Oxidation of cis- and trans-3,5-Di-tert-butyl-3,5-diphenyl-1,2,4-trithiolanes: Isolation and Properties of the 1-Oxides and the 1,2-Dioxides

Article abstract of DOI:10.1021/jo0354591

Oxidation of trans-3,5-di-tert-butyl-3,5-diphenyl-1,2,4-trithiolane with dimethyldioxirane (DMD) or m-chloroperbenzoic acid (MCPBA) gave two stereoisomeric (1S*,3S*,5S*) - and (1R*,3S* ,5S*)-1-oxides (16 and 17, respectively). Oxidation of 16 with DMD gave the (1S*,2R*,3S*,5S*)-1,2-dioxide (18) and the 1,1-dioxide 19, and that of 17 yielded the (1R*,2R*,3S* ,5S*)-1,2-dioxide (20) mainly along with 18 and 19. The structures of the 1,2-dioxides 18 and 20 were determined by X-ray crystallography. 1,2-Dioxides 18 and 20 isomerized to each other in solution, and the equilibrium constant K (20/18) is 19 in CDCl₃ at 295 K. The kinetic study suggested a biradical mechanism for the isomerization. Isomerization of 16 and 17 to cis-3,5-di-tert-butyl-1,2,4-trithiolane 1-oxides by treatment with Me ₃O⁺BF₄^- is also described.

Full text of DOI:10.1021/jo0354591

Oxid a tion of cis- a n d
tr a n s-3,5-Di-ter t-bu tyl-3,5-d ip h en yl-1,2,4-tr ith iola n es: Isola tion a n d
P r op er ties of th e 1-Oxid es a n d th e 1,2-Dioxid es
Hideaki Oshida, Akihiko Ishii,* and J uzo Nakayama*
Department of Chemistry, Faculty of Science, Saitama University, Sakura-ku, Saitama 338-8570, J apan
ishiiaki@chem.saitama-u.ac.jp
Received October 4, 2003
Oxidation of trans-3,5-di-tert-butyl-3,5-diphenyl-1,2,4-trithiolane with dimethyldioxirane (DMD)
or m-chloroperbenzoic acid (MCPBA) gave two stereoisomeric (1S*,3S*,5S*)- and (1R*,3S*,5S*)-
1-oxides (16 and 17, respectively). Oxidation of 16 with DMD gave the (1S*,2R*,3S*,5S*)-1,2-dioxide
(18) and the 1,1-dioxide 19, and that of 17 yielded the (1R*,2R*,3S*,5S*)-1,2-dioxide (20) mainly
along with 18 and 19. The structures of the 1,2-dioxides 18 and 20 were determined by X-ray
crystallography. 1,2-Dioxides 18 and 20 isomerized to each other in solution, and the equilibrium
constant K (20/18) is 19 in CDCl3 at 295 K. The kinetic study suggested a biradical mechanism for
the isomerization. Isomerization of 16 and 17 to cis-3,5-di-tert-butyl-1,2,4-trithiolane 1-oxides by
treatment with Me3O+BF4 is also described.
-
CHART 1
In tr od u ction
The chemistry of vic-disulfoxides [RS(O)S(O)R′] has
been drawing much attention.1-6 Recently, we succeeded
in the first isolation and structure determination of
compounds bearing a -S(O)-S(O)- linkage by the oxida-
tion of tetrathiolanes 1 with an acetone solution of
dimethyldioxirane (DMD) (eq 1).7 The two oxygen atoms
of the tetrathiolane 2,3-dioxides 2 take the diaxial
orientations characteristically, where the anomeric effect
by adjacent sulfur atoms7b,8,9 at both ends seems to
contribute to the stability of 2. Naturally, our attention
was turned to the synthesis of vic-disulfoxides not having
such a special stabilization effect, that is, those which
have a C-S(O)-S(O)-C linkage. The above-mentioned
study, as well as the study by Folkins and Harpp on the
oxidation of 4,5-dithiabicyclo[3.2.1]octanes 3 (Chart 1),3
suggests that vic-disulfoxides derived from cyclic disul-
fides possess fair stability compared with those derived
from acyclic disulfides,4 thus leading us to investigate the
oxidation of 1,2,4-trithiolanes.10 In our recent com-
munication,11 we reported that the oxidation of tetra-
substituted 1,2,4-trithiolane cis-4 with DMD furnished
the two diastereomeric 1-oxides and the desired 1,2-
(1) For reviews, see: (a) Freeman, F. Chem. Rev. 1984, 84, 117-
135. (b) Lacombe, S. In Reviews on Heteroatom Chemistry; Oae, S.,
Ed.; Myu: Tokyo, 1999; Vol. 21, pp 1-41.
(2) For recent papers on vic-disulfoxides, see: (a) Freeman, F.; Lee,
C. J . Org. Chem. 1988, 53, 1263-1266. (b) Block, E.; Bayer, T. J . Am.
Chem. Soc. 1990, 112, 4584-4585. (c) Gu, D.; Harpp, D. N. Tetrahedron
Lett. 1993, 34, 67-70. (d) Clennan, E. L.; Zhang, H. J . Org. Chem.
1994, 59, 7952-7954. (e) Nakayama, J .; Mizumura, A.; Yokomori, Y.;
Krebs, A.; Schu¨tz, K. Tetrahedron Lett. 1995, 36, 8583-8586. (f)
Clennan, E. L.; Stensaas, K. L. J . Org. Chem. 1996, 61, 7911-7917
and references therein.
(8) Harpp, D. N.; Gleason, J . G. J . Org. Chem. 1971, 36, 1314-1316.
(9) (a) J uaristi, E.; Ordon˜ez, M. In Organosulfur Chemistry; Page,
P., Ed.; Academic Press: San Diego, CA, 1998; Vol. 2, Chapter 3. (b)
Kleinpeter, E. In Conformational Behavior of Six-Membered Rings;
J uaristi, E., Ed.; VCH Publishers: New York, 1995; Chapter 6.
(10) For oxidation of 1,2,4-trithiolanes, see: (a) Wratten, S. J .;
Faulkner, D. J . J . Org. Chem. 1976, 41, 2465-2467. (b) Weigand, W.;
Wu¨nsch, R.; Polbrn, K.; Mloston, G. Z. Anorg. Allg. Chem. 2001, 627,
1518-1522. (c) Bra¨utigam, S.; Wu¨nsch, R.; Weigand, W.; Majchrzak,
A.; Mloston, G. Book of Abstracts, The Sixth International Conference
on Heteroatom Chemistry (ICHAC-6), Lodz, Poland, 2001; S4-O-2, p
108. (d) Majchrzak, A.; Mloston, G.; Ostycharz, E.; Skarzewski, J .;
Weigand, W. Book of Abstracts, The Sixth International Conference
on Heteroatom Chemistry (ICHAC-6), Lodz, Poland, 2001; P-25, p 153.
