Remarkable effect of metal fluoride catalyst on reaction of hexafluoropropene, sulfur and vinyl ethers. Convenient synthesis of 2,2-bis(trifluoromethyl)-4-R-thietanes, 3,3-bis(trifluoromethyl)-5-R-1,2- dithiolanes and 2,2-bis(trifluoromethyl)-4-R-1,3-dithiolanes

Article abstract of DOI:10.1016/j.jfluchem.2010.06.011

It was demonstrated that the outcome of the reaction of hexafluoropropene, sulfur and vinyl ether strongly depends on the catalyst and reaction conditions. The reaction of HFP and S_x leading to the formation of 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietane (1) when it is catalyzed by CsF, proceeds under milder conditions and is easier to control compared to KF catalyzed process. The order of addition of reagents plays a crucial role on the outcome of the reaction. For example, the addition of vinyl ether to pregenerated solution of 1 in DMF solvent results in slow reaction, leading to the corresponding 2,2-bis(trifluoromethyl)-4-R-thietanes in 8-91% yield, and it is catalyzed by either by KF or CsF. The addition of second mole of sulfur to the solution of 2,2-bis(trifluoromethyl)-4-R-thietanes in the presence MF catalyst leads to insertion of sulfur into thietane ring with the formation of the corresponding cyclic disulfides-3,3-bis(trifluoromethyl)-5-R-1,2- dithietanes. On the other hand, the addition of second mole of sulfur to the solution of 1 in DMF in the presence of CsF catalyst, followed by addition of vinyl ether results in exothermic reaction, and it produces the corresponding 2,2-bis(trifluoromethyl)-4-alkoxy-1,3-dithiolanes in good yield. It was also demonstrated that 2,2-bis(trifluoromethyl)-4-R-thietanes can undergo disproportionation under action of fluoride anion, producing a mixture of the corresponding 1,2-dithiolane and CF₂C(CF₃)CH ₂CFHOR. The nucleophilic attack of fluoride anion in this case proceeds selectively on the carbon of the thietane ring, bearing alkoxy group. The structure of 2,2-bis(trifluoromethyl)-4-R-thietanes forming as the result of 2 + 2 cycloaddition reaction between hexafluorothioacetone generated in situ from dimer 1 and vinyl ether was firmly supported by single crystal X-ray diffraction data, obtained for thietane bearing t-BuO-group.

Full text of DOI:10.1016/j.jfluchem.2010.06.011

Journal of Fluorine Chemistry 131 (2010) 1144–1155
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Remarkable effect of metal fluoride catalyst on reaction of
hexafluoropropene, sulfur and vinyl ethers. Convenient synthesis
of 2,2-bis(trifluoromethyl)-4-R-thietanes, 3,3-bis(trifluoromethyl)-5-R-1,2-
dithiolanes and 2,2-bis(trifluoromethyl)-4-R-1,3-dithiolanes
b
Viacheslav A. Petrov a, , Will Marshall
*
a DuPont CR&D, Experimental Station, PO Box 80500, Wilmington, DE 19880-0500, United States1
b DuPont Corporate Center for Analytical Sciences, Experimental Station, PO Box 80500, Wilmington, DE 19880-0500, United States1
A R T I C L E I N F O
A B S T R A C T
Article history:
It was demonstrated that the outcome of the reaction of hexafluoropropene, sulfur and vinyl ether
strongly depends on the catalyst and reaction conditions. The reaction of HFP and Sx leading to the
formation of 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietane (1) when it is catalyzed by CsF, proceeds
under milder conditions and is easier to control compared to KF catalyzed process. The order of addition
of reagents plays a crucial role on the outcome of the reaction. For example, the addition of vinyl ether to
pregenerated solution of 1 in DMF solvent results in slow reaction, leading to the corresponding 2,2-
bis(trifluoromethyl)-4-R-thietanes in 8–91% yield, and it is catalyzed by either by KF or CsF. The addition
of second mole of sulfur to the solution of 2,2-bis(trifluoromethyl)-4-R-thietanes in the presence MF
catalyst leads to insertion of sulfur into thietane ring with the formation of the corresponding cyclic
disulfides—3,3-bis(trifluoromethyl)-5-R-1,2-dithietanes. On the other hand, the addition of second mole
of sulfur to the solution of 1 in DMF in the presence of CsF catalyst, followed by addition of vinyl ether
results in exothermic reaction, and it produces the corresponding 2,2-bis(trifluoromethyl)-4-alkoxy-1,3-
dithiolanes in good yield.
Received 31 March 2010
Received in revised form 13 June 2010
Accepted 15 June 2010
Available online 23 June 2010
Keywords:
Hexafluorothioacetone
[2 + 2] cycloaddition
2,2,4,4-Tetrakis(trifluoromethyl)-1,3-
dithietane
2,2-Bis(trifluoromethyl)-4-R-thietanes
(R = OR
SC2H5)
2,2,4,4-Tetrakis(trifluoromethyl)thietane
3,3-Bis(trifluoromethyl)-5-alkoxy-1,2-
dithiolanes
It was also demonstrated that 2,2-bis(trifluoromethyl)-4-R-thietanes can undergo disproportionation
under action of fluoride anion, producing
a mixture of the corresponding 1,2-dithiolane and
CF255C(CF3)CH2CFHOR. The nucleophilic attack of fluoride anion in this case proceeds selectively on
the carbon of the thietane ring, bearing alkoxy group.
2,2-Bis(trifluoromethyl)-4-alkoxy-1,3-
dithiolanes
The structure of 2,2-bis(trifluoromethyl)-4-R-thietanes forming as the result of 2 + 2 cycloaddition
reaction between hexafluorothioacetone generated ‘‘in situ’’ from dimer 1 and vinyl ether was firmly
supported by single crystal X-ray diffraction data, obtained for thietane bearing t-BuO-group.
ß 2010 Elsevier B.V. All rights reserved.
2,2-Bis(trifluoromethyl)-4-alkoxy-1,3-
dithiolene
1. Introduction
2,2-Bis(trifluoromethyl)-4-alkoxythietanes originally were pre-
pared by the reaction of monomeric hexafluorothioacetone (HFTA)
Due to presence of sulfur in strained four-membered ring,
fluorinated thietanes possess an interesting reactivity and were
used as starting materials for the preparation of fluorinated sulfur
containing materials [1,2]. For example, 2,2-bis(trifluoromethyl)-
4-R-thietanes (R = –OR) were converted to fluorinated 1,2-
dithiolanes [3]; a number of unsaturated products, were prepared
as the result of ring opening processes [3,4], along with the
corresponding S-oxides [5], and 5-R-2-fluoro-3-trifluoromethyl-
2,3-dihydrothiophenes [5].
with vinyl ethers [6], but the development of simpler synthesis [3],
which does not involve handling monomeric, gaseous HFTA made
thismaterialsreadilyavailable.Itisbasedonthereactionof,stableat
ambient temperature, 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithie-
tane (1, cyclic dimer of HFTA, prepared by reaction of sulfur and
hexafluoropropene (HFP) in the presence of KF catalyst [7,8]) with
methyl- or ethyl-vinyl ethers [3]. Recently we reported, a ‘‘one-pot’’
process for preparation of 5-alkoxy-2-fluoro-3-trifluoromethyldi-
hydrothiophenes starting with sulfur, HFP and vinyl ether [5]. In
course of that work we discovered an interesting effect of the
catalyst on the reaction of sulfur, HFP and vinyl ethers, which is
reported in this publication. This study was also focused on the
optimization of the synthesis of 2,2-bis(trifluoromethyl)-4-R-
thietanes and the corresponding 1,2- and 1,3-dithiolanes.
* Corresponding author. Tel.: +1 302 695 1958; fax: +1 302 695 8281.
E-mail address: viacheslav.a.petrov@usa.dupont.com (V.A. Petrov).
1
Publication No. 2010-54.
0022-1139/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2010.06.011

