Structural Aspects of Thermally Cleavable Adducts Derived from the Reaction of Imidazolines with Isocyanates

Article abstract of DOI:10.1055/s-0035-1562626

The reaction of isocyanates with substituted imidazolines and the thermally induced cleavage of the resulting adducts are presented. For this purpose, reactions of various isocyanates [ethyl isocyanate, p-methylphenyl isocyanate, phenyl isocyanate, p-(trifluoromethyl)phenyl isocyanate] with 1-alkylimidazoline derivatives have been studied as a function of the substituent at the 2-position of the imidazoline ring. Three equivalents of isocyanate react with one equivalent of 1-ethylimidazoline to give a stoichiometric well-defined adduct. However, 1-ethyl-2-isopropylimidazoline reacts with isocyanates at 0 °C in another way, with formation of 2:1 adducts which belong to the family of 1,3-diphenyltetrahydroimidazo[1,2-a][1,3,5]triazine-2,4(1H,3H)-diones. The reaction of 1-ethyl-2-methylimidazoline with aromatic isocyanates at 0 °C also leads to 2:1 adducts, in this case of a malonamide type, which can react at 60 °C with an additional isocyanate equivalent to give the known pyrimidinediones. Thermal analysis (TG-MS/DSC) and trapping reactions with nucleophilic reagents, such as diphenylamine, show the release of isocyanate during the thermally induced cleavage reaction. Thus, blocked isocyanates are available by the reaction of isocyanates with 1-ethylimidazoline or 1-ethyl-2-isopropylimidazoline.

Full text of DOI:10.1055/s-0035-1562626

SYNTHESIS
0
0
3
9
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7
8
8
1
1
4
3
7
-
2
1
0
X
©
Georg Thieme Verlag Stuttgart · New York
2016, 48, A–L
A
paper
Synthesis
A. Laue et al.
Paper
Structural Aspects of Thermally Cleavable Adducts Derived from
the Reaction of Imidazolines with Isocyanates
Andreas Lauea
Andrea Preußa
Manuel Hecka
Mandy Martina
Marcus Binnerb
Tobias Rüfferc
Susann Andersd
Carsten Wernerb
Lothar Krolld
Heinrich Langc
Stefan Spange*a
a
Technische Universität Chemnitz, Institute of Chemistry,
Polymer Chemistry, 09107 Chemnitz, Germany
stefan.spange@chemie.tu-chemnitz.de
Leibniz Institute of Polymer Research Dresden, Hohe
b
Strasse 6, 01069 Dresden, Germany
Technische Universität Chemnitz, Institute of Chemistry,
c
Inorganic Chemistry, 09107 Chemnitz, Germany
Technische Universität Chemnitz, Faculty of Mechanical
d
Engineering, Department of Lightweight Structures and
Polymer Technology, 09107 Chemnitz, Germany
Received: 03.05.2016
Accepted after revision: 22.07.2016
Published online: 09.09.2016
urethane materials.1–4 Recent applications of isocyanates
include their use in the synthesis of new lactam precursors
for potential antibiotics and protein inhibitors.5 Other ap-
plications include their use in the total synthesis of a vari-
ety of natural products and the synthesis of phthalimide, a
well-known core structure of natural products and biologi-
cal compounds.7 However, one major drawback of isocya-
nates is their inherent toxicity, especially of aromatic deriv-
,6
DOI: 10.1055/s-0035-1562626; Art ID: ss-2016-z0312-op
Abstract The reaction of isocyanates with substituted imidazolines
and the thermally induced cleavage of the resulting adducts are pre-
sented. For this purpose, reactions of various isocyanates [ethyl isocya-
nate, p-methylphenyl isocyanate, phenyl isocyanate, p-(trifluorometh-
yl)phenyl isocyanate] with 1-alkylimidazoline derivatives have been
studied as a function of the substituent at the 2-position of the imidaz-
oline ring. Three equivalents of isocyanate react with one equivalent of
,8
4
atives. An approach to circumvent this problem is to use
4
blocked isocyanates. These compounds are metastable ad-
1-ethylimidazoline to give a stoichiometric well-defined adduct. Howev-
ducts which are obtained by reversible formation of isocya-
er, 1-ethyl-2-isopropylimidazoline reacts with isocyanates at 0 °C in an-
other way, with formation of 2:1 adducts which belong to the family of
4
nate-based covalent bonds. Commonly, blocking agents are
1
,3-diphenyltetrahydroimidazo[1,2-a][1,3,5]triazine-2,4(1H,3H)-diones. The
reaction of 1-ethyl-2-methylimidazoline with aromatic isocyanates at
°C also leads to 2:1 adducts, in this case of a malonamide type, which
hydrogen-active X–H-type nucleophiles where X is an oxy-
gen, sulfur, nitrogen or carbon atom. Those reagents pos-
0
sess moderate acidity (pK range from 10 to 20). Such X–H
a
can react at 60 °C with an additional isocyanate equivalent to give the
known pyrimidinediones. Thermal analysis (TG-MS/DSC) and trapping
reactions with nucleophilic reagents, such as diphenylamine, show the
release of isocyanate during the thermally induced cleavage reaction.
Thus, blocked isocyanates are available by the reaction of isocyanates
with 1-ethylimidazoline or 1-ethyl-2-isopropylimidazoline.
nucleophiles facilely undergo addition reactions with the
electrophilic isocyanate group at low temperatures, accord-
ing to Scheme 1.9
deblocked state
blocked state
H
Key words blocked isocyanates, imine bases, isocyanates, imidazo-
lines, amidine/isocyanate adducts
blocking
N
O
R
N
C
O
R' XH
R
ΔT
deblocking
X
R'
X = O, S, NH, NR''
R, R', R'' = aliphatic or aromatic groups
The chemistry of isocyanates has been extensively ex-
plored since their discovery in 1848 by Wurtz. Isocyanates
play an important role in the industrial production of poly-
Scheme 1 Reaction principle of the established blocking reaction of
isocyanates with moderately acidic X–H compounds
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A. Laue et al.
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The blocked state is characterized by a decreased reac-
tivity, and hence minor toxicity, as long as the temperature
remains below the cleavage temperature (Scheme 1). At
higher temperatures, free isocyanates can be released. The
reversible blocking of isocyanates plays an important role in
cidation of the molecular adduct structure which is clearly
determined by the substitution pattern of the imidazolines,
as was proven by single crystal X-ray diffraction analysis.
The structures of the reactants, and their abbreviations,
used in this work are shown in Figure 1.
4,10–14
the polyurethane engineering process.
Malonic esters,
Imine Bases
oximes, phenols, lactams and secondary aromatic amines
have been the mostly used and well-studied blocking
N
N
N
15–19
N
agents.
Recently, the implementation of isocyanate
1
3
groups, blocked by 3,5-dimethylpyrazole, into polymer ar-
chitectures was described.2 Another family of blocked iso-
cyanates are the uretdiones, the dimers of isocyanates,2
which also eliminate isocyanate at elevated temperatures.
