Synthesis, properties and application of electronically-tuned tetraarylarsonium salts as phase transfer catalysts (PTC) for the synthesis of gem-difluorocyclopropanes

Article abstract of DOI:10.1016/j.jfluchem.2017.03.014

Preparation of gem-difluorocyclopropane from α-methylstyrene and chlorodifluoromethane was investigated under basic two-phase conditions. Although simple tetraalkylammonium salts appeared uneffective as phase-transfer catalysts (PTC) for this purpose, tetraphenylarsonium chloride displayed moderate activity, and inspired studies of the phenomena. To improve its efficiency we synthesized set of electronically-tuned tetraarylarsonium analogues. Their preparation revealed interesting exchange process of aryl substituents on the arsonium center, whereas activity studies demonstrated a correlation of catalytic efficiency with electronic effects of the substituents. Two of the tetraarylarsonium catalysts were characterized by X-ray studies.

Full text of DOI:10.1016/j.jfluchem.2017.03.014

Journal of Fluorine Chemistry 197 (2017) 106–110
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis, properties and application of electronically-tuned
tetraarylarsonium salts as phase transfer catalysts (PTC) for the
synthesis of gem-difluorocyclopropanes
a
a, ,1
ꢀa
*
Krzysztof Grudzien , Tymoteusz Basak , Michał Barbasiewicz
,
b
b
ꢀ
Tomasz M. Wojciechowski , Michał Fedorynski
Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
a
b
Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
A R T I C L E I N F O
A B S T R A C T
Article history:
Preparation of gem-difluorocyclopropane from
a-methylstyrene and chlorodifluoromethane was
Received 3 March 2017
Received in revised form 27 March 2017
Accepted 28 March 2017
Available online 1 April 2017
investigated under basic two-phase conditions. Although simple tetraalkylammonium salts appeared
uneffective as phase-transfer catalysts (PTC) for this purpose, tetraphenylarsonium chloride displayed
moderate activity, and inspired studies of the phenomena. To improve its efficiency we synthesized set of
electronically-tuned tetraarylarsonium analogues. Their preparation revealed interesting exchange
process of aryl substituents on the arsonium center, whereas activity studies demonstrated a correlation
of catalytic efficiency with electronic effects of the substituents. Two of the tetraarylarsonium catalysts
were characterized by X-ray studies.
Keywords:
Phase transfer catalysis
Arsonium salts
gem-Difluorocyclopropanes
Difluorocarbene
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
appeared to be virtually impossible. As soon as in 1971 Weyerstahl
reported that 1-bromo-1-fluoro- and 1-chloro-1-fluorocyclopro-
Synthesis of gem-dihalocyclopropanes [1] and their trans-
formations [2,3] gained widespread interest in chemical
panes can be synthesized under basic two-phase conditions, in
contrast to 1,1-difluoroanalogues [16]. Soon thereafter Buddrus
proposed an alternative procedure, utilizing chlorodifluorome-
thane, ethylene oxide, and tetraalkylammonium bromide, as a
catalyst [17]. Under homogeneous conditions bromide anion
opened oxirane ring giving bromoethoxide, which acted as a base.
Despite high efficiency of this protocol in the synthesis of gem-
difluorocyclopropanes, its application was limited by harsh
reaction conditions: heating in autoclave to 100–140 ꢁC. Another
a
literature, and method of choice of their preparation is two-phase
catalytic system utilizing trihalomethanes and solution of inor-
ganic base. According to the mechanism proposed by Ma˛kosza
[4–6] deprotonation of trihalomethane at the interfacial region
generates an alkali metal salt, which remains trapped until it
exchanges with lipophilic organic cation of the catalyst, usually a
quaternary ammonium salt (Q+Xꢀ). Then, the newly formed
lipophilic pair enters the organic phase, where trihalomethyl
anion spontaneously dissociates into the dihalocarbene and halide
anion. Then, dihalocarbene adds to the double bond of the olefin,
while Q+Xꢀ migrates back to the interface and exchanges anion in a
following turnover of the catalytic cycle (Fig. 1).
