Acylthioketene-Thioacylketene-Thiet-2-one Rearrangements

Article abstract of DOI:10.1021/jo991776p

Flash vacuum thermolysis (FVT) of 6-aryl-1,3-dioxine-4-thiones 9 leads to the formation of acylthioketenes 10, which are characterized by Ar matrix IR spectroscopy as well as on-line tandem mass spectrometry. The thioketenes 10 undergo a 1,3-shift of the aryl group to generate thioacylketenes 11. Ketenes 11 cyclize to 3-aryl-thiet-2-ones 12, which are also characterized by matrix IR spectroscopy and tandem mass spectrometry. The thiet-2-ones 12 undergo two kinds of reaction under the FVT conditions: (i) cheletropic CO extrusion with formation of arylthioketenes 13, and (ii) cycloreversion to COS and arylacetylene.

Full text of DOI:10.1021/jo991776p

2706
J . Org. Chem. 2000, 65, 2706-2710
Acylth iok eten e-Th ioa cylk eten e-Th iet-2-on e Rea r r a n gem en ts
J effrey R. Ammann,1a Robert Flammang,1b Ming Wah Wong,1c and Curt Wentrup*,1a
Chemistry Department, The University of Queensland, Brisbane, Qld. 4072, Australia, Laboratory of
Organic Chemistry, University of Mons, Belgium, and Department of Chemistry, National University of
Singapore, Kent Ridge, Singapore 119260
Received November 15, 1999
Flash vacuum thermolysis (FVT) of 6-aryl-1,3-dioxine-4-thiones 9 leads to the formation of
acylthioketenes 10, which are characterized by Ar matrix IR spectroscopy as well as on-line tandem
mass spectrometry. The thioketenes 10 undergo a 1,3-shift of the aryl group to generate
thioacylketenes 11. Ketenes 11 cyclize to 3-aryl-thiet-2-ones 12, which are also characterized by
matrix IR spectroscopy and tandem mass spectrometry. The thiet-2-ones 12 undergo two kinds of
reaction under the FVT conditions: (i) cheletropic CO extrusion with formation of arylthioketenes
13, and (ii) cycloreversion to COS and arylacetylene.
In tr od u ction
these 1,3-shifts are highly facilitated by electron-donating
migrating groups, especially those possessing lone pairs
that can interact favorable with the LUMOs of the
ketenes (RO, RS, R2N, Cl).6 1,3-Shifts of this kind have
been established in acylketenes (7a ), acylketenimines/
imidoylketenes (7b /8b ), and acylallenes/vinylketenes
(7c/8c).7
Thiet-2-ones (1) are usually delicate compounds, isol-
able as crystalline solids in the naphtho-annelated cases,2
but oligomerizing in the benzo2,3 and monocyclic cases4
and being highly susceptible to nucleophilic attack at the
carbonyl group with ensuing ring opening. The unstable
monocyclic thiet-2-one 4 was fully characterized, includ-
ing low temperature 13C NMR spectroscopy, and a 13C
labeling experiment demonstrated that its formation by
flash vacuum thermolysis (FVT) of the thiophenedione
2 proceeded via an unprecedented 1,3-shift of a phenyl
group, thus interconverting the two thioacylketenes 3 and
5. The ketenes are observable by low temperature IR
spectroscopy, but the thiet-2-ones are the isolated prod-
ucts, being thermodynamically more stable. The 13C
labeling experiment demonstrated complete scrambling
of the label between the two CdO carbons in 3/5, but the
CdS group was not (irreversibly) involved.4 The experi-
ments now reported explain why: acylthioketenes are of
higher energy than thioacylketenes.
Here we report our studies on the acylthioketene-
thioacylketene rearrangement (7d /8d ).
Resu lts a n d Discu ssion
1. F VT-Ma tr ix Isola tion . Sublimation of the 1,3-
dioxine-4-thione 9a at 50 °C with concomitant Ar matrix
isolation on a BaF2 window at 14 K gave rise to strong
IR bands due to 9a at 1602, 1575, 1368, 1265, and 1165
cm-1. FVT of 9a at 500 °C with Ar matrix isolation of
the product gave rise to acetone (1722, 1443, 1432, 1416,
1362, 1223, and 1094 cm-1). A second set of bands was
assigned largely to benzoylthioketene 10a because they
all disappear on thermolysis at higher temperature (750
°C), and most of these band positions agree well with the
calculated IR spectrum, at the HF/6-31G*, and B3LYP/
6-31G*, and B3LYP/6-311+G* levels (the calculated IR
data is given in Table S1 in the Supporting Information).
