Nanocrystalline magnesium oxide stabilized palladium(0): An efficient heterogeneous catalyst for heck and sonogashira coupling of aryl halides

Article abstract of DOI:10.1055/s-2006-950260

Nanocrystalline magnesium oxide supported palladium(0) catalyst [NAP-Mg-Pd(0)], prepared by the counter-ion stabilization of PdCl ₄² followed by reduction with hydrazine hydrate, was effectively used in the Heck olefination of haloarenes (chloro, bromo, and iodo) to afford good to excellent yields of substituted olefins. This ligand-free heterogeneous NAP-Mg-Pd(0) catalyst was quantitatively recovered from the reaction by a simple filtration and reused for a number of cycles with almost no loss of activity. Moreover, NAP-Mg-Pd(0) efficiently catalyzed the Sonogashira coupling of haloarenes with terminal alkynes without any copper co-catalyst under milder conditions to afford excellent yields of substituted alkynes. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-950260

LETTER
2747
Nanocrystalline Magnesium Oxide Stabilized Palladium(0): An Efficient
Heterogeneous Catalyst for Heck and Sonogashira Coupling of Aryl Halides1
N
anocrystalline Magne
.
sium
Oxide
L
Stabilized Palla
a
dium(0) kshmi Kantam,*a Sarabindu Roy,a Moumita Roy,a M. S. Subhas,a Pravin R. Likhar,a Bojja Sreedhar,a
B. M. Choudaryb
a
Indian Institute of Chemical Technology, Inorganic & Physical Chemistry Division, Hyderabad 500007, India
Fax +91(40)27160921; E-mail: mlakshmi@iict.res.in
Ogene Systems (I) Pvt. Ltd., Hyderabad 500037, India
b
Received 30 July 2006
catalytic systems for coupling reactions of haloarenes.3 It
Abstract: Nanocrystalline magnesium oxide supported palladi-
would be more beneficial if chloroarenes, which are far
cheaper and more widely available than iodo- and bro-
moarenes, could be activated for such coupling reactions.
um(0) catalyst [NAP-Mg-Pd(0)], prepared by the counter-ion stabi-
2–
lization of PdCl4 followed by reduction with hydrazine hydrate,
was effectively used in the Heck olefination of haloarenes (chloro,
bromo, and iodo) to afford good to excellent yields of substituted Previously we have reported3e the effective Heck, Suzuki,
olefins. This ligand-free heterogeneous NAP-Mg-Pd(0) catalyst
Sonogashira, and Stille type-coupling reactions of chloro-
was quantitatively recovered from the reaction by a simple filtration
arenes using a basic-layered double-hydroxide-supported
and reused for a number of cycles with almost no loss of activity.
nano-palladium catalyst. Recently Cwik et al.3i reported
Moreover, NAP-Mg-Pd(0) efficiently catalyzed the Sonogashira
basic Mg–Ln mixed-oxide-supported palladium as a het-
coupling of haloarenes with terminal alkynes without any copper
erogeneous catalyst for Heck coupling of haloarenes,
which gives a moderate yield with bromobenzene (67%,
20 h) and a poor yield with chlorobenzene (17%, 25 h).
Recently, nano-metal oxides including MgO, CaO, Al2O3,
and ZnO have attracted great attention due to their unusu-
al magnetic, optical, physical, and surface chemical and
catalytic properties.4 In an effort to develop new hetero-
geneous catalytic systems, we explored highly basic
nanocrystalline magnesium oxide (NAP-MgO) as a sup-
port.5 The high surface area and the presence of edge, cor-
ner, and other defect sites allow the nanostructured MgO
to possess a high concentration of reactive surface ions,
wherein the highly reactive ions could be stabilized by
forming adducts with the ‘reactive–accepting’ surface
sites on the nanocrystalline MgO. Recently, by adopting a
co-catalyst under milder conditions to afford excellent yields of
substituted alkynes.