V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
1145
2. Results and discussion
by adjusting the rate of addition of HFP or by applying external
cooling. In order to ensure full consumption of sulfur, typically ꢀ5–
10% excess HFP was employed. The reaction can be stopped at this
stage and compound 1 can be isolated in 80–90% yield after
distillation (crude product after water quench typically contained
ꢀ5% of (CF3)2CFSCH(CF3)2 as major impurity), or it can be used
without isolation for further reactions. It should be also pointed out
thatthisprocessissensitivetotheamountofCsFcatalystand highest
yields of 1 were obtained when ꢀ2–5 mol% of CsF was used. In sharp
contrast to KF catalyzed process, which can lead to the formation of
higher molecular weight byproducts [8], the CsF catalyzed process
does not suffer this disadvantage and it stops once one mole of HFP is
consumed. The detailed study of the reaction of HFP and sulfur and
CsF will be the subject of the forthcoming publication.
2.1. Effect of metal fluoride catalyst on reaction of HFP, Sx and vinyl
ethers. One-pot synthesis of polyfluorinated thietanes
The Ishikawa group reported the synthesis of 2,2-bis(trifluor-
omethyl)-4-R-thietanes (R = OCH3, OC2H5) using reaction of 1 and
vinyl ethers in the presence of KF catalyst [3]. Since in the synthesis
of 1 same catalyst was employed [8] we decided to combine both
steps in one-pot synthesis to simplify the preparation of
fluorinated thietanes by eliminating step involving isolation of
1. Indeed, it was found that thietanes 3a–d can be prepared
without isolation of 1, by KF catalyzed reaction of HFP/Sx/vinyl
ether in DMF solvent (Eq. (1)):
The addition of dry vinyl ethers 2a–i or vinyl sulfide 2j to the
reaction mixture containing
1 (generated in CsF catalyzed
reaction) results in the formation of the corresponding thietanes
3a–j (Eq. (2)):
(1)
(2)
In a typical experiment gaseous HFP was continuously added
into preheated (to 35–50 8C), well agitated mixture of sulfur and
dry KF catalyst (5–10 mol%) suspended in anhydrous DMF and
placed in a reaction vessel equipped with dry-ice condenser and
thermocouple. The reaction of HFP with sulfur is relatively fast,
however this step requires careful adjustment of the rate of
addition of HFP, in order to avoid the condensation of HFP on the
dry-ice condenser on one hand, and the overheating of the reaction
mixture leading to the formation of byproducts [8], on the other
hand. Vinyl ether was usually added to the reaction mixture after
all the sulfur was dissolved, at 25–50 8C. Although the formation of
thietanes is a slow process (ꢀ2 days at ambient temperature) the
reaction is clean, producing thietanes 3a–d in high yield (Eq. (1)).
The KF catalyzed thietane synthesis was incorporated in a recently
reported ‘‘one-pot’’ type synthesis of various 5-R-2-fluoro-3-
trifluoromethyl-2,3-dihydrothiophenes [5].
Interestingly, the replacement of KF catalyst by CsF has a drastic
effect on the reactionofHFP withsulfur. WhenCsF is used as catalyst,
the addition of HFP (started at ambient temperature) results in
exothermic reaction. Due to quicker HFP uptake and higher
exothermicity, the reaction is faster and easier to control, compared
to the KF catalyzed process. The end of the reaction can be judged, by
the disappearance of sulfur and the formation of yellow or orange-
yellow, slightly hazy, homogenous solution. Typically this step is
carried out at 45–65 8C and the temperature can be easily controlled
Vinyl ethers 2a–h could be added to the reaction mixture
rapidly, since the formation of the corresponding thietanes is slow
at ambient temperature. Longer reaction time (up to 8 days) leads
to the formation of other byproducts, derived from disproportion-
ation of thietanes under action of FÀ (see Section 2.2).
It should be pointed out that isolated yields of thietanes
prepared in the CsF catalyzed process involving vinyl ethers are
slightly lower compared to the KF catalyzed process, due to the
formation ꢀ5–15% of the corresponding 1,3-dithiolane byproduct
(see Section 2.2 for additional discussion). Although the formation
of byproducts lowers the yield, it does not affect the purity of the
isolated thietanes, due to substantial difference in boiling points of
thietanes and 1,3-dithiolanes. Compounds 3a–j (typical purity

1146
V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
Table 1
Yields, boiling points and mass spectrometry data for new materials.
Entr. no.
Compound no.
Yield (%)
Boiling point (8C/mm Hg) (melting point, 8C)
MS (m/z)
1
2
3a
3b
3c
3d
3e
3f
71a–86b
45/12c
254(M+, C7H8F6OS+)
268(M+, C8H10F6OS+)
268(M+, C8H10F6OS+)
282(M+, C9H12F6OS+)
282(M+, C9H12F6OS+)
282(M+, C9H12F6OS+)
308(M+, C11H14F6OS+)
288(M+, C7H7ClF6OS+)
69a–72b
82a–85b
72a–91b
75
78–79/50
70–72/25
94–96/30
88–89/30
55–57/5
60/0.1
3
4
5
6
72
7
3g
3h
3i
86
8
62
8d
100–101/20
80–83/50
30–32/0.7
29–30/0.1
112–113
44/2f
9
308((M+, C7H5F9OS+)
+
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
29
3j
68
270(M+, C7H8F6S2
)
3k
3l
45e
75
252(M+, C7H6F6OS+)
346(M+, C7H2F12S+)
286(M+, C7H8F6OS2
63a–73b
53a–83
87
)
+
4a
4b
4c
4d
4e
4f
b
+
108/25
300(M+, C8H10F6OS2
300(M+, C8H10F6OS2
314(M+, C9H12F6OS2
250(M+, C9H12F6O+)
302(C9H13F7OS+)
)
)
+
46–48/1
84–85/2
–
+
82
)
–
–
–
4g
5a
5b
5c
5d
5e
5f
–
–
288(C8H11F7OS+)
286(M+, C7H8F6OS2
)
+
66
52–54/0.7 (38–39)
63–64
300(M+, C8H10F6OS2
300(M+, C8H10F6OS2
314(M+, C9H12F6OS2
314(M+, C9H12F6OS2
)
)
+
83
+
20
102–104/25 (46–47)
60–62/0.5
68–69/1
81–84/1
99–105/50
81–87/3g
(60–61)
+
51
)
+
64
)
+
40
320(M+, C7H7ClF6OS2
)
340(M+, C7H5F9OS2
)
+
5g
5h
7
15
+
58
284(C7H6F6OS2
)
356(M+, C9H6F6O4S2
)
+
50
a
Yield in KF catalyzed reaction.
Yield in CsF catalyzed reaction.
b
c
d
e
f
Reported b.p. 78–80 8C/70 mm Hg [3]; 43 8C/10 mm Hg [6].
Crude product contained 35% of 5g.
Mixture of cis- and trans-isomers, ratio 98:2.
Reported for 4a b.p. 73–75 8C/11mm Hg [3].
Mixture of cis- and trans-isomers, ratio 65:35.
g
>98%,) were obtained after fractionational distillation of crude
reaction mixture under reduced pressure (see Table 1).
Electron deficient vinyl ethers 2h and 2i (R = CH2CH2Cl and
CH2CF3, respectively) have lower reactivity towards HFTA, which
results in longer reaction times, lower isolated yields of thietanes
3h and 3i and the formation of substantial amount of the
corresponding of 1,3-dithiolane byproducts (see Table 1 and
Section 2.2 for discussion on formation of 1,3-dithiolanes).
Ethyl vinyl sulfide 2j has the highest reactivity towards 1 and
should be added to the reaction mixture slowly, due to
[(ig._1)TD$FIG]
Fig. 1. Crystal structure of 3l. Thermal ellipsoids drawn to the 50% probability level. Disordered positions are omitted for clarity.

