Palladium/di-1-adamantyl-n-butylphosphine-catalyzed reductive carbonylation of aryl and vinyl halides

Article abstract of DOI:10.1016/j.tet.2007.02.043

A general and efficient palladium-catalyzed reductive carbonylation with low catalyst loadings (0.5 mol % Pd or below) has been developed. The formylation of aryl and heteroaryl bromides proceeds smoothly in the presence of palladium/di-1-adamantyl-n-butylphosphine at ambient pressure of synthesis gas to afford the corresponding aromatic aldehydes in good yields and excellent selectivity. In addition, vinyl halides react under similar conditions to form α,β-unsaturated aldehydes in good yield.

Full text of DOI:10.1016/j.tet.2007.02.043

Tetrahedron 63 (2007) 6252–6258
Palladium/di-1-adamantyl-n-butylphosphine-catalyzed
reductive carbonylation of aryl and vinyl halides
a
Anne Brennfuhrer, Helfried Neumann, Stefan Klaus, Thomas Riermeier,
a
a
b
€
Juan Almenab and Matthias Bellera,
*
aLeibniz-Institut fu€r Katalyse e.V. an der Universita€t Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
bDegussa AG, Rodenbacher Chaussee 4, 63457 Hanau, Germany
Received 19 December 2006; revised 9 February 2007; accepted 9 February 2007
Available online 15 February 2007
Abstract—A general and efficient palladium-catalyzed reductive carbonylation with low catalyst loadings (0.5 mol % Pd or below) has been
developed. The formylation of aryl and heteroaryl bromides proceeds smoothly in the presence of palladium/di-1-adamantyl-n-butylphos-
phine at ambient pressure of synthesis gas to afford the corresponding aromatic aldehydes in good yields and excellent selectivity. In addition,
vinyl halides react under similar conditions to form a,b-unsaturated aldehydes in good yield.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
between industry and academia to explore the potential of
various palladium catalysts and ligands. After an initial com-
munication,11 here we describe a full account of our investi-
gations, which led to the most general, active, and productive
palladium catalyst known to date for reductive carbonyl-
ations of aryl and vinyl halides.
The palladium-catalyzed carbonylation of aryl and hetero-
aryl halides is a versatile reaction and easily provides access
to aromatic ketones,1 carboxylic acids,2 esters,3 amides,4
and the corresponding a-oxo-derivatives.5 With respect to
the different variants of carbonylations aromatic aldehydes
are probably the most useful class of products, as the highly
reactive aldehyde group can be easily employed in numerous
C–C- and C–N-coupling reactions, reductions as well as
other transformations (Scheme 1). Obviously, the resulting
substituted benzaldehydes are important substrates for the
preparation of numerous biologically active molecules and
their intermediates. Although the first palladium-catalyzed
formylation was reported by Heck et al. already in 1974,6
still this method had several limitations until very recently.
In the past, often the use of expensive reduction reagents
such as silicon7 and tin8 hydrides was necessary to achieve
the formylation at lower pressures of CO. A more economical
method to perform palladium-catalyzed reductive carbonyl-
ations is based on the use of readily available formate salts9 or
acetic formic anhydride.10 However, also these formylation
procedures require the use of high catalyst loadings.
2. Results and discussion
Based on our experience in palladium-catalyzed coupling12
and carbonylation reactions,13 the formylation of 4-bromo-
anisole with synthesis gas to give 4-methoxybenzaldehyde
was tested in the presence of 20 different phosphine ligands.
Selected results are shown in Table 1. Apart from standard
phosphines, ligands developed in our group such as di-1-
adamantylalkylphosphines14 and N-arylated heteroaryldial-
kylphosphines15 were compared under identical conditions
(100 ꢀC; 5 bar CO/H2). In order to ensure a more rapid test-
ing all experiments were carried out in a modified sixfold
parallel autoclave (reaction volume 4 mL). To our surprise
under these conditions only one ligand (di-1-adamantyl-n-
butylphosphine; cataCXiumÒ A) permits efficient formyl-
ation of the model substrate (92%, Table 1, entry 10).