Keywords: nanocrystalline magnesium oxide, palladium, hetero-
geneous reaction, Heck reaction, Sonogashira reaction
In recent times palladium-catalyzed Heck and related cou-
pling reactions have gained considerable attention as the
resulting products have been applied as intermediates in
the synthesis of materials, natural products, and bioactive
compounds.2 The ready availability of starting materials,
simplicity and generality of the methods, and the broad
tolerance of palladium catalysts towards various function-
al groups make these coupling reactions particularly
attractive for organic synthesis. Despite the synthetic
elegance these coupling reactions suffer from serious
limitations, such as: (1) non-reusability of the precious
palladium catalysts and (2) use of toxic and/or expensive
ancillary phosphine ligands. To avoid the use of expen-
sive and air-sensitive basic ligands, several groups are try-
ing to develop ligand-free and recyclable heterogeneous
2–
counter-ionic stabilization of PdCl4 with the Mg2+ of
the nanocrystalline MgO, followed by reduction with
hydrazine hydrate, we prepared a palladium(0) catalyst
[NAP-Mg-Pd(0)] supported on nanocrystalline MgO
(Scheme 1). This was efficiently used for Suzuki and
Stille reactions, which demonstrated that NAP-MgO is
HO
HO
HO
Na
HO
HO
O–
O–
Mg+
Mg+
Na2PdCl4,
H2NNH2·H2O
O–
Mg+
Mg+
Mg+
Mg+
H2O, 12 h, N2
Mg+
O–
Mg+
O–
HO
Mg+
O–
HO
HO
+
OH
NAP-MgO
OH
OH
NAP-Mg-Pd0
NAP-Mg-PdCl4
Scheme 1 Preparation of NAP-Mg-Pd(0) catalyst9
SYNLETT 2006, No. 17, pp 2747–2750
1
7
.1
0
.2
0
0
6
Advanced online publication: 09.10.2006
DOI: 10.1055/s-2006-950260; Art ID: D22906ST
© Georg Thieme Verlag Stuttgart · New York

2748
M. L. Kantam et al.
LETTER
not only an excellent basic support but could also enhance quaternary ammonium compound.3j The reaction with
the catalytic activity of the supported metal from their ho- electron-poor chloroarenes was accomplished within 8–
mogeneous counterpart.5c The catalyst was characterized 12 hours. Even electron-rich 4-chloroanisole was activat-
by XPS, UV-Vis/DRS, TEM, and SEM-EDX.5c
ed by this catalytic system but less effectively (25% yield
after 24 h).
Herein, we wish to report the Heck and Sonogashira cross-
coupling of haloarenes catalyzed by NAP-Mg-Pd(0) cata- After completion of the reaction, the catalyst was recov-
lyst. Moreover, a thorough investigation was performed to ered by simple filtration, subsequent washing with water
know the true nature of the catalyst, i.e. whether this sup- followed by acetone, and air-drying. The recovered cata-
ported catalyst acts as a heterogeneous catalyst, or merely lyst was used in the next cycle with almost the same level
acted as a reservoir of palladium. Initially, we attempted of activity (Table 2; entries 1 and 3).
the Heck reaction of iodobenzene with styrene using a cat-
The heterogeneous nature of the catalyst was also evalu-
alytic amount of NAP-Mg-Pd(0) (0.1 mol%), which fur-
ated. As mentioned significant amounts of Pd were shown
nished 95% of the trans-stilbene within one hour in
to leach from heterogeneous Pd catalysts and the reaction
may be mainly catalyzed by Pd species in the liquid
dimethylacetamide (DMAc) as the solvent in the presence
of NaOAc at 130 °C under a nitrogen atmosphere. Several
phase.3h,k It is also known that almost all Pd is redeposited
other iodoarenes were reacted under the same conditions
after completion of the reaction. Therefore, a true evalua-
(Table 1). Bromoarenes were also found to be active un-
tion of the heterogeneous nature can be carried out by in-
der the optimized conditions but required a longer reac-
terrupting the reaction at low conversion and then
tion time (6–8 h; Table 1, entries 6–8). The reactivity
continuing the process with both the catalyst and the fil-
order of the haloarenes (i.e. ArI>ArBr) is correlated to the
trate. In this way, information about the presence or ab-
nucleophlicity of the aromatic ring. When we employed
sence of active species in solution and the activity of such
chlorobenzene under these reaction conditions almost no
species can be acquired.
