Generation and rearrangement of some spirocycloaliphatic thiosulfines and dithiiranes

Article abstract of DOI:10.1002/ejoc.200800023

The flash-vacuum pyrolysis of selected dispirodicycloaliphatic 1,2,4-trithiolanes was studied by using matrix isolation techniques. The formation of thiosulfines and dithiiranes along with the corresponding thioketones was detected spectroscopically and confirmed by comparison with computed spectra. In the case of tetramethylcyclobutanone 1,2,4-trithiolane, the thermal formation of the dithiolactone was observed. Pyrolysis of the (dichloro)tetramethylcyclobutane derivative resulted only in the formation of a mixture of the thiosulfine and dithiirane. In this case, conversion into the corresponding dithiolactone could be achieved photochemically. The dispirodiadamantane derivative gave a mixture of the respective thiosulfine and dithiirane but no dithiolactone could be detected in the mixture. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800023

FULL PAPER
DOI: 10.1002/ejoc.200800023
Generation and Rearrangement of Some Spirocycloaliphatic Thiosulfines and
Dithiiranes
Jarosław Roman´ski,[a] Hans Peter Reisenauer,[b] Holm Petzold,[c] Wolfgang Weigand,[c]
Peter R. Schreiner,[b] and Grzegorz Mloston´*[a]
Keywords: Density functional calculations / Flash pyrolysis / Matrix isolation / Sulfur heterocycles
The flash-vacuum pyrolysis of selected dispirodicycloali-
phatic 1,2,4-trithiolanes was studied by using matrix isolation
techniques. The formation of thiosulfines and dithiiranes
along with the corresponding thioketones was detected spec-
troscopically and confirmed by comparison with computed
spectra. In the case of tetramethylcyclobutanone 1,2,4-tri-
thiolane, the thermal formation of the dithiolactone was ob-
served. Pyrolysis of the (dichloro)tetramethylcyclobutane de-
rivative resulted only in the formation of a mixture of the
thiosulfine and dithiirane. In this case, conversion into the
corresponding dithiolactone could be achieved photochemi-
cally. The dispirodiadamantane derivative gave a mixture of
the respective thiosulfine and dithiirane but no dithiolactone
could be detected in the mixture.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
Thiocarbonyl S-sulfides 1 (thiosulfines) belong to the
class of so-called S-centered 1,3-dipoles that have only been
described as elusive intermediates and have, in contrast to
the relatively stable thiocarbonyl S-oxides (sulfines),[1] never
been isolated.[2] Structures of type 1 can be trapped in solu-
tion through the reaction with dipolarophiles (C=C, CϵC,
C=S) to give the corresponding five-membered sulfur het-
erocycles.[2] Thiosulfines 1 can be generated by various
methods; the most representative include (a) formal elimi-
nation of acetyl chloride from α-chloro-substituted acety-
lated disulfanes in the presence of morpholine (“unzipping
reaction”),[3] (b) sulfur transfer from reactive three-mem-
bered heterocycles (intermediate formation of thiazirid-
ines,[4] oxathiiranes,[5] or thiiranes[6,7]) to thioketones, and
(c) thermal [2+3] cycloreversion of 1,2,4-trithiolanes.[6–8]
The latter is the most general and most widely applied ap-
proach. In pioneering work on the chemistry of thiosulfines,
Senning et al. postulated that in situ generated thiosulfines
1 (method a) equilibrate with dithiiranes 2, which sub-
sequently undergo isomerization to dithioesters 3 through
1,3-migration of the R2 substituent.[3a]
Reactions of thiobenzophenone S-sulfide (4) were exten-
sively studied by Huisgen and Rapp.[6] They generated 4 in
solution by thermal [2+3] cycloreversion of 3,3,5,5-tet-
raphenyl-1,2,4-trithiolane (method c) and trapped it with
activated acetylene derivatives or cycloaliphatic thio-
ketones.[6] The equilibrium between thiosulfine 4 and dithi-
irane 5 was postulated but evidence for the formation of
phenyl dithiobenzoate (6) through migration of the Ph
group could not be found (Scheme 1).
Scheme 1. Postulated equilibrium of thiosulfine 4 p dithiirane 5
system.
