Bis(dimesitylmethylene)-1,3-dithietane, -1,2,4-trithiane, and -1,2,4,5-tetrathiane. Conformation and DNMR study. Observable dimesityl thioketene

Article abstract of DOI:10.1021/jo960911k

The reaction of dimesityl ketene with P₂S₅ and pyridine gives 2,4-bis(dimesitylmethylene)-1,3-dithietane (3), 3,6-bis(dimesitylmethylene)-1,2,4,5-tetrathiane (4), 3,5-bis(dimesitylmethylene)-1,2,4-trithiane (5), and dimesityl thioket

Full text of DOI:10.1021/jo960911k

7326
J . Org. Chem. 1996, 61, 7326-7334
Bis(d im esitylm eth ylen e)-1,3-d ith ieta n e, -1,2,4-tr ith ia n e, a n d
-1,2,4,5-tetr a th ia n e. Con for m a tion a n d DNMR Stu d y. Obser va ble
Dim esityl Th iok eten e
Tzvia Selzer and Zvi Rappoport*
Department of Organic Chemistry, The Hebrew University, J erusalem 91904, Israel
Received May 17, 1996X
The reaction of dimesityl ketene with P2S5 and pyridine gives 2,4-bis(dimesitylmethylene)-1,3-
dithietane (3), 3,6-bis(dimesitylmethylene)-1,2,4,5-tetrathiane (4), 3,5-bis(dimesitylmethylene)-1,2,4-
trithiane (5), and dimesityl thioketene 2 as a transient. The structures of 3 and 4 were determined
by X-ray crystallography. The dimesitylmethylene moieties in 3 and 4 have a propeller conforma-
tion, and the tetrathiane ring in 4 has a twist-boat conformation. Static NMR data are consistent
with the presence of two enantiomers and one meso form for 3 and of three pairs of enantiomers
for 4. The several aromatic signals observed for 3 and 4 at slow exchange at 160 K coalesce to a
single signal at higher temperatures. The threshold barriers for these dynamic processes are 12.7
(3) and 13.3 (4) kcal mol-1, and the dynamic behavior was analyzed in terms of flip processes. On
standing, a solution of 3 develops a blue color which is attributed to formation of 2, by
retro-dimerization of 3. Diphenylacetyl chloride gives with P2S5 the analog of 5 and its one-double
bond reduction product. Ditipylketene forms a product identified tentatively as the analog of 3.
In tr od u ction
of two of the compounds obtained. Also, although 2 is
apparently formed but not accumulated in the CdO f
CdS transformation, it is apparently generated by retro-
dimerization of its dimer.
Thioketenes 1 (R1R2CdCdS) are mostly reactive, short-
lived species which dimerize rapidly,1 similarly to their
ketene analogs.2 Bulky substituents reduce the reactivi-
ties of ketenes,3 and crystal structures of dimesityl4 and
ditipyl5 ketenes (mesityl ) Mes ) 2,4,6-Me3C6H2; tipyl
) Tip ) 2,4,6-i-Pr3C6H2) were determined by X-ray
diffraction,5,6 and both are stable to thermal dimerization.
The structure of 2,6-di-tert-butylcyclohexyl thioketene
was determined by X-ray diffraction,7a and di-tert-butyl
thioketene is isolable and stable to dimerization.7b How-
ever, in attempts to apply a known method for a CdO f
CdS transformation1,8 for preparing dimesityl thioketene
2 and analogs from the corresponding ketene and P2S5
in pyridine, the dimer of 2 and trithiane- and tetrathiane-
substituted compounds were formed. Fewer analogs
were also obtained from ditipyl ketene and diphenylacetyl
chloride. These compounds contain two 2,2-diarylmeth-
ylene groups, and since the dynamic behavior of dimesityl
and related vinyl propellers were extensively studied by
us,9,10 we investigated by DNMR the rotational behavior
Resu lts
Syn t h esis: (a ) Mesit yl-Su b st it u t ed Der iva t ives.
In the reaction of dimesityl ketene and P2S5 in pyridine,
a blue color ascribed to dimesityl thioketene 2 was
initially formed at the beginning of the reaction, but it
disappeared after a few minutes. Instead, three exo-bis-
(2,2-dimesitylmethylene) heterocycles 3-5 were formed
(eq 1 in Scheme 1).
2,4-Bis(dimesitylmethylene)-1,3-dithietane, 3, the dimer
of 2, was isolated in 7% yield and identified by mi-
croanalysis, X-ray diffraction, and spectral properties. In
CDCl3 at rt its 1H NMR spectrum displays only two
signals in a 4.5:1 ratio: at 2.17 ppm, ascribed to the o-
and p-Me-H and at 6.77 ppm, ascribed to the m-mesityl-
H. Its 13C spectrum displays eight signals: at 20.8 and
21.2 ppm (2:1 ratio) ascribed to the o- and p-Me groups,
at 121.1 and 137.1 ppm, ascribed to the Mes2CdC and
the CdC(S-)2 carbons, respectively, and four mesityl-C
signals at 128.2-136.8 ppm. The mass spectrum shows
a molecular peak at m/z 588 and a peak at m/z 294
ascribed to Mes2CdCdS+.
X Abstract published in Advance ACS Abstracts, September 15, 1996.
(1) (a) Campaigne, E. In The Chemistry of the Carbonyl Group; Patai,
S., Ed., Wiley: Chichester, 1966; Chap. 17, pp 917-959. (b) Schau-
mann, E. Tetrahedron 1988, 44, 1827. (c) Schaumann, E. In The
Chemistry of Double Bonded Functional Groups; Patai, S., Ed., Wiley:
Chichester, 1989; Chap. 17, pp 1269-1274.
(2) Tidwell, T. T. Ketenes; J ohn Wiley: New York, 1995.
(3) For an example of relative rates of hydration of ketenes, see ref
2, pp 578-580.
(4) Fuson, R. C.; Rowland, S. P. J . Am. Chem. Soc. 1943, 65, 992.
(5) Frey, J .; Rappoport, Z. J . Am. Chem. Soc. 1996, 118, 5169.
(6) Biali, S. E.; Gozin, M.; Rappoport, Z. J . Phys. Org. Chem. 1989,
2, 271.
(7) (a) Schaumann, E.; Harts, S.; Adiwidjaja, G. Angew Chem. 1976,
88, 25. (b) Elam, E. U.; Rash, F. H.; Dougherty, J . T.; Goodlett, V. W.;
Brannock, K. C. J . Org. Chem. 1968, 33, 2738.
(8) (a) Cava, M. P.; Levinson, M. I. Tetrahedron 1985, 41, 5061. (b)
Henry, L. Ann. Chem. Pharm. 1869, 152, 148. (c) Campagnie, E. Chem.
Rev. 1946, 39, 1.
(9) For example, (a) Biali, S. E.; Rappoport, Z. J . Am. Chem. Soc.
1984, 106, 477. (b) Nugiel, D. A.; Biali, S. E.; Rappoport, Z. J . Am.
Chem. Soc. 1984, 106, 3357. (c) Biali, S. E.; Nugiel, D. A.; Rappoport,
Z. J . Am. Chem. Soc. 1989, 111, 846.
(10) (a) Rappoport, Z.; Biali, S. E. Acc. Chem. Res. 1988, 21, 442.
