Palladium-catalyzed Sonogashira and Hiyama reactions using phosphine-free hydrazone ligands

Article abstract of DOI:10.1021/jo061734i

(Chemical Equation Presented) Palladium/copper-catalyzed Sonogashira cross-coupling reaction of aryl halides with a variety of terminal alkynes under amine-free conditions in dimethylformamide (DMF) at 80 °C gave internal arylated alkynes using PdCl₂(MeCN)₂ with phosphine-free hydrazone 2a as a ligand and CuI as the cocatalyst in good yields. We also found PdCl₂/hydrazone ligand 1d in PhMe at 80°C was a phosphine-free efficient catalyst system for a Hiyama cross-coupling reaction of aryl bromides with aryl(trialkoxy)silanes in good yields.

Full text of DOI:10.1021/jo061734i

hydrazone as an effective ligand for the Suzuki-Miyaura2 and
Mizoroki-Heck cross-coupling reaction.3
Palladium-Catalyzed Sonogashira and Hiyama
Reactions Using Phosphine-Free Hydrazone
Ligands
The Sonogashira cross-coupling reaction of aryl halides with
terminal acetylenes, which provides a powerful tool for the
formation of alkynes, has been widely applied to such diverse
areas as natural product syntheses and material science.4 The
most common catalytic system for this reaction is using such
palladium-phosphine complexes as PdCl2(PPh3)2 and Pd(PPh3)4
in large amounts of amines as solvents or cosolvents with CuI
as the cocatalyst.5-7 Recently a copper-free Sonogashira cross-
coupling reaction was reported that used a combination of at
least one phosphine as a ligand or an amine and a large amount
of tetra-n-butyl ammonium salt as an activator.8-10 However,
their phosphines in palladium complexes are often air-sensitive.
Amines also have a characteristic foul smell and pungent flavor.
We now report the use of air-stable phosphine-free hydrazone
ligands 1 and 2 for an amine-free palladium/copper-catalyzed
Sonogashira cross-coupling reaction.
Takashi Mino,* Yoshiaki Shirae, Takeshi Saito,
Masami Sakamoto, and Tsutomu Fujita
Department of Applied Chemistry and Biotechnology, Faculty of
Engineering, Chiba UniVersity, 1-33, Yayoi-cho, Inage-ku,
Chiba 263-8522, Japan
tmino@faculty.chiba-u.jp
ReceiVed August 21, 2006
We applied the coupling of 4-iodotoluene and phenyl
acetylene in the presence of 2 mol % of PdCl2(MeCN)2 with
K3PO4 as a base under an argon atmosphere at 80 °C to
determine the optimum reaction conditions (Table 1). The effect
of various hydrazone ligands in this reaction was investigated
(entries 1-5). In the presence of glyoxal bis(N-methyl-N-
phenylhydrazone) (1a), which was the effective ligand for the
(2) (a) Mino, T.; Shirae, Y.; Sakamoto, M.; Fujita, T. Synlett 2003, 882.
(b) Mino, T.; Shirae, Y.; Sakamoto, M.; Fujita, T. J. Org. Chem. 2005, 70,
2191.
(3) Mino, T.; Shirae, Y.; Sasai, Y.; Sakamoto, M.; Fujita, T. J. Org.
Chem. 2006, 71, 6837.
Palladium/copper-catalyzed Sonogashira cross-coupling reac-
tion of aryl halides with a variety of terminal alkynes under
amine-free conditions in dimethylformamide (DMF) at 80
°C gave internal arylated alkynes using PdCl2(MeCN)2 with
phosphine-free hydrazone 2a as a ligand and CuI as the
cocatalyst in good yields. We also found PdCl2/hydrazone
ligand 1d in PhMe at 80 °C was a phosphine-free efficient
catalyst system for a Hiyama cross-coupling reaction of aryl
bromides with aryl(trialkoxy)silanes in good yields.
