Rhodium fluorapatite catalyst for the synthesis of trisubstituted olefins via cross coupling of Baylis-Hillman adducts and arylboronic acids

Article abstract of DOI:10.1021/jo701982m

(Chemical Equation Presented) Treatment of fluorapatite (prepared by incorporating basic species F^- in apatite in situ by coprecipitation) with an aqueous solution of RhCl₃ resulted in rhodium-exchanged fluorapatite catalyst (RhFAP),

Full text of DOI:10.1021/jo701982m

BHA was successfully carried out by using palladium catalysts,
but such coupling required the activation of the hydroxyl group
with acetate or carbonate.4 The use of nonactivated BHA would
be more desirable, particularly from the point of view of atom
economy.5a,b Recently Darses, Genet, et al. reported the synthesis
of trisubstituted olefins using homogeneous rhodium catalyst
via an unexpected mechanism involving 1,4-addition/â-hydroxy
elimination steps.1c
Rhodium Fluorapatite Catalyst for the Synthesis
of Trisubstituted Olefins via Cross Coupling of
Baylis-Hillman Adducts and Arylboronic Acids
M. Lakshmi Kantam,* K. B. Shiva Kumar, and B. Sreedhar
Inorganic and Physical Chemistry DiVision, Indian Institute of
Chemical Technology, Hyderabad 500 007, India
Despite the advantages of homogeneous metal complex
catalysts, difficulties in recovering the expensive catalyst metals
and ligands from the reaction mixture severely limit their
industrial applications. Apatites are metal basic phosphates for
which the chemical formula is M10(PO4)6(X)2 [M ) divalent
metal, X ) monovalent anion] and various kinds of cations and
anions can be readily introduced into their framework due to
their large ion exchange ability and such exchanged apatites
are already in use in several organic transformations.5c,6,7 Very
recently, we reported the preparation of recyclable heterogeneous
Cu-exchanged fluorapatite and copper exchanged tert-butoxya-
patite catalysts, for N-arylation of imidazoles and other hetero-
cycles with iodo-, bromo-, chloro-, and fluoroarenes (EW) with
good to excellent yields.8a,b We also reported PdFAP catalyst
(Fluorapatite-supported palladium catalyst) for the Suzuki and
Heck coupling reaction.8c Thus in continuation of our work with
fluorapatite we herein report the preparation of recyclable
heterogeneous rhodium-exchanged fluorapatite catalyst (RhFAP)
for cross coupling of Baylis-Hillman adducts with arylboronic
acids to yield trisubstituted olefins.
Calcium Fluorapatite (Ca/P) of 1.56 FAP (Ca10(PO4)6(F)2)
was synthesized according to the literature procedure9 and
exchanged with RhCl3, yielding the RhFAP as a yellowish
orange powder. The rhodium content was measured as 0.1 mmol
g-1 with ICP-AES. XRD and FTIR of the RhFAP were similar
to those of parent FAP. The (Rh+Ca)/P ratio of the RhFAP
was 1.56, which shows the occurrence of a substitution of Rh
for Ca2+ at the column of Ca and O atoms parallel to the
hexagonal axis. XPS spectra were recorded for the RhFAP
catalyst. A high-resolution narrow scan of Rh showed peaks at
mlakshmi@iict.res.in
ReceiVed September 10, 2007
Treatment of fluorapatite (prepared by incorporating basic
species F- in apatite in situ by coprecipitation) with an
aqueous solution of RhCl3 resulted in rhodium-exchanged
fluorapatite catalyst (RhFAP), which successfully promoted
cross coupling of Baylis-Hillman adducts with arylboronic
acids to yield trisubstituted olefins. A variety of arylboronic
acids and Baylis-Hillman adducts were converted to the
corresponding trisubstituted olefins, demonstrating the ver-
satility of the reaction. The reaction is highly stereoselective.
RhFAP was recovered quantitatively by simple filtration and
reused with almost consistent activity.
Rhodium-catalyzed carbon-carbon bond formation via cross
coupling of organoboron compounds and organic electrophiles
is one of the most important reactions in organic synthesis.1
The Baylis-Hillman reaction of an aldehyde and an activated
olefin produces Baylis-Hillman adducts (BHA), an interesting
class of disubstituted olefins possessing both allylic alcohol and
R,â-unsaturated ester moieties in which the carbon-carbon
double bond is an integral part of both allyl alcohol and R,â-
unsaturated ester moieties, which makes it valuable in a number
of stereoselective processes2 and offers multiple opportunities
for further transformations.3 Arylation with trifluoro(organo)-
borates and organosilanes to R,â-unsaturated ester moieties of
(3) Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. ReV. 2003, 103,
811.
