Synthesis of cyclic trithiocarbonates from cyclic ethers and carbon disulfide catalyzed by titanium complex

Article abstract of DOI:10.1016/S0040-4020(01)00685-8

This work deals with reaction of oxetane derivatives with carbon disulfide in the presence of (2-propanolato) titanatrane. It afforded six-membered cyclic trithiocarbonates in good yields. Reaction of propylene oxide with carbon disulfide also proceeded in a similar manner to give a five-membered cyclic trithiocarbonate in excellent yield.

Full text of DOI:10.1016/S0040-4020(01)00685-8

TETRAHEDRON
Pergamon
Tetrahedron 57 (2001) 7149±7152
Synthesis of cyclic trithiocarbonates from cyclic ethers and carbon
disul®de catalyzed by titanium complex
Suguru Motokucho, Daisuke Takeuchi, Fumio Sanda and Takeshi Endop
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
Received 23 April 2001;accepted 22 June 2001
AbstractÐThis work deals with reaction of oxetane derivatives with carbon disul®de in the presence of (2-propanolato) titanatrane. It
afforded six-membered cyclic trithiocarbonates in good yields. Reaction of propylene oxide with carbon disul®de also proceeded in a similar
manner to give a ®ve-membered cyclic trithiocarbonate in excellent yield. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
carbonates by reaction of oxiranes and CS2 catalyzed by
metal halides in high yields.4 The reaction proceeds via
nucleophilic attack of metal halides to CS2, followed by
the reaction of the produced xanthate anion with oxiranes.
Cyclic thiocarbonates attract much attention in view of
biological activity1 and material science.2 Recently, we
have found that ®ve- and six-membered cyclic thio-
carbonates undergo ring-opening polymerization in
controlled fashion to afford the corresponding polythio-
carbonates with narrow molecular weight distribution.2
Some ef®cient methods have been reported as for synthesis
of ®ve-membered cyclic thiocarbonates. Reaction of
oxiranes with carbon disul®de (CS2) is one of the most facile
and effective methods for synthesizing cyclic dithio-
carbonates (1±3), trithiocarbonates (4), and episul®de (5),
where the product ratio depends on catalysts and reaction
conditions (Scheme 1).3,4 For example, ®ve-membered
cyclic trithiocarbonates are predominantly synthesized
from oxiranes and CS2 in the presence of base such as
amines or potassium alcoholates.3,4 Recently, we have
selectively synthesized ®ve-membered cyclic dithio-
In contrast, synthesis of six-membered cyclic thio-
carbonates is quite limited. Kubota et al. have synthesized
six-membered cyclic trithiocarbonates from 1,3-dimesyl-
propane derivatives and CS2.5 Sugawara et al. have synthe-
sized six-membered cyclic trithiocarbonates by reaction of
1,3-dihaloalkanes with sodium trithiocarbonate in the
presence of a phase-transfer catalyst in 66% yield.6 On the
other hand, no one has synthesized six-membered cyclic
thiocarbonates by base-catalyzed reaction of oxetanes with
CS2 so far, presumably due to insuf®cient reactivity of
oxetanes toward nucleophililic attack. Recently, we have
reported that titanium complexes bring about nucleophilic
ring-opening reaction of oxetane, leading to copolymeriza-
tion of oxetane with cyclic acid anhydrides or bislactones.7
In this case, Lewis acidity of the titanium complexes is high
enough to activate oxetane molecule toward nucleophilic
attack, which is considered as key importance.8 As an exten-
sion of the study, this article deals with synthesis of ®ve- and
six-membered cyclic trithiocarbonates by reaction of
oxiranes and oxetanes with CS2 using (2-propanolato)
titanatrane (6) as the catalyst.
2. Results and discussion
2.1. Synthesis of 1,3-dithiane-2-thione #9) from oxetane
and CS2 by titanium complex
Scheme 1.
The reaction of CS2 with oxetane (OX) was carried out in
the presence of (2-propanolato) titanatrane (6) at 100±
1408C for 12±60 h as summarized in Table 1. At 1208C
for 48 h, the corresponding trithiocarbonate 9 was obtained
in 90% yield, when the feed molar ratio of CS2/OX/6 was
Keywords: oxetane;oxirane;molar ratio.
Corresponding author. Address: Department of Polymer Science and
Engineering, Faculty of Engineering, Yamagata University, 4-3-16
Jonan, Yonezawa, Yamagata 992-8510, Japan. Tel.: 181-238-26-3090;
fax: 181-238-26-3092;e-mail: tendo@poly.yz.yamagata-u.ac.jp
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(01)00685-8

