Catalytic reaction of methyl formate with amines to formamides

Article abstract of DOI:10.1016/j.tet.2009.10.047

A feasible procedure of using methyl formate as cheap reagent for the conversion of aliphatic and aromatic amines into formamides with high yields is reported. The improved amine formylation method proceeds mainly at room temperature and in presence of bicyclic guanidines as catalysts. A verifiable key intermediate of outstanding formylating activity is generated from methyl formate and the catalyst in the reaction mixture.

Full text of DOI:10.1016/j.tet.2009.10.047

Tetrahedron 65 (2009) 10365–10369
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Tetrahedron
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Catalytic reaction of methyl formate with amines to formamides
*
Jens Deutsch , Reinhard Eckelt, Angela Ko¨ckritz, Andreas Martin
Leibniz Institute for Catalysis at University Rostock, Albert-Einstein-Straße 29a, 18059 Rostock, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 August 2009
Received in revised form 13 October 2009
Accepted 14 October 2009
Available online 31 October 2009
A feasible procedure of using methyl formate as cheap reagent for the conversion of aliphatic and aro-
matic amines into formamides with high yields is reported. The improved amine formylation method
proceeds mainly at room temperature and in presence of bicyclic guanidines as catalysts. A verifiable key
intermediate of outstanding formylating activity is generated from methyl formate and the catalyst in the
reaction mixture.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Amides
Amines
Formylation
Homogeneous catalysis
1. Introduction
the synthesis of formamides from amines during the last decades.
The weak carbonyl activity of the carbon oxides requires harsh
The transformation of primary or secondary amines into form-
amides is an important chemical reaction. The reaction products
are used as polar solvents or as intermediates for the production of
pharmaceuticals.1 In synthetic organic chemistry, the N-bonded
formyl group is introduced commonly as a temporary protection
group2 or reduced to a methyl group.3 The formamides, which
derived from primary amines grant easy access to isocyanides.4
Various N-formylating reagents have already been reported in the
literature. The most conventional of them are formic acid,1,5 form-
amide,6 acetic formic anhydride,7 chloral,8 trialkyl orthoformates,9
enol formates,10 cyanomethyl formate,11 2,2,2-trifluoroethyl for-
mate,12 pentafluorophenyl formate,13 diformamide,14 N-for-
mylimidazole,15 N-formylbenzotriazole,16 and potassium cyanide/
dimethyl malonate.17 Formic acid and formamide are inexpensive
formylating compounds. Regrettably, their only moderate reactivity
demands increased reaction temperatures, especially for the for-
mylation of sterically hindered and aromatic amines. In contrast, the
mentioned activated formic acid esters and amides show a consid-
erably higher formylating power and can be used under milder re-
action conditions. Nevertheless, their practical application seems to
be limited to laboratory use only. The main disadvantages of these
reagents are their accessibility, poor atom economy and, for some of
them, the stoichiometric liberation of toxic byproducts.
reaction conditions, a considerable technical expenditure, the ad-
dition of homogeneous or heterogenised ruthenium or platinum
catalysts to the reaction mixture, and impedes the synthesis of
formanilides from aromatic amines.
