C-H bond functionalization of benzoic acid: Catalytic synthesis of 2-hydroxy-6 H -benzo[c]chromen-6-ones using (Cp*IrCl2) 2

Article abstract of DOI:10.1021/om200343b

Catalytic H/D exchange reactions of benzene and benzoic acid with deuterated solvents have been studied using (Cp*IrCl₂) ₂. A 1:1 mixture of D₂O/CD₃OD produced the highest turnover numbers for benzene. High levels of deuterium incorporation into benzoic acid were observed only when sodium acetate was added to the reaction mixture. Attempts at producing hydroxybenzoic acid by catalytic C-H functionalization of benzoic acid with benzoquinone were unsuccessful. Instead, 2-hydroxy-6H-benzo[c]chromen-6-one was isolated as the major product. An array of substituted benzoic acids was analyzed for this functionalization reaction. Preliminary mechanistic studies indicate that the benzochromenones are formed by C-H bond activation of benzoic acid followed by insertion of benzoquinone into the iridium-carbon bond.

Full text of DOI:10.1021/om200343b

ARTICLE
pubs.acs.org/Organometallics
CÀH Bond Functionalization of Benzoic Acid: Catalytic Synthesis of
2
-Hydroxy-6H-benzo[c]chromen-6-ones Using (Cp*IrCl )
2 2
Kristi L. Engelman, Yuee Feng, and Elon A. Ison*
Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695-8204, United States
ABSTRACT: Catalytic H/D exchange reactions of benzene
and benzoic acid with deuterated solvents have been studied
using (Cp*IrCl ) . A 1:1 mixture of D O/CD OD produced
2
2
2
3
the highest turnover numbers for benzene. High levels of
deuterium incorporation into benzoic acid were observed only
when sodium acetate was added to the reaction mixture.
Attempts at producing hydroxybenzoic acid by catalytic CÀH functionalization of benzoic acid with benzoquinone were
unsuccessful. Instead, 2-hydroxy-6H-benzo[c]chromen-6-one was isolated as the major product. An array of substituted benzoic
acids was analyzed for this functionalization reaction. Preliminary mechanistic studies indicate that the benzochromenones are
formed by CÀH bond activation of benzoic acid followed by insertion of benzoquinone into the iridiumÀcarbon bond.
’
INTRODUCTION
Chart 1. Natural 6H-Benzo[c]chromen-6-ones
As current fuel supplies continue to diminish, the need for
alternative fuel sources becomes increasingly apparent. One
pathway currently being examined is CÀH bond activation
1,2
and functionalization of natural gas, primarily CH . The first
4
transition metal promoted CÀH bond activation was reported
3
by Chatt et al. in 1965. Many transition metal CÀH bond
1,4À15
activation catalysts have been reported since.
Despite the vast amount of literature on transition metal
catalyzed CÀH bond activation, as generally demonstrated by
H/D exchange studies, strategies for the insertion of a function-
ality in the new metalÀcarbon bond once a CÀH bond has been
cleaved (CÀH functionalization) have been less successful. The
majority of catalytic CÀH bond functionalization reactions
7,16À19
center around activation using either rhodium or palladium.
Given the prominence of iridium catalysts in the CÀH bond
activation literature, the development of catalytic methods for
CÀH bond functionalization using iridium complexes is highly
4
4À47
strategically functionalized starting materials.
For example,
1
9À29
Vishnumurthy et al. recently reported the one-step synthesis of
benzochromenones; however, the reaction proceeds by a SuzukiÀ
Miyaura cross-coupling of o-hydroxylarylboronic acids and bromo-
arylcarboxylates. A similar pathway using o-amidoarylboronic
acids and bromoaryl ethers was reported by Snieckus and co-workers
desirable.
We herein report the CÀH bond activation of benzene and
benzoic acid by (Cp*IrCl ) resulting in H/D exchange with
2
2
46
deuterated solvents. In addition, CÀH bond functionalization of
benzoic acid with benzoquinone using (Cp*IrCl ) produced a
2
2
44
(
Scheme 1).
series of benzo[c]chromen-6-ones.
