The thiosulfinyl group serves as a stereogenic center and shows diamagnetic anisotropy similar to that of the sulfinyl group

Article abstract of DOI:10.1021/ja035892s

The pseudotetrahedral geometry of the thiosulfinyl group (>SS) in the thionosulfite which was prepared by treatment of cis-3,4-di-tert-butylthiolane-3,4-diol with 1,1'-thiobisbenzimidazole is stable enough to allow the isolation of two diastereomers. X-ray crystallographic analysis revealed that the configuration of the >S S group of the major diastereomer (45% isolated yield) is syn to the thiolane ring, while that of the minor diastereomer (10% isolated yield) is anti to the thiolane ring. ¹H NMR spectrum analysis clarified that the shielding and deshielding zones of the >SS group are similar to those >SS group; Chemical properties of the > 5 S group toward thermolysis, hydrolysis, and oxidation were clarified. The absorptions or bands in the UV/ vis IR and Raman spectra, which originate from the > SSgroup, were assigned on the basis of the B3LYP/ 6-31G* level calculations. Copyright

Full text of DOI:10.1021/ja035892s

Published on Web 07/04/2003
The Thiosulfinyl Group Serves as a Stereogenic Center and Shows
Diamagnetic Anisotropy Similar to That of the Sulfinyl Group
Sanae Tanaka, Yoshiaki Sugihara, Akira Sakamoto, Akihiko Ishii, and Juzo Nakayama*
Department of Chemistry, Faculty of Science, Saitama UniVersity, Sakura-ku, Saitama, Saitama 338-8570, Japan
Received May 1, 2003; E-mail: nakaj@post.saitama-u.ac.jp
The chemistry of compounds having the general structure of
R2SdS has attracted much attention because of the expected
intriguing properties of the thiosulfinyl group.1 Although thio-
sulfoxides (R ) alkyl or aryl for R2SdS) have long been proposed
as transient intermediates, they still elude even detection by
spectroscopies.1 On the other hand, thionosulfites [(RO)2SdS] are
more stable than thiosulfoxides because of electronic stabilization
by the oxygen atoms.2,3 Thus, Harpp et al. succeeded in the synthesis
and X-ray single-crystal structure analysis of the thionosulfite 1.3a
Here, we report the synthesis, X-ray crystallographic analysis, and
chemical and spectroscopic properties of a pair of isolable,
diastereomeric thionosulfites 4a and 4b.
and are comparable with that of 1 (1.901(2) Å). The two tert-butyl
groups of 4a and 4b are twisted with dihedral angles of 43.7(2)°
and 38.0(3)°, respectively, to reduce the steric repulsion. The
optimized molecular structures of 4a and 4b (Figure 3), predicted
by density functional theory (DFT) calculations (B3LYP/6-31G*
level), are in good agreement with the experimental structures.9
Initially, we obtained sulfite 5 as a mixture of diastereomers 5a
and 5b,4 as the precursor to 4, by condensation of cis-3,4-di-tert-
butylthiolane-3,4-diol (2)5 with SOCl2.6 Disappointingly, however,
attempted conversion of 5 to 4 by treatment with Lawesson’s
reagent was unsuccessful. We then applied the Harpp method to
obtain 4 from 2 directly.3a Thus, 2 was treated with 4 molar amounts
of 1,1′-thiobisbenzimidazole (3)7 in MeCN for 72 h at room tem-
perature. The expected reaction took place to give a diastereomeric
mixture of thionosulfites 4a and 4b in the ratio 82:18 (Scheme 1).
Separation of the diastereomers could be satisfactorily performed
by HPLC to afford 4a and 4b in 45% and 10% isolated yields,
respectively.8
Figure 1. Molecular structures of 4a and 4b.
Figure 2. Bond angles and bond lengths around the SdS group of 4a and
the SdO group of 5a.
Scheme 1. Synthesis of 4a and 4b
Figure 3. Optimized structures of 4a and 4b.
No thermal isomerization was observed between 4a and 4b, even
when each isomer was heated at 120 °C in toluene-d8, indicating
that the pseudotetrahedral geometry around the thiosulfinyl group
is rigid enough to serve as a stereogenic center.10 However,
decomposition of 4 took place instead; 4a gave 6, 7,5 and 4a in the
ratio 39:13:48 after heating for 96 h, while 4b decomposed
completely to produce 6 and 7 in the ratio 6:94 after heating for
24 h (Scheme 2). The experimental ratio of 4a and 4b, 82:18, is
therefore kinetically controlled. The DFT calculations predicted that
4a is more stable than 4b by 1.69 kcal/mol. 4a and 4b are
susceptible to alkaline hydrolysis. Thus, 4a was hydrolyzed to give
the diol 2 in 93% yield in the presence of NaHCO3 in a 1:1 mixture
The stereochemistry of 4a and 4b was established by X-ray
crystallographic analyses. Molecular structures of 4a and 4b are
shown in Figure 1. Figure 2 shows the bond angles and bond lengths
around the SdS group of 4a and the SdO group of 5a.6 The sum