product formation was observed after 24 hours, however,
To check the heterogeneous nature of the catalyst, a series
of experiments was performed. In experiment 1, a reaction
the addition of TBAB yielded 45% of trans-stilbene with
>99% selectivity within 24 hours. Further increasing the
between 4-bromoanisole and styrene was terminated after
amount of catalyst from 0.1 mol% to 1.0 mol% gave 78%
30 min (37% conversion) and the catalyst was separated
of the product within 15 hours. The beneficial effect ob-
(hot filtration). Then the reaction was continued with the
served with TBAB may result from the adsorption of the
filtrate for an additional 10 hours and the conversion
quaternary ammonium compound onto the surface of the
Pd clusters, thus stabilizing them against excessive
sintering3j and enhancing the solubility of the base in the
Table 2 Heck Olefination of Chloroarenes Using NAP-Mg-Pd(0)
Catalysta,9
Table 1 Heck Olefination of Iodo and Bromoarenes with Olefins
Entry
Chloroarene
PhCl
Olefin
Time (h) Isolated
yield (%)
Using NAP-Mg-Pd(0) Catalysta,9
Entry
Haloarene
Olefin
Time (h) Isolated
Yield (%)
1
2
3
4
5
6
7
8
Ph
15
10
10
10
10
12
24
24
78 (73)b
Ph
1
2
PhI
PhI
1
1
95
94
4-CNC6H4Cl
4-MeCOC6H4Cl
4-CNC6H4Cl
4-MeCOC6H4Cl
4-PhCOC6H4Cl
4-MeC6H4Cl
4-MeOC6H4Cl
93
Ph
Ph
CO2Bu
92 (89)b
89
3
4
5
6
7
8
PhI
1
2
92
92
94
95
92
94
CO2Et
Ph
CO2Bu
4-MeOC6H4I
4-MeOC6H4I
PhBr
90
CO2Bu
Ph
2
CO2Bu
Ph
90
6
45
Ph
4-MeC6H4Br
4-MeOC6H4Br
9
Ph
25
Ph
10
Ph
a Reaction conditions: haloarene (2 mmol), olefin (2.2 mmol), NaOAc
(6 mmol), NAP-Mg-Pd(0) (0.1 mol%), DMAc (5 mL), 130 °C, N2 at-
mosphere.
a Chloroarene (2 mmol), olefin (2.2 mmol), NaOAc (6 mmol), TBAB
(2 mmol), DMAc (5 mL), 135 °C, N2 atmosphere.
b Yield after the 5th cycle.
Synlett 2006, No. 17, 2747–2750 © Thieme Stuttgart · New York

LETTER
Nanocrystalline Magnesium Oxide Stabilized Palladium(0)
2749
remained identical. The filtrate was tested for palladium
by ICP-AES and a negligible amount (0.02%) of palladi-
um was leached into the solution. In experiment 2, the
reaction between 4-bromoanisole and styrene was termi-
nated after 2 hours (58% conversion) and the catalyst was
separated (hot filtration). Then the reaction was continued
with the filtrate for an additional 10 hours and the conver-
sion remained the same. The filtrate was tested for palla-
dium by ICP-AES and 0.018% of the total palladium was
leached into the solution. In experiment 3, the reaction be-
tween 4-bromoanisole and styrene was continued till
completion and the amount of leached palladium was
measured at different intervals. Almost constant leaching
was observed throughout the reaction, i.e. 0.02–0.017% of
total palladium used. This is in contrast to the observation
when acidic metal oxides and zeolites (such as TiO2,
Al2O3, NaY etc.) supported on palladium catalysts were
employed in the Heck reaction.3h In those cases the solid
catalyst functions as a reservoir for molecular palladium
species in solution and their concentration in solution cor-
relates exactly with the course of the reaction. These stud-
ies and the reusability of the catalyst demonstrate that the
palladium bound to nanocrystalline magnesium oxide was
mainly responsible for the reaction and the reaction pref-
erentially proceeded on the heterogeneous surface. It is
reported6 that significant amounts of supported palladium
metal can be dissolved during the reaction and would re-
deposit quickly on the solid during the filtration as a result
of unavoidable minor temperature differences during the
filtration, so the catalytic effect of any such dissolved
palladium from MgO cannot be ruled out at this stage.
Table 3 Sonogashira Coupling of Haloarenes with Alkynes Using
NAP-Mg-Pd(0) Catalysta,9
NAP-Mg-Pd0 (1 mol%)
X
Et3N (2 equiv)
R2
R2
+
THF–H2O, r.t. or DMF,
80 °C
R1
R1
Entry
R1
X
R2
Time (h) Yield (%)
1
2
H
I
Ph
16
24
24
12
14
8
96
4-Me
4-MeO
4-NO2
H
I
Ph
95
3
I
Ph
92 (90)b
98
4
I
Ph
5
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Ph
90
6
4-NO2
4-Me
4-NO2
4-NO2
4-MeO
H
Ph
94
7
Ph
14
8
90 (88)b
93
8
4-MeC6H4
Me(CH2)4
Ph
9
8
88
10
11
12
13
14
15
14
24
14
40
18
24
16
20
92
CH2OH
4-MeC6H4
CH2OH
Me(CH2)4
Ph
65
H
89
4-MeO
H
82
88
H
20
Buoyed with the impressive results obtained in the Heck 16
olefination reaction, we further examined the efficacy of
4-NO2
4-MeCO
Ph
86
17
Ph
82
the NAP-Mg-Pd(0) catalyst in another important C–C
coupling reaction namely Sonogashira cross-coupling of a Reaction conditions: haloarene (0.5 mmol), alkyne (0.6 mmol), Et3N
(2 equiv), NAP-Mg-Pd(0) (1 mol%), THF–H2O (1:1, 3 mL); r.t. for
haloarenes with terminal alkynes to yield substituted
alkynes. Usually Sonogashira coupling is performed with
a palladium catalyst, a basic ligand, and a copper co-cata-
iodoarenes or DMF (3 mL), 80 °C for bromo- and chloroarenes.
