Flash vacuum pyrolysis (fvp) of some hexahydroquinazolin-4(1H)-ones

Article abstract of DOI:10.1016/j.tet.2007.07.010

Some cis/trans-2-thioquinazolin-4-ones and their 2,4-dione analogs were subjected to flash vacuum pyrolysis. The cis- and trans-thio compounds reacted at lower temperatures than the cis- and trans-dioxo analogs, showing a lower thermal stability. All of these compounds afforded similar reactions: ring opening to the corresponding iso(thio)cyanate, the loss of H^{{radical dot}} and ^{{radical dot}}NCS to form three isomeric cyclohexadienes and then aromatization to form the corresponding benzamide. The cis-dioxo compound also underwent a competitive retro Diels-Alder (RDA) reaction to form 3-phenylpyrimidine-2,4(1H,3H-dione(3-phenyluracil)) and butadiene. Kinetic measurements of the ring opening reaction supported a concerted β-elimination as the most probable mechanism.

Full text of DOI:10.1016/j.tet.2007.07.010

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 1049–1057
Flash vacuum pyrolysis (fvp) of some
hexahydroquinazolin-4(1H)-ones
a
Walter J. Pelaez, Zsolt Szakonyi, Ferenc Fulop and Gloria I. Yranzo
b
b
a,
*
ꢀ
€ €
aINFIQC—Departamento de Quꢀımica Orgaꢀnica, Facultad de Ciencias Quꢀımicas, Universidad Nacional de Coꢀrdoba,
Ciudad Universitaria, 5016 Coꢀrdoba, Argentina
bInstitute of Pharmaceutical Chemistry, University of Szeged, PO Box 427, Hungary
Received 6 March 2007; revised 16 June 2007; accepted 5 July 2007
Available online 6 August 2007
Dedicated to Professor C. Szantay on the occasion of his 80th birthday
Abstract—Some cis/trans-2-thioquinazolin-4-ones and their 2,4-dione analogs were subjected to flash vacuum pyrolysis. The cis- and
trans-thio compounds reacted at lower temperatures than the cis- and trans-dioxo analogs, showing a lower thermal stability. All of these
ꢀ
compounds afforded similar reactions: ring opening to the corresponding iso(thio)cyanate, the loss of Hꢀ and NCS to form three isomeric
cyclohexadienes and then aromatization to form the corresponding benzamide. The cis-dioxo compound also underwent a competitive retro
Diels–Alder (RDA) reaction to form 3-phenylpyrimidine-2,4(1H,3H-dione(3-phenyluracil)) and butadiene. Kinetic measurements of the ring
opening reaction supported a concerted b-elimination as the most probable mechanism.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
synthesis of uracils and thiouracils.6–8 These reactions, in
which cyclopentadiene is splitted-off, were carried out with-
out solvent above the melting point, i.e., at temperatures
ranging from 150 to 250 ꢁC.
Many retro Diels–Alder (RDA) reactions involve the split-
ting-off of cyclopentadiene or aromatic moieties, which
are stable enough to lower the energy of activation of the
reaction. There are many examples of these reactions, which
are used for different purposes, for instance in transfer tech-
nology,1 in the synthesis of natural products2 and in connec-
tion with protective groups for unstable reagents such as
selenoaldehydes.3 On the other hand, it is expected that the
splitting-off of a butadiene moiety should require higher
energy than RDA reactions affording cyclopentadiene or
an aromatic fragment, and for this reason the information
on this particular type of RDA reaction is scarce. A sponta-
neous RDA reaction affording 1-(2-furyl)-3-dimethylamino-
2-propene-1-thione, a butadiene-like fragment, was reported
to occur during the process of purification of 2-aryl-4-(dime-
thylamino)-3-nitro-6-(2-furyl)-3,4-dihydro-2H-thiopyrans.4
A RDA reaction in the fvp of cis-1,2,3,6-tetrahydrophthalic
anhydride, affording butadiene and maleic anhydride, has
also been described.5
The above-described RDA results encouraged us to carry out
flash vacuum pyrolysis (fvp) reactions of cis/trans-2-thioxo-
quinazolin-4-ones (1a–d,f) and their 2,4-dione analogs (1e,g)
(Fig. 1). These compounds could afford thiouracils or uracils
in RDA reactions, but in this case the diene partner is
butadiene and not cyclopentadiene, so, these reactions are
expected to require higher energy. For this reason, the het-
erocyclic moiety in these molecules can also lead to different
reactions, such as ring opening, isomerization, the loss of
small molecules, etc., as competitive or lower energy
O
Ar
N
N
H
X
1a: cis; X = S; Ar = Ph
The RDA reactions of some norbornene-fused uracils or
thiouracils have been extensively studied as routes for the
1b: cis; X = S; Ar = m-ClC6H4
1c: cis; X = S; Ar = p-MeC6H4
1d: cis; X = S; Ar = m-MeOC6H4
1e: cis; X = O; Ar = Ph
Keywords: Flash vacuum pyrolysis; Retro Diels–Alder; Isothiocyanates;
Isocyanates.
* Corresponding author. Tel.: +54 351 433 4170/4173/3030; fax: +54 351
433 4170x151; e-mail: yranzogi@fcq.unc.edu.ar
1f: trans; X = S; Ar = Ph
1g: trans; X = O; Ar = Ph
Figure 1.
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.07.010

1050
W. J. Pelaꢀez et al. / Tetrahedron 64 (2008) 1049–1057
reactions during fvp experiments. In this article, we describe
the results of fvp reactions of 1a–g, including kinetic
measurements of some of these reactions that support the
proposed mechanism. The fvp reactions of 1a–g furnished
information on the effects of cis/trans isomerism, the hetero-
atoms and the aryl substituents on the reactivity.
(8e,g: 64 and 65%; 1e,g: 30 and 60%), this fact was attrib-
uted to the competition of the hydrolysis reaction.
2.2. Flash vacuum pyrolysis of 1a–d
The results of the fvp of 1a–d are described in Scheme 2 and
Tables S1–S4 in Supplementary data. All of them underwent
ring opening to an isomeric cis-isothiocyanate (9a–d), which
ꢀ
ꢀ
2. Results and discussion
2.1. Synthesis of 1a–g
in turn lost NCS and H or HNCS to give three isomeric
dienes 10a–d, 11a–d and 12a–d between 230 and 420 ꢁC.
The presence of the three dienes may be taken as an evidence
of the first possibility, i.e., the radicals; a concerted elimina-
tion of a neutral molecule would lead to one or two dienes.
These dienes were aromatized to the corresponding benz-
amide (13a–d) under fvp conditions.