(4) For reviews, see the following: (a) Sonogashira, K. In Metal-
Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.;
Wiley-VCH: New York, 1998; Chapter 5. (b) Brandsma, L.; Vasilevsky,
S. F.; Verkruijsse, H. D. Application of Transition Metal Catalysts in
Organic Synthesis; Springer-Verlag: Berlin, 1998; Chapter 10. (c) Sono-
gashira, K. In ComprehensiVe Organic Synthesis; Trost, B. M., Ed.;
Pergamon: New York, 1991; Vol. 3, Chapter 2.4.
(5) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975,
44, 4467. (b) Cassar, L. J. Organomet. Chem. 1975, 93, 253. (c) Dieck, H.
A. Heck, R. F. J. Organomet. Chem. 1975, 93, 259.
(6) For examples, see the following: (a) Thorand, S.; Krause, N. J. Org.
Chem. 1998, 63, 8551. (b) Hundertmark, T.; Litter, A. F.; Buchwald, S. L.;
Fu, G. C. Org. Lett. 2000, 2, 1729. (c) Chow, H.-F.; Wan, C.-W.; Low,
K.-H.; Yeung, Y.-Y. J. Org. Chem. 2001, 66, 1910. (d) Nova´k, Z.; Szabo´,
A.; Re´pa´si, J.; Kotschy, A. J. Org. Chem. 2003, 68, 3327. (e) Remmele,
H.; Ko¨llhofer, A.; Plenio, H. Organometallics 2003, 22, 4098. (f) Elangovan,
A.; Wang, Y.-H.; Ho, T.-I. Org. Lett. 2003, 5, 1841. (g) Adjabeng, G.;
Brenstrum, T.; Frampton, C. S.; Robertson, A. J.; Hillhous, J.; McNulty,
J.; Capretta, A. J. Org. Chem. 2004, 69, 5082. (h) Son, S. U.; Jang, Y.;
Park, J.; Na, H. B.; Park, H. M.; Yun, H. J.; Lee, J.; Hyeon, T. J. Am.
Chem. Soc. 2004, 126, 5026. (i) Hierso, J.-C.; Fihri, A.; Amardeil, R.;
Meunier, P. Org. Lett. 2004, 6, 3473.
(7) Recently copper-catalyzed Sonogashira cross-coupling reaction under
palladium and phosphine-free conditions was reported: Ma, D.; Liu, F.
Chem. Commun. 2004, 1934.
(8) For a selected paper on the copper-free conditions using phosphine/
amine, see the following: Soheili, A.; Albaneze-Walker, J.; Murry, J. A.;
Dormer, P. G.; Hughes, D. L. Org. Lett. 2003, 5, 4191.
(9) For selected papers on the copper and amine-free conditions using
phosphine, see the following: (a) Cheng, J.; Sun, Y.; Wang, F.; Guo, M.;
Xu, J.-H.; Pan, Y.; Zhang, Z. J. Org. Chem. 2004, 69, 5428. (b) Liang, Y.;
Xie, Y.-X.; Li, J.-H. J. Org. Chem. 2006, 71, 379. (c) Yi, C.; Hua, R. J.
Org. Chem. 2006, 71, 2535.
(10) For selected papers on the copper and phosphine-free conditions
using amine or tetra-n-butyl ammonium salt, see: (a) Park, S. B.; Alper,
H. Chem. Commun. 2004, 1306. (b) Urgaonkar, S.; Verkade, J. G. J. Org.
Chem. 2004, 69, 5752. (c) Liang, B.; Dai, M.; Chen, J.; Yang, Z. J. Org.
Chem. 2005, 70, 391.
Palladium-catalyzed C-C coupling reactions have been
recognized as powerful tools in multiple organic transforma-
tions.1 We recently demonstrated air-stable phosphine-free
(1) For reviews, see the following: (a) Larhed, M.; Hallberg, A. In
Handbook of Organopalladium Chemistry for Organic Synthesis; Negishi,
E., Ed.; Wiley-Interscience: New York, 2002; Vol. 1, p 1133. (b)
Whitcombe, N. J.; Hii, K. K.; Gibson, S. E. Tetrahedron 2001, 57, 7449.
