Formation of arylboronates by a Cul-catalyzed coupling reaction of pinacolborane with aryl iodides at room temperature

Article abstract of DOI:10.1021/ol052633u

The coupling reaction of pinacolborane with aryl iodides under the catalysis of 10 mol % Cul and the action of sodium hydride in THF works at room temperature to provide corresponding arylboronates in good yields. Aryl bromides give poor conversion under these reaction conditions.

Full text of DOI:10.1021/ol052633u

ORGANIC
LETTERS
2
006
Vol. 8, No. 2
61-263
Formation of Arylboronates by a
CuI-Catalyzed Coupling Reaction of
Pinacolborane with Aryl Iodides at
Room Temperature
2
Wei Zhu and Dawei Ma*,‡
†
Department of Chemistry, Fudan UniVersity, Shanghai 200433, China, and State Key
Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of
Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032,
China
madw@mail.sioc.ac.cn
Received October 30, 2005
ABSTRACT
The coupling reaction of pinacolborane with aryl iodides under the catalysis of 10 mol % CuI and the action of sodium hydride in THF works
at room temperature to provide corresponding arylboronates in good yields. Aryl bromides give poor conversion under these reaction conditions.
II
Arylboronic acids and their esters have found increasing
application in organic synthesis and medical treatments.
is assumed to proceed through an Ar-Pd -B(OR)
2
inter-
1
mediate, which results from the ligand exchange of Ar-
Pd -X, an oxidative addition product of Pd(0) with aryl
II
Traditionally, they were prepared by the reaction of trialkyl
2
3
borates with Grignard or lithium reagents. The drawback
halides, with the boryl anion analogue.
of this methodology is the limitation of substrates available.
This prompted research that lead to the Miyaura-Masuda
reaction, in which the arylboronates were assembled via a
Pd-catalyzed cross-coupling of aryl halides with pinacol-
Recently, we have demonstrated that CuI/L-proline is a
powerful catalytic system for coupling reactions of aryl
5a
halides with some nucleophiles such as azide and methane-
5
b
sulfinate. We envisaged that their possible mechanisms
might be similar to that of the Miyaura-Masuda reaction,
and therefore, a CuI-catalyzed coupling reaction of aryl
halides with pinacolborane was explored. Herein, we wish
to disclose our results.
borane or dialkoxyborane.3,4 Mechanistically, this reaction
†
Fudan University.
Shanghai Institute of Organic Chemistry.
‡
(
1) For reviews, see: (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95,
457. (b) Soloway, A. H.; Tjarks, W.; Barnum, B. A.; Rong, F.-G.; Barth,
R. F.; Codogni, I. M.; Wilson, J. G. Chem. ReV. 1998, 98, 1515.
2) (a) Wong, K.-T.; Chien, Y.-Y.; Liao, Y.-L.; Lin, C.-C.; Chou, M.-
Initially, our experiment was conducted by refluxing a
mixture of 4-iodoanisole 1a, pinacolborane 2, 10 mol % CuI,
2
(
2
0 mol % L-proline sodium salt, and triethylamine in THF.
Y.; Leung, M.-K. J. Org. Chem. 2002, 67, 1041. (b) Diorazio, L. J.;
Widdowson, D. A.; Clough, J. M. Tetrahedron 1992, 48, 8073 and
references therein.
At this time, triethylamine was used as a base, as in the case
3
of the Miyaura-Masuda reaction. However, no desired
(
3) (a) Ishiyama, T.; Murata, M.; Miyaura, N. J. Org. Chem. 1995, 60,
coupling product was determined from this reaction system
7
6
2
508. (b) Murata, M.; Watanabe, S.; Masuda, Y. J. Org. Chem. 1997, 62,
458. (c) Murata, M.; Oyama, T.; Watanabe, S.; Masuda, Y. J. Org. Chem.
000, 65, 164.
(5) (a) Zhu, W.; Ma, D. Chem. Commun. 2004, 888. (b) Zhu, W.; Ma,
D. J. Org. Chem. 2005, 70, 2696. For other studies on amino-acid-promoted
Ullmann-type reactions from our group, see: (c) Cai, Q.; Zhu, W.; Zhang,
H.; Zhang, Y.; Ma, D. Synthesis 2005, 496. (d) Zhang, H.; Cai, Q.; Ma, D.
J. Org. Chem. 2005, 70, 5164. (e) Pan, X.; Cai, Q.; Ma, D. Org. Lett. 2004,
6, 1809. (f) Ma, D.; Liu, F. Chem. Commun. 2004, 1934. (g) Ma, D.; Cai,
Q. Org. Lett. 2003, 5, 3799.
(4) For recent studies on cross-coupling reactions of aryl halides or
triflates with alkoxydiboron or dialkoxyborane, see: (a) Melaimi, M.;
Mathey, F.; Floch, P. L. J. Organomet. Chem. 2001, 640, 197. (b) Ishiyama,
T.; Ishida, K.; Miyaura, N. Tetrahedron 2001, 57, 9813. (c) F u¨ rstner, A.;
Seidel, G. Org. Lett. 2002, 4, 541. (d) Doux, M.; M e´ zailles, N.; Melaimi,
M.; Ricard, L.; Floch, P. L. Chem. Commun. 2002, 1566.
1
0.1021/ol052633u CCC: $33.50
© 2006 American Chemical Society
Published on Web 12/23/2005