However, phosphine catalysts have to be used to form uret-
diones. This method is only applicable for aromatic isocya-
nates and there are still free isocyanate groups available
due to the reversibility of the reaction.21,22 Thus, it is desir-
able to find alternative methods for the selective and con-
trolled release of isocyanates from blocked isocyanates to
make a reasonable and safe handling of this versatile group
1
-Ethylimidazoline;
1-Ethyl-2-methylimidazoline;
0
EtIm
EtMeIm
1,22
N
N
N
N
2
4
1
-Ethyl-2-isopropylimidazoline; 1,2-Diphenylimidazoline;
EtiPrIm
DiPhIm
Isocyanates
9
NCO
possible.
NCO
Recently, we reported on the properties of several 2:1
isocyanate/imine base adducts arising from 1,5-diazabicy-
clo[4.3.0]non-5-ene (DBN) and several structurally differ-
5
a
5c
Ethyl isocyanate;
4-Methylphenyl isocyanate;
EtIC
MePIC
9
ent isocyanates. The covalent adduct formation of imine
F3C
NCO
bases with isocyanates is attributed to the zwitterionic in-
termediate which is formed in the primary step of this reac-
tion. The anionically charged fragment of the intermediate
rapidly reacts with a second molecule of an isocyanate and
ring closure occurs at the positively charged carbon atom of
the amidinium ion. We have shown that these labile ad-
ducts are able to initiate a radical polymerization of vinyl
NCO
5
b
5d
Phenyl isocyanate;
4-(Trifluoromethyl)phenyl
PIC
isocyanate;
CF3PIC
Figure 1 Imine bases and isocyanates used in this work
9
monomers such as methyl methacrylate. Furthermore, the
Isocyanate/Imidazoline 3:1 Adducts Based on 1-Ethyl-
imidazoline
In the reaction of isocyanates with imidazolines, the
molecular structure of the imidazoline plays a crucial role
in the resulting product formation. Therefore, different sub-
stituted imidazolines 1–4 were used to classify this type of
reaction. The substituent R at the 2-position of the five-
membered heterocyclic ring determines the molecular
structure of the obtained adduct (Scheme 2).
release of free isocyanate is readily possible by subjecting
the adduct to elevated temperatures. The reversible adduct
formation of monoisocyanates with imine bases was previ-
ously investigated in the 1960s by Ulrich, Richter and
23–26
Tucker
who reported the formation of 2:1 adducts con-
1
sisting of a six-membered heterocyclic triazinedione ring.
Later, Giesecke and others reported the formation of 3:1 ad-
27,28
ducts.
In the current work, we have focused on the structure of
several amidine/isocyanate adducts resulting from the re-
action of different isocyanates with substituted imidazo-
lines (Figure 1). Furthermore, we have compared the ther-
mal properties of these adducts, as measured by thermo-
gravimetric analysis (TGA) and differential scanning
calorimetry (DSC). A possible thermally induced cleavage
reaction was investigated by scavenging reactions with an
appropriate N-nucleophile such as diphenylamine which
undergoes urea derivative formation with the released free
isocyanate. Hence, an application of the adducts as blocked
isocyanates can be noted, particularly in the case where 1-
ethyl-2-isopropylimidazoline (2) is used as the blocking
agent. However, the general focus of this work was the elu-
The products 6–9 were classified as x:y adducts with re-
spect to the composition of the isocyanate (x) to imidazo-
line proportion (y). The formation of 3:1 adducts by the re-
action of 1-alkylimidazolines with isocyanates has already
been established.2
7,28
These previous publications reported
on neither the single crystal X-ray diffraction analysis of the
adducts nor their cleavage reactions at elevated tempera-
tures. The reaction of 1-ethylimidazoline (EtIm, 1) with iso-
cyanates 5a–c proceeds immediately at ambient tempera-
25,29
ture, forming 3:1 adducts in an exothermic reaction.
Hence, the reactions were carried out at 0 °C to prevent un-
wanted side product formation and the back-reaction. The
resulting adducts 6a–c were obtained in good to quantita-
tive yields (83–99%). A single crystal X-ray diffraction study
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A. Laue et al.
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O
N
NH
R2
N
O
6a EtIm3EtIC; R2 = C H ;
91%
99%
R1 = H
2 5
2
6
b EtIm3PIC; R = C6H5;
R2
N
R2 NCO
5
2
3
N
6c EtIm3MePIC; R = 4-MeC H ; 83%
6 4
R2
O
6a–c
R2
N
O
N
R1
7b EtiPrIm2PIC; R2 = C H ;
R1 = iPr
R2 NCO
89%
7c EtiPrIm2MePIC; R = 4-MeC6H4; 76%
R2
6 5
2
N
2
N
N
N
5
O
1
–3
7b–c
O
R2
O
N
8b EtMeIm2PIC; R2 = C H ;
71%
8c EtMeIm2MePIC; R = 4-MeC H ; 51%
R1 = Me
R2 NCO
6 5
H
R2
N
2
6
4
2
H
2
N
8d EtMeIm2CF3PIC; R = 4-CF3C6H4; 27%
5
NH
8b–d
R2
N
O
Ph
N
R2
N
Ph
N
N
R2 NCO
5
2
N
O
4
9
Scheme 2 Overview of the imine base/isocyanate adduct formations which occur upon reaction of imines 1–4 with isocyanates 5a–d (Et O, 0 °C)
2
of representative 6a was performed to verify the molecular
structure of adducts 6a–c. The molecular structure of 6a in
the solid state is shown in Figure 2; selected bond lengths
and angles are given in the Supporting Information (Tables
S1–S3). Imidazoline 1 does indeed react with three equiva-
lents of isocyanate 5a, whereby one equivalent is bonded to
the imidazoline N atom via the NCO carbon atom to form a
substituted urea function. The second and third equivalents
of 5a are bonded to the imino C atom of 1 by the C atom of
one NCO group and the N atom of the other NCO group by
formation of a five-membered heterocycle. Thus, the pro-
posed structure of 6a (Scheme 2) was confirmed. Based on
the related NMR shifts, the structures of 6b and 6c are re-
garded as being analogous to that of 6a.