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S. Motokucho et al. / Tetrahedron 57 .2001) 7149±7152
Table 1. Reaction of carbon disul®de with oxetane in the presence of 6
Run CS2/OX/6 (molar ratio) Temperature (8C) Time (h) Yield (%)
Table 2. Reaction of various cyclic ethers and thioethers with carbon
disul®de in the presence of 6
Run
Cyclic ether
Product
Yield (%)
1
2
3
4
5
6
7
75/50/1
120
120
120
120
100
140
120
48
48
48
48
60
12
48
52
90
25
5
31
60
32
100/50/1
200/50/1
400/50/1
100/50/1
100/50/1
200/100/1
100/50/1 (run 2). When the CS2/OX molar ratio was
decreased from 100/50 to 75/50, the yield of 9 diminished
to 52% (run 1).9 Upon increase of the ratio to 200/50 and
400/50, the yield diminished to 25 and 5%, respectively,
with recovery of unreacted OX (runs 3 and 4).10 Employ-
ment of 1,2-dichloroethane or THF (OX: 1.25 mmol,
solvent 0.5 mL) as a solvent resulted in no formation of 9
and recovery of OX. Runs 2, 5 and 6 in Table 1 show the
effect of reaction temperature trithiocarbonate synthesis,
which was studied by the isolated yields. At 1008C, the
yield of 9 was only 31% even for elongation of the reaction
time (run 5). At 1408C, the yield was 60% (run 6). These
conditions were lower than that at 1208C about yield.
Chloroform-insoluble compounds precipitated in run 6,
suggesting some side reactions such as decomposition of
the catalyst11 and polymerization of the products. It was
concluded that the trithiocarbonate could be synthesized
most ef®ciently at 1208C with the feed molar ratio of CS2/
OX/6ˆ100/50/1. Titanium complex 7, Ti(OiPr)4 and a
Ti(OiPr)4/Et3N (1/1) system were also examined as the
catalysts, but unreacted OX was recovered quantitatively
from the reaction mixture in all cases. Neither LiBr or
NEt3 was effective, although they had been reported to
catalyze the reaction of oxiranes with CS2.3,4
Conditions: temperatureˆ1208C, reaction timeˆ48 h, cyclic ether/CS2/6ˆ
50/100/1 molar ratio.
a Oxetane/CS2/6ˆ25/50/1 molar ratio.
b Unreacted cyclic ether or thioether was quantitatively recovered, which
was determined by H NMR.
1
Scheme 2.

S. Motokucho et al. / Tetrahedron 57 .2001) 7149±7152
7151
2.2. Synthesis of thiocarbonates from cyclic ethers and
CS2 by titanium complex
Other cyclic ethers and thioethers, such as substituted
oxetanes, oxiranes, and thietane were submitted for the
reaction with CS2 catalyzed by 6. As shown in Table 2,
3-methyloxetane and 3,3-dimethyloxetane reacted with
CS2 satisfactorily to afford the corresponding trithio-
carbonates (10, 11) in excellent yields (runs 2 and 3). The
reaction was tolerant with ether group at the 3-position (run
4). In contrast, 2-methyloxetane or thietane did not react
with CS2 (run 5 and 6). 2-Methyloxirane also reacted with
CS2 in the presence of 6 to afford the corresponding ®ve-
membered cyclic trithiocarbonate (13) quantitatively (run
7). Interestingly, 2,2-dimethyloxirane did not afford a
trithiocarbonate but a dithiocarbonate, 5,5-dimethyl-1-oxa-
3-thiolane-2-thione (14) selectively and quantitatively (run
8). On the other hand, tetrahydrofuran did not react with CS2
(run 9).
2.3. Comments on plausible mechanism
Scheme 2 illustrates a plausible mechanism of the reaction.
First, the titanatrane complex (60) is formed by the one-to-
one reaction with CS2 which brings about ring-opening of
oxetane, followed by intramolecular cyclization to afford a
six-membered cyclic dithiocarbonate (8) with regeneration
of 6. At present, we have not detected the formation of 8,
presumably because it reacts rapidly with 60 to give the
thioalkanolate titanatrane intermediate (600) with releasing
carbonyl sul®de (COS). The complex 600, thus formed,
affords trithiocarbonate (9) with regeneration of 6. In
conformity with this mechanism, we isolated a ®ve-
membered cyclic dithiocarbonate as the product in the
reaction of 2,2-dimethyloxirane with CS2 (Table 2, run 8).
In this case, further reaction of dithiocarbonate with 60
might be sterically prohibited by the dimethyl group at the
5-position.
Figure 1. 1H NMR spectra of the mixtures obtained by the reaction
of 5DTC in the presence and absence of CS2 catalyzed by 6 at 1208C.
(a) and (b)ˆCS2/5DTC/6 of 50/50/1 molar ratio. (c)ˆ5DTC/6 of 20/1
molar ratio.
membered cyclic trithiocarbonates from oxetanes and CS2
catalyzed by the titanium complex (6). The reaction of
2-methyloxirane proceeded in a similar manner to give a
®ve-membered cyclic trithiocarbonates, while 2,2-
dimethyloxirane afforded a cyclic dithiocarbonate.
In order to con®rm the reaction process, we examined the
reaction of 5-methyl-1,3-oxathiane-2-thione (5DTC) with
CS2 in the presence of 6 at 1208C. H NMR spectroscopic
1
studies of the reaction mixture showed that 5DTC com-
pletely converted into a trithiocarbonate after 48 h (Fig. 1
(a),(b)). When the reaction was performed in the absence of
CS2, polythiirane was formed ꢀMn ˆ 14 000 Mw=Mn ˆ 1:68†
(Fig. 1(c)), presumably by the successive reaction of
titanatrane with 5DTC with releasing COS. All these results
were well consistent with the mechanism proposed in
Scheme 2.
3. Experimental
3.1. Measurements
1H and 13C NMR spectra were recorded in chloroform-d
(CDCl3) on a JEOL EX-300 (1H, 300 MHz; 13C, 75 MHz)
spectrometer, with tetramethylsilane (TMS) as an internal
standard. IR spectra were obtained with a Perkin±Elmer
Spectrum One. GC-mass spectra were recorded on a
In summary, we demonstrated the facile synthesis of six-