(3) J ørgensen, T.; Pedersen, C. Th.; Flammang, R.; Wentrup, C. J .
Chem. Soc., Perkin Trans. 2 1997, 173.
(4) Wentrup, C.; Winter, H.-W.; Gross, G.; Netsch, K.-P.; Kollenz,
G.; Ott, W.; Biedermann, A. G. Angew. Chem. 1984, 96, 791. Angew.
Chem., Int. Ed. Engl. 1984, 23, 800.
(5) Wentrup, C.; Netsch, K.-P. Angew. Chem. 1984, 96, 792. Angew.
Chem., Int. Ed. Engl. 1984, 23, 802.
(6) Finnerty, J .; Andraos, J .; Wong, M. W.; Yamamoto, Y.; Wentrup,
C. J . Am. Chem. Soc. 1998, 120, 1701. Koch, R.; Wong, M. W.; Wentrup,
C. J . Org. Chem. 1996, 61, 6809. Wong, M. W.; Wentrup, C. J . Org.
Chem. 1994, 59, 5279.
(7) Wentrup, C.; Rao, V. V. R.; Frank, W.; Fulloon, B. E.; Moloney,
D. W. J .; Mosandl, T. J . Org. Chem. 1999, 64, 3608. Rao, V. V. R.;
Wentrup, C. J . Chem. Soc., Perkin Trans. 1 1998, 2583. Bibas, H.;
Wong, M. W.; Wentrup, C. Chem. Eur. J . 1997, 3, 237. Fulloon, B.;
Wentrup, C. J . Org. Chem. 1996, 61, 1363. Wentrup, C.; Bibas, H.;
Fulloon, B. E.; Moloney. D.; Wong, M. W. Pure Appl. Chem. 1996, 68,
891.
Phenyl group migration in acylketenes such as 3 have
high activation barriers, necessitating flash vacuum
thermolysis at ca. 700 °C.5 Subsequently, we found that
(1) (a)
University
of
Queensland.
E-mail:
wentrup@
chemistry.uq.edu.au. (b) University of Mons. (c) National University
of Singapore.
(2) Wentrup, C.; Bender, H.; Gross, G. J . Org. Chem. 1987, 52, 3838.
10.1021/jo991776p CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/12/2000

Acylthioketene-Thioacylketene-Thiet-2-one Rearrangements
J . Org. Chem., Vol. 65, No. 9, 2000 2707
Sch em e 1
which undergoes electrocyclization to thiet-2-one 12a .
The ketene 11a itself is hardly seen, except perhaps for
a weak peak at 2120 cm-1 which is present only when
the thiet-2-one is present. The thiet-2-one decomposes by
cycloreversion as soon as it is formed, to give OCS and
phenylacetylene 14a . A second mode of decomposition is
cheletropic extrusion of CO (2138 cm-1) to furnish phe-
nylthioketene 13a , formally by means of a Wolff rear-
rangement of the putative thiobenzoylcarbene.
F igu r e 1. FVT of 1,3-dioxine-4-thione 9a . IR spectra (Ar, 10
K) of the products formed at (a) 500 °C, (b) 750 °C, (c) 950 °C.
Letters denote acetone (A), benzoylthioketene 10a (B), phe-
nylthioketene 12 (P), thietone 12 (T), phenylacetylene 14a
(PA). SCO appears at 2050, 2035 cm-1 and CO at 2139, 2148
cm-1
.
A corresponding CO extrusion was not observed in the
case of the 3-benzoyl-4-phenylthiet-2-one (4/6), which
underwent quantitative cycloreversion to benzoyl(phe-
nyl)acetylene and OCS.4 However, competing cyclorever-
sion and CO extrusion were observed in the mass
spectrometric fragmentation of the molecular ion of 4/6.
Benzothiet-2-one undergoes high-temperature extrusion
of CO to furnish thiocarbonylcyclopentadiene.3
These bands were at 1742, 1661, 1648, 1630, 1583, 1294,
1271, 1192, 908, 892, 724, and 707 cm-1 (Figure 1a).
