Structure elucidation of 6-t-butyl-6-phenylpentathiane monoxides by X-ray crystallography and DFT calculations

Article abstract of DOI:10.1246/bcsj.75.319

6-t-Butyl-6-phenylpentathiane was oxidized with trifluoroperacetic acid (CF₃CO₃H) or dimethyldioxirane (DMD) at -20°C. Oxidation with CF₃CO₃H yielded pentathiane 3-oxide as the main product, whereas that of DMD gave 1- and 3-oxides. The structures of 1- and 3-oxides were finally determined by X-ray crystallographic analysis. DFT calculations of the NMR chemical shifts were performed on the chair and twist forms of the pentathiane and sixteen isomers of the monoxides with the GIAO method at the B3LYP/6-31G* level. The calculated chemical shifts were verified to be in practical agreement with the experimental data of the pentathiane and the isolated 1- and 3-oxides.

Full text of DOI:10.1246/bcsj.75.319

c. Jpn.
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 319–328 (2002)
319
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Structure Elucidation of 6-t-Butyl-6-phenylpentathiane Monoxides by
X-ray Crystallography and DFT Calculations
Structure Elucidation of Pentathiane Oxides
A. Ishii et al.
Akihiko Ishii,* Hideaki Oshida, and Juzo Nakayama*
02
9
8
Department of Chemistry, Faculty of Science, Saitama University, Saitama, Saitama 338-8570
(Received August 16, 2001)
SJA8
09-2673
277
6-t-Butyl-6-phenylpentathiane was oxidized with trifluoroperacetic acid (CF3CO3H) or dimethyldioxirane (DMD)
at −20 °C. Oxidation with CF3CO3H yielded pentathiane 3-oxide as the main product, whereas that of DMD gave 1-
and 3-oxides. The structures of 1- and 3-oxides were finally determined by X-ray crystallographic analysis. DFT calcu-
lations of the NMR chemical shifts were performed on the chair and twist forms of the pentathiane and sixteen isomers
of the monoxides with the GIAO method at the B3LYP/6-31G* level. The calculated chemical shifts were verified to be
in practical agreement with the experimental data of the pentathiane and the isolated 1- and 3-oxides.
01
01
The oxidation of cyclic polysulfides has been drawing much
attention not only due to the fundamental interest in the regio-
and stereochemistries1–8 compared with acyclic tri- and
tetrasulfides9,10 but also for the potential of the resulting oxides
as precursors of reactive sulfur species.2,7,8,11 Recently, we re-
ported on the oxidation reactions of tetrathiolanes and pen-
tathianes; the oxidation of 5-(1-adamantyl)-5-t-butyltetrathi-
olane (1) with dimethyldioxirane (DMD) took place first at the
2-position to give the 2-oxide 2, and then at the 3-position to
give the 2,3-dioxide 3.7 Decomposition of the 2,3-dioxide 3 in
solution at temperatures higher than −10 °C gives rise to the
dithiirane 1-oxide 4 and S2O (Scheme 1). On the other hand,
and 7 were prepared by a method which we reported previous-
ly,12 or by a reaction of the corresponding thioketones 8 with
elemental sulfur in 1,3-dimethyl-2,4-imidazolidinone (DMI) at
room temperature (Eq. 2). In the latter reaction, 5 and 7 were
obtained in improved yields along with hexathiepanes 9 and
1,2,4-trithiolanes 10. The reaction of 8 with elemental sulfur
took place in DMF and DMSO similarly, and did not occur in
nonpolar solvents, such as benzene, CHCl3, or CS2.
(2)
An X-ray crystallographic analysis of 5 revealed that it takes
a chair conformation in the solid state similarly to the reported
pentathianes,13 where the phenyl and t-butyl groups possess
axial and equatorial orientations, respectively (Fig. 1). A dy-
namic 1H NMR spectroscopic analysis showed that 5 takes the
chair conformation in solution as well.8 The cis-substituted
structure of 1,2,4-trithiolane 10a was also determined by X-ray
crystallography (Fig. 2). This contrasts with a recent report
that both the cis and trans isomers of 3,5-diaryl-3,5-di-t-butyl-
1,2,4-trithiolanes were obtained by a reaction of the corre-
sponding ketones with Lawesson’s reagent in refluxing tolu-
ene.14
Scheme 1.
the oxidation of 6-t-butyl-6-phenylpentathiane (5) with
CF3CO3H yielded mainly 3-oxide 6 (Eq. 1).8 We also prelimi-
narily reported that 3-oxide 6 takes a twist conformation both
in the solid state and in solution. Here, we report on details of
the structure elucidation of pentathiane monoxides formed by
the oxidation of the pentathiane 5 with CF3CO3H and DMD
based on X-ray crystallography and density functional theory
(DFT) calculations.