The thermal stability of the 3:1 adducts was determined
by DSC (Table 1). All adducts 6a–c show endothermic pro-
cesses in the temperature interval from 200 to 250 °C. As an
example, the DSC trace of 6b is shown in Figure 3. The
graph dQ/dT as a function of temperature shows two endo-
thermic processes: the first at Tonset = 205 °C (Tpeak = 210 °C)
correlates with the melting of 6b; the second at
Tonset = 213 °C (Tpeak = 230 °C) indicates the cleavage reac-
tion of 6b. This cleavage reaction results in the ring opening
of 6b with elimination of the isocyanate 5b, a behavior
which is actually the reverse reaction of the adduct forma-
tion. The start of the cleavage reaction is associated with
the melting process of the sample. TG-MS studies of 6b
Table 1 Results of the Thermal Analysis (DSC) of the 3:1 Adducts 6a–c
and the 2:1 Adducts 7b,c
Adduct
Substituent Tmelt
(°C)
T
cleavage
(°C)
R
O
N
6a
EtIm3EtIC
C
C
2
H
H
5
5
145
230
NH
R
N
O
6b
EtIm3PIC
6
205–207
226
213
N
R
N
R
O
6c
4-MeC
6
H
H
4
4
226
O
EtIm3MePIC
R
7b
C
6
H
5
117–120
117–120
EtiPrIm2PIC
N
N
R
N
7c
Figure 2 ORTEP diagram of the molecular structure of 6a (50% ellip-
soid probability). All carbon-bonded hydrogen atoms are omitted for
clarity.
N
4-MeC
6
128–131
128–131
EtiPrIm2MePIC
O
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were carried out in the temperature range of 30 to 500 °C
Figure 4). The adduct 6b decomposes with a weight loss of
nearly 100% in the range of 200 to 250 °C.
the release of the corresponding isocyanate 5a, as proven by
the mass spectrum (m/z = 71, see the Supporting Informa-
tion).
(
Trapping of the released isocyanates with a suitable nu-
cleophile was not achieved due to the high cleavage tem-
peratures. Nevertheless, a release of isocyanate can be stat-
ed, as evidenced by the TG-MS measurements. Thus, the
3:1 adducts are suitable as blocked isocyanates for systems
where a temperature of more than 200 °C is used. The ob-
served cleavage temperatures (Tcleavage) of the 3:1 adducts
6a–c were observed in a narrow temperature interval of
213 to 230 °C (Table 1). Tcleavage is not a function of the mo-
lecular structure of the isocyanate. The adduct cleavage oc-
curs at a temperature which is in the same region as, or
even higher than, the established isocyanate blocking sys-
tems, namely those based on ε-caprolactam, phenols or tri-
azoles.9
,10,12,13,15–17
1-Alkylimidazolines even facilitate a
blocking of three isocyanate equivalents, which is possibly a
stoichiometric advantage compared to the established
blocking reagents. On the other hand, 1-alkylimidazolines
can be used as cleavable cross-linking agents, especially to
form networks of isocyanate-endcapped pre-polymers or
other isocyanate-functionalized polymers.
Figure 3 DSC trace of 6b (EtIm3PIC) (0–350 °C, 10 K/min, He flow)
Isocyanate/Imidazoline 2:1 Adducts Based on 1-Ethyl-
2
-isopropylimidazoline
Substitution of the H atom at the 2-position of the imid-
azoline ring by an isopropyl group changes the course of
the reaction with isocyanates 5b and 5c to formation of the
2:1 adducts 7b and 7c. This type of adduct is known from
the reaction of the imine bases DBN or DBU (1,8-diazabicy-
clo[5.4.0]undec-7-ene) with aromatic and aliphatic isocya-
nates.9
,25,26
Thus, to reproduce the triazinedione structure
with 1-alkylimidazoline derivatives, an isopropyl group
was attached at the 2-position. The relationship between
the structure of the imidazoline derivative and that of the
resulting product of the reaction with isocyanates can now
be better explained. We have previously reported addition-
al information concerning the 2:1 adducts based on DBU
and DBN.9
The formation of 7b and 7c presumably proceeds via the
zwitterionic intermediate 10 which arises from the addi-
tion of one equivalent of isocyanate 5b or 5c with imidazo-
line 2 (Scheme 3). Intermediate 10 is able to add another
equivalent of isocyanate 5b or 5c by forming the zwitter-
ionic intermediate 12. The ring-closure reaction of the neg-
atively charged nitrogen atom with the positively charged
amidinium carbon atom leads to the favored 2:1 adduct for-
mation, 7b and 7c. As expected, the 1:1 adduct 11 is not fa-
vored and was not obtained. The molecular structure was
determined by a single crystal X-ray diffraction study of
product 7c. The molecular structure of 7c in the solid state
is shown in Figure 5; selected bond lengths and angles are
given in the Supporting Information (Tables S4–S6). Imidaz-
oline 2 does indeed react with two equivalents of isocya-
nate 5c, whereby both are bonded to the C–N double bond
Figure 4 Top: TG trace of 6b (EtIm3PIC) (30–500 °C, 10 K/min, He
flow); bottom: mass spectrum of a gaseous sample of the 6b TG analy-
sis at 223 °C.
The mass spectrum taken at 223 °C showed a peak at
m/z = 119 which can be assigned to phenyl isocyanate (5b),
released from 6b (Figure 4). TG-MS analysis of 6a showed
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A. Laue et al.
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N
N
N
N
N
O
C
N
R
N
R
N
O
N
2
5b,c
O
R
R = C6H5 (5b), 4-MeC6H4 (5c)
10
11
disfavored 1:1 adduct
O
C N R
N
N
N
N
R
N
N R
O
N
O
O
N
R
O
R
12
7b,c
favored 2:1 adduct
7b R = C6H5; EtiPrIm2PIC;
89%
7c R = 4-MeC6H4; EtiPrIm2MePIC; 76%
Scheme 3 Formation of the 2:1 adducts 7b and 7c from the reaction of imidazoline 2 with two equivalents of isocyanate, via the zwitterionic interme-
diates 10 and 12
of 2, additionally giving rise to the formation of a six-mem-
bered triazinedione heterocycle. Thus, the proposed struc-
ture of 7c (Scheme 3) was verified. Based on the related
NMR signals, the structure of 7b is regarded as being analo-
gous to that of 7c.
Figure 6 DSC trace of 7b (EtiPrIm2PIC) (0–300 °C, 10 K/min, He flow)
position and consecutive reactions. Black solids were
Figure 5 ORTEP diagram of the molecular structure of 7c (50% ellip-
soid probability). All carbon-bonded hydrogen atoms are omitted for
clarity.
obtained after the thermal treatment, which are insoluble
in organic solvents.
The TG-MS study of 7b showed the release of phenyl
isocyanate (5b) (m/z = 119, Figure 7). An analogous result
was also found in the TG analysis of 7c (see the Supporting
Information). The TG trace of 7b shows a stepwise weight
loss caused by different processes, namely decompositions
and an unknown post-reaction.
Furthermore, the release of phenyl isocyanate (5b) from
7b was evidenced by a trapping experiment with diphenyl-
amine (13) in toluene at 100 °C for 12 hours. The released
phenyl isocyanate (5b) reacted readily with 13 to give the
expected N,N,N′-triphenylurea (14) (Scheme 4). The trap-
The thermal stability of 7b and 7c was investigated by
DSC and TG-MS analysis. In contrast to the 3:1 adducts 6,
DSC traces of the 2:1 adducts 7 show only one single endo-
thermic peak (Table 1) correlating to both the melting and
cleavage process of the triazinedione function and the as-
sumed elimination of isocyanate 5 (Figure 6). The subse-
quent broadened DSC peak is subdivided into different en-
dothermic peaks (see experimental) and relates to decom-
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ethyl ether at 0 °C (Scheme 2); however, there was no for-
mation of the supposed adduct 9, even at higher tempera-
ture (60 °C, in THF).