(11) Oshida, H.; Ishii, A.; Nakayama, J . Tetrahedron Lett. 2002, 43,
5033-5037.
(3) Folkins, P. L.; Harpp, D. N. J . Am. Chem. Soc. 1991, 113, 8998-
9000.
(4) (a) Freeman, F.; Angeletakis, C. N. J . Am. Chem. Soc. 1981, 103,
6232-6235. (b) Freeman, F.; Angeletakis, C. N. J . Am. Chem. Soc.
1982, 104, 5766-5774. (c) Freeman, F.; Angeletakis, C. N. J . Am.
Chem. Soc. 1983, 105, 4039-4049.
(5) (a) Lacombe, S.; Loudet, M.; Dargelos, A.; Robert-Banchereau,
E. J . Org. Chem. 1998, 63, 2281-2291. (b) Gregory, D. D.; J enks, W.
S. J . Phys. Chem. A 2003, 107, 3414-3423.
(6) (a) Steudel, R.; Drozdova, Y. Chem.sEur. J . 1996, 2, 1060-1067.
(b) Clenann, E. L.; Stensaas, K. L. Org. Prep. Proced. Int. 1998, 30,
551-600.
(7) (a) Ishii, A.; Nakabayashi, M.; Nakayama, J . J . Am. Chem. Soc.
1999, 121, 7959-7960. (b) Ishii, A.; Nakabayashi, M.; J in, Y.-N.;
Nakayama, J . J . Organomet. Chem. 2000, 611, 127-135.
10.1021/jo0354591 CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/03/2004
J . Org. Chem. 2004, 69, 1695-1703
1695

Oshida et al.
dioxide depending on the amount of DMD. In this paper,
after a short summary of the oxidation of cis-4, we report
the oxidation of tr a n s-4 that yields the two isomeric
1-oxides and the two isomeric 1,2-dioxides and the
properties of these oxides.
that in 6 [2.1133(9) Å], which is the result of an anomeric
effect in 7 (nS f σ*S-O orbital interaction7b,8,9). Recently,
it was reported that the oxidation of 3,3,5,5-tetraphenyl-
1,2,4-trithiolane with m-chloroperbenzoic acid (MCPBA)
yielded the 1-oxide with the oxygen atom possessing the
axial orientation in the solid state.10b Incidentally, no
formation of 4-oxides of cis-4 was observed in the present
reaction, in contrast to the case of the oxidation of the
parent10a,d and 3,3,5,5-tetramethyl-1,2,4-trithiolanes which
gives the corresponding 1- and 4-oxides.10c
Resu lts a n d Discu ssion
P r ep a r a tion of cis- a n d tr a n s-1,2,4-Tr ith iola n es
cis-4 a n d tr a n s-4. 1,2,4-Trithiolanes cis-4 and tr a n s-4
were prepared by reaction of thiopivalophenone (5) with
elemental sulfur (eqs 2 and 3).12 Thus, treatment of 5
Trithiolane 1-oxides 6 and 7 thus obtained were
allowed to react with DMD in CH2Cl2 at -20 °C.
Oxidation of 6 with an excess of DMD (2 mol equiv)
yielded the desired 1,2-dioxide 8 quantitatively (eq 5).
In contrast, the reaction of 7 with DMD was so slow that
a large excess of DMD (4 mol equiv) and a longer reaction
time were required for the complete consumption of 7 to
give 1,1-dioxide 9 (Scheme 1). Although 9 was unstable
in solution at room temperature and decomposed to
quickly form 2 mol equiv of thioketone 5 (94%), the yield
with elemental sulfur in N,N-dimethylformamide (DMF)
at room temperature for 14 days gave a mixture of 1,2,4-
trithiolane cis-4 and 5, from which cis-4 was isolated in
42% yield as the only isomer. In contrast, the reaction
in refluxing toluene yielded 1,2,4-trithiolanes tr a n s-4
(43%) and cis-4 (19%). The synthesis of cis- and trans-
substituted 3,5-di-tert-butyl-3,5-diaryl-1,2,4-trithiolanes
by the reaction of the corresponding ketones with P2S5
has also been reported.13
1
of 9 was quantitative, judging from the H NMR spec-
trum of the reaction mixture measured at -20 °C. The
lower reactivity of 7 compared with 6 might be attributed
to a lowering of the energy level of the lone pair of
electrons on the S(2), owing to the anomeric effect
described above.
Oxid a tion of 1,2,4-Tr ith iola n e cis-4. Oxidation of
cis-4 with 1.2 mol equiv of DMD14 gave two stereo-
isomeric monoxides 6 and 7 in 54% and 39% yields,
respectively (eq 4). These two isomers were separated by
SCHEME 1
1,2-Dioxide 8 was also obtained directly by oxidation
of cis-4 with 4 mol equiv of DMD in 42% yield. Oxidation
of (1-adamantyl)-substituted 1,2,4-trithiolane 10 with
DMD proceeded similarly to give the 1,2-dioxide 11 in
60% yield (eq 6). The structure of 11 was determined by
silica gel column chromatography, and their structures
were determined by X-ray crystallographic analyses.11 In
the solid state, 1-oxide 6 takes a half-chair conformation
with the oxygen atom being cis to the phenyl group and
occupying the equatorial orientation, while the other
1-oxide 7 takes an envelope conformation [ S(1)-S(2)-
C(3)-S(4) of 3.07(12)°] with the oxygen atom trans to the
phenyl group and occupying the axial orientation. The
S-S bond in 7 [2.052(2) Å] is significantly shorter than
X-ray crystallography.11 In the crystalline state, the
trithiolane ring of 11 takes a near-envelope conformation
[ C(5)-S(4)-C(3)-S(2) of 11.4(3)°]. The S(1)-S(2) bond
length of 2.249(2) Å is elongated by ∼10% compared with
the usual S-S bond lengths.15 For reference, the S-S
bond length of cis-4 is 2.024(2) Å.12
(12) Ishii, A.; Oshida, H.; Nakayama, J . Bull. Chem. Soc. J pn. 2002,
75, 319-328.
