CuI-catalyzed Suzuki-Miyaura and Sonogashira cross-coupling reactions using DABCO as ligand

Article abstract of DOI:10.1021/Jo0623742

In the presence of TBAB, CuI-catalyzed Suzuki-Miyaura cross-coupling of vinyl halides and aryl halides with arylboronic acids was conducted smoothly to afford the corresponding diarylethenes and polyaryls in moderate to good yields using DABCO (1,4-diazabicyclo[2.2.2]octane) as the ligand. We also found that the inexpensive CuI/DABCO catalytic system was effective for Sonogashira cross-couplings of aryl halides and vinyl halides. A variety of aryl halides and vinyl halides including activated aryl chlorides underwent the coupling with terminal alkynes in moderate to excellent yields.

Full text of DOI:10.1021/Jo0623742

CuI-Catalyzed Suzuki-Miyaura and Sonogashira Cross-Coupling
Reactions Using DABCO as Ligand
Jin-Heng Li,* Ji-Lan Li, De-Ping Wang, Shao-Feng Pi, Ye-Xiang Xie, Man-Bo Zhang, and
Xi-Chao Hu
Key Laboratory of Chemical Biology & Traditional Chinese Medicine Research (Ministry of Education),
College of Chemistry and Chemical Engineering, Hunan Normal UniVersity, Changsha 410081, China
jhli@hunnu.edu.cn
ReceiVed NoVember 17, 2006
In the presence of TBAB, CuI-catalyzed Suzuki-Miyaura cross-coupling of vinyl halides and aryl halides
with arylboronic acids was conducted smoothly to afford the corresponding diarylethenes and polyaryls
in moderate to good yields using DABCO (1,4-diazabicyclo[2.2.2]octane) as the ligand. We also found
that the inexpensive CuI/DABCO catalytic system was effective for Sonogashira cross-couplings of aryl
halides and vinyl halides. A variety of aryl halides and vinyl halides including activated aryl chlorides
underwent the coupling with terminal alkynes in moderate to excellent yields.
Introduction
transition metal catalyst complexes,2,4-7 in particular, copper,
to replace the palladium. However, only a few copper-catalyzed
Both the Suzuki-Miyaura and Sonogashira cross-coupling
reactions have proven to be two important transformations, as
the resulting biaryl and acetylenic products are extremely
valuable intermediates in organic synthesis as well as important
units found in a tremendous range of natural products and
bioactive molecules.1-3 The original and general Suzuki-
Miyaura and Sonogashira coupling procedures involves the use
of palladium-ligand (often a phosphine ligand) complexes as
catalysts.1 Nevertheless, the high price of Pd renders commercial
processes based on Pd less attractive unless extremely active
and/or recyclable catalysts are available. For these reasons, much
recent attention has been attracted on employing less expensive
(3) (a) Viehe, H. G. Chemistry of Acetylene; Marcel Dekker: New York,
1969. (b) Bohlmann, F.; Burkhart, F. T.; Zero, C. Naturally Occurring
Acetylenes; Academic Press: London and New York, 1973. (c) Traha-
novsky, W. S. Oxidation in Organic Chemistry; Academic Press: New York
and London, 1973; Vol. 5-B. (d) Hudlicky, M. Oxidation in Organic
Chemistry, ACS Monograph 186; American Chemical Society: Washington
DC, 1990. (e) Bringmann, G.; Gunther, C.; Ochse, M.; Schupp O.; and
Tasler, S. In Progress in the Chemistry of Organic Natural Products; Herz,
W., Falk, H., Kirby, G. W., Moore, R. E., Eds.; Springer: New York, 2001;
Vol. 82, pp 1-293.
(4) For representative papers on the nickel-catalyzed Suzuki-Miyaura
cross-coupling reaction, see: (a) Saito, S.; Ohtani, S.; Miyaura, N. J. Org.
Chem. 1997, 62, 8024. (b) Zim, D.; Lando, V. R.; Dupond, J.; Monteiro,
A. L. Org. Lett. 2001, 3, 3049. (c) Percec, V.; Golding, G. M.; Smidrkal,
J.; Weichold, O. J. Org. Chem. 2004, 69, 3447.