Compounds 1a–g were prepared as described in Scheme 1
by modification of the previously described methodo-
logy.9–12 The starting material for the cis and trans isomers
was cis-1,2,3,6-tetrahydrophthalic anhydride (2). For the
cis isomers, 1 was transformed to amino acid 3 and then to
the methyl ester 4. The reaction of 4 with an aryl isocyanate
or isothiocyanate afforded 8a–e, which gave the cyclic com-
pounds 1a–e on refluxing in 25% HCl.
To check whether the first step was an equilibrium, fvp
reactions of 9c,d were carried out at 340 ꢁC, as at this
temperature the starting materials, isothiocyanates and di-
enes, were present in good yields. As expected, 1c,d and
dienes 10–12c,d were found, confirming the equilibrium
proposed in Scheme 2.
Alternatively, 2 was isomerized to the trans isomer 5; on
treatment with the same reagents as for 2, 5 afforded the
trans isomers 1f,g. The yields of these reactions were high
in the reactions affording the thioureas 8a–d,f (70–85%)
and for the cis/trans-2-thioquinazolin-4-ones 1a–d,f (80–
95%). The yields of the 2-oxo compounds were lower
The results of fvp reactions of 1a–d at 300 and 340 ꢁC
(Table 1) serve to make an evaluation of substituent effect
on reactivity. This analysis reveals that 1a–d have the
same reaction with a slight substituent effect. Compound
O
O
O
O
H
A,B
C
OCH3
NH
OCH3
OH
NH2
O
NH2
4
O
Ar
3
X
N
2
H
8a–d cis X = S
8e cis X = O
H
8e trans X = S
8f trans X = O
D–G
I
O
O
O
O
O
O
Ar
A,B
OCH3
C
OH
NH2
N
NH2
N
H
X
5
6
7
1a–d cis X = S
1e cis X = O
1f trans X = S
1g trans X = O
Scheme 1. (A) NH4OH, NaOH, 0 ꢁC, then HCl; (B) NaOH, NaOCl, 0 ꢁC, then HCl; (C) SOCl2, MeOH, ꢂ15 ꢁC, then KOH; (D) H2SO4, MeOH, 80 ꢁC;
(E) NaOMe, reflux; (F) NaOH, rt, then HCl, 0 ꢁC; (G) Ac2O, reflux; (H) PhNCO or ArNCS, toluene, rt; (I) 25% HCl, reflux.
O
O
O
O
- .NCS
- .H
Ar
Ar
Ar
Ar
S
N
H
N
H
N
H
N
H
N
C
N
10a–d
12a–d
11a–d
9a–d
O
O
Ar
S
Ar
N
H
N
H
1a–d
13a–d
Scheme 2.

W. J. Pelaꢀez et al. / Tetrahedron 64 (2008) 1049–1057
1051
Table 1. Fvp reactions of 1a–d at 300/340 ꢁC
reaction. Isocyanate 9e was detected by IR (2205 cmꢂ1) at
all temperatures, but could not be quantified because of its
decomposition at the given reaction temperatures. Dienes
10a–12a were detected by GC/MS.
cis, X¼S
1a (%) 9a %
10+11+12b (%) 13a (%)
a, Ar¼Ph
72/65
82/67
77/74
12/15 16/14
0/6
b, Ar¼m-ClC6H4
c, Ar¼p-MeC6H4
11/18
23/9
9/15
8/7
0/17
0/0
0/8
0/0
0/0
2.4. Flash vacuum pyrolysis of 1f
d, Ar¼m-OMeC6H4 91/85
See full tables in Supplementary data.
The fvp reactions of 1f were carried out between 340 and
440 ꢁC and the results are given in Scheme 4 and Table
S6 in Supplementary data. These reactions may be com-
pared with those of 1a–d because the same products were
formed, with the exception that the isothiocyanate was
trans, as expected (IR: 2090 cmꢂ1, trans-NCS). It was note-
worthy that the trans isomers were more stable than the
cis isomers, which was reflected by the higher reaction
temperatures.
Relative quantification by 1H NMR.
See relative ratios in Section 4.
a
b
1a was the most reactive starting material, whereas the least
reactive was 1d. This fact can easily be seen comparing the
recovery of 1a (72%) and 1d (91%) in pyrolysis at 300 ꢁC.
The most reactive isothiocyanates were 9a and 9d, which
at all the studied temperatures decomposed to the corre-
sponding dienes, whereas isothiocyanates 9b and 9c could
be quantified without decomposition at lower reaction
temperatures. The dienes were observed to have different
stabilities: those arising from 1a–c could be detected and
quantified at temperatures where the corresponding benz-
amides were not formed.
2.5. Flash vacuum pyrolysis of 1g
The fvp of 1g between 540 and 600 ꢁC gave the results
reported in Scheme 4 and Table S7 in Supplementary data.
As the reaction temperatures were higher than those for 1f,
the corresponding isocyanate and dienes could not be quan-
tified due to their instability under those conditions, but they
were detected by IR (2255 cmꢂ1, trans-NCO) and GC/MS
(dienes).
2.3. Flash vacuum pyrolysis of 1e
Compound 1e was subjected to fvp at temperatures between
500 and 580 ꢁC. The results are depicted in Scheme 3 and
Table S5 in Supplementary data.
The results of fvp of 1a–g revealed that the formation of the
isomeric isothiocyanates or isocyanates is the lower energy
reaction, involving C2–N3 bond breaking and H transfer.
At higher temperatures, the RDA reaction is a competitive
reaction for 1e, demonstrating that this is a higher energy
reaction. Although the fvp of 1g was carried out at
There were two main differences in the reactions of 1e when
compared with those of 1a–d: the reaction temperatures
were significantly higher, and uracil 14 and butadiene
appeared as new products formed in a competitive RDA
O
N
O
O
O
Ph
O
Ph
Ph
Ph
N
H
N
H
N
H
N
H
C
10a
11a
12a
9e
O
O
O
Ph
Ph
O
Ph
N
H
N
N
N
H
N
H
O
13a
14
1e
Scheme 3.
O
O
N
O
O
- .NCX
- .H
Ph
Ph
X
Ph
Ph
N
N
N
H
N
H
H
C
H
12a
10a
11a
9f: X = S
9g: X = O
O
O
Ph
Ph
N
N
H
N
H
X
13a
1f: X = S
1g: X = O
Scheme 4.