(13) Okuma, K.; Shibata, S.; Shioji, K.; Yokomori, Y. J . Chem. Soc.,
Chem. Commun. 2000, 1535-1536.
(14) Adam, W.; Bialas, J .; Hadjiarapoglou, L. Chem. Ber. 1991, 124,
2377. Adam, W.; Hadjiarapoglou, L.; Smerz, A. Chem. Ber. 1991, 124,
227-232.
(15) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. 2 1987, S1-S19.
1696 J . Org. Chem., Vol. 69, No. 5, 2004

Oxidation of Trithiolanes
In relation to the unexpected instability of 1,1-dioxide
9 compared with 1,2-dioxide 8, thermal reactions of 8 and
monoxides 6 and 7 were examined. Heating of 8 in
refluxing CDCl3 yielded 2 mol equiv of thioketone 5 (93%)
(eq 7). The formation of 2 mol equiv of 5 is explained in
terms of the extrusion of SO2 from a rearrangement
product 9 or the O,S-sulfenyl sulfinate 12.1 Elemental
sulfur was not detected by TLC in this thermolysis.
F IGURE 1. ORTEP drawing of 1,2-dioxide 18.
SCHEME 2
and 17 were confirmed by X-ray crystallography. When
DMD (1.2 mol equiv) was employed as the oxidant, the
oxide 17 (88%) was obtained preferably together with a
small amount of 16 (4%). The preferred formation of 17
is interpreted by the steric repulsion between the oxidant
and the substituents of tr a n s-4. Thus, sterically more
demanding DMD approaches the sulfur atom to be
oxidized from the less hindered phenyl group side. The
lower reaction temperature might serve as an additional
factor for the high selectivity.
Oxidation of trithiolane 1-oxide 16 with 4 mol equiv of
DMD in CH2Cl2 at -20 °C for 7 h gave 1,2-dioxide 18
and 1,1-dioxide 19 in 20% and 71% yields, respectively
(eq 10). In the IR spectrum of 18, two strong absorptions
On the other hand, thermal reactions of 6 and 7 in
refluxing xylene gave the identical trans-episulfide 13 in
high yields (Scheme 2). The stereoselective reactions of
6 and 7 would proceed through the common thiocarbonyl
ylide intermediate 14 in a manner similar to that in the
N2-extrusion reaction of 1,3,4-thiadiazolines reported by
Kellogg and Wassenaar.16 The trans stereochemistry of
13 was verified by the oxidation of 13 to give a single
episulfoxide 15 having spectroscopically nonequivalent
tert-butyl groups (eq 8).
due to the SdO stretching vibrations (1075 and 1129
Oxid a tion of 1,2,4-Tr ith iola n e tr a n s-4. Oxidation
of 1,2,4-trithiolane tr a n s-4 with 1.2 mol equiv of MCPBA
in CH2Cl2 at 0 °C gave two monoxides 16 and 17 in 33%
and 54% yields, respectively (eq 9). The structures of 16
1
cm-1) were observed, and the H and 13C NMR spectra
showed that the 1,2-dioxide did not have C2-symmetry.
The definitive assignment provided by X-ray crystal-
lography showed it to be the (1S*,2R*,3S*,5S*)-1,2-
dioxide 18 (Figure 1). Thus, in the solid state, 1,2-dioxide
18 takes a half-chair conformation with an S(1)-S(2)
bond length of 2.241(1) Å and a torsional angle C(5)-
S(1)-S(2)-C(3) of -62.3(1)°. The two oxygen atoms in
18 are cis with respect to the S(1)-S(2) bond, and the
dihedral angle O(1)-S(1)-S(2)-O(2) is -62.2(2)°. In-
terestingly, the oxidation of 16 with trifluoroperacetic
acid (4 mol equiv) yielded 1,2-dioxide 18 as the main
product in 60% yield. Hydrogen bonding at the oxygen
(16) Buter, J .; Wassenaar, S.; Kellogg, R. M. J . Org. Chem. 1972,
37, 4045-4060.
J . Org. Chem, Vol. 69, No. 5, 2004 1697

Oshida et al.
dominant formation of 19 from 16 in the oxidation with
DMD (eq 10) is noteworthy. This exceptional regioselec-
tivity is also discussed later.
Thermolysis of 1-oxides 16 and 17 was examined with
the expectation of the stereoselective formation of cis-
episulfide 21 through the corresponding thiocarbonyl
ylide intermediate. Thus, heating of 16 in refluxing
xylene for 16 h gave the expected cis-episulfide 2119 (8%)
and trans-episulfide 13 (2%) with 85% recovery of 16 (eq
12). Elongated heating led to decomposition of the
F IGURE 2. ORTEP drawing of 1,2-dioxide 20.
atom of 16 would increase the positive charge at the
sulfinyl sulfur atom17 to change the selectivity.
The other 1-oxide 17 was also treated with 2 mol equiv
of DMD in CH2Cl2 at -20 °C for 2 h to give an alternative
1,2-dioxide, (1R*,2R*,3S*,5S*)-20, in 70% yield along
with 19 (21%) and 18 (4%) (eq 11). The two tert-butyl
products to give mainly ketone 24 along with a small
amount of 13. The thermal decomposition of 17 was
rather complex to yield thioketone 5, sulfines 22 and 23,
and ketone 24 as the main products along with a small
amount of trans-episulfide 13 (eq 13).
groups, as well as the phenyl groups, in dioxide 20 are
1
equivalent to each other in the H and 13C NMR spectra,
indicating the C2-symmetry of the structure. An X-ray
analysis showed that 20 has a half-chair form with an
S(1)-S(2) bond length of 2.237(1) Å and a torsional angle
C(5)-S(1)-S(2)-C(3) of 72.4(1)° (Figure 2). The two
oxygen atoms of 20 occupy equatorial orientations with
a dihedral angle O(1)-S(1)-S(2)-O(2) of 59.8(2)°.
In both 18 and 20, the tert-butyl groups possess the
pseudoequatorial orientations to reduce steric hindrance.
As described later, because neither 1,2-dioxide 18 nor
20 isomerizes to 1,1-dioxide 19 under ambient conditions,
19 is considered to be formed directly from 16 and 17.