V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
1147
exothermicity of the reaction, which in this case was completed in
a few hours, leading to thietane 3j.
The one-pot process was tested in the lab on up to 0.5 mol scale
(using both KF or CsF catalysts), and the corresponding fluorinated
thietanes 3a–h, were prepared in 62–91% yield.
CsF, DMF solvent), despite the fact that the formation of the
corresponding cycloadduct was previously mentioned in Ref. [11]
for the KF catalyzed reaction of dimethylmaleate and 1.
2.2. Effect of order of reagents addition. Preparation of 1,2- and 1,3-
dithiolanes
The CsF catalyzed reaction of 2,3-dihydrofurane (2k) with 1
resulted in formation of bicyclic thietane 3k in moderate yield:
2.2.1. Preparation of 3,3-bis(trifluoromethyl)-5-alkoxy-1,2-
dithiolanes
Another interesting feature of the reaction between sulfur, HFP
and vinyl ethers is a surprising sensitivity of the process to the
order of reagents addition.
We found, that, the addition of a second mole of sulfur to the
reaction mixture containing thietane 3a and b prepared in the CsF
catalyzed ‘‘one-pot’’ reaction of HPF/Sx/vinyl ether (see Section
2.1), leads to the formation of the corresponding 1,2-dithiolane 4a
or 4b (Eq. (5)):
(3)
It is interesting that, the cycloaddition step is stereoselective,
leading to predominant formation of cis-isomer 3k (Eq. (3)).
2,3-Dihydropyran, containing a less strained double bond has
significantly lower reactivity towards 1. The reaction at ambient
temperature was very slow, but at elevated temperature (50–
65 8C) it led to a mixture of equal amount of the corresponding
thietane and unsaturated product containing the –SCH(CF3)2 group
(NMR data). Later probably derives from the well-known ene-
reaction of HFTA [6,9] involving the allylic hydrogen of 2,3-
dihydropyran. It should be also mentioned that monomeric HFTA
seems to have higher reactivity, since it was reported to react with
2,3-dihydropyran giving the corresponding cycloadduct in 40%
yield under mild conditions [6].
(5)
Zeifman and Postovoii reported that electrondeficient
CF255C(CF3)2 (perfluoroisobutene, PFIB) can undergo cycloaddition
in CsF catalyzed reaction with 1, producing perfluoro-(2,2,4,4-
tetramethyl)thietane [10]. We found that less electrophilic
CH255C(CF3)2 (hexafluoroisobutene, HFIB), also gives the corre-
sponding thietane 3l in one-pot reaction with HFP/Sx/CsF mixture
in DMF solvent (Eq. (4)):
The reaction is relatively slow and takes 24–36 h (GC, NMR).
Values of chemical shifts and coupling constants of 19F NMR
spectra for compound 1,2-dithiolane 4a are in reasonable
agreement with reported values, for the material synthesized in
the reaction of 3a with sulfur and diethylamine [3].
It should be pointed out, that the crude products 4a and 4b
isolated in ‘‘one-pot’’ process (Eq. (5)), were contaminated by the
corresponding 1,3-dithiolanes (forming at the stage of preparation
of thietane, see Section 2.1), and isolated by thiolanes 4a and 4b
contained 2–4% 1,3-isomers. This problem was resolved by
reacting pure, isolated thietanes 3 with sulfur in the presence of
CsF catalyst. Using this protocol 1,2-dithiolanes 4a–d were isolated
in 73–87% yield and fully characterized (Eq. (6), Tables 1 and 2).
(4)
(6)
The thietane 3l is a liquid at ambient temperature, however, in
contrast to compounds 3a–e, g–j it readily crystallizes being placed
in ice. We were able to confirm symmetrical structure of 3l by
single crystal X-ray diffraction data (Fig. 1, see also Section 2.3 for
the discussion on the mechanism of cyclization).
It should by pointed out, that potassium fluoride can also be
used as the catalyst for this process, however, the reaction was
found to be significantly slower (typical conversion ꢀ20% after 5
On the other hand, attempt to involve in the reaction with 1
electron deficient dimethylmaleate was not successful (7d, 25 8C,

