Iminopropadienethiones, Ar-N=C=C=C=S

Full text of DOI:10.1021/jo001595j

J . Org. Chem. 2001, 66, 1827-1831
1827
Im in op r op a d ien eth ion es, Ar -NdCdCdCdS
C. Oliver Kappe,1a David Kvaskoff,1a Daniel W. J . Moloney,1a Robert Flammang,1b and
Curt Wentrup*,1a
Department of Chemistry, The University of Queensland, Brisbane, Qld. 4072, Australia and Organic
Chemistry Laboratory, University of Mons, B-7000 Mons, Belgium
wentrup@chemistry.uq.edu.au
Received November 9, 2000
Aryliminopropadienethiones 9 have been generated by flash vacuum thermolysis of isoxazolones
of the type 5 and characterized by mass spectrometry and matrix isolation IR spectroscopy in
conjunction with DFT calculations and chemical trapping.
Sch em e 1
In tr od u ction
Iminopropadienones (1), a new class of compounds,
have been investigated in our laboratory in recent
years.2,3 While the simple alkyl derivatives have the
character of reactive intermediates, most aryl derivative
can be handled at temperatures between ca. -100 and 0
°C, but a few of these compounds are isolable at room
temperature, e.g., the mesityl and neopentyl deriva-
tives.3,4 This class of compounds show a rich chemistry,
inter alia to produce acylketenimines 2 in stoichiometric
reactions with nucleophiles (HX) and new five- to nine-
membered heterocyclic rings 3 on reaction with bisnu-
cleophiles.3,4
Our next goal was to prepare and characterize the
corresponding thiones, R-NdCdCdCdS. The first re-
sults are reported in this paper.
mal fragmentations and rearrangements of isoxazolones5
made us target compounds of type 5 as possible sources
of the desired iminopropadienethiones 9 by means of
elimination of CO2 and ethylene or isobutene to generate
a transient nitrene 6, 1,2-phenyl group shift in the
nitrene to generate the cumulene 7, a second elimination
of alkene to furnish a bis-thiol 8, and elimination of H2S
to deliver the final product, 9 (Scheme 1). As detailed
below, the study of the mass spectra as a function of
temperature revealed that the sequence of eliminations
shown in Scheme 1 is actually followed.
Resu lts a n d Discu ssion
The iminopropadienones 1 are best prepared by flash
vacuum thermolysis (FVT) of Meldrum’s acid derivatives
of type 4 (Y ) NR′2, SMe, or OMe).2,3 Since thioxo
derivatives of Meldrum’s acid are unknown, a different
methodology had to be sought for the preparation of the
iminopropadienethiones. Previous research on the ther-
(1) (a) University of Queensland. (b) University of Mons.
(2) (a) Mosandl, T.; Kappe, C. O.; Flammang, R.; Wentrup, C. J .
Chem. Soc., Chem. Commun. 1992, 1571. (b) Mosandl, T.; Stadtmu¨ller,
S.; Wong, M. W.; Wentrup, C. J . Phys. Chem. 1994, 98, 1080. (c) Plu¨g,
C.; Frank, W.; Wentrup, C. J . Chem. Soc., Perkin Trans. 2 1999, 1087-
1094.
The required starting materials 5 were prepared by
coupling of the anion of 3-phenylisoxazolone with CS2 in
(3) Wentrup, C.; Rao, V. V. R.; Frank, W.; Fulloon, B. E.; Moloney,
D. W. J .; Mosandl, T. J . Org. Chem. 1999, 64, 3608.
(4) Bibas, H.; Neumann, R.; Shtaiwi, M.; Wentrup, C. Unpublished
results.
(5) Wolf, R.; Stadtmu¨ller, S.; Wong, M. W.; Flammang, R.; Barbieux-
Flammang, M.; Wentrup, C. Chem. Eur. J . 1996, 2, 1318-1329.
Wentrup, C.; Kappe, C. O.; Wong, M. W. Pure Appl. Chem. 1995, 67,
749.
10.1021/jo001595j CCC: $20.00 © 2001 American Chemical Society
Published on Web 02/07/2001

1828 J . Org. Chem., Vol. 66, No. 5, 2001
Kappe et al.
the 4-position, followed by double alkylation of the
dithiocarboxylate formed.