Some of the bands may be due to matrix sites, and some
minor ones to impurities, but there can be little doubt
that the spectrum is due essentially to thioketene 10a
as a mixture of E and Z forms. At this temperature, very
weak bands in the 1800 cm-1 range were also present;
these are due to the thiet-2-one 12 which becomes more
prominent at 750 °C (see below). A third major band in
the 500 °C experiment at 1753 cm-1 is ascribed to
phenylthioketene 13. This compound has much weaker
bands at 1451, 1232, and 897 cm-1, and was identified
by comparison with the previous IR studies3 as well as
the mass spectra reported below. At 750 °C, medium
strength bands appear at 1827, 1816, and 1808 cm-1
(Figure 1b) in the range expected for thiet-2-ones.2 The
strongest calculated band for 12a is at 1863 (HF/6-31G*),
1864 (B3LYP/6-31G*), or 1871 cm-1 (B3LYP/6-311+G*).
The triad of experimental bands is ascribed to different
matrix sites. New bands at 1528 (m-w) and 741 (w) cm-1
are also ascribed to 12a (calculated 1573/1536/1548 and
761/726/736 cm-1, at the HF/6-31G*, B3LYP/6-31G*, and
B3LYP/6-311+G* levels, respectively). Also seen at 750
°C is a strong band at 2050 cm-1 due to OCS as well as
several bands due to phenylacetylene 14a (3340, 3328,
3315 (sites), 1490, 1217, 1071, 1026, and 759 cm-1). The
bands due to OCS and 14a grow further on FVT at 950
°C, whereas those ascribed to thiet-2-one 12 disappear
completely (Figure 1c).
The p-methoxyphenyl (anisyl) derivative 9b reacted
completely analogously, with the only exception that
the thiet-2-one 12b appeared already at 550 °C and
reached its maximum intensity at 650 °C. This is as
expected, as the electron-rich anisyl substituent should
undergo the 1,3-shift more readily, giving 11b and hence
12b (see section 3). IR absorptions at 1754, 1734, 1644,
1632, 1606, 1261, 1227, 1170, 889, and 771 cm-1 can be
ascribed to the acylthioketene 10b in good agreement
with B3LYP/6-31G* calculatated data (Table S2). A weak
peak at 2115 cm-1 (650-750 °C) may be due to the ketene
11b. Difference spectroscopy allowed the extraction of the
IR spectrum of the thiet-2-one 12b: 1825, 1821, 1499,
1216, 1174 cm-1. These bands match the strongest
calculated vibrations for the molecule (1863, 1488, 1264,
1165 cm-1 at the B3LYP/6-31G* level; Table S2). The
decomposition of this material above 600 °C led to OCS,
acetylene 14b, CO, and anisylthioketene 13b (this com-
pound also absorbs at 1754 cm-1).3 The difference spec-
trum and the calculated data are given in the Supporting
Information.
The number of bands observed for thioketenes 10
in both cases indicates that a mixture of the s-Z and
s-E forms was present. The fact that no temperature
dependence on the relative intensities was observed
indicates that the two conformers are nearly isoenergetic,
The results are interpreted in Scheme 1. Loss of
acetone from 9a under mild FVT conditions leads to the
identifiable benzoylthioketene 10a . At slightly higher
temperatures, 10a rearranges to the thioacylketene 11a ,

2708 J . Org. Chem., Vol. 65, No. 9, 2000
Ammann et al.
F igu r e 3. CAMS of m/z 162 at different temperatures (going
from thioketene 10a to thietone 12a ).
on thermolysis of 9b in refluxing xylene in the presence
of benzyl alcohol.
2. F VT-MS. Complete confirmation of the above results
was obtained by on-line mass spectrometry studies of the
thermolysis products using an FVT reactor fitted inside
the ion source housing of a six-sector mass spectrometer.
The mass spectra of 9a and those resulting from FVT
are shown in Figure 2 as a function of temperature. The
starting material (m/z 220) has disappeared at 400 °C
(Figure 2b). The species at m/z 162 is now likely to have
the thioketene structure 10a . This species undergoes
simple cleavage to m/z 105 (PhCO+) as the predominant
fragmentation as seen in the collisional activation (CA)
mass spectrum (CAMS) of m/z 162 in an MS/MS experi-
ment (Figure 3). This is also true of the m/z 162 ion from
Figure 2a (170 °C). As the temperature increases to 560
°C (Figure 2c), the thermal formation of PhCHdCdS
(13a , m/z 134) becomes prominent, the benzoyl cation is
reduced in intensity (m/z 105), and phenylacetylene is
already becoming important (14a , m/z 102). These
two fragmentation products become dominant at
800 °C, where only a little of the m/z 162 species is left
(Figure 2d).