(b) Hart, H.; Rappoport, Z.; Biali, S. E. In The Chemistry of Enols;
Rappoport, Z., Ed.; Wiley: Chichester, 1990; Chapter 8, pp 481-590.
3,6-Bis(dimesitylmethylene)-1,2,4,5-tetrathiane, 4, was
obtained in 17% yield and identified by microanalysis,
X-ray crystallography, and spectral properties. At 400
1
K its H NMR spectrum in Cl2CDCDCl2 displayed 3:1.5:1
signals at 2.21, 2.25, and 6.79 ppm ascribed to the 24
o-Me, 12 p-Me, and 8 Ar-H protons. The 13C NMR
spectrum (330 K, Cl2CDCDCl2) displayed eight signals
at 22.2, 22.5 (in a 2:1 ratio) ascribed to the o- and p-Me-
C, and at 130.8-141.1 ppm ascribed to the CdC and Ar-
C. In the MS the molecular peak is at m/z 652 and
peaks showing consecutive loss of sulfur atoms [620
((Mes2CdC)2S3+), 588 ((Mes2CdC)2S2+] or cleavage [294
(Mes2CdCdS+)] were also observed.
The formation of 5 was deduced from the NMR study
(see below).
S0022-3263(96)00911-5 CCC: $12.00 © 1996 American Chemical Society

Bis(dimesitylmethylene)-1,3-dithietane and -1,2,4,5-tetrathiane
J . Org. Chem., Vol. 61, No. 21, 1996 7327
Sch em e 1
Sch em e 2
Sch em e 3
(b) P h en yl-Su bstitu ted Der iva tives. Reaction of
diphenylacetyl chloride and P2S5 in pyridine did not give
diphenyl thioketene, 6. Instead, 14% of 3,5-bis(diphe-
nylmethylene)-1,2,4-trithiane (7) and 5% of 3-(diphenyl-
methylene)-5-(diphenylmethyl)-1,2,4-trithiane (8) were
obtained (eq 2 in Scheme 2).
The latter observation suggests the presence of two
enantiomers and one meso form in analogy with 3 (see
below). We did not have enough material for a detailed
study.
Dim esityl Th iok eten e. When the reaction mixture
from dimesityl ketene was chromatographed, the fraction
identified as 3 was initially light yellow, but on standing
at rt it reproducibly developed a deep blue color. At 0
°C, pale yellow crystals of 3 precipitated, and TLC of the
blue filtrate displayed only the two spots corresponding
to 3 and the blue compound. Yellow solutions of 3 in
CDCl3 or CD2Cl2 did not change color during several
months at 0 °C, but turned blue when brought to rt.
A UV-vis spectrum of the blue solution in CD2Cl2
showed λmax at 582 nm. The IR spectrum displayed
The known 711 shows a molecular peak at m/z 452 and
1
a fragment at 210 (Ph2CdCdS+). The H NMR (CDCl3,
rt) displays an aromatic multiplet at δ 7.24-7.39. The
13C spectrum (CDCl3, rt) displays 10 signals at the 127.9-
142.0 region.
Compound 8, the reduction product of one CdC of 7
displays peaks at m/z 454 (M+), 242 (Ph2CdCS2+), 212
1
(Ph2CHCHS+), and 210 (B, Ph2CdCdS+). The H NMR
spectrum (CDCl3, rt) display two vicinal aliphatic 1H
absorptions at 1608 and 1742 cm-1
. Mass spectra of
doublets at 4.56 and 5.75 ppm and an Ar-H multiplet at
δ 7.16-7.37. The 13C NMR (CDCl3, rt) displays signals
at 55.2 (Ph2C), and at 69.0 ppm (saturated ring C), twelve
C-Ph signals at 127.3-129.4 ppm, two signals at 132.5
and 140.9 ppm (CdC), and four ipso signals at 141.7-
142.6 ppm.
the blue solution without attempted separation gave
signals once at m/z 588 (100%, B of 3) and 295 (100%,
Mes2CdCdSH+), but after a different reaction time, no
signal at m/z 588 was observed, indicating the possibility
that the mixture contains two compounds.
1
(c) Tipyl-Su bstitu ted Der ivatives. Ditipyl thioketene
(9) was not obtained from ditipyl ketene5 and P2S5.
Instead, ditipylacetic acid (10)5 (24%) and 40% of a
compound, tentatively identified as 11, the dimer of 9,
were obtained (eq 3 in Scheme 3). The +DCI mass
spectrum of 11 showed signals at m/z 725 (MH3+ - Tip),
521 (MH3+ - 2Tip), 464 (Tip2CdCdSH2+, 100%); -DCI:
m/z 927 (MH3, 100%), 463 (Tip2CdCdSH, 7%).
A H NMR spectrum (CD2Cl2, rt) display five signals
at 2.16, 2.19, 2.27, 6.78 and 6.89 in a 6:2:3:0.6:2 ratio,
respectively. Two of these belong to 3 and three to the
blue species. In nitrobenzene, signals at 2.25 (o-Me), 2.28
(p-Me), 6.84 (Ar-H) for 3 and 2.03 (o-Me), 2.40 (p-Me),
and 6.75 (Ar-H) for the blue compound were observed.
The 13C NMR spectrum of the mixture at CD2Cl2 (rt)
displayed 15 signals at 20.7, 20.7, 21.0, 21.1, 86.3, 121.0,
126.1, 128.2, 129.4, 129.8, 132.2, 136.8, 137.2, 137.7, and
257.0 ppm.
From the separate signals in C6D5NO2 the monomer:
dimer ratio after it reached a constant value was 3.3:1
at rt starting with ca. 0.03 M of the dimer. It is unknown
if this is the equilibrium ratio, but if this is the case the
[2]2/[3] ratio is ca. 0.12.
1
In the H NMR spectrum (CDCl3, rt) only tipyl rings
were observed as judged by the 18:3:2 ratio of three
groups of signals: (i) i-Pr-Me overlapping doublets at
0.87-1.35 ppm, (ii) a multiplet at 2.65-3.20 (i-Pr-H), and
(iii) three 1:1:2 Ar-H signals at 6.90, 6.97, and 7.06 ppm.
(11) Kyi, H. J .; Praefcke, K. Tetrahedron Lett. 1975, 555.

7328 J . Org. Chem., Vol. 61, No. 21, 1996
Selzer and Rappoport
F igu r e 1. Stereoview of 4.
The λmax, the νmax ) 1742 cm-1, and δ13C ) 257.0 ppm
identify convincingly the new species as a thioketene; e.g.,
λmax (nm) for 1, R1 ) R2 ) t-Bu, p-ClC6H4, Ph are 570,7b
627,12a 624,12a respectively, and for R1) H, R2) t-Bu, 575
nm.12a Diaryl and dialkyl thioketenes display a strong
IR stretching around νmax ) 1750 cm-11b (e.g., 1725-1758
cm-1 for the ketenes above)7b,12a due to a νasym of the
CdCdS group,1b and a very low field CdS signal at 215-
285 ppm.1b,12b The blue compound is therefore probably
dimesityl thioketene 2, and the phenomenon observed is
a dimer (3) h monomer (2) retro-dimerization. On this
basis we can extract the signals for 2 from the spectra of
the 2/3 mixtures. They are 1H NMR δ: 2.16(o-Me), 2.27-
(p-Me), and 6.89(Ar-H) ppm;13C NMR δ: 86.3(allenic C)
and 257.0(CdS) ppm.