In recent years, Ishii and Nakayama reported the synthe-
ses and reactions of several dithiiranes, which were isolated
as stable compounds.[9] On the one hand, the ring opening
of dithiirane 7 to the corresponding thiosulfine 8 was
proven by intramolecular [2+3] cycloaddition with the C=O
group, which led to the corresponding 1,3,4-oxadithiolane
9, but on the other hand, no rearrangement through mi-
gration of the phenyl or aliphatic group to give dithioester
10 was observed[9a] (Scheme 2).
[a] University of Lodz, Department of Organic and Applied
Chemistry,
Narutowicza 68, 90-136 Lodz, Poland
E-mail: gmloston@uni.lodz.pl
[b] Justus-Liebig-Universität, Institut für Organische Chemie,
Heinrich-Buff-Ring 58, 35392 Giessen, Germany
[c] Institut für Anorganische und Analytische Chemie, Friedrich-
Schiller-Universität Jena,
August-Bebel-Str. 2, 07743 Jena, Germany
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Generation and Rearrangement of Some Spiro Sulfur Heterocylces
Results and Discussion
1,2,4-Trithiolanes 19–21 are crystalline, stable com-
pounds that are accessible by sulfur-transfer reactions by
using the parent thioketones, that is, 2,2,4,4-tetramethyl-3-
thioxocyclobutanone (22),[10] 3,3-dichloro-2,2,4,4-tetra-
methylcyclobutanethione (23),[11] or adamantanethione
(24),[12] respectively (Scheme 4). Reactions are postulated to
occur via the in situ generated thiosulfines, which sub-
sequently undergo regioselectively the [2+3] cycloaddition
with the C=S bond to yield heterocyclic products 19–21.
Scheme 2. Formation of 1,3,4-oxadithiolane 9.
Our recent studies employed matrix isolation techniques
for the spectroscopic characterization of products formed
after gas-phase flash-vacuum pyrolysis (FVP) of the parent
1,2,4-trithiolane (11)[8a] and its 3,3,5,5-tetramethyl deriva-
tive 15[8b] (Scheme 3). Subsequently, we studied the reactiv-
ity of the matrix-isolated products by irradiation with UV
light or by annealing of the matrix.
Scheme 4. Preparation of trithiolanes 19–21.
Scheme 3. Transformations of 1,2,4-trithiolanes 11 and 15.
Gas-phase thermolysis of 1,2,4-trithiolanes 19–21 was
In the case of 11, we observed the formation of compar- performed under high-vacuum (≈10–4 mbar) conditions by
able amounts of both thioformaldehyde S-sulfide (12) and using an empty quartz tube that was heated up to 700 °C.
isomeric dithiirane (13). Upon irradiation with λ = 570 nm A stream of the reaction products was condensed on a CsI
light, parent thiosulfine 12 isomerized to 13 and further window cooled to ca. 10 K together with a large excess of
into dithioformic acid (14).[8a] Gas-phase thermolysis of 15 argon. The pyrolysate collected in the matrix was probed
led to the formation of the product resulting from a [1,4] by recording the UV and IR spectra. The observed bands
H-shift, identified as vinyldisulfane 18 (Scheme 3). Along were compared with those of authentic samples of the cor-
with thioacetone, the presence of thioacetone S-sulfide (16) responding thioketones 22–24 as well as with computed (see
and dimethyldithiirane (17) was proven on the basis of spec- details below) spectra of expected thiosulfines 25–27 and
troscopic evidence (UV and IR spectra).[8b] Neither photol- dithiiranes 28–30.
ysis nor thermal conversion of the pyrolysate led to methyl
Two FVP experiments at 500 and 600 °C of 19
dithioacetate as the product of the Me-group migration. (Scheme 5) were aimed at immediate trapping of the prod-
These results showed that the rearrangement of the thiosul- ucts with an excess amount of argon on a CsI window at
fine/dithiirane system into dithioacid and its derivatives is 10 K. Decomposition of 19 was almost complete, and
unlikely to occur under thermal conditions.