(c) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009. (d)
Hegedus, L. S. Transition Metals in the Synthesis of Complex Organic
Molecules, 2nd ed.; University Science Books: Sausalito, CA, 1999; Chapter
4.6. (e) Brase, S.; de Meijere, A. In Metal-Catalyzed Cross-Coupling
Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH: Weinheim,
Germany, 1998; Chapter 3. (f) Link, J. T.; Overman, L. E. In Metal-
Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.;
Wiley-VCH: Weinheim, Germany, 1998; Chapter 6. (g) Beller, M.;
Riermeier, T. H.; Stark, G. In Transition Metals for Organic Synthesis;
Beller, M., Bolm, C., Eds.; Wiley-VCH: Weinheim, Germany, 1998; Vol.
1, p 208. (h) Crisp, G. T. Chem. Soc. ReV. 1998, 27, 427. (i) Tsuji, J.
Palladium Reagents and Catalysts: InnoVations in Organic Synthesis;
Wiley: Chichester, U.K., 1995.
10.1021/jo061734i CCC: $33.50 © 2006 American Chemical Society
Published on Web 11/08/2006
J. Org. Chem. 2006, 71, 9499-9502
9499

TABLE 1. Optimization of Reaction Conditions on Sonogashira
Reactiona
TABLE 2. Sonogashira Reaction of Aryl Halides with Alkynesa
a Reaction conditions: 4-iodotoluene (1 mmol), phenyl acetylene (1.2
mmol), base (1.4 mmol), solvent (2 mL), palladium source (0.02 mmol),
ligand (0.02 mmol), CuI (0.05 mmol). b Isolated yields.
a Reaction conditions: aryl halide (1 mmol), alkyne (1.2 mmol), K3PO4
(1.4 mmol), DMF (2 mL), PdCl2(MeCN)2 (0.02 mmol), ligand 2a (0.02
mmol), CuI (0.05 mmol). b Isolated yields. c 4-Iodotoluene (0.5 mmol) and
alkyne (1.0 mmol) were added. d This reaction was carried out at 70 °C.
e This reaction used 2 equiv of phenyl acetylene.
monly used palladium sources were also tested (entries 4, 14-
16); PdCl2(MeCN)2 preferred this reaction (entry 4).
The effect of various aryl iodides in the Sonogashira cross-
coupling reaction was investigated using phenyl acetylene
(entries 1-8, Table 2). Using 4-substituted aryl iodides led to
good yields of the desired products (entries 1-6). Moreover,
2-substituted aryl iodides also led to good yields (entry 7). Using
a 4 mol % palladium catalyst, the reaction of 1-iodonaphthalene
with phenyl acetylene gave corresponding product with good
yield (entry 8). The effect of varying alkynes was also
investigated using 4-iodotoluene as the substrate (entries 9-13).
Using 4-ethynyltoluene led to good yield of the corresponding
product (entry 9). The reaction of 4-bromo-1-nitorobenzene with
phenyl acetylene was necessary for longer reaction times such
as 24 h (entry 14).