(5) For representative papers on the nickel-catalyzed Sonogashira cross-
coupling reaction, see: (a) Wang, L.; Li, P.; Zhang, Y. Chem. Commun.
2004, 514. (b) Beletskaya, I. P.; Latyshev, G. V.; Tsvetkov, A. V.; Lukashev,
N. V. Tetrahedron Lett. 2003, 44, 5011.
(6) For papers on the copper-catalyzed Suzuki-Miyaura cross-coupling
reaction, see: (a) Thathagar, M. B.; Beckers, J.; Rothenberg, G. J. Am.
Chem. Soc. 2002, 124, 11858. (b) Thathagar, M. B.; Beckers, J.; Rothenberg,
G. AdV. Synth. Catal. 2003, 345, 979.
(7) For papers on the Sonogashira cross-coupling reaction catalyzed by
a catalytic amount of copper, see: (a) Okuro, K.; Furuune, M.; Enna, M.;
Miura, M.; Nomura, M. J. Org. Chem. 1993, 58, 4716. (b) Gujadhur, R.
K.; Bates, C. G.; Venkataraman, D. Org. Lett. 2001, 3, 4315. (c) Thathagar,
M. B.; Beckers, J.; Rothenberg, G. Green Chem. 2004, 6, 215. (d) Ma, D,
Liu, F. Chem. Commun. 2004, 1934. (e) Wang, Y. F.; Deng, W.; Liu, L.;
Guo, Q. X. Chin. Chem. Lett. 2005, 16, 1197. (f) Saejueng, P.; Bates, C.
G.; Venkataraman, D. Synthesis 2005, 1706. (g) Xie, Y.-X.; Deng, C.-L.;
Pi, S.-F.; Li, J.-H.; Yin, D.-L. Chin. J. Chem. 2006, 24, 1290.
(1) For reviews, see: (a) Bringmann, G.; Walter, R.; Weirich, R. Angew.
Chem., Int. Ed. Engl. 1990, 29, 977-991. (b) Miyaura, N.; Suzuki, A. Chem.
ReV. 1995, 95, 2457-2483. (c) Diederich, F.; Stang, P. J. Metal-Catalyzed
Cross-coupling Reactions; Wiley-VCH: Weinheim, 1998. (d) Miyaura, N.
Cross-Coupling Reaction; Springer: Berlin, 2002. (e) Negishi, E. Handbook
of Organopalladium Chemistry for Organic Synthesis; Wiley-Inter-
science: New York, 2002. (f) Yong, B. S.; Nolan, S. P. Chemtracts: Org.
Chem. 2003, 205. (g) Tang, S.; Liang, Y.; Liu, W.-J.; Li, J.-H. Chin. J.
Org. Chem. 2004, 24, 1133. (h) de Meijere, A.; Diederich, F. Metal-
Catalyzed Cross-Coupling Reactions; Wiley-VCH: Weinheim, 2004.
(2) For special reviews on copper-catalyzed cross-couplings, see: (a)
Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int Ed. 2000,
39, 2632. (b) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M.
Chem. ReV. 2002, 102, 1359. (c) Ley, S. V.; Thomas, A. W. Angew. Chem.,
Int. Ed. 2003, 42, 5400. (d) Beletskaya, I. P.; Cheprakov, A. V. Coord.
Chem. ReV. 2004, 248, 2337.
10.1021/jo0623742 CCC: $37.00 © 2007 American Chemical Society
Published on Web 02/08/2007
J. Org. Chem. 2007, 72, 2053-2057
2053

Li et al.
TABLE 1. Efficient CuI/DABCO-Catalyzed Suzuki-Miyaura
SCHEME 1
Cross-Couplings of Vinyl Halides with Arylboronic Acids in the
Presence of TBABa
Suzuki-Miyaura and Sonogashira cross-coupling procedures
exist.2,6,7 In 2002, a pioneering work on the copper-catalyzed
Suzuki-Miyaura coupling reaction was reported by Rothenberg
and co-workers.6 In the presence of copper or copper-based
nanocolloids, a variety of aryl halides coupled with phenylbo-
ronic acid efficiently in moderate to excellent yields. Neverthe-
less, only the couplings of aryl iodides were investigated when
the catalyst was copper alone.