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W. J. Pelaꢀez et al. / Tetrahedron 64 (2008) 1049–1057
temperatures where the RDA reaction might be expected, it
was not observed, suggesting a concerted RDA reaction in
1e. The possible product arising from a concerted RDA in
1g has high strain energy.
compounds react by the same mechanism, as shown by the
DGz values, which were almost the same. It should be men-
tioned here that DGz for 1f was calculated from the results at
340 ꢁC; the calculated value for 300 ꢁC is 33.0 kcal/mol,
which is quite similar to the ones of 1c,d. From the possible
reaction mechanisms depicted in Scheme 5, the diradical
mechanism should afford positive entropies of activation,
while a concerted way should have negative values. The en-
tropies of activation in Table 2 indicate that 1c,d (cis) have
strong negative values, while 1f (trans) has a slightly posi-
tive value, greatly different from that expected for a diradical
mechanism. The log A values for a diradical mechanism
are between 14.5 and 16,14,15 while that calculated for the
b-elimination through a four-membered transition state in
the thermal reaction of pyruvic acid is 13.53.16 This result
is quite similar to that calculated for 1f, which may be taken
as confirmation of a concerted reaction via a cyclic transition
state for this compound. The log A values for 1c,d are much
lower, indicating more negative entropies of activation; this
fact cannot be explained by a substituent effect, so a confor-
mational effect should be explored.
Up to this point, we were interested in the mechanism of for-
mation of compounds 9a–g, i.e., the first step of the reaction.
There was no previous evidence concerning the mechanism
of this equilibrium isomerization step that could take place
in a stepwise manner via a diradical intermediate or in a con-
certed way. On the other hand, as these compounds are pres-
ent in tautomeric equilibrium, it was of interest to examine,
which tautomer was reacting. These alternatives are shown
in Scheme 5.
Kinetic measurements on the reactions of 1c,d,f were carried
out to get more information on the reaction mechanism.
These compounds were the only starting materials that
afforded the corresponding isothiocyanates without decom-
position to dienes at lower reaction temperatures (see Tables
S1–S7 in Supplementary data).
1
Reaction constants were measured at each temperature with
the relative concentrations of the starting materials and prod-
ucts determined by 1H NMR and averaged over at least three
determinations. Reaction times were calculated as V0/m
(contact time), V0 being the volume of the reaction tube
inside the hot zone and m, the carrier gas flow. Arrhenius
parameters were calculated via the classical equation
(ln k vs 1/T). To validate the system, the kinetic parameters
of ethyl acetate pyrolysis were measured and compared with
those reported for a static system; these results, together with
a detailed description of the methodology, were described
earlier.13
Some H NMR conformational studies have been carried
out on 2,4-dioxodecahydroquinazolines and 2-thioxo-4-oxo-
decahydroquinazolines,17 compounds that are similar to
those described in this article with the exception that 1a–g
contain a cyclohexene ring. The trans-fused 2,4-dioxo-
decahydroquinazoline was found to have a biased chair–
sofa conformation, whereas the cis isomer consists of an
approximately 61:39 conformational mixture of the N(1)-
out and N(1)-in forms (Fig. 2).17
This difference in conformation may be the clue for the
difference in DSz as, although the cis isomers have two
conformations, they are more constrained suggesting a
tighted structure in a cyclic transition state. As both iso-
mers react by the same mechanism (as shown by the DGz
values), DHz should be much lower for the cis isomers to
maintain DGz.
The reactions proved to be of first order; the rate constants
for the reactions of 1c,d,f are given in Tables S8–S10 in Sup-
plementary data, and the Arrhenius parameters in Table 2.
From the results in Table 2, it can be stated that all these
O
O
Ar
Ar
N
H
N
H
N
X
N
X
O
O
N
Ar
X
Ar
N
9a–g
9a–g
N
N
H
O
XH
O
Ar
X
Ar
N
1a–g NH
1a–g XH
N
N
H
N
XH
Scheme 5.
Table 2. Arrhenius parameters for 1c,d,f
Compd
Ar
Isomerism
Ea (kcal/mol)
log A
DSz (e.u.)
DHz (kcal/mol)
DGz (kcal/mol)
1c
1d
1f
p-MePh
m-OMePh
Ph
cis
cis
trans
12.0ꢃ0.3
10.8ꢃ0.3
35.3ꢃ0.9
6.2ꢃ0.2
4.9ꢃ0.1
ꢂ32.3ꢃ0.2
ꢂ38.1ꢃ0.1
+1.9ꢃ0.5
ꢂ10.9ꢃ0.3a
34.0ꢃ0.9b
29.4ꢃ0.5a
31.5ꢃ0.4a
35.0ꢃ1.0b
9.7ꢃ0.3a
13.6ꢃ0.5
a
Obtained at 300 ꢁC.
b
Obtained at 340 ꢁC (calculated 33.0 kcal/mol at 300 ꢁC).

W. J. Pelaꢀez et al. / Tetrahedron 64 (2008) 1049–1057
1053
O
R
3. Conclusions
H
N
X
N
HN
HN
The reactions described in this article confirmed that the
RDA reaction affording butadiene involves higher energy
than that affording cyclopentadiene, but it is possible to
produce it in fvp experiments.
O
N
O
X
X
N
R
R
cis N(1)-out
trans
cis N(1)-in
R = H, Ar; X = O, S
R = H, Ar; X = O, S
Figure 2.
Ring opening and formation of isothiocyanates or isocya-
nates is the lower energy reaction in 1a–g. This reaction is
proposed to take place via a cyclic transition state from the
thiol or enol tautomer. The only competing reaction is
RDA in the cis-oxygenated compound 1e, as oxygenated
compounds are more stable than the sulfur ones and thus
the reaction temperatures are higher. The trans oxygenated
compound does not afford uracil and butadiene by RDA as
the expected compound formed by a concerted RDA reac-
tion has a high strain energy; this fact confirms the concerted
reaction for the cis isomer.
As depicted in Scheme 5, 1a–g have a tautomeric equilib-
rium, thiocarbonyl/thioenol and keto/enol, so it is important
to determine, which tautomer is reacting. There are many
references concerning the predominant species in the gas
phase, some of which will be discussed here. Theoretical
calculations on the tautomerism of neutral and protonated
6-thioguanine predict that the N9(H) thiol is the most stable
tautomer. Results at the highest computational level indi-
cated the surprisingly high stability of the thiol tautomer.18
Theoretical calculations on 6-thiopurine,19 6-thioguanine20
and 2-thiocytosine21 also showed that these compounds exist
as thiol-amino forms in the gas phase, whereas thione-amino
forms predominate in aqueous solution. In the cases of 2,4-
dithiouracil and 2,4-dithiothymine, the dithione tautomers
are the most stable in both phases.21 As concerns keto/enol
The trans isomers are more stable than the cis ones and have
slight positive entropies of activation, while the cis isomers
have strong negative values, which were attributed to a con-
formational effect.