ꢀ
approach was demonstrated by Jonczyk, et al. [18] Under basic PTC
conditions mixture of bromoform and dibromodifluoromethane
generated difluorocarbene, which added to alkenes. Important
mechanistic difference was based on the presence of bromoform,
which deprotonated at the interface, and so-formed tribromo-
methyl anion, after transportation to the organic phase, induced
halophilic reaction with CF2Br2. Then, difluorocarbene, generated
in the absence of hydroxide, efficiently added to alkenes.
The presented data suggest that limitations of efficient
generation of difluorocarbene and its addition to alkenes under
basic two-phase conditions most likely arise from unfavorable
position of the CX3ꢀ?CX2 + Xꢀ equilibrium that results in
decomposition of halodifluoromethyl anion at the interface, prior
to the migration to the bulk organic phase. In this context
Although the presented protocol is very efficient, and does not
require application of strictly anhydrous conditions as other
homogeneous systems [7], preparation of analogous gem-difluor-
ocyclopropanes [8–15] from chlorodifluoromethane (1, freon 22)
* Corresponding author.
E-mail addresses: barbasiewicz@chem.uw.edu.pl (M. Barbasiewicz),
ꢀ
mifed@ch.pw.edu.pl (M. Fedorynski).
1
www.aromaticity.pl.
http://dx.doi.org/10.1016/j.jfluchem.2017.03.014
0022-1139/© 2017 Elsevier B.V. All rights reserved.

ꢀ
K. Grudzien et al. / Journal of Fluorine Chemistry 197 (2017) 106–110
107
Fig. 1. Mechanism of synthesis of gem-dichlorocyclopropanes under PTC conditions with quaternary ammonium salt [4–6].
important observations were described by Dehmlow, who studied
effect of PT-catalysts on product distribution in reaction of
bromoform with allyl bromide under basic conditions [19]. In
the process two competitive reactions may simultaneously occur:
published recently for other PTC process (concd aqueous solution
of KOH with mechanical stirring of the mixture) [22]. As a model
olefin we applied
a-methylstyrene (2-phenylpropene), alkene of
moderate nucleophilicity. Samples of upper organic phase were
taken and analyzed with GC. Original sample of 1-methyl-1-
phenyl-2,2-difluorocyclopropane 3 was synthesized according to
the literature method [18].
addition of dibromꢀocarbene to the C
¼
C bond, and SN2 substitution
of Brꢀ with CBr3 (CH2 = CHCH2Br + CBr3ꢀ ! CH2 = CHCH2CBr3 +
Brꢀ). As both species CBr2 and CBr3 remain in equilibrium
ꢀ
(CBr2 + Brꢀ ? CBr3ꢀ), catalysts, which favor reaction of the latter
form, are expected to shift the equilibrium toward anionic form.
Interestingly, in this role tetraphenyl arsonium chloride appeared
to be very efficient catalyst [20], strongly favoring formation of the
substitution product. Although exact nature of the effect remained
unclear, we believed that similar approach may help to stabilize
the short-living chlorodifluoromethyl anion, generated by depro-
tonation of 1, by shifting unfavorable equilibrium of decomposition
to difluorocarbene [21].
With simple benzyltriethylammonium chloride as a catalyst
(TEBACl, 5 mol%) we observed ꢂ3% of conversion of 2 according to
GC. However, with commercially available tetraphenylarsonium
chloride (5 mol%), the process run much better, giving 35% of
conversion to 3. It is worth to stress that hydrodynamic conditions
substantially affect the process ꢀ mechanical stirring is crucial to
reproduce the results. In routine experiments at the beginning
(usually first 3–4 h) we observed
a moderately exothermic
hydrolysis of 1 (temperature was kept at 25–35 ꢁC with cold
water-bath), and gradual conversion of alkene. Then the reaction
stopped, and further stirring and bubbling of the chlorodifluoro-
methane resulted in no changes of the mixture. Besides at lower
temperatures (e.g. ice-water bath) viscosity of the mixture, after
partial hydrolysis of 1, made the stirring difficult (at least at scale
19 mmol of 2, applied in our studies). Unfortunately all attempts to
further improve the conversion have failed.