F igu r e 2. FVT-MS of 9a at different temperatures.
Ta ble 1. Ca lcu la ted Rela tive En er gies of Th iok eten es,
Keten es, Th ieton es, a n d Tr a n sition Sta tes Con n ectin g
a ,b
Th em (k J m ol-1
)
species
R ) H (a )
R ) OCH3 (b)
s-E-acylthioketene (E10)
s-Z-acylthioketene (Z10)
s-E-thioacylketene (E11)
s-Z-thioacylketene (Z11)
1,3-C6H4R shift TS (E10 f E11)
thiet-2-one (12)
11.0
8.2
0.0
-5.0
148.2
1.0
10.5
6.8
0.0
-6.7
130.1
-2.6
8.3
ring closure TS (Z11f 12)
10.7
a
b
B3LYP/6-311+G**//B3LYP/6-31G* + ZPVE level. 4.184 kJ
mol-1 ) 1 kcal mol-1
.
in agreement with the results of energy calculations
(Table 1).
Sato has provided evidence for the formation of tran-
sient acylthioketenes in solution upon thermolysis of
dioxinethiones by means of trapping reactions.8 Similarly,
we obtained the enol O-benzyl thioate 15 in 80% yield
The changing structure of the m/z 162 species is
illustrated in the CAMS of the mass-selected ion in
Figure 3. At 650 °C, formation of a m/z 134 species
(8) Sato, M.; Ban, H.; Uehara, F.; Kaneko, C. Chem. Commun. 1996,
775.

Acylthioketene-Thioacylketene-Thiet-2-one Rearrangements
J . Org. Chem., Vol. 65, No. 9, 2000 2709
a ,b
Ta ble 2. Ca lcu la ted Rela tive En er gies of Th iet-2-on e 12a a n d Th ioa cylk eten e Z11a (k J m ol-1
)
level
relative energy
level
B3LYP/6-31G*
B3LYP/6-311G**
B3LYP/6-311+G**
B3LYP/cc-pVDZ
relative energy
HF/6-31G*
MP2/6-31G*
MP3/6-31G*
17.3
2.3
-5.9
3.2
1.9
11.4
5.2
MP4SDQ/6-31G*
2.7
QCISD/6-31G*
3.1
B3LYP/cc-pVTZ
1.6
QCISD(T)/6-31G*
-0.9
-1.5
-0.7
B3LYP/6-311+G(3df,2p)
B3LYP/6-311+G(3df,2p) (ꢀ ) 40)
B3LYP/6-311+G(3df,2p)d (ꢀ ) 40)
1.6
-4.8
-4.0
QCISD(T)/6-311+G(3df,2p)c
QCISD(T)/6-311+G(3df,2p)c,d
a
b
Based on the B3LYP/6-31G* optimized geometry. 4.184 kJ mol-1 ) 1 kcal mol-1
.
c Estimated using basis-set additivity at the MP2
d
level. Including zero point energy correction (B3LYP/6-31G*).
competes with the simple cleavage to m/z 105, i.e., two
different species with a mass of 162 are now present. At
800 °C the second isomer has become dominant. This
isomer is identified as the thiet-2-one 12a because of its
ready extrusion of CO to give m/z 134 in accord with the
IR observations above. The CAMS in Figure 3c is similar
to that of PhCHdCdS (13a ) itself3 below m/z 100. This
interpretation is also supported by the MIKE spectra: as
mentioned above, the CA spectrum of the “cold” m/z 162
species derived from 9a at 170 °C features essentially
only m/z 105 (simple cleavage). The MIKE spectrum
under the same conditions features a ca. 4:1 ratio of m/z
105 and m/z 134, indicating that the latter is formed in
a rearrangement process.
by ca. 13 kJ mol-1 (Table 1). For both 10 and 11, the s-Z
conformation is the preferred conformer, but the E/ Z
energy differences are small.