Typical bidentate ligands such as 1,3-bis(diphenylphosphino)-
propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb)
or 1,10-bis(diphenylphosphino)ferrocene (dppf) did not
lead to significant conversion and 4-methoxybenzaldehyde
formation (Table 1, entries 1–4). Triarylphosphines and
dialkylheteroarylphosphines were less active or nearly
inactive (Table 1, entries 5 and 6, entries 13–19). The
electron rich and sterically bulky ligands such as
In addition, most palladium-catalyzed formylations are ac-
companied by side reactions, especially the reductive deha-
logenation of the aryl halide. In order to overcome the
limitations of known procedures, we started a joint program
* Corresponding author. Tel.: +49 381 1281 113; fax: +49 381 1281 51113;
e-mail address: matthias.beller@catalysis.de
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.02.043

A. Brennfu€hrer et al. / Tetrahedron 63 (2007) 6252–6258
6253
R
OH
R'
N
R''
O
R
R
H
N
O
R'
N
R'
HN
R''
N
H
R'
O
H
N
R
H2N
R'
H2N
R'
R
O
HN
NO2
O
H3C
NH2
H
N
R
R
R
EWG
EWG
EWG
EWG
H2
NH3
O
CN-
CN-
H
R
R
NH2
CN
CN
R
R
Scheme 1. Synthetic application of aromatic aldehydes.
Table 1. Effect of ligands on the formylation of 4-methoxybromobenzene
Br
CHO
Pd(OAc)2, ligand
TMEDA, CO/H2
MeO
MeO
PR2
N
R
PR2
PCy2
Cy2P
N
N
N
P
PCy2
1a, R=n-Bu
1b, R=Bn
1c, R=H
2a, R=Cy
2b, R=t-Bu
2c, R=Ad
3a, R=Cy
3b, R=t-Bu
4
5
Entry
Ligand
Ligand [mol %]
Conversiona [%]
Yielda [%]
Selectivitya [%]
1
2
3
4
5
6
7
8
dppp
dppp
dppb
dppf
PPh3
P(o-Tol)3
P(n-Bu)3
P(t-Bu)3
PCy3
1a
1b
1c
2a
2b
2c
3a
3b
4
0.75
0.375
0.75
0.375
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.375
3
2
9
6
2
0
1
7
3
0
0
50
78
50
0
1
1
0
0
0
0
22
13
97
26
7
9
2
2
4
18
11
92
19
4
6
0
1
2
82
85
95
73
57
67
0
50
50
0
9
10
11
12
13
14
15
16
17
18
19
1
13
3
0
9
0
69
0
5
Reaction conditions: 2 mmol 4-bromoanisole, 0.25 mol % Pd(OAc)2, 0.75 equiv TMEDA, 0.2 equiv hexadecane (internal standard), 2 mL toluene, 5 bar CO/H2
(1:1), 100 ꢀC, 16 h.
Determined by gas chromatography.
a

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A. Brennfu€hrer et al. / Tetrahedron 63 (2007) 6252–6258
100
90
80
70
60
50
40
30
20
10
0
di-1-adamantylbenzylphosphane (1b) and P(t-Bu)3, which
can be compared to cataCXiumÒ A, also gave only low
yields of the desired product (<20%, Table 1, entries 8
and 11).
Next to the ligand screening, we studied the influence of
different solvents, pressure, and bases. In general, N-methyl-
pyrrolidinone (NMP), 1,2-dimethoxyethane, and acetoni-
trile were less suitable compared to toluene. It is important
to note that a low synthesis gas pressure (<5 bar) is neces-
sary in order to achieve complete conversion. Obviously,
a higher CO concentration leads to deactivation of the cata-
lyst system. In Figure 1, the influence of carbon monoxide
pressure on the yield of 4-methoxybenzaldehyde is shown
in detail for seven different bases. For all tested bases the
maximum yield of 4-methoxybenzaldehyde is achieved
at a total pressure of about 5 bar (CO/H2¼1:1). Due to
the low solubility and competing formation of 4-methoxy-
benzoic acid, inorganic bases, for example, K2HPO4,
were less effective compared to organic nitrogen bases
such as DABCO, TMEDA, NEt3, and N(n-Bu)3. Notably,
N,N,N0,N0-tetramethylethylenediamine (TMEDA) has been
rarely used as a base for palladium-catalyzed coupling reac-
tions, but is the most active base for our model substrate.
conversion of 4-bromoanisole
yield of 4-methoxybenzaldehyde
0
0,1
0,2
0,3
0,4
0,5
Pd(OAc)2 [mol %]
Figure 2. Influence of catalyst concentration on conversion and yield of the
model reaction. Reaction conditions: 2 mmol 4-bromoanisole, Pd(OAc)2/
cataCXiumÒ A¼1:3, 0.75 equiv TMEDA, 0.2 equiv hexadecane (internal
standard), 2 mL toluene, 5 bar CO/H2 (1:1), 100 ꢀC, 16 h.
faster. On the other hand, decreasing the temperature re-
tarded the conversion but increased the chemoselectivity.