Generally, in the multistep oxidation of disulfides with
electrophilic oxidants, the initial oxidation products,
S-substituted thiosulfinates (1-oxides), are further oxi-
dized at the sulfenyl sulfur atoms to give the correspond-
ing vic-dioxides (1,2-dioxides) predominantly, and then
the vic-dioxides isomerize to the thiosulfonates (1,1-
dioxides),1-6 whereas the oxidation of thiosulfinates with
nucleophilic oxidants such as NaIO4 takes place at the
sulfinyl sulfur atoms.18 In this respect, the direct, pre-
Thermolysis of 1,1-dioxide 19 in refluxing CDCl3
yielded 2 mol equiv of thioketone 5 quantitatively (eq 14).
1,2-Dioxide 20 mainly decomposed to thioketone 5 (eq 15).
DFT calculations were performed on trithiolane 1-
oxides 6, 7, 16, and 17 and 1,2-dioxides 8, 18, and 20 at
the B3LYP/6-31G* level.20 Table 1 summarizes relevant
bond length and torsion angle data of their experimental
and calculated structures. Compound 16 is, however, not
included in the discussion because its oxygen atom is
disordered in the X-ray analysis. Except that the calcu-
lated S-S and C-S bond lengths are slightly longer than
the experimental ones, the optimized structures were
quite similar to those in the solid state. The calculations
reproduced the tendency that the S-S bond lengths of
(17) For example: Drago, R. S.; Wayland, B.; Carlson, R. L. J . Am.
Chem. Soc. 1963, 85, 3125-3128.
(18) (a) Kim, Y. H.; Takata, T.; Oae, S. Tetrahedron Lett. 1978,
2305-2308. (b) Oae, S.; Takata, T. Tetrahedron Lett. 1980, 21, 3213-
3216. (c) Takata, T.; Kim, Y. H.; Oae, S. Bull. Chem. Soc. J pn. 1981,
54, 1443-1147.
(19) cis-Episulfide 21 isomerizes to trans-episulfide 13 by an un-
known mechanism under the present conditions.
1698 J . Org. Chem., Vol. 69, No. 5, 2004

Oxidation of Trithiolanes
TABLE 1. Obser ved a n d Ca lcu la ted Bon d Len gth s (Å) a n d Tor sion An gles (d eg) of 1,2,4-Tr ith iola n e 1-Oxid es 6, 7, 16,
a n d 17 a n d 1,2-Dioxid es 11/8, 18, a n d 20
6
7
16
17
11/8
18
20
obsda/calcdb
obsda/calcdb
obsda/calcdb
obsda/calcdb
obsda/calcdb
obsda/calcdb
obsda/calcdb
S1-S2
2.113(1)/2.197
1.838(2)/1.871
1.855(2)/1.903
1.814(2)/1.854
1.880(2)/1.927
1.457(2)/1.504
2.052(2)/2.142
1.858(3)/1.893
1.832(4)/1.878
1.818(3)/1.844
1.897(3)/1.944
1.460(4)/1.500
c/2.147
c/1.865
c/1.893
c/1.865
c/1.938
c/1.499
2.104(2)/2.185 2.249(2)/2.342
1.825(3)/1.924 1.860(6)/1.935
1.881(3)/1.923 1.862(6)/1.893
1.831(3)/1.868 1.829(5)/1.868
1.881(3)/1.854 1.838(5)/1.906
1.464(3)/1.504 1.468(5)/1.509
1.455(5)/1.508
2.241(1)/2.355
1.876(3)/1.905
1.847(3)/1.876
1.855(3)/1.897
1.868(3)/1.910
1.434(3)/1.502
1.471(2)/1.509
2.237(1)/2.337
1.863(3)/1.907
1.868(3)/1.898
1.869(3)/1.898
1.848(3)/1.907
1.463(2)/1.507
1.475(2)/1.507
S2-C3
C3-S4
S4-C5
C5-S1
S1-O1
S2-O2
C5-S1-S2-C3
45.82(9)/-47.1 -32.0(2)/37.4
c/51.4
-60.2(2)/61.8
-57.3(2)/-54.6 -62.3(1)/-60.4 72.4(1)/70.4
73.6(3)/78.0
O1-S1-S2-O2d
-62.2(2)/-63.6 -59.8(1)/-63.5
a
d
X-ray. b Structure optimizations were made by DFT calculations at the B3LYP/6-31G* level. c The oxygen atom is disordered. O1‚ ‚ ‚O2
distances (obsd/calcd) [Å]: 11/8, 3.500(8)/3.672; 18, 3.49(6)/3.761; 20, 3.427(4)/3.633.
is 7.5 kcal mol-1 lower in energy than the HOMO, where
the lobe is a little smaller than that at S(4) and
comparable to that at S(1). In contrast, in the HOMO of
17, the lobe at S(2) is comparable to that at S(1) though
smaller than that at S(4), and in the next-HOMO, 4.1
kcal mol-1 lower in energy than the HOMO, the lobe at
S(2) has the greatest contribution (Figure 3b). A straight-
forward interpretation for the above calculations is as
follows. In 16, the energy level of the S(2) lone pair is
energetically below that of S(4) probably because of a
stereoelectronic interaction (nS(2) f σ*S(1)-O9). In 17, since
the stereoelectronic effect is negligibly small, the lone
pair on S(2) is kept at a high energy level, comparable to
those of S(4) and S(1).21 In the actual oxidation of 16,
DMD, an electrophilic oxidant, is unable to approach the
sterically congested S(4); therefore, as the second choice,
it attacks at S(1) to give the 1,1-dioxide 19 as the main
product (eq 10). In the case of 17, the oxidation occurs at
S(2) preferably to give the 1,2-dioxide 20 as the main
product, where the S(4) resists oxidation because of the
same reason as that in the case of 16. The above
considerations, based on ground-state frontier orbitals
and steric effects, provide reasonable explanations for the
regioselectivities shown in eqs 10 and 11. This is also true
for the regioselective oxidations of 6 (eq 4) and 7 (Scheme
2).
Isom er iza t ion b et w een 1,2-Dioxid es 18 a n d 20.
1,2-Dioxides 18 and 20 isomerized to each other in
F IGURE 3. HOMOs and next-HOMOs of (a) 16 and (b) 17.
solution at room temperature, whereas they did not in
the axial-O monoxides 7 (obsd 2.052(2)/calcd 2.142 Å) and
the crystalline state. Both 18 and 20 gave the equilibrium
16 (calcd 2.147 Å) are shorter than those of the equato-
mixture after several days in CDCl3 at 295 K, and the
rial-O monoxides 6 (obsd 2.113(1)/calcd 2.197 Å) and 17
(obsd 2.104(2)/calcd 2.185 Å).