Suzuki-Miyaura reaction, Sonogashira cross-coupling product
3a was obtained in moderate yield (entry 1). Bishydrazone
ligand 1b with a seven-membered ring was not effective for
this reaction. The use of 2a as a ligand led to high yield for
this reaction (entry 4). Without the presence of ligand 2a, the
reaction gave low yield of the desired product (entry 4 vs entry
6). The effect of various bases in the Sonogashira cross-coupling
reaction was investigated (entries 4, 7-10). Among inorganic
bases (K3PO4, Cs2CO3, and K2CO3), NaOAc, and KOtBu
examined in DMF (N,N-dimethylformamide), K3PO4 proved
very effective. Other solvents proved less effective in this
reaction than DMF (entry 4 vs entries 11-13). Several com-
We next tried Hiyama cross-coupling of aryl bromides with
aryl(trialkoxy)silanes using air-stable phosphine-free hydrazones
1 and 2 as a ligand. This reaction also provides a powerful tool
for the C-C bond formation of biaryls, which has been widely
9500 J. Org. Chem., Vol. 71, No. 25, 2006

TABLE 3. Optimization of Reaction Conditions on Hiyama
Reactiona
applied to such diverse areas as natural product and biologically
active compound synthesis.11 The use of such silicon-derived
compounds as transmetalation reagents has attracted much
attention as a viable option to these processes for its low cost,
easy availability, nontoxic byproducts, and stability under many
reaction conditions.12 Generally, the Hiyama cross-coupling
reaction is also carried out using an air-sensitive phosphine-
palladium catalyst such as Pd(OAc)2/PPh3 and PdCl2(MeCN)2/
(o-Tol)3P.12f,l We now report the use of air-stable hydrazone
ligands 1 and 2 for phosphine-free palladium-catalyzed Hiyama
cross-coupling reactions. We optimized the coupling conditions
of 4-bromoacetophenone with phenyl(triethoxy)silane at 80 °C
(Table 3). The effect of ligands in this reaction was investigated
(entries 1-5). In the presence of 1d, cross-coupling product 4a
was obtained in good yield (entry 3). Pyridine-type hydrazone
ligands 2a and 2b were ineffective for this reaction. The effect
of various solvents was investigated using ligand 1d (entries 3,
6-10). Toluene proved very effective for 5 h (entry 10). Other
solvents proved less effective in this reaction. Without the
presence of ligand 1d, the yield was decreased (entry 10 vs
entry 11). Several commonly used palladium sources were also
tested (entries 4, 12-14). We found the following optimized
conditions: using the PdCl2/hydrazone 1d system, the reaction
proceeded with 83% in toluene at 80 °C under an argon
atmosphere (entry 14).
On the basis of those results, the Hiyama reaction of aryl
bromides with various siloxanes was investigated (Table 4). The
reaction of 4-bromoacetophenone and phenyl(triethoxy)silane
gave corresponding product with 73% yield for 3 h (entry 2).
Using phenyl(trimethoxy)silane, instead of phenyl(triethoxy)-
silane, also led to good yield (entry 3). Although a 4-methox-
yphenyl bromide led to low yield (entry 6), the reactions of
other 4-substituted aryl bromides gave good yields of the
corresponding products (entries 5, 7, and 8). Moreover, 3-sub-
stituted aryl bromides and 1-bromonaphthalene also led to good
yields (entries 9-11). We also investigated the reaction of
2-substituted aryl bromides. Using 3 equiv of phenyl(triethoxy)-
silane led to moderate yields of the corresponding products
(entries 12 and 13). The reaction of bromobenzene with various
aryl(triethoxy)silanes gave corresponding products with moder-
ate to good yields (entries 14-17).
a Reaction conditions: p-bromoacetophenone (0.5 mmol), phenyl(tri-
ethoxy)silane (1.0 mmol), TBAF (1.0 mmol) in THF (1 M, 1 mL), solvent
(1.5 mL), palladium source (0.02 mmol), ligand (0.03 mmol). b GC yields.
c Isolated yields.
system for Hiyama cross-coupling reaction of aryl bromides with
aryl(trialkoxy)silanes in good yields.