1
tautomerism, gas-phase H NMR studies of acetylacetone,
methyl acetoacetate and ethyl acetoacetate revealed the pre-
dominance of the enol tautomers in the gas phase.22 Theoret-
ical calculations and mass spectrometric studies confirmed
a noteworthy tendency to enolic structure formation when
the sulfur is replaced by oxygen in different ketones.23 The
fvp reactions and theoretical calculations on pyrazolinones
pointed out the enol as the reacting tautomer in the gas
phase.24
4. Experimental
4.1. General
1H NMR (400 MHz or 200 MHz) and 13C NMR (50 MHz)
spectra were recorded at 300 K with TMS as an internal
reference (0 ppm for all). IR spectra were measured with
an FTIR spectrophotometer. Melting points are uncor-
rected. GC/MS were performed with an SE-30 column,
using helium as eluent at a flow rate of 1 mL/min, with
a heating ramp of 7 ꢁC/min from 240 to 270 ꢁC and
of 10 ꢁC/min up to 280 ꢁC. Mass spectra were obtained
in the electron impact mode (EI), with 70 eV ionization
energy. Column and thin-layer chromatographies were
performed on silica gel. Solvents were of analytical
grade.
We do not have direct evidences on which is the most stable
tautomer of our compounds in the gas phase, but taking into
account the above-described results, we propose that the
reacting tautomer is 1a–g XH (thioenol or enol). Besides,
on the basis of kinetic measurements, mainly the entropies
of activation, we propose a concerted reaction as the mech-
anism for the fvp of 1a–g as depicted in Scheme 6.
O
O
O
N
O
Ar
Ar
X
Ar
Ar
N
N
H
N
N
H
N
H
NCX
XH
N
X
9a–d
1a–g NH
1a–g XH
– .NCX
– .H
X= O, cis
Ar= Ph
X= O, cis
Ar= Ph
O
O
N
O
O
O
Ph
Ph
Ar
Ar
Ar
N
N
N
N
H
N
H
H
N
H
O
OH
12a–d
11a–d
10a–d
14 NH
14 OH
O
Ar
N
H
13a–d
Scheme 6.

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W. J. Pelaꢀez et al. / Tetrahedron 64 (2008) 1049–1057
Fvp reactions were carried out in a Vycor glass reactor, using
a tube furnace with a temperature-controller device. Oxy-
gen-free dry nitrogen was used as carrier gas. Approximately
40 mg samples were pyrolyzed. Contact times were around
10ꢂ2 s and a pressure ofw0.02 Torr was used. Products were
trapped at liquid air temperature, extracted with solvent
(CDCl3) and subjected to different analyses or separation
techniques. In all fvp experiments, the recovery of material
was >90%.
175.2. IR (KBr) cmꢂ1: 3318, 1743, 1656, 1556. Anal. Calcd
for C15H18N2O3 (274.32): C, 65.68; H, 6.61; N, 10.21.
Found: C, 65.30; H, 6.42; N, 9.83.
Compound 8f: yield 92%. Mp: 167–169 ꢁC. 1H NMR
(CDCl3) d (ppm): 1.83–1.96 (1H, m), 2.15–2.26 (1H, m),
2.51–2.73 (2H, m), 2.91 (1H, dd, J¼14.2, 7.5 Hz), 3.69
(3H, s), 4.80–4.94 (1H, m), 5.58 (1H, d, J¼10.6 Hz), 5.66
(1H, d, J¼10.6 Hz), 6.11–6.19 (1H, m), 7.20 (2H, d,
J¼7.0 Hz), 7.29 (1H, t, J¼7.4 Hz), 7.45 (2H, t, J¼7.8 Hz),
7.92 (1H, br s). 13C NMR (CDCl3) d (ppm): 26.6, 30.9,
44.0, 52.2, 52.8, 124.6, 125.6, 125.9, 127.9, 130.8, 136.7,
156.3, 173.1. IR (KBr) cmꢂ1: 3327, 1741, 1653, 1551.
Anal. Calcd for C15H18N2O2S (290.38): C, 62.04; H, 6.25;
N, 9.65. Found: C, 62.43; H, 6.62; N, 9.28.
Compounds 3–7 and 8a were prepared according to the
previously described methodology.9–12
4.2. General procedure for the preparation of thiourea
(8b–d,f) and urea (8e,g) derivatives
The appropriate aryl isothiocyanate or phenyl isocyanate
(10 mmol) was added to 4 (1.47 g, 9.5 mmol) dissolved in
30 mL of dry toluene, and the mixture was stirred at room
temperature for 1 h. The solution was then evaporated and
the product obtained was recrystallized from ethyl acetate/
n-hexane.
Compound 8g: yield: 81%. Mp: 151–153 ꢁC. 1H NMR
(CDCl3) d (ppm): 1.99 (1H, m), 2.33 (1H, d, J¼18.1 Hz),
2.48–2.58 (2H, m), 2.72 (1H, m), 3.70 (3H, s), 4.18 (1H,
m), 5.45 (1H, br), 5.64 (2H, coalesced signals), 7.09 (1H,
m), 7.2–7.33 (4H, m), 7.46 (1H, br). 13C NMR (CDCl3)
d (ppm): 28.0, 32.4, 45.9, 48.1, 52.7, 121.1, 124.0, 125.2,
125.5, 129.7, 139.5, 156.4, 175.5. IR (KBr) cmꢂ1: 3279,
3036, 1730, 1640. Anal. Calcd for C15H18N2O3 (274.32):
C, 65.68; H, 6.61; N, 10.21. Found: C, 65.28; H, 6.20;
N, 9.82.
Compound 8b: yield 77%. Mp: 102–105 ꢁC. 1H NMR
(CDCl3) d (ppm): 2.14–2.20 (1H, m), 2.45–2.58 (3H, m),
3.03 (1H, s), 3.66 (3H, s), 4.96 (1H, s), 5.60–5.68 (2H, m),
7.14 (2H, br d, J¼6.0 Hz), 7.25 (2H, br d, J¼6.0 Hz), 7.36
(1H, br m), 7.76 (1H, br s). 13C NMR (CDCl3) d (ppm):
27.0, 28.4, 42.2, 51.9, 52.8, 123.2, 125.2, 125.5, 125.6,
4.3. Cyclic compounds 1a–e
127.6, 131.7, 134.7, 137.9, 174.2, 182.8. IR (KBr) cmꢂ1
:
The appropriate thioureas (8a–d) or urea (8e) (5 mmol) were
refluxed in 30 mL of 25% HCl solution for 30 min. After
cooling, the crystalline products (1a–d) were separated by
vacuum filtration, washed with water and dried. Compound
1e was obtained after extraction with CHCl3 (3ꢄ50 mL),
drying (Na2SO4) and evaporation. The solid obtained was
purified by column chromatography on silica gel with a
mixture of toluene/EtOH (9:1) as eluent.