1148
V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
Table 2
1H, 19F and 13C NMR data for new materials.
Entr. no.
1
Comp. no.
1H NMR (
d
, ppm, J, Hz)a
19F NMR (
d
, ppm, J, Hz)a
13C NMR ( , ppm, J,Hz)a,b
d
3a
1.27(3H, t, 7.3), 3.24(1H, ddq, 14.3, 5.1, 1.1), 3.36(1H, dd, 14.3, 7.2),
3.45(1H, m), 3.56(1H, m), 5.36(1H, dd, 7.2, 5.1)
À73.73(m)c
À73.72(m)
À73.61(m)
À74.14(m)
12.92, 36.48, 46.08(sept., 32.0),
64.20, 74.51, 122.98(q, 279),
124.28(q, 280.5)
2
3
4
5
3b
3c
3d
3e
0.98(3H, t, 7.7 Hz), 1.66(2H, m, 7.7), 3.25(1H, ddq, 14.3, 5.2, 1.5),
3.40(3H, m), 5.35(1H, dd, 7.2, 4.9)
8.87, 21.42, 36.34, 46.01
(sept., 32.0), 70.28, 74.29,
122.93(q, 280), 124.23(q, 280)
20.13, 20.69, 37.44, 46.33
(sept. 32.0), 72.42, 72.97,
122.94(q, 280), 124.40(q, 280)
21.31, 18.35, 30.35, 36.40,
46.09(sept., 32.0), 68.42, 74.87,
122.95(q, 276), 124.23(q, 276)
15.70, 15.72, 25.42, 34.32,
44.11(sept., 33), 73.02,
1.18(3H, d, 4.0), 1.19(3H, d, 3.8), 3.22(1H, ddq, 14.1, 5.6, 0.8),
3.33(1H, dd, 14.1, 7.2), 3.68(1H, sept., 6.1), 5.4(1H, dd, 6.9, 5.8)
0.95(3H, t, 7.5), 1.42(2H, m), 1.61(2H, m), 3.23(1H, ddq, 14.3, 5.1, 1.2),
3.37(1H, dd, 14.3, 7.2), 3.40(1H, m), 3.48(1H, m), 5.35(1H, dd, 7.2, 5.1)
0.92(3H, d, 1.5), 0.93(3H, d, 1.5), 1.88(1H, sept., 7.0), 3.13(1H, m),
3.21(2H, m), 3.35(1H, m), 5.30, 1H, dd, 7.1, 4.9)
À73.63(3F, q, 9.6),
À73.77(3F, q, 9.6)
121.05(q, 280), 122.30(q, 280)
–
6
7
8
3f
0.2(9H, s), 2.22(1H, ddq, 14.3, 6.0, 1.3), 2.32(1H, dd, 14.3, 7.2),
4.53(1H, t, 6.6)
À74.70(m)
À74.00(m)
À73.64(m)
3g
3h
1.34(5H, m), 1.55(1H, m), 1.80(4H, m), 3.27(1H, dd, 14.1, 5.5),
3.35(1H, dd, 14.1, 7.1), 5.48(1H, t, 6.9)
–
3.25(1H, ddq, 13.9, 5.0, 1.2), 3.40(1H, dd, 14.0, 7.1), 3.66(3H, m),
5.79(1H, m), 5.38(1H, dd, 7.3, 5.0)
34.28, 39.02, 43.74(sept., 32.5),
66.87, 72.79, 12079(q, 282),
121.98(q, 282)
9
3i
3.27(1H, dddq, 14.8, 4.5, 1.0), 3.43(1H, dd, 14.8, 7.2), 3.82(1H, m),
3.92(1H, m), 5.40(1H, dd, 7.3, 4.7)
À73.62(3F, q, 9.8),
À73.67(3F, q, 8.4),
À73.73(3F, q, 9.8)
À73.25(3F, q, 9.9),
À74.45(3F, q, 9.9)
36.83, 46.41(sept., 33.5),
66.06(q, 34.4), 76.34,
122.99(q, 286), 124.35(q, 280)
14.40(m), 24.48, 36.00, 42.20,
47.83(sept., 32), 123.31(q, 282),
124.72(q, 282)
10
11
3j
1.29(3H, t, 7.7), 2.75(2H, m), 3.29(2H, m), 4.90(1H, t, 8.3)
3kd
Cis-isomer: 1.92(1H, m, 14.7), 2.39(1Hdd, 14.7, 4.9),
3.95(1H, dd, 10.1, 5.8), 4.32(1H, t, 8.9), 4.50(1H, ddd, 11.6,
10.5, 4.4), 5.92(1H, d, 5.8)
Cis-isomer:
–
À68.60(3F, q, 10.0),
À74.88(3F, q, 10.0)
trans-isomer:
À71.02(3F, q, 10.6),
À73.23(3F, q, 10.3)
À72.54
12
13
3l
3.49(s)
27.85(s), 45.54(br s),
122.48(q, 284.3)
4a
1.3.1(3H, t, 7.2), 2.76(1H, ddq, 14.3, 4.7, 1.6), 2.82(1H, dd, 14.3, 3.7),
3.61(1H, m), 3.84(1H, m), 5.56(1H, t, 4.2)
À68.75(3F, q, 10.4),
À71.05(3F, q, 10.4)e
10.98, 40.59, 63.78, 65.58
(sept., 27.9), 92.59, 121.11
(q, 282), 121.90(q, 282)
7.28, 19.57, 40.72, 65.58
(sept., 27.6), 69.95, 92.78,
121.05(q, 283.5),
14
15
16
17
4b
4c
4d
4e
0.94(3H, t, 7.6 Hz), 1.66(2H, m), 2.68(1H, dd, 14.6, 3.3), 2.79
(1H, dd, 14.6, 3.1), 3.45(1H, m), 3.68(1H, m), 5.51(1H, t, 3.8)
À68.52(3F, q, J = 10.0)
À71.15(3F, q, J = 10.0)
122.00(q, 283.5)
1.21(3H, d, 6.2), 1.23(3H, d, 6.2), 2.67(1H, ddq, 14.4, 5.2, 1.2),
2.72(1H, ddq, 14.4, 4.6, 1.0), 3.91(1H, sept., 6.3), 5.56(1H, t, 4.7)
À69.43(3F, q, 9.5),
À70.74(3F, q, 9.5)
17.37, 19.29, 40.48,
64.32(sept., 27.3),
70.19, 91.60, 121.28
(q, 282), 121.86(q, 282)
10.32, 16.31, 28.32,
40.74, 65.91(sept., 29.0),
68.00, 92.91, 121.10
(q, 282.5), 122.05(q, 282.5)
–
0.94(3H, t, 7.5), 1.40(2H, m), 1.61(2H, m), 2.69(1H, dd, 14.4, 4.6),
2.81(1H, dd, 14.4, 3.8), 3.49(1H, m), 3.75(1H, m), 5.50(1H, t, 4.0)
À68.61(3F, q, 10.4),
À71.21(3F, q, 10.4)
–
–
À60.96(3F, ddd),
20.2, 11.3, 2.3),
À74.39(1F, dm, Jd =20.2),
À78.24(1F, m),
À124.00(1F, dt, 66.0, 14.0)
À67.75(3F, q, 8.8),
18
19
20
21
22
23
4f
–
–
À67.82(3F, q, 8.8),
À124.61(1F, dm, JH–F = 67.0)
À66.91(3F, q, 10.4),
À67.32(3F, qd), 10.4, 4),
À115.82(1F, dtd, 66.0, 12.0)
À67.98(3F, q, 9.8),
4g
5a
5b
5c
5d
1.25(3H, t, 7.2), 2.34(3H, sept., 1.0), 2.40(2H, m), 3.65(1H, m),
3.90(1H, m), 5.60(1H, dt, 65.8, 12.2)
1.03(3H, t, 7.0), 3.22(1H, m), 3.33(11H, d, 13.1), 3.38(1H, dd, 13.1, 3.0),
3.55(1H, m), 5.49(1H, br.s)
14.83, 46.25, 65.77,
À70.58(3F, q, 9.8)
72.72(sept., 30), 95.28,
123.90(q, 282), 14.65(q, 282)
10.41, 22.17, 46.55, 71.17,
72.34(sept., 30), 95.19,
123.55(q, 282), 124.72(q, 282)
20.17, 22.26, 46.69, 71.71,
72.14(sept., 32), 92.48,
123.38(q, 280), 124.20(q, 282)
14.02, 19.05, 27.89, 43.57,
72.28(sept., 31.0), 76.12,
95.43, 123.50(3F, q, 280),
124.27(3F, q, 280)
0.96(3H, t, J = 7.3 Hz), 1.66(2H, m, J = 7.5), 3.34(1H, m), 3.56(1H, d, 12.2),
À67.63(3F, q, 10.7)
À70.45(3F, q, 10.7)
3.61(1H, dd, 12.2, 3.2), 3.68(1H, m), 5.71(1H, s)
1.17(3H, d, J = 6.0), 1.21(1H, d, 6.3), 3.47(1H, d, 11.7), 3.58(1H, dd,
À67.67(3F, q, 9.8),
À70.58(3F, q, 9.8)
11.7, 3.1), 3.85(1H, sept., 6.1), 5.83(1H, br.s)
0.92(3H, d, 2.5), 0.94(3H, d, 2.5), 1.91(1H, m), 3.11(1H, dd, 8.7, 3.8),
3.45(1H, dd, 8.7, 7.0), 3.58(2H, m), 5.69(1H, br.s)
À67.51(3F, q, 10.1),
À70.52(3F, q, 10.1)

