Rhodium-catalyzed cross-coupling of allyl alcohols with aryl- and vinylboronic acids in ionic liquids

Article abstract of DOI:10.1021/ol034067d

The direct coupling of aryl-and vinylboronic acids with allylic alcohols has been achieved in ionic liquids using a rhodium catalyst.

Full text of DOI:10.1021/ol034067d

ORGANIC
LETTERS
2003
Vol. 5, No. 6
893-895
Rhodium-Catalyzed Cross-Coupling
of Allyl Alcohols with Aryl- and
Vinylboronic Acids in Ionic Liquids
George W. Kabalka,* Gang Dong, and Bollu Venkataiah
Departments of Chemistry and Radiology, The UniVersity of Tennessee,
KnoxVille, Tennessee 37996-1600
kabalka@utk.edu
Received January 14, 2003
ABSTRACT
The direct coupling of aryl- and vinylboronic acids with allylic alcohols has been achieved in ionic liquids using a rhodium catalyst.
Ionic liquids, especially ambient-temperature ionic liquids
consisting of 1,3-dialkylimidazolium cations, have shown
great promise as environmentally benign reaction media
because of their negligible vapor pressure, as well as their
excellent chemical and thermal stabilities.1 Furthermore, their
compatibility with transition-metal catalysts and limited
miscibility with common solvents simplifies catalyst recy-
cling.
of atom economy,7 the ability to use allylic alcohols in
allylation reactions would be highly beneficial. However,
they are rarely used because hydroxide is a poor leaving
group. A few approaches have been reported, but they require
either severe reaction conditions or unique ligands.8
Boronic acids are widely used reagents in organic synthesis
because they are commercially available, stable, generally
nontoxic, and compatible with a variety of functional groups.
Coupling reactions of boronic acids with allyl halides3c and
esters4c are well-known, but to the best of our knowledge,
the direct coupling of boronic acids with allylic alcohols has
not been reported. In a continuation of our studies of boron
chemistry in ionic liquids,9 we wish to report the direct
allylation of cinnamyl alcohols using boronic acids catalyzed
by ligandless rhodium catalysts (Scheme 1).
Transition-metal-catalyzed allylic alkylation using π-allyl
complexes represents an important carbon-carbon bond-
forming reaction that is widely used for constructing complex
organic molecules.2 Allylic halides,3 carboxylates,4 carbon-
ates,5 phosphates,6 and related compounds are generally
utilized as allylation reagents. On the basis of the viewpoint
* To whom correspondence should be addressed.
(1) (a) Dupont, J.; Souza, R. F.; Suarez, A. Z. Chem. ReV. 2002, 102,
3667. (b) Welton, T. Chem. ReV. 1999, 99, 2071. (c) Sheldon, R. Chem.
Commun. 2001, 2399. (d) Wasserscheid, P.; Keim, W. Angew. Chem., Int.
Ed. 2000, 39, 3773.
Scheme 1. Cross-Coupling of Boronic Acid and Cinnamyl
Alcohol
(2) Tsuji, J. Transition Metal Reagents and Catalysts; Wiley: New York,
2000.
(3) (a) Sheffy, F. K.; Godschalx, J. P.; Stille, J. K. J. Am. Chem. Soc.
1984, 106, 4833. (b) Godschalx, J. P.; Stille, J. K. Tetrahedron Lett. 1980,
21, 2599. (c) Moreno-Nanas, M.; Pajuelo, F.; Pleixats, R. J. Org. Chem.
1995, 60, 2396.
(4) (a) Hayashi, T.; Kawasura, T.; Uozumi, Y. Chem. Commun. 1997,
561. (b) Miyaura, N.; Yamada, K.; Suginome, H.; Suzuki, A. J. Am. Chem.
Soc. 1985, 107, 972.
(5) Evans, P. A.; Nelson, J. D. J. Am. Chem. Soc. 1998, 120, 5581.
(6) (a) Okude, Y.; Hirano, S.; Hiyama, T.; Nozaki, H. J. Am. Chem.
Soc. 1977, 99, 3179. (b) Tanigawa, Y.; Nishimura, K.; Kawasaki, A.;
Murahashi, S. Tetrahedron Lett. 1982, 23, 5549.
Various rhodium catalysts, solvents, and reaction condi-
tions were examined using p-tolylboronic acid and cinnamyl
10.1021/ol034067d CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/22/2003

