Systematic study on the catalytic synthesis of unsaturated 2-ketocarboxamides: Palladium-catalyzed double carbonylation of 1-iodocyclohexene

Article abstract of DOI:10.1016/j.tet.2011.10.065

1-Iodocyclohexene, a benchmark substrate, has been double carbonylated in the presence of palladium-phosphite precatalysts. Triarylphosphites with OR substituents, able to act both as P-monodentate and hemilabile P,O-heterobidentate ligands were used in t

Full text of DOI:10.1016/j.tet.2011.10.065

Tetrahedron 68 (2012) 204e207
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Tetrahedron
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Systematic study on the catalytic synthesis of unsaturated 2-ketocarboxamides:
palladium-catalyzed double carbonylation of 1-iodocyclohexene
a
a
b
b,
*
ꢀ
ꢀ
ꢀ
ꢀ
Rui M.B. Carrilho , Mariette M. Pereira , Attila Takacs , Laszlo Kollar
a Department of Chemistry, University of Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
Department of Inorganic Chemistry, University of Pecs, H-7624 Pecs, PO Box 266, Hungary
b
ꢀ
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 August 2011
Received in revised form 28 September 2011
Accepted 17 October 2011
Available online 23 October 2011
1-Iodocyclohexene, a benchmark substrate, has been double carbonylated in the presence of palladium-
phosphite precatalysts. Triarylphosphites with OR substituents, able to act both as P-monodentate and
hemilabile P,O-heterobidentate ligands were used in this reaction. Systematic investigations have re-
vealed that the chemoselectivity towards cyclohexenylglyoxylamides, i.e., the products obtained in
aminocarbonylation by the insertion of two carbon monoxide, is strongly influenced by the amine nu-
cleophile, temperature and carbon monoxide pressure. The highest yields of 2-ketocarboxamides were
obtained at low temperature (30 ꢀC) and high carbon monoxide pressure (110 bar). However, the
structure of the phosphite ligand has practically no effect either on catalytic activity or chemoselectivity.
This fact refers to the P-monodentate coordination of the ligands in catalytic intermediates or that
palladium nanoparticles are the catalytically active species.
Keywords:
Carbonylation
Palladium
Homogeneous catalysis
Amino acids
Ó 2011 Elsevier Ltd. All rights reserved.
Carbon monoxide
1. Introduction
As a part of our continuing research in this field, newly de-
veloped arylphosphites as heterobidentate P,O-ligands10 were
Since the early discovery of the carbonylation of aryl halides in
the presence of O- and N-nucleophiles, resulting in the corre-
sponding esters and amides, respectively,1 hundreds of examples
have shown its synthetic potential.2e4 Various types of complicated
skeletons, most of them with practical importance,5,6 were func-
tionalized as well. The intramolecular version of this reaction
provides the corresponding cyclic derivatives, lactones and lac-
tames, respectively.7 The alkoxy- and aminocarbonylation of aryl
halides has become an indispensable tool for the synthesis of esters
as amides of unprecedented structures. The synthetic potential of
palladium-catalyzed carbonylations of aromatic halides, including
the first industrial applications, has been reviewed recently.8,9
Similar to aryl halides, iodo- and bromoalkenes of various struc-
tures readily undergo alkoxy- and aminocarbonylations resulting in
tested in palladium-catalysed aminocarbonylation of an iodoalkene
model compound. A high-yielding double carbonylation of 1-
iodocyclohexene in the presence of N-nucleophiles is reported.
2. Results and discussion
1-Iodocyclohexene (1) was aminocarbonylated in the presence of
palladium catalysts formed in situ by the reaction of palladium(II) ac-
etate and two molar equivalents of triarylphosphite (tris(20-benzy-
loxy-1,10-binaphthalene-2-yl)phosphite) (L2), (tris(20-methoxy-1,10-
binaphthalene-2-yl)phosphite) (L1), (tris(20-adamanthyloxy-1,10-bina
phthalene-2-yl)phosphite) (L4), (tris(20-diphenylmethoxy-1,10-binaph
a,b-unsaturated esters and carboxamides, respectively. The major
P
difference to the corresponding aromatic substrates lies in the lack of
double carbon monoxide insertion, i.e., neither the formation of 2-
keto-carboxylic esters nor that of 2-ketocarboxamides were re-
ported using this methodology. Although several types of iodo-
alkenes were carbonylated under the variety of conditions (solvent,
ligand, carbon monoxide pressure), to the best of our knowledge,
unsaturated 2-keto-carboxylic acid derivatives have not been syn-
thesized in palladium-catalyzed alkoxy- and aminocarbonylations.5,6
O
O
R
3
L1 (R = Me)
L2 (R = Bn)
L3 (R = CHPh2)
L4 (R = Ad)
ꢀ
* Corresponding author. E-mail address: kollar@ttk.pte.hu (L. Kollar).