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S. Motokucho et al. / Tetrahedron 57 .2001) 7149±7152
Shimadzu GCMS-QP5050A. Number- and weight-average
molecular weights (Mn and Mw) and polydispersity ratios
(Mw/Mn) were estimated by gel permeation chromatography
(GPC) on a Tosoh HPLC HLC-8120 system, equipped with
two consecutive polystyrene gel columns (G2500HXL, and
3.2.4. Synthesis of 5-ethoxymethyl-5-methyl-1,3-
dithiane-2-thione #12). Yield 94%. H NMR (CDCl3): d
1
1.18±1.22 (2H, t, Jˆ7.0 Hz, CH3CH2O), 1.30 (3H, s,
CH3C), 2.87±2.91 (2H, d, Jˆ13.2 Hz, SCH2), 3.15±3.19
(2H, d, Jˆ13.2 Hz, SCH2), 3.44 (2H, s, OCH2C), 3.49±
3.56 (2H, Jˆ7.0 Hz, q, CH3CH2O). 13C NMR (CDCl3): d
14.8, 22.2, 33.2, 43.4, 66.9, 75.7, 224.5. MS: 222 (M1), 178.
EA: Calcd C, 45.72;H, 6.82;S, 40.69. Found C, 45.89;H,
6.75;S, 40.88.
G5000HXL), using THF as
,
a
polystyrene calibration, and refractive
eluent (¯ow rate
1.0 mL min21
index (RI) and ultraviolet (UV, 254 nm) detectors.
3.2. Materials
3.2.5. Synthesis of 4-methyl-1,3-dithiolane-2-thione
1
#13).6b Yield quantitative. H NMR (CDCl3): d 1.63 (3H,
d, Jˆ6.6 Hz, CH3), 3.65±3.72 (1H, dd, Jˆ7.5, 11.7 Hz,
SCH2), 4.00±4.64 (1H, dd, Jˆ5.1, 11.7 Hz, SCH2), 4.44±
4.51 (1H, m, SCH). 13C NMR (CDCl3): d 18.8, 50.1, 55.2,
228.1. IR: 1076, 1050, 1033. MS: 150 (M1), 106.
Carbon disul®de (CS2) was dried over CaCl2 and distilled
under nitrogen after re¯uxing over CaH2. THF was re¯uxed
over sodium benzophenone ketyl and distilled under nitro-
gen. Dichloroethane was re¯uxed over CaH2 and distilled
under nitrogen. Chloroform, hexane, cyclohexane, CDCl3
and acetone-d6 were used as received. Oxetane was distilled
from sodium under nitrogen. 2-Methyloxirane and 2,2-
dimethyloxirane were distilled from CaH2 under nitrogen.
2-Methyloxetane, 3-methyloxetane,12 3,3-dimethyloxetane,14
(2-propanolato) titanatrane,13 bis(2-propanolato) titanium
2,20-methylenebis(6-tert-butyl-4-methylphenolate)8 5-methyl-
1,3-oxathiane-2-thione4 were prepared according to the
reported procedure.
3.2.6. Synthesis of 5-methyl-1-oxa-3-thiolane-2-thione
1
#14).4 Yield quantitative. H NMR (acetone-d6): d 1.68
(6H, s, CH3), and 3.51 (2H, s, CH2). 13C NMR (acetone-
d6): d 25.7, 45.1, 96.7, 210.7. IR: 1251, 1134 cm21. MS:
148 (M1), 104. Bp: 1148C/2.5 mmHg (lit.4 1118C/
2.0 mmHg).
References
3.2.1. Synthesis of 1,3-dithiane-2-thione #9). To a 5 mL
glass ample ®tted with a three-way stopcock containing
(2-propanolato) titanatrane (6.3 mg, 0.025 mmol) and a
Te¯on-coated stirring bar was added oxetane (0.081 mL,
1.25 mmol) and carbon disul®de (0.15 mL, 2.5 mmol) by
a syringe under dry nitrogen at room temperature. The
tube was freezed, evacuated, sealed off, and heated at