Besides the formylating agents listed above, methyl formate can
be utilised for the synthesis of formamides. However, its reaction
with amines has only been reported for single examples and has
not yet been investigated systematically. The literature indicates
that long reaction times and/or a large excess of the ester are re-
quired to achieve acceptable product yields, even for aliphatic
formamides.20
2. Results and discussion
The aim of the investigations was to establish a practicable and
improved method of using methyl formate for amine formylations
R1
R2
O
R1
R2
catalyst
- MeOH
N
H
N
+
OMe
O
Scheme 1. Catalytic formylation of various amines with methyl formate. Amines:
Piperidine: R1–R2¼(CH2)5; morpholine: R1–R2¼(CH2)2-O-(CH2)2; n-hexylamine:
R1¼n-Hex, R2¼H; benzylamine: R1¼Ph–CH2, R2¼H; cyclohexylamine: R1¼c-Hex,
R2¼H; 1-phenylethylamine: R1¼Ph–CH(Me), R2¼H; t-butylamine: R1¼t-Bu, R2¼H;
4-methoxyaniline: R1¼4-MeO–C6H4, R2¼H; 4-methylaniline: R1¼4-Me-C6H4, R2¼H;
N-methylaniline: R1¼Ph, R2¼CH3; aniline: R1¼Ph, R2¼H; 4-chloroaniline: R1¼4-Cl–C6H4,
R2¼H; ethyl-i-propylamine: R1¼Et, R2¼i-Pr; 4-amino methyl benzoate: R1¼4-MeO2C–
C6H4, R2¼H; 4-nitroaniline: R1¼4-O2N–C6H4, R2¼H.
Carbon monoxide18 or carbon dioxide in combination with hy-
drogen18,19 were developed as alternative and clean reagents for
* Corresponding author. Tel.: þ49 3811281266; fax: þ49 381128151266.
E-mail address: jens.deutsch@catalysis.de (J. Deutsch).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.10.047

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J. Deutsch et al. / Tetrahedron 65 (2009) 10365–10369
(Scheme 1). The main aspects were i) the exploration of suitable
catalysts for the reaction, ii) the optimisation of the reaction con-
ditions according to the reactivity of the amine to be converted into
a formamide, and iii) studies on the catalytic cycle. Methyl formate
might become a useful future platform chemical as it is available
from methanol, hydrogen and the exhaust gas carbon dioxide in the
presence of ruthenium catalysts.19b,19d,21
An initial model experiment revealed that morpholine is able to
react slowly at room temperature in the absence of a catalyst with
methyl formate to N-formylmorpholine (Table 1 entry 1a). Re-
markably, the known N-acylation catalysts 4-dimethylaminopyr-
idine22, 1-methylimidazole,23 imidazole,11 and 1,2,4-triazole24 were
inactive and did not accelerate this reaction. For that reason, the
considerably stronger bases 1,5-diazabicyclo[4.3.0]non-5-ene
(DBN), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 7-methyl-
1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) were evaluated as
possible alternatives (Table 1). DBN and DBU have been reported as
stoichiometrically usable dehydrohalogenating agents for the
transformation of alkyl halogenides into alkenes.25 Furthermore,
DBN was applied as catalyst for Michael additions.26 The present
experiments have shown that the three bases have noticeable
catalytic influences on the formylation of morpholine (Table 1,
entries 1b–d). Consequently, the structurally related bicyclic
guanidine bases 1,4,6-triazabicyclo[3.3.0]oct-4-ene (TBO), 1,4,6-tri-
azabicyclo[3.4.0]non-4-ene (TBN),1,5,7-triazabicyclo[4.4.0]dec-5-ene
(TBD-1), 1,4,6-triazabicyclo[3.5.0]dec-4-ene (TBD-2) and 1,5,6-tri-
azabicyclo[4.5.0]undec-5-ene (TBU) (Table 1) were included addi-
tionally into the investigations. It is known from the literature that
TBD-1 can be applied in a semicatalytic amount of 30 mol % as acti-
vating additive in the aminolysis of alkanoic and benzoic acid esters.