Fig. 1. Binaphthyl-based triarylphosphites used in this study.
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.10.065

R.M.B. Carrilho et al. / Tetrahedron 68 (2012) 204e207
205
thalene-2-yl)phosphite) (L3) (Fig. 1). tert-Butylamine (a), aniline (b),
methyl alaninate (c), morpholine (d) and piperidine (e)wereusedasN-
nucleophiles (Scheme 1).
formation of 3a in case of low temperature (30 ꢀC) only (entries 4
and 6), (iii) at higher temperature (80 ꢀC) the effect of the pressure
on chemoselectivity is almost negligible. Consequently, the highest
chemoselectivity of 67% towards 2-ketocarboxamide 3a has been
obtained at 30 ꢀC under 110 bar CO pressure (entry 4).
Screening the amines in aminocarbonylation, an efficient syn-
thesis of the corresponding ketoamides 3d and 3e was carried out
with secondary amines (d and e) resulting in chemoselectivities of
67 and 71%, respectively (entries 16 and 17). Low chemoselectivity
towards the double carbonylation product 3c was observed with
methyl alaninate (c) (entries 12 and 13). It is worth mentioning that
no double carbon monoxide insertion was observed with aromatic
amine (b) as a nucleophile. However, unexpectedly high activities
for the formation of the corresponding carboxamide (2b) was ob-
served (entries 8e10).
The tert-butylaminocarbonylation with the other ligands (L1, L3
and L4) show similar chemoselectivities and activities as L2 (Table
2). Ketocarboxamides (3) of unprecedented structure are the major
products in all cases at low temperature and high carbon monoxide
pressure (entries 2, 4, 7 and 10). All of these ligands provide car-
boxamides (2) exclusively in the presence of tert-butylamine (a) as
the N-nucleophile under mild conditions (entries 1, 3 and 9). It can
be stated that the OR moiety does not influence thoroughly either
the reactivity or the chemoselectivity. These results suggest that
the phosphite ligands (L1eL4), which are able to coordinate also in
P,O-heterobidentate manner in catalytic precursors,10 could bound
to palladium as monodentate P-ligands (upon the activation of the
iodoalkene substrate) under aminocarbonylation conditions.
Although the formation of 2-oxo-carboxamides from haloar-
omatics can be explained in two ways, namely, both the ‘glyoxyl-
route’ and the ‘acyl-carbamoyl-route’ can be operative, detailed
mechanistic studies revealed that the latter is responsible for
double carbonylation.14,15 A similar mechanism could be operative
in one case of our phosphiteepalladium systems containing steri-
cally hindered heterobidentate ligands. The facile oxidative addi-
tion of in situ formed palladium(0) species resulted in an alkenyl-
palladium(II) (A) intermediate, which is able to coordinate carbon
monoxide (B). The acyl complex (C), formed in carbon monoxide
insertion, is ready to coordinate the ‘second’ carbon monoxide as
a terminal carbonyl, which undergoes a nucleophilic attack by the
N-nucleophile (D). In this way, the bulky hemilabile ligands
(L1eL4) favour the formation of the acyl-carbamoyl-palladium(II)
(Pd{RC(O)}{C(O)NR1R2}) intermediate (E), which readily un-
dergoes reductive elimination providing 2-ketocarboxamides
(Scheme 2).
NR1R2
O
NR1R2
O
I
O
CO, HNR1R2
+
Pd(OAc)2 (2.5 mol%)
L1-L4 (5 mol%)
1
2
3
R1 R2
a
b
c
d
e
H
H
H
tBu
Ph
CH(CH3)COOMe
(CH2)2O(CH2)2
(CH2)5
Scheme 1. Aminocarbonylation of 1-iodocyclohexene.
