Simple protocol for preparation of Diels-Alder adducts of perfluorinated thioketones

Article abstract of DOI:10.1016/j.jfluchem.2019.06.003

A simple procedure for the preparation of new Diels-Alder adducts of perfluorinated thioketones is reported. The corresponding adducts were prepared in 30–78% yield by reaction of alicyclic perfluorinated olefin, sulfur, diene and CsF catalyst. While the synthesis of quadricyclane, cyclohexadiene-1,3, cycloheptatriene-1,3,5 and 2,3-dimethylbutadiene-1,3 adducts was straightforward, a modified protocol was used in the case of the reaction of cyclopentadiene-1,3,F-pentene-2 and sulfur in order to avoid the formation of cycloadduct of cyclopentediene and F-pentene-2. In this case the olefin first was reacted with sulfur and cyclopentadiene was added later. In separate experiments it was demonstarted that the reaction of F-pentene-2, sulfur and CsF catallyst leds to the formation of two isomeric perfluorinated 1,3-dithiolanes along with equimolar amount of branched polysulfides (R_f)₂S_x. Due to broadening of signals in ¹⁹F NMR spectra of the most cycloadducts, additiononal variable temperature NMR experiments were carried out, and rotational barriers several adducts were found to be in the range 9.5–11 Kcal/mol.

Full text of DOI:10.1016/j.jfluchem.2019.06.003

Journal of Fluorine Chemistry 225 (2019) 1–10
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Simple protocol for preparation of Diels-Alder adducts of perfluorinated
thioketones
a,⁎
b
b
b
Viacheslav Petrov , Rebecca J. Dooley , Alexander A. Marchione , Elizabeth L. Diaz ,
b
Brittany S. Clem
a
b
Chemours Co., Chemours Fluoroproducts, 200 Powder Mill Rd., Experimental Station, Wilmington, DE 19803, USA
Chemours Co., Chemours Fluoroproducts Analytical, 200 Powder Mill Rd., Experimental Station, Wilmington, DE 19803, USA
A R T I C L E I N F O
A B S T R A C T
Keywords:
A simple procedure for the preparation of new Diels-Alder adducts of perfluorinated thioketones is reported. The
corresponding adducts were prepared in 30–78% yield by reaction of alicyclic perfluorinated olefin, sulfur, diene
and CsF catalyst. While the synthesis of quadricyclane, cyclohexadiene-1,3, cycloheptatriene-1,3,5 and 2,3-di-
methylbutadiene-1,3 adducts was straightforward, a modified protocol was used in the case of the reaction of
cyclopentadiene-1,3,F-pentene-2 and sulfur in order to avoid the formation of cycloadduct of cyclopentediene
and F-pentene-2. In this case the olefin first was reacted with sulfur and cyclopentadiene was added later. In
separate experiments it was demonstarted that the reaction of F-pentene-2, sulfur and CsF catallyst leds to the
formation of two isomeric perfluorinated 1,3-dithiolanes along with equimolar amount of branched polysulfides
Perfluoroolefins
Sulfur
Perfluorothioketones
Diels-Alder reaction
1
9
(
R
f
)
2
S . Due to broadening of signals in F NMR spectra of the most cycloadducts, additiononal variable tem-
x
perature NMR experiments were carried out, and rotational barriers several adducts were found to be in the
range 9.5–11 Kcal/mol.
1
. Introduction
hexafluoropropene [8,10,11]). Evidence supporting intermediate for-
mation of the corresponding thioketone was obtained in the reaction of
Cycloaddition reactions of perfluorinated thioketones are limited
2-chloroheptafluorobutene-2, 2,3-dimethylbutadiene (DMBD), sulfur
and excess of KF at 180 °C [9] - the corresponding cycloadduct of
perfluorothiobutanone-2 and DMBD was reported to form under these
conditions, although no experimental details were provided in this
publication.
mostly to the reaction involving hexafluorothioacetone [1], due to its
high reactivity and the fact that it can be easily generated “in situ” from
the readily available cyclic dimer [2–6]. Examples of cycloadditions of
higher perfluorinated thioketones are extremely rare, due to the lack of
simple and practical methods of their generation. All known examples
of perfluorinated thioketones were reported by W. Middleton, and the
Recently [12], we reported results of a preliminary study describing
a simple protocol for the preparation of the Diels-Alder adducts of
perfluorinated thioketones and dienes, avoiding preparation, isolation
or handling of unstable perfluorothioketones (perfluorinated thioke-
tones rapidly undergo dimerization at ambient temperature [13]).
The current publication provides new examples of Diels-Alder ad-
ducts of perfluorinated thioketones, obtained through the reaction of
internal (F-butene-2, F-pentene-2) or cyclic (F-cyclobutene, F-cyclo-
pentene and F-cyclohexene) perfluoroolefins with various conjugated
dienes and sulfur, along with an additional variable temperature NMR
characterization of new cycloadducts.
list
is
limited
to
perfluorothiobutanone-2
and
per-
fluorodithiobutyrolactone [7]. Typical synthesis of these involves a
reaction of 2-iodoperfluorobutane or 1,4-diiodoperfluorobutane with
P
2
5
S at 550 °C [7]. In a pioneering work, the Knunyants group reported
the first example of a reaction of hexafluoropropene and F-cyclobutene
with elemental sulfur in the presence of KF, leading to a mixture of
sulfur-containing compounds. The formation of hexafluorothioacetone
and perfluorothiocyclobutanone as reaction intermediates was postu-
lated in this work [8]. Later the Burton group reported a KF- catalyzed
reaction of F-butene-2 (1) and F-pentene-2 (3) with sulfur leading to the
formation of perfluorinated 1,3-dithiolanes [9], (rather than the ex-
pected 1,3-dithietane, observed in the analogous reaction of sulfur and
⁎
Corresponding author.