b Yield after the 5th cycle.
lyst. But use of a copper catalyst promotes the Glaser-type
homocoupling of alkynes;6 these side-products are diffi-
cult to separate from the products. So it is highly desirable
to the formation of some unknown red oil without any
improvement in the conversion of the chloroarenes.
to develop a protocol for ligand- and copper-free
Sonogashira reaction.3f,g,8
In conclusion, we have developed an efficient heteroge-
neous protocol for Heck coupling of haloarenes including
chloroarenes using a nanocrystalline magnesium oxide
supported nanopalladium catalyst, which can be easily
separated from the reaction mixture and reused with con-
sistent activity. Furthermore, this catalyst can accomplish
the ligand- and copper-free Sonogashira coupling of
haloarenes. Moreover the heterogeneous nature of the
catalysis is examined through a study of Pd leaching into
the solution.
The NAP-Mg-Pd(0) (1.0 mol%) can effectively couple 4-
iodoanisole with phenylacetylene in THF–water and tri-
ethylamine at room temperature but failed to activate 4-
bromoanoisole even at 70 °C. Switching from THF–water
to DMF and raising the temperature to 80 °C, 4-bromo-
anisole was completely converted into the corresponding
substituted alkyne. Then several iodo- and bromoarenes
were reacted with a diverse range of terminal alkynes
(Table 3). The catalyst was recycled five times with con-
sistent activity (Table 3, entries 3 and 7). Chloroarenes
were found to be less reactive and had a longer reaction
time (Table 3, entries 15–17). Here we did not observe
any rate enhancement by adding TBAB. Addition of CuI
only enhanced the formation of the homocoupling of the
alkyne whereas an increase in temperature (130 °C) leads
Acknowledgment
We wish to thank the CSIR for financial support under the Task
Force Project COR-0003. S.R. and M.S.S. thank CSIR and M.R.
thanks UGC, New Delhi for providing research fellowships.
Synlett 2006, No. 17, 2747–2750 © Thieme Stuttgart · New York

2750
M. L. Kantam et al.
LETTER
(9) Preparation of NAP-Mg-Pd(0) Catalyst:5c NAP-MgO
References and Notes
(1 g, BET 600 m2/g, purchased from NanoScale Materials
Inc., Manhattan, USA) was treated with Na2PdCl4 (294 mg,
1 mmol) dissolved in decarbonated H2O (100 mL) and the
resulting mixture was stirred for 12 h under a nitrogen
atmosphere to afford the brown colored NAP-Mg-PdCl4.
Then the catalyst was filtered, washed with deionized H2O
and acetone, and dried. Then NAP-Mg-PdCl4 (1g) was
reduced with hydrazine hydrate (1 g, 20 mmol) in anhyd
EtOH (20 mL) for 3 h under a nitrogen atmosphere to give
the black colored air-stable NAP-Mg-Pd(0) (Pd 0.99
mmol/g).
(1) IICT communication No. 060818.
(2) (a) Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000,
100, 3009. (b) Zapf, A.; Beller, M. Chem. Commun. 2005,
431. (c) Miyaura, N. Cross-Coupling Reactions; Springer:
Berlin, 2002. (d) Diederich, F.; Stang, P. J. Metal-Catalyzed
Cross-Coupling Reactions; Wiley-VCH: Weinheim, 1998.
(e) Sonogashira, K. J. Organomet. Chem. 2002, 653, 46.
(3) For the heterogeneous Heck and related coupling reactions,
see: (a) Zhao, F.; Bhanage, B. M.; Shirai, M.; Arai, M.
Chem. Eur. J. 2000, 6, 843. (b) Djakovitch, L.; Koehler, K.