Oxidation of Pentathianes 5 and 7 with CF3CO3H and
DMD. (i) CF3CO3H. Pentathiane 5 was oxidized with 2 mo-
lar amounts of CF3CO3H in CH2Cl2 at −20 °C to give monox-
ide 6 in 25% isolated yield.8 When 5 was oxidized with 1.4
(1)
1
molar amounts of CF3CO3H, the H NMR spectrum of the
mixture showed the formation of 6 in 41% yield along with un-
reacted 5 (30%), thioketone S-oxide 11a (1%), and several un-
Results and Discussion
Improved Preparation of Pentathianes. Pentathianes 5

320 Bull. Chem. Soc. Jpn., 75, No. 2 (2002)
Structure Elucidation of Pentathiane Oxides
Fig. 3. ORTEP drawing of the 3-oxide 6 (50% ellipsoidal
probability). Selected bond lengths (Å) and angles (deg.):
C1–S1, 1.845(3); S1–S2, 2.008(1); S2–S3, 2.182(1); S3–
S4, 2.157(2); S4–S5, 1.999(1); S5–C1, 1.887(3); C1–C2,
1.525(4); C1–C8, 1.585(4); S3–O1, 1.432(4); S2–S1–C1,
102.8(2); S1–S2–S3, 104.7(1); S2–S3–S4, 96.9(1); S2–
S3–O1, 113.2(2); S4–S3–O1, 102.7(2); S3–S4–S5,
103.8(1); S4–S5–C1, 105.7(2), S1–C1–S5, 107.6(2), C2–
C1–C8, 113.3(3).
Fig. 1. ORTEP drawing of 6-t-butyl-6-phenylpentathiane (5)
(50% ellipsoidal probability). Selected bond lengths (Å)
and angles (deg): C1–S1, 1.856(3); S1–S2, 2.034(2); S2–
S3, 2.061(2); S3–S4, 2.057(2); S4–S5, 2.037(2); S5–C1,
1.842(3); C1–C2, 1.525(4); C1–C8, 1.598(4); S2–S1–C1,
103.7(1); S1–S2–S3, 103.9(1); S2–S3–S4, 99.4(1); S3–
S4–S5, 103.1(1); S4–S5–C1, 104.5(1), S1–C1–S5,
108.3(2), C2–C1–C8, 112.6(2).
tathiane 5, which takes a chair conformation. It was reported
that S6O takes a chair conformation with the oxygen atom oc-
cupying the axial position.15
(3)
(ii) DMD. The scope of the oxidation of 5 with DMD was
quite different from that with CF3CO3H. After pentathiane 5
was treated with an equimolar amount of DMD in CH2Cl2 at
−20 °C, the mixture was warmed to room temperature. The fi-
nal products were dithiirane 1-oxide 1211 (25%), (E)- and (Z)-
thioketone S-oxides 11a (17%) and 11b (9%), 5 (13%),
hexathiepane 9a (8%), ketone 13 (12%), 3-oxide 6 (9%), 1,2,4-
trithiolane 10a (1%) (Eq. 4). The yields were estimated based
on the 1H NMR integral ratio of the mixture.
Fig. 2. ORTEP drawing of cis-3,5-di-t-butyl-3,5-diphenyl-
1,2,4-trithiolane (10a) (50% ellipsoidal probability). Se-
lected bond lengths (Å) and angles (deg): S1–S1, 2.024(2);
S2–C3, 1.831(4); C3–S4, 1.845(4); S4–C5, 1.846(4); C5–
S1, 1.863(4); C3–C20, 1.540(5); C3–C16, 1.589(6); C5–
C10, 1.530(6); C5–C6, 1.588(6); S1–S2–C3, 94.6(2); S2–
C3–S4, 104.1(2); C3–S4–C5, 104.0(2); S4–C5–S1,
106.8(2); C5–S1–S2, 100.3(2); C20–C3–C16, 112.0(3);
C10–C5–C6, 111.7(4).
identified compounds. This observation indicates that 6 was
formed in at least 58% yield, based on the consumed pen-
tathiane 5 (Eq. 3).
The structure of 6 was finally established by X-ray crystal-
lography to be the 3-oxide (Fig. 3).8 The 3-oxide 6 takes a
twist conformation in the solid state with the oxygen atom cis
to the t-butyl group, which is in contrast with the starting pen-
(4)

A. Ishii et al.
Bull. Chem. Soc. Jpn., 75, No. 2 (2002) 321
Scheme 2.
min, and again cooled to −20 °C. The main signals due to 15a
then became weak and, instead, signals due to an alternative
intermediate (16a) became strong at δ = 1.13 (t-Bu) and 7.03
1
(ortho-phenyl) in the H NMR spectrum (Fig. 4b) and δ =
74.6 in the 13C NMR spectrum. Leaving the mixture to stand
at room temperature for 1 week resulted in a complete disap-
pearance of the signals due to the two intermediates, 15a and
16a (Fig. 4c). These observations suggest that 15a is a kinetic
product, and that it isomerizes to 16a at room temperature
(Scheme 2).
The NMR data mentioned above were not sufficient to de-
termine the structures of 15a and 16a unambiguously. Since
we could not obtain single crystals of 15a or 16a suitable for
X-ray crystallography in spite of much effort, we next exam-
ined the oxidation of 6-(1-adamantyl)-6-phenylpentathiane (7)
with DMD. The oxidation proceeded in a course quite similar
to that for 5 to give monoxide 15b and 16b, corresponding to
15a and 16a, respectively. In the 13C NMR spectrum, the pen-
tathiane carbons due to 15b and 16b were observed at δ =
90.5 and 76.2, respectively (Scheme 2). Single crystals of a
Fig. 4. 1H NMR spectra of the reaction mixture of pen-
tathiane 5 and DMD: (a) at −20 °C, (b) −20 °C → r.t. (15
min) → −20 °C, (c) after standing at r.t. for 1 week.