Solid Sta te Str u ctu r es of 3 a n d 4. X-ray diffraction
structures of both 3 and 4 have been determined. That
of 3 is the first 1,3-dithietane structure having two exo
diarylmethylene groups, i.e., 12, m ) n ) 1.13 The central
ring is planar having an inversion center in the middle
of the ring exchanging the two pairs of the mesityl groups
on its both sides. A C2 axis passing through the double
bonds, exchanges two geminal mesityl rings. The Mes-
CdC dihedral angles are 59.8°. The double bond tor-
sional angle is 8.7°.
Several 1,2,4,5-tetrathiane crystal structures are avail-
able and that of 4 is the second structure 12, n ) m ) 2,
determined by X-ray diffraction. The tetrathiane ring
exists in a twist boat conformation as shown by its
stereoview in Figure 1.13 The four Mes-CdC torsional
angles are nearly the same, being 58.7°, 59.5°, 61.2° and
62.1°. The two double bonds are appreciably twisted,
their torsional angles being 15.1° and 13.5°.
Dyn a m ic NMR Stu d y of 3. When a solution of 3 in
1
CD2Cl2 is cooled to 160 K, the H NMR aromatic singlet
at 6.77 ppm split to four signals at 6.59, 6.62, 6.75 and
6.84 ppm (1:2:2:1 intensities, respectively) and the ali-
phatic signal at 2.17 ppm split to four singlets at 1.70,
2.07, 2.41 and 2.52 ppm with 3:3:2:1 intensities, respec-
tively (Figure 2A).
Since the two dimesitylvinyl moieties are chiral due
to their helicity, three stereoisomers should be present
at equilibrium at the low temperature: two enantiomers
13a and 13b for which we assign two pairs of signals
and a meso isomer 13c to which we assign the other two
pairs of signals. The three isomers with letters a-f
F igu r e 2. A dynamic NMR experiment for 3 in CD2Cl2. A:
At 160 K; B: at 235 K; C: at 255 K; D: at 263 K; E: at 273
K; F: at 295 K.
labeling the ortho- and para-positions and letters with
bars aj-hf designating the corresponding enantiotopic sites
are shown in Figure 3. Similar designations apply for
the aromatic hydrogens.
In each enantiomer the four rings are twisted in the
same sense and they have opposite right and left helici-
ties and a D2 symmetry. The meso isomer 13c has C2h
(12) (a) Seybold, G.; Heibl, C. Angew. Chem. 1975, 87, 171. (b)
Okazaki, R.; Ishii, A.; Fukuda, N.; Oyama, H.; Inamoto, N. J . Chem.
Soc., Chem. Commun. 1982, 1187.
(13) The author has deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.

Bis(dimesitylmethylene)-1,3-dithietane and -1,2,4,5-tetrathiane
J . Org. Chem., Vol. 61, No. 21, 1996 7329
Based on the data in Table 1 and the Gutowsky-Holm
equation, ∆G# ) 13.0 kcal mol-1. Overlap of the p-Me
c
signal with the average o-Me signal increase the error
in Tc, and the estimated error in ∆G# is (0.3-0.4 kcal
c
mol-1. The average ∆G# value from all probes is 12.7
c
kcal mol-1
.
Since the Gutowsky-Holm equation is
strictly applicable for an exchange of two signals with
identical intensities and our processes involve exchange
at four sites (the Ar-H or the o-Me of 13c with those in
13a ,b), its use is not necessarily correct. However, we
believe that the equation gives an approximate barrier,
although its error is higher than the quoted (0.2 kcal
mol-1
.
Dyn a m ic NMR Stu d y of 4. When a solution of 4 in
CD2Cl2 is cooled to 160 K the 1H NMR rt aromatic singlet
at 6.77 ppm split to five signals. Partial overlap inter-
feres with exact relative integration but the two slightly
<1:1 signals at 6.58 and 6.80 ppm consist ca. 85% of the
intensity, and three 1:1:1 signals at δ 6.65, 6.83, and 6.87
ppm have ca. 15% intensity. An additional small signal
(of 5% intensity) may be hidden below the δ 6.58 signal.
The aliphatic signal appearing at fast exchange at 400
K at δ 2.21 split on cooling to ca. 1:1:1 signals at 1.60,
2.09, and 2.31 ppm (80% intensity) and to two 1:1 signals
at 1.75 and 2.46 ppm (20% intensity).
These signals are ascribed to eight groups of hydrogens
belonging to three enantiomeric pairs. The central ring
of 4 has in the crystal a twist-boat (TB) conformation,
and since 1,2,4,5-tetrathianes probably have a similar
conformation in solution,15 we assume it also for 4 in
solution. Since a TB conformation is chiral and each pair
of mesityl rings can have either a right handed or a left
handed helicity, the maximum possible number of ste-
reoisomers is six (14a -16a , 14b-16b) as drawn in
Figure 4, with labeling similar to that for 13a -c.
Assuming a negligible mutual influence of the two
Mes2CdC groups, and identical enthalpies, statistics
suggest a 1:2:1 ratio of 14a ,b:15a ,b:16a ,b.
There are several alternative assignments based on the
relative intensities of the observed five signals, plus the
hidden one at 6.58 ppm to the six isomers. (i) The four
1:1:1:1 signals at (6.58), 6.65, 6.83, and 6.87 ppm belong
to the two enantiomers 15a ,b having C2 symmetry, where
each pair of geminal mesityl rings have a different
helicity and the two large signals to the 14a ,b, 16a ,b with
D2 symmetry, assuming that they appear at the same δ
value due to accidental isochrony. The 15a ,b/14a ,b +
16a ,b equilibrium ratio is then 1:2. (ii) The two large
signals belong each to 14a ,b or 16a ,b, and one of these
isomers has a lower population. Isomers 15a ,b and
14a ,b or 16a ,b are then at equilibrium ratio of 1:4,
respectively. (iii) The four small signals belong to 14a ,b
and 16a ,b and the two large signals to 15a ,b, assuming
that due to accidental isochrony the signals for protons
c, d, e, and f appear as two signals only. The ratio 14a ,b:
15a ,b:16a ,b is then ca. 1:9:1. The two pairs with different
intensities were assigned to the other two pairs (14a ,b;
16a ,b). We cannot decide between the alternatives but
possibility i seems most likely.
F igu r e 3. The two enantiomers 13a and 13b and the meso
form 13c of 3.
Ta ble 1. DNMR Da ta for 3 a n d 4 in CD2Cl2
signals/
ppma
∆G#c/kcal
compound
∆ν/Hza Tc/K
δb
kc/s-1 c
mol-1
3
6.62, 6.75
6.59, 6.84
1.70, 2.52 327.5
6.58, 6.80
6.65, 6.87
1.60, 2.31 285
52.6
99.2
263 6.77
263 6.77
287 2.17
278 6.79
278 6.79
117
12.8
12.5
13.0
13.3
13.3
13.3
220.5
727.5
197.2
201.5
4
88.8
90.7
252 2.21d 633.1
a
b
At slow exchange at 160 K. δ of the average signal obtained
after coalescence. c At Tc. In Cl2CDCDCl2.
d
symmetry, with a symmetry plane passing through the
two sulfur atoms and bisecting the central ring plane.