J. Am. Chem. Soc. 2001, 123, 5990. (c) Djakovitch, L.;
Koehler, K. J. Mol. Catal. A: Chem. 1999, 142, 275.
(d) Mori, K.; Yamaguchi, K.; Hara, T.; Mizugaki, T.;
Ebitani, K.; Kaneda, K. J. Am. Chem. Soc. 2002, 124,
11572. (e) Choudary, B. M.; Madhi, S.; Chowdari, N. S.;
Kantam, M. L.; Sreedhar, B. J. Am. Chem. Soc. 2002, 124,
14127. (f) Djakovitch, L.; Rollet, P. Adv. Synth. Catal. 2004,
346, 1782. (g) Li, P.; Wang, L.; Li, H. Tetrahedron 2005, 61,
8633. (h) Prockl, S. S.; Kleist, W.; Gruber, M. A.; Koehler,
K. Angew. Chem. Int. Ed. 2004, 43, 1881. (i) Cwik, A.;
Hell, Z.; Figueras, F. Adv. Synth. Catal. 2006, 348, 523.
(j) Dams, M.; Drijkoningen, L.; Pauwels, B.; Tendeloo, G.
V.; De Vos, D. E.; Jacobs, P. A. J. Catal. 2002, 209, 225.
(k) Andrews, S. P.; Stepan, A. F.; Tanaka, H.; Ley, S. V.;
Smith, M. D. Adv. Synth. Catal. 2005, 347, 647.
(4) (a) Gesser, H. D.; Goswami, P. C. Chem. Rev. 1989, 89,
765. (b) Fendler, J. H. Chem. Rev. 1987, 87, 877. (c) Itoh,
H.; Utamapanya, S.; Stark, J. V.; Klabunde, K. J.; Schlup, K.
J. Chem. Mater. 1993, 5, 71. (d) Klabunde, K. J.; Stark, J.;
Koper, O.; Mohs, C.; Park, D. G.; Decker, S.; Jiang, Y.;
Lagadicand, I.; Zhang, D. J. Phys. Chem. 1996, 100, 12142.
(e) Jiang, Y.; Decker, S.; Mohs, C.; Klabunde, K. J. J. Catal.
1998, 180, 24. (f) Mishakov, I. V.; Bedilo, A. F.; Richards,
R. M.; Chesnokov, V. V.; Volodin, A. M.; Zaikovskii, V. I.;
Buyanov, R. A.; Klabunde, K. J. J. Catal. 2002, 206, 40.
(g) Sun, N.; Klabunde, K. J. J. Catal. 1999, 185, 506.
(h) Guzman, J.; Gates, B. C. Nano Lett. 2001, 1, 689.
(i) Lai, F. S.; Gates, B. C. Nano Lett. 2001, 1, 583.
(j) Choudary, B. M.; Mulukutla, R. S.; Klabunde, K. J. J.
Am. Chem. Soc. 2003, 125, 2020. (k) Choudary, B. M.;
Kantam, M. L.; Ranganath, K. V. S.; Mahendar, K.;
Sreedhar, B. J. Am. Chem. Soc. 2004, 126, 3396.
(l) Choudary, B. M.; Ranganath, K. V. S.; Pal, U.; Kantam,
M. L.; Sreedhar, B. J. Am. Chem. Soc. 2005, 127, 13167.
(m) Kantam, M. L.; Shiva Kumar, K. B.; Sridhar, Ch. Adv.
Synth. Catal. 2005, 347, 1212. (n) Jeevanandam, P.;
Klabunde, K. J. Langmuir 2002, 18, 5309. (o) Klabundae,
K. J.; Mulukutla, R. Nanoscale Materials in Chemistry;
Wiley Interscience: New York, 2001, Chap. 7, 223.
(5) (a) Choudary, B. M.; Jyothi, K.; Kantam, M. L.; Sreedhar, B.
Adv. Synth. Catal. 2004, 346, 45. (b) Choudary, B. M.;
Jyothi, K.; Roy, M.; Kantam, M. L.; Sreedhar, B. Adv. Synth.
Catal. 2004, 346, 1471. (c) Kantam, M. L.; Roy, S.; Roy,
M.; Sreedhar, B.; Choudary, B. M. Adv. Synth. Catal. 2005,
347, 2002.
(6) Lipshutz, B. H.; Tasler, S.; Chrisman, W.; Spliethoff, B.;
Tecsche, B. J. Org. Chem. 2003, 68, 1177.