It is worth mentioning, that the above in situ catalyst is the
phosphite analogue of the widely used palladium(0)-tertiary
phosphine systems. It has been proved that palladium(II) is re-
duced to palladium(0) while one of the 2 equiv of ligands is oxi-
dized.11e13 In our case, the formation of coordinatively highly
unsaturated Pd(L)(S)n (S stands for solvent (DMF)) complex is
supposed while the ‘second’ equivalent of L is oxidized to the cor-
responding triaryl phosphate. Under the reaction conditions used
(see below) the action of other compounds (amine, carbon mon-
oxide) as reducing agents cannot be excluded.
Although the tert-butylaminocarboxamide derivative (2a) is the
only product under standard conditions (1 bar CO, 50 ꢀC) in the
presence of palladium-L2 catalytic system (Table 1, entry 1), 2-
ketocarboxamide (3a) is also formed under 20e110 bar CO pres-
sure (entries 2e7). The reaction conditions were optimized towards
the formation of 3a; the following effects are worth mentioning: (i)
the decrease of the temperature favours the formation of 3a, (ii) the
increase in the CO pressure has a positive influence on the
Table 1
Aminocarbonylation of 1-iodocyclohexene (1) in the presence of palladium-L2 in
situ catalystsa
Entry Amine T [ꢀC] p(CO) [bar] tR [h] Conv.b Turnover
Molar
ratio of 2/3
[%]
frequencyc [hꢁ1
]
1
2
3
4
5
6
7
8
a
a
a
a
a
a
a
50
50
50
30
30
30
30
50
50
30
50
50
30
50
30
30
30
1
40
60
110
110
20
20
1
40
120
1
40
120
1
110
110
110
0.5
3
1
2
6
2
3
1
0.5
2
1
1
2
1
2
4
4
100
100
100
75
100
69
>80
>13
>40
15
100/0
75/25
66/34
33/67
46/54
61/39
60/40
100/0
100/0
100/0
100/0
97/3
Table 2
>7
tert-Butylaminocarbonylation of 1-iodocyclohexene (1) in the presence of
13.8
10.7
25.6
>80
>20
>40
>40
17.4
>40
18.4
>10
>10
palladium-triarylphosphite (L1eL4) in situ catalystsa
80
64
Entry Ligand T [ꢀC] p(CO) tR [h] Conv.b [%] Turnover
Molar ratio
of 2/3
bd
bd
bd
ce
ce
ce
df
df
df
ef
[bar]
frequencyc [hꢁ1
]
9
100
100
100
100
87
100
92
100
100
10
11
12
13
14
15
16
17
1
2
3
4
5
6
7
8
L1
L1
L2
L2
L2
L3
L3
L3
L4
L4
L4
50
30
50
30
30
30
30
30
50
30
30
1
110
1
110
110
110
110
110
1
1
4
0.5
2
6
1
2
6
1
100
100
100
75
100
59
>40
>10
>80
15
100/0
39/61
100/0
33/67
46/54
43/57
28/72
43/57
100/0
33/67
50/50
93/7
100/0
34/66
33/67
29/71
>7
23.6
14.2
>7
>40
15.2
>7
71
100
100
76
9
10
11
a
Reaction conditions (unless otherwise stated):
1 mmol of substrate (1);
110
110
2
6
0.025 mmol of Pd(OAc)2; 0.05 mmol of ligand (L2); 3 mmol of a; 0.5 mL of trie-
100
thylamine; solvent: 10 mL of DMF.
b
a
Determined by GC and GCeMS (naphthalene as internal standard).
Reaction conditions (unless otherwise stated): 1 mmol of substrate (1);
c
(mmol of 1)ꢂ(mmol of Pd)ꢁ1ꢂ(reaction time)ꢁ1
.
0.025 mmol of Pd(OAc)2; 0.05 mmol of ligand (L1eL4); 3 mmol of a; 0.5 mL of
d
e
f
Compound b (2 mmol).
triethylamine; solvent: 10 mL of DMF.
b
Compound c (1.1 mmol) (as a hydrochloride salt).
Compounds d, e(1.5 mmol).
Determined by GC and GCeMS (naphthalene as internal standard).
c
(mmol of 1)ꢂ(mmol of Pd)ꢁ1ꢂ(reaction time)ꢁ1.