In our report we present studies of two-phase reaction of 1 with
model
a-methylstyrene under basic conditions catalyzed with
tetraarylarsonium salts. We demonstrate also our attempts on
synthesis of electronically-tuned tetraarylarsonium salts, novel
catalysts for the PTC processes.
2. Results and discussion
2.1. Preliminary experiments with chlorodifluoromethane (1) under
PTC conditions
2.2. Attempts of synthesis of unsymmetrical aryltriphenylarsonium
salts
Our studies started from preliminary experiments, to define
initial reaction conditions and parameters. As one of the reagents is
a gas at RT (1; b.p. = ꢀ41 ꢁC) we decided to bubble it through the
reaction mixture (see Scheme 1), and use ethereal solvent, which
display high solubility of 1 at RT.
To reduce blowing away of the solvent by the bubbled gas we
used 1,2-dimethoxyethane, which has relatively high boiling point
(b.p. = 85 ꢁC). Other parameters were inspired by protocol
Therefore we decided to synthesize modified arsonium
catalysts to increase efficiency of the process. Inspiration of this
work was a possibility of stabilization and transportation of the
unstable CClF2ꢀ anion in the form of hypervalent complex with the
catalyst, instead of simple electrostatic interaction, typical for the
ion pairs. Promising candidates for the specific task seemed to be
arsonium salts, which may act as simple PTC catalysts [19], and also
extend coordination sphere with ancilary ligands to give neutral 5-
coordinated arsanes [23]. Interestingly this kind of hypervalent
catalysis was demonstrated on organostannanes, applied in
synthesis of alkyl fluorides [24]. Both electron-donors and
electron-acceptors were selected as substituents in para position
of the aromatic rings, namely methoxy and chlorine groups. We
assumed that hypothetical equilibrium of formation of arsene
derivative Ph4As+ + CClF2ꢀ ? Ph4AsCF2Cl can be controlled by
electronic properties of the arsenium center, modulated with
substituents. Optimally, the equilibrium should be established at
similar concentrations of the reacting species (K ꢃ 1), to favor both:
association of the anion at the interface, and its release in the bulk
organic phase.
Scheme 1. Studies of model synthesis of gem-difluorocyclopropane 3.

ꢀ
K. Grudzien et al. / Journal of Fluorine Chemistry 197 (2017) 106–110
108
assumed that individual components of the mixture are arsonium
salts, which differ in a number of aromatic rings substituted with
methoxy groups, and the observed differences in chemical shifts
arise from electronic effects of the substituents transmitted by the
tetracoordinated arsonium center. Indeed, when the mixture was
analyzed with mass spectrometry, we observed a similar set of
peaks at 383, 413, 443, 473, attributable to AsPh4, AsPh3Ar,
AsPh2Ar2, and AsPhAr3 cations, respectively (confirmed with
HRMS, Ar = 4-C6H4OMe; Fig. 2, right) [26]. The obtained data
clearly suggested that during the reaction aromatic ligands
equilibrate on the arsonium center, leading to inseparable mixture
of tetraarylarsonium salts. Interestingly, a similar pattern was
observed on MS spectrum of mixture 7b with 4-chlorophenyl
magnesium bromide, but in this case NMR spectra were more
difficult to interpret. On the base of literature data [23] this kind of
exchange most likely proceeds by the formation of intermediate
pentavalent arsanes (Scheme 2, bottom). It is worth to remind, that
formation of such hypervalent species (namely Ar4AsCClF2) was
inspiration for our studies.
Scheme 2. Reactions of triphenylarsine oxide (5) with arylmagnesium bromides
(top), and postulated scrambling mechanism (bottom).