E-mail address: viacheslav.petrov@chemours.com (V. Petrov).
https://doi.org/10.1016/j.jfluchem.2019.06.003
Received 2 May 2019; Received in revised form 6 June 2019; Accepted 12 June 2019
Available online 13 June 2019
0022-1139/ © 2019 Elsevier B.V. All rights reserved.

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
2
. Results and discussion
dithiolanes 7a,b in the reaction of 3, sulfur, and CsF was demonstrated
in a separate experiment. Indeed, the exothermic reaction of an equi-
molar mixture of the olefin 3 and sulfur in the presence of catalytic
amount of CsF in DMF solvent resulted in the formation of mixture 7a,b
2.1. Reaction of internal perfluoroolefins
Previously, it was shown that the reaction of quadricyclane (Q) with
and branched polysulfides 7c – [(i-C
5
11
F )
2
S , n = 2-4, NMR, GC/MS]
n
F-butene-2 (1), sulfur and KF (130 °C, sulfolane) led to low yield for-
mation of the corresponding cycloadduct [4]. In this work, it was found
that this reaction does not require heating and proceeds at ambient
temperature. Indeed, when a mixture of 1, sulfur, quadricyclane (Q),
and CsF catalyst was kept in DMF solvent at ambient temperature, it
resulted in the formation of the corresponding two isomeric Diels-Alder
cycloadducts 2a and 2b (Eq. (1)).
(Eq. (4)).
(
4)
The removal of the polysulfides 7c was achieved by a treatment of
crude reaction mixture with imidazole in DMF solvent, and a mixture of
compounds 7a,b was isolated in 44% yield (based on the amount of 3
used in the reaction). There are several features of this reaction that are
noteworthy:
(
1)
As in many other cycloadditions involving Q [4,14–16], this reac-
tion led to exclusive formation of cycloadducts containing a four-
membered ring in the exo- position. The formation of the two isomers
a) Reaction proceeds at ambient temperature and leads to the forma-
tion of 7b as major product
2
a and 2b in this case is related to different orientation of the fluor-
b) Compounds 7a,b and polysulfides 7c are formed in equimolar
amount
oalkyl groups, relative to the one-carbon bridge of the norbornene
fragment. The structural assignment of isomers was carried out based
c) No formation of monosulfide (i-C
5
F
11
) S was observed in this pro-
2
1
19
on H and F NMR spectroscopy.
cess (GS/MS), but the reaction leads to a mixture of polysulfides
The reaction of F-pentene-2 (3), sulfur, Q and CsF catalyst was
slightly exothermic, leading to the formation of three isomers - 4a, 4b
and 4c, with significant prevalence of symmetrical isomer 4a (Eq. (2);
for reaction mechanism, see the Section 2.4)
(
f
R )
2
n
S (n = 2–4), with disulfide being major component (up to 80%
of total)
The formation of compound 7a (along with the corresponding
branched bis(perfluoroalkyl)polysulfides) in the reaction of 3, sulfur
and KF at 180 °C was previously reported by Burton et al. [9], but since
no formation of isomer 7b was observed under these conditions, it was
suggested that compound 7b was a kinetic product and underwent
isomerization into 7a at elevated temperature [9]. The formation of 7b
under milder reaction conditions agrees well with this hypothesis.
Although the formation of 7a,b as by-products was also observed in
the reaction of 9-methylanthracene (MANTHR), 3 and sulfur (due to
low solubility of MANTHR in DMF, this reaction was carried out at
6
5 °C), the reaction led to the formation of cycloadduct 8a along with
smaller amount of isomer 8b (Eq. (5))
(
2)
Cyclopentadiene-1,3 (5) also was found to be active in this reaction,
but the synthetic protocol in this case was significantly modified in
order to avoid the formation of Diels-Alder adduct of 5 and F-pentene-2.
Olefin 3 was reacted first with an S /CsF mixture (DMF, 25 °C), and
x
after 2 days, freshly prepared cyclopentadiene was added to the reac-
tion mixture. The reaction led to the formation of the cycloadducts 6a-
c, along with smaller amount of isomeric 1,3-dithiolanes 7a,b (Eqs. (3)
and (4))
(
5)
It should be pointed out that neither 9-bromo-, nor 9,10-dimethyl-
anthracenes produced any Diels-Alder cycloadducts in the reaction with
3
and sulfur under similar conditions (65 °C, 6 days); instead, the re-
action resulted in the formation of compounds 7a-c. A significant pre-
ference for the formation of the non-symmetrical isomer 8a in this re-
action (Eq. (5)) may be the result of steric repulsion between the
perfluoroalkyl groups and the condensed aromatic system, since in the
(
3)
As in the case of Q reaction (Eq. (2)), symmetrical isomer 6a was a
major product, while minor isomers 6b (exo-CF ) and 6c (endo-CF
were formed in approximately equal amounts. The formation of 1,3-
19
F NMR spectrum of isomers 8a/8b acquired at ambient temperature a
3
3
)
significant broadening of signals was observed, as a result of restricted
rotation of perfluoroalkyl groups (see Section 2.2.1 on dynamic NMR
2

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
Fig. 1. Dynamic NMR analysis of 18. Top: 19F NMR spectra in the fast exchange regime, from 353 K (80 °C) to 443 K (170 °C). Middle: F NMR spectra at 213 K with
19
selective inversion of (major) conformer resonance at −132 ppm. Bottom: Eyring plot of interconversion kinetics of the major ⇌ minor conformer equilibrium.
spectroscopy). Interestingly, no restricted rotation of CF
3
groups was
exclusively the nonsymmetrical cycloadduct, structurally similar to 8a,
while no formation of the symmetrical isomer was observed [12]. At
this point, such difference in the behaviour between anthracene and its
9-methyl- derivative is not well understood, although predominant (or
observed for Diels-Alder adducts of hexafluorothioacetone and an-
thracene or its 9-bromo- and 9-methyl- derivatives [6]. It should be also
pointed out that reported reaction of anthracene and 3 yielded
3

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
Table 1
enthalpies and heats of formation.
