organomet. Chem. 2002, 650, 157. (c) Yuan, K.; Zhang,
T.-K.; Hou, X.-L. J. Org. Chem. 2005, 70, 6085.
Encouraged by the high catalytic activity of NHC–palla-
dium catalyst generated in situ from triarylphosphine-
functionalized imidazolinium salt 2b with Pd(OAc)2 in
the hydroarylation of norbornene, we further extend the
scope of substrate to other types of bicyclic olefins includ-
ing oxa- and aza-bicyclic alkenes (Scheme 2). The reac-
tions of different bicyclic alkenes with iodobenzene
proceeded smoothly under the optimal reaction conditions
to afford the corresponding products in good yields.18 It is
worthy to note that the reaction of 2,5-norbonadiene stops
at monophenylation stage, with exo-phenylnorbornene
being an exclusive product.
(5) Larock, R. C.; Johnson, P. L. J. Chem. Soc., Chem. Commun.
1989, 18, 1368.
Ph
(6) (a) Herrmann, W. A.; Köcher, C. Angew. Chem., Int. Ed.
Engl. 1997, 36, 2162. (b) Jafarpour, L.; Nolan, S. P. Adv.
Organomet. Chem. 2000, 46, 181. (c) Bourissou, D.;
Guerret, O.; Gabbaï, F. P.; Bertrand, G. Chem. Rev. 2000,
100, 39. (d) Herrmann, W. A.; Weskamp, T.; Böhm, V. P.
W. Adv. Organomet. Chem. 2001, 48, 1. (e) Herrmann, W.
A. Angew. Chem. Int. Ed. 2002, 41, 1290.
(7) (a) Peris, E.; Crabtree, R. H. Coord. Chem. Rev. 2004, 248,
2239. (b) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev.
2004, 248, 2247. (c) McGuinness, D. S.; Cavell, K. J.
Organometallics 2000, 19, 741. (d) Arnold, P. L.;
Scarisbrick, A. C.; Blake, A. J.; Wilson, C. Chem. Commun.
2001, 2340. (e) Danopoulos, A. A.; Winston, S.;
10
11 (93%)
X
X
PhI
Ph
X =
Pd(OAc)2/2b
(2.5·10–3 mol%)
CH2 13a (87%)
13b (69%)
TsN 13c (86%)
O
12
Ph
CO2Me
CO2Me
CO2Me
CO2Me
15 (67%)
14
Motherwell, W. B. Chem. Commun. 2002, 1376.
Scheme 2 Hydroarylation of bicyclic alkenes with iodobenzene.
(f) Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F.
Angew. Chem. Int. Ed. 2003, 42, 3690. (g) Liu, J.; Zhao, Y.;
Zhou, Y.; Li, L.; Zhang, T. Y.; Zhang, H. Org. Biomol.
Chem. 2003, 1, 3227.
In conclusion, we have designed and synthesized a new
type of triarylphosphine-functionalized NHCs and de-
monstrated they are highly efficient ligands for palladi-
um-catalyzed hydroarylation of bicyclic alkenes and up to
1.9·105 TON and 6.3·104 TOF were achieved. The high
activity of the palladium complexes of phosphine-func-
tionalized NHCs is mainly due to the excellent stability of
the carbon–palladium bond in the catalysis. The investiga-
tion on the application of these novel triarylphosphine-
functionalized NHC ligands in other coupling reactions is
in progress in our laboratory.
(8) (a) Yang, C.; Lee, H. M.; Nolan, S. P. Org. Lett. 2001, 3,
1511. (b) Danopoulos, A. A.; Winston, S.; Gelbrich, T.;
Hursthouse, M. B.; Tooze, R. P. Chem. Commun. 2002,
482. (c) Seo, H.; Park, H.-J.; Kim, B. Y.; Lee, J. H.; Son, S.
U.; Chung, Y. K. Organometallics 2003, 22, 618.
(d) Tsoureas, N.; Danopoulos, A. A.; Tulloch, A. A. D.;
Light, M. E. Organometallics 2003, 22, 4750. (e) Bappert,
E.; Helmchen, G. Synlett 2004, 1789. (f) Wang, A.-E.;
Zhong, J.; Xie, J.-H.; Li, K.; Zhou, Q.-L. Adv. Synth. Catal.