1
The oxidation of 5 with DMD was followed by H and 13C
NMR spectroscopies to detect any intermediates. After a treat-
ment with DMD at −20 °C for 1 h, volatile materials, includ-
ing the unreacted DMD, were removed in vacuo below −20
°C, and the residue was subjected to NMR spectroscopy (Fig.
4). In the 1H NMR measured at −20 °C (Fig. 4a), new signals
due to t-butyl groups were observed at δ = 1.31 (45%, 15a),
1.19 (17%), and 1.13 (2%, 16a), along with known signals due
to 3-oxide 6 (9%), dithiirane 1-oxide 12, and sulfines 11a and
11b. In the aromatic region, a characteristic doublet, isolated
from the other signals, appeared at δ = 8.16 (d, J = 6.3 Hz,
ortho-phenyl). Based on the intensity, the doublet seemed to
be assigned to 15a. In the 13C NMR, a pentathiane carbon due
to 15a appeared at δ = 89.0. The mixture was warmed to
room temperature, left standing at room temperature for 15
Fig. 5. Molecular structure of 6-(1-adamantyl)-6-phenylpen-
tathiane 1-oxide (15b).
Chart 1.

322 Bull. Chem. Soc. Jpn., 75, No. 2 (2002)
Structure Elucidation of Pentathiane Oxides
Fig. 6. ∆E (kcal mol−1) and calculated down-field shifts [∆δC (calcd) = 106.4 (chair-5) − σ ] of pentathiane carbons. Experimental
values [δC (exp.)] are also given.
kinetic product 15b were obtained by repeating low-tempera-
ture recrystallization and, despite the low quality of the crys-
tals, an X-ray crystallographic analysis exhibited undoubtedly
that 15b is a 1-oxide taking a chair conformation with the oxy-
gen atom sharing an equatorial position (Fig. 5). We assigned
the structure of 16 as the epimer of 15 (Chart 1) based on the
NMR behavior mentioned above and DFT calculations of the
NMR chemical shifts, as discussed later.
possible regio- and stereoisomers of pentathiane monoxides
and the two conformers of the starting pentathiane 5 at the
B3LYP/6-31G* level.17 There are chair and twist conforma-
tions for each monoxide, and a monoxide has two epimers
with respect to the SwO group. In addition, a twist 1-oxide
(see 1TBu in Fig. 6) and the corresponding twist 5-oxide (see
5TBu in Fig. 6) are diastereomeric to each other because the
twist conformation of pentathiane 5 has two enantiomeric
forms. The same is true of the twist forms of the 2- and 3-ox-
ides. Thus, calculations were performed on sixteen pen-
DFT Calculations. The energies (E) and NMR shielding
constants (σ) by the GIAO method16 were calculated for all

A. Ishii et al.
Bull. Chem. Soc. Jpn., 75, No. 2 (2002) 323
tathiane monoxides.
Relative Energies. Figure 6 summarizes the optimized
structures and the relative energies (∆E) of pentathiane monox-
ides, where we use abbreviations for convenience; for exam-
ple, 1CBu means that it is the 1-oxide taking a chair conforma-
tion with the oxygen atom cis to the t-Bu group, and 1TPh
means 1-oxide, a twist conformation, and the oxygen atom cis
to the phenyl group. Figure 6 also includes the calculated
down-field shifts (∆δC) of pentathiane carbons relative to that
of pentathiane 5.
The most stable form of monoxides is 3CBu, which is 0.3
kcal mol−1 (1 cal = 4.184 J) more stable than 3TBu, corre-
sponding to the actual structure of the 3-oxide.8 The third
monoxide in the energy level is 3TPh, which is the epimer of
3TBu. Another isolable isomer, 1CPh, is the fourth in the en-
ergy level, and is more stable than the epimer 1CBu by 0.5
kcal mol−1. It is worth noting that the twist forms of the mon-
oxides (nTR: n = 1,2,4,5; R = Bu, Ph), except for 3-oxides
(3TBu and 3TPh), are rather less stable than the most stable
3CBu by from 4.9 (2TBu) to 10.6 (1TPh) kcal mol−1. The re-
sults of calculations are approximately in harmony with the
fact that 3TBu and 1CPh are isolable monoxides.
NMR Shielding Constants. Throughout this paper, pen-
tathiane 5 is taken as the reference compound and the follow-
ing criteria are adopted (see Figs. 7a and 7b). In the aliphatic
region of the 1H NMR spectra, the averaged value of calculated
shielding constants (σ given with the ppm unit) of nine hydro-
gens of the t-butyl (σ = 31.17) is put at δ = 1.07, which is the
experimental chemical shift of the t-butyl at 272 K. Similarly,
1
in the aromatic region of the H NMR spectra, the σ value of
the para-hydrogen (σ = 24.91) is put at δ = 7.42, the experi-
mental chemical shift of the corresponding proton at 272 K.
Thus, calculated chemical shifts are given by the following
equations: δH = (31.17 + 1.07) − σ for methyls and δH
(24.91 + 7.42) − σ for aromatic protons (Table 1).