Figure 3 depicts the HOMOs and the next-HOMOs of
ratio of 20/18 was determined to be 95/5 by 1H NMR
spectroscopy (eq 16). This value corresponds to ∆G295
monoxides 16 and 17. In the HOMO of 16, the lobes at
S(4) and S(1) are the main contributors, and there is no
contribution of the lone pair of S(2) (Figure 3a). The lobe
of the lone pair of S(2) appears in the next-HOMO, which
(20) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
[G295(18) - G295(20)] ) 1.7 kcal mol-1. DFT calculations
on the 1,2-dioxides 18 and 20 at the B3LYP/6-31G* level
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Baboul, A. G.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; J ohnson, B.; Chen,
W.; Wong, M. W.; Andres, J . L.; Gonzalez, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J . A. Gaussian 98, revision A.9; Gaussian, Inc.:
Pittsburgh, PA, 1998.
indicated that C2-symmetric 20 is more stable than
nonsymmetric 18 by 1.5 kcal mol-1 in Gibbs free energy
(Table 2).
(21) For more sophisticated and quantitative consideration on
stereoelectronic effects with the natural bond orbital (NBO) analysis,
see the following recent papers and references therein: (a) Sproviero,
E. M.; Burton, G. J . Phys. Chem. A 2003, 107, 5544-5554. (b) Alabugin,
I. V. J . Org. Chem. 2000, 65, 3910-1919.
J . Org. Chem, Vol. 69, No. 5, 2004 1699

Oshida et al.
TABLE 2. Ca lcu la ted Electr on ic En er gies (Eelec),
Th er m a l Cor r ection s to Gibbs F r ee En er gies (TCG),
Gibbs F r ee En er gies (G), a n d Differ en ces of G (∆G) of
1,2-Dioxid es 18, 20, a n d 8 a n d 1-Oxid es 6, 7, 16, a n d 17 a t
th e B3LYP /6-31G* Level
TABLE 4. Ap p r oxim a te Ra te Con sta n ts (k1′) of th e
Isom er iza tion of 18 to 20
temp (K)
k1′ (10-5 s-1
)
295
303
308
313
318
3.93 ( 0.02
15.4 ( 0.01
34.4 ( 0.2
75.2 ( 0.4
150 ( 1
a
Eelec
TCGa-c
Ga,b
∆Gb,d
1,2-dioxides
18
20
8
-2200.101 637 0.389 829 -2199.711 808
-2200.104 298 0.390 046 -2199.714 252
1.5
0.0
-2200.106 386 0.391 091 -2199.715 295 -0.7
SCHEME 4
1-oxides
6
7
16
17
-2124.931 943 0.387 646 -2124.544 297
-2124.935 617 0.388 967 -2124.546 650
-2124.931 577 0.388 111 -2124.543 466
-2124.930 399 0.388 040 -2124.542 359
1.5
0.0
2.0
2.7
a
b
In hartrees. At 298.15 K and 1.00 atm. c After scaling by the
factor 0.9804.22 In kcal mol-1
.
d
TABLE 3. Ra te Con sta n ts of th e Isom er iza tion s of 18 to
20 (k1) a n d 20 to 18 (k-1) a t 295 K
run
solvent
additive
k1 (10-5 s-1
)
k-1 (10-6 s-1
)
1
2
3
4
5
CDCl3
CD3CN
CD3OD
CDCl3
CDCl3
none
none
none
DPPH
CF3CO2H
3.94 ( 0.01
4.44 ( 0.02
5.51 ( 0.03
4.89 ( 0.01
1.43 ( 0.01
2.08 ( 0.01
2.34 ( 0.01
2.90 ( 0.02
2.58 ( 0.01
0.75 ( 0.04
catalyzed by a radical contaminant.23 In the present case,
the rate of the isomerization between 18 and 20 was not
influenced by DPPH (run 4), indicating the operation of
a mechanism different from that of isomerization be-
tween 29 and 30. In addition, even when a solution of
18 in CDCl3 was contained in a Teflon vessel, the
isomerization proceeded at a rate similar to that in a
glass vessel, indicating that the rough surface of a glass
vessel does not catalyze the isomerization and the surface
acidic SiOH groups on glass also do not affect the rate of
isomerization, unlike the case of CF3CO2H (vide infra).
When an excess amount of CF3CO2H (10 mol equiv)
was added to a CDCl3 solution of 18, the isomerization
became about 3 times slower, probably because of the
stabilization of the ground state of 18 and 20 by the
hydrogen bonding at the sulfoxide oxygen (run 5).17
The isomerization of 18 was followed by 1H NMR
spectroscopy in the temperature range 295-318 K in
CDCl3 to obtain activation parameters. Because the exact
equilibrium constants could not be determined in the
higher temperature range, owing to the partial decom-
position of the 1,2-dioxides, the approximate rate con-
stants (k1′) were estimated from decreasing rates of 18
over a half-life period where the contribution of the
reverse reaction to the rates is negligible (Table 4). The
activation parameters thus obtained are ∆Eq ) 29.6 (
0.2 kcal mol-1, ∆Hq ) 29.0 ( 0.2 kcal mol-1, and ∆Sq )
19.8 ( 0.7 eu.
The instability of vic-disulfoxides is attributed to low
dissociation energies of the S-S bonds.1-5 Folkins and
Harpp observed the isomerization between vic-disulfox-
ides 26 and 27 by H and 13C NMR spectroscopies, and
1
they proposed intervention of a biradical intermediate
28 for the isomerization (Scheme 3).3
SCHEME 3
The isomerization starting with 18 obeyed reversible
first-order kinetics very well at least over a period of 3
half-lives of 18. The results of several kinetic runs are
summarized in Table 3. The equilibrium constants K (k1/
k-1) were the same in all cases examined (K ) 95/5 )
19) (runs 1-5). Runs 1-3 showed clearly that the rate
constants were almost independent of the solvent polar-
ity, indicating that the polarity change of the reactant is
small in the rate-controlling step.
We have previously reported the isomerization between
dithiirane 1-oxides 29 and 30 (eq 17).23 The isomerization
The large positive ∆Sq for the isomerization is in
harmony with a biradical mechanism (Scheme 4).1-5 The
isomerization would involve homolysis of the S-S bond
to give the biradical intermediate 31 with loss of stereo-
chemistry. Rotation about the C-S(O) bond followed by
recombination completes the isomerization. Sulfinyl radi-
cals have been recognized as π radicals.24 The difference
of the spin densities does not appear to be large for the
sulfur 3p and the oxygen 2p orbitals, although it is a
between 29 and 30 did not take place in the presence of
a radical scavenger such as diphenylpicrylhydrazyl
(DPPH), so we concluded that the isomerization is
(22) Wong, M. W. Chem. Phys. Lett. 1996, 256, 391-399.