Ph
N
O
toluene
00 °C
12 h
NCO
1
N
Ph
N
2
N
N
N
O
7b
2
5b
Ph
2
N H
Ph
13
O
Ph
Ph
2
N
N
N
H
N
Ph
14
2
quantitative
quantitative
Scheme 4 Thermal cleavage of adduct 7b and formation of N,N,N′-
triphenylurea (14) by reaction of the released isocyanate 5b with diphe-
1
nylamine (13) as trapping agent. Yields were determined by in situ H
NMR spectroscopy (see experimental and Supporting Information).
Isocyanate/Imidazoline 2:1 Adducts Based on 1-Ethyl-
2
-methylimidazoline
The molecular structural formation of the product re-
sulting from the reaction of 1-ethyl-2-methylimidazoline
(
3) with aryl isocyanates is strongly temperature depen-
dent. It is known that the pyrimidinedione structure 15 and
Figure 7 Top: TG trace of 7b (EtiPrIm2PIC) (10 K/min, 25 mL/min He
flow); bottom: mass spectrum of a gaseous sample of the 7b TG analy-
sis at 101 °C.
the side product, N,N′-diarylurea 16 are formed in acetoni-
trile at 80 °C (Scheme 5).3
0,31
This process takes place via the
reaction of the acidic H atoms of the methyl group at the 2-
position of the imidazoline ring. These protons can be ab-
stracted due to the imine–enamine tautomerism of com-
pound 3. Here, we report the formation of the malonamide
analogous 2:1 adducts 8b–d obtained in diethyl ether at
0 °C (Scheme 5). Compounds 8b–d cannot be stored at ele-
vated temperatures. The formation of 15a takes place upon
treating 8b with an additional two equivalents of phenyl
isocyanate (5b) in acetonitrile at 80 °C. Thus, mixed adducts
are obtainable by using a structurally different isocyanate
in the second step. Therefore, 8b–d can be classified as pre-
adducts of 15. A single crystal X-ray diffraction study of 8b
in the solid state was performed. The molecular structure of
8b is shown in Figure 8; selected bond lengths and angles
are given in the Supporting Information (Tables S7–S9). Im-
idazoline 3 does react with two equivalents of isocyanate
5b, whereby both are bonded to the enamine C atom of 3 to
form a malonamide functionality, due to the imine–enam-
ine tautomerism of 3. Thus, the proposed structure of 8b
(Scheme 2) was verified.
1
ping experiment was monitored by H NMR spectroscopy;
1
see the Supporting Information for a comparison of the H
NMR spectrum of the pure adduct 7b with that of the crude
products of the trapping reaction. Both the cleavage of 7b
and the quantitative formation of 14 can be simultaneously
measured. Yields of the products were determined by in
situ H NMR spectroscopy. The resulting H NMR spectrum
of the crude products showed a 2:1 mixture of 14 (NH sig-
nal at 5.99 ppm) and the re-formed imidazoline 2 (septet
for CH of the isopropyl group at 2.56 ppm; see the Support-
ing Information). So, the release of isocyanate 5b proceeds
quantitatively. These results show that 2:1 adducts based
on imidazoline 2 are applicable as blocked isocyanates in
the same way as 2:1 adducts which are based on DBN or
1
1
9
DBU. The reversibility of the adduct formation and the ad-
ditional fact that 3:1 adducts are only formed if the 1-al-
kylimidazoline bears a hydrogen atom at the 2-position
leads to the assumption that a reaction of imidazoline and
isocyanate only occurs when the substituent at the 2-posi-
tion of the imidazoline ring bears at least one C–H acidic
hydrogen atom. To prove this assumption, 1,2-diphenylim-
idazoline (4) was treated with phenyl isocyanate (5b) in di-
The solid state structure of 8b is similar to that of the
products resulting from the reaction of isocyanates with
ketene N,N′-acetals: a malonamide structural type is pro-
duced.3
0,31
Structurally similar components have been de-
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O
R
O
O
HN
N
80 °C, MeCN, 12 h
NCO
N
R
R
+
known reaction pathway
N
R
N
N
4
R
N
H
H
3
5
N
O
16
15
15a R = C6H5; 57%
O
formation of
decomposable
intermediate product
R
O
N
H
80 °C, MeCN
12 h
0
°C, Et2O
NCO
R
N
H
2
R NCO
2
R
N
5
NH
5
8b–d
8
8
8
b R = C6H5; EtMeIm2PIC;
c R = 4-MeC6H4; EtMeIm2MePIC; 51%
d R = 4-CF3C6H4; EtMeIm2CF3PIC; 27%
71%
Scheme 5 Reaction pathways of 1-ethyl-2-methylimidazoline (3) with aryl isocyanates. Upper known reaction path: formation of a pyrimidinedione
30,31
1
5;
bottom path: formation of the 2:1 adducts 8b–d. Pyrimidinedione derivative 15a was obtained by the reaction of intermediate 8b with two
equivalents of phenyl isocyanate (5b).
Figure 9 Comparison of the DSC traces of 8b (EtMeIm2PIC) (black)
and pyrimidinedione 15a (red) (10 K/min, He flow)
Figure 8 ORTEP diagram of the molecular structure of 8b (50% ellip-
soid probability). All carbon-bonded hydrogen atoms and packing sol-
vent molecules are omitted for clarity.
The thermally induced reaction of 8b to 15a without
additional aryl isocyanate 5b was carried out in acetonitrile
1
scribed in several publications. For example, similar struc-
tures were obtained by the reaction of 2-methyl-2-oxazoline
or 2-methyl-2-thiazolines with isocyanates.32 Such com-
pounds are used to obtain polyamides, by the reaction of 2-
at 80 °C, and the outcome analyzed by H NMR spectrosco-
py. The absence of both characteristic NH signals (9.98 and
9.48 ppm) of 8b indicated complete decomposition. A new
signal at 10.55 ppm due to the NH group of 15a proved the
formation of 15a. Signals of imidazoline 3 could be ob-
served after the reaction in acetonitrile at 80 °C. A TG-MS
study showed a stepwise weight loss and an undefined de-
composition of the adduct (see Supporting Information).
However, the simple thermal treatment of adduct 8b leads
to the formation of 15a and decomposition. Thus, 8b elimi-
nates phenyl isocyanate (5b) at elevated temperatures. This
fact shows that the formation of 15a does require four
equivalents of 5b. There was no formation of N,N,N′-tri-
phenylurea upon thermal treatment of 15a in the presence
of diphenylamine in acetonitrile at 80 °C. Thus, 15a is not
33
methyl-2-oxazoline with aromatic diisocyanates.