Benzo[c]chromen-6-ones (dibenzo[b,d]pyran-6-ones) have
In this paper, we report a new reaction for the synthesis of
benzochromenone that proceeds by two steps. First, CÀH bond
activation of the benzoic acid occurs, resulting in the formation of
an iridium metallacycle. Second, CÀH bond functionalization
occurs by insertion of the benzoquinone into the metal carbon
bond of the metallacycle. Due to the rare nature of reactions
involving CÀH bond activation and functionalization utilizing
electrophilic iridium catalysts, the catalytic synthesis of benzo-
chromenones by CÀH bond functionalization of benzoic acid
been found in numerous natural products, including citrus fruits,
30
herbs, and vegetables. These compounds act as progesterone
3
1,32
33
receptor agonists
and endothelial cell growth inhibitors.
Among known natural 6H-benzo[c]chromen-6-ones are autum-
34À37
nariol, autumnariniol, alternariol, and altenuisol (Chart 1).
There are several known pathways to synthesize benzochro-
menones. Langer and co-workers developed a series of predo-
minantly organic pathways for the synthesis of these complexes;
however these reactions generally require highly functionalized
38À43
starting materials and often have low yields.
Metal-catalyzed
Received: April 21, 2011
Published: August 10, 2011
processes have significantly higher yields, but also require
r 2011 American Chemical Society
4572
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Organometallics
ARTICLE
Scheme 1
Table 2. H/D Exchange of Benzoic Acid Using (Cp*IrCl2)2
and NaOAc with Deuterated Solvents
a
b
3
CD OD solvent
8
toluene-d solvent
(
Cp*IrCl
2
)
2
/
(Cp*IrCl
)
2 2
/
entry isotopologue (Cp*IrCl
2
)
2
NaOAc (Cp*IrCl
2
)
2
NaOAc
c
1
2
3
4
5
6
7
% benzoic acid-d
% benzoic acid-d
% benzoic acid-d
% benzoic acid-d
% benzoic acid-d
% benzoic acid-d
% benzoic acid-d
0
1
2
3
4
5
6
77(6)
8(4)
29(8)
44(2)
17(9)
3(2)
0
83(3)
4(1)
15(4)
33(2)
31(3)
14(3)
3(1)
0
20(4)
15(3)
3(1)
1(1)
0
0
0
0
0
0
0
0
Table 1. Catalytic H/D Exchange of Benzene Using
(
Cp*IrCl ) in Deuterated Solvents
2 2
0
a
Conditions: (Cp*IrCl
2
)
2
(10 mol %, 0.025 mmol), NaOAc (when
OD (25
added, 10 mol %, 0.025 mmol), benzoic acid (0.25 mmol), CD
3
mmol); 120 °C for 24 h. Numbers represent an average of three runs
b
with standard deviations in parentheses. Conditions: (Cp*IrCl ) (10
2
2
a
b
mol %, 0.025 mmol), NaOAC (when added, 10 mol %, 0.025 mmol),
benzoic acid (0.25 mmol), toluene-d (8.33 mmol); 120 °C for 24 h.
Numbers represent an average of three runs with standard deviations in
parentheses. % Benzoic acid-d calculated by GC-MS relative to total
n
benzoic acid intensity
entry
solvent
TON
8
1
2
3
CD
3
OD
1(1)
c
1:1 CD
3
OD/D
2
O
86(3)
4(3)
TFA-d
1
a
Conditions: (Cp*IrCl
2 2
) (2 mol %, 0.025 mmol), benzene (111 μL,
The influence of sodium acetate as an additive was also
investigated. Previous reports by Jones and co-workers indicated
that the presence of sodium acetate enhances the rate of CÀH
1
.25 mmol), solvent (25 mmol); 150 °C for 24 h. Numbers represent an
b
average of three runs with standard deviations in parentheses. TON
calculated by GC MS assay.
49,50
6
bond activation of phenyl imines by (Cp*IrCl ) . When cataly-
2
2
with (Cp*IrCl ) is an elegant example of the capabilities of these
tic quantities of (Cp*IrCl ) were reacted with benzoic acid in
2 2
2
2
catalysts. We demonstrate that, in addition to activating arene
CÀH bonds, Cp*Ir complexes can be used for further functio-
nalization of CÀH bonds.
deuterated solvents in the presence of NaOAc, higher isotopo-
logues of benzoic acid were observed when compared to the
reactions run without NaOAc (Table 2). For the reaction in
CD OD, benzoic acid-d was produced in the highest relative
3
2
percent yield when NaOAc was added to the reaction mixture.