=
First, we inspected the agreement of the calculations with
the experimental values on the chair form of pentathiane 5 and
1
the 3-oxide 6 (3TBu) to support the results of dynamic H
NMR spectroscopies.8 Figures 7a and 7b depict the experi-
mental 1H NMR spectrum (272 K) and the corresponding cal-
culated one of pentathiane 5, respectively. At 183 K in CD2Cl2
(Fig. 7c), three methyls of the t-butyl are divided into two sin-
glets at δ = 0.87 and 1.47 in a ratio of 2:1. The calculated
chemical shift difference between the two (δH = 0.88 and 1.45,
Fig. 7d) is 0.57 ppm, which is very close to the experimental
value of 0.60 ppm (Fig. 7). Meanwhile, the calculated chemi-
cal shifts of three methyls in the twist form of 5 are δH = 0.89,
0.95, and 1.65. Thus, the calculated spectra for the chair form
(Figs. 7b and 7d) are in good agreement with the experimental
spectra (Figs. 7a and 7c).
The calculated spectra for 3-oxide 6 also gave good agree-
ment with the experimental ones. Figures 8a–c show an exper-
imental spectrum of 6 at 285 K in CD2Cl2 and the correspond-
ing calculated spectra of the two forms, 3TBu and 3CBu, re-
spectively. At this temperature, the t-butyl and the phenyl
groups rotate freely. On the other hand, Figs. 8e and 8f are the
calculated spectra of 3TBu and 3CBu, respectively, which cor-
respond to an experimental spectrum at 183 K (Fig. 8d), where
the free rotation of the t-butyl and the phenyl groups is restrict-
Fig. 7. Experimental and calculated NMR spectra of pen-
tathiane 5: (a) 272 K in CD2Cl2; (b) chair-5; (c) 183 K in
CD2Cl2; (d) chair-5.
ed so that the three methyls of the t-butyls and the five phenyl
protons are put independently. In both cases, the calculated
spectra of 3TBu are in much better agreement with the experi-
mental spectra, particularly in the aromatic region, than those
of 3CBu. Some small unidentified signals appear in Figs. 8a
and 8d. These signals (ticked by #) might be assigned to those
due to 3CBu. However, at present, we do not have any other
evidence showing the existence of 3CBu.
Another probe for elucidating the structures of pentathiane
monoxides is by comparing the 13C NMR chemical shifts; spe-

324 Bull. Chem. Soc. Jpn., 75, No. 2 (2002)
Structure Elucidation of Pentathiane Oxides
Table 1. Calculated 1H NMR Chemical Shifts (δH) of Pentathiane 5 and the Monoxides
Compounds Me(1)a) Me(2)a) Me(3)a) tBua) H(1)b) H(2)b) H(3)b) H(4)b) H(5)b)
5(chair)
5(twist)
1CBu
1CPh
1TBu
1TPh
2CBu
2CPh
2TBu
2TPh
3CBu
3CPh
3TBu
3TPh
4TBu
4TPh
5TBu
5TPh
1.45
1.65
1.21
1.43
1.69
1.38
1.54
1.35
1.52
1.45
1.74
1.55
1.73
1.47
1.39
1.14
2.11
1.82
0.88
0.95
1.08
1.24
1.17
1.00
1.05
0.96
1.15
1.11
1.00
0.95
1.10
0.99
0.91
0.78
1.12
0.95
0.88
0.89
0.77
0.96
0.76
0.89
1.03
0.95
0.84
1.00
1.00
0.95
1.13
1.20
1.20
1.25
1.21
0.88
1.07
1.16
1.02
1.21
1.21
1.09
1.21
1.08
1.17
1.18
1.25
1.15
1.32
1.22
1.16
1.06
1.48
1.22
7.68
7.71
6.97
8.42
7.37
8.79
8.03
8.08
7.85
8.05
7.77
7.82
7.84
7.89
7.97
8.02
7.50
7.64
7.51
7.38
7.42
7.55
7.37
7.50
7.46
7.42
7.32
7.27
7.47
7.61
7.43
7.48
7.48
7.49
7.44
7.40
7.42
7.36
7.43
7.47
7.45
7.51
7.37
7.38
7.31
7.27
7.40
7.51
7.37
7.44
7.38
7.44
7.40
7.41
7.51
7.32
7.56
7.46
7.48
7.39
7.40
7.41
7.37
7.25
7.47
7.61
7.31
7.42
7.33
7.41
7.36
7.36
7.68
7.23
7.64
7.29
7.66
7.51
7.50
7.67
7.81
7.19
7.77
7.82
7.18
7.59
7.60
7.75
7.32
7.46
a) δH = (31.17 + 1.07) − σ. b) δH = (24.91 + 7.42) − σ.
cifically, the chemical-shift difference between the pentathiane
carbons of a monoxide and pentathiane 5 (Fig. 6). The calcu-
lated down-field shift (∆δC) between chair-5 and 3TBu (twist-
6), that is, σ 106.4 (chair-5) − σ 89.0 (3TBu), was 17.4 ppm,
which is close to the experimental value of 19.4 ppm [δ 84.7
(6) − δ 65.3 (5)]. Similarly, the ∆δC value for 15a (1CPh) was
21.8 ppm; the deviation from the experimental value is only
1.9 ppm. The values of ∆δC shown in Fig. 6 have a range from
−0.5 ppm (4TBu) to 31.3 ppm (2CBu), indicating that the val-
ues are considerably sensitive to any structure change. Mean-
while, the shielding constant for tetramethylsilane carbon
(TMS) at the same level was 189.7, giving the calculated
chemical shift of the pentathiane carbon of 5 relative to TMS
as δ = 83.3.