monothione 22 was easily identified as one of the reaction
In this paper, we describe new results on the gas-phase products (comparison of IR with the authentic matrix spec-
thermolysis of 1,2,4-trithiolanes 19–21 bearing dispirodicy- trum of 22). Because 22 undergoes further conversion under
cloaliphatic substituents at C-3 and C-5. These systems the pyrolysis conditions, small bands of the decomposition
were chosen because isomerizations of the initially formed products dimethylketene, dimethylthioketene, CO, and pro-
thiosulfines by [1,4] H-shifts are not likely and other photo- pene were also detected. Together with these compounds,
chemical or thermal reactions of dithiiranes can be re- small amounts of thiosulfine 25, which is easily detectable
vealed.
by its UV band around 400 nm,[8] dithiirane 28, and dithio-
Scheme 5. Transformation of 1,2,4-trithiolane 19.
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G. Mloston´ et al.
FULL PAPER
lactone 31 were also identified. The latter two were formed
as main products in approximately 1:1 ratio (Figure 1). At
600 °C, the yield of 31 was higher than that of 28 at 500 °C,
which indicates that 31 forms via 28. Upon irradiation of
the matrix-isolated pyrolysis products with λ = 366 nm,
which corresponds to the absorption of the thiosulfine sys-
tem, 25 quickly converts into 28 (10 min.). Like other dithi-
iranes, 28 displays a very weak Ϫ and therefore undetect-
able Ϫ UV absorption around 500 nm; it slowly isomerized
into 31 by irradiation of the matrix with visible light (λ Ͼ
395 nm, Figure 2). Dithiolactone 31 shows a prominent UV
absorption at λmax = 304 nm. This photoisomerization was
monitored by the respective difference IR spectrum, which
also allows the unambiguous identification of both com-
pounds 28 and 31 by comparison with their computed
[B3LYP/6-311+G(d,p)] IR spectra (Figure 3).
Figure 3. Middle: difference IR spectrum, before and after 4 h irra-
diation with visible light (λ Ͼ 395 nm) showing the photoisomer-
ization of dithiirane 28 (negative bands) into dithiolactone 31 (posi-
tive bands). Bottom and top: computed [B3LYP/6-311+G(d,p)] IR
spectra of 28 and 31.
1H NMR spectroscopy, which showed the presence of sing-
lets located at δ = 1.35 and 1.62 ppm (attributed to 31) and
at 1.33 ppm (attributed to 22). Both reaction products were
formed in a ca. 1:1 ratio. However, repetition of the experi-
ment at 700 °C (10–2 mbar) gave 31 as the only product.
Under these conditions, thioketone 22 undergoes a [2+2]
cycloreversion to yield dimethylketene and dimethylthio-
ketene, which cannot be trapped at –78 °C. Dimethylketene
and dimethylthioketene were also observed among the
products identified in the matrix by IR spectroscopy. Both
compounds showed characteristic absorptions at 2127 cm–1
for dimethylketene and at 1798 cm–1 for dimethylthioketene.
This type of conversion is known for analogs of 22 such as
2,2,4,4-tetramethylcyclobutane-1,3-dithione.[13]
Figure 1. IR spectrum of the matrix-isolated products taken after
FVP of 19.
In comparison with 19, thermolysis of 20 at 600 °C led
to a different composition of products formed in the pyro-
lysate at 10 K (Scheme 6). In this case, trace amounts of
thiosulfine 26 were identified on the basis of its weak ab-
sorption in the UV spectrum around 390 nm. Irradiation of
this matrix with λ = 366 nm light resulted in the disappear-
ance of this maximum after 10 min. Unlike the experiment
with 19, the matrix obtained after thermolysis of 20 did not
contain the expected dithiolactone 32, as evident from the
lack of the characteristic absorption at ca. 300 nm. In con-
trast, the IR spectrum of the crude pyrolysate showed the
absorption bands of thioketone 23 and dithiirane 29 located
at positions predicted by the computations. On the basis of
the comparison of the intensities of calculated and regis-
tered absorption bands, it is likely that both compounds
appeared in comparable amounts (Figure 4). Longer irradi-
ation of the matrix with visible light (λ Ͼ 395 nm) led to
rearrangement of 29 into dithiolactone 32. Absorption
bands in the UV (λmax = 304 nm) and IR spectra character-
istic for 32 grew during the reaction.