Table 1. Effect of Catalysts and Solvents on the Reaction of Cinnamyl Alcohol with p-Tolylboronic Acid
entry
catalysta
reaction media
T (°C)
reaction time (h)
isolated yield (%)
1
2
3
4
5
6
7
8
9
RhCl3‚xH2O
RhCl3‚xH2O
RhCl3‚xH2O
RhCl3‚xH2O
RhCl3‚xH2O
CH2Cl2
toluene
50
50
50
50
rt
50
50
50
50
50
50
50
5
12
5
2
12
2
2
2
1.5
2
2
10
10
trace
62
0
62
61
0
66
59
67
72
BmimBF4
BmimPF6
BmimPF6
BmimPF6
BmimPF6
BmimPF6
BmimPF6
BmimBF4
BmimPF6
BmimPF6
Rh(acac)(1,5-cyclooctadiene)Cl
Rh(PPh3)3Cl
RhCl3‚xH2O and KOAc (10 mol %)
RhCl3‚xH2O and CH3COOH (10 mol %)
RhCl3‚xH2O and HFb
RhCl3‚xH2O, CuI (10 mol %)
RhCl3‚xH2O, Cu(OAc)2 (10 mol %)
10
11
12
2
a 3 mol % of Rh catalyst used. b One equivalent of aqueous HF (48%) used.
alcohol as model substrates (Table 1). Dramatic differences
in yields were observed (Table 1, entries 1-4). 1-Butyl-3-
methylimidazolium hexafluorophosphate (BmimPF6) was
found to be the most effective solvent. No reaction was
observed in polar solvents such as water and DMF. Three
common rhodium catalysts were evaluated (Table 1, entries
4-7), and both Rh(I) and Rh(III) were found to be effective.
Although bases are commonly used in transition-metal-
catalyzed coupling reactions,10 they inhibited this reaction
(Table 1, entry 8). However, acids increased the reaction
rate (Table 1, entries 9 and 10). The addition of copper salts
such as cupric acetate enhanced reaction yields by ap-
proximately 10%. This effect has been observed previously.11
The highest yields were obtained using a mixture of RhCl3‚
xH2O (3 mol %) and Cu(OAc)2 (10 mol %) in BmimPF6 at
50 °C for 2 h.
To enhance the utility of the reaction, we evaluated a
variety of organoboronic acids (aryl, alkenyl, heteroaryl) and
allylic alcohols12 (Table 2). Electron-rich boronic acids
generated higher yields than electron-deficient boronic acids.
Steric factors also affected the yield. Ortho- and meta-
substituted arylboronic acids (Table 2, entries 9 and 10)
typically gave lower yields than the para-substituted aryl-
boronic acids. Sterically hindered alcohols (Table 2, entries
12 and 13) also led to lower yields. Aliphatic alcohols were
Table 2. Coupling of Organoboronic Acids with Allylic
Alcoholsa
yieldb
entry
boronic acid
p-tolyl
phenyl
p-methoxyphenyl
p-chlorophenyl
alcohol
(%)
1
2
3
4
5
6
7
8
9
10
11
12
13
cinnamyl
cinnamyl
cinnamyl
cinnamyl
72
65
76
41
78
0
50
33
55
61
52
60
65
p-methylthiophenyl cinnamyl
p-acylphenyl
trans-â-styrenyl
2-thiophene
o-tolyl
m-tolyl
1-naphthyl
p-tolyl
cinnamyl
cinnamyl
cinnamyl
cinnamyl
cinnamyl
a-methylcinnamyl
1,3-diphenyl-2-propen-1-ol
1,3-diphenyl-2-propen-1-ol
p-methoxyphenyl
a Reactions were carried out using RhCl3‚xH2O (3 mol %) and Cu(OAc)2
(10 mol %) in BmimPF6 at 50 °C for 2 h. b Isolated yields.
(7) Trost, B. M. Science 1991, 254, 1471.
(8) (a) Fumiyuki, O.; Hideyuki, O.; Seiji, K.; Shogo, Y.; Tatsuya, M.;
Masaaki, Y. J. Am. Chem. Soc. 2002, 124, 10968. (b) Bricout, H.; Carpentier,
J. F.; Mortreux, A. J. Mol. Catal. A 1998, 136, 243. (c) Sakakibara, M.;
Ogawa, A. Tetrahedron Lett. 1994, 35, 8013. (d) Bergbreiter, D. E.;
Weatherford, D. A. Chem. Commun. 1989, 883. (e) Haudegond, J.-P.;
Chauvin, Y.; Commeureuc, D. J. Org. Chem. 1979, 44, 3063. (f) Atkins,
K. E.; Walker, W. E.; Manyik, R. M. Tetrahedron Lett. 1970, 3821. (g)
Hata, G.; Takashi, K.; Miyake, A. Chem. Commun. 1970, 1392.
(9) (a) Kabalka, G. W.; Malladi, R. R. Chem. Commun. 2000, 2191. (b)
Kabalka, G. W.; Venkataiah, B. Tetrahedron Lett. 2002, 43, 3703.
(10) (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457. (b) Suzuki,
A. J. Organomet. Chem. 1998, 576, 147. (c) Stanforth, S. P. Tetrahedron
1998, 54, 263.
found to be unreactive. It is noteworthy that the catalyst
system can be recycled with no significant loss in reaction
yields (Table 3).
Although a detailed mechanistic study has not been
undertaken, the reaction most likely proceeds via the pathway
outlined in Scheme 2. Oxidative addition of cinnamyl alcohol
(12) General Procedure: allylic alcohol (1 mmol) and boronic acid (1.2
mmol) are dissolved in BmimPF6 (1.5 mL) contained in a two-necked round-
bottomed flask and RhCl3‚xH2O (3 mol %) along with Cu(OAc)2(1mole%)
are added. The reaction mixture is allowed to stir for 2 h at 5 °C under a
N2 atmosphere. The product can then be isolated by distillation. For
convenience, the product is extracted into diethyl ether (4 × 3 mL). The
combined extracts are dried over anhydrous MgSO4, concentrated and
purified by flash chromatography using silica gel.
(11) (a) Savarin, C.; Srogl, J.; Liebeskind, L. S. Org. Lett. 2001, 3, 91.
(b) Du, X.; Suguro, M.; Hirabayashi, K.; Mori, A. Org. Lett. 2001, 3, 3313.
(c) Chan, D. M. T.; Monaco, K. L.; Wang, R.; Winters, M. P. Tetrahedron
Lett. 1998, 39, 2933. (d) Evans, D. A.; Katz, J. L.; West, T. R. Tetrahedron
Lett. 1998, 39, 2937.
894
Org. Lett., Vol. 5, No. 6, 2003