Table 1. CuI-Catalyzed Cross-Coupling Reaction of
-Iodoanisole 1a with Pinacolborane 2a
Table 2. CuI-Catalyzed Cross-Coupling Reaction of Aryl
Iodides with Pinacolboranea
4
entry
base
Et3N
additiveb temp (°C)/time (h) yield (%)c
1
2
3
4
5
6
7
8
9
A
A
B
C
70/24
70/24
70/24
70/24
70/4
0
10
11
12
24
t-BuOK
t-BuOK
t-BuOK
t-BuOK
Cs2CO3
NaHMDS
NaH
70/24
70/24
70/4
22
trace
58
NaH
25/4
75
a
Reaction conditions: 4-iodoanisole 1a (1 mmol), pinacolborane 2 (1.5
mmol), base (1.5 mmol), CuI (0.1 mmol), additive (0.2 mmol), THF (4
b
mL). Additive: A, L-proline sodium salt; B, N-methylglycine sodium salt;
c
C, N,N-dimethylglycine sodium salt. Isolated yield.
(Table 1, entry 1). We reasoned that triethylamine might be
too weak a base for this reaction, and therefore, some
stronger bases were attempted. To our delight, when t-BuOK
was employed, the desired coupling product 3a was isolated
although the yield was only 10% (entry 2). Changing the
additive to N-methylglycine sodium salt or N,N-dimethyl-
glycine sodium salt failed to improve the reaction yields
(entries 3 and 4), whereas deletion of the additive gave a
better yield (entry 5). These results indicated that the amino
acid additives were useless for the present coupling reaction.
For other bases tested, Cs CO delivered a yield similar to
2 3
that of t-BuOK and NaHMDS provided a trace of the
coupling product (entries 6 and 7). However, when sodium
hydride was used, the yield jumped to 58% under the same
reaction temperature (entry 8). Further investigations dem-
onstrated that when this reaction was carried out at room
temperature a satisfactory coupling yield was obtained (entry
9).
With the above optimized reaction conditions in hand,6
the reaction scope was explored by varying the aryl iodides.
As shown in Table 2, it was found that both electron-rich
and electron-deficient aryl iodides were compatible with these
reaction conditions, providing the corresponding coupling
products in good yields (entries 2, 5, 8, and 9). The successful
couplings of 4-iodophenol, 2-methylphenyl iodide, and
naphthyl iodide with pinacolborane indicated that either a
free hydroxyl group or steric hindrance did not alter this
reaction process greatly (entries 2-4). In the case of 1,4-
diiodobenzene, mono-coupling product 3g was isolated in
a
Reaction conditions: aryl iodide 1 (2 mmol), pinacolborane 2 (3 mmol),
b
sodium hydride (3 mmol), CuI (0.2 mmol), THF (8 mL). Isolated yield.
c
mmol of sodium hydride was added. d The bis coupling product was
5
isolated in about 5% yield.
6
1% yield together with a bis-coupling product in about 5%
yield (entry 5). Good selectivity was seen when 4-bromo-
phenyl iodide was used, as only a mono-coupled product
3h was obtained (entry 6), which meant that coupling with
the C-I bond was significantly faster than that with the
C-Br bond. Noteworthy is that both 4-hydroxyphenylbor-
onate 3c and 4-iodophenylboronate 3g have not been
obtained via previous methods. Considering the fact that
their additional function groups are ready for further
transformations, this advantage may find special usage in
(6) The typical procedure for a CuI-catalyzed coupling reaction of aryl
iodide with pinacolborane is as follows: To a solution of aryl iodide (2
mmol), CuI (0.2 mmol), and sodium hydride (3 mmol) in THF was added
pinacolborane (3 mmol) via syringe under argon atmosphere. The resultant
mixture was stirred at room temperature until the aryl iodide disappeared,
as monitored by TLC. After the reaction was quenched by adding 10 mL
of saturated NH4Cl, the mixture was extracted with ethyl acetate. The
combined organic layers were washed with brine and dried over MgSO4.
The solution was concentrated and the residue was chromatographed, eluting
with 1:10 ethyl acetate/petroleum ether to afford arylboronate.
3
,4
262
Org. Lett., Vol. 8, No. 2, 2006