Eyring parameters for compounds 2a, 2b, 8a, 18, and 20.
An unusual result was obtained in the reaction of 3, sulfur, cyclo-
heptatriene-1,3,5 (CHPTr) and CsF. Instead of the expected Diels-Alder
cycloadduct 9a, [this type of adduct was reported to form exclusively in
‡
−1
ΔS‡ (cal mol−1 K−1
)
Compound
Interconversion
ΔH (kcal mol
)
2
2
2
2
8
8
1
1
2
2
a
a
b
b
a
a
8
8
0
0
Major to minor
minor to Major
Major to minor
minor to Major
Major to minor
minor to Major
Major to minor
minor to Major
Major to minor
minor to Major
9.52
9.55
10.2
10.4
9.52
9.55
10.7
10.5
11.1
10.8
−5.25
−4.21
−6.30
−2.30
−5.25
−4.21
−6.38
−1.30
−4.72
0.36
the reaction of 1 and CHPTr (R
f
=CF
3
, R
f
’=C
2
5
F )] [12], the reaction
resulted in the formation of a mixture of two isomeric materials,
identified by NMR and mass spectroscopy as tetracyclic compounds 9b
and 9c (Eq. (6)). Structures of 9b (major) and 9c (minor) were eluci-
dated using a full suite of NMR experiments, including 1,1-ADEQUATE
13
to assign the C skeletons (see also Section 2.3).
(
6)
The reaction required a stochiometric amount of CsF, since under
catalytic conditions it stopped with only partial conversion of the
starting materials. Although the mechanism of this process is not clear,
the formation of compounds 9b and 9c was likely a result of two-step
process involving cycloaddition and dehydrofluorination (likely to be
sequential processes), since monitoring of the reaction mixture by NMR
revealed transient formation of cycloadduct 9a at earlier stages of the
reaction.
Scheme 1. Generation and cycloadditon reaction of perfluoprinated thioke-
tones.
2.2. Reactions of cyclic perfluorinated olefins
Cyclic perfluoroolefins were also found to be active in this process;
however, their reactivity varied substantially. F-cyclobutene (10) seems
to have the lowest reactivity among studied cyclic olefins. Due to gas-
eous nature of 10, all reactions were carried out in a closed system (see
Experimental). The corresponding cycloadducts 11-13 were isolated in
the reaction of 10 with DMBD, CHPTr and CHD in 64, 35 and 15%
yield, respectively (Eq. (7)).
(
7)
It should also be pointed out that in the case of the CHPTr, the
formation of small amount of polysulfide type by-products was ob-
served. These were presumably derived from the reaction of 10 and
sulfur and identified by GC/MS, but their structure was not determined.
Both F-cyclopentene (14) and F-cyclohexene (16) were found to be
more active in this process. The reaction of 14/S and CHD under si-
x
milar conditions led to cycloadduct 15 in 74% yield (Eq. (8)).
Scheme 2. Catalytic cycle of fluoride de anion.
(8)
Similarly, F-cyclohexene (16) showed high activity in the reaction
involving sulfur and conjugated dienes. For example, the CsF catalysed
reaction of 16, sulfur and CHPTr resulted in high yield formation of
compound 17, while similar reactions of 16/DMBD and 16/anthracene
(ANTHR) led to the formation of cycloadduct 18 and 19 isolated in 85
and 62% yield (Eq. (9)). It should be pointed out that the sample of the
olefin 16 used in this study contained ˜10% of two isomeric F-
exclusive) formation of nonsymmetrical adducts in the reaction of 3
with MANTHR or anthracene may be related to the unfavourable sterics
of the symmetrical thioketone (C
2
F
5
) C = S. These may be manifested
2
only in the transition states of formation, as a computational study
carried out in this work for the unsymmetrical and symmetrical isomers
8
a and 8b themselves found them to be of essentially identical
4

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
Scheme 3. Mechanism of formation 1,3 dithiolanes 7a,b.
methylcyclopentenes. However, under reaction conditions, only olefin
spectra of these compounds using variable temperature NMR.
Hindered rotation of the CeC bond between the bridgehead carbon
1
6 was involved in the reaction, indicating its higher reactivity relative
to isomeric F-methylcyclopentenes, which once again may be a reflec-
tion of the higher steric demand of F-methylcyclopentene ring.
and the adjacent CF moiety was studied in compounds 2a, 2b, and 8a,
2
and the dynamics of the chair-chair interconversion of the deca-
fluorocyclohexyl moiety were studied in compound 18 and compound
2
0, the synthesis of which was reported previously [12]. In each case,
two regimes of exchange kinetics were studied. The compound was
3
4
heated to reach a regime of fast exchange (ca. 10 – 10 Hz), and cooled
0
2
to reach a regime of slow exchange (ca. 10 – 10 Hz). In the fast ex-
change regime, the degree of spectral line broadening at each tem-
perature was determined by spectral simulation in comparison with a
multiplet of ordinary linewidth, and the degree of broadening was
correlated to the rate constant of interconversion k by the following
relation [17]
2
2
k
A
A
= 4πp p
B
(δν) W*
where k
A
is the rate constant of conversion of rotamer (or conformer) A
(
9)
to B, p
A
is the population of rotamer (or conformer) A, p is the cor-
B
responding population of B, δν is the difference in Hz between the
multiplets corresponding to each rotamer or conformer, and W* is the
broadening of the peaks at half-maximum height as derived from the
Compounds 17-19 were isolated and fully characterized by NMR
and MS spectroscopy. While NMR spectra of spiro- adducts containing
four- and five- membered rings (compounds 11-13, 15) were well-re-
1
9
spectral simulation. Inversion of all A and B terms yields k The slow
B.