Recently, copper (CuI or copper nanoclusters) has also
emerged as a catalyst of choice partly for the Sonogashira cross-
coupling reaction.7 In 1993, Miura and co-workers reported the
first catalytic Sonogashira cross-coupling between aryl iodides
with terminal alkynes using CuI/PPh3 as the catalytic system.7a
Subsequently, Venkataraman and co-workers found that 1,10-
phenanthroline was an effective ligand for the copper-catalyzed
couplings of aryl iodides and vinyl iodides with terminal
alkynes.7b,f Recently, Rothenberg applied copper nanoclusters
in the reaction and extended the scope to the activated aromatic
bromides without aid of any ligand.7c Ma and Liu have described
that the deactivated aryl bromides could undergo the coupling
smoothly using CuI as the catalyst and N,N-dimethylglycine as
the ligand.7d Very recently, we found that pyrimidines, in
particular 2-aminopyrimidine-4,6-diol, could promote the Cu-
(OAc)2-catalyzed couplings between aryl halides and terminal
alkynes under solvent-free and aerobic conditions, but only aryl
iodides and the activated aryl bromides were suitable substrates.7g
Although ethylenediamine combined with CuI was found to be
an effective catalytic system for the couplings of aryl iodides
and bromides, N1,N1,N2,N2-tetramethylethene-1,2-diamine, a
tertiary amine, provided rather poor results.7e Our recent results
showed that DABCO, another tertiary amine, was an efficient
ligand for the cross-coupling reactions using palladium8 or
copper9,10 as catalysts. Thus, we expected to extend the
application of the ligand in other copper-catalyzed procedures.
Indeed, DABCO was found to be an effective ligand for both
the Suzuki and Sonogashira cross-coupling reactions.12 Here,
we wish to report our results in detail (Scheme 1).10
a Unless otherwise indicated, the reaction conditions were as follows: 1
(0.3 mmol), 2 (0.4 mmol), CuI (10 mol %), DABCO (20 mol %), TBAB
(1 equiv), and Cs2CO3 (2 equiv) in DMF (3 mL) at 125-130 °C. b Isolated
yield. c Without TBAB. d Without DABCO. e Ratio of (E)-isomer/(Z)-isomer
was 15:1 determined by GC-MS. f Ratio of (E)-isomer/(Z)-isomer was
about 14:1 determined by GC-MS.
iodides and the activated aryl bromides with arylboronic acids
catalyzed by catalytic amounts of CuI and DABCO were carried
out smoothly in moderate to excellent yields. Although a
stoichiometric amount of CuI together with TBAB was neces-
sary for the couplings of the less activated aryl bromides,
satisfactory yields were still obtained. Encouraged by the results,
we decided to apply the CuI/DABCO system in coupling of
vinyl halides with arylboronic acids. As shown in Table 1,
treatment of 1-(2-iodovinyl)benzene (1a) with phenylboronic
acid (2a), CuI, and DABCO in 20 h afforded the corresponding
product 3aa in a moderate yield (entry 1). We were happy to
find that the yield of 3aa was enhanced to 83% when 1 equiv
of TBAB (n-Bu4NBr) was added (entry 2). However, the yield
of 3aa was reduced to 63% in the absence of DABCO (entry
3). Under the standard reaction conditions, a variety of other
vinyl halides 1b-e underwent the coupling with arylboronic
acids in moderate to good yields (entries 4-11). For example,
the reactions of 1-(2-bromovinyl)benzene (1d) with arylboronic
acids 2a and 2b were conducted smoothly to give the corre-
sponding products 3aa and 3ca in 67% and 50% yields,
respectively (entries 6 and 7). However, a trace amount of the
target product was isolated from the coupling substrate 1d with
the bulky boronic acid 2c (entry 8). It is noteworthy that 1-(1-
bromovinyl)benzene (1e) can be coupled with boronic acids 2a,
Results and Discussion
CuI/DABCO-Catalyzed Suzuki-Miyaura Cross-Coupling
Reaction. In our preliminary communication,10 couplings of aryl
(8) For papers on DABCO as the ligand for the palladium-catalyzed
cross-coupling reactions, see: (a) Li, J.-H.; Liu, W.-J. Org. Lett. 2004, 6,
2809. (b) Li, J.-H.; Zhang, X.-D.; Xie, Y.-X. Synthesis 2005, 804. (c) Li,
J.-H.; Liu, W.-J.; Xie, Y.-X. J. Org. Chem. 2005, 70, 5409. (d) Li, J.-H.;
Liang, Y.; Wang, D.-P.; Liu, W.-J.; Xie, Y.-X.; Yin, D.-L. J. Org. Chem.