The DSC trace of adduct 8b (Figure 9, black curve) indi-
cates the formation of compound 15a. The endothermic
peak at Tonset = 145 °C (Tpeak = 150 °C) can be assigned to
melting and decomposition of the adduct structure. The
second exothermic peak (Tpeak = 153 °C) indicates the for-
mation of 15a. The pyrimidinedione derivative 15a is stable
even at high temperatures (>250 °C), in contrast to 8b. The
DSC trace of 15 (endothermic melting peak at Tonset
45 °C, Tpeak = 247 °C; Figure 9, red curve) confirms this re-
sult.
=
2
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–L

H
Synthesis
A. Laue et al.
Paper
O
O
N
H
N
N
N
O
17a
20%
O
O
N
H
O
O
N
N
N
H
6
0 °C, MeCN, 12 h
N
O
N
H
NCO
N
17b
3%
2
NH
5
H3C
8b
5c
O
O
N
H
N
N
N
O
17c
10%
O
O
N
H
N
N
N
O
17d
17%
Scheme 6 Pyrimidinedione derivatives 17a–d produced in the reaction of 8b with 4-methylphenyl isocyanate (5c). The quantitative analysis was per-
formed by HPLC-MS.
suitable as a blocked isocyanate. Both the NMR experiment
and the TG-MS study (see Supporting Information) indicat-
ed that there is no isocyanate elimination upon thermal
treatment of 15a.
selves. A quantitative elimination of isocyanates is not pos-
sible; therefore, this type of adduct is not suitable as
blocked isocyanate, in contrast to the 3:1 (6a–c) and 2:1 ad-
ducts (7b,c). Further information, including ESI-MS mea-
surement of the different fractions and HPLC-MS analysis of
the mixture obtained by the reaction of adduct 8c with
phenyl isocyanate (5b), is given in the Supporting Informa-
tion. The results of the reaction of 8c with 5b support the
theory of a decomposition of 8b,c and subsequent reaction
with additional isocyanate.
Pyrimidinedione derivatives with different aromatic
substituents and can be formed by using different aromatic
substituted isocyanates (Schemes 5 and 6). Adduct 8b was
treated with 4-methylphenyl isocyanate (5c) at an elevated
temperature (60 °C) to investigate the reversibility of the
adduct formation (Scheme 6). After purification by column
chromatography, compounds 17a–d were obtained in one
Table 2 HPLC-MS Data of All Products Obtained by the Reaction of 8b
with 5c at 60 °C
1
fraction. A comparison of the H NMR spectrum of 15a with
that of the product mixture 17a–d (see Supporting Infor-
mation) indicated the presence of four different com-
pounds. The identity of 17a–d was also confirmed by HPLC-
ESI-MS analysis (Table 2). A complete summary of the
HPLC-MS data is given in the Supporting Information. The
data indicate that elimination of isocyanate 5b from
malonamide 8b during the reaction takes place in a direc-
tion to provide the more stable products 17a–d. If there
was no such reaction, only the formation of 17a and 17c
would occur. The release of phenyl isocyanate (5b) means
that the formation of 17a–d can occur. Nevertheless, the 2:1
adducts 8b–d are not useful as blocked isocyanates because
of their tendency to form more stable adducts by them-
Product
Molecular
composition
m/z [M]+
(calcd)
m/z [M]+
(found)
Proportion (%)
1
1
7a
7b
C
C
C
21
22
22
H
H
H
20
22
22
N
N
N
4
4
4
O
O
O
3
3
3
3
376.1661
390.1818
390.1818
404.1974
376.1669
390.1765
390.1765
404.1921
20
53
10
17
17c
17d
C23H24N O
4
In summary, isocyanates react with substituted imidaz-
olines to give 3:1 adducts, 2:1-triazinedione-based adducts
and 2:1 adducts with a malonamide-based structure. The
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–L

I
Synthesis
A. Laue et al.
Paper
substituent at the 2-position (methyl or isopropyl group, or
a hydrogen atom) of the 1-alkylimidazoline ring deter-
mines the molecular structure of the obtained imidazo-
line/isocyanate adducts. Thermally cleavable 3:1 adducts
are obtained by the reaction of isocyanates with 1-ethylim-
idazoline. All adducts undergo an elimination reaction, by
releasing isocyanate, with cleavage temperatures in the
range of 210–230 °C. By using 1-ethyl-2-isopropylimidazo-
line, the known 2:1 adducts with a triazinedione structure
(ESI) mass spectra were recorded with a Bruker Daltonics micrOTOF
QII (ESI-Qq-TOF) instrument. Excitation voltages ranged between
4
500 and 8500 V. Differential scanning calorimetry measurements
were performed with a DSC 1 apparatus (Mettler, Toledo). All mea-
surements were done in alumina pans at a heating rate of 10 K/min.
TG-MS measurements were recorded with a Thermo-Microscales TG
09 Iris® apparatus coupled with an MS 403C Aëolos® mass spec-
2
trometer (Netzsch). While heating the samples, a constant helium gas
flow (25 mL/min) was applied. As detector of the mass spectrometer,
a quadrupole-MS detector (QMA200) was used (measuring range
m/z = 0–300). Analytical HPLC experiments were performed on an
Agilent 1100 Series unit (Agilent Technologies, Santa Clara, USA)
equipped with a degasser, binary pump, autosampler and UV–vis di-
ode array detector (DAD, 1-cm path length cell). Samples of 1 μL
9
were obtained. These adducts are characterized by lower
cleavage temperatures (120–130 °C). Both adduct types
eliminate isocyanate which was evidenced by TG-MS stud-
ies and trapping experiments with diphenylamine. Thus,
these two types of imine base/isocyanate adducts are suit-
able as blocked isocyanates. The reaction of 1-ethyl-2-
methylimidazoline with aryl isocyanates does not result in
blocked isocyanates in the common sense. Instead of cleav-
able adducts, very stable pyrimidinedione structures were
ultimately obtained. 2:1 Pre-adducts of the pyrimidinedi-
one structure, namely malonamides, are formed at 0 °C in
diethyl ether. These adducts react at elevated temperatures
to give the known pyrimidinediones, via the elimination of
isocyanate. Therefore, this type of adduct is not suitable as a
blocked isocyanate, because of an incomplete release of iso-
cyanate.
In conclusion, the structure of the formed imidazo-
line/isocyanate adduct strongly depends on the substituent
at the 2-position of the imidazoline. The presence of a C–H
acidic hydrogen atom in this substituent is necessary, oth-
erwise there is no reaction between imidazoline and isocy-
anate and no adduct formation. The use of the adducts as
blocked isocyanates requires sterically large substituents at
the 2-position, such as the isopropyl group.