2.3. Modified synthetic plan ꢀ synthesis of tetraarylarsonium salts
Initially, to make the preparation of modified arsonium salts
simple, we tried to introduce substituents to one aromatic ring of
the cation. For this purpose commercially-available triphenylar-
sine 4 was oxidized with hydrogen peroxide in acetone to
triphenylarsine oxide 5 in 82% of yield, and then transformed
into tetraphenylarsonium chloride-hydrochloride in reaction with
phenyl magnesium bromide [25]. After crystallization from
The unsuccessful attempts of synthesis of unsymmetrically
substituted salts led us to new synthetic targets. We focused on
symmetrical tetrasubstituted arsonium salts, which after scram-
bling of the aromatic rings should lead to the same, well-defined
products. Indeed, reaction of Grignard reagents derived from 4-
bromoanisole, 1-bromo-4-chlorobenzene, 1-bromo-3,5-dichloro-
benzene, and 1-bromo-3,5-bis(trifluoromethyl)benzene with
AsCl3 gave arsines 8a-d, which were oxidized to arsine oxides
9a-d, and subjected to next reaction with arenemagnesium
bromides, to obtain 4 new tetraarylarsonium bromides 10a-d of
excellent purity, according to 1H and 13C NMR (see the Supporting
information for details; Scheme 3, top).
Tetra(4-methoxyphenyl)- (10a), tetra(4-chlorophenyl)- (10b),
tetrakis(3,5-dichlorophenyl)- (10c) and tetrakis[3,5-bis(trifluoro-
methyl)phenyl]arsonium bromide (10d) were characterized with
MS, which confirmed identity of the cations. Unfortunately,
attempt of synthesis of analog tetrakis(3,4,5-trimethoxyphenyl)
arsonium catalyst appeared to be unsuccessful (Scheme 3,
bottom). First we observed that generation of Grignard reagent
from 1-bromo-3,4,5-trimethoxybenzene in diethyl ether is ex-
tremely slow [27], so we metallated the aryl halide with n-BuLi in
THF at ꢀ78 ꢁC, and treated with AsCl3 to obtain methoxysub-
stituted arsine 8e in 79% of yield. Then, the arsine was oxidized
aqueous solution of HCl product 6
based on arsine oxide 5 (Scheme 2, top).
ꢄ
HCl was obtained in 91%,
Then, we generated 4-methoxyphenyl magnesium bromide,
and 4-chlorophenyl magnesium bromide and treated with Ph3AsO
(5) under the same conditions. In both cases after quench and
aqueous work-up we obtained solid products, but attempts of
further crystallization were unsuccessful. Surprisingly 1H and 13C
NMR analysis of product 7a revealed a complex mixture. Although
aromatic region (6–8 ppm) was poorly diagnostic at 1H NMR, close
examination of signals around 3.8 ppm revealed presence of 4
singlets, characteristic for the OMe groups, with very close
chemical shift values (ꢅ 0.01 ppm; Fig. 2, left).
Interestingly, a similar pattern was observed also at 13C NMR for
signals around 164 and 56 ppm, attributable to Carom-OCH3, and
Carom-OCH3, respectively (Fig. 2, center). Corresponding compo-
nents of the mixture differed very slightly in structure, giving a
gradual change of chemical shifts of the resonances. Therefore, we
Fig. 2. Selected fragments of 1H and 13C NMR spectra and mass spectrum of mixture 7a [26].

ꢀ
K. Grudzien et al. / Journal of Fluorine Chemistry 197 (2017) 106–110
109
Scheme 3. Syntheses of arsines 8a-d, arsine oxides 9a-d, and arsonium salts 10a-d (top), and attempt on synthesis of arsonium salt 10e (bottom).
with H2O2/acetone system, but so-formed arsine oxide 9e, failed to
react further with ArLi. Most likely, presence of nine electron-
donor methoxy groups electronically enriched the arsonium
center, so the corresponding salt was not formed, or decomposed
on attempts of isolation.