2005, 70, 2832. (e) Li, J.-H.; Wang, D.-P.; Xie, Y.-X. Synthesis 2005, 2193.
(f) Li, J.-H.; Deng, C.-L.; Liu, W.-J.; Xie, Y.-X. Synthesis 2005, 3039. (g)
Li, J.-H.; Hu, X.-C.; Liang, Y.; Xie, Y.-X. Tetrahedron 2006, 62, 31. (h)
Li, J.-H.; Zhu, Q.-M.; Xie, Y.-X. Tetrahedron 2006, 62, 10888. (i) Li, J.-
H.; Hu, Q.-C.; Xie, Y.-X. Tetrahedron Lett. 2006, 47, 9239.
(9) For a paper on the use of the CuI/DABCO catalytic system for Heck
reaction, see: Li, J.-H.; Wang, D.-P.; Xie, Y.-X. Tetrahedron Lett. 2005,
46, 4941.
(10) For a preliminary communication, see: Li, J.-H.; Wang, D.-P. Eur.
J. Org. Chem. 2006, 2063.
(11) The loading level of Pd is 6.27 × 10-5 mmol/mmol CuI, which
was determined by means of an inductively coupled plasma-atomic emission
spectrometer (ICP-AES).
(12) Stephens, R. D.; Castro, C. E. J. Org. Chem. 1963, 28, 2163.
2054 J. Org. Chem., Vol. 72, No. 6, 2007

CuI-Catalyzed Suzuki-Miyaura and Sonogashira Cross-Coupling Reactions
TABLE 3. CuI/DABCO-Catalyzed Sonogashira Cross-Coupling
SCHEME 2
Reactions of Aryl Halides (1) with Terminal Alkynes (4)a
TABLE 2. CuI-Catalyzed Sonogashira Cross-Coupling Reaction of
1-Iodo-4-methoxybenzene (1j) with Phenylacetylene (4a)a
entry
ligand
base
solvent
time (h)
yieldb (%)
1
2c
3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
Et3N
DMF
DMF
DMF
DMF
DMF
DMF
DMF
MeCN
DMF
DMF
DMF
12
6
6
6
12
6
6
6
12
6
6
trace
65
95
96
45
56
80
55
trace
98
DABCO
DABCO
DABCO
Et3N
TMEDA
HMPA
DABCO
DABCO
DABCO
DABCO
4d
5
6
7
8
9e
10
11
61
a Unless otherwise indicated, the reaction conditions were as follows:
1j (0.5 mmol), 4a (0.6 mmol), CuI (10 mol %), ligand (20 mol %), K2CO3
(2 equiv), and solvent (3 mL) at 135-140 °C under N2. b Isolated yield.
c DABCO (10 mol %). d DABCO (40 mol %). e At 100 °C. f Cs2CO3 (2
equiv) instead of K2CO3.
2b, and 2d, respectively, in good yields (entries 9-11).
Unfortunately, 1-bromo-1,2,2-triphenylethene (1f) was not a
suitable substrate under the standard conditions (entry 12).