(7) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem.
Int. Ed. 2000, 39, 2632.
(8) Copper- and ligand-free Sonogashira reactions:
(a) Urgaonkar, S.; Verkade, J. G. J. Org. Chem. 2004, 69,
5752. (b) Park, S. B.; Alper, H. Chem. Commun. 2004,
1306. (c) Liang, B.; Dai, M.; Chen, J.; Yang, Z. J. Org.
Chem. 2005, 70, 391. (d) Li, J.; Liang, Y.; Xie, Y. J. Org.
Chem. 2005, 70, 4393.
Heck Coupling of Iodo and Bromoarene: 4-Bromoanisole
(2 mmol), styrene (2.2 mol), NaOAc (6 mmol), dimethyl-
acetamide (DMAc, 5 mL), and NAP-Mg-Pd(0) (0.1 mol%)
were taken in a 20-mL reaction vessel and stirred under a
nitrogen atmosphere at 135 °C (monitored by GC). After
completion of the reaction the catalyst was separated by
filtration, washed with H2O and acetone, and dried in air.
The filtrate was diluted with Et2O and washed with H2O. The
organic layer was concentrated to give the crude product,
which was purified by column chromatography (hexane–
EtOAc, 9:1) to give pure 4-methoxy-trans-stilbene in 94%
yield (395 mg); mp 135–137 °C. 1H NMR (300 MHz,
CDCl3): d = 3.84 (s, 3 H), 6.81–7.07 (m, 4 H), 7.17–7.53 (m,
7 H). EI-MS: m/z (%) = 210 (M+), 195, 167, 165, 152. Anal.
Calcd for C15H14O: C, 85.68; H, 6.71. Found: C, 85.45;
H, 6.83.
Heck Coupling of Chloroarenes: 4-Chloroacetophenone (2
mmol), styrene (2.2 mol), NaOAc (6 mmol), TBAB (2
mmol), DMAc (5 mL), and NAP-Mg-Pd(0) (1.0 mol%) were
taken in a 20-mL reaction vessel and stirred under a nitrogen
atmosphere at 135 °C (monitored by GC). After completion
of the reaction the catalyst was separated by filtration,
washed with H2O and acetone, and dried in air. The filtrate
was diluted with Et2O and washed with a solution of 1% HCl
(to remove the amine formed from decomposition of TBAB)
and then a sat. solution of NaCl. Then organic layer was
dried over Na2SO4 and concentrated to get the crude product,
which was purified by column chromatography (hexane–
EtOAc, 8:2) to give pure 4-acetyl-trans-stilbene in 92%
yield (408 mg); mp 134–136 °C. 1H NMR (300 MHz,
CDCl3): d = 2.6 (s, 3 H), 7.12 (d, J = 16.6 Hz, 1 H), 7.22 (d,
J = 16.6 Hz, 1 H), 7.28–7.41 (m, 3 H), 7.53 (d, J = 6.8 Hz, 2
H), 7.59 (d, J = 8.3 Hz, 2 H), 7.95 (d, J = 8.3 Hz, 2 H). EI-
MS: m/z = 222 (M+), 207, 178, 149, 77, 51, 43. Anal. Calcd
for C16H14O: C, 86.45; H, 6.35. Found: C, 86.28; H, 6.47.
Sonogashira Reaction: 4-Bromoanisole (0.5 mmol),
phenylacetylene (0.6 mol), Et3N (1 mmol), DMF (3 mL),
and NAP-Mg-Pd(0) (1.0 mol%) were taken in a 10-mL
reaction vessel and stirred under a nitrogen atmosphere at
75 °C (monitored by GC). After completion of the reaction,
the catalyst was separated by filtration, washed with H2O
and acetone, and dried in air. The filtrate was diluted with
Et2O and washed with a sat. solution of NaCl. The organic
layer was concentrated to give the crude product, which was
purified by column chromatography(hexane) to give pure 4-
methoxydiphenylacetylene in 92% yield (96 mg); mp 55–
57 °C. 1H NMR (300 MHz, CDCl3): d = 3.8 (s, 3 H), 6.83 (d,
J = 8.3 Hz, 2 H), 7.25–7.35 (m, 3 H), 7.39–7.51 (m, 4 H). EI-
MS: m/z = 208 (M+), 194, 167, 166, 140. Anal. Calcd for
C15H12O: C, 86.51; H, 5.81. Found: C, 86.39; H, 5.96.
Synlett 2006, No. 17, 2747–2750 © Thieme Stuttgart · New York