To confirm structure of the synthesized arsonium salts, two of
them were characterized with X-ray studies. In both cases
arsonium center displayed a tetrahedral geometry, and other
parameters similar to structure of the parent tetraphenylarsonium
cation (Fig. 3) [28,29].
unsatisfactory for preparative purposes (analysis of the mixture
with 1H NMR confirmed presence of approximately equimolar
mixture of 2 and 3, as only detectable compounds). As pairs of
alkenes and their 1,1-difluorocarbene adducts usually display very
similar properties (boiling point, polarity, etc.), they are poorly
separable by routine methods. Therefore, we did not attempted
isolation of the synthesized product, although our experience in
preparation of dihalocyclopropanes and literature data[18] suggest
that both alkene 2 and its CF2 adduct 3 remain stable under the
reaction conditions.
Although, the obtained data do not give a definite conclusion
about origin of activities of the tetraarylarsonium catalysts (simple
electrostatic interaction vs. hypervalent mechanism) best results
were obtained with catalyst 10a, in which positive charge of the
arsonium center is delocalized into entire molecule, by the
presence of electron-donor methoxy substituents. According to
Dehmlow rationale [19], this can be explained by ‘soft' character of
the large cation, which favors in equilibrium ‘softer' trihalomethyl
anion, instead of more ‘hard' halide anion, stabilizing this form in
the organic phase. Alternatively, in terms of the postulated
hypervalent mechanism, less electrophilic arsonium center in
10a, as compared with 6 and more electrophilic salts, tends to
release the CF2Clꢀ anion (Ph4AsCF2Cl ? Ph4As+ + CClF2ꢀ), when the
process is rate-determining in the catalytic cycle. Unfortunately,
2.4. Studies of catalytic activity of the synthesized tetraarylarsonium
salts under PTC conditions
With the synthesized salts in hand we tested model reaction of
a
-methylstyrene with KOH, 1 and 1,2-dimethoxyethane, catalyzed
by 10a, 10c and 10d, and compared with activity of the parent
catalyst 6 [31]. The results are presented in Table 1.
In consistency with our expectations we observed an intensive
trend of conversions as a function of electronic properties of the
arsonium salts. Those substituted with electron-acceptors dis-
played smaller catalytic activity, whereas donor substituted salt
10a appeared superior to the parent salt 6. Unfortunately, the
obtained conversion reached maximum 53% that was still
Fig. 3. ORTEP [30] representations of tetraarylarsonium cations (10a, left; 10d right; counterions were omitted for clarity), shown as displacement ellipsoids drawn at the 50%
probability level.

ꢀ
K. Grudzien et al. / Journal of Fluorine Chemistry 197 (2017) 106–110
110
Table 1
[4] M. Ma˛kosza, Two-phase reactions in the chemistry of carbanions and
halocarbenes. A useful tool in organic synthesis, Pure Appl. Chem. 43
(1975) 439–462.
Conversions of alkene 2 to difluorocyclopropane 3 catalyzed with tetraarylarso-
nium salts.
ꢀ
[5] M. Ma˛kosza, M. Fedorynski, Catalysis in two-phase systems: phase transfer
Catalyst
Structure
Conversion of 2 to 3 (GC)
and related phenomena, Adv. Catal. 35 (1987) 375–422.
ꢀ
[6] M. Ma˛kosza, M. Fedorynski, Phase transfer catalysis in dichlorocarbene
10a
6
10c
10d
As(4-C6H4OMe)4 Br
AsPh4 Cl
As(3,5-C6H3Cl2)4 Br
As[3,5-C6H3(CF3)2]4 Br
53%
35%
25%
13%
chemistry: basic principles and specific features, Russ. Chem. Bull. 60 (2011)
2141–2146.
[7] W. von, E. Doering, A.K. Hoffmann, The addition of dichlorocarbene to olefins, J.
Am. Chem. Soc. 76 (1954) 6162–6165.
[8] P. Rulliére, P. Cyr, A.B. Charette, Difluorocarbene addition to alkenes and
alkynes in continuous flow, Org. Lett. 18 (2016) 1988–1991.
synthesis of (expectedly) more active catalyst 10e, bearing four
trimethoxyphenyl substituents, was unsuccessful, as described in
section 2.3.