V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
1149
Table 2 (Continued )
Entr. no.
24
Comp. no.
1H NMR (
d
, ppm, J, Hz)a
19F NMR (
d
, ppm, J, Hz)a
13C NMR ( , ppm, J,Hz)a,b
d
5e
0.94(3H, t, 7.5), 1.40(2H, m), 1.61(2H, m), 2.69(1H, dd, 14.4, 4.6),
2.81(1H, dd, 14.4, 3.8), 3.49(1H, m), 3.75(1H, m), 5.50(1H, t, 4.0)
À67.65(3F, q, 10.7),
À70.48(3F, q, 10.7)
14.02, 19.58, 31.53, 46.92,
69.60, 72.75(sept., 31),
95.34, 123.910(q, 280),
124.60(q, 282)
25
26
5f
3.65(5H, m), 3.99(1H, m), 5.79(1H, br.s)
À67.64(3F, q, 10.3),
À70.42(3F, q, 10.3)
39.06, 43.58, 66.18,
69.47(sept. 31), 92.29,
120.70(q, 281),
121.37(q, 281)
5g
3.67(2H, m), 3.86(1H, m), 4.05(1H, m), 5.85(1H, br.s)
À67.75(3F, q, 10.0),
À70.37(3F, q, 10.1),
À73.08(3F, t, 8.8)
46.50, 65.19(q, 36.0),
72.60(q, 31.0), 94.47,
123.33(q, 280),
123.47(q, 280),
124.00(q, 280)
27
28
29
cis-5h
trans-5h
7
2.15(1H, ddt, 13.5, 6.2, 2.3), 2.33(1H, dm, 13.5), 4.14(td, 8.6, 2.3),
4.47(1H, m), 4.60(1H, t, 5.3), 6.25(1H, d, 4.8)
2.10(1H, m), 2.33(1H, m), 3.85(1H, m), 4.58(1H, m), 4.64(1H, m),
5.21(1H, d, 9.3)
À76.41(q, 10.6),
À71.01(q, 10.6)
À70.21(3F, q, 10.3),
À70.82(3F, q, 10.3)
À70.74(s)
–
–
3.87(s)
53.42, 70.50(sept. 31.0),
122.45(q, 286),
128.10, 158.69
30
31
1
8f
–
–
À72.63(s)
40.79(br.s), 122.38(q, 284)
63.35(br.s), 112.06(t, 303.0),
121.08(q, 286.0)
–
a
In CDCl3.
b
c
d
e
f
{H}13C NMR spectra.
Reported for 3a [3]: 19F NMR: À73.4(m) ppm.
3k ratio cis/trans-98: 2.
Reported for 4a [3]: 19F NMR: À67.9(q), À70.1(q), ppm, J = 10.4 Hz.
Reported for compound 8 [10]: 19F NMR: À67.0(t, 10.0), À91.8(m, 10.0); 13C NMR: 70.0(m), 118.4(t, 284.7), 127.1(q, 300.8) ppm.
days at ambient temperature), which can be attributed to lower
solubility of KF in DMF solvent.
It should be pointed out that formation of neither 1,2- or 1,3-
dithiolanes was not observed in the case of thietane 3l, even when
a large excess of sulfur was employed in the reaction of 1 and HFIB
(DMF, 25 8C, 3 days).
Mechanistically the formation of compounds 4d–g upon
treatment of thietane 3a or 3d with CsF can be the result of
thietane ring opening by fluoride anion (Scheme 1). Since FÀ is a
[(cShme_1T)ID$F]G
hard nucleophile, it attacks on carbon carrying an alkoxy group,
It was also demonstrated, that thietanes 3 can undergo
disproportionation in the presence of CsF catalyst. For example,
90% conversion of 3d in the reaction with CsF was achieved after 2
weeks at 25 8C (DMF), leading to a mixture of 1,2-dithiolane 4d,
olefin 4e and thiol 4f (Eq. (7); compound 4f probably formed as the
result of quench of the reaction mixture by water, see Section 4.7).
It should be pointed out, that his process is significantly slower
compared to the formation of the corresponding thietanes and the
formation of significant amount of compounds similar to 4e and 4f
was not observed in typical reaction of 1 with vinyl ethers:
(7)
In the reaction of thietane 3a with excess CsF and CH3I 1,2-
dithiolane 4a did not form, but instead it resulted in clean formation
of compound 4g (Eq. (8)):
(8)
Scheme 1.

1150
V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
rather than on sulfur of the thietane ring. The intermediate thiolate
anion 4i can be trapped by either reaction with CH3I or water
leading to 4g or 4f, respectively. The formation of 1,2-dithiolanes
4a–d, in this process is the result of nucleophilic attack of soft
thiolate 4i on the sulfur of second molecule of thietane, leading to
the intermediate 4j. Intramolecular cyclization in intermediate 4j
through the attack of carbanion center on sulfur results in
formation of 1,2-dithiolanes (4a–d) and elimination of anion 4k,
which gives olefin 4e after elimination of fluoride anion.
2,3-Dihydrofurane 2k under similar conditions gave 1,3-
dithiolane 5h as a mixture of cis- and trans-isomers (Eq. (10),
ratio 65:35, NMR).
(10)
2.2.2. Preparation of 2,2-bis(trifluoromethyl)-4-alkoxy-1,3-
dithiolanes
Since trans-isomer 5h has higher solubility, relatively pure
(96%, NMR) sample of cis-5h was obtained by crystallization of
distilled product from hexane and its structure confirmed by single
crystal X-ray diffraction (see Fig. 2).
As it was mentioned in Section 2.2.1, a small change in order of
addition of sulfur to the reaction mixture has significant impact on
the outcome of the reaction of 1, sulfur and vinyl ethers. Indeed,
when a second mole of sulfur is added right after generation of 1
and is followed by the addition of vinyl ether, the reaction becomes
exothermic, and it results in fast formation of the corresponding
1,3-dithiolanes 5 as major product (Eq. (9)). In this case, the
addition of vinyl ethers 2a–e, h, should be carried out slowly, in
order to control the heat evolution. In sharp contrast to the
reaction of sulfur with thietanes 3a–d (Eqs. (5) and (6)), which is
relatively slow, this process is fast and typically is completed
within 1–3 h after the addition of vinyl ether. It does not produce
expected 1,2-dithiolanes, but results in the formation of the
corresponding 1,3-dithiolane 5a–f, as principal product, along with
smaller amount (5–15%) of the corresponding thietanes 3a–e, h. In
the case of vinyl ether 2b it was demonstrated that dry KF is also
catalyzes the reaction. The process is less exothermic, but it also
results in the formation of 1,3-dithiolane 5b, along with smaller
amount of thietane 3b (ratio 5b:3b—84:16, calculated yield 5b—
86%):
It should be pointed out that the interaction of 2,3-dihydrofur-
ane (2k) with a mixture of 1 and sulfur seems to have a high
selectivity for the cis-cycloadduct, since the reaction which carried
out at lower conversion and shorter time resulted in selective
formation of cis-5h (95% selectivity at 50% conversion, NMR). This
data suggest, that the cis-isomer forms first, but under reaction
conditions it undergoes base catalyzed cis/trans-isomerization. It is
probably initiated by the abstraction of relatively acidic proton
from carbon connected to oxygen and sulfur, resulting in the
generation of carbanion A (Scheme 2). Since the addition of H+ to
intermediate A can proceed from either ‘‘top’’ or ‘‘bottom’’, this
process leads to the formation of both cis- and trans-isomers of 5h.
The formation of approximately equal amount of cis- and trans-
isomers in this reaction is indicative of small difference in energy
between two isomers of 5h. It is interesting, that the bicyclic
compound3k(containingthietane, rather, 13-dithiolanering)forms
predominantly as cis-isomer under similar conditions (see Eq. (3)).
This difference can be attributed to higher flexibility of compound
5h, containing five-membered ring with two sulfur atoms.
The reaction of a mixture of 1/Sx/CsF with electron deficient
olefins, such as dimethylmaleate or HFIB failed to produce the
corresponding 1,3-dithiolanes (2 and 7 days at 25 8C, respectively,
DMF solvent, NMR). Surprisingly, acetylene 6 was found to be
highly reactivity towards the mixture of 1 and sulfur, rapidly
producing the corresponding 1,3-dithiolene 7, along with some
polymeric material. The structure of 7 was confirmed by single
crystal X-ray diffraction.
(9)
(11)
2.3. Structure of thietanes and NMR spectra of 1,2- and 1,3-
dithiolanes
The structure of compound 5c (crystallized from hexane) was
confirmed by single crystal X-ray diffraction data.
Although products of the cycloaddition reaction HFTA with vinyl
ethers/vinyl sulfides are known for over 40 years, analysis of