The promising results obtained with di-1-adamantyl-n-bu-
tylphosphine (cataCXiumÒ A) encouraged us to study the
general scope and limitations of this catalyst system for
the formylation of different aryl and heteroaryl bromides
(Table 2).
Among the different palladium sources tested, Pd(OAc)2
proved to be the best since it is better soluble in toluene
than, for example, PdBr2 or Pd2(dba)3. With respect to
minimization of the catalyst loading, one should note that
high conversion and good yield of 4-methoxybenzaldehyde
are already obtained at a palladium concentration of
0.25 mol % (Fig. 2).
High conversion and excellent selectivity (>90%) are ob-
served for the formylation of various monosubstituted aryl
bromides such as 4-bromoanisole, 4-bromofluorobenzene,
4-bromobenzonitrile,
4-(dimethylamino)bromobenzene,
To prevent the formation of palladium carbonyl clusters and
to stabilize the palladium catalyst, a threefold excess of the
ligand (P/Pd¼3:1) is necessary. The amount of palladium
can be reduced at constant ligand concentration by raising
the temperature from 100 ꢀC to >120 ꢀC. Typically a higher
reaction temperature increased the conversion, but some-
times diminished the chemoselectivity of the reaction, since
reductive dehalogenation of the aryl bromide becomes
methyl 4-bromobenzoate, 4-bromoacetophenone, and 4-bro-
mochlorobenzene (Table 2, entries 1, 5, 7, 2, 14, 13, and 9).
Problematic is the carbonylation of 4-bromonitrobenzene
due to deactivation of the catalyst. The formylation protocol
works well also with 1-bromo-3,5-xylene, different bromo-
naphthalenes (Table 2, entries 15–18), and heteroaryl halides
such as 3-bromothiophene and 3-bromopyridine (Table 2,
entries 11 and 12). This is of special importance since heter-
oaromatic aldehydes are particularly useful intermediates
for the synthesis of a number of biologically active mole-
cules.16 In case of 2-bromopyridine the catalyst seems to
be deactivated by the formation of inactive dimers after
the oxidative addition step.
100
TMEDA
NEt3
90
80
70
60
50
40
30
20
10
0
N(n-Bu)3
pyridine
K2HPO4
DABCO
N,N-dimethyl-
glycine ethyl ester
Since all experiments shown in Table 2 were performed
under similar conditions no significant difference in the
rate of electron-rich substrates (e.g., 4-bromoanisole, 4-(di-
methylamino)bromobenzene) and electron-deficient educts
(e.g., 4-bromobenzonitrile, 4-bromoacetophenone) was ob-
served. Thus, we conducted competition experiments in
order to investigate the effect of electron-withdrawing and
electron-donating substituents. Equimolar amounts of bro-
mobenzene and the corresponding para-substituted deriva-
tives were reacted with synthesis gas for 2 h. For data
interpretation, we employed the Hammett equation
0
5
10
15
20
25
30
pCO/H [bar]
2
Figure 1. Influence of base and carbon monoxide pressure on the yield of
4-methoxybenzaldehyde. Reaction conditions: 2 mmol 4-bromoanisole,
0.33 mol % Pd(OAc)2, 1 mol % cataCXiumÒ A, 1.5 equiv base, 0.2 equiv
hexadecane (internal standard), 2 mL toluene, 100 ꢀC, 16 h.
k
log ¼ sr
k0

A. Brennfu€hrer et al. / Tetrahedron 63 (2007) 6252–6258
6255
Table 2. Scope and limitations of the Pd(OAc)2/di-1-adamantyl-n-butyl-
phosphine (cataCXiumÒ A) catalyst system
where k is the rate constant of the reaction of the substituted
compound, k0 is the value for bromobenzene, s is a constant
characteristic of the substituent, and r is the specific reaction
constant. For six different substituents the Hammett s-
values were linearly correlated with the change in relative
rate constants.17
Entry (Hetero)aryl bromide Conversiona [%] Yielda [%] Selectivitya [%]
Br
1
2
98
99
94
98
95
99
MeO
Br
As shown in Figure 3, the reaction mechanism is consistent
for the different substituted bromoarenes. The relative rate
constant increases with increasing s, reflecting a reaction
rate that is enhanced by a decreased electron density of the
aromatic ring. As a result it is likely that the oxidative addi-
tion of the active palladium species to the aryl halide consti-
tutes the rate-determining step.