We have shown previously that 1,3-shifts in acylketenes
and related molecules are facile processes when the
migrating group possesses an unshared pair of electrons
capable of overlap with the vacant central carbon p
orbital of the ketene LUMO.6,7 1,3-Alkyl migrations in
contrast have very high calculated barriers and have not
been observed. The observed 1,3-phenyl migration in
benzoylketene4 has a calculated barrier of 147 kJ mol-1
(35 kcal mol-1). The rearrangement of acylthioketene
E10a to thioacylketene E11a via a 1,3-phenyl shift is
likewise calculated to have a barrier of 148 kJ mol-1 (35
kcal mol-1). The migratory aptitude of a phenyl group
can be rationalized in terms of the availability of the
HOMO (π orbital) in the rotated phenyl group as an
electron donor. E10b is expected to have a lower 1,3-shift
barrier because of the increased electron-donating ability
of the migrating group. Indeed, the calculated barrier is
130 kJ mol-1 (31 kcal mol-1) in agreement with the
experimental observation that 1,3-migration in 10b oc-
curred at a lower FVT temperature than for 10a .
Thiet-2-one (12) and s-Z-thioacylketene (Z11) are
predicted to lie very close in energy. At the B3LYP/6-
311+G** + ZPVE level, 12 is slightly higher in energy,
but the relative energies are rather sensitive to the basis
set and the level of correlation treatment employed (Table
2). The HF treatment and moderate-sized basis sets
strongly favor the open form Z11, but the cyclic structure
is stabilized at higher levels of theory. Thus 12a is
preferred over Z11a by ca. 1 kJ mol-1 at the QCISD(T)/
6-31G* level. At our best level of theory, QCISD(T)/
6-311+G(3df,2p) + ZPVE, 12a is more stable than Z11a
by ca. 1.5 kJ mol-1 (Table 3). Thiet-2-ones are polar
molecules (µ ) 5.12 and 6.52 D for 12a and 12b,
respectively). Thus, the thiet-2-one/acylthioketene equi-
librium will be shifted toward the cyclic structure in the
presence of a polar environment. In a dielectric medium
of ꢀ ) 40, 12a is predicted to be more stable than Z11a
by 4 kJ mol-1, using Onsager’s SCRF model.12 The barrier
toward ring closure (Z11 f 12) is of the order of 8-11
kJ mol-1 (2-3 kcal mol-1) (Table 1). Thus, calculations
agree with the experimentally observed preference for
the thiet-2-ones in matrixes. As we have noted before,
molecules experience polar effects even in Ar matrixes,
which cannot be regarded simply as the frozen gas
phase.13
The structures of the ions assigned as PhCHdCdS,
PhCCH, and OCS (m/z 60) were confirmed by CAMS of
the mass-selected ions and comparison with those of
authentic samples and are reported in the Supporting
Information.
The anisyl derivative 9b behaved in a similar manner,
and the ions were identified as described above. The
essential spectra are shown in the Supporting Informa-
tion. Here too, the thioketene (10b) is characterized by
simple cleavage (m/z 192 f 135, prominent at 300-400
°C). As in the IR investigation, rearrangement occurred
at lower temperature in this case, the thiet-2-one being
dominant already at ca. 500 °C (characterized by m/z 192
f 164). The structures of the ions corresponding to 13b,
14b and OCS were confirmed by their CA mass spectra.
3. Th eor y. Structures and IR spectra of 10, 11, and
12 (a and b series) and related transition structures
were calculated at the B3LYP/6-31G* level,9 using the
Gaussian 98 programs.10 IR spectra for the a series were
also calculated at the B3LYP/6-311+G* level. The com-
puted IR spectral data and Cartesian coordinates are
given in the Supporting Information. Improved relative
energies were obtained through B3LYP/6-311+G** cal-
culations, including B3LYP/6-31G* zero-point energy
correction (scaled by 0.9804).11 The thioacylketenes (11)
are predicted to be more stable than acylthioketenes (10),
(9) (a) Becke, A. D. J . Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(10) 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.; 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; Gaussian, Inc.: Pittsburgh, PA, 1998.
(11) Wong, M. W. Chem. Phys. Lett. 1996, 256, 391.
(12) (a) Wong, M. W.; Frisch, M. J .; Wiberg, K. B. J . Am. Chem.
Soc. 1991, 113, 4776. (b) Wong, M. W.; Wiberg, K. B.; Frisch, M. J . J .