solved at ambient temperature, signals in F NMR spectra of 17-19
were extremely broad at ambient temperature, to the point that spectra
didn’t provide any structural information (see Section 2.2.1).
exchange region was probed by selective inversion recovery experi-
ments [17], wherein the spin polarization of one site was selectively
inverted, a delay period for chemical exchange between sites was in-
serted, and a hard excitation pulse was applied before acquisition. The
delay period was arrayed, and the degree of polarization exchange
between conformers was fitted according to a simple first-order return
to equilibrium with rate constants k and k . The rate constants ob-
2
.2.1. Dynamic NMR spectroscopy
19
In F NMR spectra of cycloadducts 2a,b, 4a-c, 8a,b acquired at
ambient temperature, resonances of CF and CF groups were broa-
3
2
A
B
dened. A similar phenomenon was previously reported for other Diels-
Alder adducts obtained in the reaction of olefins 1 and 3 with con-
jugated dienes [12]. In all these cases the signal broadening was likely
related to restricted rotation of fluoroalkyl groups. On the other hand,
the substantial broadening of signals in the case of compounds con-
taining F-cyclohexyl fragment (compounds 17-19 and 20 (cycloadduct
of F-cyclohexylthione and CHD, [12]) could be a result of a different
dynamic process related to the slow chair-chair interconversion of the
F-cyclohexyl ring. In order to obtain resolved NMR spectra and ther-
tained in these two regimes were then fitted to an Eyring plot. Using
these two complementary experimental approaches, the rate constants
of interconversion were obtained over wide temperature ranges
(> 150 K), greatly improving the precision of the derived Eyring
parameters. The results of these experiments on 18 are summarized in
Fig. 1.
The Enthalpies and Entropies of Activation for compounds 2a, 2b,
8a, 18, and 20 are listed in Table 1.
While rotational barriers in all cases were reasonable (9.5–11.1
1
9
modynamic parameters of dynamic processes, we studied F NMR
5

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
Table 2
Reaction Conditions, Yields and Boiling (melting) Points of New Materials.
Entry No
Reagents, (mmol)
DMF (mL)
Temp., oC, time (h)
Product(s)
B.p. oC/mm Hg (m.p., oC, from hexane)
Isolated yield (%)
45
1
1(100), Q (109),
35
25 (24)
2a, 2b (ratio 65:35)
52–55 °C /2
93–97 °C/10
Clear oil
x
S (100),
KF(10)
2
3
4
3(100), Q(110),
12
35
15
22a (96)
22(120)
25(120)
4a, 4b, 4c (ratio 70:20:10)
55
x
S (10),
CsF(10)
3(20), 5 (20),
6a-c (ratio 65:19:16)
7a,b (ratio 20:80)
44
22
x
S (20),
CsF(11)
3(20),
7a-c
171–195 °C
96
x
S (20),
CsF(5)
5
6
7a-c (15),
Imidazole (20)
3(12),
20
15
25 (24)
65(72)
7a,b (ratio 20:80)
84–85 /10
(122–123)c
44b
c
8a,b (ratio 86:14)
7a,b (ratio 13:87)
19
MATHR (11),
24
47
64
x
S (10),
CsF(3)
7
8
3(110), CHPTr (100),
15
12
25(72)
22(5d)
9b,c (ratio 84:16)
118–121/8
(48.5)
x
S (100),
CsF(10)
10 (14),
11
DMBD (62),
x
S (28),
CsF(10)
9
10(38),
12
25
12
12
12
12
22(4d)
22–25(3d)
25(5d)
25(5d)
25(2d)
65(2d)
12
13
15
17
18
19
(33–34)
35
CHPTr(25),
x
S (25),
CsF(5)
10
11
12
13
13
10(20),
CHD(25),
Clear oild
(50.5–51)
(67–68)
15%
74
x
S (20),
CsF(4)
14(20),
CHD(22),
x
S (25),
CsF(4)
16(20),
CHTr(20),
85
x
S (20),
CsF(5)
16(25),
96–97/10
(164–165)e
85
DMBD(25),
x
S (25),
CsF(10)
16(25),
62
ANTHR (25),
x
S (25),
CsF(10)
a
b
c
d
e
reaction was slightly exothermic.
yield calculated on amount of 3 used in the reaction.
isolated by column chromatography, purity 98%, 2% of MANTHR.
isolated after passing hexane solution through short silicagel plug.
purity 98%, 2% of ANTHR.
Kcal/mol), reflecting restricted rotation of fluoroalkyl groups in com-
pounds 2a, 2b, and 8a), notable as a general trend was the fact that the
population difference between the two states seems to result less from
differences in the enthalpies of transition (which are all quite similar
between conformers) and more from the entropies of transition, sug-
gesting that the transition state is simply statistically less accessible by
the major isomer than by the minor, in each case. In order to identify
the major and minor rotamer (or conformer) in each case, low tem-
perature HOESY NMR experiments were attempted, but unfortunately
none of these experiments proved to be successful, even at temperatures
as low as 183 K. The slight degree of exchange present even at that
2.3. NMR Identification of compounds 9b and 9c
Structures of 9b (major isomer) and 9c (minor isomer, see Eq. (6))
were elucidated using a full suite of NMR experiments to confirm that
the sulfur was not attached to the 3-membered ring. The carbon ske-
leton of the bicyclo[4.1.0]hept-3-ene substructure (bonds highlighted
1
13
1
in bold below) of 9b/9c can be assigned unambiguously with He
C
1
13
13
HSQC and He Ce C 1,1-ADEQUATE experiments (optimized for
J
1
1
1
(CH)]155 Hz and J(CC)]55 Hz and/or J(CH)]170 Hz and J(CC)]
1
13
35 Hz). With those H/ C assignments determined, three bridgehead
carbons are identified, which allowed unambiguous assignment of
structures 9b and 9c.
temperature seemed to accelerate spin-lattice relaxation (T relaxation
1
1
9
times were typically < 0.5 s at 183 K for all F nuclei in the molecule),
which greatly attenuated cross-relaxation via the nOe.