’
RESULTS
When the reaction was performed in toluene-d , both benzoic
8
As recently reported by our group, several Cp*Ir(NHC)
acid-d and benzoic acid-d were observed in high concentrations
2 3
complexes catalyze H/D exchange between an arene and various
with the addition of NaOAc.
4
8
deuterated solvents. The catalytic H/D exchange reactions by
these iridium complexes reflect their propensity to activate
aromatic CÀH bonds. Similarly, the complex (Cp*IrCl ) , 1,
CÀH bond functionalization was then investigated using
(Cp*IrCl ) as the catalyst and benzoic acid as the substrate.
2 2
Yu et al. reported the catalytic synthesis of hydroxybenzoic acid
2
2
catalyzes H/D exchange of benzene with deuterated solvents as
shown in Table 1. In accordance with our previous findings, there
is a large solvent dependence, with a 1:1 mix of CD OD and D O
using benzoic acid as the substrate and benzoquinone as the
5
1
oxygen atom transfer reagent. Percent yields as high as 82% were
observed when 10 mol % Pd(OAc) was used as the catalyst.
3
2
2
producing the highest turnover numbers (TON).
However, the reaction of benzoic acid, benzoquinone, and
sodium acetate in the presence of stoichiometric amounts of
Catalytic H/D exchange studies were also performed using
benzoic acid as the substrate. However, when the reaction was
performed in either CD OD or toluene-d , the distribution of
(Cp*IrCl ) in air did not produce the desired hydroxybenzoic
2 2
acid. Instead, 2-hydroxy-6H-benzo[c]chromen-6-one was iso-
lated (Scheme 2).
3
8
benzoic acid isotopologues indicated that predominantly benzoic
acid-d was observed in the GC-MS spectrum and that minimum
deuterium incorporation occurred (Table 2).
An initial study of the substrate scope indicated a high
functional group tolerance at the para position of the benzoic
0
Scheme 2
4
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ARTICLE
Table 3. Yields of Benzochromenone Formation by Reaction with Various Benzoic Acid Derivatives
a
compound
X
percent yield
2
2
2
2
2
a
b
c
H
98(63)
90(60)
66(34)
57(36)
64(20)
Me
t
Bu
d
e
Cl
NO
2
a
Percent yield of benzochromenone by crude NMR versus an internal DSS standard. Numbers in parentheses are isolated yields.
Table 4. Percent Yield, TON, and Percent Conversion for Various Catalyst Loadings
catalyst loading (mol %)
2
%
5%
7.5%
10%
a
%
yield
24(3)
12(2)
63(10)
31(1)
6(1)
35(5)
5(1)
83(2)
9(1)
a
TON
b
%
conversion
81(1)
82(3)
82(1)
a
b
Determined by crude NMR versus an internal DSS standard. Average of three runs. Numbers in parentheses are standard deviations. Conversion of
benzoquinone as determined by crude NMR versus an internal DSS standard. Average of three runs. Numbers in parentheses are standard deviations.
acid (Table 3). Benzochromenone formation was observed for
both electron-withdrawing and electron-donating substituents.
Catalyst loading studies using benzoic acid as the substrate
indicated that the highest yields were obtained with 10% catalyst
loading (Table 4). The percent conversions of benzoquinone
were anomalously high for 2, 5, and 7.5% catalyst loading relative
to the percent yield. Percent yields for all substrates using a 10%
catalyst loading along with percent conversions of benzoquinone
are reported in Table 5.
activation to produce an iridium metallacycle (Scheme 4). The
metallacycle has not been observed by NMR, even when the
reaction is performed in the absence of benzoquinone. A similar
iridium metallacycle was proposed by Satoh et al. as an inter-
5
2
mediate in the catalytic coupling of benzoic acids with alkynes.
Reaction of (Cp*IrCl ) with 2,6-dimethylbenzoic acid and
2
2
benzoquinone in the presence of NaOAc did not produce the
analogous benzochromenone; however consumption of the acid
was still observed. This suggests that although OÀH bond
activation may have occurred, a CÀH bond activation at the
ortho position of benzoic acid is required for product formation.