The FVT reactions of 5 were monitored by on-line mass
spectrometry, using a thermolysis reactor fitted inside
the ion source housing of a six-sector tandem mass
spectrometer. Individual ions were investigated by col-
lisional activation mass spectrometry (CAMS) and in the
case of the molecular ions of 9 also neutralization-
reionization mass spectrometry (NRMS).6 In parallel with
these experiments, FVT coupled with Ar matrix isolation
at 7-10 K permitted infrared spectroscopy of the prod-
ucts, and preparative FVT experiments allowed the
isolation of the trapping product 10.
DFT calculations of structures and IR spectra of the
iminopropadienethiones were performed at the B3LYP/
6-31G** level of theory. This method has been found to
give the best overall agreement with reference values
from higher level calculations.7 It has also been applied
successfully to a variety of ketenes in several recent
publications,8 and specific comparisons with experimen-
tal data and with Hartree-Fock, MP2/6-31G*, G2(MP2,-
SVP), or QCISD(T)/6-31G* calculations of energies, ge-
ometries, and/or spectra for ketenes have been made.9
In each of these studies the DFT method has been found
to give excellent agreement with experiment and to
compare well with higher level ab initio calculations. The
calculations10 were carried out using the GAUSSIAN 98
suite of programs.11,12 The B3LYP formulation of density
functional theory corresponds to Becke’s three-parameter
exchange functional12a in combination with the Lee-
Yang-Parr correctional functional.12b Calculated wave-
numbers were scaled by a factor 0.9613.13
F igu r e 1. Mass spectra arising from the FVT of 5a at (a) 200
°C, (b) 600° C, (c) 720 °C.
F VT-MS. The mass spectra of the thermolysates were
monitored over the temperature range 200 to ca. 800 °C.
A selection is shown in Figure 1. The starting material
5a was stable till FVT temperatures above 300 °C, when
molecular ions at m/ z 235 and m/ z 193 appeared,
(6) For a review of NRMS, see e.g., Schalley, C. A.; Hornung, G.;
Schro¨der, D.; Schwarz, H. Chem Soc. Rev. 1998, 27, 91.
(7) . Schleyer, P. von R.; Allinger, N. L.; Clark, T.; Gasteiger, J .;
Kollman, J . A.; Schaefer, H. F., III; Schreiner, P. R. Encyclopedia of
Computational Chemistry; Wiley: New York, 1998; Vol. 3.
(8) Kuhn, A.; Plu¨g, C.; Wentrup, C. J . Am. Chem. Soc. 2000, 122,
1945. Plu¨g, C.; Wallfisch, B.; Andersen, H. G.; Bernhardt, P. V.; Baker,
L.-J .; Clark, G. R.; Wong, M. W.; Wentrup, C. J . Chem. Soc., Perkin
Trans 2 2000, 2096. Ye, X.; Andraos, J .; Bibas, H.; Wong, M. W.;
Wentrup, C. J . Chem. Soc., Perkin Trans 1 2000, 401. Bibas, H.; Kappe,
C. O.; Wong, M. W.; Wentrup, C. J . Chem. Soc., Perkin Trans. 2 1998,
493.
(9) Ma, N. L.; Wong, M. W. Eur. J . Org. Chem. 2000, 1411. Koch,
R.; Wentrup, C. J . Chem. Soc., Perkin Trans. 2 2000, 1846. Couturier-
Tamburelli, I.; Aycard, J .-P.; Wong, M. W.; Wentrup, C. J . Phys. Chem.
A 2000, 104, 3466. Finnerty, J .; Andraos, J .; Yamamoto, Y.; Wong, M.
W.; Wentrup, C. J . Am. Chem. Soc. 1998, 120, 1701. Moloney, D. W.
J .; Wong, M. W.; Flammang, R.; Wentrup, C. J . Org. Chem. 1997, 4240.
(10) Hehre, W. J .; Radom, L.; Schleyer, P. v. R.; Pople, J . A. Ab Initio
Molecular Orbital Theory; Wiley: New York, 1986.
(11) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Baboul, A. G.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A,; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
J ohnson, B.; Chen, W.; Wong, M. W.; Andres, J . L.; Gonzalez, C.; Head-
Gordon, M.;. Replogle, E. S.; Pople, J . A. Gaussian 98, Revision A.7,
Gaussian, Inc., Pittsburgh, PA, 1998.