6

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
Table 3
NMR and MS data for New Materials.
1
a
19
a
Entry Comp.
H NMR
F NMR
MS
No.
1
No.
(δ, ppm, J, Hz)
(δ, ppm, J, Hz)
(m/z, EI)
2a
1.57(1H,m), 2.65(1H, d), 2.90(1H,d), 3.03(1Hs), 3.14(1H,s),
3.23(1H, d), 5.95(1H,m), 6.16(1H,m)
−65.19(3 F, sixt., 9.4),
−78.66(3 F, q, 9.9),
324(M+, C11
H
8
F
8
S+
)
2
b
1
2
2
3
5
.57(1H,m),
−113.93(1 F, dq, 283.2, 9.4),
−116.94(1 F, dq, 283.2, 8.2)
−73.02(3 F, hex, 9.4),
.61(1H, d),
.86(1H, d), 3.04(1H,m),
.20(1H, s), 3.31(1H,d),
.95(1H,m), 6.16(1H,m)
−80.39(3 F, q, 10.7),
−110.09(1 F, dq, 288.4, 10.7),
−
113.23(1 F, dq, 288.4, 9.4)
+
2
3
4a
Mixture of isomers:
1.25 1H,m),
−77.86 (3 F, octet 7.5),
−78.44(3 F, m),
374(M
,
4
4
b
c
C
12
H
8
F
10S+
)
1.75 (1H,m),
−99.70 (2 F, d, 281.0),
−105.62(2 F, br),
2
3
3
6
.20 (2H,m),
.57(1H,m),
−65.66(3 F, br),
.70(1H,m),
−80.46(3 F,t, 12.7),
−105.12(2 F, AB q, 294.1),
.35(1H,m), 6.58(1H,m)
−
−
−
−
−
123.24(2 F, AB q, 290.5),
62.40(3 F, m),
80.79(3 F, t, 13.3),
103.93(2 F, br.s),
123.81(2 F, br.s)
+
6a
1.57(1H, d, 9.9),
−77.54(3 F, dm, 20.8, 5.1),
−77.78(3 F,m),
348(M
,
6
b, 6c 2.07(2H, d, 9.9), 4.18(1H,s), 5.88(1H,m), 6.50(1H,m)
C
10
H
6
F
10S+
)
(
mixture of two isomers):
−97.69(1 F, dq, 297.0, 20.8),
−101.31(1 F, d, 289.0),
1
3
.57(1H, d), 1.63(1H,d, 9.2), 1.98(1H,d,9.2), 2.12(2H,d, 10.2),
.82(1H,s), 3.90(1H,s), 5.88(m), 6.46(1H,m)
−104.20(1 F, d quint., 284.6, 9.9),
−
−
−
104.81(1 F, dg, 284.6, 19.7)
59.01(3 F,m),
61.94(3 F,m), −
9
7.81(1 F br.d ˜ 290 Hz),
−
−
−
−
−
−
102.631 F,d, 299.0),
105.78(1 F, dm, 289.10,
119.00(1 Fdm, 287.0),
121.54(1 F,dm, 287.0),
123.00(1 F,d, 2911.1),
124.06(1 F,dm, 291.1, 13.8)
3
7a
——
−53.97 (3 F, tq, 16.1, 6.4),
−72.17(3 F, m),
526(M+, C10F18S+
)
7
b
———
−
−
−
−
−
−
−
−
−
80.81(3 F, t, 12.0),
105.16(2 F, AB q, 287.2),
106.78(2 F, AB q, 282.0),
123.46(2 F, dm, 12.6) ppm.
53.94(3 F, tq, 16.8, 5.7),
77.11(6 F, quint., 5.7),
83.41(3 F, q, 5.7),
106.56(2 F, qq, 16.8, 2.2),
110.06(4 F, s)
4
5
8a
2.30 (3H,s), 5.32(1H, s), 7.12–7.41 (8H, m)
3.10(3H, s), 5.34(1H,s),
−65.24(3 F, qd, 14.3,6.8),
−805.0(3 F, t, 12.5),
−98.00(1 F, br.s),
8
b
7
.12–7.41 (8H, m)
−
−
−
−
−
106.35(1 F, 301.9),
123.24(2 F, s)
77.38(3 F, br.s),
99.84(1 F, dq, 288.2, 13.2),
106.35(2 F?)
9bb1
(600 MHz, CDCl
)
(470 MHz, CDCl
)
354 (M
+
,
3
3
1
.88 (1H, m), 2.11 (1H, m), 2.18 (1H, m), 3.70 (1H, m), 4.12 (1H, −68.03 (m, 3 F), −79.11 (dq, 19.9, 3.1 Hz, 3 F), −107.58 (ddq,
m), 6.33 (1H, m), 7.04 (1H, m) 288, 22, 12.2 Hz, 1 F), −112.01 (dqm, 288, 8.7 Hz, 1 F), −139.04
m, 1 F)
(600 MHz, CDCl (470 MHz, CDCl
C
12
H
7
F
9
S
+)
(
+
9
cb2
3
)
3
)
354 (M
,
1
.88 (1H, m), 2.11 (1H, m), 2.20 (1H, m), 3.70 (1H, m), 4.02 (1H, −66.32 (dd, 28.8, 18.9 Hz, 3 F), −80.63 (d, 21.3 Hz, 3 F), −98.37
C
12
H
7
F
9
S
+)
m), 6.36 (1H, m), 7.06 (1H, m)
(dd, 280, 5.4 Hz, 1 F), −120.53 (dqd, 280, 28.8, 3.9 Hz, 1 F),
143.87 (m, 1 F)
−
+
6
7
11c
12d
1.76(6H,s), 2.51(2H, s), 3.20(2H,s)
−123.40(2 F, dq, 215.0, 3.6),
276 (M
,
−
−
−
125.76(2 F, dt, 215.0, 5.6),
127.69 (1 F, dm, 232.5),
C
10
H
10
F
6
S
+)
129.65, 1 F, d quint., 232.5, 4.9)
+
0.21 (1H, t, 3.5), 0.32(1H, q, 6.5), 1.03 (1H, m), 1.46 (1H, m, 3.8), −111.21(1 F, dm, 218.1),
286 (M
,
3
.75 (1H, s), 3.98(quint. 4.7), 5.78(1H, q, 4.6, 6.28 (1H, t, 7.8)
−116.29(1 F, dm, 216.6),
C
11
H
8
F
6
S
+)
−
−
−
−
121.65 (1 F, dq, 216.5, 5.6),
125.49 (1 F, dt, 218.1, 7.6),
130.80 (1 F, d. quint., 224.5, 5.7),
132.20(1 F, dt, 224.5, 7.4)
8
13
274(M+, C10
H
8
F
6
S+
)
(
continued on next page)
7

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
Table 3 (continued)
1
H NMR a
19
a
Entry Comp.