(4) (a) Kabalka, G. W.; Dong, G.; Venkataiah, B.; Chen, C. J. Org. Chem.
2005, 70, 9207. (b) Kabalka, G. W.; Venkataiah, B.; Dong, G. Org. Lett.
2003, 5, 3803.
(5) (a) Trost, B. M. Science 1991, 254, 1471. (b) Trost, B. M. Angew.
Chem., Int. Ed. 1995, 24, 259. (c) Elliott, J. C. Structure and chemistry of
the apatites and other calcium orthophosphates; Elsevier: Amsterdam, The
Netherlands, 1994; p 111.
(6) Sugiyama, S.; Minami, T.; Hayashi, H.; Tanaka, M.; Shigemoto, N.;
Moffat, J. B. J. Chem. Soc., Faraday Trans. 1996, 92, 293.
(7) (a) Yamaguchi, K.; Mori, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K.
J. Am. Chem. Soc. 2000, 122, 7144. (b) Mori, K.; Yamaguchi, K.; Mizugaki,
T.; Ebitani, K.; Kaneda, K. Chem. Commun. 2001, 461. (c) Mori, K.;
Yamaguchi, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K. New J. Chem. 2002,
26, 1536. (d) Mori, K.; Yamaguchi, K.; Hara, T.; Mizugaki, T.; Ebitani,
K.; Kaneda, K. J. Am. Chem. Soc. 2002, 124, 11572. (e) Mori, K.; Hara,
T.; Oshiba, M.; Mizugaki, T.; Ebitani, K.; Kaneda, K. New J. Chem. 2005,
29, 1174.
(1) (a) Zou, G.; Wang, Z.; Zhu, J.; Tang, J. Chem. Commun. 2003, 2438.
(b) Fujita, N.; Motokura, K.; Mori, K.; Mizugaki, T.; Ebitani, K.; Jitsukawa,
K.; Kaneda, K. Tetrahedron Lett. 2006, 47, 5083. (c) Navarre, L.; Darses,
S.; Genet, J. P. Chem. Commun. 2004, 9, 1108. (d) Hayashi, T.; Yamasaki,
K. Chem. ReV. 2003, 103, 2829. (e) Sakai, M.; Hayashi, H.; Miyaura, N.
Organometallics 1997, 16, 4229. (f) Takaya, Y.; Ogasawara, M.; Hayashi,
T.; Sakai, M.; Miyaura, N. J. Am. Chem. Soc. 1998, 120, 5579. (g) Mora,
G.; Darses, S.; Genet, J. P. AdV. Synth. Catal. 2007, 349, 1180.
(8) (a) Choudary, B. M.; Sridhar, Ch.; Kantam, M. L.; Venkanna, G. T.;
Sreedhar, B. J. Am. Chem. Soc. 2005, 127, 9948. (b) Kantam, M. L.;
Venkanna, G. T.; Sridhar, Ch.; Shiva Kumar, K. B. Tetrahedron Lett. 2006,
47, 3897. (c) Kantam, M. L.; Shiva Kumar, K. B.; Srinivas, P.; Sreedhar,
B. AdV. Synth. Catal. 2007, 349, 1141.
(2) (a) Drewes, S. E.; Ross, G. H. P Tetrahedron 1996, 44, 4653. (b)
Basavaiah, D.; Dharmarao, P.; Suguna. H. R. Tetrahedron 1996, 52, 8001.
(9) Sebti, S.; Nazih, R.; Tahir, R.; Salhi, L.; Saber, A. Appl. Catal. A
2000, 197, 187.
10.1021/jo701982m CCC: $40.75 © 2008 American Chemical Society
Published on Web 12/12/2007
320
J. Org. Chem. 2008, 73, 320-322

TABLE 1. Screening Reaction Parameters for the Synthesis
2-Benzyl-3-phenylacrylic Acid Methyl Estera
TABLE 2. Synthesis of Trisubstituted Olefins Catalyzed by
RhFAP Catalysta
yield (%)b
entry
R1
R2
R3
yield (%)b
entry
catalyst
solvent
additive
1d
2d
3
4
5
6
7
8
9
RhCl3
RhCl3
methanol
methanol
methanol
methanol
ethanol
water
1,4-dioxane
DMF
-
-
1
2
3
4
5
6
7
8
9
10
11
12
13
14
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
4-Cl-C6H4
4-NO2-C6H4
4-CH3-C6H4
furyl
CO2CH3
CO2CH3
CO2CH3
CO2CH3
CO2CH3
CO2CH3
CO2CH3
CO2Et
C6H5
94
96
94
92
89
91
69
93
92c
86
79
93
97
95
4-CH3-C6H4
4-OCH3-C6H4
4-Cl-C6H4
4-F-C6H4
2,4-OCH3-C6H3
3-NO2-C6H4
C6H5
C6H5
C6H5
C6H5
C6H5
1,5-cod
-
-
RhFAP
RhFAP
RhFAP
RhFAP
RhFAP
RhFAP
RhFAP
-
1,5-cod
1,5-cod
1,5-cod
1,5-cod
1,5-cod
1,5-cod
1,5-cod
1,5-cod
94, 90c
86
trace
42
58
70
-
-
CN
DMSO
methanol
methanol
CO2CH3
CO2CH3
CO2CH3
CO2CH3
CO2CH3
10
11
RhFAP (impregnated)
Rh/SiO2
a Reaction conditions: 1a (1 mmol), 2a (1.2 mmol), catalyst (100 mg),
solvent (4 mL), 1,5-cyclooctadiene (1,5-cod) (0.05 mmol), reaction time
(6 h), 65 °C. b Isolated yields. c Yield after fourth recycle. d Entries 1 and
2, 2 mol % of RhCl3 was used.