Me2N
Br
3
4
5
6
74
95
71
95
89
84
96
99
91
84
H3C
Br
Br
Next, we studied the reductive carbonylation of vinyl halides
in the presence of different catalyst systems. Here, the for-
mylation of (E)-2-bromo-2-butene was investigated as
a model system in the presence of six different phosphines
(Table 3, entry 1, entries 7–11).
98
F
Br
100
F3C
Br
Br
In agreement with the results obtained for aryl bromides only
cataCXiumÒ A permitted an efficient formylation of our
model system (yield: 98%; Table 3, entry 1). Triphenylphos-
phine, the standard bidentate ligand 1,4-bis(diphenylphos-
phino)butane, and P(t-Bu)3 gave only low yields of trans-
2-methyl-2-butenal (1–12%) (Table 3, entries 7, 8, 11). On
the other hand, PCy3 and 1,10-bis(diphenylphosphino)ferro-
cene (dppf) gave slightly higher, but no sufficient yields (22–
30%) of the desired product (Table 3, entries 9–10).
7
8
99
8
74
0
75
0
NC
O2N
Br
Br
9
100
100
97
89
87
82
77
88
89
87
85
79
88
Cl
10
11
12
13
After the ligand screening, the influence of different sol-
vents, pressure, and bases (Table 3, entries 1–6) has also
been studied. In general, we obtained similar trends as for
the formylation of (hetero)aryl bromides. Toluene and
THF gave better results than the more polar solvents DMF,
N,N-dimethylacetamide, and NMP. N,N,N0,N0-Tetramethyl-
ethylenediamine (TMEDA) is again the most active base
OHC
Br
S
Br
97
N
Br
100
Br
Br
CHO
CHO
O
O
Br
0,8
0,6
0,4
0,2
0,0
-0,2
+
+
CN
14
15
16
17
100
85
91
85
92
86
91
>99
92
X
H
X
H
O
Br
CF3
Br
Linear Regression: Y = A + B * X
100
100
Parameter Value
----------------------------------------------------
Error
Br
A
B
-0,02526
1,01394
0,01909
0,05242
H
86
CH3
R
R-Square(COD)
--------------------------------
0,9947
Br
NMe2
-0,2
0,98942
OCH3
0,0
18
19
100
100
99
85
99
85
O
0,2
σn
0,4
0,6
0,8
N
Br
p
N
Figure 3. Relationship between rate constant and Hammett s-values for
para-substituents. Reaction conditions: 1 mmol bromobenzene, 1 mmol
para-substituted bromobenzene, 0.25 mol % Pd(OAc)2, 0.75 mol %
cataCXiumÒ A, 0.75 equiv TMEDA, 0.2 equiv hexadecane (internal stan-
dard), 2 mL toluene, 5 bar CO/H2 (1:1), 100 ꢀC, 2 h.
Reaction conditions: 2 mmol (hetero)aryl bromide, 0.25 mol % Pd(OAc)2,
0.75 mol % cataCXiumÒ A, 0.75 equiv TMEDA, 0.2 equiv hexadecane
(internal standard), 2 mL toluene, 5 bar CO/H2 (1:1), 100 ꢀC, 16 h.
a
Determined by gas chromatography.

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A. Brennfu€hrer et al. / Tetrahedron 63 (2007) 6252–6258
Table 3. Palladium-catalyzed formylation of (E)-2-bromo-2-butene
Br
CHO
Pd(OAc)2, ligand
base, CO/H2
Entry
Ligand
Base
CO/H2 [bar]
T [ꢀC]
Conversiona [%]
Yielda [%]
Selectivitya [%]
1
2
3
4
5
6
7
8
cataCXiumÒ
A
TMEDA
NEt3
DABCO
(CH3)2NCH2COOC2H5
K2CO3
K2HPO4
TMEDA
TMEDA
TMEDA
TMEDA
TMEDA
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
100
100
100
100
100
100
100
100
100
100
100
100
88
88
89
99
52
86
40
51
98
46
98
48
50
19
46
1
98
54
56
22
46
1
PPh3
1
1
P(t-Bu)3
PCy3
dppf
12
22
30
9
30
44
31
19
9
10
11
dppb
Reaction conditions: 2 mmol (E)-2-bromo-2-butene, 0.5 mol % Pd(OAc)2, 1.5 mol % cataCXiumÒA, 0.75 equiv TMEDA, 0.2 equiv dodecane (internal stan-
dard), 2 mL toluene, 16 h.