2004, 346, 595. (g) Wang, A.-E.; Xie, J.-H.; Wang, L.-X.;
Zhou, Q.-L. Tetrahedron 2005, 61, 259.
(9) Physical Data of Amide 5.
White solid, mp 94–96 °C. 1H NMR (300 MHz, CDCl3): d =
1.41 (s, 9 H, CH3), 6.88 (m, 1 H, Ar-H), 6.92 (t, J = 7.2 Hz,
1H, Ar-H), 7.26–7.36 (m, 12 H, Ar-H, NH), 7.93 (dd,
J = 8.1, 4.5 Hz, 1 H, Ar-H). 13C NMR (75 MHz, CDCl3):
d = 28.2, 80.4, 120.6, 123.6, 125.0, 125.2, 128.7, 128.8,
129.1, 130.4, 133.5, 133.7, 134.1, 134.9, 135.0, 141.7,
142.0, 152.9. 31P NMR (121 MHz, CDCl3): d = –21.2. MS
(ESI): m/z = 378 [M + 1]. Anal. Calcd for C23H24NO2P: C,
73.19; H, 6.41; N, 3.71. Found: C, 73.01; H, 6.26; N, 3.68.
(10) Physical Data.
Acknowledgment
We thank the National Natural Science Foundation of China, the
Major Basic Research Development Program (Grant
G2000077506), the Ministry of Education of China for financial
support.
Compound 6a: oil. 1H NMR (300 MHz, CDCl3): d = 1.09 (s,
9 H, CH3), 3.12 (m, 1 H, NCH2), 3.21 (m, 1 H, NCH2), 3.40
(m, 1 H, NCH2), 4.25 (br s, 2 H, NCH2, NH), 6.44 (d, J = 8.1
Hz, 2 H, Ar-H), 6.58 (t, J = 7.2 Hz, 1 H, Ar-H), 6.93–7.22
Synlett 2006, No. 8, 1193–1196 © Thieme Stuttgart · New York

1196
J. Zhong et al.
LETTER
(m, 16 H, Ar-H). 13C NMR (75 MHz, CDCl3): d = 27.8, 42.5,
49.0, 49.1, 79.9, 112.1, 116.6, 127.4, 128.1, 128.2, 128.3,
128.4, 128.9, 129.6, 129.7, 133.4, 133.6, 133.7, 134.9,
136.0, 136.1, 136.7, 136.8, 145.8, 146.2, 148.0. 31P NMR
(121 MHz, CDCl3): d = –17.9. HRMS (ESI): m/z calcd for
C31H34N2O2P: 497.2352; found: 497.2359.
(12) Physical Data.
Compound 2a: white solid, mp 235–237 °C. 1H NMR (300
MHz, CDCl3): d = 4.50 (s, 4 H, NCH2), 6.90 (m, J = 6.8, 4.0
Hz, 1 H, Ar-H), 7.25–7.45 (m, 17 H, Ar-H), 8.17 (dd,
J = 7.6, 4.0 Hz, 1 H, Ar-H), 8.85 (s, 1 H, NCH). 13C NMR
(75 MHz, CDCl3): d = 49.8, 52.9, 119.3, 127.9, 128.9, 129.4,
130.1, 130.2, 130.6, 131.3, 133.9, 134.2, 134.3, 134.5,
135.4, 135.5, 135.7, 138.5, 138.7, 155.6. 31P NMR (121
MHz, CDCl3): d = –14.6. HRMS (ESI): m/z calcd for
C27H24N2P: 407.1593; found: 407.1593.
Compound 6b: white solid, mp 92–93 °C. 1H NMR (300
MHz, CDCl3): d = 1.16 (s, 9 H, CH3), 2.18 (s, 6 H, CH3),
2.21 (s, 3 H, CH3), 3.01–3.35 (m, 4 H, NCH2), 4.18 (br s, 1
H, NH), 6.78 (s, 2 H, Ar-H), 7.03 (m, 1 H, Ar-H), 7.15–7.31
(m, 13 H, Ar-H). 13C NMR (75 MHz, CDCl3): d = 18.7, 20.6,
28.1, 47.2, 50.8, 80.0, 127.7, 128.4, 128.5, 128.6, 128.8,
129.5, 130.5, 133.7, 134.0, 135.3, 136.4, 136.6, 137.1,
137.2, 143.8, 146.5, 146.9, 155.5. 31P NMR (121 MHz,
CDCl3): d = –18.2. MS (ESI): m/z = 539 [M + 1]. Anal.