3331, 3162, 1702, 1597, 1531. Anal. Calcd for
C15H17ClN2O2S (324.83): C, 55.46; H, 5.28; N, 8.62. Found:
C, 55.09; H, 4.89; N, 8.24.
Compound 8c: yield 70%. Mp: 121–124 ꢁC. 1H NMR
(CDCl3) d (ppm): 2.12–2.21 (1H, m), 2.37–2.54 (3H, m),
2.42 (3H, s), 3.02 (1H, s), 3.61 (3H, s), 4.96 (1H, s), 5.61
(2H, m), 6.93 (1H, br s), 7.09 (2H, d, J¼8.1 Hz), 7.23
(2H, d, J¼8.1 Hz), 7.55 (1H, br s). 13C NMR (CDCl3)
d (ppm): 21.5, 27.0, 29.6, 41.9, 51.6, 52.3, 125.3, 125.4,
131.0, 132.2, 137.4, 173.8, 180.4. IR (KBr) cmꢂ1: 3332,
3153, 1707, 1526, 1242. Anal. Calcd for C16H20N2O2S
(304.41): C, 63.13; H, 6.62; N, 9.20. Found: C, 62.79; H,
6.22; N, 8.84.
Compound 1a: this compound was obtained as a white
crystalline product, yield: 85%. Mp: 241–244 ꢁC (lit.:10
243–245 ꢁC). The spectral data and physical properties
matched those reported previously.
Compound 1b: yield 81%. Mp: 208–212 ꢁC. 1H NMR
(DMSO-d6) d (ppm): 2.32 (3H, br s), 2.54 (1H, br s), 3.25
(1H, m), 3.93 (1H, m), 5.60 (1H, d, J¼10.1 Hz), 5.70 (1H,
d, J¼10.6 Hz), 7.13 (1H, br s), 7.30 (1H, br s), 7.42 (2H,
m), 10.22 (1H, br s). 13C NMR (DMSO-d6) d (ppm): 22.5,
26.6, 37.6, 46.3, 123.2, 124.7, 127.8, 129.8, 132.4, 140.7,
169.3, 180.0. IR (KBr) cmꢂ1: 3164, 1733, 1541, 1181.
Anal. Calcd for C14H13ClN2OS (292.78): C, 57.43; H,
4.48; N, 9.57. Found: C, 57.80; H, 4.85; N, 9.95.
Compound 8d: yield 84%. Mp: 137–139 ꢁC. 1H NMR
(CDCl3) d (ppm): 2.12–2.19 (1H, m), 2.36–2.57 (3H, m),
3.04 (1H, s), 3.63 (3H, s), 3.82 (3H, s), 4.98 (1H, s), 5.62
(2H, m), 6.76 (1H, s), 6.81 (1H, dd, J¼8.3, 16.4 Hz), 7.15
(1H, br s), 7.33 (1H, t, J¼8.1 Hz), 7.70 (1H, br s). 13C
NMR (CDCl3) d (ppm): 27.3, 29.8, 42.2, 52.0, 52.6, 56.1,
110.7, 113.6, 117.2, 125.6, 131.5, 132.0, 137.5, 160.6,
174.1. IR (KBr) cmꢂ1: 3374, 3172, 1736, 1530. Anal. Calcd
for C16H20N2O3S (320.41): C, 59.98; H, 6.29; N, 8.74.
Found: C, 60.36; H, 6.65; N, 9.18.
Compound 1c: yield 93%. Mp: 243–243 ꢁC. 1H NMR
(DMSO-d6) d (ppm): 2.27–2.32 (3H, m), 2.32 (3H, s),
3.17–3.39 (2H, m), 3.90 (1H, m), 5.60 (1H, d, J¼10.1 Hz),
5.67 (1H, d, J¼10.1 Hz, 6.97 (2H, d, J¼7.0 Hz), 7.17 (2H,
d, J¼8.1 Hz), 10.1 (1H, br s). 13C NMR (DMSO-d6)
d (ppm): 20.7, 22.7, 26.7, 37.7, 46.2, 123.2, 124.9, 128.9,
129.3, 136.8, 136.9, 169.4, 180.6. IR (KBr) cmꢂ1: 3163,
3023, 1730, 1541, 1234. Anal. Calcd for C15H16N2OS
(272.37): C, 66.15; H, 5.92; N, 10.29. Found: C, 66.52; H,
6.29; N, 10.65.
Compound 8e: yield 65%. Mp: 109–111 ꢁC. 1H NMR
(CDCl3) d (ppm): 2.16–2.27 (1H, m), 2.31–2.44 (2H, m),
2.46–2.56 (1H, m), 2.84–2.91 (1H, m), 3.67 (3H, s), 4.39–
4.48 (1H, m), 5.63 (2H, dd, J¼10.3, 19.1 Hz), 5.74–5.76
(1H, m), 7.04 (1H, t, J¼6.6 Hz), 7.12 (1H, br s), 7.22–7.32
(4H, m). 13C NMR (CDCl3) d (ppm): 26.4, 31.5, 42.9,
46.5, 52.6, 121.3, 124.1, 125.6, 125.7, 129.8, 139.5, 156.2,

W. J. Pelaꢀez et al. / Tetrahedron 64 (2008) 1049–1057
1055
1
Compound 1d: yield 94%. Mp: 242–245 ꢁC. 1H NMR
(DMSO-d6) d (ppm): 2.31 (3H, br s), 3.20–3.40 (2H, m),
3.74 (3H, s), 3.90 (1H, m), 5.60 (1H, d, J¼9.6 Hz), 5.67
(1H, d, J¼9.1 Hz), 6.70 (2H, br s), 6.90 (1H, d, J¼8.1 Hz),
7.28 (1H, t, J¼8.1 Hz), 10.12 (1H, br s). 13C NMR
(DMSO-d6) d (ppm): 22.6, 26.6, 37.6, 46.2, 55.2, 113.1,
115.6, 121.9, 123.2, 124.8, 128.9, 140.4, 159.3, 169.2,
180.3. IR (KBr) cmꢂ1: 3166, 1718, 1545, 1184. Anal. Calcd
for C15H16N2O2S (288.36): C, 62.48; H, 5.59; N, 9.71.
Found: C, 62.10; H, 5.19; N, 9.32.
(100%), 51 (27%). H NMR (200 MHz, CDCl3) d (ppm):
individual signal: 4.16 (m, 1H). Relative % (10a–12a) at
340 ꢁC: 42%.
Compound 11a: GC/MS (ret. time/min): 5.96. MS: 199 (M+,
20%), 198 (33%), 107 (100%), 105 (39%), 79 (45%), 77
1
(97%), 51 (27%). H NMR (200 MHz, CDCl3) d (ppm):
individual signal: 6.20 (dd, J1¼9.50 Hz, J2¼4.7 Hz, 1H).