These reactions were performed for 12 h at 75 ꢀC.27 Surprisingly it was
found out that TBO, TBN, TBD-1, TBD-2 and TBU effected a nearly
complete reaction between methyl formate and morpholine within
30 min at room temperature (Table 1, entries 1e–i). Thus, the
Table 1
Evaluation of amidine and guanidine catalysts in the reactions of morpholine and t-butylamine with methyl formate at room temperature according to Scheme 1a
N
N
N
N
1,5-Diazabicyclo[4.3.0]non-5-ene
DBN
1,8-Diazabicyclo[5.4.0]undec-7-ene
DBU
N
N
N
N
N
N
H
Me
1,4,6-Triazabicyclo[3.3.0]oct-4-ene
TBO
7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene
MTBD
N
N
N
N
H
N
N
H
1,5,7-Triazabicyclo[4.4.0]dec-5-ene
1,4,6-Triazabicyclo[3.4.0]non-4-ene
TBN
TBD-1
N
N
N
N
N
N
H
H
1,5,6-Triazabicyclo[4.5.0]undec-5-ene
1,4,6-Triazabicyclo[3.5.0]dec-4-ene
TBU
TBD-2
Amine
Reaction time [h]
0.5
Entry
Catalyst
Product yield [%]
Morpholine
1a
1b
1c
1d
1e
1f
1g
1h
1i
Blank test
DBN
DBU
MTBD
TBO
TBN
TBD-1
TBD-2
TBU
2
6
14
9
89
87
90
88
87
t-Butylamine
7
2a
2b
2c
2d
2e
2f
2g
2h
2i
Blank test
DBN
DBU
MTBD
TBO
TBN
TBD-1
TBD-2
TBU
0
0
0
0
9
38
70
57
24
a
All the reactions were carried out using 10 mmol morpholine or t-butylamine, 12 mmol methyl formate, 120 mmol toluene as solvent, and 0.5 mmol (5 mol %) catalyst.

J. Deutsch et al. / Tetrahedron 65 (2009) 10365–10369
10367
Table 2
the very reactive amines piperidine, morpholine and benzylamine
(Table 2, entries 1,2,4). In contrast, TBD-1 was catalytically effective
for the formylation of various secondary, primary and even of
aromatic amines (Table 2, entries 1–9). As an exception, the sterically
hindered amine diisopropylamine could not be formylated with
methyl formate in presence of TBD-1 (not given in Table 2).
To develop a convenient synthetic method for the preparation of
formamides with methyl formate, the TBD-1 catalysed experiments
reported above were repeated under optimised reaction conditions
(Table 3). For formylations of reactive amines, a catalyst amount of
2.5 mol % was sufficient (Table 3, entries 1–6). The reactions of
aromatic amines and ethyl-i-propylamine were done with 5 mol %
TBD-1, an increased amount of methyl formate and in the absence
of solvent (Table 3, entries 7–15). Compared to previously reported
amine formylations with methyl formate,28 4-methylformanilide
and 4-methoxyformanilide were synthesised in the presence of
TBD-1 much faster, under milder conditions and with higher yields.
Formylations of aromatic amines with electron withdrawing
groups like 4-amino methyl benzoate and 4-nitroaniline were run
above the boiling point of methyl formate in an autoclave. As
expected, the weak nucleophilic compound 4-nitroaniline gave the
lowest product yield (Table 3, entry 15).
Some of the formamides to be isolated from the organic reaction
mixture are water soluble compounds. By the neutralisation with
the solid acid KHSO4 followed by filtration product loss, caused by
an extractive removal of unreacted amine and catalyst with water,
was avoided.
On the whole, the amines were converted without any side
products into the desired formamides with high purities and
yields.
To identify the active formylating species in the reaction, an
equimolar mixture of methyl formate and TBD-1 was prepared. The
signals in the 1H NMR spectrum of the obtained oil could be assigned
without any doubt to 7-formyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene
(FTBD-1) formed according to Scheme 2 with an NMR yield of 65%.
Moreover, its IR spectrum shows typical bands for a formamide
carbonyl group (1668 cmꢁ1) and a C]N bond (1626 cmꢁ1). FTBD-1
proved to have a limited thermal stability because of a probable
propensity for decarbonylation into TBD-1 and carbon monoxide.
Consequently, neither a sure GC–MS identification nor the separa-
tion of FTBD-1 from unreacted TBD-1 by distillation or flash chro-
matography was successful.