of the two O-S-S bond angles and the one O-S-O bond angle
of 4a is 311.5° and comparable to that of 5a (309.5°), while it is
smaller than the sum of the three H-C-H bond angles of methane
(328.5°). Thus, the pseudotetrahedral geometry of the thiosulfinyl
sulfur atom of 4a is deeper than that of methane. Incidentally, the
sum of the corresponding angles for 4b is 310.4°. The SdS bond
lengths of 4a and 4b are 1.9154(6) and 1.8964(13) Å, respectively,
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C O M M U N I C A T I O N S
of H2O and THF, whereas it remained unchanged in the absence
of NaHCO3 for several days. Oxidation of 4a with 1.1 molar
amounts of MCPBA gave 8 and 9 in the ratio 94:6 (8 was isolated
in 77% yield), while oxidation with 3.3 molar amounts of MCPBA
furnished 9 and 10 in the ratio 90:10. The structure of 8 was
determined by X-ray crystallographic analysis, while 9 and 10
agreed with the authentic samples prepared by oxidation of 5b.6
These results reveal that the SdS group is more resistant toward
oxidation than the sulfide sulfur atom, and interestingly the SdS
group is converted to the SdO group with inversion of the
configuration.
and the medium-sized Raman band mainly due to the contribution
of the SdS stretching vibration at 639 cm-1. Therefore, these strong
infrared and Raman bands at about 650 cm-1 can be assigned to
the SdS stretching vibration. Similarly, the strong Raman band
assignable to the SdS stretching vibration was observed at 666
cm-1 for 4b. The corresponding infrared absorption band was
observed at 665 cm-1 as a shoulder of the strong 670 cm-1 band.
The DFT calculations of 4b predicted the medium-sized infrared
absorption band and the strong Raman band at 647 cm-1, which
are assigned to the SdS stretching vibration. The observed SdS
stretching infrared and Raman bands at about 650 cm-1 for 4a and
at about 666 cm-1 for 4b are in good agreement with the observed
Scheme 2. Reactions of 4a
infrared and Raman bands for 1 at about 650 cm-1 3b
. The UV/vis
spectrum of 4a showed the two absorption maxima at 253 (ꢀ )
2790) and 324 (142) nm, while the time-dependent DFT calculations
predicted the appearance of two strong absorptions at 249 and 263
nm and a weak absorption at 361 nm. Similarly, 4b showed the
two absorption maxima at 245 (ꢀ ) 3060) and 313 (203) nm,
although the calculation predicted the appearance of the two strong
absorptions at 241 and 262 nm and the weak absorption at 351
nm. Also for 1, the strong absorption at 250 nm and the weak
absorption at 311 nm were reported.3b
Supporting Information Available: Procedures for the preparation
of 4 and other reactions, plausible mechanisms of the formation of 4
and other reactions, X-ray crystallographic data of 4a, 4b, and 8, and
calculated structural and spectral data of 4a and 4b (PDF, CIF, TIF).
This material is available free of charge via the Internet at http://
pubs.acs.org.
References
As to the diamagnetic anisotropy of the SdS group, no data
information has been available. Figure 4 shows the chemical shift
data of the methylene protons of 4a and 4b and those of 5a and
5b; each methylene proton appeared as a doublet with J ) 13-14
Hz due to geminal coupling.6 The assignments were based on NOE
experiments. The inspection of these data reveals that the shielding
and deshielding zones of the SdS group are similar to those of the
SdO group. Therefore, the shielding and deshielding zones of the
SdS group are assigned as depicted in Figure 5 by analogy of the
well-documented corresponding zones of the SdO group.11
(1) For a leading review, see: Kutney, G. W.; Turnbull, K. Chem. ReV. 1982,
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(8) The use of other solvents, such as CH2Cl2, C6H6, THF, and DMSO,
resulted either in no reaction or in the formation of 4a and 4b in decreased
yields. The use of 1,1′-dithiobisbenzimidazole gave 4a and 4b in very
low yield.
(9) (a) The calculations have been performed by using the Gaussian 98
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Figure 4. Chemical shift data of 4a,b and 5a,b.
(10) The inversion energy of (MeO)2SdS was calculated to be 32.3 kcal/mol
(see Supporting Information of ref 3b).
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Figure 5. Shielding (+) and deshielding (-) zones of the SdS group.
The strong infrared absorption and Raman bands were observed
for 4a at 653 and 650 cm-1, respectively. The DFT calculations of
4a predicted the appearance of the strong infrared absorption band
JA035892S
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