F NMR
(δ, ppm, J, Hz)
MS
No.
No.
(δ, ppm, J, Hz)
(m/z, EI)
1
3
.48 1H,m), 1.67(1H,m), 1.92(1H,m), 2.22(1H,m),
−113.45 (1 F, dq, 217.5, 6.5), −117.67(1 F, dq, 215.3, 7.2),
−122.42 (1 F, dq, 215.3, 6.6),
.50(1H,t, 5.7), 3.74(1H, dm, 6.7), 6.26(1H,m), 6.78(1H, t, 7.8)
−
−
−
126.72(1 F, dt, 217.5, 7.7),
130.94(1 F, d quint., 224.4, 7.7),
132.63(1 F, dt, 224.4, 7.7)
15e
1.28 (1H, tt, 13.2, 4.5), 1.64(1H, tt, 12.6, 3.6), 1.95(1H,t, 12.0),
−113.54(1 F, dd, 242.5, 10.0),
−117.10 (1 F, dq, 242.5, 10.0, 5.4),
−116.63(1 F, dd, 245.4),
324 (M
+
,
9
2
7
.09(1H, m), 3.53(1H, t, 4.4), 3.7(1H,m), 6.23(1H,t, 7.5), (1H, t,
.2), 6.66(1H, t, 7.5)
C
11
H
8
F
8
S
+)
−
−
−
−
−
118.13(1 F, d, 245.5, 5.6),
124.51(1 F, dt, 253.0, 8.0),
124.55(1 F, dt, 251.6,8.0),
129.53(1 F, dt, 253.0, 6.3),
131.83(1 F, d q., 252.2, 4.9)
+
1
0
17
0.15(1H,m),
−110.2, −111.8, −113.0, −116.0, −120.0,
−125.0, −139.6,
376(M
,
0
1
1
4
4
5
6
.25(1H, dt, 7.8,7.2),
.32(1H,m),
C
13
H
8
F
10S+
)
−141.7
.62(1H,m),
(all broad signals)
.03(1H,t, 5.3),
.18, 1H, dd, 7.2, 4.1),
.77 (1H,q, 4.2),
.22(1H,t, 7.6)
+
1
1
2
18
19
1.81(3H,s), 1.85(3H,s),
−100.0 to −144.0 (all broad signals)
376(M
,
2
3
.62(2H,s),
.11(2H,s)
C
12
H
10
F
10S+
)
+
1
5.33(1H,s),
−112.28(2 F, br.d, ˜269.0),
−116.77(2 F, br.d, ˜269.0),
−120.61(2 F, br.d, ˜279.0),
−124.93(1 F, br.d, ˜273.0),
−139.92(2 F, br.d, ˜ 279),
472(M
,
5
7
7
7
.55(1H,s),
.23(4H,m),
.38(2H,d),
.45(2H,d)
C
20
H
10
F
10S+
)
−142.00(1 F, br.d, ˜273)
a
in CDCl as lock solvent, unless indicated otherwise.
3
b1 13
C{H} (J, Hz): 28.37 (dd, 3.3, 0.8 Hz), 29.24 (d, 7.4 Hz), 31.77 (dd, 1.3, 0.7 Hz), 32.49 (dq, 28, 1.7 Hz), 42.78 (m), 59.84 (dt, 24.9, 18.6 Hz), 100.35 (dqd, 205,
3
2
0.3, 3.8 Hz), 113.7 (ddqd, 262, 256.7, 38.1, 1.5 Hz), 118.9 (qdd, 288, 36.8, 36.5 Hz), 122.0 (qd, 283.5, 34.5 Hz), 129.5, 141.26 ppm.
b2 13
C{H} (J, Hz): 28.51 (d, 3.3 Hz), 29.15 (d, 7.3 Hz), 31.90, 33.26 (dm, 28 Hz), 43.18 (m), 58.85 (qdm, 29, 17.7 Hz), 102.0 (dt, 202, 24 Hz), 112.64 (dddq,
67.3, 260.7, 44.3, 36.1 Hz), 119.02 (qdd, 288, 36.3, 35.2 Hz), 124.4 (qd, 281, 1.9 Hz), 129.24, 141.38 ppm.
c
13
C{H} (J, Hz): 19.09, 20.01, 30.43(m), 30.52(t, 2.3), 58.75(tt, 22.1, 5.5), 114.24(tt, 304.5, 27.5), 114.27(tt, 301.9, 27.6), 115.79 (tm, 292.5), 123.89, 124.06
13C{H} (J, Hz): 4.58, 5.76(dd, 5.7, 2.6), 14.96(d, 1.7), 32.88(q, 4.1), 38.87, 71.10(quint. 23.0), 114.14(tt, 304.3, 27.5), 116.07 (tm, 296.0), 117.64(tm, 289.8),
ppm.
d
1
25.58, 133.05 ppm.
e
13C{H} (J, Hz): 18.65(t, 3.3), 27.10(d, 2.0), 28.62(t, 6.6), 35.92, 62.12(quint., 20.8), 110.15(t, 280.0), 115.81(t, 270.6), 117.14(t, 271), 130.36, 137.13 ppm.