Figure 2. Photoisomerization of thiosulfine 25 into dithiolactone
31 via dithiirane 28. Solid line: argon matrix of pyrolysis products,
unirradiated; dotted line: matrix after 10 min irradiation with
366 nm light; dashed line: after irradiation with λ Ͼ 395 nm light.
Finally, 1,2,4-trithiolane 21 was thermolyzed under con-
Independently, FVP of 19 was carried out on preparative ditions comparable to those described for 19 and 20. The
scale at 450 °C and 10–2 mbar. The crude reaction mixture analysis of the UV spectrum of the crude pyrolysate showed
was washed from the cold finger (–78 °C) and analyzed by an absorption band at 384 nm characteristic of thiosulfine
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Generation and Rearrangement of Some Spiro Sulfur Heterocylces
Scheme 6. Transformations of trithiolanes 20 and 21.
The present study shows that the flash-vacuum pyrolyses
of symmetrically substituted trithiolanes 19–21 led in each
case to mixtures of variable amounts of the corresponding
thiosulfines 25–27 and dithiiranes 28–30. Photolyses of ma-
trix-isolated thiosulfines 25–27 result in complete conver-
sion into the corresponding dithiiranes 28–30 after short
irradiation times with monochromatic light at λ = 366 nm.
The irreversible thermal conversion into dithiolactone 31
was observed in the gas phase only for the most sterically
congested dithiirane 28. 3,3-Dichloro derivative 29 was iso-
merized into 32 only in the matrix upon photolysis with
visible light λ Ͼ 395 nm. In the case of spiroadamantane
derivative 21, matrix-isolated dithiirane 30 could not be iso-
merized to the ring-expanded dithiolactone 33 even under
photolytic conditions.
Figure 4. Bottom: IR spectra of pyrolysis products (600 °C) of 20
(Ar matrix, 10 K); top: computed [B3LYP/6-311+G(d,p)] IR spec-
trum of a 1:1 mixture of thioketone 23 and dithiirane 29.
A plausible explanation for this isomerization may be
that dithiirane 28 readily forms the corresponding diradical
34, which opens the cyclobutane ring to form the more
stable diradical 35. Subsequent ring closure leads to five-
membered dithiolactone 31 (Scheme 7). The formation of
diradical 35 benefits from the release of the strain energy
from the four-membered ring and additionally from the sta-
bilization effect of the carbonyl group. A similar stabiliza-
tion of the diradical intermediate is not possible in the case
of dispirodiadamantane derivative 30, and therefore, the
formation of dithiolactone 33 in this system is not observed.
Because of the lack of stabilizing effect of the carbonyl
group, the formation of the expected dithiolactone 32 oc-
curred only photochemically. The photochemical isomeriza-
tion into dithiolactone 32 with participation of another
diradical formed by alternative S–S bond cleavage is
likely.
27. There was no absorption near 300 nm, excluding the
formation of the corresponding dithiolactone 33. In anal-
ogy to 25 and 26, short irradiation with λ = 366 nm light
led to complete disappearance of 27. However, even longer
irradiation times did not, in contrast to 25 and 26, afford
the corresponding dithiolactone 33. A comparison of ab-
sorption bands intensities observed in the experimental IR
spectrum of the crude pyrolysate with that computed for
adamantanethione (24) and dithiirane 30 showed that both
compounds are formed in approximately equal amounts
(Figure 5).
Scheme 7. Proposed mechanism for the formation of dithiolactone
31 from dithiirane 28.
It would be desirable to explore the mechanistic proposal
outlined in Scheme 7 with computational methods. How-
ever, computing the reaction paths involving biradical spe-
cies such as 35 with expectedly low-lying open-shell singlet
Figure 5. Bottom: IR spectra of pyrolysis products (600 °C) of 21
(Ar matrix, 10 K); top: computed [B3LYP/6-311+G(d,p)] IR spec-
trum of a 1:1 mixture of thioketone 24 and dithiirane 30.
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G. Mloston´ et al.