For a further verification of the validity of the calculations
for the 13C NMR chemical shifts, we carried out calculations
on 5,5-di-t-butyltetrathiolane 2-oxide 17, 2,3-dioxide 18, and
the tetrathiolane 19 as a reference compound (Fig. 9). These
compounds correspond to 1-adamantyl-t-butyl derivatives 2, 3,
and 1 (Scheme 1).7 The tetrathiolane carbon of 3 (δ = 153.9)
is considerably deshielded, and this large down-field shift is
satisfactorily reproduced. Thus, the calculated ∆δC values
would be valid within a few ppm in a range of 0–40 ppm for
compounds of the same skeleton.
pearing in Fig. 4, was thus assigned to be 1CBu. Figure 10
shows the calculated H NMR spectra of a pair of epimers,
1
1CPh (15a) and 1CBu (16a), below the experimental spec-
trum of the reaction mixture. The calculations well reproduced
the down- and up-field shifts of the H(1) protons of the phenyl
groups of 15a and 16a, respectively, despite a relatively large
deviation of H(1) in 15a. In 13C NMR spectroscopy, the calcu-
lated ∆δC of the pentathiane carbon of 16a was 10.9 ppm,
which is in good agreement with the experimental value of 9.3
ppm [δ = 74.6(exp.)].
In Figs. 4a and 4b, clear but unassigned signals were ob-
served at δ = 1.19 (t-Bu) and 8.04 (d, J = 7.3 Hz, o-Ph).
Monoxides 2CBu and 2CPh might be candidates from the
viewpoint of the calculated chemical shifts (Table 1) and the
relative stabilities shown in Fig. 6. In the 13C NMR spectrum
of the reaction mixture, however, we observed not the pen-
tathiane carbon signal due to 2CBu (∆δC = 31.3 ppm) or
2CPh (∆δC = 0.4 ppm), but a small unknown signal at δ =
103.0 (∆δC = 38.0 ppm). We therefore cannot rule out the
possibility that the signals are due to a higher oxide of pen-
tathiane 5.
Regioselectivity of Oxidation of Pentathiane 5. The ox-
idation of 5 with CF3CO3H took place at the 3-position to give
6 in at least 58% yield; we did not observe the formation of 1-
oxide, 15a or 16a, at all. Because 20% is the statistical per-
centage for one sulfur atom of the pentasulfide linkage of 5,
the oxidation with CF3CO3H is meaningfully regioselective.
Table 2 gives the charge distributions of pentathiane 5, calcu-
The results described above enable us to elucidate the struc-
tures of unisolable isomers of pentathiane monoxides by com-
paring the experimental 1H and 13C NMR data with the calcu-
lated NMR chemical shifts. The structure of 1-oxide 16a, ap-

A. Ishii et al.
Bull. Chem. Soc. Jpn., 75, No. 2 (2002) 325
Fig. 9. Calculated ∆δC values of tetrathiolane carbons of 5,5-
di-t-butyltetrathiolane (19), the 2-oxide (17), and the 2,3-
dioxide (18). Experimental values of 5-(1-adamantyl)-5-t-
butyltetrathiolane (1) and the oxides 2 and 3 are given in
brackets.
Fig. 10. Calculated 1H NMR spectra of 15a (1CPh) and 16a
(1CBu).
31G* and MP2/6-31G* levels. Except for the results of the
CHelpG scheme, the charge distribution is the highest at the 3-
position. Thus, the regioselectivity would be explained in
terms that CF3CO3H attacks the most electron-rich and steri-
cally least hindered 3-position.
On the other hand, oxidation with DMD gave 1-oxide 15a,
mainly in 45% yield, and 3-oxide 6 in 9% yield. The oxidation
in the presence of trifluoroacetic acid did not influence the re-
sults. The yields were roughly estimated from the 1H NMR in-
tegral ratio of the reaction mixture, and we could not determine
whether pentathiane 2-oxides were formed or not. Neverthe-
Fig. 8. Experimental and calculated 1H NMR spectra of pen-
tathiane 3-oxide 6: (a) 285 K in CD2Cl2, (b) 3TBu, (c)
3CBu, (d) 183 K in CD2Cl2, (e) 3TBu, (f) 3CBu.
lated by the Mulliken population analysis, the natural popula-
tion analysis (NPA),18 the Breneman CHelpG scheme,19 and
the Merz–Kollman–Singh scheme (MK)20 at the B3LYP/6-

326 Bull. Chem. Soc. Jpn., 75, No. 2 (2002)
Table 2. Charge Distribution of Pentathiane 5
Structure Elucidation of Pentathiane Oxides
temperature for 6 days in the dark. The mixture was diluted with
ether and hexane, and the precipitates were collected by filtration
and washed with hexane several times to give hexathiepane 9a
(2.91 g, 51%). The filtrate was washed with water, dried over
MgSO4, and evaporated to dryness. The residue was subjected to
column chromatography (hexane) to give a mixture of pentathiane
5 and 9a and a mixture of 8a and 1,2,4-trithiolane 10a. The mix-
ture of 5 and 9a was separated by HPLC (hexane) to give 512 (599
mg, 11%) and 9a12 (200 mg, 3%). The mixture of 8a and 10a was
subjected to GPC to give 10a (294 mg, 9%).