The role of benzoquinone was also studied. It was first
postulated that benzoquinone acted only as an oxidant. However,
reactions in which benzoquinone was replaced with various other
oxidants, including dioxygen, potassium chromate, and hydrogen
peroxide, did not produce the desired benzochromenone. In
addition, catalytic reactions in which benzoquinone and an
additional oxidant were used did not exhibit an increased yield
of benzochromenone, indicating that a sacrificial oxidant is not
necessary for conversion. Reactions using hydroquinone instead
of benzoquinone did not lead to any product formation, suggest-
ing that reduction of the benzoquinone occurs after incorpora-
tion into the metal fragment.
’
DISCUSSION
The H/D exchange studies of benzoic acid suggest that sodium
acetate is involved in the formation of the active catalyst. Under the
same conditions as in Scheme 2, a variety of other bases were
examined in the absence of NaOAc, including pyridine, triethyla-
mine, and aniline. No product formation was observed with these
other bases, indicating that sodium acetate is not merely acting as a
base in the reactions. We believe that the starting iridium complex
(
Cp*IrCl ) , 1, is the catalyst precursor to the active catalyst
2 2
+
Cp*Ir(OAc) , 3, for the synthesis of benzochromenones, identical
to the formation of 3 that was observed by Jones and co-workers in
the reaction with phenyl imines (Scheme 3).
6
We propose that benzoic acid consumption proceeds by both
OÀH bond activation of the acid moiety and ortho CÀH bond
On the basis of initial results, we propose a general catalytic
cycle as shown in Scheme 5. The first half of the cycle consists of
4
574
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ARTICLE
Table 5. Percent Yield and Percent Conversion for the
Catalytic Reaction with Benzoic Acid Derivatives
allows for synthesis of 2-hydroxy-6H-benzo[c]chromen-6-one.
The benzoquinone acts not only as a substrate but also as an
intramolecular oxidant to regenerate the active catalyst.
a
The discrepancy between the high percent conversions of
benzoquinone compared with the moderate percent yields as
demonstrated in Table 5 indicates that there is a nonproductive
side reaction involving benzoquinone. Amouri et al. reported a
series of studies on the binding of hydroquinone with [Cp*Ir-
53,54
6
(
Solvent)][BF ] .
In these studies, η -binding of the hydro-
4
2
b
c
compound
X
percent yield
percent conversion
quinone was observed. Reaction with two equivalents of base
4
provided the η -bound benzoquinone adduct along with the
2
2
2
2
2
a
b
c
H
83%
86%
58%
23%
33%
100%
100%
100%
96%
reduction of the oxidation state of the metal from (III) to (I).
Subsequently, reaction of the Cp*Ir-benzoquinone complex with
two equivalents of acid reproduces the hydroquinone adduct
Scheme 7). As we previously noted, reaction of benzoic acid and
Cp*IrCl ) /NaOAc in the presence of hydroquinone does not
lead to benzochromenone production. We conclude that our
active catalyst binds benzoquinone competitively with benzoic
acid and converts a portion of the benzoquinone to hydroqui-
none in a nonproductive side reaction. This is supported by the
observation of hydroquinone in the crude benzochromenone
NMR spectra.
Me
t
Bu
d
e
Cl
(
(
NO
2
93%
2
2
a
Conditions: (Cp*IrCl ) (10 mol %, 0.038 mmol), benzoquinone
0.380 mmol), substrate (0.380 mmol), NaOAc (0.380 mmol) in
toluene; 120 °C for 24 h. Percent yield of benzochromenone as
determined by crude NMR versus an internal DSS standard. Percent
conversion of benzoquinone as determined by crude NMR versus an
internal DSS standard.
2
2
(
b
c
Scheme 3
’
CONCLUSIONS
Catalytic H/D exchange of benzene and benzoic acid with
deuterated solvents was achieved using the readily synthesized
catalyst (Cp*IrCl ) . Reaction of this catalyst with benzoic acid
2
2
and benzoquinone results in the formation of 2-hydroxy-6H-
benzo[c]chromen-6-one. The reaction is a rare example of CÀH
functionalization with an electrophilic Ir(III) catalyst and in-
volves two important steps, CÀH activation of benzoic acid and
CÀH functionalization to produce benzochromenone. Further
mechanistic studies are currently underway.