Determined by gas chromatography.
a
CHO
for the model substrate. Complete conversion and excellent
yield (>98%) are obtained at a synthesis gas pressure of
7.5 bar.
Br
CHO
Finally, the scope of the optimized catalyst system for the re-
ductive carbonylation of vinyl halides was tested with eight
different substrates (Table 4). In addition to 2-bromo-2-
butene, 1-chloro-1-cyclopentene, 1-bromostyrene, and 2-
bromo-3-methyl-2-butene yielded the corresponding
a,b-unsaturated aldehydes in mediocre to very good yield
(41–98%). Unfortunately, no desired reaction is observed
applying 1-bromo-1-propene and methyl 2-bromoacrylate
as substrates. Noteworthy, the formylation of (Z)-2-bromo-
2-butene and cis-b-bromo-styrene18 gave selectively the
corresponding trans-aldehydes (Scheme 2).
Br
Scheme 2. Reductive carbonylation leading to a,b-unsaturated trans-
aldehydes.
in contrast with other palladium-catalyzed coupling reac-
tions of vinyl halides.19
3. Conclusion
Apparently, the initially generated oxidative addition prod-
uct is not stable under these conditions and rearranges to
the thermodynamically more stable trans-product. This is
In conclusion, we presented a general reductive carbonyl-
ation procedure for the synthesis of aromatic and heteroaro-
matic aldehydes, as well as a,b-unsaturated aldehydes.
Table 4. Reductive carbonylation of different vinyl halides
Entry
1
Vinyl halide
Pd(OAc)2 [mol %]
0.5
cataCXiumÒ A [mol %]
Conversiona [%]
100
Yielda [%]
98
Selectivitya [%]
98
Br
1.5
Br
Cl
2b
3
0.5
0.5
0.5
1.5
1.5
1.5
92
96
76
87
59
82
91
59
Br
4
100
5c
6
0.5
0.5
1.5
1.5
100
64
51
41
51
59
Br
Br
Reaction conditions: 2 mmol vinyl halide, 0.75 equiv TMEDA, 0.2 equiv dodecane (internal standard), 2 mL toluene, 7.5 bar CO/H2 (1:1), 100 ꢀC, 16 h.
Determined by gas chromatography.
a
b
As product only trans-2-methyl-2-butenal is formed.
Only trans-cinnamaldehyde is observed.
c

A. Brennfu€hrer et al. / Tetrahedron 63 (2007) 6252–6258
6257
Advantageously, the most simple and environmentally be-
nign formylation source synthesis gas can be used at ambient
pressure and low catalyst concentration. The ligand di-1-
adamantyl-n-butylphosphine (cataCXiumÒ A) leads to a
highly active catalyst species, but is comparably stable to
air and moisture, and thus easy to handle. Due to its superior
performance compared with other palladium catalysts, this
system is employed for the industrial production of a drug
intermediate on multi-1000 kg scale.
CDCl3): d¼9.78 (s, 1H, CHO), 6.87 (m, 1H, CH]CCHO),
2.60 (m, 2H, CH2), 2.51 (m, 2H, CH2), 1.99 (m, 2H,
CH2CH2CH2). 13C NMR (75 MHz, CDCl3): d¼189.9
(C]O), 153.2 (CH), 147.9, 33.7 (CH2), 28.3 (CH2), 22.9
(CH2). MS (EI, 70 eV): m/z (%)¼96 (62) M+, 67 (100)
[MꢁCHO]+, 41 (29), 39 (30). IR (capillary): 2957 (m),
2714 (w), 1679 (vs) [C]O], 1615 (m) cmꢁ1. HR-MS (EI):
calcd for C6H8O: 96.0570; found: 96.0571 [M]+.