®
(~0.007 μmol) were injected and separated using an analytical Luna
C-18 column (250 × 3 mm, 5-μm particle size, 100-Å pore size; Phe-
nomenex, Aschaffenburg, Germany) over 45 min using a linear gradi-
ent [solvent A: 5% MeCN/95% ultra-high purity (UHP) water with 0.1%
formic acid; solvent B: 95% MeCN/5% UHP water with 0.1% formic ac-
id] with a flow rate of 0.5 mL/min. For HPLC separations, the monitor-
ing wavelength was set to 278 nm and the fraction of each compound
in the product was calculated from peak area integration of the HPLC
chromatograms. ESI mass spectrometry was recorded with an Agilent
6200 Series Accurate Mass Time-of-Flight (TOF) unit, equipped with a
dual nebulizer ion source connected to the HPLC system (DAD outlet).
The ESI unit was operated in a 4-GHz positive ion mode with a nitro-
gen gas flow of 8 L/min at 325 °C, capillary voltage of 3500 V and frag-
mentor voltage of 175 V. For accurate mass determinations, spectra
were calibrated with an internal calibration standard/reference solu-
tion by use of a second reference sprayer orthogonal to the sample
sprayer in the ion source. Mass calibration was performed with an
Agilent tuning mix from 100 to 2200 m/z prior to measurement.
3:1 Adducts 6a–c; General Procedure
A solution of 1-ethylimidazoline (1; 0.30 g, 3.05 mmol) in anhydrous
Et O (10 mL) was added slowly to an ice-cooled solution (0 °C) of an
2
isocyanate 5a–c (9.15 mmol) in anhydrous Et O (20 mL). The solution
2
was stirred for 12 h at r.t. After removal of the solvent by rotary evap-
orator (40 °C), the crude product was recrystallized (chloroform/n-
hexane mixture) and dried under reduced pressure (5 mbar, 40 °C).
All products were obtained as white solids.
The isocyanates ethyl isocyanate (EtIC, Aldrich), phenyl isocyanate
(PIC, ABCR), 4-methylphenyl isocyanate (MePIC, TCI), and 4-(trifluo-
romethyl)phenyl isocyanate (CF PIC, TCI) were used as received. The
3
starting materials for the imidazolines, 1-ethylimidazoline (N-ethy-
lethylenediamine, TCI and N,N-dimethylformamide dimethyl acetal,
TCI), 1-ethyl-2-methylimidazoline (N-ethylethylenediamine, TCI and
N,N-dimethylacetamide dimethyl acetal, TCI), 1-ethyl-2-isopropylim-
idazoline (N-ethylethylenediamine, TCI and methyl 2-methylpropion-
imidate hydrochloride, Alfa Aesar) and 1,2-diphenylimidazoline [N-
N,1,3,9-Tetraethyl-2,4-dioxo-1,3,6,9-tetraazaspiro[4.4]nonane-6-
carboxamide (EtIm3EtIC, 6a)
Yield: 0.86 g (91%).
IR (ATR): 3429, 1721, 1675 cm–1
.
1
H NMR (250.13 MHz, CDCl ): δ = 4.27 (s, 1 H, NH), 3.57 (m, 4 H,
3
(2-chloroethyl)benzamide, Sigma Aldrich, aniline, Acros and poly-
CH CH ), 3.23 (m, 6 H, CH CH ), 2.45 (m, 2 H, NHCH CH ), 1.16 (m, 12
2 2 2 3 2 3
phosphoric acid, Sigma Aldrich], were purchased commercially and
H, CH CH ).
2 3
used as received. Et O, toluene and MeCN were purified by standard
2
13
C NMR (62.90 MHz, CDCl ): δ = 171.1, 155.8, 154.3, 90.6, 51.8, 46.3,
34
35
3
methods. Compounds 1 (1-ethylimidazoline, EtIm), 2 (1-ethyl-2-
43.4, 40.2, 35.2, 33.4, 15.9, 14.3, 13.7, 13.6.
36
isopropylimidazoline, EtiPrIm), 3 (1-ethyl-2-methylimidazoline, Et-
+
MeIm) and 4 (1,2-diphenylimidazoline, DiPhIm)37,38 were prepared
35
HRMS (ESI-TOF): m/z [M + H] calcd for C14H25N O : 312.2036; found:
5
3
312.2030.
according to literature procedures.
Anal. Calcd for C14H25N O : C, 54.00; H, 8.09; N, 22.49. Found: C,
53.61; H, 8.10; N, 22.42.
NMR spectra were recorded on a Bruker Avance DRX 250 spectrome-
5
3
1
13
ter ( H: 250.13 MHz, C: 62.90 MHz) using CDCl as solvent; all spec-
3
tra are referenced to CDCl . ATR-FT-IR spectra were monitored on an
DSC (°C, J/mol): 140.6 (0.177), 229.6 (2.277).
3
FTS-165 spectrometer (BioRad) equipped with a Golden Gate device.
Elemental analyses were performed with a Vario EL apparatus (Ele-
mentar Analysensysteme GmbH, Hanau). Electrospray ionization
Tmelt = 145 °C.
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–L

J
Synthesis
A. Laue et al.
Paper
9-Ethyl-2,4-dioxo-N,1,3-triphenyl-1,3,6,9-tetraazaspiro[4.4]-
Tmelt = 117–120 °C.
nonane-6-carboxamide (EtIm3PIC, 6b)
Yield: 1.38 g (99%).
IR (ATR): 3430, 1720, 1672 cm–1
8-Ethyl-8a-isopropyl-1,3-di-p-tolyltetrahydroimidazo[1,2-
a][1,3,5]triazine-2,4(1H,3H)-dione (EtiPrIm2MePIC, 7c)
.
1
Yield: 0.66 g (76%).
IR (ATR): 2972, 1708, 1671, 1508 cm–1
H NMR (250.13 MHz, CDCl ): δ = 7.34 (m, 15 H, Ph), 6.43 (s, 1 H, NH),
3
3
3
.09 (m, 5 H, NCHHCH , CH CH ), 2.72 (dd, J = 11.0, 6.5 Hz, 1 H, NCH-
.
3
2
2
3
HCH ), 1.24 (t, J = 6.4 Hz, 3 H, CH CH ).
1
3
2
3
H NMR (250.13 MHz, CDCl ): δ = 7.19 (m, 8 H, Ph), 4.15 (m, 1 H,
3
13
C NMR (62.90 MHz, CDCl ): δ = 169.4, 154.6, 152.1, 137.9, 134.0,
CH
2
CHH), 3.72 (m, 1 H, CH
2
CHH), 3.58 (m, 1 H, CHHCH
2
), 2.86 (m, 1 H,
), 2.28 (m,
), 1.44 (d, J = 6.8 Hz, 3 H, CH ),
3
3
1
4
31.8, 129.1, 129.0, 128.4, 128.2, 128.0, 126.9, 123.9, 120.4, 92.1, 46.7,
3.9, 40.5, 13.6.