Mesityl rings on one side of the plane have the same
helicity, opposite to that of the other rings.
The two Mes2Cd groups are remote from one another
and assuming that they exert a negligible mutual influ-
ence, the three forms should have a similar enthalpy.
Statistically, the meso:d,l ratio should then be 1:1.
However, the observed ratio is strongly temperature-
dependent, before broadening due to coalescence inter-
feres with its determination (cf. A and B in Figure 2). At
160 K the ratio is either ca. 1:2 or ca. 2:1 since we are
unable to assign a certain signal to a certain isomer.
Six methyl signals are expected at slow exchange: one
for the p-Me and two for the o-Me groups of 13a ,b and
similarly for 13c. However, all the p-Me groups appear
accidentally isochronous at 2.07 ppm with one-third of
the intensity. This is corroborated by the nearly constant
δ and shape during the dynamic process. The signal at
1.70 ppm with one-third of the intensity is again ascribed
to accidental isochrony of one o-Me group of 13c and one
o-Me in 13a ,b. The 2:1 signals at 2.41 and 2.52 ppm are
assigned to the second o-Me in 13a ,b and in 13c,
respectively.
When the temperature was raised, signal broadening,
coalescence, and then sharpening of both the aliphatic
and aromatic signals took place (Figure 2). The pair of
Ar-H signals at 6.62 and 6.75 ppm and the other pair of
Ar-H signals at 6.59 and 6.84 ppm coalesce at the same
temperature (Tc ) 263 K) giving an average signal at rt
at 6.77 ppm. The ∆G#c values for the two processes which
lead to interconversion of stereoisomers were calculated
from the Gutowsky-Holm14 and the Eyring equations
On raising the temperature, the usual broadening,
coalescence, and resharpening of signals of the DNMR
experiments were observed (Figure 3). In CD2Cl2 for the
large signals at 6.58 and 6.80 ppm, Tc ) 278 K, ∆G#
)
c
(Table 1). The average ∆G# is 12.7 ( 0.2 kcal mol-1
.
c
13.3 kcal mol-1. The average signal of all four signals
The three singlets at 1.70, 2.41, and 2.52 ppm coalesce
at 287 K. At rt, the average signal appears at 2.17 ppm.
(15) For
a recent review see Conformational Behavior of Six-
Membered Rings. Analysis, Dynamics and Stereoelectronic Effects;
J uaristi, E., Ed.; VCH: New York, 1995; pp 202-209.
(14) Gutowsky, S. H.; Holm, C. H. J . Chem. Phys. 1956, 25, 1228.

7330 J . Org. Chem., Vol. 61, No. 21, 1996
Selzer and Rappoport
F igu r e 4. The six stereoisomers of 4.
appear at 6.79 ppm at 400 K in Cl2CDCDCl2. The two
dents are known.11,17 Compound 12, m ) n ) 2, A-D )
CF3 apparently gives the analog of 5 by sulfur loss on
heating. The latter or another bis(disubstituted meth-
ylene)trithiane gives analogs of 3.17 A photochemical
analogy is also known.11
Ph2CHCOCl and P2S5 in pyridine form the two 1,2,4-
trithiane derivatives 7 and 8. Interestingly, diphenyl
ketene and P2S5 did not give a defined product,18 but with
p-thiophosphoric anhydride, the tetraphenyl analog of 3
was obtained19 probably by dimerization of 6. An initial
formation of 6 and then a reaction analogous to eq 7 can
form 7. It is unclear why only one double bond of 7 is
reduced to 8, but since we were unable to isolate other
products from the oil remaining after obtaining 7 and 8,
mechanistic speculations are unwarranted.
Dim esityl Th iok eten e. The spectral data of the blue
solution left little doubt that it contains the thioketene
2, formed by the thionation or the dissociation of 3
(eqs 4 and 5). Most thioketenes tend to dimerize to
2,4-bis(dialkylmethylene)-1,3-dithietanes.1b,c However,
t-Bu2CdCdS is obtained by thionation of t-Bu2CdCdO
or t-Bu2CHCOCl with P2S5 in pyridine.7b Our thionation
resembles this synthesis, but 2 apparently disappears
under the thionation conditions by reacting rapidly with
P2S5 or with 17, according to eqs 6 and 7.
The ease of cleavage of dimer 3 to 2 is remarkable. [2
+ 2] Cycloreversion of 2,4-bis(alkylidene)-1,3-dithietanes
usually requires high temperature,20 and bis(trifluorom-
ethyl) thioketene was prepared by this route.21 The steric
crowding in dimer 3 is probably responsible for its slow
cleavage under mild conditions.
small aromatic signals at 6.65 and 6.87 ppm give Tc )
278 K, ∆G# ) 13.3 kcal mol-1 (Table 1).
c
The two aliphatic signals at δ 1.60 and 2.31 ascribed
to the two types of o-Me signals in one or two of the
isomeric pairs coalesce in CD2Cl2 at 252K, ∆G# ) 13.3
c
kcal mol-1. The average signal appears in Cl2CDCDCl2
at 400 K at 2.21 ppm (Table 1). The ∆G# value for the
c
exchange between several sites was calculated by the
Gutowsky-Holm equation14 and the reservation raised
above concerning its accuracy applies here too.
Discu ssion
F or m a tion of th e Cyclic Com p ou n d s. One of our
goals was to obtain thioketenes 2, 6, and 9 by thionation
of the corresponding diaryl ketenes with P2S5. Although
they may be transiently formed as observed for 2, none
of them was accumulated during the reaction. The
reaction gave instead heterocyclic compounds containing
n atoms with n - 2 sulfur atoms (n ) 4-6) with two exo
diarylmethylene groups or their derivatives. 1,3-Dithi-
etanes, 1,2,4-trithianes, and 1,2,4,5-tetrathianes are well
known, but we are unaware of their formation by
thionation of ketenes. The formation of the various rings
can be accounted for by an initial formation of the
diarylthioketene, as demonstrated with 2.
Initially 2 is formed by thionation (eq 4 in Scheme 4),
as a short-lived intermediate which may dimerize by a
reversible [2 + 2] cycloaddition to 3 (eq 5 in Scheme 4).
-
An additional P2S5 molecule or the species SPS2 derived
from it and suggested as the reactive thionation species
with P2S516 traps 2 rapidly to give anion 17. Nucleophilic
attack of 17 on the sulfur of another anion 17 with
Sta tic a n d Dyn a m ic Beh a vior of 3. A. Sta tic
Con for m a tion . The Cambridge Structural Database
lists eight X-ray diffraction structures 12, m ) n ) 1.
Except for one, all are thioketene dimers (A ) D, B )
C). They are centrosymmetric, with planar dithiacy-
clobutane rings with C-S bond lengths of 1.74-1.79 Å,
-
expulsion of PS2 and an intramolecular displacement
in the resulting anion gives tetrathiane 4 (eq 6 in Scheme
5). Likewise, addition of 17 to 2 leads to an anionic
-
product which by an intramolecular displacement of PS2
gives trithiane 5 (eq 7 in Scheme 5).