C6H5
C6H5
(CH3)2CH-CH2
a Reaction conditions: 2c (1 mmol), 2b (1.2 mmol), catalyst (100 mg),
methanol (4 mL), 1,5-cycloctadiene (0.05 mmol), reaction time (5-7 h),
65 °C. b Isolated yields. c Z isomer (99%) was obtained.
308.8 and 313.6 eV which are due to Rh 5d5/2 and Rh 5d3/2
,
respectively, in the +3 oxidation state (see the Supporting
Information). The presence of chlorine was confirmed by XPS
and EDAX analyses and the atomic ratio of Rh to Cl was 1:1.
Thus the rhodium species in RhFAP are surrounded by oxygen
and a chlorine atom, which is in concordance with ruthenium-
(III) hydroxyapatite reported earlier.7a,b
confirms no leaching of rhodium during the reaction (detection
limit is <1ppb) and provides evidence for heterogeneity
throughout the reaction.
We chose a variety of structurally divergent nonactivated
Baylis-Hillman adducts and arylboronic acids possessing a
wide range of functional groups to understand the scope and
the generality of the RhFAP-promoted cross coupling reaction
to yield trisubstituted olefins and the results are summarized in
Table 2. Phenylboronic acids with an electron-donating group
afforded better yields (Table 1, entries 2, 3, and 6) than those
with electron-withdrawing groups (Table 2, entry 7). Among
the Baylis-Hillman adducts, electron-donating groups on the
aromatic moiety of the adduct gave better yield than that of
withdrawing groups such as nitro and chloro which gave
moderate yield. An electron-rich Baylis-Hillman adduct such
as 2-(furan-2-yl-hydroxy-methyl)-acrylic acid methyl ester
reacted faster than a Baylis-Hillman adduct with electron-
withdrawing groups on the aromatic moiety to give the
corresponding olefin in excellent yields (Table 2, entry 13). The
aliphatic Baylis-Hillman adduct 2-(1-hydroxy-3-methylbutyl)-
acrylic acid methyl ester was also successfully coupled with
phenylboronic acid to give the respective olefin in excellent
yields (Table 2, entry 14). The reaction is highly stereoselective.
The stereochemistry of the products was established by compar-
ing the NMR of olefinic and methylene protons with the
literature value and the E/Z ratio was determined by both GC-
In an effort to develop a better catalytic system, various
reaction parameters were screened for cross coupling of 3-hy-
droxy-2-methylene-3-phenylpropanoate with phenylboronic acid
to yield 2-benzyl-3-phenylacrylic acid methyl ester (2a) and are
presented in Table 1. RhFAP catalyst combined with 1,5-
cyclooctadiene (1,5-cod) in methanol at 65 °C exhibited the
highest catalytic activity giving 2, (Table 1, entry 4), while the
reaction conducted in the absence of 1,5-cod did not yield the
product 2a (Table 1, entry 3). There is no reaction with
homogeneous RhCl3 catalyst in the presence and absence of
1,5-cod under similar conditions (Table 1, entries 1 and 2). To
evaluate the catalytic active species, we conducted the reaction
with RhCl3 impregnated on FAP support (RhFAP-impregnated
(for catalytic characterization see the Supporting Information))
and there was no reaction (Table 1, entry 10). It clearly
emphasizes that the rhodium chemisorbed on the FAP surface
is not the active species. Conversely a unique monomeric Rh
species (RhFAP) surrounded by oxygen and a chlorine atom
on the FAP support (Ca exchanged by Rh) is the real catalytic
active species. There is no reaction with Rh/SiO2 (Table 1, entry
11).
1
MS and H NMR. The reaction of 3-hydroxy-2-methyleneal-
The solvent has a pronounced effect in these reactions.