Chem. Phys. 1991, 89, 8991.
(13) Ye, X.; Andraos, J .; Bibas, H.; Wong, M. W.; Wentrup C. J .
Chem. Soc., Perkin Ttrans. 1 2000, 401.

2710 J . Org. Chem., Vol. 65, No. 9, 2000
Ammann et al.
2H, J ) 9 Hz), 6.96 (s, 3H), 3.85 (s, 3H), 1.81 (s, 6H); 13C NMR
(CDCl3) 200, 163, 156, 128, 122, 114, 106, 103, 55, 24 ppm; IR
(KBr) 1588 s, 1509 s, 1257 s, 1160 s cm-1. Anal. Calcd for
Con clu sion
The thermal rearrangement of acylthioketenes to
thioacylketenes, followed by electrocyclization of the
latter to thiet-2-ones, has been demonstrated. The rear-
rangement is accelerated by an electron-donating sub-
stituent (OMe) on the migrating phenyl group, consis-
tently with a donor-acceptor interaction between the
migrating group and the ketene LUMO. Thioacylketenes
are lower in energy than acylthioketenes, and thiet-2-
ones are slightly lower in energy than the thioa-
cylketenes.
C
13H14O3S: C, 62.38; H, 5.64. Found: C, 62.49; H, 5.59.
Ben zyl An isoylth ion oa ceta te (En ol F or m ) (15). A solu-
tion of 9b (100 mg; 0.4 mmol), benzyl alcohol (41 µL; 0.4 mmol),
and xylene (15 mL) was refluxed for 4 h and cooled to RT,
and the solvent was removed in vacuo, affording 97 mg (80%)
1
of the thiono ester. H NMR (CDCl3) 14.2 (s, 1H), 7.8 (d, 2H,
J ) 9 Hz), 7.4 (m, 5H), 6.9 (d, 2H, J ) 9 Hz), 6.4 (s, 1H), 5.5
(s, 2H), 3.8 (s, 3H) ppm; 13C NMR (CDCl3) 207, 173, 163, 135,
131, 129, 128.4, 128.1, 126, 114, 100, 71, 55 ppm; IR (KBr)
1599 s, 1507 m, 1172 s cm-1. Anal. Calcd for C17H16O3S: C,
67.89, H, 5.38. Found: C, 67.96; H, 5.41.
Exp er im en ta l Section
Ack n ow led gm en t. The Brisbane laboratory thanks
the Australian Research Council, the Mons laboratory
the Fonds national de la Recherche Scientifique, and
the NUS laboratory the National University of Sin-
gapore for financial support. We thank Dr. Arvid Kuhn
(UQ) for assistance with the preparation of IR spectral
figures.
Apparatus for FVT-matrix isolation and IR spectroscopy14
and for FVT-MS were as previously described.15
6-An isyl-1,3-d ioxin e-4-th ion e (9b) was prepared by a
method similar to that reported for 9a .8 Lawesson’s reagent
(2.39 g; 6 mmol) was added to a benzene solution (25 mL) of
6-anisyl-1,3-dioxine-4-one (0.92 g; 4 mmol), and the solution
was refluxed for 4 h. The reaction mixture was cooled to 25
°C and filtered, and the solvent was removed in vacuo to yield
a brown oil. Flash chromatography (silica gel, hexane-diethyl
ether 1:1) followed by recrystallization from hexane-diethyl
ether (5:1) afforded orange-yellow needles (265 mg; 37%); mp
Su p p or tin g In for m a tion Ava ila ble: Difference-IR spec-
trum from the FVT of 9b, showing thietone 12b and anisoylth-
ioketene 10b. FVT-MS of 9b at different temperatures. CAMS
of m/z 192 from the FVT-MS of 9b at various temperatures
(from thioketene 10b to thietone 12b). CAMS of 13a ,b, 14a ,b,
and OCS. Calculated IR data (Tables S1 and S2) and Cartesian
coordinates (Tables S3 and S4) for all compounds 10-12a ,b.
This material is available free of charge via the Internet at
http://pubs.acs.org.
1
71-73 °C; H NMR (CDCl3) 7.68 (d, 2H, J ) 9 Hz), 6.95 (d,
(14) Kappe, C. O.; Wong, M. W.; Wentrup, C. J . Org. Chem. 1995,
60, 1686.
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