Experimental Section
Preparation of Glyoxal Bis(N-methyl-N-3-tolylhydrazone)
(1c). A solution of N-methyl-N-3-tolylhydrazine (0.163 g, 1.2 mmol)
in MeOH (2 mL) was added to 40 wt % of glyoxal in water (0.073
g, 0.5 mmol) at 0 °C. The mixture was stirred for 5.5 h at room
temperature. The yellow solid precipitated and was collected by
filtration, washed with hexane, and dried under reduced pressure:
0.140 g, 0.48 mmol, 95% as a yellow solid; mp 157-159 °C; IR-
We found that hydrazone 2a was useful as a phosphine-free
ligand for the palladium/copper-catalyzed Sonogashira cross-
coupling reaction of aryl halides with a variety of terminal
alkynes under amine-free conditions in DMF at 80 °C with
PdCl2(MeCN)2. We also found that Pd(OAc)2/hydrazone ligand
1d in PhMe at 80 °C was a phosphine-free efficient catalyst
1
(KBr) 1542 cm-1; H NMR (CDCl3) δ 2.36 (s, 6H), 3.37 (s, 6H),
6.71-6.81 (m, 2H), 7.03-7.11 (m, 2H), 7.14-7.23 (m, 4H), 7.51
(s, 2H); 13C NMR (CDCl3) δ 21.8, 33.5, 112.4, 116.1, 121.7, 128.9,
133.7, 138.9, 147.6; FAB-MS m/z (rel. intens.) 294 (M+, 80);
HRMS (FAB-MS) m/z calcd for C18H22N4 294.1844, found
294.1818.
(11) For reviews, see: (a) Hiyama, T. In Metal-Catalyzed Cross-Coupling
Reactions; Diederich, F., Stang, P. J., Eds.; Weinheim, Germany, 1998.
(b) Hiyama, T. J. Organomet. Chem. 2002, 653, 58. (c) Denmark, S. E.;
Sweiss, R. F. Acc. Chem. Res., 2002, 35, 835. (d) Spivey, A. C.; Gripton,
C. J. G.; Hannah, J. P. Curr. Org. Synth. 2004, 1, 211.
(12) (a) Gouda, K.; Hagiwara, E.; Hatanaka, Y.; Hiyama, T. J. Org.
Chem. 1996, 61, 7232. (b) Pilcher, A. S.; DeShong, P. J. Org. Chem. 1996,
61, 6901. (c) Hagiwara, E.; Gouda, K.; Hatanaka, Y.; Hiyama, T.
Tetrahedron Lett. 1997, 38, 439. (d) Brescia, M.-R.; DeShong, P. J. Org.
Chem. 1998, 63, 3156. (e) Mowery, M. E.; DeShong, P. J. Org. Chem.
1999, 64, 3266. (f) Mowery, M. E.; DeShong, P. Org. Lett. 1999, 1, 2137.
(g) Mowery, M. E.; DeShong, P. J. Org. Chem. 1999, 64, 1684. (h)
Denmark, S. E.; Wu, Z. Org. Lett. 1999, 1, 1495. (i) Denmark, S. E.; Choi,
J. Y. J. Am. Chem. Soc. 1999, 121, 5821. (j) Li, J.-H.; Deng, C.-L.; Liu,
W.-J. Xie, Y.-X. Synthesis 2005, 3039. (k) Donmin, D.; Benito-Garagorri,
D.; Mereiter, K.; Fro¨hlich, J.; Kirchner, K. Organometallics 2005, 24, 3957.
(l) Li, J.-H.; Deng, C.-L.; Xie, Y.-X. Synthesis 2006, 969.
Preparation of N,N-Bis(indolin-1-yl)ethane-1,2-diimine (1d).