Methanol and ethanol have proven to be good solvents whereas
DMF, DMSO, and 1,4-dioxane provided moderate yields. The
reaction was also carried out in water but only a trace amount
of product 2a was detected (Table 1, entries 5-9).
kanoates with a variety of arylboronic acids yielded 2-substituted
2-aldenoates with E/Z isomers >96%. Interestingly, when
3-hydroxy-2-methylenealkanenitrile was reacted with phenyl-
boronic acid, only the Z isomer (99%) was obtained as the major
product (Table 2, entry 9).
The controlled reaction conducted under identical conditions
without RhFAP and 1,5-cod gave no coupled product, despite
prolonged reaction times. RhFAP was recovered quantitatively
by simple centrifugation and reused for four cycles with minimal
loss of activity (Table 1, entry 4). Moreover, the absence of
rhodium in the filtrate was confirmed by ICP-AES, which
The used RhFAP catalyst was well characterized by XRD,
FTIR, XPS, ICP-AES, and EDAX analysis. XRD and FTIR of
the used RhFAP catalyst were similar to those of fresh RhFAP
catalyst. The XPS, high-resolution narrow scan of Rh showed
peaks at 308.5 and 312.7 eV which are due to Rh 5d5/2 and Rh
5d3/2, respectively, in the +3 oxidation state (see the Supporting
J. Org. Chem, Vol. 73, No. 1, 2008 321

reduced pressure to give the crude product. The crude product was
purified by column chromatography on silica gel to afford the
corresponding trisubstituted olefins. The centrifuged catalyst was
washed with methanol, dried, and reused for the next cycle.
2-Benzyl-3-phenylacrylic acid methyl ester (Table 2, entry
Information). The absence of chlorine was confirmed by XPS
and EDAX analyses. The (Rh+Ca)/P ratio of the used RhFAP
showed 1.56. The rhodium content of used RhFAP was
measured as 0.1 mmol g-1 with ICP-AES.
Based on retention of the +3 oxidation state of Rh and the
absence of chlorine in the used RhFAP catalyst, we assume
that the reaction proceeds via a 1,4-addition type mechanism1c
involving â-hydroxy elimination resulting in a rhodium hy-
droxide species. Thus the rhodium species in the used RhFAP
catalyst are surrounded by oxygens and a hydroxyl group (see
the Supporting Information).
In conclusion, we have developed a simple and efficient
method for the preparation of trisubstituted olefins, using RhFAP
catalyst. A variety of arylboronic acids and nonactivated Baylis-
Hillman adducts were converted to the corresponding trisub-
stituted olefins, demonstrating the versatility of the reaction.
The catalyst can be readily recovered and reused.
1
1): H NMR (300 MHz, CDCl3) δ 7.88 (s, 1H), 7.34-7.31 (m,
10H), 3.91 (s, 2H), 3.74 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
168.4, 140.9, 139.3, 135.2, 130.5, 129.1, 128.7,128.5, 128.4, 127.8,
126.0, 52.0, 33.1; MS m/z 252 (M+). Anal. Calcd for C17H16O2:
C, 80.93; H, 6.39. Found: C, 80.81; H, 6.34.
2-Benzyl-3-(4-chlorophenyl)acrylic acid methyl ester (Table
2, entry 10): 1H NMR (300 MHz, CDCl3) δ )7.82 (s, 1H), 7.30-
7.10 (m, 9H), 3.89 (s, 2H), 3.74 (s, 3H); 13C NMR (75 MHz, CDCl3)
δ 168.4, 139.6, 139.0, 134.5, 133.7, 131.2, 130.5, 128.8 128.6,
127.8, 126.2, 52.2, 33.1; MS m/z 286 (M+). Anal. Calcd. for C17H15-
ClO2: C, 71.20; H, 5.27. Found: C, 71.09; H, 5.23.
Acknowledgment. K.B.S.K. thanks UGC, India for a
fellowship.
Note Added after ASAP Publication. Structures in Table 1
and 2 were corrected and the corrected version was published
December 18, 2007.
Experimental Section
General Procedure for the Synthesis of Trisubstituted Olefins.
RhFAP (100 mg or Rh ) 0.01 mmol) was added to a mixture of
Baylis-Hillman adduct (1 mmol), arylboronic acid (1.2 mmol),
and 1,5-cod (0.05 mmol) in methanol (4 mL) at 65 °C, and the
mixture was stirred for 6 h. The progress of the reaction was
monitored by TLC and on completion of the reaction, the reaction
mixture was centrifuged and the centrifugate was concentrated under
Supporting Information Available: Detailed experimental
procedures and compound characterization data for all compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JO701982M
322 J. Org. Chem., Vol. 73, No. 1, 2008