Calcd for C34H39N2O2P: C, 75.81; H, 7.30; N, 5.20. Found:
C, 75.71; H, 7.16; N, 5.25.
Compound 2b: white solid, mp 255–257 °C. 1H NMR (300
MHz, CDCl3): d = 2.28 (s, 3 H, CH3), 2.36 (s, 6 H, CH3),
4.40 (m, 2 H, NCH2), 4.83 (m, 2 H, NCH2), 6.89 (m, 3 H, Ar-
H), 7.25 (m, 4 H, Ar-H), 7.40 (m, 7 H, Ar-H), 7.58 (m, 1 H,
Ar-H), 8.13 (s, 1 H, NCH), 8.53 (m, J = 7.8, 4.5 Hz, 1 H, Ar-
H). 13C NMR (75 MHz, CDCl3): d = 18.1, 18.2, 18.3, 21.0,
52.0, 53.7, 53.8, 119.0, 129.2, 129.3, 129.9, 130.5, 131.7,
133.7, 133.9, 134.4, 135.5, 140.5, 158.1, 158.2. 31P NMR
(121 MHz, CDCl3): d = –18.1. MS (ESI): m/z = 449 [M –
Cl]. Anal. Calcd for C30H30ClN2P: C, 74.29; H, 6.23; N,
5.78. Found: C, 74.32; H, 6.38; N, 5.80.
Compound 6c: oil. 1H NMR (300 MHz, CDCl3): d = 1.15 (s,
9 H, CH3), 1.19 (d, J = 5.4 Hz, 12H, CH3), 2.97 (m, 1 H,
NCH2), 3.21 (m, 4 H, NCH2, CH), 3.45 (m, 1 H, NCH2), 4.29
(br s, 1 H, NH), 7.05 (m, 4 H, Ar-H), 7.23–7.32 (m, 13 H,
Ar-H). 13C NMR (75 MHz, CDCl3): d = 24.4, 24.5, 27.9,
28.2, 50.2, 50.9, 76.9, 77.2, 50.9, 80.1, 123.7, 127.8, 128.6,
128.7, 128.8, 128.9, 130.0, 130.2, 133.9, 134.0, 134.1,
135.4. 31P NMR (121 MHz, CDCl3): d = –17.1. HRMS
(ESI): m/z calcd for C37H46N2O2P: 581.3291; found:
581.3297.
Compound 2c: white solid, mp 268–270 °C. 1H NMR (300
MHz, CDCl3): d = 1.28 (d, J = 6.6 Hz, 6 H, CH3), 1.32 (d,
J = 6.6 Hz, 6 H, CH3), 3.35 (m, 2 H, CH), 4.39 (m, 2 H,
NCH2), 4.80 (m, 2 H, NCH2), 6.95 (dd, J = 7.5, 3.6 Hz, 1 H,
Ar-H), 7.21–7.28 (m, 6 H, Ar-H), 7.36–7.48 (m, 8 H, Ar-H),
7.60 (t, J = 7.5 Hz, 1 H), 8.13 (s, 1 H, NCH), 8.53 (dd,
J = 7.8, 4.5 Hz, Ar-H). 13C NMR (75 MHz, CDCl3): d =
24.6, 25.2, 28.5, 53.9, 54.6, 125.0, 128.8, 129.1, 129.2,
129.3, 129.6, 130.0, 130.5, 131.2, 131.8, 133.5, 133.6,
133.9, 134.1, 134.2, 134.4, 138.7, 139.0, 146.8, 157.4,
157.5. 31P NMR (121 MHz, CDCl3): d = –18.6. HRMS
(ESI): m/z calcd for C33H36N2P: 491.2611; found: 491.2606.
(13) (a) Kasyan, A.; Wagner, C.; Maier, M. E. Tetrahedron 1998,
54, 8047. (b) Namyslo, J. C.; Kaufman, D. E. Synlett 1999,
804.
(11) Physical Data.