Methods
S-1
S-2
S-3
C-1
(S-5)
(S-4)
B3LYP/6-31G*
MP2/6-31G*
Mulliken 0.034 −0.017 −0.021 −0.350
NPA 0.116 −0.005 −0.015 −0.291
CHelpG −0.076 −0.020 0.008 −0.380
MKS 0.029 0.014 0.007 −1.189
Mulliken 0.052 −0.007 −0.010 −0.373
NPA 0.134 0.004 −0.005 −0.335
CHelpG −0.082 −0.013 0.011 −0.454
MKS 0.072 0.020 0.019 −1.522
6-t-Butyl-6-phenylpentathiane (5). Crystal data: C11H14S5,
Mw 360.5, colorless prisms, 0.40 × 0.28 × 0.20 mm3, orthorhom-
bic, space group P21nb, a = 12.363(3), b = 16.838(4), c =
6.607(1) Å, V = 1375.3(5) Å3, ρcalcd = 1.480 g cm−3, Z = 4,
µ(Cu-Kα) = 74.364 mm−1. Mac Science MXC3KHF diffracto-
meter with graphite-monochromated Cu-Kα radiation (λ =
1.54178 Å), θ/2θ scans method in the range 3° < 2θ < 140° (0 <
h < 15, 0 < k < 20, −8 < l < 0), 1594 reflections measured,
1364 independent reflections. The structure was solved by direct
methods using SIR9223 in the CRYSTAN GM program system,
and refined by a full-matrix least-squares method using all (1364)
reflections for 191 parameters. An absorption correction was
made by the psi-scan method. The non-hydrogen atoms were re-
fined anisotropically. The final R (Rw) = 0.0350 (0.0470) and
GOF = 1.907; max/min residual electron density = 0.23/−0.45 e
less, oxidation with DMD is regarded to be much less regiose-
lective than that with CF3CO3H, which might be ascribed to
the high electrophilic reactivity of DMD.21
Conclusion
We determined the structures of oxidation products of pen-
tathianes 5 and 7 by a combination of X-ray crystallography,
experimental NMR spectroscopies, and calculations of the
NMR chemical shifts. We verified that the calculations on ox-
ides of cyclic polysulfides reproduced the experimental data
within an acceptable error, even at a relatively inexpensive lev-
el. Therefore, the calculations would be important for sulfur
Å−3
cis-3,5-Di-t-butyl-3,5-diphenyl-1,2,4-trithiolane
Colorless crystals, mp 131–132 °C decomp (hexane/CH2Cl2); H
NMR: δ 1.22 (s, 18H), 6.99–7.01 (m, 6H), 7.51–7.54 (m, 4H); 13
.
(10a).
1
chemistry in particular because it is not easy to measure the 33
NMR spectra in the structure elucidation process.
S
C
NMR: δ 28.8 (CH3), 41.8 (C), 98.0 (C), 125.9 (CH), 126.4 (CH),
130.7 (CH), 140.9 (C); MS: m/z 388 (M+). Found: C 68.30, H
7.31%. Calcd for C22H28S3: C 67.99, H 7.26%. Crystal data for
10a: C22H28S3, Mw 388.64, colorless prisms, 0.28 × 0.28 × 0.20
mm3, monoclinic, space group C2/c, a = 31.653(8), b = 6.913(2),
c = 19.274(4) Å, β = 96.25(2)°, V = 4192(2) Å3, ρcalcd = 1.231 g
Experimental
General: Melting points were determined on a Mel-Temp
capillary tube apparatus and are uncorrected. 1H (400 MHz) and
13C NMR (100.6 MHz) spectra were determined on Bruker AM
400 and ARX400 spectrometers at 25 °C using CDCl3 as the sol-
vent, unless otherwise noted. IR spectra were taken on a Hitachi
270-50 spectrometer. Mass spectra were determined on a JEOL
JMS-DX303 spectrometer operating at 70 eV in the EI mode. El-
emental analyses were performed by the Chemical Analysis Cen-
ter of Saitama University.
An acetone solution of dimethyldioxirane (DMD) was prepared
by a reported method,22 and its concentration was determined pri-
or to use by oxidizing thioanisole to its sulfoxide with this solu-
tion.
Column chromatography was performed with silica gel; the
eluent is given in parentheses. Gel permeation chromatography
(GPC) was performed on a Japan Analytical Industry LC-908 us-
ing chloroform as the eluent. High-pressure liquid chromatogra-
phy (HPLC) was performed with a packed SiO2 column, INERT-
SIL PREP-SIL (10 mm i.d. 250 mm, GL Science INC.); the eluent
is given in parentheses.
Computational Methods: All calculations were performed
with Gaussian 98W running on the Windows® operating system.