Scheme 4
’
EXPERIMENTAL SECTION
General Procedures. Unless otherwise noted, reagents and sol-
vents were used as received from commercial suppliers. (Cp*IrCl ) was
2
2
5
5 1
13
prepared according to a known procedure. H and C NMR spectra
were recorded at room temperature on either a Varian 300 MHz or a
Varian 400 MHz NMR. H/D exchange experiments were analyzed using
an Agilent Technologies GCMS 5975 instrument. H/D turnover
the formation of an iridium metallacycle by ortho CÀH bond
activation of the benzoic acid. Attempts at isolating this metalla-
cycle were unsuccessful, which is consistent with previous
49,50
6
,52
numbers were calculated using a worksheet reported by Sanford.
FT-IR spectra were obtained from KBr thin films on a JASCO FT/IR
100 infrared spectrometer. HRMS were recorded using electrospray
literature attempts.
Functionalization of the carbon occurs
by insertion of the benzoquinone into the iridiumÀcarbon bond,
followed by intramolecular reduction of the benzoquinone
fragment and elimination of the benzochromenone.
4
ionization (ESI) on an Agilent Technologies 6210 LC-TOF mass
spectrometer.
Several control reactions have been performed to ensure that
the catalyst is necessary for benzochromenone production.
Reaction of benzoic acid, benzoquinone, and NaOAc in toluene
in the absence of catalyst did not lead to benzochromenone
production. To rule out an acid-assisted organic coupling reac-
tion, benzoic acid and benzoquinone were combined in acetic
acid and heated at 120 °C for 24 h. No benzochromenone
formation was observed. Similar results were obtained for the
reaction in hydrochloric acid.
General Procedure for H/D Exchange of Benzene. (Cp*IrCl2)2
(
20 mg, 0.025 mmol), 50 equiv of benzene (111 μL, 1.25 mmol), and
solvent (25 mmol) were combined in a screw-cap NMR tube and heated to
50 °C for 24 h. The reaction mixture was cooled to room temperature and
filtered through Celite. The Celite plug was washed with CH Cl . The
1
2
2
resulting solution was then analyzed by GC-MS.
Procedure for H/D Exchange of Benzene in 1:1 CD OD/
3
D O. (Cp*IrCl
2
2
)
2
(20 mg, 0.025 mmol), 50 equiv of benzene (111 μL,
1
.25 mmol), 500 equiv of CD OD (507 μL, 12.5 mmol), and 500 equiv
3
The mechanism for the elimination of the benzochromenone
has not been thoroughly studied. However, a proposed mechan-
ism is shown in Scheme 6. Intramolecular proton transfer results
in aromatization of the benzoquinone ring. Protonation of the
benzoate oxygen followed by rotation about the arylÀaryl bond
of D O (226 μL, 12.5 mmol) were combined in a screw-cap NMR tube
2
and heated to 150 °C for 24 h. The reaction mixture was cooled to room
temperature, and Na SO was added to remove D O. The resulting
2
4
2
solution was filtered through Celite, and the Celite plug was washed with
CH Cl . The solution was then analyzed by GC-MS.
2
2
4
575
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Organometallics
ARTICLE
Scheme 5
Scheme 6
cooled to room temperature and filtered through Celite. The Celite plug
was washed with CH Cl . The solution was then analyzed by GC-MS.
2 2
Procedure for H/D Exchange of Benzoic Acid in Toluene-
d8 with NaOAc Additive. The procedure above was followed, but
1
equiv of NaOAc (2 mg, 0.025 mmol) was added to the reaction
mixture prior to heating.
General Procedure for Stoichiometric Benzochromenone
Synthesis. (Cp*IrCl ) (60 mg, 0.075 mmol), benzoquinone (16 mg,
2
2
0.150 mmol), sodium acetate (12 mg, 0.150 mmol), and acid (0.150
mmol) were combined in a storage tube with 10 mL of toluene. The
solution was heated to 120 °C for 24 h. The solution was cooled to 0 °C,
and 5 equiv of a 1:1 acetic anhydride/18 M sulfuric acid mixture was
added to decompose the catalyst. After stirring at room temperature for
14 h, the solvent was removed in vacuo. Chromatography on silica with a
2
:2:1 mixture of CH Cl /hexanes/EtOAc produced a white powder.