1208C for 48 h. After the mixture was cooled to room
temperature and the volatile fractions were evaporated, the
residue was puri®ed by silica gel column chromatography
eluted with chloroform/hexane (9/1, volume ratio), followed
by recrystallization from cyclohexane to obtain 1,3-
dithiane-2-thione as yellow needles in 90% yield (0.17 g).
1. Kubota, S.;Taguchi, E.;Eto, M.;Maekawa, K. J. Fac. Agric.,
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2. (a) Choi, W.;Sanda, F.;Endo, T. Macromolecules 1998, 31,
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1
Mp: 78±798C (lit.5, 77±788C). H NMR (CDCl3): d 2.38±
2.46 (2H, m, CH2), 3.24±3.26 (4H, t, Jˆ4.4 Hz, SCH2). 13
C
.
4. Kihara, N.;Nakawaki, Y.;Endo, T. J. Org. Chem. 1995, 60, 473.
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NMR (CDCl3): d 20.3, 34.2, 221.1. IR: 1019, 931 cm21
MS: 150 (M1), 106.
6. (a) Sugawara, A.;Ishiyama, M.;Abe, Y.;Segawa, T.;Sato, R.
Sulfur Lett. 1990, 12, 55. (b) Sugawara, A.;Sato, T.;Sato, R.
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5-Methyl-1,3-dithiane-2-thione, 5,5-dimethyl-1,3-dithiane-
2-thione, 5-ethoxymethyl-5-methyl-1,3-dithiane-2-thione,
4-methyl-1,3-dithiolane-2-thione, and 5,5-dimethyl-1-oxa-
3-thiolane-2-thione were synthesized in a manner similar
to 9.
7. Takeuchi, D.;Aida, T.;Endo, T. Macromol. RapidCommun.
1999, 20, 646.
8. Takeuchi, D.;Nakamura, T.;Aida, T. Macromolecules 2000,
33, 725.
3.2.2. Synthesis of 5-methyl-1,3-dithiane-2-thione #10).
Yield 96%. Mp: 65±668C (lit.5, 63±648C). 1H NMR
(CDCl3): d 1.25±1.31 (3H, d, Jˆ13.2 Hz, CH3), 2.53±
2.63 (1H, m, CH), 2.99±3.06 (2H, dd, Jˆ8.3, 12.7 Hz,
SCH2), 3.18 (2H, dd, Jˆ3.9, 13.3 Hz, SCH2). 13C NMR
9. The structures of the by-products could not be elucidated.
GPC of the reaction mixture indicated the formation of oligo-
meric compounds (Mn,400).
10. This might be responsible for formation of a titanium complex
with 2 equiv. of CS2, which hinders the reaction, but we have
no concrete evidence.
11. 1H NMR studies showed that titanatrane 6 was stable at 1208C
for 48 h but decomposed at 1408C within 6 h.
(CDCl3): d 19.4, 25.6, 40.9, 221.7. IR: 994, 934 cm21
.
MS: 164 (M1), 120.
3.2.3. Synthesis of 5,5-dimethyl-1,3-dithiane-2-thione
#11). Yield quantitative. Mp: 98±998C (lit.5 99±1008C).
1H NMR (CDCl3): d 1.32 (6H, s, CH3) 2.99 (4H, s, CH2).
13C NMR (CDCl3): d 26.6, 27.9, 47.0, 223.1. IR: 1005, 962,
945, 922, 889 cm21. MS: 178 (M1), 134.
12. Searles Jr, S.;Pollart, K. A.;Lutz, E. F. J. Am. Chem. Soc.
1957, 79, 948.
13. Menge, W. M. P. B.; Verkade, J. G. Inorg. Chem. 1991, 30, 4628.
14. Watanabe, N.;Umehara, S.;Okano, M. Bull. Chem. Soc. Jpn
1979, 52, 3611 and references cited therein.