organic synthesis. In addition, a heteroaromatic iodide also
gave the corresponding coupling product 3k in 62% yield
Scheme 2
(entry 10).
The highly reductive ability of the combination of pina-
colborane and sodium hydride was found to be troublesome
for couplings of some functionalized aryl iodides. For
example, when 4-acylphenyl iodide was used, a reduction
product, R-hydroxy-4-iodophenylethane, was isolated in 77%
yield. This problem was simply solved by employing
protected 4-acylphenyl iodide 1m as a substrate, which
produced the desired arylboronate 3m in 76% yield (entry
11). Similarly, 4-methoxycarbonylphenyl iodide furnished
a reduction product, 4-iodobenzyl alcohol, in 69% yield, and
reaction of the tert-butyl ester 1n smoothly proceeded to
deliver the corresponding arylboronate 3n in 78% yield,
indicating that a bulky tert-butyl ester moiety could survive
under these reaction conditions (entry 12).
To explore the reaction scope further, a coupling reaction
of 4-bromoanisole with pinacolborane was tested. At room
temperature after 48 h, this reaction produced 3a in only
proposed catalytic cycles for Ullmann-type coupling reac-
5d,8
tions
and the Miyaura-Masuda reaction. Oxidative ad-
dition of CuI with an aryl iodide afforded a Cu(III)
intermediate 6, which reacted with pinacolborane 2 under
the assistance of sodium hydride to produce intermediate 7.
Reductive elimination of 7 would deliver the arylboronate
and regenerate the catalyst.
In conclusion, we have demonstrated here a CuI-catalyzed
cross-coupling reaction of aryl iodide with pinacolborane.
Although it requires more reactive sodium hydride as a base
and shows poor conversion for aryl bromides, its inexpensive
catalyst and room-temperature reaction condition, as well
as its suitability for assembling 4-hydroxyphenylboronate and
20% yield, with recovery of 61% of 4-bromoanisole (Scheme
1). Raising the reaction temperature to 70 °C did not give
Scheme 1
4
-iodophenylboronate, are attractive for practical usage. In
addition, the present results provided another new CuI-
catalyzed reaction, which should stimulate the investigations
on coupling reactions using CuI as a catalyst.8 Further
studies on the optimization of the reaction conditions to
expand the reaction scope are in progress.
a,b
Acknowledgment. The authors are grateful to the Chinese
Academy of Sciences, National Natural Science Foundation
of China (grants 20321202 and 20132030), and the Science
and Technology Commission of Shanghai Municipality
(grants 02JC14032 and 03XD14001) for their financial
support.
Supporting Information Available: Experimental pro-
cedures and copies of H NMR spectra for compounds 3
and 5. This material is available free of charge via the Internet
at http://pubs.acs.org.
increased conversion. Further experimentation is required to
overcome this problem.
1
To demonstrate the usage of the present coupling reaction
further, iodide 4 was prepared from L-phenylalanine accord-
ing to the known procedure. We were pleased to observe
that the coupling reaction of 4 with pinacolborane provided
arylboronate 5 in 71% yield (Scheme 1). It is notable that
some related arylboronates have already been used in
elaboration of natural products and phenylalanine deriva-
tives.7
OL052633U
(7) (a) Firooznia, F.; Gude, C.; Chan, K.; Marcopulos, N.; Satoh, Y.
Tetrahedron Lett. 1999, 40, 213. (b) Nakamura, H.; Fujiwara, M.;
Yamamoto, Y. Bull. Chem. Soc. Jpn. 2000, 73, 231. (c) Decicco, C. P.;
Song, Y.; Evans, D. A. Org. Lett. 2001, 3, 1029. (d) Deng, H.; Jung, J.-K.;
Liu, T.; Kuntz, K. W.; Snapper, M. L.; Hoveyda, A. H. J. Am. Chem. Soc.
2
003, 125, 9032.
Although a detailed mechanistic investigation of the
present reaction awaits further experimentation, tentative
proposals are depicted in Scheme 2, which relied on the
(8) (a) Ley, S. V.; Thomas, A. W. Angew. Chem., Int. Ed. 2003, 42,
400. (b) Beletskaya, I. P.; Cheprakov, A. V. Coord. Chem. ReV. 2004,
48, 2337. (c) Zhang, S.; Zhang, D.; Liebeskind, L. S. J. Org. Chem. 1997,
5
2
62, 2312.
Org. Lett., Vol. 8, No. 2, 2006
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