Alternatively, loss of sulfur from the ring of 4 can give
the trithiane ring 5, and further loss can give 3. Prece-
(17) (a) Kirby, A. J . Tetrahedron 1966, 22, 3001. (b) Raash, M. S. J .
Org. Chem. 1970, 35, 3470.
(18) Staudinger, H. J ustus Liebigs Ann. Chem. 1907, 356, 51.
(19) Dunmur, R. E.; Fluck, E. Phosphorus 1974, 5, 13.
(20) Seybold, G.; Heibl, C. Chem. Ber. 1977, 110, 1225.
(21) Raasch, M. S. (a) Chem. Commun. 1966, 577. (b) J . Org. Chem.
1970, 35, 3470.
(16) Scheeren, J . W.; Ooms, P. H. J .; Nivard, R. J . F. Synthesis 1973,
149.

Bis(dimesitylmethylene)-1,3-dithietane and -1,2,4,5-tetrathiane
J . Org. Chem., Vol. 61, No. 21, 1996 7331
whereas in tetramesitylethylene the mutual interaction
between the two close moieties leads to twist of all rings
in the same direction,23a in the X-ray diffraction of the
isolated crystal of 3 the two moieties have opposite
helicities. However, the two diastereomeric conforma-
tions were apparently observed in solution.
B. Dyn a m ic Beh a vior . Two possible dynamic pro-
cesses in polyarylvinyl propellers9a may be relevant to
that observed for 3. (i) Rotation around the CdC bond
will exchange the two geminal rings and may lead to
coalescence. The high barrier to such rotation in
tetramesitylethylene23b and the stability of methoxy-
substituted trimesitylvinyl acetates and ethers to E h Z
isomerization24 exclude this route. (ii) Rotation around
the Mes-Cd bonds can proceed either by independent
rotation of each ring or by correlated rotation. Correlated
rotations in vinylic propellers9a are discussed in terms
of flip mechanisms involving helicity reversal, based on
the definitions and analysis of Mislow for rotations
around Ar-C bonds.25 A flip is a passage of a ring during
its rotation through a plane perpendicular to the refer-
ence plane, while the nonflipping rings rotate in the
opposite direction and pass through the reference plane.
We define the reference plane in 3 by the (Cipso)2CdC.
According to the number of the flipping rings the routes
are called n-ring flips with n ) 0, 1, 2 in our system
(Figure 6).
The two important features of the DNMR behavior are
the following: (a) four aromatic signals at slow exchange
coalesce to one average signal; (b) four o- and p-Me
signals coalesce to one signal, due to accidental isochro-
nicity of the average para and ortho signals.
The two Mes2-Cd groups are treated as independent.
Three- or four-ring flips are regarded as occurring ac-
cidentally simultaneously and not as a correlated rotation
of all rings. Only zero-, one-, and two-ring flips are
therefore analyzed.
Rotation around the double bond cannot be followed
by NMR since it will exchange homotopic sites (e.g., a
and aj). A ring flip exchanges the magnetic sites b and
dh, a and ej, b and ej, a and dh, a and d, and b and e (cf.
Figure 3) with a consequent coalescence of the corre-
sponding signals. The 180° rotation with retained he-
licity will lead to coalescence of sites a and b, and d and
e. Table 2 lists the exchanging sites by the various
rotation routes. Only inversion of helicity, i.e., by the
flip routes, will lead to (stereo) isomerization. Only the
one-ring and two-ring flip routes account for exchange
of all the groups residing in diastereotopic sites, leading
at a fast exchange to one average aromatic signal.
For 2,2-dimesityl-1-R-ethenols9 a 1-ring flip takes place
only when R ) H since interference by the hydrogen for
passage of the mesityl ring via the reference plane is
small. When R ) bulkier alkyl, the low energy route is
F igu r e 5. A dynamic NMR experiment for 4 in CD2Cl2. A:
At 160 K; B: at 220 K; C: at 250 K; D: at 275 K; E: at 278
K; F: at 295 K; G: at 400 K in Cl2CDCDCl2.
the two-ring flip. The average ∆G# value of 12.7 kcal
c
mol-1 for 3 resembles the two-ring flip barriers for the
2,2-dimesityl-1-alkylethenols (10.5-12.5 kcal mol-1).9b,c
A likely mechanism for 3 is therefore a two-ring flip.
St a t ic a n d Dyn a m ic Beh a vior of 4. A. St a t ic
Con for m a tion . The Cambridge Structural Database
lists only the partial structure of 3,6-bis(2-oxobut-3-
2-
in line with Csp S bond lengths in other systems. The
SCS and CSC angles (ca. 98° and 82°, respectively) are
in the range as in all known structures. The twist in
the same direction around the Mes-Cd bonds on each
side is consistent with the propeller conformation of
diarylvinyl moieties.9,10 The Mes-Cd torsion angles of
59.8° are similar to that for Mes2CdC(OH)Pr-i.22
(23) (a) Blount, J . F.; Mislow, K.; J acobus, J . Acta Crystallogr. Sect.
A. 1972, 28, S12; Nazran, A. S.; Lee, F. L.; Gabe, E. J .; Lepage, Y.;
Northcolt, D. J .; Park, J . M.; Griller, D. J . Phys. Chem. 1984, 88, 5251.
(b) Gur, E.; Kaida, Y.; Okamoto, Y.; Biali, S. E.; Rappoport, Z. J . Org.
Chem. 1992, 57, 3689.
Structure 3 resembles a tetramesitylethylene with a
“spacer” between the two Mes2Cd moieties. However,
(24) Rochlin, E.; Rappoport, Z. (a) J . Org. Chem. 1994, 59, 3857. (b)
Unpublished results.
(25) For a review see, Mislow, K. Acc. Chem. Res. 1976, 9, 26.
(22) Kaftory, M.; Nugiel, D. A.; Biali, S. E.; Rappoport, Z. J . Am.
Chem. Soc. 1989, 111, 8181.

7332 J . Org. Chem., Vol. 61, No. 21, 1996
Selzer and Rappoport
Sch em e 4
Sch em e 5
1,2,4,5-tetrathiane-containing structures, but lacking the
3,6-exocyclic bonds, are known. 3,3,6,6-Tetramethyl-s-
tetrathiane (18) exists as a D2 twist-boat (TB) conforma-
tion both in the solid27 and in solution28a and has
significantly short S-S bonds of 2.015 Å27 compared with
the average length (2.08 Å). The tetrathiane 19 exists
as a chair conformation in the solid, but with only a 0.75
kcal mol-1 preponderance over the TB in solution29 with
an S-S bond length of 2.035 Å.30
F igu r e 6. The zero-, one-, and two-ring flips for the diarylvi-
nyl group in one half of 2,4-bis(diarylmethylene)-1,3-dithiet-
ane. The solid rectangle indicates a ring perpendicular to the
reference plane.
The tetrathiane ring in 4 has a nonperfect TB confor-
mation (Figure 1) since the two CdC bonds are at a angle
of 166.5°, rather than 180°. The S-S bond lengths of
2.039 and 2.044 Å are close to that in orthorbombic S8
(2.037 Å).31 The Csp2-S bonds of 1.764-1.780 Å are
Ta ble 2. Ma gn etic Sites in 3 a n d 4 Wh ich Exch a n ge by
F lip a n d Non flip Rou tes
ring
3-
shorter than the Csp S bonds in 18 and 19 (1.84 Å) which
compound flip route
flip
nonflip
are typical for a S-C single bond due to the carbon sp2
hybridization. All the Mes-Cd torsion angles of 58.7-
62.0° are in the same direction. Again, we envision the
structure as having two independent propeller moieties.