A solution of N-aminoindoline (1.47 g, 11 mmol) in MeOH (5 mL)
was added to 40 wt % of glyoxal in water (0.725 g, 5 mmol) at 0
°C. The mixture was stirred for 3 h at room temperature. The yellow
solid precipitated and was collected by filtration, washed with
hexane, and dried under reduced pressure: 1.349 g, 4.65 mmol,
1
93% as a yellow solid; mp 251-253 °C; IR(KBr) 1532 cm-1; H
NMR (CDCl3) δ 6.81 (t, J ) 7.3 Hz 2H), 3.19-3.25 (m, 4H), 3.80-
3.86 (m, 4H), 7.07-7.19 (m, 6H), 7.34(s, 2H); 13C NMR (CDCl3)
δ 27.0, 48.2, 108.6, 120.3, 124.8, 127.5, 127.8, 134.4, 147.5; EI-
J. Org. Chem, Vol. 71, No. 25, 2006 9501

TABLE 4. Hiyama Reaction of Aryl Bromides with Siloxanesa
ecarboxaldehyde (0.032 g, 0.3 mmol) at room temperature. The
mixture was stirred for 24 h at 50 °C. The mixture was directly
concentrated under reduced pressure. The residue was purified by
silica gel chromatography (hexane/EtOAc ) 1/1): 0.022 g, 0.10
mmol, 33% as a yellow solid; mp 111-112 °C; IR(KBr) 1557
1
cm-1; H NMR (CDCl3) δ 3.27 (t, J ) 8.3 Hz, 2H), 3.92 (t, J )
8.2 Hz, 2H), 6.86 (dt, J ) 1.4 and 7.2 Hz, 1H), 7.11-7.26 (m,
5H), 7.46 (s, 1H), 7.66 (dt, J ) 1.7 and 7.7 Hz, 1H), 8.01 (d, J )
8.1 Hz, 1H), 8.52 (d, J ) 4.9 Hz, 1H); 13C NMR (CDCl3) δ 27.1,
48.0, 109.1, 118.9, 120.9, 121.9, 125.0, 127.8, 127.9, 133.3, 136.1,
147.3, 149.1, 155.6; EI-MS m/z (rel. intens.): 223 (M+, 18); HRMS
(FAB-MS) m/z calcd for C14H13N3 + H 224.1188, found 224.1182.
Sonogashira Cross-Coupling Reaction of Aryl Halides with
Alkynes (Table 2). Under an atmosphere of argon, alkyne (1.2
mmol) was added to the mixture of aryl halide (1 mmol), K3PO4
(1.4 mmol), PdCl2(MeCN)2 (0.02 mmol), ligand (0.02 mmol), and
CuI (0.05 mmol) in DMF (2 mL) at room temperature. The mixture
was stirred at 80 °C. After 5 h, the mixture was diluted with ethyl
acetate and water. The organic layer was washed with brine, dried
over MgSO4, and concentrated under reduced pressure. The residue
was purified by silica gel chromatography.
(4-Fluorophenyl)-4-tolylacetylene (3j). 70% as a white solid;
mp 91-92 °C; IR (KBr) 2216 cm-1; 1H NMR (CDCl3) δ: 2.36 (s,
3H), 6.96-7.08 (m, 2H), 7.15 (d, J ) 7.84 Hz, 2H), 7.41 (d, J )
7.65 Hz, 2H), 7.42-7.52 (m, 2H); 13C NMR (CDCl3) δ 21.5, 87.6,
89.2 (d, J ) 1.1 Hz), 115.6 (d, J ) 22.1 Hz), 119.6 (d, J ) 3.5
Hz), 120.0, 129.1, 131.4, 133.4 (d, J ) 8.3 Hz), 138.5, 162.4 (d, J
) 249.2 Hz); EI-MS m/ z (rel. intens.): 210 (M+, 100); HRMS
(FAB-MS) m/z calcd for C15H11F 210.0845, found 210.0840.