[(ig._2)TD$FIG]
V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
1151
Fig. 2. X-ray crystal structure of cis-5h. Thermal ellipsoids drawn to the 50% probability level. Disordered positions are omitted for clarity.
literaturedata showsthatactualstructureofthesecycloadductswas
not firmly established. In the original paper [6], the structure of 2,2-
bis(trifluoromethyl)-4-R-thietane (vs. 2,2-bis(trifluoromethyl)-3-R-
thietane) was assigned based on data of mass spectrometry and low
resolution 1H and 19F NMR spectroscopy [3,6]. It should be pointed
out that the absence of significant coupling constants between CH2-
and CF3-groups in thietanes 3 (see discussion below) makes
standard of 1H and 19F NMR techniques insufficient for assigning
the structure of the regioisomers. In addition, well-known dual
reactivity of HFTA may be responsible for the formation of different
regioisomers depending on the nature of nucleophile. For example,
in reactions of HFTA, the attack of soft nucleophiles such as RSÀ may
proceed on sulfur [12], while hard ROÀ or FÀ [12,13], are known to
attack the carbon of C55S fragment of HFTA. That brings the
question—what is the actual orientation of HFTA cycloaddition with
vinyl ethers or fluorinated olefins? Single crystal X-ray diffraction
data reported recently for 2,2-bis(trifluoromethyl)-4-SO2C2H5-
of HFTA and vinyl ethers by Middleton is correct. However, 2,2-
bis(trifluoromethyl)-4-SO2C2H5-thietane did not derived from
direct cycloaddition reaction, but was synthesizes by selective
oxidation of the corresponding thietane 3j.
In this study we were able unambiguously establish the
structure of thietane 3f (R = O–Bu–t) using single crystal X-ray
diffraction and confirm that the cycloadduct indeed has the
structure
of
2,2-bis(trifluoromethyl)-4-(t-butoxy)-thietane
(Fig. 3), rather than isomeric 2,2-bis(trifluoromethyl)-3-(t-butox-
y)thietane. The structures of 3f and 3j suggest that in the reaction
with vinyl ethers and vinyl sulfides, HFTA acts as if the negative
charge is localized on sulfur of C55S fragment.
We also were able to confirm the structure of perfluoro(2,2,4,4-
tetramethyl)thietane (8, PFIB/HFTA cycloadduct, sample was
prepared in this laboratories by Dr. D. England). According to a
single crystal X-ray structure the thietane
symmetrical structure, similar to the structure of 3l (see Fig. 1),
with all four CF3-groups located in the -position to sulfur, as it
8 indeed has a
[(g._3)TD$FIG]
ti hietane [5], suggested that structural assignment of cycloadducts
a
Fig. 3. X-ray crystal structure of 3f. Thermal ellipsoids drawn to the 50% probability level. Disordered positions are omitted for clarity.

1152
V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
_
was suggested earlier by Zeifman and Postovoii [10], based on data
of 19F and 13C NMR spectroscopy. An interesting feature of
thietanes 3l and 8 is flattening of the thietane ring as reflected in
small values of torsion angle S–C2–C3–C4 (3.18 and 0.18,
respectively) vs. value 268 reported for the parent thietane [14].
While 1H and 19F spectra of thietanes 3a–l and 8, 1,2-
dithiolanes 4 and 1,3-dithiolanes are typical for this type of
materials and differ only slightly, all the spectra share one common
feature—the absence of observable coupling constant between
CF3-groups and CH2 hydrogens of the thietane or 1,2- or 1,3-
dithiolane ring, which makes impossible the identification of
regioisomers using 1H and 19F NMR spectroscopy.
While in 19F NMR spectra of thietanes 3, the resonances of CF3-
groups usually appear between À73 and À74 ppm as either
overlapped or not well separated quartets, the corresponding
resonances in 1,2- and 1,3-dithiolanes are well separated by ꢀ2–
3 ppm. The resonances of trifluoromethyl groups in 1,3-dithiolanes
5a–g are shifted upfield by ꢀ0.5 ppm compared to 1,2-dithiolanes
4a–d.
On the other hand, in the 13C NMR spectra a significant
difference in chemical shifts of the carbon carrying two trifluor-
omethyl groups was observed for thietanes, 1,2- and 1,3-
dithiolanes (see Table 2). Indeed, resonances of C-2 in 13C NMR
spectra of thietanes 3a–l, all appear within the narrow range of 43–
Scheme 3.
47 ppm (cf.
parent thietane [15]), with deviation of the chemical shift for
perfluorinated thietane 8 ( = 63.35 ppm). While in 4-alkoxy
thietanes 3 this signal is well resolved (septet, J = 32–33 Hz), in
compounds 1, 3l and 8 it is broadened (Dy1/2 = 70–80 Hz) and does
not have fine structure (CDCl3, 25 8C). The resonance of the same
carbon in 1,2-dithiolanes 4 is shifted downfield and located in the
d = 40.79 ppm for compound 1 and d = 26.1 ppm for
thietanes 3a–j is still not clear. Both HFTA and hexafluoroacetone
(HFA), react with vinyl ethers selectively forming 4-alkoxy-
thietanes [6] or -oxetanes [16], respectively. On the other hand,
in ene-reaction different regiochemistries of insertion into allylic
C–H bond was observed for HFA and HFTA. For example the
reaction propylene with HFA gives allylhexafluoroisopropanol
[17], however, similar process involving HFTA results in selective
formation of CH255CHCH2SCH(CF3)2 [6].
d
range of
carbon carrying two CF3-groups is shifted even further and appears
within the narrow range of = 69–72 ppm.
d = 64–66 ppm, while in 1,3-isomers 5 the septet of the
d
One of the explanations of unusual charge distribution in the
C55S moiety of HFTA was suggested by Fukui [18] involves the
participation of d-orbitals of sulfur, leading to higher electron
2.4. Mechanistic considerations
[(chme_4T)D$FI]G
dS ensity on sulfur. The observed regiochemistry of cycloaddition
While the regiochemistry of cycloaddition of HFTA to vinyl
ethers is now reliably confirmed, the mechanism of formation of
[(Schme_2)TD$FIG]
Scheme 2.
Scheme 4.