The double bond torsional angles of 13.5° and 15.1° are
higher than for 3 but resemble that for Mes2CdC(OH)-
Bu-t.22
3
zero-ring (adh)(bej)(chf)(ad)(be)(cf) (a)(b)(c)(d)(e)(f)
(ajd)(bhe)(cjf)(ajdh)(bhej)(cjhf)
one-ring (aej)(bdh)(chf)(adh)(bej)(ad) (ab)(ba)(c)(de)(ed)(f)
(bc)(cf)(bhd)(aje)(cjf)(bhe)
(ajd)(ajdh)(bhej)(cjhf)
two-ring (aej)(bdh)(chf)(ad)(be)(cf) (ab)(ba)(c)(de)(ed)(f)a
(aje)(bhd)(cjf)(ajdh)(bhej)(cjhf)
4
zero-ring (ae)(bf)(ac)(bd)
(cg)(dh)(eg)(fh)
(a)(b)(c)(d)(e)(f)(g)(h)
one-ring (be)(af)(bf)(ae)(ac)(bd) (ab)(cd)(ef)(gh)
(ch)(dg)(dh)(cg)(ge)(fh)
two-ring (af)(be)(ac)(bd)
(ch)(dg)(ge)(hf)
(27) Korp, J . D.; Bernal, I.; Watkins, S. F.; Fronczek, F. R.
Tetrahedron Lett. 1981, 22, 4767.
(28) (a) Bushweller, C. H. J . Am. Chem. Soc. 1967, 89, 5978. (b)
Bushweller, C. H. ibid. 1968, 90, 2450. (c) Bushweller, C. H.; Golini,
J .; Rao, G. U.; O'Neil, J . W.ibid. 1970, 92, 3055. (d) Bushweller, C. H.
Ibid. 1969, 91, 6019.
(ab)(cd)(ef)(gh)a
a
180° rotation of the two geminal rings.
(29) From a correlation between S-S bond lengths and dihedral
angles of the S-S valencies (Hordvik, A. Acta Chem. Scand. 1966, 20,
1885), this bond length corresponds to ca. 90° angle, as was indeed
observed.
(30) Bushweller, C. H.; Bhat, G.; Letendre, L. J .; Brunelle, J . A.;
Bilofsky, H. S.; Ruben, H.; Templeton, D. H.; Zalkin, A. J . Am. Chem.
Soc. 1975, 97, 65.
ylidene)-1,2,4,5-tetrathiane as having structure 12, m )
n ) 2 (A ) D ) Me; B ) C ) Ac).26 The molecule is
centrosymmetric and nearly planar, and there is no
additional information for comparison with 4. Two other
(26) Alcock, N. W.; Kirby, A. J . Tetrahedron 1966, 22, 3007.
(31) Abraham, S. C. Acta Cryst. 1955, 8, 661.

Bis(dimesitylmethylene)-1,3-dithietane and -1,2,4,5-tetrathiane
J . Org. Chem., Vol. 61, No. 21, 1996 7333
inversion cannot be studied since all the diastereotopic
sites are already exchanged by the flip process. However,
as mentioned above the observed threshold mechanism
for Mes2CdCR1R2 was uniformly a two-ring flip when R1
) R2 * H, Ar. Moreover, the ∆G#c value is only 0.6 and
1.6 kcal mol-1 lower than that of the two-ring flip for 3
whose Mes-Cd torsion angle resemble those of 4, and for
Mes2CdC(OH)Pr-i where these angles are slightly
higher.9b,c These analogies strongly suggest a threshold
two-ring flip route which, however, is insufficient to
render equivalent all the o-Me groups in the three
diastereomers (Table 2). Hence, we assume that coales-
cence of all o-Me groups into a single signal involves both
Mes rings rotation and ring inversion. This does not
necessarily contradict analogy with Bushweller’s data
since the effect of the Mes2Cd groups on the ring
inversion is unknown. We then regard the central ring
as being planar on the average, and the analysis is
identical to that given for 3.
F or m a tion of 5. The 1H NMR spectrum of pure 4
obtained by crystallization, differed from that of the crude
yellow oil obtained from the 4-containing fraction from
chromatography on silica. The rt spectrum of the latter
in CD2Cl2 contained the two signals of 4, and additional
two aromatic signals at 6.75 and 6.80 ppm and four
aliphatic signals at δ 2.13, 2.14, 2.18, and 2.20 ppm. In
Cl2CDCDCl2 at 400 K these signals were sharpened and
appeared at δ 2.22, 2.23, 2.24, 2.27, 6.77, and 6.82 in
relative intensities of 6:6:3:3:2:2. This suggested that
crude 4 was accompanied by another compound.
The mass spectrum of the same sample showed two
signals with (presumably) molecular peaks at m/z 652
and 620. Two different spectra taken at different times
gave different relative intensities. At a lower tempera-
ture the m/z 620 peak was the highest and was ac-
companied by signals at 588 (26%), 294 (100%), 262
(47%), 246 (57%), 245 (25%), and 231 (25%), whereas at
a higher temperature the highest peak was at m/z 652.
This suggested again that the presence of an additional
compound, i.e., 3,5-bis(dimesitylmethylene)-1,2,4-trithiane,
5, with M at m/z 620. Crystallization of the mixture from
petroleum ether gave pure 4, and several recrystalliza-
tions of the filtrate enriched it to a 3:7 4:5 mixture, but
pure 5 was not obtained so far.
F igu r e 7. Possible routes for a TB h TB equilibration in 3,6-
divinylidene-1,2,4,5-tetrathiane.
Whereas six-membered rings containing one, two,
three, or five sulfur atoms are generally more stable in
the chair conformations,14,28a for the 1,2,4,5-tetrathiane
rings, investigated by Bushweller's group,28 the TB
conformation is mostly preferred. For the parent 1,2,4,5-
tetrathiane, both the chair and a less stable twist
conformer were identified in solution.32 The barrier to
the TB h chair interconverison is relatively high (15-
16 kcal mol-1). Even a cyclohexane ring with exocyclic
1,4-double bonds, e.g., 1,4-cyclohexanedione, also exist in
a TB conformation.33
B. Dyn a m ic Beh a vior . The rotational routes de-
scribed for 3 are also applicable for 4, but an additional
TB h TB tetrathiane ring interconversion involving
either a boat or a chair conformation as an intermediate
or a transition state (Figure 7) should be also considered.
Relevant for the analysis is that with the change 160 Kf
400 K the five observed (+ 1 hidden) aromatic signals at
slow exchange coalesce to a single average signal. Since
the observed ratio 14a ,b:15a ,b:16a ,b of 1:2:1 differs from
the predicted one, we cannot assign the different signals
to the different stereoisomers.
We regard 4 as a combination of independent, two
dimesitylvinyl groups and a TB 1,2,4,5-tetrathiane ring.