Compound 7a: white foam. 1H NMR (300 MHz, CDCl3):
d = 3.83 (s, 2 H, NCH2), 3.89 (s, 2 H, NCH2), 6.98 (s, 2 H,
Ar-H), 7.17–7.37 (m, 15 H, Ar-H), 7.71 (s, 2 H, Ar-H). 13
NMR (75 MHz, CDCl3): d = 49.5, 50.3, 123.6, 128.8, 128.9,
129.1, 129.2, 129.5, 129.8, 130.2, 130.3, 130.6, 130.9,
131.0, 131.6, 133.9, 134.1, 135.7, 136.1. 31P NMR (121
MHz, CDCl3): d = –18.6. HRMS (ESI): m/z calcd for
C26H26N2P: 397.1828; found: 397.1834.
C
Compound 7b: white foam. 1H NMR (300 MHz, CDCl3):
d = 2.23 (s, 3 H, CH3), 2.48 (s, 6 H, CH3), 3.87 (m, 2 H,
NCH2), 4.21 (m, 2 H, NCH2), 6.80 (s, 2 H, Ar-H), 7.22 (m,
2 H, Ar-H), 7.37–7.65 (m, 12 H, Ar-H). 8.56 (br s, 2 H),
10.84 (br s, 2 H). 13C NMR (75 MHz, CDCl3): d = 19.0, 19.1,
20.7, 44.3, 48.2, 118.6, 118.7, 123.3, 124.1, 129.1, 129.2,
130.8, 131.0, 132.1, 133.3, 133.8, 134.0, 135.9, 139.2,
145.6, 145.7, 145.9. 31P NMR (121 MHz, CDCl3): d = –17.9.
MS (ESI): m/z = 439 [M – 2 HCl + 1]. Anal. Calcd for
C29H33Cl2N2P: C, 68.10; H, 6.50; N, 5.48. Found: C, 68.07;
H, 6.68; N, 5.56.
(14) General Experimental Procedure.
Under an atmosphere of nitrogen, 5.0 mL DMSO were
injected to a Schlenk tube charged with Pd(OAc)2 (0.01
mmol), imidazolinium salt 2 (0.01 mmol) and t-BuOK (0.01
mmol). The mixture was stirred at r.t. for 2 h. An appropriate
amount of this catalyst solution was taken and added to the
solution of iodobenzene (204 mg, 1 mmol), norbornene (320
mg, 3.4 mmol), Et3N (379 mg, 3.75 mmol) and formic acid
(138 mg, 3 mmol) in 5.0 mL of DMSO. The mixture was
stirred at 120 °C, and the course of reaction was monitored
by GC. After the starting material was completely consumed
the reaction mixture was cooled to r.t., and 50 mL of H2O
was added. The product was extracted with pentane (3 × 30
mL), and the extract was dried over anhyd Na2SO4. The
product was purified by column chromatography on silica
gel eluting with PE.
Compound 7c: white foam. 1H NMR (300 MHz, CDCl3):
d = 1.19 (d, J = 6.0 Hz, 6 H, CH3), 1.32 (d, J = 6.0 Hz, 6 H,
CH3), 3.37 (m, 1 H, NCH2), 3.47 (m, 2 H, NCH2), 3.57 (m,
2 H, CH), 4.04 (m, 1 H, NCH2), 4.23 (m, 1 H, NCH2), 6.66
(t, J = 7.2 Hz, 1 H, Ar-H), 6.78 (m, 2 H, Ar-H), 7.14–7.40
(m, 14 H, Ar-H), 10.90 (br s, 4 H). 13C NMR (75 MHz,
CDCl3): d = 23.9, 27.3, 27.4, 36.5, 38.7, 50.8, 52.8, 109.8,
117.5, 119.0, 119.1, 123.2, 124.6, 124.7, 127.5, 127.6,
127.8, 128.5, 128.7, 128.9, 129.0, 129.9, 132.6, 132.8,
133.9, 134.1, 134.2, 142.2, 142.4, 148.2, 148.4. 31P NMR
(121 MHz, CDCl3): d = –22.5. HRMS (ESI): m/z calcd for
C32H36N2P: 481.2767; found: 481.2770.
(15) Brunner, H.; Kramler, K. Synthesis 1991, 1121.
(16) Sakuraba, S.; Awano, K.; Achiwa, K. Synlett 1994, 291.
(17) Wu, X.-Y.; Xu, H.-D.; Tang, F.-Y.; Zhou, Q.-L.
Tetrahedron: Asymmetry 2001, 12, 2565.
(18) Catalyst loading for the reaction of 13c is 0.5 mol%.
Synlett 2006, No. 8, 1193–1196 © Thieme Stuttgart · New York