[9] K. Oshiro, Y. Morimoto, H. Amii, Sodium bromodifluoroacetate:
difluorocarbene source for the synthesis of gem-difluorocyclopropanes,
Synthesis (2010) 2080–2084.
[10] J. Zheng, J.-H. Lin, J. Cai, J.-C. Xiao, Conversion between difluorocarbene and
difluoromethylene ylide, Chem. Eur. J. 19 (2013) 15261–15266.
[11] L. Li, F. Wang, C. Ni, J. Hu, Synthesis of gem-difluorocyclopropa(e)nes and O-, S-
N-, and P-difluoromethylated compounds with TMSCF2Br, Angew. Chem. Int.
Ed. 52 (2013) 12390–12394.
a
3. Conclusions
Pioneered more than 50 years ago phase-transfer catalysis
remains a method of choice for the synthesis of gem-dihalocyclo-
propanes, except for difluoroderivatives. Preparation of the latter is
still challenging, and justify search of other methods of generation
and addition of difluorocarbene to alkenes, as demonstrated by
recent achievements in the field [8–15]. We presented exploration
of idea of hypervalent stabilization of chlorodifluoromethyl anion
generated at the interphase in basic two-phase system by
deprotonation of chlorodifluoromethane. Despite promising
results (conversion of alkene to difluorocyclopropane adduct
exceeded 50%) further improvement seems to be difficult to
achieve, due to problems with preparation of electron-rich
tetraarylarsonium salts.
[12] F. Wang, T. Luo, J. Hu, Y. Wang, H.S. Krishnan, P.V. Jog, S.K. Ganesh, G.K.S.
Prakash, G.A. Olah, Synthesis of gem-difluorinated cyclopropanes and
cyclopropenes: trifluoromethyltrimethylsilane as a difluorocarbene source,
Angew. Chem. Int. Ed. 50 (2011) 7153–7157.
[13] F. Wang, W. Zhang, J. Zhu, H. Li, K.-W. Huang, J. Hu, Chloride ion-catalyzed
generation of difluorocarbene for efficient preparation of gem-difluorinated
cyclopropenes and cyclopropanes, Chem. Commun. 47 (2011) 2411–2413.
[14] Y. Chang, C. Cai, Sodium trifluoroacetate: an efficient difluorocarbene
precursor for alkenes, Chem. Lett. 34 (2005) 1440–1441.
[15] F. Tian, V. Kruger, O. Bautista, J.-X. Duan, A.-R. Li, W.R. Dolbier Jr., Q.-Y. Chen, A
novel and highly efficient synthesis of gem-difluorocyclopropanes, Org. Lett. 2
(2000) 563–564.
[16] P. Weyerstahl, G. Blume, C. Müller, Zur Darstellung von 1-Fluor-1-brom- und 1-
Fluor-1-chlor-cyclopropanen, Tetrahedron Lett. 12 (1971) 3869–3872.
[17] M. Kamel, W. Kimpenhaus, J. Buddrus, Basisches Verhalten von Epoxiden in
Gegenwart von Halogenid-Ionen, IV: gem-Difluorcyclopropane aus
Chlordifluormethan und Alkanolat-Ionen in geringer Konzentration, Chem.
Ber. 109 (1976) 2351–2369.
ꢀ
ꢀ
[18] P. Balcerzak, M. Fedorynski, A. Jonczyk, Synthesis of gem-
difluorocyclopropanes in a phase-transfer catalysed system, J. Chem. Soc.
Chem. Commun. (1991) 826–827.
4. Experimental section
Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication nos.
CCDC 1530413 (10a) and 1530544 (10d). 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.ac.uk).
[19] E.V. Dehmlow, J. Wilkenloh, Reaktionssteuerung durch die Struktur eines
Phasentransfer-Katalysators bei Tribrommethyl-Anion-/Dibromcarben-
Umsetzungen, Liebigs Ann. Chem. 12 (1990) 125–128.