As demonstrated in Scheme 2, synthesis of polyaryls was
then tested under the standard conditions. To our delight,
diiodobenznes 1g,h and triiodobenzene 1i could selectively
undergo the coupling with phenylboronic acid (2a) in moderate
yields. In the presence of CuI, DABCO and TBAB, the reac-
tion of 1,3-diiodobenzene (1g) or 1,4-diiodobenzene (1h) with
2a provided the target products 3ga and 3ha in 75% and
80% yields, respectively. It was interesting to reveal that the
coupling of 1,3,5-triiodomobenzene (1i) with 2a was performed
chemoselectively to afford the desired product 3ka in a 48%
yield.
a Reaction conditions: 1 (0.5 mmol), 4 (0.6 mmol), CuI (10 mol %),
DABCO (20 mol %), Cs2CO3 (2 equiv), and DMF (3 mL) at 135-140 °C
under N2. b Isolated yield. c TBAB (1 equiv).
SCHEME 3
CuI/DABCO-Catalyzed Sonogashira Cross-Coupling Re-
action. Subsequently, we tried to apply the CuI/DABCO system
in Sonogashira cross-coupling reaction, and the results are
summarized in Tables 2 and 3 and Scheme 3. Initially, the
catalytic activity of CuI/DABCO was tested in the Sonogashira
reaction between 1-iodo-4-methoxybenzene (1j) and pheny-
lacetylene (4a) (Table 1). It was found that the combination of
CuI and DABCO was an effective catalytic system for the
coupling of iodide 1j with 4a, and the amount of DABCO
affected the reaction to some extent. Without the aid of any
ligands, treatment of substrate 1j with 4a, CuI (10 mol %), and
K2CO3 (2 equiv) afforded a trace amount of the corresponding
coupled product 5ja, whereas the yield of 5ja was enhanced
sharply to 95% when 20 mol % of DABCO was added (entries
J. Org. Chem, Vol. 72, No. 6, 2007 2055

Li et al.
TABLE 4. CuI/DABCO-Catalyzed Sonogashira Cross-Couplings
1 and 2). Identical results were observed when DABCO was
further increased to 40 mol % (entry 4). Other tertiary amine
ligands, such as Et3N, TMEDA, and HMPA, were less effective
than DABCO (entries 3 and 5-7). Another solvent, MeCN, was
then examined, and it was less effective than DMF (entries 3
and 8). It is noteworthy that the reaction temperature plays a
crucial role in the reaction. Trace amount of 5ja was isolated
when the reaction was conducted at 100 °C (entry 9). Finally,
two other bases were evaluated (entries 10 and 11). Results
identical to those of entry 3 were observed using Cs2CO3 as
the base, but only a moderate yield of 5ja was isolated when
Et3N, an organic base, was used.
of Vinyl Halides (1) with Terminal Alkynes (4) in the Presence of
TBABa
As demonstrated in Table 2, CuI/DABCO as the catalytic
system for the Sonogashira reactions of various aryl halides
1j-u with alkynes 4a-e proved exceptionally active. Treatment
of aryl iodides 1j-o with alkynes 4a-c, 10 mol % of CuI, 20
mol % of DABCO, and 2 equiv of Cs2CO3 provided moderate
to excellent yields (entries 1-9). Under the same reaction
conditions, a number of aryl bromides were found to be quite
reactive. In the presence of 10 mol % of CuI, 20 mol % of
DABCO, and 2 equiv of Cs2CO3, the couplings of bromides
1p-r with alkynes 4a, 4b, 4d, and 4e were carried out smoothly
to afford the corresponding cross-coupled products in good
yields (entries 10-16). For example, treatment of 1p with
alkynes 4a, 4b, 4d, or 4e gave the corresponding products 6ka,
6kb, 6pd, and 6pe in 95%, 85%, 86%, and 88% yields,
respectively (entries 10-13). It is interesting to note that the
CuI/DABCO catalytic system is also effective for the activated
aryl chloride (1s). A moderate yield of the desirable product
5ka was isolated from the reaction of substrate 1s with 4a
performed under 10 mol % of CuI, 20 mol % of DABCO, and
2 equiv of Cs2CO3 (55% yield, entry 17). We also found that
TBAB (n-Bu4NBr) could promote the reaction. The yield of
5ka was increased sharply to 92% when 1 equiv of TBAB was
presented (entry 18). The reaction of 1s with 4b also proceeded
smoothly to produce 51% yield of the corresponding product
5kb under the same conditions (entry 19). However, the CuI/
DABCO catalytic system was ineffective for the reaction of
the other aryl chlorides 1t and 1u even in the presence of 1
equiv of TBAB (entries 20 and 21).