2.4. Reaction of perfluoroolefins with sulfur – mechanistic aspects
A
mechanism of fluoride anion catalysed reaction of per-
fluoroolefins, sulfur and conjugated dienes is depicted by Scheme 1
exemplified by reaction with CHD). The reaction of the olefin with
(
fluoride anion results in the reversible formation of carbanion A. Nu-
cleophilic attack of A on sulfur leads to the formation of thiolate salt B,
which can exist in an equilibrium with thioketone C (reversible addi-
tion/elimination of fluoride anion). In the case of nonsymmetrical
olefins, this process can lead to the formation of two isomeric carba-
nions, due to attack of fluoride anion on two different carbons of the
double bond, resulting in the formation of two isomeric thioketones C.
Subsequent cycloaddition reaction of thioketone C and diene leads
to the formation of the Diels-Alder adducts D. In the case of non-
symmetrical thioketones and cyclic substrates such as Q, CHD or
CHPTr, the reaction leads to the formation of the adducts with different
orientation of fluoroalkyl group relative to carbon bridge (exo- and
endo- isomers). The formation of thiolanes 7a,b as by-products in some
cycloaddition reactions may be a result of several interconnected
transformations (Scheme 2).
Cycloaddition converts the two olefinic carbons of the F-pentene-2
3
13
(
3) into sp carbon centers with unique C chemical shifts and J(CF)
couplings. For compound 9b (major), these two carbon centers are
observed at 100.35 ppm (dq, the CF carbon) and 59.84 ppm (dt, qua-
ternary carbon center with CF and CF neighbour carbons). For com-
2
pound 9c (minor), they are observed at 102.0 ppm (dt, the CF carbon)
and 58.85 ppm (dq, quaternary carbon center with CF and CF as
3
neighbour carbons). The 1,1-ADEQUATE experiments make clear that
one of the erstwhile olefinic carbons of olefin 3 is attached to the cy-
clopropyl end the bicyclo[4.1.0]hept-3-ene fragment, and the other is
attached to a bridgehead carbon alpha- to the double bond of the bi-
cyclo[4.1.0]hept-3-ene fragment. The latter also connects to the third
bridgehead carbon through a sulfide linkage, forming isomers 9b and
The thioketone C is likely to exist in equilibrium with thiolate salt B.
Under the reaction conditions e, thiolate B can undergo oxidation by
sulfur, producing disulfide 7c (along with some tri- and tetra- sulfides,
as a result of further reaction with sulfur) and one mole of cesium (or
9
c.
8

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
potassium) sulfide M
2
S (this process may be reversible). The formation
3.1. Preparation of compounds 2a,b, 4a-c, 6a-c, 8a,b, 9b,c, 11-13, 15,
of equimolar amounts of polysulfides and 1,3-dithiolanes 7a,b in the
17-19 (typical procedure)
reaction of 3 and sulfur (Eq. (4)) suggests that the formation of 7a,b
and 7c may be interconnected. The anhydrous alkali metal sulfide M
2
S
A reaction vessel containing a magnetic stir bar was charged with
dry CsF inside a nitrogen dry box. Dry DMF was added via syringe,
followed by addition of sulfur. In the case when reaction mixture was
kept anhydrous, the addition of sulfur resulted in immediate develop-
ment of blue colour. The reaction mixture was agitated for 5–15 min at
ambient temperature and the corresponding diene (˜ 5–10 mol % ex-
cess) was added, followed by addition of an olefin, which usually re-
sulted in a disappearance of blue-brown colour. The reaction vessel was
closed, and the reaction mixture was agitated at 25–65 °C for 1–5 days.
The reaction mixture was then diluted with 300 mL of water and ex-
tracted by hexane (50mLx3). Extracts were combined and washed with
water (100mLx3) to remove residual DMF. Organic phase was dried
(
M = K or Cs) released in this process is a strong nucleophile, and it can
react with starting fluoroolefin to produce either thioenolate E or
thiirene F as a result of nucleophilic substitution of one or two vinylic
fluorines in the perfluoroolefin (depicted by Scheme 3), resulting in
release of two moles of MF, which can be involved again in the catalytic
cycle. Subsequent [3 + 2] cycloaddition reaction of either thioenolate E
or thiirene F and thioketone C leads to the formation of the corre-
sponding 1,3-dithioles 7a,b.
The overall process includes the transfer of two fluorine atoms from
F-pentene-2 to two moles of thioketone C with the formation of di- and
poly- sulfide [i-C
F
5 11
]
S
2 x
(7c) and one mole of M S (M = Cs or K),
2
which can react with fluoroolefin giving either thioenolate E or thiirene
F (Scheme 3) and releasing two moles of fluoride anion, which can be
involved in the catalytic cycle again.
over MgSO , solvent was removed under reduced pressure, and the
4
residue was distilled under vacuum, crystallized from hexane or iso-
lated by column chromatography (compounds 8a,b). Ratio of reagents,
reaction conditions, yields, boiling (melting) points, NMR and MS data
for new materials are given in Tables 2 and 3.
3
. Experimental
Reactions involving gaseous olefins 1 and 10 were carried out in heavy
®
wall glass tube equipped with a Teflon stopcock and a magnetic stir bar. In
NMR spectra for structural characterization were acquired on a
a typical experiment, dry CsF (3–5 mmol) was loaded inside of dry box and
25 mL of DMF was injected into reaction vessel under nitrogen blanket,
followed by addition of 20–30 mmol of sulfur. The colour of the reaction
mixture immediately changed to blue. The reaction mixture was agitated
for 5 min and the corresponding diene (10–20 % molar excess) was added.