V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
1153
vinyl ethers and HFTA can be explained using three-centered
coordination mechanism suggested for 2 + 2 cycloaddition reac-
tions by Fukui [19].
Sx\CsF or (25 8C, DMF, 2–5 days, NMR, Eq. (12)). That fact is
considered as an argument in favor of the mechanism involving
nucleophilic attack on carbon, since in compounds 9 and 3l
a-
The formation of thietane 3l in the reaction of 1 and HFIB
(Eq. (4)) can be explained by mechanism postulated by Zeifman
and Postovoii for the reaction of PFIB and 1 [10]. It includes attack
of (CF3)2CFSÀ on positively charged carbon of CH2 group of HFIB
and further reaction of the intermediate carbanion with HFTA and
intermolecular cyclization with the formation of 3l and release of
(CF3)2CFSÀ, which can be involved in the cyclization process again
(Scheme 3).
carbon of thietane ring is sterically hindered and is not susceptible
to nucleophilic attack.
It should be pointed out, that at this point an alternative
mechanism involving an single electron transfer step and the
formation of intermediate zwitter-ion ÀC(CF3)2CH2C(CF3)2S+ can-
not be completely ruled out.
(12)
The formation of1,2-dithiolanes 4a–d inthe reaction of thietanes
3 with sulfur (Eq. (4)) can be explained by the mechanism presented
in Scheme 4. Sulfur anion B (formed as the result of the reaction of Sx
withCsFinpolarsolvent)attacksthecarboncarryingalkoxygroupof
the thietanes ring. The ring opening process leads to the generation
of intermediate C. Intramolecular nucleophilic attack on a sulfur
atom, followed by elimination of the sulfur anion results in the
formation of 1,2-dithiolanes 4a–d.
It should be mentioned that the mechanism depicted in Scheme
4 is preferred over an alternative one involving attack on sulfur
anion on sulfur atom of the thietane ring, since it agrees with
transformation of thietanes 3a and d under action of CsF (Eqs. (5)
and (6)). We also found that both norbonenthietane 9 [20] and
The mechanism of the formation of 1,3-dithiolanes 5a–g and
1,3-dithiolene 7 is not quite clear at this point. One of several
possible mechanisms is depicted by Scheme 5 is based on
the assumption that HFTA generated from 1 under action of
fluoride anion can react with sulfur anion B forming dithiirane D.
Intermediate D can further undergo cycloaddition to vinyl
ethers giving the corresponding 1,3-dithiolanes. The formation
of the corresponding cyloadducts with both electron rich and
electron deficient substrates (acetylene 6) may suggest that the
reactive intermediate involved in this process has zwitter-ionic
structure E, however, the participation in this process inter-
mediates such as dithiirane D or biradical F also cannot be
excluded either.
t[(Schme_5)TD$FIG] hietane 3k are inert towards the action of CsF or the mixture of
3. Conclusion
Described in this paper one-pot procedure for the preparation
of 2,2-bis(trifluoromethyl)-4-R-thietanes simplifies the synthesis
of fluorinated thietanes. It is applicable for the preparation of a
wide variety of thietanes 3, including 2,2-bis(trifluoromethyl)-4-S-
Et-thietane (3j) and 2,2,4,4-tetrakis(trifluoromethyl) thietane (3l).
The structures of 2,2-bis(trifluoromethyl)-4-t-BuO-thietane (3f),
along with structures of thietanes 3l and 8 was confirmed by single
crystal X-ray diffraction data.
Metal fluoride catalyzed reaction of thietanes 3a–d with second
mole of sulfur provided an easy access to3,3-bis(trifluoromethyl)-5-
alkoxy-1,2-dithiolanes 4a–d. Thietanes 3 under the action of
fluoride anion can undergo disproportionation, forming a mixture
ofthecorresponding1,2-dithiolane(4)and CF255C(CF3)CH2CHF(OR).
This reaction is significantly slower and doesn’t compete with
formation of thietanes or thiolanes. Preliminary mechanistic studies
indicate that ring opening of thietanes 3 proceeds through attack of
nucleophile on C-4 carbon of thietanes ring.
A simple modification of the synthetic protocol, by reversing an
order of reagent addition leads to predominant formation of the
2,2-bis(trifluoromethyl)-4-alkoxy-1,3-dithiolanes 5a–h, providing
an access to new group of fluorinated sulfur containing hetero-
cycles.
4. Experimental
1H NMR and 19F NMR spectra were recorded on a Bruker DRX-
500 (499.87 MHz) instrument using CFCl3 or TMS as internal
standards. CDCl3 was used as a lock solvent, unless stated
Scheme 5.