CHHCH
2
), 2.61 (sept, J = 6.7 Hz, 1 H, CH), 2.36 (s, 6 H, p-CH
3
3
1 H, CHHCH
), 1.83 (m, 1 H, CHHCH
3
3
3
3
3
0.97 (d, J = 6.8 Hz, 3 H, CH ), 0.75 (t, J = 6.8 Hz, 3 H, CH CH ).
3
2
3
Anal. Calcd for C26H25N O : C, 68.56; H, 5.53; N, 15.37. Found: C,
6
5
3
13C NMR (62.90 MHz, CDCl
): δ = 152.0, 151.7, 138.5, 137.8, 134.2,
32.9, 129.4, 129.1, 128.6, 119.5, 93.8, 47.7, 46.8, 43.0, 37.1, 21.3,
1.2, 19.1, 17.0, 13.8.
8.51; H, 5.63; N, 15.32.
3
1
2
DSC (°C, J/mol): 204.5 (2.025), 213.4 (0.762).
Tmelt = 205–207 °C.
+
HRMS (ESI-TOF): m/z [M + H] calcd for C24H30N O : 407.2447; found:
4
2
407.2442.
9-Ethyl-2,4-dioxo-N,1,3-tri-p-tolyl-1,3,6,9-tetraazaspiro-
Anal. Calcd for C24H30N O : C, 70.91; H, 7.44; N, 13.78. Found: C,
[
4.4]nonane-6-carboxamide (EtIm3MePIC, 6c)
4
2
70.88; H, 7.33; N, 13.59.
Yield: 1.26 g (83%).
IR (ATR): 3433, 1722, 1643 cm–1
DSC (°C, J/mol): 120.69 (1.171), 216.64 (0.373), 321.73 (0.062).
Tmelt = 128–131 °C.
.
1
H NMR (250.13 MHz, CDCl ): δ = 7.21 (m, 12 H, Ph), 6.24 (s, 1 H, NH),
3
3
.27 (m, 4 H, CH CH ), 2.86 (m, 2 H, NCH CH ), 2.33 (m, 9 H, p-CH ),
2 2 2 3 3
3
2:1 Adducts 8b–d; General Procedure
1.23 (t, J = 6.1 Hz, 3 H, CH CH ).
2 3
1
3
A solution of 1-ethyl-2-methylimidazoline (3; 0.30 g, 2.67 mmol) in
C NMR (62.90 MHz, CDCl ): δ = 169.6, 154.9, 152.2, 138.2, 137.8,
3
anhydrous Et O (10 mL) was added slowly to an ice-cooled solution
2
1
9
35.3, 133.4, 131.2, 129.7, 129.6, 129.5, 129.2, 128.2, 126.9, 120.7,
2.0, 46.7, 43.8, 40.4, 21.3, 21.3, 20.9, 13.6.
(
0 °C) of an isocyanate 5b–d (5.35 mmol) in anhydrous Et O (10 mL).
2
After the solution was stirred for 1 h at r.t., the precipitate was collect-
Anal. Calcd for C29H31N O : C, 70.00; H, 6.28; N, 14.07. Found: C,
7
5
3
ed by filtration. The crude product was washed with cold Et O and
2
0.28; H, 6.31; N, 13.82.
dried under reduced pressure (5 mbar, r.t.). All products were ob-
tained as white solids.
DSC (°C, J/mol): 51.91 (0.158), 225.58 (1.549).
Tmelt = 226 °C.
1
3
2
-(1-Ethylimidazolidin-2-ylidene)-N ,N -diphenylmalonamide
(
EtMeIm2PIC, 8b)
2:1 Adducts 7b and 7c; General Procedure
Yield: 0.66 g (71%).
IR (ATR): 3255, 1671, 1590, 1522, 1435 cm–1
.
A solution of 1-ethyl-2-isopropylimidazoline (2; 0.30 g, 2.14 mmol) in
anhydrous Et O (10 mL) was added slowly to an ice-cooled solution
2
(
0 °C) of isocyanate 5b or 5c (4.28 mmol) in anhydrous Et O (20 mL).
1
2
H NMR (250.13 MHz, CDCl ): δ = 9.98 (s, 1 H, CH NH), 9.48 (s, 2 H,
3 2
The solution was stirred for 12 h at r.t. The solvent was removed by
rotary evaporator (40 °C). All products were obtained as colorless sol-
ids.
CONH), 7.53 (m, 4 H, Ph), 7.30 (m, 4 H, Ph), 7.03 (m, 2 H, Ph), 3.66 (m,
2
1
3
H, CH CH ), 3.49 (m, 2 H, CH CH ), 3.29 (q, J = 7.3 Hz, 2 H, CH CH ),
2
3
2
2
2
2
3
.08 (t, J = 7.1 Hz, 3 H, CH CH ).
2
3
13
C NMR (62.90 MHz, CDCl ): δ = 168.0, 167.9, 145.9, 139.3, 129.0,
3
8
-Ethyl-8a-isopropyl-1,3-diphenyltetrahydroimidazo[1,2-
1
23.0, 119.9, 78.6, 48.6, 47.8, 42.1, 13.1.
a][1,3,5]triazine-2,4(1H,3H)-dione (EtiPrIm2PIC, 7b)
+
HRMS (ESI-TOF): m/z [M + H] calcd for C20H22N O : 351.1855; found:
4
2
Yield: 0.72 g (89%).
IR (ATR): 2971, 1671, 1669, 1440 cm–1
351.1815.
.
DSC (°C, J/mol): 144.92 (0.219), 152.23 (–0.027), 187.77 (0.492).
1
H NMR (250.13 MHz, CDCl ): δ = 7.35 (m, 10 H, Ph), 4.17 (m, 1 H,
3
Tmelt = 115–120 °C.
CH CHH), 3.73 (m, 1 H, CH CHH), 3.60 (m, 1 H, CHHCH ), 2.85 (m, 1 H,
CHHCH ), 2.64 (sept, J = 6.6 Hz, 1 H, CH), 2.33 (m, 1 H, CHHCH ), 1.79
2
2
2
3
2
3
1
3
3
3
2-(1-Ethylimidazolidin-2-ylidene)-N ,N -di-p-tolylmalonamide
(EtMeIm2MePIC, 8c)
(
m, 1 H, CHHCH ), 1.47 (d, J = 6.8 Hz, 3 H, CH ), 0.98 (d, J = 6.8 Hz, 3
3
3
3
H, CH ), 0.72 (t, J = 7.0 Hz, 3 H, CH CH ).
3
2
3
1
3
Yield: 0.52 g (51%).
IR (ATR): 3328, 3177, 1673, 1582, 1508, 1402 cm–1
C NMR (62.90 MHz, CDCl ): δ = 151.7, 151.3, 136.8, 135.4, 128.9,
3
1
28.8, 128.6, 128.0, 122.1, 119.0, 93.9, 47.6, 45.7, 43.0, 37.0, 18.9,
.
1
6.9, 13.6.