Hence, we consider only zero-, one-, or two-ring flips for
dynamic processes the Mes2Cd moiety undergoes. We
use Figure 4 for magnetic sites assignment and analysis
using a scheme analogous to Figure 6 which assumes that
at slow exchange all processes take place at a TB
conformation.
If we assume that the ring undergoes a TB h TB
interconversion without a detectable intermediate and
that the activation energy for the interconversion of each
one of the stereoisomeric pairs is similar, the process will
exchange the (dhf)(cej)(dhf)(cje)(agj)(bhh)(ajg)(bhh) sites, giving
four aromatic signals at fast exchange. Consequently,
the results are inconsistent with a ring inversion process
alone. It should be coupled to other processes, thus
reducing the number of observed signals. Analysis
similar to that for the dynamic process of 3 suggests that
these are rotations around the Mes-Cd bonds. The
magnetic sites exchanged in the various rotation routes
are summarized in Table 2. The flip routes exchange
diastereotopic groups between stereoisomers having iden-
tical TB conformations of the central ring, i.e., in 14a ,
15a , or 16a (or 14b, 15b, and 16b). We assume that all
the n-ring flips having the same n have the same energy.
The only route in Table 2 which exchanges all the
groups at diastereotopic sites and hence give only one
average aromatic signal is a one-ring flip with a barrier
Analysis of the static 1H NMR spectrum of 5 at 400 K
assumes that any dynamic process taking place is fast
on the NMR time scale and that 5 is an average planar
molecule with a C2v symmetry. The lack of a C2 axis or
a plane of symmetry passing through the four CdC
carbons means that the mesityl-Me groups of one ring
are in a diastereotopic site compared with those in the
geminal ring. Hence, each of the signals at 2.22 and 2.23
ppm is ascribed to the two o-Me groups of one mesityl
ring. Likewise, the signals at 2.24 and 2.27 ppm are
ascribed to the two p-Me groups on geminal rings, and
the signals at 6.77 and 6.82 ppm are ascribed to the two
m-H of each one of the geminal mesityl rings. Unfortu-
nately, the DNMR study of the 7:3 5:4 mixture was too
complex for obtaining a ∆G# value for 5.
c
of ∆G# ) 13.3 kcal mol-1. If we assume a TB h chair
c
Exp er im en ta l Section
interconversion barrier of 16 kcal mol-1 for 4, as deter-
mined by Bushweller for four tetrathiane rings,28,30 then
the one-ring flip for 4 is the threshold process. The ring
Solven ts a n d Ma ter ia ls. Preparation of solvents and the
apparatus used were described in a previous publication.34 P2S5
was purchased from BDH. Dimesityl ketene4,9a and ditipyl
ketene5 were prepared as previously described.
(32) For a review see: Susilo, R.; Gmelin, R.; Roth, K.; Bauer, R. Z.
Naturforsch. 1982, 37B, 234. Franck, W. Sulfur Rep. 1991, 10, 233.
(33) Grothand, P.; Hassel, O. Proc. Chem. Soc. 1963, 218. Mossel,
A.; Romers, C.; Havinga, E. Tetrahedron Lett. 1963, 1247.
(34) Selzer, T.; Rappoport, Z. J . Org. Chem. 1996, 61, 5462.

7334 J . Org. Chem., Vol. 61, No. 21, 1996
Selzer and Rappoport
Dim esityl Th iok eten e, 2,4-Bis(d im esitylm eth ylen e)-
1,3-d it h iet a n e (3), 3,5-Bis(d im esit ylm et h ylen e)-1,2,4-
tr ith ia n e (5), a n d 3,6-Bis(d im esitylm eth ylen e)-1,2,4,5-
tetr a th ia n e (4). A suspension of dimesityl ketene (0.5 g, 1.8
mmol) and P2S5 (0.45 g, 2 mmol) in pyridine (8 mL) was
refluxed for 21 h, after which the ketene peak at 2100 cm-1
disappeared completely. A transient blue color appeared and
disappeared rapidly at the beginning of the reaction. After
reaching rt, the solution was cooled to 0 °C, an aqueous
phosphate buffer solution (pH 6.8, 16 mL) was slowly added
and the mixture was stirred for 2 h. The organic phase was
extracted with ether (5 × 20 mL), washed with dilute HCl (3
× 30 mL), saturated aqueous NaHCO3 solution (2 × 30 mL),
and water, and dried (MgSO4). The ether was evaporated, and
the remaining brown solid was chromatographed on silica with
95:5 petroleum ether-CH2Cl2 eluent.
ride (2 g, 8.7 mmol) and P2S5 (2 g, 9 mmol) in pyridine (28
mL) was refluxed for 17 h. All the precursor had disappeared.
The solution was cooled to 0 °C, aqueous phosphate buffer (pH
6.8, 50 mL) was added, and the solution was stirred for 2 h.
The organic phase was extracted with ether (5 × 20 mL),
washed with dilute HCl (3 × 30 mL), then with saturated
NaHCO3 solution (2 × 30 mL), and water (30 mL), and dried
(MgSO4). Evaporation of the ether left a brown solid which
was chromatographed on silica with 8:2 petroleum ether: ether
eluent. Two compounds were separated and identified. (i) 3,5-
Bis(diphenylmethylene)-1,2,4-trithiane (7), (0.27 mg, 14%), mp
195-6 °C (lit. 193-4 °C).11 IR νmax(Nujol): 1594 cm-1 (CdC).
1H NMR (CDCl3) δ: 7.24-7.39 (20H, m); 13C NMR (CDCl3) δ:
127.9, 128.0, 128.2, 128.3, 129.4, 129.4, 135.7, 136.5, 141.2,
142.0. Mass spectrum: m/z (relative abundance, assign-
ment): 452 (28%, M+), 420 (6%, M - S+), 211 (19%,
Ph2CdCdSH+), 210 (100%, Ph2CdCdS+), 178 (9%, Ph2C2+),
165 (35%, Ph2CH+), 89 (5%, PhC+), 77 (4%, Ph+). HRMS:
452.0721. Calcd for C28H20S3: 452.0727. Microanalysis: C,
74.67; H, 4.23. Calcd for C28H20S3: C, 74.30; H, 4.45%.
(ii) 3-(Diphenylmethylene)-5-(diphenylmethyl)-1,2,4-trithiane
(8) (60 mg, 3%), mp 190-1 °C. IR νmax(Nujol): 1598 cm-1
The yellowish first fraction in the eluent turned blue after
standing for a few hours at rt. When kept in the cold for one
week yellow crystals, 37 mg (7%) of 2,4-bis(dimesitylmethyl-
ene)-1,3-dithietane (3), mp 312-314 °C, were separated. IR
ν
max (Nujol): 1600 cm-1 (CdC); 1H NMR (CD2Cl2) δ: 2.17 (36H,
s), 6.77 (8H, s); 13C NMR (CD2Cl2) δ: 20.8, 21.1, 121.1
(Mes2Cd), 128.2, 129.5, 132.3, 136.8, 137.8 (CdCS2). Mass
spectrum: m/z (relative abundance, assignment): 588 (100%,
M+), 294 (23%, Mes2CdCdS+), 262 (20%, Mes2CdC+), 246
(19%), 231 (8%), 175 (3%, MesCdCdS+), 119 (3%, Mes+).