Relative % (10a–12a) at 340 ꢁC: 14%.
Compound 12a: GC/MS (ret. time/min): 4.93. MS: 199 (M+,
22%), 198 (15%), 121 (17%), 105 (11%), 93 (66%), 80
(80%), 79 (100%), 77 (94%). H NMR (200 MHz, CDCl3)
d (ppm): individual signal: 6.68 (br s, 1H). Relative %
(10a–12a) at 340 ꢁC: 44%.
Compound 1e: yield 34%. Mp: 155–158 ꢁC (lit.:9 167–
170 ꢁC). 1H NMR (DMSO-d6) d (ppm): 2.25 (1H, d,
J¼15.1 Hz), 2.45 (2H, m), 2.76 (1H, d, J¼18.1 Hz), 3.08
(1H, m), 3.93 (1H, m), 5.63 (2H, br d, J¼12.1 Hz), 5.76
(1H, d, J¼9.1 Hz), 7.16 (2H, d, J¼7.6 Hz), 7.41 (3H, m).
IR (KBr) cmꢂ1: 3236, 3103, 1732, 1690. Anal. Calcd for
C14H14N2O2 (242.27): C, 69.41; H, 5.82; N, 11.56. Found:
C, 69.17; H, 5.53; N, 11.21.
1
Compound 13a: GC (ret. time/min): 5.86 min. MS: 197 (M+,
28%), 106 (6%), 105 (100%), 77 (45%), 65 (4%), 51 (18%);
95% match with NIST database, spectrum no. 33395, CAS
no. 93-98-1. 1H NMR (200 MHz, CDCl3) d (ppm): individ-
ual signal: 7.86 (d, J¼7.9 Hz).
Compound 1f: this compound was obtained as a white
crystalline product, yield: 95%. Mp: 263–266 ꢁC (lit.:10
265–266 ꢁC). The spectral data and physical properties
matched those reported previously.
4.5. Flash vacuum pyrolysis of 1b
The fvp of 1b was carried out between 260 and 380 ꢁC, at
a pressure of w10ꢂ2 Torr and contact time of w10ꢂ2 s. Be-
tween 240 and 320 ꢁC, the only products were isothiocya-
nate 9b and dienes 10b–12b, while at higher temperatures
(over 320 ꢁC), amide 13b was formed. Reactions were stud-
ied up to 33.2% of 1b because the mass balance decreased
by more than 90% at higher yields due to decomposition
reactions.
Compound 1g: yield 67%. Mp: 227–230 ꢁC. 1H NMR
(CDCl3) d (ppm): 2.15–2.31 (2H, m), 2.47 (1H, m), 2.65–
2.78 (2H, m), 3.7 (1H, m), 5.61 (1H, s, br), 5.67 (1H, m),
5.80 (1H, m), 7.19 (2H, d, J¼7.0 Hz), 7.39 (1H, t, J¼
7.3 Hz), 7.45 (2H, t, J¼7.3 Hz). IR (KBr) cmꢂ1: 3303,
3032, 1741, 1688. Anal. Calcd for C14H14N2O2 (242.27):
C, 69.41; H, 5.82; N, 11.56. Found: C, 69.10; H, 5.44; N,
11.18.
Compound 9b: this was obtained by column chromato-
graphy on silica gel 60 with CHCl3/n-hexane (1:1, 6:4, 7:3
4.4. Flash vacuum pyrolysis of 1a
1
and 8:2) as eluent. Mp: 124–125 ꢁC. H NMR (200 MHz,
The fvp of 1a was performed between 240 and 420 ꢁC, at
a pressure of w10ꢂ2 Torr and contact time of w10ꢂ2 s.
Between 240 and 320 ꢁC, the only products were isothiocya-
nate 9a and dienes 10a–12a, while at higher temperatures
(over 340 ꢁC), amide 13a was formed. Reactions were stud-
ied up to recovery of 46% of 1a; at higher temperatures
competitive decomposition reactions with formation of tarry
products were present.
CDCl3) d (ppm): 2.38–2.82 (m, 5H), 4.48 (m, 1H), 5.76
(m, 2H), 7.11 (d, J¼8.0 Hz, 1H), 7.26 (t, J¼8.0 Hz, 1H),
7.37 (d, J¼8.4 Hz, 1H), 7.39 (br s, 1H, NH), 7.67 (m, 1H).
13C NMR (50 MHz, CDCl3) d (ppm): 24.5, 32.4, 45.4,
53.3, 118.5, 120.7, 123.0, 124.9, 125.1, 130.2, 131.8,
134.9, 138.5, 169.6. MS: 292 (M+, 5%), 234 (20%), 129
(14%), 127 (45%), 107 (10%), 81 (17%), 80 (30%), 79
(100%), 77 (35%), 72 (18%). IR (KBr) cmꢂ1: 3553, 3297,
3258, 3037, 2911, 2850, 2100 (NCS), 1675, 1597, 1536,
1428, 785, 678.
Compound 9a: it was obtained by column chromatography
on silica gel 60 with CHCl3/n-hexane (1:1, 6:4, 7:3 and
8:2) as eluent. Mp: 149–150 ꢁC. 1H NMR (200 MHz,
CDCl3) d (ppm): 2.38–2.81 (m, 5H), 4.51 (m, 1H), 5.77
(m, 2H), 7.15 (t, J¼7.3 Hz, 1H), 7.34 (t, J¼7.7 Hz, 2H),
7.40 (br, 1H, NH), 7.53 (d, J¼7.7 Hz, 2H). 13C NMR
(50 MHz, CDCl3) d (ppm): 24.4, 32.5, 45.4, 53.4, 120.6,
123.0, 125.1, 129.2, 137.4, 144.5, 169.5. MS: 258 (6%),
200 (33%), 139 (7%), 120 (11%), 107 (6%), 93 (100%),
79 (90%). IR (KBr) cmꢂ1: 3434, 3250, 3185, 3138, 2933,
2105 (NCS), 1657, 1592, 1545, 1454, 749, 676.
Compounds 10b–12b: these dienes were separated as a mix-
ture with amide 13b and were identified by GC/MS and 1H
NMR (one characteristic signal for each).
Compound 10b: GC/MS (ret. time/min): 6.74. MS: 235
(5%), 234 (5%), 233 (M+, 16%), 157 (3%), 156 (3%), 155
(11%), 154 (7%), 129 (6%), 127 (22%), 79 (100%), 77
1
(44%), 51 (19%). H NMR (200 MHz, CDCl3) d (ppm):
individual signal: 6.68 (br s, 1H). Relative % (10b–12b) at
340 ꢁC: 50%.