Scheme 2
Table 3. Reaction of p-Tolylboronic Acid with Cinnamyl
Alcohol Using Recycled Catalytic Systema
entry
isolated yield (%)
first cycle
70
72
73
71
68
second cycle
third cycle
fourth cycle
fifth cycle
a Catalyst was recovered by filtration and utilized in subsequent
experiment (cycle).
to rhodium would generate π-allylrhodium intermediate 1.
The formation of intermediate 2 drives the reaction by
elimination of water in the presence of HF that is present in
BmimPF6 due to the relatively facile decomposition of PF6
anion in the presence of trace amounts of water.13 Subse-
quently, the transmetalation of 2 by boronic acid produces
intermediate 3. Reductive elimination of rhodium then
generates the product. It is noteworthy that the reaction does
not occur in BmimBF4 (Table 1, entry 3) unless HF is added
to the reaction media (Table 1, entry 10). At this time, it is
not possible to rule out a mechanism involving the conversion
of the allylic alcohol to the corresponding halide or phos-
phate. However, control experiments in which cinnamyl
alcohol was heated in BmimPF6 at 50 °C for 2 h led to
recovery of only the alcohol. In addition, an experiment
carried out using toluene (which would obviate the formation
of a halo or phosphate intermediate) in place of BmimPF6
produced a 10% yield of the coupled product.
protocol is applicable to aryl, vinyl, and heteroarylboronic
acids and aromatic allyl alcohols. The catalyst system and
the ionic liquid can be recycled several times without
significant loss in product yield.
Acknowledgment. We wish to thank the U.S. Department
of Energy and the Robert H. Cole Foundation for support
of this research.
Supporting Information Available: Experimental pro-
cedures and analytical data. This material is available free
of charge via the Internet at http://pub.acs.org.
In summary, the coupling reactions of a wide variety of
boronic acids with cinnamyl alcohols have been studied. The
(13) Dupont, J.; Silva, S. M.; de Souza, R. F. Catal. Lett. 2001, 77, 131.
OL034067D
Org. Lett., Vol. 5, No. 6, 2003
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