Reaction of amines with methyl formate at room temperature over various catalystsa
Entry Amine
Product yield according to GC analysis [%]
Reaction Blank test Catalyst
time [h]
DBN DBU MTBD TBD-1
1
2
3
4
5
6
7
8
9
Piperidine
Morpholine
0.5
0.5
0.5
1
2
4
24
48
240
13
2
2
3
3
0
0
0
1
14
6
2
7
2
3
1
2
2
22
14
3
7
2
20
9
2
4
3
98
90
95
98
93
94
90
72
74
n-Hexylamine
Benzylamine
Cyclohexylamine
1-Phenylethylamine
t-Butylamine
n.d.b n.d.b
1
0
4-Methylaniline
N-Methylaniline
n.d.b n.d.b
2
1
a
All the reactions were carried out at room temperature using 10 mmol of amine,
12 mmol of methyl formate, 120 mmol of toluene as solvent, and 0.5 mmol (5 mol %)
of the catalyst.
b
Not determined, exact GC separation of target product and catalyst not possible.
guanidine bases exhibited by far higher activities than DBN, DBU and
MTBDandprovedtobeexcellentcatalystsforamineformylationswith
methyl formate. It has to be noted that a real catalytic amount of
5 mol % guanidine base was sufficient for the reaction.
The superior formylating activities of TBO, TBN, TBD-1, TBD-2
and TBU to DBN, DBU and MTBD that were found lead to the as-
sumption that their guanidine function with one NH group is the
essential structural moiety of the catalyst molecule. For verification
of this hypothesis, the formylation of t-butylamine was used as
a second, and more challenging test reaction. Indeed, Table 1 shows
that only TBO, TBN, TBD-1, TBD-2 and TBU are actually able to ca-
talyse the formation of t-butyl formamide (entries 2a–i). Their
performances were found to increase in the order TBO<T-
BU<TBN<TBD-2<TBD-1. In accordance with these results, the
symmetric ten-membered bicyclic structure of TBD-1 proved as
optimal catalyst property.
In continuation of the experiments reported above, the in-
vestigations were extended to reactions of methyl formate with
amines of differing nucleophilic power. As given in Table 2, DBN,
DBU, MTBD and TBD-1 were chosen as catalysts for the for-
mylations. Additionally, every reaction was performed without
catalyst for comparison. It was observed that relevant catalytic in-
fluences of DBN, DBU and MTBD were limited to the formylations of
Table 3
TBD-1 catalysed formylation of amines according to Scheme 1 under optimised conditionsa
Entry
Amine
Molar ratio methyl formate/amine
Catalyst amount [mol %]
Reaction temperature [ꢀC]
Reaction time [h]
Product yield [%]b
1
2
3
4
5
6
7
8
Piperidine
Morpholine
n-Hexylamine
Benzylamine
1.2
1.2
1.2
1.2
1.2
1.2
1.2
2.4
2.4
2.4
2.4
2.4
2.4
2.4
2.5
2.5
2.5
2.5
2.5
2.5
5
5
5
5
5
25
25
25
25
25
25
25
25
25
25
25
25
25
70
1
1
1
2
8
16
24
8
16
48
48
96
96
96
98
97
96
94
87
93
86
88
87
91
85
95
71
65
Cyclohexylamine
1-Phenylethylamine
t-Butylamine
4-Methoxyanilinec
4-Methylanilinec
N-Methylanilinec
Anilinec
9
10
11
12
13
14
4-Chloroanilinec
Ethyl-i-propylaminec
4-Amino methyl
benzoatec
5
5
5
15
4-Nitroanilinec
2.4
5
70
96
w30d
a
All the reactions were carried out using 30 mmol of amine, 36 or 72 mmol of methyl formate, 360 mmol of toluene as solvent, and 0.75 or 1.5 mmol (2.5 or 5 mol %)
catalyst.
b
After isolation and purification (entries 1–13: Kugelrohr distillation, entry 14: flash chromatography).
Reaction in absence of solvent.