F igu r e 2. (a) CAMS (O2), and (b) NRMS (NH3/O2) of m/z 159
from the FVT of 5a .
corresponding to the thiol 7a and the bis-thiol 8a . These
were the major products at 500 °C, where only a small
peak for the molecular ion of 9a , m/z 159, was detected.
High temperatures, 700-800 °C, are required in order
to achieve major decomposition to 9a .
The CAMS of the m/z 159 ions is shown in Figure 2a
and features m/z 77 and 51 due to the phenyl cation as
major fragment peaks. The second most important set
(12) (a) Becke, A. D. J . Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(13) Wong, M. W. Chem. Phys. Lett. 1996, 256, 391.

Iminopropadienethiones
Sch em e 2
J . Org. Chem., Vol. 66, No. 5, 2001 1829
of peaks at m/z 115 and 114 is due to loss of CS and HCS.
These fragmentations are completely analogous to those
of the PhNCCCO cations, thus supporting the expected
structure of 9a . The NRMS of the m/z 159 ions features
a recovery signal at m/z 159, thus confirming that neutral
9a is at least stable on the microsecond time scale of the
NRMS experiment. However, the NRMS is quite different
from the CAMS, featuring a strong signal at m/z 82 in
particular. This corresponds to reionization of radicals
NCCCS formed in the process m/z 159 f m/z 77. Thus
the mass spectral investigation is completely in accord
with the Ph-NdCdCdCdS structure.
The diethyl derivative 5b behaved in a manner very
similar to that of 5a , eliminating ethylene instead of
propene, and giving the same m/z 159 ion.
Further confirmation of the identity of the molecular
ions of 9a is given by the observation that the same m/z
159 ions, i.e., with the same CAMS and NRMS, are
obtained by fragmentation of the cation radical of the
isoxazolopyrimidinethione 11 in the mass spectrometer
(Scheme 2). We show below that neutral 9a (minor) and
PhNCCCO (major) are also produced in the FVT of 11.
A similar set of spectra arising from the FVT of the
anisyl derivative 5c is shown in Figures S4 and S5 in
the Supporting Information and support the sequence of
the thermal fragmentations (Scheme 1) and the structure
of p-MeO-C6H4NCCCS (9c) in a similar manner. In this
case, the loss of 15 mass units from the molecular ions
of 9c is, not surprisingly, the main fragmentation in the
CAMS.
Ma tr ix Isola tion . FVT of 5a with matrix isolation of
the products in Ar at 7-10 K was investigated over the
temperature range 500-1100 °C. A representative series
of spectra is shown in the Supporting Information. The
intensity of a cumulenic species absorbing strongly at
2167 cm-1 (often observed at 2163 cm-1 except in high
quality matrixes) increased from 600 to 900 °C and then
decreased again due to extensive decomposition. Other
bands assigned to the same species because they rise and
fall with the same rates were observed at 2023vw, 1593m,
1493m, and 1355w cm-1. Virtually all the other bands
in the spectrum are accounted for; they are due to
propene, water, CO2, CS2, benzonitrile, and unreacted
starting material (Figure 3). The peaks ascribed to the
cumulene are in excellent agreement with DFT calcula-
F igu r e 3. (Upper) Calculated (B3LYP/6-31G**) IR spectrum
of PhNCCCS (9a ), and (lower) Ar matrix IR spectrum of the
products of FVT of 5a at 700 °C. The calculated data are scaled
by 0.9613. C ) carbon dioxide, D ) carbon disulfide, H )
hydrogen sulfide, N ) benzonitrile, P ) propene, R ) starting
material 5a , S ) phenyliminopropadienone 9a , W ) water, X
) unassigned; the peak at 2049 cm-1 is most probably due to
the CN radical.
tions for PhNCCCS (9a ) as shown in Figure 3. Full
listings of the experimental and calculated wavenumbers
are reported in the Supporting Information. The very
weak band at 2023 cm-1 is reproducible and is tentatively
matched to the calculated band at 1974 cm-1. Other very
weak and unassigned bands are present in the vicinity
of 2000 cm-1. A significant peak at 2049 cm-1, which
continues to increase in intensity up to 1100 °C but is
unstable at 50 K in matrixes without Ar, is probably due
to the CN radical.14 This peak also appears in the
spectrum of 9c (see below).