1
H NMR (250.13 MHz, CDCl ): δ = 9.75 (s, 1 H, CH NH), 9.52 (s, 2 H,
3
2
+
HRMS (ESI-TOF): m/z [M + H] calcd for C22H26N O : 379.2134; found:
CONH), 7.44 (m, 4 H, Ph), 7.10 (m, 4 H, Ph), 3.57 (m, 2 H, CH
(m, 2 H, CH
1
2
CH
2
), 3.38
),
4
2
3
379.2131.
2
CH
2
), 3.24 (q, J = 7.1 Hz, 2 H, CH
2
CH
3
), 2.29 (s, 6 H, p-CH
3
3
.02 (t, J = 7.2 Hz, 3 H, CH CH ).
2
3
Anal. Calcd for C22H26N O : C, 69.82; H, 6.92; N, 14.80. Found: C,
4
2
13C NMR (62.90 MHz, CDCl
20.0, 78.7, 48.7, 48.0, 42.1, 20.9, 13.2.
): δ = 168.0, 167.8, 136.7, 132.5, 129.5,
3
6
9.43; H, 6.81; N, 14.61.
DSC (°C, J/mol): 104.56 (0.433), 117.68 (–0.073), 206.62 (0.208),
28.46 (0.240).
1
3
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–L

K
Synthesis
A. Laue et al.
Paper
Anal. Calcd for C22H26N O : C, 69.82; H, 6.92; N, 15.80. Found: C,
Anal. Calcd for C21H20N O : C, 67.01; H, 5.36; N, 14.88. Found: C,
4
2
4
3
69.62; H, 6.86; N, 15.51.
66.83; H, 5.44; N, 14.74.
DSC (°C, J/mol): 141.41 (0.137), 147.15 (–0.112), 196.62 (0.681).
DSC (°C, J/mol): 245.01 (0.21).
Tmelt = 129–134 °C.
Tmelt = 243–248 °C.
1
3
2
-(1-Ethylimidazolidin-2-ylidene)-N ,N -bis(4-(trifluorometh-
X-ray Crystallography
yl)phenyl)malonamide (EtMeIm2CF PIC, 8d)
3
Single crystal X-ray diffraction studies were carried out with an Ox-
ford Gemini S diffractometer at 110 K by applying Mo Κα (0.71 Å) and
Cu Kα (1.54 Å) radiation. The structures were solved using SHELXS-
Yield: 0.35 g (27%).
IR (ATR): 3245, 1678, 1578, 1479, 1408 cm–1
.
2
013 and refined by full-matrix least-squares produced on F2 using
1
H NMR (250.13 MHz, CDCl ): δ = 9.92 (s, 1 H, CH NH), 9.67 (s, 2 H,
3
2
SHELXL-2013. All non-hydrogen atoms were refined anisotropically.
All carbon-bonded hydrogen atoms were geometrically placed and
refined isotropically in riding modes using default parameters. The
positions of nitrogen-bonded hydrogen atoms were taken from differ-
ence Fourier maps and refined isotropically. CCDC 1450531 (6a),
CCDC 1450532 (7c) and CCDC 1450533 (8b) contain the supplemen-
tary crystallographic data for this paper. The data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/getstructures.
CONH), 7.66 (m, 4 H, Ph), 7.54 (m, 4 H, Ph), 3.73 (m, 2 H, CH CH ), 3.58
2
3
2
3
(
m, 2 H, CH CH ), 3.27 (q, J = 7.2 Hz, 2 H, CH CH ), 1.09 (t, J = 7.2 Hz,
2
2
2
3
3
H, CH CH ).
2
3
1
3
C NMR (62.90 MHz, CDCl ): δ = 168.6, 167.8, 142.3, 126.6–122.3 (d,
3
1JCF = 271.5 Hz), 126.4–126.2 (d, JCF = 3.7 Hz), 125.0–124.5 (d, 2JCF
3
=
32.8 Hz), 119.3, 78.9, 48.8, 48.4, 42.4, 31.1, 13.3.
HRMS (ESI-TOF): m/z [M + H]+ calcd for C22H20F N O : 487.1569;
6
4
2
found: 487.1563.
DSC (°C, J/mol): 84.68 (0.021), 103.68 (–0.036), 127.75 (0.057), 144.78
0.286), 259.82 (0.032).
(
Acknowledgment
Tmelt = 103–110 °C.
We thank the Technische Universität Chemnitz for funding this work
and Dr. Roy Buschbeck (TU Chemnitz) for measuring the ESI-MS ex-
periments.
Trapping Experiment: Thermal Decomposition of Adduct 7b
A solution of 7b (0.14 g, 0.38 mmol) and diphenylamine (13; 0.13 g,
0.79 mmol) in anhydrous toluene (40 mL) was stirred at 100 °C for 12
h, which was followed by removal of the solvent under reduced pres-
sure. A sample of the crude product mixture was dissolved in CDCl3.
The yields of the resulting N,N,N′-triphenylurea (14, quantitative) and
imidazoline 2 (quantitative) were determined by H NMR spectrosco-
py.
Supporting Information
1
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1562626.
S
u
p
p
ortioIgnfmr oaitn
S
u
p
p
o
nrtogI
i
f
rm oaitn
1
H NMR (250.13 MHz, CDCl ): δ = 9.20 (s, 0.2 H, NH 13 rest), 7.55–
3
7
1
1
2
.52 (m, 1.4 H, Ph 13 rest), 7.37–7.24 (m, 9 H, Ph 13 rest and product
References
4), 7.12–6.94 (m, 14 H, Ph 13 rest and product 14), 5.99 (s, 2 H, NH
3
3
4), 3.72 (t, J = 9.7 Hz, 2 H, CH CH 2), 3.33 (t, J = 9.6 Hz, 2 H, CH CH
2
(1) Wurtz, A. Justus Liebigs Ann. Chem. 1849, 71, 326.
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2
2
2
), 3.19 (q, 3J = 7.1 Hz, 2 H, CH CH 2), 2.56 (sept, J = 7.0 Hz, 1 H,
3
3
2
CH CHCH 2), 1.26–1.16 (m, 9 H, CH CH , CH CHCH , 2).
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2
3
3
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(
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1
3
A solution of phenyl isocyanate (5b; 0.48 g, 4 mmol) in anhydrous
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(
(
(
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(
(
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IR (ATR): 3042, 1708, 1664, 1565, 1488, 1379 cm–1
.
1
H NMR (250.13 MHz, CDCl ): δ = 10.69 (s, 1 H, NH), 7.62–7.48 (m, 5
3
(
H, Ph), 7.32–7.24 (m, 3 H, Ph), 7.08–7.02 (m, 2 H, Ph), 4.18–4.11 (m, 2
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3
2
2
2
2
3
2
3
2
3
(
13
C NMR (62.90 MHz, DMSO-d ): δ = 162.9, 162.2, 153.3, 148.0, 139.3,
6
135.6, 129.3, 128.8, 128.0, 123.1, 119.3, 84.5, 48.0, 43.4, 41.9, 11.8.
(
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