FULL PAPER
3,3,5,5-Tetramethyl-2-thioxothiolane-4-one (31): Yield 38% (40 mg,
0.21 mmol). M.p. 36–39 °C (n-pentane) (ref.[14] 39–41 °C). 1H
NMR (200 MHz, CDCl3): δ = 1.62 (s, 3 H, CH3), 1.35 (s, 3 H,
CH3) ppm. 13C NMR (50 MHz, CDCl3): δ = 242.8 (s, C=S), 216.5
(s, C=O), 63.2 (s, Cq), 61.2 (s, Cq), 28.0 (q, CH3), 27.7 (q, CH3)
and triplet states is a very demanding task, as standard
MCSCF and CASSCF methods are not sufficiently accu-
rate to draw firm mechanistic conclusions.[16]
ppm. IR (KBr): ν = 1736 [s (C=O)] cm–1. MS (EI): m/z (%) = 188
˜
Conclusions
(100) [M]+, 86 (90) [Me2C=C=S]+.
The irreversible conversion of dithiiranes into the corre-
sponding dithiolactones depends on the substitution
pattern. Thermal and photolytic isomerizations leading to
the ring-enlarged dithiolactone 31 were observed only for
strained spiro derivative 28. The analogous photochemical
conversion was observed for matrix-isolated dithiirane 29,
which afforded dithiolane 32. In this case, thermal isomer-
ization in the gas phase did not take place. Moreover, nei-
ther thermal nor photochemical transformation of 30 into
33 was observed.
Acknowledgments
J. R. and G. M. thank the Rector of the University of Lodz for
financial support (Grant # 505/712).
[1] B. Zwanenburg, B. G. Lenz in Houben-Weyl, Methoden der Or-
ganischen Chemie (Eds.: D. Klamann), Thieme, Stuttgart, 1985;
vol. E11, p. 911.
[2] a) J. Fabian, A. Senning, Sulfur Rep. 1998, 21, 1–42; b) J.
Nakayama, A. Ishii, Adv. Heterocycl. Chem. 2000, 77, 221–284.
[3] a) A. Senning, Angew. Chem. Int. Ed. Engl. 1979, 18, 941–942;
b) G. Mloston´, A. Majchrzak, A. Senning, I. Søtofte, J. Org.
Chem. 2002, 67, 5690–5695.
[4] a) G. Mloston´, J. Roman´ski, A. Linden, H. Heimgartner, Helv.
Chim. Acta 1993, 76, 2147–2154; b) G. Mloston´, M. H.
Heimgartner, Helv. Chim. Acta 1995, 78, 1298–1310.
[5] a) R. Huisgen, G. Mloston´, K. Polborn, F. Palacios-Gambra,
Liebigs Ann. Recueil 1997, 179–185; b) W. Adam, R. M. Bar-
gon, G. Mloston´, Eur. J. Org. Chem. 2003, 4012–4015.
[6] a) R. Huisgen, J. Rapp, J. Am. Chem. Soc. 1987, 109, 902–903;
b) R. Huisgen, J. Rapp, Tetrahedron 1997, 53, 939–960.
[7] K. Okuma, Sulfur Rep. 2002, 23, 209–241.
[8] a) G. Mloston´, J. Roman´ski, H. P. Reisenauer, G. Maier, An-
gew. Chem. Int. Ed. 2001, 40, 393–396; b) G. Maier, H. P. Re-
isenauer, J. Roman´ski, H. Petzold, G. Mloston´, Eur. J. Org.
Chem. 2006, 3721–3729.
[9] a) A. Ishii, T. Akazawa, T. Maruta, J. Nakayama, M. Hoshino,
M. Shiro, Angew. Chem. Int. Ed. Engl. 1994, 33, 777–779; b)
A. Ishii, T. Maruta, K. Teramoto, J. Nakayama, Sulfur Lett.
1995, 18, 237–242; c) A. Ishii, T. Akazawa, M.-X. Ding, T.
Honjo, T. Maruta, S. Nakamura, H. Nagaya, M. Ogura, K.
Teramoto, M. Shiro, M. Hoshino, J. Nakayama, Bull. Chem.
Soc. Jpn. 1997, 70, 509–523; d) A. Ishii, T. Kawai, M. Noji, J.