1154
V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
otherwise. IR spectra were recorded on a Perkin-Elmer 1600 FT
spectrometer (KCl plates, liquid film or in KBr for solids). Moisture
sensitive materials were handled in a glove box, under nitrogen. GC
and GC/MS analysis were carried out on a HP-6890 instrument,
using HP FFAP capillary column and either TCD (GC) and mass
selective (GS/MS) detectors, respectively. Dry DMF (anhydrous,
water content 0.005%), dimethylacetylene carboxylate (6)
(Aldrich), sulfur (sublimed, 99.5%, ꢀ100 mesh, Alfa Aesar),
hexafluoropropene, HFIB (DuPont), vinyl ethers 2a–k (Aldrich,
TCI), were obtained from commercial sources and used without
further purification. CsF and KF (Aldrich) were dried at 100–120 8C
under dynamic vacuum for 4–8 h and were stored and handled
inside of the dry box.
Caution: All reactions described in the paper are affected by
trace amounts of water, so using anhydrous solvents and reagents
and proper drying and handling of CsF and KF is essential. Trace
amount of water may significantly reduce the yield or completely
inhibit the reaction, due to deactivation of metal fluoride catalyst.
Due to a high ratio of sulfur to fluorine, elemental analysis was
not attempted for new materials. The purity of all isolated
compounds established by GC and NMR spectroscopy was at least
98%.
4.3. One-pot preparation of thietanes 3a–k catalyzed by CsF (typical
procedure)
Inside of dry box 250–500 mL three-neck, round bottom flask
was charged with 1–2 g of dry CsF. The flask was taken out, brought
into a fume hood, and under flow of nitrogen was equipped with
thermocouple, dry-ice condenser, gas inlet tube and magnetic stir
bar. Dry DMF (50–250 mL) was added using syringe and sublimed
sulfur (3.2–16 g, 0.1–0.5 mol) was added to agitated reaction
mixture. The addition of sulfur resulted in the appearance of green
or blue color, which quickly disappeared after addition of HFP was
started. The addition of gaseous hexafluoropropene (HFP) was
started at ambient temperature and resulted in rapid raise of
internal temperature to 45–50 8C. HFP was fed into reaction
mixture at a rate, which allowed to maintain internal temperature
between 50 and 65 8C, but at same time avoid the condensation of
an excessive amount of HFP on dry-ice condenser. After the
required amount of HFP (0.1–0.5 mol, measured by weight
difference of the HFP cylinder) was added and all sulfur went
into solution, the reaction mixture was allowed to cool down to
ambient temperature. Required amount (0.1–0.5 mol) of vinyl
ether 2 was added to the reaction mixture and it was agitated at
ambient temperature for 24–48 h. The reaction was monitored by
GC and when the conversion of starting materials would exceed
90%, the reaction mixture was diluted with 200–300 mL of water,
extracted with hexane (50–75 mL Â2), combined organic layer was
washed by water (100 mL Â3), dried over MgSO4. Solvent was
removed under reduced pressure and the residue was distilled
under vacuum to give thietanes 3a–k. Yields, boiling points and
data of mass spectrometry for 3a–k are given in Table 1 and NMR
data in Table 2.
4.1. Crystallography
X-ray data for 3l, 3f, 5c, 5h, 7 and 8 were collected at À100 8C
using a Bruker 1K CCD system equipped with a sealed tube
molybdenum source and a graphite monochromator.
The structures were solved and refined using the Shelxtl [21]
software package, refinement by full-matrix least squares on F2,
scattering factors from Int. Tab. Vol C Tables 4.2.6.8 and 6.1.1.4.
Crystallographic data (excluding structure factors) for the struc-
tures in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication nos.
CCDC #769157 to #769162. Copies of the data can be obtained, free
of charge, on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44 1223 336033 or e-mail: deposit@ccdc.cam.a-
c.uk).
4.4. Preparation of thietane 3l
To a DMF solution of 1 (0.1 mol; prepared from 6.4 g of sulfur
and 33 g HPF, 1.0 g of CsF in 100 mL of DMF, as describe in Section
4.3) placed in 250 mL three-neck flask equipped with thermocou-
ple, dry-ice condenser and gas inlet tube, it was slowly added 33 g
(0.2 mol) of gaseous CH255C(CF3)2 at 25–35 8C. The reaction
mixture was agitated at ambient temperature for 48 h, diluted
by 300 mL of water, organic layer was separated, washed by water
(100 mL) dried over MgSO4 and distilled to give 52 g (75%) of 3l,
b.p. 112–113 8C. Data for compound 3l are given in Tables 1 and 2.
4.2. Preparation of thietanes 3a–d catalyzed by KF (typical procedure)
Inside of dry box 250–500 mL three-neck, round bottom flask
was charged with 1–2 g of dry KF. The flask was taken out, brought
into a fume hood, and under flow of nitrogen was equipped with
thermocouple, dry-ice condenser, gas inlet tube and magnetic stir
bar. Dry DMF (50–100 mL) was added using syringe and sublimed
sulfur (3.2–6.4 g, 0.1–0.2 mol) was added to agitated reaction
mixture. The additionof sulfur resulted intheappearanceof greenor
blue color, which quickly disappeared after addition of HFP was
started. The reaction mixture was brought up to ꢀ30–35 8C and
gaseous hexafluoropropene (HFP) was fed into reaction mixture at a
rate, which allowed to maintain internal temperature between 35
and 45 8C, but at same time avoid the condensation of an excessive
amount of HFP on dry-ice condenser. After the required amount of
HFP (0.11–0.22 mol, measured by weight difference of the HFP
cylinder) was added and all sulfur went into solution, the reaction
mixture was allowed to cool down to ambient temperature.
Required amount (0.1–0.2 mol) of vinyl ether 2 was added to the
reaction mixture and it was agitated at ambient temperature for 24–
48 h. The reaction was monitored by GC and when the conversion of
starting materials exceed 90% the reaction mixture was diluted by
200–300 mL of water, extracted by hexane (50–75 mL Â2),
combined organic layer was washed by water (100 mL Â3), dried
over MgSO4. Solvent was removed under reduced pressure and the
residue was distilled under vacuum to give thietanes 3a–d. Data for
compound 3a–d are given in Tables 1 and 2.
4.5. Preparation of 1,2-dithiolanes 4a–d (typical procedure)
Dry three-neck flask was charged with 0.5–1.0 g of dry CsF
inside of dry box. The flask was taken out, brought into a fume
hood, and under flow of nitrogen was equipped with thermocou-
ple, reflux condenser and magnetic stir bar. Under nitrogen
blanket via syringe it was added 30 mL of dry DMF, 1.0–1.6 g
(0.03–0.05 mol) of sulfur and 2.5–7.5 g (0.01–0.03 mol) of
thietane 4. The reaction mixture was agitated at ambient
temperature for 24–36 h and the progress was monitored by
GC. After all starting thietane was consumed the reaction mixture
was poured into 300 mL of water, extracted with hexane (50 mL
Â3), organic layer was washed by water (100 mL Â3), dried over
MgSO4 and solvent was removed under reduced pressure. The
residue was distilled under vacuum. Yields, boiling points and
data of mass spectrometry for 4a–d are given in Table 1 and NMR
data can be found in Table 2.
4.6. Preparation of 1,3-dithiolanes 5a–h and 1,3-dithiolene 7
Dry three-neck flask was charged with 1.0–2.0 g of dry CsF inside
of dry box. The flask was taken out, brought into a fume hood, and

V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 131 (2010) 1144–1155
1155
under flow of nitrogen was equipped with thermocouple, dry-ice
condenser and inlet tube and magnetic stir bar. Under nitrogen
blanket via syringe was added 50 mL of dry DMF and 3.2 g (0.1 mol)
ofsublimedsulfur.Theadditionofgaseoushexafluoropropene(HFP)
was started at ambient temperature and resulted in exothermic
reaction and rapid absorption of HFP. The HFP addition was
maintained at a rate which allowed internal temperature to remain
between at 45–65 8C, but at same time avoid the condensation of
excessive amount of HFP on the dry-ice condenser. After required
amount of HFP (ꢀ0.11–0.12 mol) was added and all sulfur went into
solution, the reaction mixture was allowed to cool down to ambient
temperature. Another portion of sulfur (3.2 g) was added to the
agitated reactionmixtureandwasfollowedbydrop-wiseadditionof
the corresponding vinyl ether (0.1 mol) at a rate, which kept the
internal temperature of the reaction mixture <35 8C. The reaction
mixture was agitated at ambient temperature for 2–4 h. It was then
diluted by 200–300 mL of water, extracted by hexane (50–75 mL
Â2), organic layer was washed by water (100 mL Â3), dried over
MgSO4. Solvent was removed under reduced pressure. According to
NMR and GC/MS, the crude product contained a mixture of 1,3-
dithiolane and the corresponding thietane in ratios between 85:15
and 90:10. Pure 5a–h, 7 (purity >98%) were isolated by vacuum
distillation. Yields, boiling points and data of mass spectrometry for
5a–h and 7 are given in Table 1 and NMR data in Table 2.
nitrogen for 18 days at 25 8C. The progress of the reaction was
monitored by GC/MS and NMR. The reaction mixture was worked
up as described above, using hexane extraction. 2.6 g of crude
product was isolated. The crude reaction mixture, according to 1H
and 19F NMR contained compounds 3a and 4g in a ratio of 1:1.
Sulfide 4g was characterized in reaction mixture and NMR data are
given in Tables 1 and 2.
Acknowledgments
Authors thank Dr. D. England for the sample of compound 8 and
Timothy Bentz for technical assistance.
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4.8. Reaction of thietane 3a with CH3I
A mixture of 2.5 g (0.01 mol) of 3a, 1.6 g of dry CsF, 2.8 g
(0.02 mol) of CH3I and 20 mL of dry DMF was agitated under