(23) Ishii, A.; Nakamura, S.; Yamada, T.; Nakayama, J . Tetrahedron
1997, 53, 12203-12214.
(24) Razskazovskii, Y. V.; Becker, D.; Sevilla, M. D. In S-Centered
Radicals; Alfassi, Z. B., Ed.; J ohn Wiley & Sons: Chichester, England,
1999; pp 245-276.
1700 J . Org. Chem., Vol. 69, No. 5, 2004

Oxidation of Trithiolanes
CHART 2
SCHEME 5
TABLE 5. Yield s of P r od u cts of th e Rea ction s of
1-Oxid es 6, 7, 16, a n d 17 w ith Me3O+BF 4
-
productsa (isolated yield (%))
entry substrate time (d)
6
7
16
17
1
2
3
4
6
7
16
17
1
3
3
1
21
6
76
3
24
15
54
64
8
a
In all cases, ketone 24 and sulfine 22 were formed as
decomposition products.
matter of some argument.24 The formation of six-
membered O,S-sulfenyl sulfinates, which correspond to
12, and another 1,2-dioxide 32 was not observed in the
isomerization.25 Compound 32 would prefer to take a
conformation with pseudoequatorial tert-butyl groups,
similar to those of 1,2-dioxides 18 and 20, leading to the
diaxial 1,2-dioxide structure. Compound 32 is estimated
to be 1.1 kcal mol-1 less stable than 20 by DFT calcula-
tions at the B3LYP/6-31G* level.26 In homolytic dissocia-
tion of S-S bonds, aromatic thiosulfinate 3327 (∆Sq ) 12.6
eu, ∆Hq ) 34.5 kcal mol-1), sulfinyl sulfone 3428 (∆Sq )
11.2 eu, ∆Hq ) 27.6 kcal mol-1), and R-disulfone 3529 (∆Sq
) 16.6 eu, ∆Hq ) 40.9 kcal mol-1) are known to have
similar ∆Sq values, although they are acyclic compounds
(Chart 2).
7 itself did not isomerize to the other oxides (entry 2).
Mutual isomerization was observed only between 6 and
16. The isomerization among the four 1-oxides would take
place by way of the carbocation intermediate 36 that is
formed by O-methylation followed by CsS(OMe) bond
cleavage. Rotations about the C+sS and SsS bonds in
36 lead to the cis-trans isomerization and the inversion
of the SdO group, respectively. It has been established
that the inversion of the SdO group in sulfoxides takes
place by treatment with R3O+BF4 followed by alkaline
-
hydrolysis, where the intermediate alkoxysulfonium salts
are isolable.30 In the present case, the corresponding
sulfonium salts were not observed by NMR spectroscopies.
Incidentally, calculations at the B3LYP/6-31G* level
showed that 1-oxide 7 is more stable than 6, 16, and 17
by 1.5, 2.0, and 2.7 kcal mol-1, respectively (Table 2).
R ea ct ion s of 1-Oxid es 6, 7, 16, a n d 17 w it h
Me3O+BF 4-. Trithiolane 1-oxides 6, 7, 16, and 17 did not
isomerize to each other by either heating or treatment
with CF3CO2H. However, isomerization was observed
-
when they were treated with Me3O+BF4 in CH2Cl2 at
Con clu sion
room temperature (Table 5 and Scheme 5). Treatment
of cis-substituted 1-oxide 6 with Me3O+BF4 for 1 day
-
We succeeded in the isolation and the structure deter-
mination of 1,2,4-trithiolane 1,2-dioxides in addition to
those of the 1-oxides. The 1,2-dioxides are the first
isolable compounds having the C-S(O)-S(O)-C linkage.
Furthermore, we observed isomerization between 1,2-
dioxides 18 and 20 in solution and proposed the biradical
mechanism based on a kinetic study.
gave 7 (6%) and, unexpectedly, trans-substituted 1-oxide
16 (24%), along with 6 (21%) and some decomposition
products (entry 1). Similarly, trans-substituted 16 pro-
vided cis-substituted 1-oxides 6 (15%) and 7 (3%) (entry
3), and 17 gave 7 in 64% yield (entry 4). While 7 was
always formed in the above three reactions, the 1-oxide
(25) In the oxidation of 16 (eq 10), the initial formation of 32 followed
by isomerization to 19 cannot be ruled out. However, the hypothetical
32, if formed, would isomerize not to 19 but to 18 and 20 through the
common intermediate 31.
Exp er im en ta l Section
P r ep a r a tion of 1,2,4-Tr ith iola n e cis-4. A mixture of tert-
butyl phenyl thioketone 531 (0.996 g, 5.59 mmol) and elemental
sulfur (179 mg, 5.58 mmol) in DMF (15 mL) under argon was
stirred for 14 d at room temperature. The mixture was diluted
with aq NH4Cl and then extracted with ether. The extract was
dried, and the solvent was evaporated. The residue was
subjected to column chromatography (SiO2, hexane) to give cis-
412 (455 mg, 42%).
(26) 32: Eelec ) -2200.101 141 hartrees, TCG ) 0.388 571 hartrees,
G ) -2199.712 57 hartrees, ∆G ) 1.1 kcal mol-1 (see Table 2). The
calculated dipole moments of 18, 20, and 32 are 3.9813, 4.4293, and
1.3753, respectively. The relative stability of 32 compared to 18 and
20 in a polar solvent may be lowered due to the small dipole moment
or by solvation on the oxygen atoms, leading to an increase in the
bulkiness around the axial-oxygen atoms. Incidentally, 1-oxides 18 and
20 do not dissolve in nonpolar solvents such as hexane.
(27) Koch, P.; Ciuffarin, E.; Fava, A. J . Am. Chem. Soc. 1970, 92,
5971-5977.
(30) (a) J ohnson, C. R.; McCants, D., J r. J . Am. Chem. Soc. 1965,
87, 5404-5409. (b) Oae, S. Organic Sulfur Chemistry: Structure and
Mechanism; CRC Press: Boca Raton, FL, 1992; pp 161-165.
(31) Ahmed, R.; Lwoski, W. Tetrahedron Lett. 1969, 10, 3611-3612.
(28) Kice, J . L.; Pawlowski, N. E. J . Am. Chem. Soc. 1964, 86, 4898-
4904.