4.2.3. 2,3-Dimethyl-2-butenal. Yield: 41%. Colorless liq-
uid, bp 57 ꢀC (20 Torr).21 1H NMR (300 MHz, CDCl3):
d¼10.12 (s, 1H, CHO), 2.19 (m, 3H, CH3), 1.96 (m, 3H,
CH3), 1.74 (m, 3H, CH3). 13C NMR (75 MHz, CDCl3):
d¼191.2 (C]O), 155.0, 132.6, 23.8 (CH3), 19.4 (CH3),
11.0 (CH3). MS (EI, 70 eV): m/z (%)¼98 (100) M+, 69
(45) [MꢁCHO]+, 55 (45), 41 (79), 39 (30). IR (capillary):
1671 (vs) [C]O], 1635 (s) [C]C] cmꢁ1. HR-MS (EI):
calcd for C6H10O: 98.0726; found: 98.0720 [M]+.
4. Experimental section
4.1. General remarks
All reactions were performed using standard Schlenk tech-
niques (argon). 1H and 13C NMR spectra were recorded on
a Bruker ARX 300 spectrometer. Chemical shifts (d) are
given in ppm and refer to the residual solvent as the internal
standard (CDCl3: 7.26/77.0). Gas chromatography was per-
formed on a Hewlett Packard HP 6890 chromatograph
with a HP1 column. Chemicals were purchased from
Fluka, Aldrich, and Strem, and used as received. The cata-
CXiumÒ A ligand is available from Strem or directly from
Degussa. Solvents were distilled from sodium and benzo-
phenone.
Acknowledgements
The authors thank Dr. H. Klein, S. Giertz, and S. Buchholz
for excellent technical and analytical assistance, as well as
Dr. R. Jackstell and Dr. T. Schareina (all at Leibniz-Institut
€
fur Katalyse, Rostock) for providing ligands and complexes.
Generous financial support from Degussa AG, Mecklen-
burg-Vorpommern, the Fonds der Chemischen Industrie,
4.2. General procedure for the formylation of (hetero)-
aryl bromides and vinyl halides
€
the Bundesministerium fur Bildung und Forschung
(BMBF), and the DFG (Leibniz Prize) is gratefully acknowl-
edged.
A 50 mL Schlenkflask was chargedwith Pd(OAc)2 (11.2 mg,
0.25 mol %), cataCXiumÒ A (53.8 mg, 0.75 mol %), and tol-
uene (20 mL). Subsequently, hexadecane (1.17 mL, internal
GC standard) and TMEDA (N,N,N0,N0-tetramethylethylene-
diamine) (2.25 mL, 15 mmol) were added. About 2.34 mL of
this clear yellow stock solution was transferred to six vials
(4 mL reactionvolume) equipped with a septum, a small can-
nula, a stirring bar, and 2 mmol of the corresponding (heter-
o)aryl bromide. Thevials were placed in an alloy plate, which
was transferred to a 300 mL autoclave of the 4560 series from
Parr InstrumentsÒ under argon atmosphere. After flushing
the autoclave three times with CO/H2 (1:1), the appropriate
synthesis gas pressure was adjusted to ambient temperature
and the reaction was performed for 16 h at 100 ꢀC. Before
and after the reaction an aliquot of the reaction mixture was
subjected to GC analysis for determination of yield and
conversion.
References and notes
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4.2.1. Quinoxaline-6-carbaldehyde. Rf (SiO2, n-heptane/
EtOAc¼3:1): 0.1. Yield: 85%. Yellow solid, mp 130–
1
131 ꢀC. H NMR (300 MHz, DMSO-d6): d¼10.28 (s, 1H,
CHO), 9.09 (m, 2H, NCH]CHN), 8.71 (s, 1H,
OHCCCHCN), 8.22 (m, 2H). 13C NMR (75 MHz, DMSO-
d6): d¼192.8 (C]O), 148.0 (CH), 147.1 (CH), 145.0,
141.9, 136.8, 134.5 (CH), 130.4 (CH), 126.6 (CH). MS
(EI, 70 eV): m/z (%)¼158 (100) M+, 129 (49) [MꢁCHO]+,
103 (32), 75 (23), 50 (13). IR (KBr): 1697 (vs) [C]O],
1353 (s), 1226 (m), 1142 (m), 1118 (s), 1024 (s), 960 (s),
914 (s), 880 (m), 832 (m), 774 (s), 760 (m) cmꢁ1. HR-MS
(EI): calcd for C9H6N2O: 158.0475; found: 158.04706 [M]+.
4.2.2. 1-Cyclopentene-1-carbaldehyde. Yield: 87%. Color-
less liquid, bp 47–48 ꢀC (14 Torr).20 1H NMR (300 MHz,

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€
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