(2-Fluorophenyl)-4-tolylacetylene (3l). 95% as a white solid;
mp 55-56 °C; IR (KBr) 2219 cm-1; 1H NMR (CDCl3) δ 2.36 (s,
3H), 7.05-7.19 (m, 4H), 7.22-7.35 (m, 1H), 7.41-7.56 (m, 3H);
13C NMR (CDCl3) δ 21.5, 82.0, 94.6 (d, J ) 3.2 Hz), 112.1 (d, J
) 15.6 Hz), 115.5 (d, J ) 21.0 Hz), 119.8, 123.9 (d, J ) 3.7 Hz),
129.1, 129.7 (d, J ) 8.0 Hz), 131.6, 133.4 (d, J ) 0.9 Hz), 138.8,
162.6 (d, J ) 251.3 Hz); EI-MS m/z (rel. intens.): 210 (M+, 100);
HRMS (FAB-MS) m/z calcd for C15H11F 210.0845, found 210.0833.
6-p-Tolylhex-5-yl-1-ol (3m). 73% as a colorless liquid; IR (KBr)
2231 and 3357 cm-1; 1H NMR (CDCl3) δ 1.46 (s, 1H), 1.58-1.82
(m, 4H), 2.33 (s, 3H), 2.45 (t, J ) 6.6 Hz, 2H), 3.71 (t, J ) 6.1
Hz, 2H), 7.08 (d, J ) 7.9 Hz, 2H), 7.28 (d, J ) 8.0 Hz, 2H); 13C
NMR (CDCl3) δ 19.2, 21.4, 25.0, 31.9, 62.5, 80.9, 89.0, 120.7,
128.9, 131.4, 137.5; EI-MS m/z (rel. intens.): 188 (M+, 15); HRMS
(FAB-MS) m/z calcd for C13H16O 188.1201, found 188.1205.
Hiyama Cross-Coupling Reaction of Aryl Bromides with
Siloxanes (Table 4). Under an atmosphere of argon, siloxane (1.0
mmol) and TBAF (1.0 mmol) in THF (1 M, 1 mL) were added to
the mixture of aryl bromide (0.5 mmol), PdCl2 (0.02 mmol), and
ligand (0.03 mmol) in PhMe (1.5 mL) at room temperature. The
mixture was stirred at 80 °C. After 3 h, the mixture was diluted
with ethyl acetate and water. The organic layer was washed with
brine, dried over MgSO4, and concentrated under reduced pressure.
The residue was purified by silica gel chromatography.
a Reaction conditions: aryl bromide (0.5 mmol), siloxane (1.0 mmol),
TBAF (1.0 mmol) in THF (1 M, 1 mL), PhMe (1.5 mL), PdCl2 (0.02 mmol),
ligand 1d (0.03 mmol). b Isolated yields. c This reaction used 3 equiv of
phenyl(triethoxy)silane.
MS m/z (rel. intens.): 290 (M+, 24); HRMS (FAB-MS) m/z calcd
for C18H18N4 290.1531, found 290.1531; X-ray diffraction analysis
data of 1d (Figure S1 of the Supporting Information). Yellow cubic
crystals from hexane-chloroform, monoclinic space group P21/c,
a ) 12.9030(4) Å, b ) 10.4680(3) Å, c ) 11.7384(4) Å, R ) 90°,
â ) 112.6840(10)°, γ ) 90°, V ) 1462.84(8) Å3, Z ) 4, F )
1.318 g/cm3, µ (Mo KR) ) 0.81 cm-1. The structure was solved
by the direct method of full matrix least-squares, where the final R
and Rw were 0.051 and 0.168 for 5462 reflections, respectively.
Preparation of N-(Indolin-1-yl)(pyridin-2-yl)methanimine
(2b). Under an atmosphere of argon, a solution of N-aminoindoline
(0.067 g, 0.5 mmol) in MeOH (1.5 mL) was added to 2-pyridin-
Acknowledgment. This work was supported in part by a
Grant-in-Aid for Scientific Research (No. 16750070) from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan.
Supporting Information Available: ORTEP drawing 1d
(Figure S1), 1H and 13C NMR spectra of all compounds, and X-ray
crystallographic file (CIF) for 1d. This material is available free
of charge via the Internet at http://pubs.acs.org.
JO061734I
9502 J. Org. Chem., Vol. 71, No. 25, 2006