(29) Kice, J . L.; Favstrisky, N. J . Org. Chem. 1970, 35, 114-118.
J . Org. Chem, Vol. 69, No. 5, 2004 1701

Oshida et al.
P r ep a r a tion of 1,2,4-Tr ith iola n e tr a n s-4. A mixture of
5 (1.99 g, 11.2 mmol) and elemental sulfur (358 mg, 11.2 mmol)
in toluene (15 mL) under argon was heated at reflux for 4 d.
The solvent was removed under reduced pressure, and the
residue was subjected to column chromatography (hexane) and
then HPLC (SiO2, hexane/CH2Cl2 97/3) to give tr a n s-4 (985
mg, 43%) and cis-4 (409 mg, 19%).
Oxid a tion of cis-4 w ith DMD (1.2 m ol equ iv). To a
solution of cis-4 (52.4 mg, 0.135 mmol) in CH2Cl2 (7 mL) was
added DMD14 (0.10 M, 1.6 mL, 0.16 mmol) at -20 °C under
argon, and the mixture was stirred for 1 h. The resulting
mixture was evaporated to dryness, and the residue was
subjected to HPLC (hexane/Et2O 95/5) to give 611 (29.4 mg,
54%) and 711 (21.3 mg, 39%).
subjected to HPLC (hexane/Et2O 96/4) to give 16 (19.1 mg,
33%) and 17 (31.2 mg, 54%).
Oxid a tion of tr a n s-4 w ith DMD. To a solution of tr a n s-4
(103 mg, 0.265 mmol) in CH2Cl2 (15 mL) was added DMD (0.10
M, 3.2 mL, 0.32 mmol) at -20 °C under argon, and the mixture
was stirred for 1 h. The mixture was evaporated to dryness,
and the residue was subjected to HPLC (hexane/Et2O 96/4) to
give 16 (4.3 mg, 4%) and 17 (94.3 mg, 88%).
Oxid a tion of 16 w ith DMD. To a solution of 16 (61.7 mg,
0.152 mmol) in CH2Cl2 (10 mL) was added DMD (0.096 M,
6.3 mL, 0.61 mmol) at -20 °C under argon, and the mixture
was stirred for 7 h. The solvent was removed in vacuo below
-20 °C, and the residue was subjected to HPLC (hexane/Et2O
90/10, 10-12 °C) to give 18 (12.8 mg, 20%) and 19 (45.1 mg,
71%). The fraction containing 18 was evaporated below -20
°C to prevent 18 from isomerization.
Oxid a tion of 16 w ith CF 3CO3H. To a mixture of 16 (51.1
mg, 0.126 mmol) and H2O2 (30%, 57.7 mg, 0.509 mmol) in
CH2Cl2 (10 mL) under argon was added (CF3CO)2O (0.21 mL,
1.5 mmol) at -20 °C, and the mixture was stirred for 7 h at
this temperature. The solvent was removed in vacuo below -20
°C, and the residue was subjected to HPLC (hexane/Et2O 90/
10, 10-12 °C) to give 18 (31.6 mg, 60%) and 19 (2.7 mg, 5%).
Oxid a tion of 17 w ith DMD. To a solution of 17 (50.5 mg,
0.125 mmol) in CH2Cl2 (10 mL) under argon was added DMD
(0.11 M, 2.3 mL, 0.25 mmol) at -20 °C, and the mixture was
stirred for 2 h. The solvent was removed in vacuo below -20
°C, and the residue was subjected to HPLC (hexane/Et2O 90/
10, 10-12 °C) to give 20 (36.8 mg, 70%), 19 (11.0 mg, 21%),
and 18 (2.1 mg, 4%).
Th er m a l Decom p osition of 16. A solution of 16 (10.7 mg,
0.0264 mmol) in xylene (6 mL) was heated at reflux for 16 h.
Yields of the products were calculated to be 8% cis-episulfide
21, 2% trans-episulfide 13, 3% (Z)-sulfine 22,32 1% (E)-sulfine
23,32 1% thioketone 5, and 85% 16, on the basis of the integral
ratio of the 1H NMR spectrum of the mixture.
Oxid a tion of 6 w ith DMD. To a solution of 6 (51.8 mg,
0.128 mmol) in CH2Cl2 (8 mL) was added DMD (0.058 M, 4.4
mL, 0.26 mmol) at -20 °C under argon, and the mixture was
stirred for 1.5 h. The solvent was removed in vacuo below -20
1
°C. The H NMR spectrum of the residue showed the quantita-
tive formation of 1,2-dioxide 8.11
Oxid a tion of 7 w ith DMD. To a solution of 7 (25.2 mg,
0.0623 mmol) in CH2Cl2 (7 mL) was added DMD (0.080 M,
3.1 mL, 0.25 mmol) at -20 °C under argon, and the mixture
was stirred for 2.5 h. The solvent was removed in vacuo below
-20 °C. The 1H NMR spectrum of the residue measured at
-20 °C showed the exclusive formation of 1,1-dioxide 9.11
The crude 9, thus obtained, rearranged to give 5 (20.9 mg,
94%), when it was dissolved in CHCl3 (5 mL) and the solution
was stirred for 0.5 h at room temperature. After removal of
the solvent, the residue was purified by HPLC (hexane) to give
5.
Oxid a tion of cis-4 w ith DMD (4 m ol equ iv). To a
solution of cis-4 (32.9 mg, 0.0846 mmol) in CH2Cl2 (7 mL) was
added DMD (0.10 M, 3.2 mL, 0.32 mmol) at -20 °C under
argon. The mixture was stirred for 1.5 h, and then the solvent
was removed under reduced pressure. The residue was sub-
jected to column chromatography (CH2Cl2) to give crude 1,2-
dioxide 8, which was recrystallized from CHCl3 to give pure 8
(14.8 mg, 42%).
Oxid a tion of 10 w ith DMD (4 m ol equ iv). In a manner
similar to the one above, 1012 (29.9 mg, 0.0549 mmol) was
oxidized with DMD (0.058 M, 3.8 mL, 0.22 mmol) at -20 °C
for 1.5 h. The mixture obtained after removal of the solvent
under reduced pressure was subjected to HPLC (hexane/Et2O
90/10) to give 1,2-dioxide 1111 (18.9 mg, 60%).
Th er m a l Decom p osition of 8. A solution of 8 (5.1 mg,
0.012 mmol) in CDCl3 (5 mL) was heated at reflux for 7 h.