As shown in Scheme 3, coupling of 2-iodophenol (1v) with
alkynes 4a or 4b gave the corresponding benzo[b]furans 5va
and 5vb in the desired yields using CuI/DABCO as the catalytic
system (eq 1 in Scheme 3).9d However, only 2-phenylethyny-
laniline (5wa) was observed in an 89% yield rather than
2-phenylindole (6) when 2-iodoaniline (1w) was reacted with
4a (eqs 2 and 3).
In the presence of CuI and DABCO, the Sonogashira
reactions of vinyl halides with terminal alkynes were also carried
out smoothly in good yields, and the results are summarized in
Table 4. The results indicated that TBAB was also required to
improve the couplings of vinyl halides (entries 1 and 2). (Z)-
1-(2-Iodovinyl)benzene (1a) was reacted with phenylactylene
(4a), CuI, and DABCO to generate the corresponding product
5aa in a 45% yield, whereas the yield of 5aa was increased to
80% in the presence of TBAB. Under the same conditions,
substrates 1b and 1d underwent coupling with alkynes in good
yields (entries 3-5). Bromide 1d coupled with 4a or 4b, for
example, was conducted smoothly in 83% and 65% yields,
respectively (entries 4 and 5). Unfortunately, coupling of another
vinyl bromide 1e with 4a was unsuccessful (entry 6).
a Unless otherwise indicated, the reaction conditions were as follows: 1
(0.3 mmol), 4 (0.4 mmol), CuI (10 mol %), DABCO (20 mol %), TBAB
(1 equiv), and Cs2CO3 (2 equiv) in DMF (3 mL) at 135-140 °C under N2
atmosphere. b Isolated yield. c Without TBAB. d Ratio of (E)-isomer/(Z)-
isomer was 15:1 determined by GC-MS. e Ratio of (E)-isomer/(Z)-isomer
was 16:1 determined by GC-MS.
SCHEME 4
Suzuki-Miyaura cross-coupling (Scheme 4).11 Although there
are 6.27 × 10-5 mmol palladium species in per mmol the
commercially available CuI (purity: 98%), the following results
showed that the key catalyst is CuI. As demonstrated in Scheme
4, identical results were observed using 99.999% purity of CuI
to those of the commercially available CuI (run 1). We then
examined the Suzuki-Miyaura cross-coupling of substrate 1d
with 2a using Pd(OAc)2 as the catalyst alone. It was interesting
to find that bromide 1d performed the coupling with 2a, Pd-
(OAc)2 (0.7 mol %), DABCO (1.4 mol %), TBAB (1 equiv),
and Cs2CO3 (2 equiv) at 125-130 °C in DMF (3 mL) for 5 h
to provide the target product 3aa in 80% yield (run 2). However,
a rather low yield of 3aa was isolated after 18 h at a loading of
0.0007 mol % Pd (the loading of Pd in 10 mol % CuI; run 3).
A working mechanism was proposed as outlined in Scheme
5 for the copper-catalyzed Suzuki cross-coupling reaction on
the basis of the previously reported mechanism.1,2,7,12 The
reaction of intermediate 7, a four-centered transition state
proposed by Castro and Stephens,12 with aryl halides or vinyl
halides afforded intermediate 8. Then transmetalation of inter-
mediate 8 with arylboronic acid occurred to form intermediate
9, followed by a reductive elimination of intermediate 9, giving
the coupled product 3 and regenerated the active copper(I)
complex 7. We deduced that mechanism of the present Sono-
Three control reactions of substrate 1d with phenylboronic
acid 2a were conducted to explore the mechanism of the present
2056 J. Org. Chem., Vol. 72, No. 6, 2007

CuI-Catalyzed Suzuki-Miyaura and Sonogashira Cross-Coupling Reactions
SCHEME 5
(the indicated amount), CuI (10 mol %), DABCO (20 mol %), Cs2-
CO3 (2.0 equiv), TBAB (1 equiv), and DMF (3 mL) in a Schlenk
tube was stirred under N2 at 125-130 °C (oil bar temperature) for
the desired time (indicated in Table 1 and Schemes 2 and 4) until
complete consumption of starting material as monitored by TLC.