The structure optimization shown in Fig. 6 took approximately 2
days per monoxide at the B3LYP/6-31G* level with a 1.2 GHz
processor, while the GIAO calculation shown in Table 1 took ap-
proximately 2 hours for each compound.
cm−3, Z = 8, µ(Cu-Kα) = 31.722 mm−1
.
Mac Science
MXC3KHF diffractometer with graphite-monochromated Cu-Kα
radiation (λ = 1.54178 Å), θ/2θ scans method in the range 3° <
2θ < 140° (0 < h < 38, −8 < k < 0, −23 < l < 23), 4553 reflec-
tions measured, 3849 independent reflections. The structure was
solved by direct methods using SIR9223 in the CRYSTAN GM
program system and refined by a full-matrix least-squares method
using 3548 reflections [I ꢀ 2σ(I)] for 338 parameters. An absorp-
tion correction was made by the psi-scan method. The non-hydro-
gen atoms were refined anisotropically. The final R (Rw) = 0.0787
(0.0969) and GOF = 2.748; max/min residual electron density =
0.38/−0.94 e Å−3
.
Preparation of Pentathiane 7. To a mixture of 1-adamantyl
phenyl thioketone (8b) (1.01 g, 3.94 mmol) and elemental sulfur
(1.02 g, 31.8 mmol) was added DMI (5 mL) under argon. The
suspension was stirred at room temperature for 4 days in the dark.
The mixture was diluted with ether, and the precipitates were col-
lected by filtration to give a mixture of pentathiane 7 and sulfur.
The mixture was purified by column chromatography (hexane) to
give 712 (1.13 g, 75%). The filtrate was washed with water, dried
over MgSO4, and evaporated to dryness. The residue was purified
by column chromatography (hexane), HPLC (hexane), and then
recrystallization to give pentathiane 7 (63 mg, 4%), hexathiepane
9b8 (58 mg, 4%), and 1,2,4-trithiolane 10b (40 mg, 4%).
Preparation of Pentathiane 5. To a mixture of t-butyl phen-
yl thioketone (8a) (3.01 g, 16.9 mmol) and elemental sulfur (1.66
g, 51.8 mmol) was added 1,3-dimethyl-2,4-imidazolidinone
(DMI) (10 mL) under argon. The suspension was stirred at room
cis-3,5-Di(1-adamantyl)-3,5-diphenyl-1,2,4-trithiolane
(10b). Colorless crystals, mp 217–218 °C decomp (hexane/
1
CH2Cl2); H NMR: δ 1.54–1.62 (m, 12H), 1.82–2.01 (m, 12H),

A. Ishii et al.
Bull. Chem. Soc. Jpn., 75, No. 2 (2002) 327
1.98 (br s, 6H), 6.94–6.98 (m, 6H), 7.44–7.46 (m, 4H); 13C NMR:
δ 28.9, 36.5, 39.8, 43.0, 98.2, 125.7, 126.3, 131.2, 140.0; MS: m/z
544 (M+); Found: C 74.67, H 7.39%. Calcd for C34H40S3: C
74.94, H 7.40%.
pentathiane 7 (162 mg, 0.422 mmol) in CH2Cl2 (50 mL) and C6H6
(10 mL) was added DMD (0.088 M, 5.7 mL, 0.50 mmol) at −20
°C under argon. The mixture was stirred for 1 h at −20 °C and
volatile materials were removed in vacuo below −20 °C. The res-
idue was washed with hexane two times and recrystallized from a
mixed solvent of hexane and CH2Cl2 three times to give crude 15b
(96 mg, 57%) contaminated with 7: Mp 78–81 °C decomp. Single
crystals subjected to X-ray crystallography were obtained by fur-
ther recrystallization.
Oxidation of Pentathiane 5 with CF3CO3H. (i) NMR ob-
servation. To a solution of pentathiane 5 (33.3 mg, 0.109 mmol)
and 30% hydrogen peroxide (17 mg, 0.15 mmol) in CH2Cl2 (5
mL) was added trifluoroacetic anhydride (0.08 mL, 0.57 mmol) at
−20 °C under argon. After the mixture was stirred for 20 min at
−20 °C, volatile materials were removed in vacuo below −20 °C.
t-6-(1-Adamantyl)-c-6-phenylpentathiane r-1-Oxide (15b):
Crystal data: C17H20OS5, Mw 400.67, yellow plates, 0.20 × 0.14 ×
0.04 mm3, space group monoclinic, P21/c, a = 18.537(4), b =
6.765(1), c = 23.372(4) Å, β = 144.06(1)°, V = 1720.3(6) Å3, Z
= 4, ρcalcd = 1.547 g cm−3, F(000) = 840, µ(Mo-Kα) = 0.67
1
An H NMR measurement of the residue showed the presence of
3-oxide 6 (41%), pentathiane 5 (30%), and thioketone S-oxide
11a24 (1%).
(ii) Isolation of 3-oxide 6. To a solution of pentathiane 5 (77.5
mg, 0.253 mmol) and 30% hydrogen peroxide (61 mg, 0.52
mmol) in CH2Cl2 (6 mL) was added trifluoroacetic anhydride
(0.11 mL, 0.79 mmol) at −20 °C under argon. The mixture was
stirred for 20 min at −20 °C, and then diluted with aq. Na2SO3.