The FVT of the diethyl analoue 5b was completely
analogous to that of 5a . The same spectrum due to
PhNCCCS (9a ) was obtained, the only difference being
that ethylene had replaced the propene peaks.
Analogous FVT/matrix isolation of the 3-anisylisox-
azolone derivative 5c gave rise to a species identified in
like manner as p-MeO-C6H4NCCCS (9c) on the basis of
good agreement with the DFT calculated spectrum and
assignment of all other peaks to propene, water, CO2,
CS2, H2S, anisonitrile, and unreacted starting material,
together with the peak at 2049 cm-1 showing the same
characteristics as reported above. The experimental and
calculated spectra are shown and tabulated in the
Supporting Information. The absorptions due to 9c are
(14) Blanch, R. J .; McCluskey, A. Chem. Phys. Lett. 1995, 241, 116.
Blanch, R. J .; McCluskey, A.; Wentrup, C. Unpublished results.

1830 J . Org. Chem., Vol. 66, No. 5, 2001
Kappe et al.
3-phenylisoxazol-5(4H)-one19 (1.61 g; 10 mmol) in 10 mL of
DMSO (previously dried over P2O5 and 6A molecular sieves)
at -15 °C, and the solution was stirred under N2 at -15 °C
for 0.5 h. Ethyl iodide (3.34 g; 20 mmol) was then added
dropwise at -15 °C over 20 min. The solution was allowed to
warm to RT, heated to 60 °C for 45 min, cooled again to RT,
and poured into 100 mL of ice-water. The aqueous layer was
removed by decanting, and the remaining solid was purified
by flash chromatography (SiO2/EtOAc-hexane; Rf 0.45) to
at 2164vs, 2020vw, 1593w, 1508s, 1356w, 1295w, 1254m,
522w cm-1
.
Now that the IR absorptions of PhNCCCS have been
identified, it is possible to detect this compound as the
minor product of FVT of the isoxazolopyrimidinethione
11. This compound is very stable thermally and under-
goes FVT to give mainly phenyliminopropadienone,
PhNCCCO, at 900 °C.15 A medium size peak at 2163 cm-1
in the published spectrum was previously unassigned.15
Now that the IR spectrum of 9a is known, this minor
product in the FVT of 11 can be identified as 9a . Not
only the 2163 cm-1 band, but all the other minor peaks
due to 9a are present in the spectrum. Thus, undoubtedly
11 undergoes thermal ring opening to a vinylnitrene (12),
which rapidly undergoes the 1,2-phenyl shift to produce
a transient ketenimine 13. Cycloreversion reactions of
this compound yields PhNCCCO and PhNCCCS (Scheme
2). The accompanying products, HCN, HNCS, and HNCO,
were also identified in the matrix IR spectrum.
Ch em ica l Tr a p p in g. Preparative FVT experiments
were conducted by condensing the thermolysis products
on a liquid nitrogen cooled coldfinger. After the end of
the experiments, diethylamine was injected onto the
coldfinger through a septum. The coldfinger was allowed
to warm to room temperature, and the thioamide 10a
(Scheme 1) was isolated by flash chromatography. The
same product was obtained from 5a and 5b, but 5a is
easier to handle and gave the best yields. The product
10 serves as chemical proof of the structure of PhNCCCS
and at the same time demonstrates the viability of
performing chemical reactions with iminopropadieneth-
iones.
1
yield 1.78 g (61%) of yellow crystals, mp 69-71 °C; H NMR
(CDCl3) δ 1.05 (3H), 1.37 (3H), 2.68 (2H), 3.22 (2H), 7.46 (m,
5H) (the signals for the CH3 and CH2 groups appear broad at
RT due to slow rotation of the ethyl groups but sharpen and
resolve into triplets and quartets at elevated temperature);
13C NMR (CDCl3) δ 13.7, 13.9, 32.2, 33.7, 107.7, 128.4, 128.5,
129.1, 130.2, 161.2, 167.3, 181.1. Anal. Calcd for C14H15NO2S2
C, 57.31; H, 5.15; N, 4.77. Found C, 57.08; H, 5.13; N, 4.48.