2
2
2
1
-Hydroxy-6H-benzo[c]chromen-6-one, 2a. Yield: 63%. H NMR
400 MHz, CD OD): δ 8.31 (dd, 1H, J = 8.2, 1.2 Hz, Ar-H), 8.19 (d, 1H,
J = 8.4 Hz, Ar-H), 7.90 (dt, 1H, J = 7.7, 1.2 Hz, Ar-H), 7.64 (dt, 1H, J =
.4, 1.2 Hz, Ar-H), 7.56 (d, 1H, J = 2.7 Hz, Ar-H), 7.22 (d, 1H, J = 8.8 Hz,
(
3
Scheme 7
8
1
3
Ar-H), 6.99 (dd, 1H, J = 9.0 Hz, 2.8 Hz, Ar-H). C NMR (400 MHz,
CD
3
OD): δ 162.0, 154.7, 144.7, 135.2, 135.1, 130.0, 128.9, 122.1, 120.0,
À1
1
18.7, 118.3, 118.2, 107.8. IR (KBr, cm ): ν 3400 (br, OH), 1698
+
8 3
(s, CdO). HRMS (ESI): calcd for C13H O [M] 213.0546; found
2
13.0546.
-Hydroxy-9-methyl-6H-benzo[c]chromen-6-one, 2b. Yield: 60%.
2
1
H NMR (300 MHz, CD OD): δ 8.11 (d, 1H, J = 8.1 Hz, Ar-H), 7.90
3
Procedure for H/D Exchange of Benzoic Acid in CD OD.
3
Cp*IrCl ) (20 mg, 0.025 mmol), benzoic acid (31 mg, 0.025 mmol),
2 2
(s, 1H, Ar-H), 7.43 (d, 1H, J = 2.7 Hz, Ar-H), 7.39 (dd, 1H, J = 8.4, 1.8
Hz, Ar-H), 7.14 (d, 1H, J = 8.7 Hz, Ar-H), 6.93 (dd, 1H, J = 9.0, 2.7 Hz,
(
À1
and CD OD (1015 μL, 25 mmol) were combined in a screw-cap NMR
3
Ar-H), 2.52 (s, 3H, Me). IR (KBr, cm ): ν 3323 (br, OH), 1693
+
tube and heated at 120 °C for 24 h. The reaction mixture was cooled to
room temperature and filtered through Celite. The Celite plug was
washed with CH Cl . The solution was then analyzed by GC-MS.
2 2
Procedure for H/D Exchange of Benzoic Acid in CD OD
3
(
2
s, CdO). HRMS (ESI): calcd for C14
27.0703.
-(tert-Butyl)-2-hydroxy-6H-benzo[c]chromen-6-one, 2c. Yield:
H
10
O
3
[M] 227.0709; found
9
1
34%. H NMR (300 MHz, AcOD-d ): δ 8.34 (d, 1H, J = 8.4 Hz,
7
with NaOAc Additive. The procedure above was followed, but
Ar-H), 8.16 (s, 1H, Ar-H), 7.73 (d, 1H, J = 8.4 Hz, Ar-H), 7.67 (d, 1H, J =
2.7 Hz, Ar-H), 7.26 (d, 1H, J = 9.0 Hz, Ar-H), 7.05 (dd, 1H, J = 8.7,
1
equiv of NaOAc (2 mg, 0.025 mmol) was added to the reaction
t
À1
mixture prior to heating.
Procedure for H/D Exchange of Benzoic Acid in Toluene-
3.0 Hz, ArÀH), 1.55 (s, 9H, Bu). IR (KBr, cm ): ν 3199 (br, OH),
+
1686 (s, CdO). HRMS (ESI): calcd for C H O [M] 269.1174;
1
7 16 3
d8. (Cp*IrCl
2
)
2
(20 mg, 0.025 mmol), benzoic acid (31 mg, 0.025
found 269.1172.
mmol), and toluene-d (885 μL, 8.33 mmol) were combined in a screw-
cap NMR tube and heated at 120 °C for 24 h. The reaction mixture was
9-Chloro-2-hydroxy-6H-benzo[c]chromen-6-one, 2d. Yield: 36%.