According to GC analysis.
c
d

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J. Deutsch et al. / Tetrahedron 65 (2009) 10365–10369
(TBD-1), 1,4,6-triazabicyclo[3.5.0]dec-4-ene (TBD-2), or 1,5,6-tri-
N
N
r.t.
azabicyclo[4.5.0]undec-5-ene (TBU). A preliminary formyl group
transfer from methyl formate to the NH function of the guanidines
generates their N-formyl derivatives as intrinsic and powerful
formylating intermediates. The catalytic performances of TBO, TBN,
TBD-1, TBD-2 and TBU depend on their molecular structure. TBD-1, the
catalytically most active of the five bicyclic guanidines that were
checked, is best suited to synthesise conveniently a wide spectrum of
formamides from methyl formate and amines with high yields.
+ HCOOMe
-MeOH
N
N
N
N
H
CHO
Scheme 2. Generation of 7-formyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (FTBD-1) from
TBD-1 and methyl formate.
The equimolar mixture of methyl formate with MTBD, the N-
methyl derivative of TBD-1, shows both the 1H NMR and IR spec-
trum as sum of the single compound spectra. Hence, MTBD cannot
be converted into detectable amounts of a reactive formyl com-
pound, evidently because of its methylated nitrogen atom. This may
explain the usually low catalytic activity or inactivity of MTBD in
the amine formylations listed in Tables 1 and 2.
The ability of FTBD-1 to transmit its formyl group onto amines
was confirmed with the formylation of benzylamine (Scheme 3).
We noticed that the stoichiometric addition of the amine to a tol-
uene solution of FTBD-1 (the obtainable crude product) resulted in
an immediate and exothermic reaction within few minutes. Benzyl
formamide and TBD-1 were identified as formed products with
GC–MS and by comparison with authentic samples.
4. Experimental
4.1. General
Chemicals and solvents were purchased commercially from
Aldrich, Fluka and Acros and used without further purification.
Exceptionally, n-hexylformamide, 1-phenylethylformamide, ethyl-
i-propylformamide, TBO, TBN, TBD-2 and TBU were synthesised
according to the procedures published in the literature.11,29 GC
experiments were performed using a Hewlett Packard 5890 chro-
matograph with an HP-5 column (30 mꢂ25 mmꢂ0.25
m
m). 1H
NMR spectra were recorded in CD3C6D5 at 500 MHz.
r.t.
N
4.2. General procedure for the catalytic experiments
N
+
+
Ph
NHCHO
Ph
NH2
N
N
H
N
N
In all catalytic experiments, the amine formylation was carried
out at room temperature and monitored with GC. For a typical
example, a mixture of amine (10 mmol), toluene as solvent
(120 mmol), internal standard (diethylene glycol dimethyl ether,
n-nonane, n-decane, n-dodecane, or n-tetradecane) and catalyst
(0.5 mmol) was prepared. The reaction was started by the addition
of methyl formate (12 mmol) and the progressing product forma-
tion was analysed periodically.
CHO
Scheme 3. The formyl group transfer reagent FTBD-1 in the stoichiometric reaction
with benzylamine.
The results of the reported studies may be summarised to
a three-step reaction cycle for TBD-1-catalysed reactions of amines
with methyl formate (Scheme 4). Methyl formate and TBD-1 react
within the initial step of giving ‘N-formyl guanidinium methoxide’
as hypothetic intermediate of short life time and/or low concen-
tration, which cannot be ascertained by common spectroscopic
methods. An elimination of methanol yields FTBD-1 as an identi-
fiable molecule in the second step. The third and final step should
be the evidenced transfer of the formyl group from FTBD-1 to the
amine under formation of the desired formamide and back-for-
mation of the catalyst TBD-1.