4-[Bis((1-m eth yleth yl)th io)m eth ylen e]-3-ph en ylisoxazol-
5(4H)-on e 5a . This compound was prepared in analogy with
5b using isopropyl iodide and purified by flash chromatogra-
phy (SiO2/CH2Cl2-acetone 1:1; Rf 0.8) to yield 1.76 g (58%) of
yellow crystals, mp 80-81 °C; subl. 65 °C (10-4 mbar); 1H NMR
δ 1.04 (d, J ) 6.3 Hz, 6 H), 1.39 (d, J ) 6.3 H, 6 H), 3.39 (br
m, 1 H), 4.25 (br m, 1 H), 7.45 (m, 5 H), 13C NMR δ 22.2, 43.3,
108.8, 128.4, 128.5, 128.9, 130.1, 161.2, 167.4, 180.1; 13C-DEPT
δ 22.2, 43.3, 128.4, 128.5, 130.0. Anal. Calcd for C16H19NO2S2
C, 59.78; H, 5.96; N, 4.36. Found C, 59.71; H, 5.96; N, 4.18.
4-[Bis((1-m eth yleth yl)th io)m eth ylen e]-3-(4-m eth oxy)-
p h en ylisoxa zol-5(4H)-on e 5c. This compound was prepared
in analogy with 5a using 3-(p-methoxyphenyl)isoxazol-5(4H)-
one.20 After aqueous workup as above, the yellow precipitate
was recrystallized from acetonitrile to afford 2.27 g (82%) of
crude product. Flash chromatography (SiO2/CH2Cl2-acetone
1:1; Rf 0.8) afforded 1.53 g (56%), mp 101 °C, subl. 85 °C (10-4
1
mbar); H NMR δ 1.02 (d, J ) 5.8 Hz, 6 H), 1.35 (d, J ) 4.4
Hz, 6 H), 3.3h (m, 1 H), 3.81 (s, 3 H), 4.20 (m, 1 H), 6.92 (d, J
) 8.8 Hz, 2 H), 7.40 (d, J ) 8.8 Hz, 2 H); 13C NMR δ 22.9,
43.2, 55.3, 109.0, 113.8, 121.0, 129.8, 161.0, 167.4, 179.7; 13C-
DEPT δ 22.2, 43.2, 55.3, 113.8, 129.9. Anal. Calcd for C17H21
NO3S2 C, 58.17, H, 5.98, N, 3.99. Found C, 58.28, H, 6.13, N,
3.97.
-
Con clu sion a n d Ou tlook
Isoxazolones 5 serve as preparatively viable precursors
of the new class of compounds, iminopropadienethiones,
R-NdCdCdCdS, whereas the isoxazolopyrimidineth-
iones 11 are useful for spectroscopic rather than prepara-
tive purposes. Experiments aimed at the synthesis of new
iminopropadienethiones, especially those carrying elec-
tronegative substituents to increase reactivity, or steri-
cally hindering ones to decrease reactivity, as well as
further exploration of their chemical reactions are un-
derway in our laboratories.
3-Diet h yla m in o-3-p h en ylim in o-N,N-d iet h ylt h iop r o-
p a n a m id e 10a . Compound 5a (50 mg; 0.155 mmol) was
sublimed at a temperature not exceeding 50 °C through the
preparative quartz pyrolysis tube16 (700 °C/3 × 10-6 mbar).
The products were isolated on a coldfinger cooled in liquid
nitrogen. After the end of the pyrolysis, diethylamine (2 mL)
was injected onto the sample on the coldfinger, which was then
warmed to RT. The resulting mixture was concentrated in
vacuo and purified by flash chromatography (SiO2/EtOAc-
hexane) to yield 27 mg (57%) of 10a as a red-brown oil; 1H
NMR δ 0.85 (t, 3 H), 1.17 (t, 3 H), 1.20 (t, 6 H), 3.11 (q, 2 H),
3.48 (q, 4 H), 3.54 (s, 2 H), 3.87 (q, 2 H), 6.82 (m, 3 H), 7.15
(m, 2 H); 13C NMR (CDCl3) δ 10.8, 12.7, 29.7, 40.4, 42.5, 45.9,
48.1, 120.7, 121.5, 122.9, 128.7, 153.7, 196.0. Anal. Calcd for
Exp er im en ta l Section
Apparatus and procedures for FVT coupled with matrix
isolation IR spectroscopy16,17 and for preparative FVT17 were
as previously described. The 6.5 K cryostat17 was used. Ar
matrixes of thermolysates were usually condensed on CsI from
a dynamic vacuum of 10-5 to 10-6 mbar at 10-20 K and
spectra recorded at 7 K. The pyrolysis unit built inside the
ion source housing of the six-sector tandem mass spectrometer
(Micromass AutoSpec 6F) was as reported.18
C
17H27N3S C, 66.91; H, 8.85, N, 13.76. Found C, 66.64, H, 8.80;
N, 13.51.