Nakayama, Tetrahedron 2005, 61, 6693–6699.
Experimental Section
Starting Materials: 1,2,4-Trithiolanes used in the study were ob-
tained according to known literature protocols: 1,1,3,3,7,7,9,9-oc-
tamethyl-5,10,11-trithiadispiro[3.1.3.2]-undecane-2,8-dione (19),[10]
2,2,8,8-tetrachloro-1,1,3,3,7,7,9,9-octamethyl-5,10,11-trithiadispiro-
[3.1.3.2]undecane (20),[11] and dispiro[adamantane-2,3Ј-(1,2,4)-tri-
thiolane-5Ј,2ЈЈ-adamantane] (21).[12]
Matrix Studies: The cryostat for matrix isolation was a helium
closed-cycle refrigeration system (compressor unit RW2 with
coldhead base unit 210 and extension module ROK) from Leybold.
The matrix IR spectra were measured by using an FTIR instrument
IFS 55 from Bruker; the UV/Vis spectra were taken with a Hewlett
Packard HP 8453 diode-array spectrophotometer. The light sources
used were a mercury high-pressure lamp (HBO 200 from Osram)
with a monochromator (Bausch and Lomb) and a mercury low-
pressure spiral lamp with a Vycor filter (Gräntzel). For the combi-
nation of high-vacuum flash pyrolysis with matrix isolation, a small
home-built water-cooled oven directly connected to the vacuum
shroud of the cryostat was used. The pyrolysis zone consisted of a
completely empty quartz tube (inner diameter 8 mm, length of
heating zone 50 mm) resistively heated by a coax heating wire. The
temperature was controlled by a Ni/CrNi thermocouple. The pre-
cursors were sublimed at 30–40 °C from a storage bulb into the
quartz pyrolysis tube. Immediately after leaving the tube, at a dis-
tance of ca. 50 mm, the pyrolysis products were cocondensed with
a large excess of argon on the surface of the 10 K matrix window.
[10] G. Mloston´, M. Woz´nicka, H. Heimgartner, Helv. Chim. Acta
2007, 90, 594–599.
[11] G. Mloston´, A. Majchrzak, M. Rutkowska, M. Woz´nicka, A.
Linden, H. Heimgartner, Helv. Chim. Acta 2005, 88, 2624–
2636.
[12] G. Mloston´, J. Roman´ski, H. Heimgartner, Pol. J. Chem. 1996,
70, 437–445.
Computational Methods: IR spectra of structures 25–33 were com-
puted by density functional theory method by using the B3LYP
functional with the 6-311+G(d,p) basis set as incorporated in the
Gaussian package of programs.[15]
[13] G. Seybold, Tetrahedron Lett. 1974, 15, 555–558.
[14] R. Huisgen, J. Rapp, H. Huber, Liebigs Ann. Recl. 1997, 1517–
1524.
[15] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr, T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tom-
asi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratch-
ian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gom-
perts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dap-
prich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q.
Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
FVP of 19: FVP was carried out by using the standard FVP appa-
ratus equipped with 15-cm heating zone without filling and cooling
finger (acetone/dry ice) under 10–2 mbar.
FVP at 450 °C: Trithiolane 19 (50 mg, 0.135 mmol) was pyrolyzed,
and a 1:1 mixture of dithiolactone 31 (1H NMR) and thioketone
22 (1H NMR: δ = 1.33 ppm) was found.
FVP at 700 °C: Trithiolane 19 (200 mg, 0.54 mmol) was pyrolyzed,
and only dithiolactone 31 and small amounts of some unidentified
products were found in the crude mixture (1H NMR). Dithiolac-
tone 31 was purified by preparative TLC (petroleum ether/CHCl3,
1:3) and subsequently recrystallized from n-pentane.
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Generation and Rearrangement of Some Spiro Sulfur Heterocylces
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayak-
kara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Revision
D.02, Gaussian, Inc., Wallingford, CT, 2004.
[16] P. R. Schreiner, A. Navarro-Vazquez, M. Prall, Acc. Chem. Res.
2005, 38, 29–37.
Received: January 9, 2008
Published Online: April 25, 2008
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