The mixture obtained after removal of the solvent under
reduced pressure was subjected to HPLC (hexane) to give 5
(4.0 mg, 93%).
Th er m a l Decom p osition of 17. A solution of 17 (17.7 mg,
0.0437 mmol) in xylene (6 mL) was heated at reflux for 12 h.
Yields of products were calculated to be 42% thioketone 5, 16%
(Z)-sulfine 22, 17% (E)-sulfine 23, 11% ketone 24, 2% episulfide
13, and 2% unidentified compounds, on the basis of the integral
1
ratio of the tert-butyl groups in the H NMR spectrum of the
mixture.
Th er m a l Decom p osition of 19. A solution of 19 (16.0 mg,
0.0380 mmol) in CDCl3 (3 mL) was heated at reflux for 2.5 h.
The 1H NMR spectrum of the reaction mixture showed the
quantitative formation of thioketone 5.
Th er m a l Decom p osition of 20. A solution of 20 (6.2 mg,
0.015 mmol) in CDCl3 (1.5 mL) was heated at reflux for 30 h.
Yields of products were calculated to be 43% thioketone 5, 20%
(Z)-sulfine 22, 7% (E)-sulfine 23, 14% dithiirane 1-oxide 25,33
5% 1,2,4-trithiolane cis-4, 3% ketone 24, and 8% unidentified
compounds, on the basis of the integral ratio of the tert-butyl
groups in the 1H NMR spectrum of the mixture.
Th er m a l Decom p osition of 6. A solution of 6 (21.0 mg,
0.0519 mmol) in xylene (7 mL) was heated at reflux for 1 d.
The residue obtained after removal of the solvent under
reduced pressure was subjected to HPLC (hexane) to give
episulfide 1311 (16.6 mg, 99%).
Th er m a l Decom p osition of 7. A solution of 7 (17.2 mg,
0.0425 mmol) in xylene (5 mL) was heated at reflux for 3 d.
The residue obtained after removal of the solvent under
reduced pressure was subjected to HPLC (hexane) to give 13
(11.7 mg, 85%).
Isom er iza tion of 18 a n d 20. The isomerizations were
carried out in a 14 mM solution of 18 under argon. Progress
1
of the reaction was monitored by H NMR spectroscopy. The
yields were estimated by integral ratios.
Rea ction of 1-Oxid e 6 w ith Me3O+BF 4-. 1-Oxide 6 (24.7
mg, 0.0610 mmol) and Me3O+BF4 (97%, 11.0 mg, 0.0721
-
mmol) were dissolved in CH2Cl2 (5 mL) under argon, and the
mixture was stirred for 1 d at room temperature. The solvent
was removed under reduced pressure, and the residue was
subjected to HPLC (hexane/Et2O 95/5) to give 6 (5.1 mg, 21%),
Oxid a tion of 13. To a solution of 13 (10.4 mg, 0.0320 mmol)
in CH2Cl2 (7 mL) was added DMD (0.080 M, 0.45 mL, 0.036
mmol) at 0 °C under argon. The mixture was stirred for 10
1
min and evaporated to dryness. The H NMR spectrum of the
1
7 (1.5 mg, 6%), and 16 (5.9 mg, 24%). The H NMR spectrum
residue showed the quantitative formation of 15.
of the reaction mixture indicated the formation of ketone 24
(33%), thioketone 5 (6%), and sulfine 22 (5%) along with 6, 7,
and 16.
Oxid a tion of tr a n s-4 w ith MCP BA. To a solution of
tr a n s-4 (55.6 mg, 0.143 mmol) in CH2Cl2 (7 mL) was added a
solution of MCPBA (purity of 91%, 32.6 mg, 0.172 mmol) in
CH2Cl2 (3 mL) at 0 °C under argon. The mixture was stirred
for 1 h, and then aq Na2SO3 was added. The mixture was
neutralized with aq NaHCO3. The organic layer was washed
with water, dried, and evaporated to dryness. The residue was
(32) Nakamura, K.; Shizume, Y.; Sugiyama, T.; Ohno, A.; Oka, S.
Phosphorus Sulfur Relat. Elem. 1983, 16, 153-155.
(33) Ishii, A.; Kawai, T.; Tekura, K.; Oshida, H.; Nakayama, J .
Angew. Chem., Int. Ed. 2001, 40, 1924-1926.
1702 J . Org. Chem., Vol. 69, No. 5, 2004

Oxidation of Trithiolanes
Rea ction of 1-Oxid e 7 w ith Me3O+BF 4-. In a manner
similar to the one above, a solution of 7 (22.9 mg, 0.0566 mmol)
and Me3O+BF4- (10.6 mg, 0.0695 mmol) in CH2Cl2 (5 mL) was
stirred at room temperature for 3 d to give 7 (17.5 mg, 76%).
Formation of ketone 24 (13%) and sulfine 22 (4%) was detected
mg, 64%) and 7 (2.5 mg, 8%). Formation of ketone 24 (16%)
and sulfine 22 (7%) was detected by H NMR spectroscopy of
the reaction mixture.
1
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research (No. 12440174)
from the Ministry of Education, Culture, Sports, Science
and Technology, J apan.
1
by H NMR spectroscopy of the reaction mixture.
Rea ction of 1-Oxid e 16 w ith Me3O+BF 4-. In a manner
similar to the one above, a solution of 16 (23.3 mg, 0.0576
mmol) and Me3O+BF4 (10.5 mg, 0.0689 mmol) in CH2Cl2 (5
-
mL) was stirred at room temperature for 3 d to give 6 (3.5
mg, 15%), 7 (0.8 mg, 3%), and 16 (12.6 mg, 54%). Formation
of ketone 24 (18%) and sulfine 22 (5%) was detected by 1H
NMR spectroscopy of the reaction mixture.
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal methods, analytical and spectroscopic data for tr a n s-4 and
15-21, X-ray data for compounds 16, 17, 18, and 20, and
optimized coordinates and thermochemical corrections of 6, 7,
8, 16, 17, 18, 20, and 32. This material is available free of
charge via the Internet at http://pubs.acs.org.
Rea ction of 1-Oxid e 17 w ith Me3O+BF 4-. In a manner
similar to the one above, a solution of 17 (30.8 mg, 0.0761
mmol) and Me3O+BF4 (14.2 mg, 0.0931 mmol) in CH2Cl2 (5
-
mL) was stirred at room temperature for 1 d to give 17 (19.7
J O0354591
J . Org. Chem, Vol. 69, No. 5, 2004 1703