Microanalysis: C, 81.55; H, 7.49; S, 10.41. Calcd for
C40H44S2: C, 81.63; H, 7.47; S, 10.89%. X-ray diffraction:
space group Cmca, a ) 25.424(4) Å, b ) 14.087(2) Å, c ) 11.274-
(2) Å, V ) 4037.5(8) Å3, z ) 4, Fcalc ) 1.03 g cm-3, µ(Cu KR) )
13.42 cm-1, R ) 0.056, Rw ) 0.081.13
1
(CdC); H NMR (CDCl3) δ: 4.56 (1H, d), 5.75 (1H, d), 7.16-
7.37 (20H, m). 13C NMR (CDCl3) δ: 55.2, 68.9, 127.3, 127.5,
127.5, 127.7, 127.71, 127.75, 128.2, 128.3, 128.76, 128.81,
129.1, 129.4, 132.5, 140.9, 141.7, 142.09, 142.17, 142.56.
Mass spectrum: m/z (relative abundance, assignment): 454
(18%, M+), 253 (11%, C15H9S2+), 242 (18%, Ph2CdCS2+), 212
(22%, Ph2CHCHdS+), 211 (33%, Ph2C2SH+), 210 (100%,
Ph2CdCdS+), 208 (10%, Ph2C2S+ - 2H), 180 (6%, Ph2CdCH2+),
178 (18%, Ph2C2+), 167 (24%, Ph2CH+), 166 (15%, Ph2C+), 165
+
Recrystallization of the second fraction from petroleum ether
gave yellow crystals (0.1 g, 17%) of 3,6-bis(dimesitylmethyl-
ene)-1,2,4,5-tetrathiane (4), mp 275-7 °C. IR νmax (Nujol):
1614 cm-1 (CdC); 1H NMR (Cl2CDCDCl2; 400 K) δ: 2.21 (24H,
s), 2.25 (12H, s), 6.79 (8H); 13C NMR (Cl2CDCDCl2; 330 K) δ:
22.2, 22.5, 130.8, 136.6, 138.4, 138.9, 140.4, 141.1 (4 Mes-C +
2CdC). Mass spectrum: m/z (relative abundance, assign-
ment): 652 (4%, M+), 620 (16% (Mes2CdC)2S3+), 588 (5%
(Mes2CdC)2S2+), 358 (3%, Mes2CdCS3+), 326 (3%, Mes2CdS2+),
294 (100%, Mes2CdCdS+), 262 (7%, Mes2CdC+), 246 (28%),
245 (12%), 231 (12%). Microanalysis: C, 73.97; H, 7.72. Calcd
for C40H44S4: C, 73.57; H, 6.79%. X-ray diffraction: Space
group P1h, a ) 13.378(2) Å, b ) 15.227(3) Å, c ) 11.719(2) Å,
R ) 104.44(1)°, â ) 110.02(1)°, γ ) 95.43(1)°, V ) 2129.2(8)
Å3, z ) 2, Fcalc ) 1.02 g cm-3, µ(Mo KR) ) 2.35 cm-1, R ) 0.062,
Rw ) 0.086.13
(52%, Ph2C+ - H), 152 (7%, Ph2 - 2H), 89 (7%, PhC+), 77
(8%, Ph+); HRMS: 454.0880. Calcd for C28H22S3: 454.0884.
Microanalysis: C, 73.92; H, 5.14. Calcd for C28H22S3: C, 73.96;
H, 4.87%.
2,4-Bis(d itip ylm eth ylen e)-1,3-d ith ieta n e (10). A sus-
pension of ditipyl ketene (0.08 g, 0.18 mmol) and P2S5 (0.1 g,
0.45 mmol) in pyridine (5 mL) was refluxed for 15 h. All the
ketene had disappeared. The solution was cooled to 0 °C, a
phosphate buffer (pH 6.8, 10 mL) was added, the mixture was
stirred for 2 h, and the organic phase was extracted with ether
(3 × 20 mL), washed with dilute HCl solution (20 × 3 mL),
saturated aqueous NaHCO3 solution (3 × 20 mL), and water
(30 mL), and dried (MgSO4). The ether was evaporated, and
the orange oil obtained was separated on a preparative TLC
plate using petroleum ether as eluent. Two compounds were
separated. (i) A colorless solid (20 mg, 24%), mp 212-3 °C
(lit.5 212-3 °C), identified as ditipylacetic acid, by its NMR
spectrum. (ii) 2,4-Bis(ditipylmethylene)-1,3-dithietane (33 mg,
40%) which was obtained as an orange oil which could not be
induced to crystallize. IR νmax(Nujol): 1592 cm-1 (CdC). 1H
NMR (CDCl3) δ: 0.87-1.35 (72H), 2.65-3.20 (12H, m), 6.90,
6.97, 7.06 (8H, 3s). Mass spectrum: DCI+ m/z (relative
abundance, assignment): 725 (45%, MH3-Tip+), 521 (23%, MH3
- 2Tip+), 464 (100%, Tip2CdCdSH2+).
The filtrate obtained after separation of 4 showed (by 1H
NMR) both additional amounts of 4 and 3,5-bis(dimesitylm-
ethylene)-1,2,4-trithiane (5). Repeated crystallization from
petroleum ether (60-80 °C) gave a 7:3 5:4 mixture from which
the following spectra for 5 were determined, although further
enrichment by 5 was not obtained. 1H NMR (Cl2CDCDCl2;
400 K) δ: 2.222 (12H, s), 2.228 (12H, s), 2.235 (6H, s), 2.271
(6H, s), 6.765 (4H, s), 6.824 (4H, s). Mass spectrum: m/z
(relative abundance, assignment): 620 (17%, M+), 588 (26%,
(Mes2CdC)2S2+), 294 (100%, Mes2CdCdS+), 279 (15%), 262
(47%, Mes2CdC+), 246 (57%), 245 (25%), 231 (25%).
Dim esityl Th iok eten e (2). The blue solution was char-
acterized by the following spectra as containing dimesityl
thioketene (2): UV λmax (CH2Cl2): 582 nm. IR νmax(Nujol):
1608 (CdC), 1742 cm-1 (CdCdS). 1H NMR (CDCl3) δ: 2.16
(12H, s), 2.27 (6H, s), 6.89 (4H, s). 13C NMR (CDCl3) δ: 20.7,
21.0, 86.3 (CdCdS), 126.1, 129.8, 137.2, 137.7, 257.0 (CdCdS).
Mass spectrum: m/z (relative abundance, assignment): 294
(100%, M+), 279 (12%, M+ - Me), 246 (7%, M+ - SH - Me),
233 (10%).
Ack n ow led gm en t. This work was supported by the
Israel Science Foundation administered by the Israel
Academy for Sciences and Humanities to which we are
indebted. We are grateful to Prof. Silvio Biali for
valuable discussions.
Su p p or tin g In for m a tion Ava ila ble: ORTEP drawings
of 3 and 4 and details of data acquisition (6 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
3,5-Bis(d ip h en ylm et h ylen e)-1,2,4-t r it h ia n e (7) a n d
3-(D i p h e n y lm e t h y le n e )-5-(d i p h e n y lm e t h y l)-1,2,4-
tr ith ia n e (8). A suspension containing diphenylacetyl chlo-
J O960911K