206
R.M.B. Carrilho et al. / Tetrahedron 68 (2012) 204e207
NR1R2
O
mild reaction conditions. The full characterization of the isolated
new ketocarboxamides (3a, 3d, 3e) is given below (Section 4.4).
O
I
4.2. Aminocarbonylation of 1-iodocyclohexene (1) in the
presence N-nucleophiles under high carbon monoxide
pressure
LnPd
1R2RN
In a typical experiment Pd(OAc)2 (5.6 mg, 0.025 mmol), phos-
phite ligand (L1eL4) (0.05 mmol), 1-iodocyclohexene (1 mmol),
amine nucleophile (3 mmol of a/2 mmol of b/1.1 mmol of c/
1.5 mmol of d) and 0.5 mL triethylamine were dissolved in DMF
(10 mL) under argon in a 100 mL autoclave. The atmosphere was
changed to carbon monoxide and the autoclave was pressurized to
the given pressure by carbon monoxide. The reaction was con-
ducted for the given reaction time upon stirring at 50 ꢀC (or 30 ꢀC)
and analyzed by GCeMS. The mixture was then concentrated and
evaporated to dryness. The residue was dissolved in chloroform
(20 mL) and washed with water (3ꢂ20 mL). The organic phase was
dried over Na2SO4, filtered and evaporated to a crystalline material
or to a waxy residue. All compounds were subjected to column
chromatography (Silicagel 60 (Merck), (0.063e0.200 mm), EtOAc/
CHCl3 (the exact ratios are specified in characterization for each
compound)).
I
PdLn
PdLn
O
O
A
E
CO
HI
R2
N
I
Pd(CO)Ln
R1
H
CO
PdLn
D
B
I
O
C
I
PdLn
O
CO, R1R2NH
4.3. Aminocarbonylation of 1-iodocyclohexene (1) in the
presence N-nucleophiles under atmospheric carbon
monoxide pressure
Scheme 2. A simplified catalytic cycle describing the formation of 1-
cyclohexenylglyoxylamides.
3. Conclusions
In a typical experiment Pd(OAc)2, phosphite ligand (L1eL4), 1-
iodocyclohexene, amine nucleophile and triethylamine were dis-
solved in DMF (for the quantity of the reagents See Section 4.2)
under argon in a 100 mL three-necked flask equipped with a gas
inlet, reflux condenser with a balloon (filled with argon) at the top.
The atmosphere was changed to carbon monoxide. The reaction
was conducted for the given reaction time upon stirring at 50 ꢀC
and analysed by GCeMS (internal standard: naphthalene). The
mixture was then concentrated and evaporated to dryness and
worked-up as described in Section 4.2.
The double carbonylation of an iodoalkene model compound
has been carried out in palladium-catalysed aminocarbonylation.
Alkenyl-glyoxylamides, valuable building blocks in synthetic
chemistry, have been synthesized for the first time using this
methodology. Arylphosphite heterobidentate P,O-ligands possess-
ing binaphthyl backbone were used as ligands in palladium cata-
lysts formed in situ from palladium(II) acetate and two molar
equivalents of the corresponding phosphite ligand.
4. Experimental
4.4. Characterization of the products
4.1. General procedures
4.4.1. Compound 3a22 1H NMR (CDCl3)
. d: 7.80 (br s, 1H, ]CH); 6.68
(br s, 1H, NH); 2.32 (m, 2H, CH2); 2.23 (br s, 2H, CH2); 1.65 (m, 4H
1H and 13C NMR spectra were recorded in CDCl3 on a Varian
Inova 400 spectrometer at 400.13 MHz and 100.62 MHz, re-
2ꢂ CH2); 1.39 (s, 9H, C(CH3)3). 13C NMR (CDCl3)
d: 189.1,162.0, 149.7,
135.5, 51.4, 28.3, 26.7, 23.1, 21.7, 21.2. IR (KBr (cmꢁ1)): 3274 (NH);
1669 (CO); 1646 (CON). MS m/z (rel int. %): 209 (12%), 194 (2%), 153
(18%), 109 (100%), 81 (46%); 57 (32%). Analysis calculated for
C12H19NO2 (209.28): C, 68.87; H, 9.15; N, 6.69; found: C, 68.72; H,
9.01; N, 6.40. Rf (2% EtOAc/CHCl3) 0.48. Mp. 81e82 ꢀC. Beige crys-
talline material. Yield: 0.125 g (60%).
spectively. Chemical shifts
d are reported in parts per million rela-
tive to CHCl3 (7.26 and 77.00 ppm for 1H and 13C, respectively).