The reaction vessel was closed, cooled down in wet ice, and the corre-
sponding olefin (F-butene-2 (1) or F-cyclobutene (10), 25–30 mmol, pre-
condensed in graduated cold trap) was added to cold reaction mixture as a
liquid. The reaction vessel was closed, and reaction mixture was agitated at
ambient temperature until all sulfur dissolved (3–5 days). The reaction
mixture was diluted with 300 mL of water, extracted by hexane (50mLx3),
extracts were combined and washed with water (100mLx3) to remove
1
3
31
Varian 500 MHz VNMRS spectrometer equipped with a 5 mm C-
P
1
19
{
H, F} probe, a Varian 400 MHz DD spectrometer equipped with a
1 19 13 31
5
mm H, F { C- P} probe, and a Bruker Neo 600 MHz spectrometer
1 19 13 15 1
equipped with a 5 mm QCI H/ F- C/ N cryoprobe. H spectra were
acquired with a 90° flip angle, 3.7 s acquisition time, and 30 s recycle
1
9
delay. F spectra were acquired with a 60° flip angle, 0.7 s acquisition
time, and 7 s recycle delay. The sample temperature was 298 K. Spectra
were typically acquired in chloroform-d, using CFCl and TMS as in-
3
ternal standards. High temperature NMR spectra were recorded in
CDCl
2
CDCl solvent.
2
Dynamic NMR experiments were performed on a Bruker AVIIIHD
spectrometer on a 9.4 T magnet equipped with a 10 mm F{H} probe
specially insulated for high or low temperature operation. Sample
temperatures in the probe were calibrated by use of methanol or
residual DMF. Organic phase was dried over MgSO , solvent was removed
4
under reduced pressure, and the residue was distilled under vacuum or
crystallized from hexane. Compounds 8a,b and 9b,c were isolated by
column chromatography (Silicagel 60, 230–400 mesh (EDM), eluent –
hexane). Ratio of reagents, reaction conditions, yields, boiling (melting)
points, NMR and MS data for new materials are given in Tables 2 and 3.
ethylene glycol standards. Analytes were dissolved in toluene-d and
8
flame-sealed in ampules with a 10 mm o.d. body and 5 mm o.d. neck
(
New Era Enterprises, Vineland, NJ, USA), so as to keep the entirety of
the ampule in the thermostated region of the NMR probe. The use of
such ampules permitted spectral acquisition above the boiling point of
3.2. Preparation of Compounds 7a-c and 7a,b
toluene-d at ambient pressure. Selective inversion experiments were
8
carried out using an IBURP-2 inversion pulse. Chemical exchange ki-
netics were fitted by simple least-squares minimization.
A round bottomed flask was charged with dry CsF (4.5 g, 30 mmol)
inside of dry box. It was equipped with thermocouple well, dry-ice
condenser and magnetic stir bar and blanketed by dry nitrogen. 100 mL
of dry DMF was added using syringe, followed by 16 g (500 mmol) of
sulfur. The reaction mixture was agitated for 10 min (deep blue colour
rapidly developed after addition of sulfur) and 125 g (500 mmol) of F-
pentene-2 was added dropwise over 10 min period. The reaction mix-
ture was agitated at 20–28 °C (slightly exothermic) for 24 h. The reac-
tion mixture was added to 1000 mL of water, the organic layer was
GC and GC/MS analyses were carried out on an HP-6890 instru-
ment, using an HP FFAP capillary column and either TCD (GC) or mass-
selective (GS/MS) detectors, respectively. Anhydrous DMF (water <
5
0 ppm), 2,3-dimethylbutadiene-1,3, cyclohexadiene-1,3, cyclohepta-
triene-1,3,5, anthracene (Aldrich), fluoroolefins 1 and 3 (Chemours
Co.), 10, 14 and 16 (SynQuest) were obtained from commercial sources
and used without further purification. The same batch of sublimed
sulfur (sulfur powder, ˜100 mesh, 99.5%, Alfa Aesar) was used in all
experiments.
separated, washed with water (300mLx3), dried over MgSO and fil-
4
tered to give 135 g of the product containing a mixture of 7a, 7b and
7c. Compound 7c was a mixture of disulfide (major component, ˜80%
of total), along with smaller amount of trisulfide and trace amount
Computational optimization of 8a and 8b structures was performed
with Gaussian 9 software. Density functional theory at B3LYP level with
a 6-311g++ basis set (Co phase) was employed.
1
9
tetrasulfide (GC/MS). Based on integration of the corresponding
F
Samples of commercial potassium or caesium fluoride (Aldrich)
were ground, dried under dynamic vacuum at 100–120 °C for 5–10 h
and were stored and handled inside a nitrogen glove box.
Due to the high ratio of sulfur to fluorine in all compounds, ele-
mental analyses were not attempted for new materials, and the purity of
all isolated compounds was established to be at least 99% (GC and NMR
spectroscopy) unless specified otherwise.
NMR signals (upfield CF groups vs. downfield eCFe resonances), the
3
molar ratio of 7a,b to 7c was found to be exactly 1:1.
A sample (10 g) of crude product (mixture 7a-c) was added to a
solution of 3 g imidazole in 25 mL of dry DMF. The reaction mixture
was agitated at ambient temperature for 20 h and the second layer was
separated, washed with water (300mLx3), dried over MgSO and dis-
4
tilled to give 4.4 g (yield 44%) of material with boiling point 84–85 °C/
0 mm Hg, which was shown to be a mixture of compounds 7a,b in the
ratio 80:20. NMR and MS data are given in Table 3.
1
9

V. Petrov, et al.
Journal of Fluorine Chemistry 225 (2019) 1–10
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