Compounds 10a–12a: these dienes were separated as a mix-
ture with amide 13a and were identified by GC/MS and 1H
NMR (one characteristic signal for each).
Compound 11b: GC/MS (ret. time/min): 6.43. MS: 235
(7%), 234 (8%), 233 (M+, 19%), 232 (15%), 108 (7%),
107 (100%), 106 (8%), 105 (60%), 80 (6%), 79 (38%),
78 (16%), 77 (83%), 51 (32%). 1H NMR (200 MHz,
Compound 10a: GC/MS (ret. time/min): 6.32. MS: 199 (M+,
22%), 198 (61%), 107 (48%), 105 (33%), 79 (55%), 77
CDCl3)
d
(ppm): individual signal: 6.25 (dd,

1056
W. J. Pelaꢀez et al. / Tetrahedron 64 (2008) 1049–1057
J1¼9.13 Hz, J2¼5.47 Hz, 1H). Relative % (10b–12b) at
NMR (200 MHz, CDCl3) d (ppm): individual signal: 7.87
(d, J¼7.9 Hz, 2H).
340 ꢁC: 15%.
Compound 12b: GC/MS (ret. time/min): 5.31. MS: 235
(5%), 234 (5%), 233 (M+, 16%), 155 (11%), 154 (7%),
129 (6%), 127 (21%), 80 (67%), 79 (100%), 78 (13%), 77
(44%), 51 (19%). H NMR (200 MHz, CDCl3) d (ppm):
individual signal: 6.70 (br s, 1H). Relative % (10b–12b) at
340 ꢁC: 35%.
4.7. Flash vacuum pyrolysis of 1d
The fvp of 1d was carried out between 280 and 400 ꢁC, at
a pressure of w10ꢂ2 Torr and contact time ofw10ꢂ2 s. Be-
tween 280 and 340 ꢁC, the only product was isothiocya-
nate 9d, while over 360 ꢁC, dienes 10d–12d and amide
13d were formed. The reactions were studied up to
75.3% of 1d because the mass balance decreased by
more than 90% due to decomposition reactions at higher
yields.
1
Compound 13b: GC/MS (ret. time/min): 6.20. MS: 233
(6%), 232 (3%), 231 (M+, 19%), 105 (100%), 77 (53%),
76 (5%), 51 (23%). H NMR (200 MHz, CDCl3) d (ppm):
1
individual signal: 7.69 (d, J¼8.03 Hz, 2H).
Compound 9d: this was obtained by column chromato-
graphy on silica gel 60 with CHCl3/n-hexane (1:1, 6:4, 7:3
4.6. Flash vacuum pyrolysis of 1c
1
and 8:2) as eluent. Mp: 128–130 ꢁC. H NMR (200 MHz,
The fvp of 1c was carried out between 230 and 400 ꢁC, at
a pressure of w10ꢂ2 Torr and contact time of w10ꢂ2 s. Be-
tween 230 and 300 ꢁC, the only product was isothiocyanate
9c, dienes 10c–12c were formed over 320 ꢁC, while over
360 ꢁC, amide 13c was formed. Reactions were studied up
to 73.7% of 1c because the mass balance decreased by
more than 90% due to decomposition reactions at higher
yields.
CDCl3) d (ppm): 2.37–2.80 (m, 5H), 3.80 (s, 3H), 4.48 (m,
1H), 5.75 (m, 2H), 6.69 (d, J¼8.2 Hz, 1H), 6.99 (d,
J¼8.5 Hz, 1H), 7.22 (t, J¼8.0 Hz, 1H), 7.29 (s, 1H), 7.40
(br s, 1H, NH). 13C NMR (50 MHz, CDCl3) d (ppm): 24.4,
32.5, 45.3, 53.3, 55.5, 106.3, 110.9, 112.7, 122.9, 125.1,
129.9, 134.5, 138.6, 160.4, 169.5. MS: 289 (4%), 288 (M+,
22%), 230 (34%), 176 (9%), 150 (17%), 149 (15%), 124
(16%), 123 (100%), 107 (17%), 94 (19%), 93 (10%), 81
(26%), 80 (31%), 79 (79%), 77 (46%), 72 (15%), 51
(14%). IR (KBr) cmꢂ1: 3297, 3010, 2930, 2849, 2096
(NCS), 1668, 1607, 1550, 1494, 1433, 1296, 1220, 1057,
914, 746, 677.
Compound 9c: this was obtained by column chromato-
graphy on silica gel 60 with CHCl3/n-hexane (1:1, 6:4, 7:3
1
and 8:2) as eluent. Mp: 138–140 ꢁC. H NMR (200 MHz,
CDCl3) d (ppm): 2.32 (s, 3H), 2.38–2.79 (m, 5H), 4.49 (br
s, 1H), 5.65–5.84 (m, 2H), 7.13 (d, J¼8.4 Hz, 2H), 7.34
(br s, 1H), 7.39 (d, J¼8.4 Hz, 2H). 13C NMR (50 MHz,
CDCl3) d (ppm): 21.0, 24.3, 32.5, 45.2, 53.4, 120.8, 122.9,
125.9, 129.7, 134.7, 134.8, 169.4. MS: 272 (M+, 10%),
214 (26%), 167 (7%), 149 (19%), 134 (10%), 108 (11%),
107 (100%), 106 (38%), 91 (10%), 80 (34%), 79 (74%),
77 (44%), 57 (14%). IR (KBr) cmꢂ1: 3290, 3188, 3126,
2922, 2849, 2102 (NCS), 1660, 1598, 1513, 1315, 811,
743, 675.
Compounds 10d–12d: these dienes were separated as a mix-
ture with amide 13d and were identified by GC/MS and 1H
NMR (one characteristic signal for each).
Compound 10d: GC (ret. time/min): 7.66. MS: 229 (M+,
22%), 228 (46%), 107 (36%), 105 (98%), 79 (38%), 77
1
(100%). H NMR (200 MHz, CDCl3) d (ppm): individual
signal: 4.13 (m, 1H). Relative % (10d–12d) at 360 ꢁC: 50%.
Compound 11d: GC (ret. time/min): 7.24. MS: 229 (M+,
7%), 228 (11%), 227 (35%), 105 (100%), 79 (12%), 77
Compounds 10c–12c: these dienes were separated as a mix-
ture with amide 13c and were identified by GC/MS and 1H
NMR (one characteristic signal for each).
1
(68%). H NMR (200 MHz, CDCl3) d (ppm): individual
signal: 6.24 (dd, J1¼9.50 Hz, J2¼5.1 Hz, 1H). Relative %
(10d–12d) at 360 ꢁC: 19%.