Elemental analyses were measured on a 1108 Carlo Erba apparatus.
Samples of the catalytic reactions were analysed with a Hewlett
Packard 5830A gas chromatograph fitted with a capillary column
coated with OV-1 (internal standard: naphthalene; injector tem-
perature 250 ꢀC; oven: starting temperature 50 ꢀC (hold-time
11 min), heating rate 15 ꢀC minꢁ1, final temperature 320 ꢀC; de-
tector temperature 180 ꢀC; carrier gas: helium (rate: 1 mL minꢁ1)).
The FT-IR spectra were taken in KBr pellets using an IMPACT 400
spectrometer (Nicolet) applying a DTGS detector in the region of
400e4000 cmꢁ1, the resolution was 4 cmꢁ1. The amount of the
samples was ca. 0.5 mg.
4.4.2. Compound 3d. 1H NMR (CDCl3)
d: 6.93 (br s, 1H, ]CH);
3.64e3.74 (m, 6H, 3ꢂ CH2); 3.30 (t, 4.8 Hz, 2H, NCH2); 2.35 (br s, 2H,
CH2); 2.26 (br s, 2H, CH2); 1.66 (m, 4H, 2ꢂ CH2). 13C NMR (CDCl3)
d:
193.1,166.1,148.9,137.0, 66.7, 66.6, 46.3, 41.4, 26.5, 21.8, 21.4, 21.3. IR
(KBr (cmꢁ1)): 1654 (CO); 1644 (CON); 1626 (C]C). MS m/z (rel int.
%): 223 (31%), 194 (2%), 109 (100%), 81 (49%), 70 (19%), 53 (10%).
Analysis calculated for C12H17NO3 (223.27): C, 64.55; H, 7.67; N,
6.27; found: C, 64.37; H, 7.51; N, 6.05. Rf (20% EtOAc/CHCl3) 0.4. Mp.
109e110 ꢀC. Off white crystalline material. Yield: 0.138 g (62%).
The amine nucleophiles were purchased from SigmaeAldrich.1-
Iodocyclohexene (1) was prepared according to the literature pro-
cedure18 starting from cyclohexanone. The ligands L1eL4 were
prepared as described before.10 The products of known structure
(2a,16,17 2c,18 2d,19 2e20,21), obtained by conventional synthetic
methods, gave identical spectra with those given in the literature.
It is worth noting that all carboxamides (2aee) can be isolated in
nearly quantitative yields (up to 98%) being the only products under
4.4.3. Compound 3e. 1H NMR (CDCl3)
d: 6.29 (br s, 1H, ]CH); 3.61
(t, 5.2 Hz, 2H, NCH2); 3.21 (t, 5.2 Hz, 2H, NCH2); 2.38 (m, 4H, 2ꢂ
CH2); 1.56e1.65 (m, 10H, 5ꢂ CH2). 13C NMR (CDCl3)
d: 193.9, 166.1,
148.2, 136.9, 47.1, 42.0, 26.5, 26.2, 25.4, 24.4, 21.8, 21.4, 21.3. IR (KBr
(cmꢁ1)): 1658 (CO), 1641 (CON). MS m/z (rel int. %): 221 (28%), 192

R.M.B. Carrilho et al. / Tetrahedron 68 (2012) 204e207
207
€
ꢀ
6. Skoda-Foldes, R.; Kollar, L. Curr. Org. Chem. 2002, 6, 1097e1119.
(6%), 109 (100%), 81 (48%); 69 (46%), 53 (15%). Analysis calculated
for C13H19NO2 (221.30): C, 70.56; H, 8.65; N, 6.33; found: C, 70.40;
H, 8.77; N, 6.17. Rf (10% EtOAc/CHCl3) 0.48. Mp. 77e78 ꢀC. Yellow
crystalline material. Yield: 0.146 g (66%).
7. Rossi, E. Palladium-Assisted Synthesis of Heterocycles via Carbonylation Re-
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8. Wu, X. F.; Neumann, H.; Beller, M. Chem.dEur. J. 2002, 16, 9750e9753.
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