[20] Interestingly, analogous phosphonium salts appeared inactive as PT-catalysts
in the process (Ref. 19) therefore we did not tested them in our studies..
[21] For application of reverse process (CF2 + Xꢀ !CF2Xꢀ
) carried out under
homogenous conditions, see: M.D. Kosobokov, V.V., Levin, M.I., Struchkova, A.
D., Dilman, Nucleophilic Bromo- and Iododifluoromethylation of Aldehydes,
Org. Lett., 16 (2014) 3784–3787.
ꢀ
[22] M. Barbasiewicz, K. Marciniak, M. Fedorynski, Phase transfer alkylation of
arylacetonitriles revisited, Tetrahedron Lett. 47 (2006) 3871–3874.
[23] G. Wittig, K. Clauß, Pentaphenyl-arsen und Pentaphenyl-antimon, Liebigs Ann.
Chem. 577 (1952) 26–39.
Acknowledgements
This work was financed by the National Science Centre, Poland
(NCN, Grant NN 209 108139, 1081/B/H03/2010/39). T.B. thanks
Warsaw Consortium of Academic Chemistry for a personal KNOW
scholarship.
[24] M. Ma˛kosza, R. Bujok, Cocatalysis in phase-transfer catalyzed fluorination of
alkyl halides and sulfonates, J. Fluor. Chem. 126 (2005) 209–215.
[25] R.L. Shriner, C.N. Wolf, Tetraphenylarsonium chloride hydrochloride, Org.
Synth. 30 (1950) 95–98.
[26] NMR peaks shown at1H and 13C NMR spectra at Fig. 2 correspond to AsPh3Ar,
AsPh2Ar2, AsPhAr3, and AsAr4 (AsPh4 has no resonances at 3.8, 56, and
164 ppm, attributable to the CH3O group). In turn at the MS spectrum AsPh4, as
well as AsPh3Ar, AsPh2Ar2, AsPhAr3 are visible, with only little representation
of AsAr4 (M = 503)..
Appendix A. Supplementary data
[27] Compare: A. Krasovskiy, B.F. Straub, P. Knochel, Highly efficient reagents for Br/
Mg exchange, Angew. Chem. Int. Ed., 45 (2006) 159–162.
[28] U. Müller, H.-D. Dörner, Eine neue Synthese, das Schwingungsspektrum und
die Kristallstruktur von Tetraphenylarsonium-hydrogendichlorid As
(C6H5)4[Cl2H], Z. Naturforsch. 37b (1982) 198–200.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.
jfluchem.2017.03.014.
[29] Surprisingly, the studies revealed that the arsonium salts were formed as
bromides, despite excessive treatment with aqueous HCl during the work-up..
[30] The ORTEP projections were generated using Mercury 2.4 program..
[31] Under similar conditions we tested also reaction of 2 with fluoroform (CHF3),
bubbled through the mixture, catalyzed with TEBACl, and 6. In both cases we
did not detected 3 in the reaction mixture according to GC. For similar
conclusions about reaction of CHF3/KOH/dioxane system with 2, see: C.S.
Thomoson, W.R. Dolbier Jr., Use of fluoroform as a source of difluorocarbene in
the synthesis of difluoromethoxy- and difluorothiomethoxyarenes, J. Org.
Chem., 78 (2013), 8904–8908.
References
ꢀ
[1] For review, see: M. Fedorynski, Syntheses of gem-dihalocyclopropanes and
their use in organic synthesis, Chem. Rev., 103 (2003) 1099–1132.
[2] W.R. Dolbier Jr., M.A. Battiste, Structure synthesis, and chemical reactions of
fluorinated cyclopropanes and cyclopropenes, Chem. Rev. 103 (2003) 1071–
1098.
[3] A.P. Thankachan, K.S. Sindhu, K.K. Krishnan, G. Anilkumar, Recent advances in
the syntheses, transformations and applications of 1,1-dihalocyclopropanes,
Org. Biomol. Chem. 13 (2015) 8780–8802 and references cited therein.