8
1
H NMR (300 MHz, CD OD): δ 8.27 (d, 1H, J = 8.5 Hz, Ar-H),
3
4
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Organometallics
.18 (d, 1H, J = 2.0 Hz, Ar-H), 7.59 (dd, 1H, J = 8.5, 2.0 Hz, Ar-H), 7.47
ARTICLE
8
(20) Voutchkova, A. M.; Crabtree, R. H. J. Mol. Catal. A: Chem.
2009, 312, 1.
(21) Leung, D. H.; Bergman, R. G.; Raymond, K. N. J. Am. Chem.
Soc. 2006, 128, 9781.
(
d, 1H, J = 2.8 Hz, Ar-H), 7.21 (d, 1H, J = 8.9 Hz, Ar-H), 7.01 (dd, 1H,
À1
J = 8.9, 2.8 Hz, Ar-H). IR (KBr, cm ): ν 3391 (br, OH), 1693 (s,
CdO). HRMS (ESI): calcd for C13
+
H
7
ClO
3
[M] 247.016; found
(
22) Yung, C. M.; Skaddan, M. B.; Bergman, R. G. J. Am. Chem. Soc.
2
47.0156.
1
2004, 126, 13033.
(
(
2
-Hydroxy-9-nitro-6H-benzo[c]chromen-6-one, 2e. Yield: 20%. H
23) Bhalla, G.; Periana, R. A. Angew. Chem., Int. Ed. 2005, 44, 1540.
24) Bhalla, G.; Liu, X. Y.; Oxgaard, J.; Goddard, W. A.; Periana, R. A.
2 2
NMR (300 MHz, CD Cl ): δ 8.91 (d, 1H, J = 2.1 Hz, Ar-H), 8.53 (s, 1H,
J = 8.7 Hz, Ar-H), 8.33 (dd, 1H, J = 8.7, 2.2 Hz, Ar-H), 7.56 (d, 1H, J =
J. Am. Chem. Soc. 2005, 127, 11372.
2
.7 Hz, Ar-H), 7.27 (d, 1H, J = 8.9 Hz, Ar-H), 7.07 (dd, 1H, J = 8.9, 2.7 Hz,
À1
(25) Clot, E.; Chen, J. Y.; Lee, D. H.; Sung, S. Y.; Appelhans, L. N.;
Faller, J. W.; Crabtree, R. H.; Eisenstein, O. J. Am. Chem. Soc. 2004,
Ar-H). IR (KBr, cm ): ν 3350 (br, OH), 1690 (s, CdO), 1533 (s, NO).
1
26, 8795.
26) Bischof, S. M.; Ess, D. H.; Meier, S. K.; Oxgaard, J.; Nielsen,
R. J.; Bhalla, G.; Goddard, W. A.; Periana, R. A. Organometallics 2010,
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K. Organometallics 2009, 28, 433.
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’
AUTHOR INFORMATION
(
Corresponding Author
E-mail: eaison@ncsu.edu. Tel: (919) 513-4376. Fax: (919)
15-8909.
2
*
5
(
(
Poelleth, M. J. Am. Chem. Soc. 2006, 128, 4210.
’
ACKNOWLEDGMENT
(29) Wiley, J. S.; Heinekey, D. M. Inorg. Chem. 2002, 41, 4961.
(
30) Myrray, R.; Mendez, J.; Brown, S. The Natural Coumarins;
Occurence, Chemistry and Biochemistry; John Wiley & Sons: New York, 1982.
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J. Med. Chem. 1999, 42, 1466.
32) Edwards, J. P.; West, S. J.; Marschke, K. B.; Mais, D. E.;
This work was supported by the National Science Foundation
through the Center for Enabling New Technologies through
Catalysis (CHE-0650456). Mass spectra were obtained at the
NCSU Department of Chemistry Mass Spectrometry Facility.
Funding was obtained from the North Carolina Biotechnology
Center and the NCSU Department of Chemistry.
(
(
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6, 1289.
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dx.doi.org/10.1021/om200343b |Organometallics 2011, 30, 4572–4577