The mixture was neutralized with aq NaHCO3 and extracted with
CH2Cl2. The extract was washed with water, dried over MgSO4,
and evaporated to dryness. The thus-obtained yellow oil was
washed with hexane two times at −30 °C, and a resulting yellow
solid was recrystallized from a mixed solvent of hexane and
CH2Cl2 to give 3-oxide 6 (20 mg, 25%).
mm−1
. Mac Science DIP3000 diffractometer with a graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å). The data re-
duction was made by the maXus program system. Intensity data
of 3358 unique reflections were collected in the range of −23 ꢁ h
ꢁ 0, −8 ꢁ k ꢁ 0, −17 ꢁ l ꢁ 29. 2329 reflections [I ꢀ 0.5σ(I)]
were used for refinement (208 parameters). Nonhydrogen atoms
were refined anisotropically and hydrogen atoms were placed at
calculated positions. The final R1 = 0.159 (0.213 for all), wR2 =
0.108, and GOF = 2.263; max/min residual electron density =
1.17/−0.88 e Å−3. Although the R values were not satisfactorily
low, the peak height of the oxygen atom (415) was high enough
compared with those of carbon atoms (423–289). We therefore
rule out a possibility that the present structure was one of plural
regio- and stereoisomers forming mixed crystals. Selected bond
lengths (Å) and angles (deg.) under such circumstances for tenta-
tive information: C1–S1, 1.90(2); S1–S2, 2.133(7); S2–S3,
2.015(8); S3–S4, 2.024(8); S4–S5, 2.025(7); S5–C1, 1.86(2); C1–
C2, 1.48(2); C1–C3, 1.57(2); S1–O1, 1.41(2); S2–S1–C1,
101.4(6); S1–S2–S3, 98.9(3); S2–S3–S4, 100.9(4); S2–S1–O1,
103.5(7); O1–S1–C1, 111.8(9); S3–S4–S5, 103.0(3); S4–S5–C1,
105.5(6); S1–C1–S5, 99.8(8); C2–C1–C3, 113.3(14).
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publi-
cation numbers CCDC-165141 (5), CCDC-165142 (10a), CCDC-
165143 (6), and CCDC-165144 (15b). Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: (+44)1223 336-033; e-mail: de-
posit@ccdc.cam.ac.uk). The details of structures have been de-
posited as Document No. 75006 at the Office of the Editor of Bull.
Chem. Soc. Jpn.
c-6-t-Butyl-t-6-phenylpentathiane r-3-Oxide (6).
Yellow
1
crystals, mp 95–96 °C decomp (hexane/CH2Cl2); H NMR (283
K): δ 1.25 (s, 9H), 7.30–7.38 (m, 3H), 7.42–7.50 (m, 2H); 13C
NMR (283 K): δ 27.0, 43.6, 84.7, 127.6, 128.1, 130.9, 136.8; IR
(KBr): 1094 cm−1 (SwO). Found: C 40.08, H 4.31%. Calcd for
C11H14OS5: C 40.96, H, 4.37% (contamination with a small
amount of elemental sulfur caused the unsatisfactory result).
Crystal data for 6: C11H14OS5, Mw 332.53, yellow plates, 0.30 ×
0.16 × 0.06 mm3, monoclinic, space group P21/c, a = 10.290(1),
b = 20.718(2), c = 6.6140(5) Å, β = 93.555(4)°, V = 1407.3(2)
Å3, Z = 4, ρcalcd = 1.522 g cm−3, F(000) = 672, µ(Mo-Kα) =
0.80 mm−1. Mac Science DIP3000 diffractometer with a graph-
ite-monochromated Mo-Kα radiation (λ = 0.71073 Å). The data
reduction was made by the maXus program system. Intensity data
of 2871 unique reflections were collected in the range of 0 ꢁ h
ꢁ13, −26 ꢁ k ꢁ 0, −0 ꢁ l ꢁ 7. 1915 reflections [I ꢀ 2σ(I)]
were used for refinement (210 parameters). The final R1 = 0.049,
wR2 = 0.064, and GOF = 1.585; max/min residual electron densi-
ty = 0.72/−0.38 e Å−3
.
Oxidation of Pentathiane 5 with DMD. (i) Determination
of final products. To a solution of 5 (25.2 mg, 0.0822 mmol) in
CH2Cl2 (5 mL) was added an equimolar amount of DMD (0.10 M,
0.81 mL, 0.081 mmol) (1 M = 1 mol dm−3) at −20 °C under ar-
gon. The mixture was stirred for 2 h at −20 °C and volatile mate-
rials were removed in vacuo below −20 °C. The residue was dis-
solved in CH2Cl2 (5 mL) and the solution was stirred for 3 h at
room temperature. The yields of products were calculated based
This work was supported by a Grant-in-Aid for Scientific
Research (No. 12440174) from the Ministry of Education,
Culture, Sports, Science and Technology. We are grateful to
Dr. Akira Sakamoto (Saitama University) for initiating us into
Gaussian 98.
1
on the integral ratio of the H NMR spectrum of the mixture as
follows: dithiirane 1-oxide 12,11 25%; 11a, 17%; 11b, 9%; 5,
13%, 9a, 8%; 13, 12%; 6, 9%; 10a, 1%.
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