4.3. General procedure for the preparation of aliphatic
formamides
A mixture of amine (30 mmol), methyl formate (36 mmol),
toluene as solvent (360 mmol) and the catalyst TBD-1 (0.75–
1.5 mmol) was stored in a closed flask at room temperature for 1–
24 h. The reaction was quenched by adding finely powdered KHSO4
and subsequent stirring of the resulting slurry for 1 h. After filtra-
tion of the solid, the remaining clear solution was concentrated in
vacuum and the obtained crude formamides were purified by
Kugelrohr distillation. The identity of all synthesised products as
known compounds was ensured with GC–MS and 1H NMR and by
analytic comparison with authentic samples.
N
R1R2NCHO
HCOOMe
N
N
H
R1R2NH
TBD-1
4.4. General procedure for the preparation of aromatic
formamides and ethyl i-propylformamide
N
N
A mixture of amine (30 mmol), methyl formate (72 mmol) and
catalyst TBD-1 (1.5 mmol) was stored in a closed flask at room
temperature for 8–96 h. Because of their lower solubility and re-
activity, 4-amino methyl benzoate and 4-nitroaniline were reacted
at 70 ꢀC under stirring in an autoclave for 96 h. The reaction was
quenched by adding 20 ml toluene (50 ml acetonitrile for the for-
mylation of 4-amino methyl benzoate; see Table 3, entry 14), finely
powdered KHSO4 and stirring of the resulting slurry for 1 h. With
exception of the not isolated 4-nitroformanilide, the target prod-
ucts were purified and identified as given for the aliphatic form-
amides. The compound 4-formylamino methyl benzoate (Table 3,
entry 14) was purified by flash chromatography (Kieselgel 60, el-
uent 3:1 ethyl acetate/n-hexane mixture). All synthesised form-
amides are known compounds. Their identity was ensured by
analytic comparison (GC–MS and 1H NMR) with authentic samples.
N
N
H
N
N
[OMe]
CHO
CHO
FTBD-1
MeOH
Scheme 4. The assumed catalytic cycle for the reaction of amines with methyl formate
in presence of TBD-1.
3. Conclusion
Inconclusionitcanbeannouncedthatmethylformateisusableasa
cheep and clean reagent for the conversion of amines into formamides,
when the reaction is catalysed by bicyclic guanidines containing a free
NH group, such as 1,4,6-triazabicyclo[3.3.0]oct-4-ene (TBO), 1,4,6-tri-
azabicyclo[3.4.0]non-4-ene (TBN), 1,5,7-triazabicyclo[4.4.0]dec-5-ene

J. Deutsch et al. / Tetrahedron 65 (2009) 10365–10369
10369
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4.5. Synthesis and identification of FTBD-1 as intermediate
formylating agent
12. Hill, D. R.; Hsiao, C.-N.; Kurukulasuriya, R.; Wittenberger, S. J. Org. Lett. 2002,
4, 111–113.
¨
13. Kisfaludy, L.; Otvo¨s, L. Synthesis 1987, 510.
14. Allenstein, E.; Beyl, V. Chem. Ber. 1967, 100, 3551–3563.
A mixture of TBD-1 (20 mmol) and methyl formate (20 mmol)
was stored overnight at room temperature in a closed flask. Sub-
sequently, unreacted methyl formate and formed methanol were
removed at room temperature under vacuum. The resulting col-
ourless oil was analysed spectroscopically and contained FTBD-1 as
the main component (65% NMR yield, see data) along with
unreacted TBD-1.
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Colourless oil; IR (CHCl3):
(500 MHz, CD3C6D5):
2.40 (m, 2H), 2.60–2.62 (m, 2H), 3.21–3.24 (m, 2H), 3.27–3.29 (m,
2H), 9.60 ppm (s, 1H).
n
¼1668, 1626 cmꢁ1
;
1H NMR
d
¼1.23–1.25 (m, 2H), 1.43–1.45 (m, 2H), 2.38–
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The authors acknowledge the financial support by the Ministry
of Education and Science of the Federal Republic of Germany (FKZ
01SF0715). In addition, the authors would like to thank U. Bentrup,
P. Bischofberger, H. Gehrmann and E. Gru¨ndemann for their valu-
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