After the mixture was filtered and evaporated, the residue was
purified by flash column chromatography (hexane or hexane/ethyl
acetate) to afford the corresponding coupled products.
Typical Experimental Procedure for the CuI/DABCO-Catalyzed
Sonogashira-Type Cross-Coupling Reactions. A mixture of aryl
halide 1 (the indicated amount), alkyne 4 (the indicated amount),
CuI (10 mol %), DABCO (20 mol %), Cs2CO3 (2.0 equiv), and
DMF (3 mL) in a Schlenk tube was stirred under N2 at 135-140
°C (oil bar temperature) for the desired time (indicated in Tables 2
and 3 and Scheme 3) until complete consumption of starting
material as monitored by TLC. After the mixture was filtered and
evaporated, the residue was purified by flash column chromatog-
raphy (hexane or hexane /ethyl acetate) to afford the corresponding
coupled products.
2-Octylbenzofuran (5vb): 1H NMR (400 MHz, CDCl3) δ 7.48
(d, J ) 8.0 Hz, 1H), 7.41 (d, J ) 8.4 Hz, 1H), 7.22-7.15 (m, 2H),
6.37 (s, 1H), 2.76 (t, J ) 7.6 Hz, 2H), 1.77-1.70 (m, 2H), 1.41-
1.27 (m, 10H), 0.88 (t, J ) 6.8 Hz, 3H); 13C NMR (100 MHz,
CDCl3) δ 159.8, 154.6, 129.0, 123.0, 122.3, 120.1, 110.7, 101.7,
31.8, 29.3, 29.2, 28.4, 27.7, 22.7, 14.1; LRMS (EI, 70 eV) m/z 230
(M+, 64), 187 (11), 173 (8), 145 (13), 131 (100); HRMS (EI) for
C16H22O (M+) calcd 230.1680, found 230.1678.
gashira cross-coupling is similar to Miura’s mechanism. Study
of the accurate mechanism is in progress.
Conclusion
In summary, an inexpensive and highly efficient CuI/DABCO
system for the cross-coupling reactions of aryl halides and vinyl
halides with arylboronic acids or terminal alkynes has been
developed. Compared with previous reports, several interesting
features are apparent on the basis of the present results, including
the following: (1) The catalytic system is efficient and general
for a variety of aryl halides and vinyl halides. (2) Several
functional groups, such as amino, methoxy, and fluoro groups,
could be tolerated well. (3) The inexpensive CuI/DABCO
system emerged as an attractive alternative to the palladium/
ligand catalyst systems. Further efforts to extend the application
of the system in other coupling transformations are underway
in our laboratory.
Acknowledgment. We thank the National Natural Science
Foundation of China (No 20572020 and 20335020), Fok Ying
Dong Education Foundation (No. 101012), the Key Project of
Chinese Ministry of Education (No. 206102), Scientific Research
Fund of Hunan Provincial Education Department (No. 05B038),
Hunan Provincial Natural Science Foundation of China (No.
05JJ1002), and Specialized Research Fund for the Doctoral
Program of Higher Education (20060542007) for financial
support.
Experimental Section
Supporting Information Available: Analytical data and spectra
(1H and 13C NMR) for all products 3 and 5. This material is
available free of charge via the Internet at http://pubs.acs.org.
Typical Experimental Procedure for the CuI/DABCO-
Catalyzed Suzuki-Type Cross-Coupling Reactions. A mixture
of vinyl or aryl halide 1 (the indicated amount), boronic acid 2
JO0623742
J. Org. Chem, Vol. 72, No. 6, 2007 2057