Refer en ce In fr a r ed Sp ectr a (Ar matrixes, 10-20 K).
Propene21 3091s, 3036s, 2893s, 2941s, 2923s, 2859m, 1650s,
1453vs, 1439s, 1415m, 1373w, 1212m, 1043s, 998s, 932m,
908vs, 578s cm-1. Ethylene22 2995m, 1440s, 946s cm-1. Carbon
disulfide23 2178m, 1528 vs cm-1. Carbon dioxide 2344vs,
2340vs cm-1. Hydrogen sulfide (dimer)24 2567 cm-1. Benzoni-
trile 3062w, 2241m, 2237m, 1494m, 1450m, 1288m, 1181w,
1072w, 761m cm-1. p-Methoxybenzonitrile 2949w, 2852w,
2245m, 238m, 1615s, 1515vs, 1470m, 1306s, 1265vs, 1172m,
4-[Bis(et h ylt h io)m et h ylen e]-3-p h en ylisoxa zol-5(4H )-
on e 5b. Triethylamine (2.8 mL; 20 mmol) and then carbon
disulfide (0.6 mL; 10 mmol) were added to a solution of
(15) Kappe, C. O.; Flammang, R.; Wentrup, C. Heterocycles 1994,
37, 1615.
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(17) Kuhn, A.; Plu¨g, C.; Wentrup, C. J . Am. Chem. Soc. 2000, 122,
1945. Wentrup, C.; Blanch, R.; Briehl, H.; Gross, G. J . Am. Chem. Soc.
1988, 110, 1874.
(18) Flammang, R.; Brown, J .; Govaert, Y.; Plisnier, M.; Wentrup,
C.; Van Haverbeke, Y. Rapid Commun. Mass Spectrom. 1992, 6, 249.
(19) Hantzsch, A. Ber. Dtsch. Chem. Ges. 1891, 24, 502.
(20) Katritzky, A. R.; Øksne, S.; Boulton, A. J . Tetrahedron 1962,
18, 777.
(21) Barnes, A. J .; Howells, J . D. R. J . Chem Soc., Faraday Trans.
2 1973, 69, 532.
(22) Durig, J . R.; Wertz, D. W. J . Chem. Phys. 1967, 46, 3069.
(23) Bier, K. D.; J odl, H. J . Chem Phys. 1986, 81, 2240.
(24) Barnes, A. J .; Howells, J . D. R. J . Chem. Soc., Faraday Trans.
2, 1972, 68, 729.

Iminopropadienethiones
J . Org. Chem., Vol. 66, No. 5, 2001 1831
1045m, 835m. Hydrogen cyanide25 3306m, 1425w, 721m cm-1
Isothiocyanic acid 3509m, 1982s cm-1
.
Su p p or tin g In for m a tion Ava ila ble: Cartesian coordi-
nates and calculated IR spectra of 9a and 9c (B3LYP/6-31G**).
Figures of mass spectra arising from the FVT of 5c as a
function of temperature. Figure showing the CAMS and NRMS
of 9c+•. Figure of the experimental and calculated IR spectrum
of 9c. Figures of the IR spectra arising from FVT of 5a and 5c
as a function of temperature. Tables of experimentally ob-
served frequencies and assignments in Ar matrix IR spectra.
This material is available via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. This work was supported by the
Australian Research Council and the Belgian Fonds
National de la Recherche Scientifique. We thank Heidi
Gade Andersen for assistance with the DFT calcula-
tions.
(25) Pacansky, J . J . Phys. Chem. 1977, 81, 2240. Evans, R. A.;
Lorencak, P.; Ha, T.-K.; Wentrup, C. J . Am. Chem. Soc. 1991, 113,
7261.
J O001595J