Compound 10c: GC (ret. time/min): 4.99. MS: 213 (M+,
29%), 135 (22%), 107 (52%), 106 (74%), 91 (21%), 78
Compound 12d: GC (ret. time/min): 6.06. MS: 229 (M+,
54%), 149 (29%), 123 (83%), 107 (26%), 92 (17%), 79
1
(100%), 79 (77%). H NMR (200 MHz, CDCl3) d (ppm):
individual signal: 4.18 (m, 1H). Relative % (10c–12c) at
1
(100%), 77 (86%). H NMR (200 MHz, CDCl3) d (ppm):
individual signal: 3.80 (s, 3H). Relative % (10d–12d) at
340 ꢁC: 57%.
360 ꢁC: 31%.
Compound 11c: GC (ret. time/min): 5.94. MS: 213 (M+,
26%), 212 (23%), 107 (100%), 105 (64%), 79 (32%), 77
Compound 13d: GC (ret. time/min): 7.03 min. MS: 227 (M+,
36%), 106 (7%), 105 (100%), 77 (53%), 51 (18%). 1H NMR
(200 MHz, CDCl3) d (ppm): individual signal: 7.87 (d,
J¼7.9 Hz, 2H).
1
(96%). H NMR (200 MHz, CDCl3) d (ppm): individual
signal: 6.23 (dd, J1¼9.50 Hz, J2¼5.7 Hz, 1H). Relative %
(10c–12c) at 340 ꢁC: 10%.
Compound 12c: GC (ret. time/min): 6.23. MS: 213 (M+,
28%), 212 (50%), 107 (69%), 105 (64%), 77 (100%),
79 (46%). 1H NMR (200 MHz, CDCl3) d (ppm): individual
signal: 6.66 (br s, 1H). Relative % (10c–12c) at 340 ꢁC: 33%.
4.8. Flash vacuum pyrolysis of 1e
The fvp of 1e was carried out between 500 and 580 ꢁC, at
a pressure of w10ꢂ2 Torr and contact time of w10ꢂ2 s. At
all the studied temperatures, the reaction products were
amide 13a, uracil 14 and butadiene. Reactions were studied
up to 4.8% of 1e because the mass balance decreased by
Compound 13c: GC (ret. time/min): 5.77. MS: 211 (M+,
33%), 106 (9%), 105 (100%), 77 (55%), 51 (14%). 1H

W. J. Pelaꢀez et al. / Tetrahedron 64 (2008) 1049–1057
1057
more than 90% due to decomposition reactions at higher
Supplementary data
yields. Butadiene was identified by GC/MS with a
95% match with the NIST library, spectrum no. 80, CAS
no. 106-99-0.
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2007.07.010.
Compound 14: this was separated from the reaction crude
products by column chromatography on silica gel 60 with
CHCl3/n-hexane (1:1, 6:4, 7:3 and 8:2) as eluent. Mp:
242–245 ꢁC (lit.:6 246–247 ꢁC). 1H NMR (200 MHz,
CDCl3) d (ppm): 5.84 (d, J¼7.7 Hz, 1H), 7.14 (d, J¼
7.7 Hz, 1H), 7.23 (d, J¼8.4 Hz, 2H), 7.30 (br s, 1H, NH),
7.43–7.54 (m, 3H). 13C NMR (50 MHz, CD3CN) d (ppm):
101.8, 129.3, 129.8, 136.9, 141.0, 152.5, 164.7.
References and notes
ꢀ
1. Gas Phase Reactions in Organic Synthesis; Vallee, Y., Ed.;
Gordon and Breach Science: Amsterdam, The Netherlands,
1997; p 66.
2. Ichihara, A. Synthesis 1987, 207–222.
3. Zhou, A.; Segi, M.; Nakajima, T. Tetrahedron Lett. 2003, 44,
1179–1182.
4.9. Flash vacuum pyrolysis of 1f
4. Bogdanowickz-Szwed, K.; Budzowsky, A. Z. Naturforsch.
2002, 57b, 637–644.
The fvp of 1f was carried out between 340 and 440 ꢁC, at
a pressure ofw10ꢂ2 Torr and contact time ofw10ꢂ2 s. Com-
pound 9f was the only product up to 360 ꢁC; at 380 ꢁC, 9f
and dienes 10a–12a were found; from 400 ꢁC, amide 13a
was also formed.
5. Aitken, R. A.; Thomas, A. W. Supplement A3: The Chemistry of
Double Bonded Functional Groups; Wiley: New York, NY,
1997; p 508.
ꢀ
ꢀ
ꢀ
ꢀ
6. Bernath, G.; Stajer, G.; Szabo, A. E.; Szoke-Molnar, Z.
Tetrahedron 1987, 43, 1921–1930.
ꢀ
ꢀ
7. Frimpong-Manso, S.; Nagy, K.; Stajer, G.; Bernath, G.; Sohar,
ꢀ
Compound 9f: this was obtained by column chromatography
on silica gel 60 with CHCl3/n-hexane (1:1, 6:4, 7:3 and 8:2)
as eluent. Mp: 138–139 ꢁC. 1H NMR (200 MHz, DMSO-d6)
d (ppm): 2.24–2.71 (m, 5H), 4.14 (m, 1H), 5.66 (m, coalesced
signals, 2H), 7.14 (t, J¼7.1 Hz, 1H), 7.29 (t, J¼7.5 Hz, 2H),
7.52 (d, J¼7.6 Hz, 2H), 7.66 (br s, 1H). 13C NMR (50 MHz,
CDCl3) d (ppm): 28.4, 32.4, 48.9, 54.9, 120.8, 123.2, 125.8,
125.3, 129.2, 133.9, 137.4, 170.7. IR (KBr) cmꢂ1: 3244,
3190, 3139, 3073, 3037, 2915, 2844, 2090 (NCS), 1652,
1555, 1448, 765, 686. MS: 259 (2%), 258 (M+, 13%), 200
(52%), 138 (6%), 120 (18%), 107 (11%), 93 (100%), 79
(91%), 66 (13%), 65 (19%), 53 (14%).
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4.10. Flash vacuum pyrolysis of 1g
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a pressure of w10ꢂ2 Torr and contact time of w10ꢂ2 s. At
all the studied reaction temperatures, the only isolated
product was 13a; isocyanate 9g was detected by IR on the re-
action crude (2255 cmꢂ1, trans-NCO) and dienes by GC/MS;
all of them were present in traces. Reactions were studied up
to 74.1% of 1g because the mass balance decreased by more
than 90% due to decomposition reactions at higher yields.
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Thanks are due for the financial support provided by CONI-
CET, FONCyT, SECyT-UNC and SECyT for the joint
Argentina–Hungary project. W.J.P. thanks CONICET for
a doctoral fellowship.
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