General synthesis of trifluoromethyl selenides utilizing selenocyanates and fluoroform

Article abstract of DOI:10.1021/jo5022844

Trifluoromethylated selenoethers are quite rare despite their potential and the interest that they generate. A series of trifluoromethylseleno derivatives, either primary and secondary aliphatic or aromatic and heterocyclic, is described herein by the reaction of easily prepared organic selenocyanates and CuCF₃. Another beneficial feature of this reaction is the use of fluoroform as a source for the CF₃ group, a compound whose chemistry is currently being intensively researched because it is a potent greenhouse gas that should not be released into the atmosphere.

Full text of DOI:10.1021/jo5022844

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Article
A General Synthesis of Trifluoromethyl Selenides
Utilizing Selenocyanates and Fluoroform
Shay Potash, and Shlomo Rozen
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo5022844 • Publication Date (Web): 05 Nov 2014
Downloaded from http://pubs.acs.org on November 11, 2014
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A General Synthesis of Trifluoromethyl Selenides Utilizing Selenocyanates and
Fluoroform
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Shay Potash and Shlomo Rozen*
School of Chemistry, Tel-Aviv University, Tel-Aviv, Israel 69978. Fax: +972 3 640
9293; Tel: +972 3 640 8378; E-mail: rozens@post.tau.ac.il
Graphical Abstract
RSeCN
HCF3
CuCF3
RSeCF3
KSeCN,
or SeO2/CH2(CN)2
RX, ArH, HetH
Abstract
Trifluoromethylated selenoethers are quite rare despite their potential and interest
they arise. A series of trifluoromethylseleno derivatives, being either primary and
secondary aliphatic or aromatic and heterocyclic is described herein by the reaction of
easily prepared organic selenocyanates and CuCF3. Another beneficial feature of this
reaction is the use of fluoroform as a source for the CF3 group, a compound whose
chemistry is currently under intensive research focus, as it is a potent greenhouse gas,
which should not be released to the atmosphere.
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Introduction
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The trifluoromethyl group is of great interest since among other features it brings
about remarkable biological properties, probably due to the increased lipophilicity it
grants to molecules attached to it.1
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Thus, trifluoromethylation has been a subject of a remarkable research efforts
especially in the last two decades. Among the various trifluoromethyl compounds,
trifluoromethylated ethers and thioethers, ROCF3 and RSCF3 respectively, have attracted
special interest since these families have some of the highest lipophilicity parameter
values.2 One general way for their preparation is through the formation of carbon ꢀ
fluorine bonds at specific sites3 while the other concentrates on transferring the whole
CF3 group from an appropriate reagent.4,5
While the procedures for the preparation of the aforementioned
trifluoromethylated families are quite general and well established, considerably less
efforts were devoted to the development of synthetic methods toward trifluoromethylated
selenoethers. Attaining this goal becomes increasingly desirable because of the medicinal
potential,6 the expected high lipophilicity,7 and the fast expending of the organo selenium
chemistry.6,8
Yagupolskii developed a trifluoromethylselenation applicable for some aryl
iodides.9 This synthetic method uses CuSeCF3, made from copper and CF3SeSeCF3,
which in its turn is difficult to prepare. 10 Several groups reported the synthesis of
PhSeCF3 (2e) by the reactions of different trifluoromethylating agents with PhSeSePh
(3e).11 These reactions, aside from being limited to the formation of 2e, suffer from the
fact that generally half of the organic diselenide is lost in a form of a leaving group.
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Recently, a general procedure was reported for the synthesis of trifluoromethyl
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selenoethers, by substituting the appropriate iodides or bromides
using the
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[(bpy)Cu(SeCF3)]2 complex, which is prepared in a two pot reaction from TMSCF3, CuI,
KF, Se and bipyridine in 41% yield.
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Fluoroform, CHF3, is of course, one of the most attractive trifluoromethylation
agent. It is a side product of manufacturing Teflon, PVDF, refrigerants and fire
extinguishing agents, and is generated in large volumes of over 20000 tons yearly.5a,13
Unfortunately although nontoxic and ozoneꢀfriendly, it is still a very potent greenhouse
gas. As a result, the Kyoto protocol of 1997 obligated industrialized countries to reduce
its emissions. Since it could be destroyed in what is a costly incineration process, it is
much more preferably to be used as a feedstock for manufacturing, but this is a nontrivial
challenge. Therefore large quantities of it are stored without a great demand, turning
CHF3 into an inexpensive reagent indeed.13
In an effort to put this gas to good use, considerable research energy has been
invested to turn it into a synthetic reagent.14 Still, its current scope in organic chemistry is
somewhat limited and confined mostly to formations of CꢀCF3 bonds.15 Recently work in
this field led to trifluoromethylation of B, Si and S centers in addition to carbon ones.13
An important reagent is the fluoroform derived CuCF3, which was used as a general
reagent for formations of different CꢀCF3 bonds and enables convenient usage of
fluoroform in large scales.5,16
For developing a general synthesis of RSeCF3 using the nucleophilic
trifluoromethyl moiety of CuCF3, a good electrophilic selenium source is needed. Organic
selenocyanates, RSeCN can fulfill this requirement. 17 Such compounds are easy to
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prepare by nucleophilic substitution of alkyl halides18 with the relatively inexpensive
KSeCN or by electrophilic substitutions with SeO2/CH2(CN)2 mixture.19
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Results and Discussion
CuCF3 solution was prepared following Grushin’s procedure,5 by bubbling
fluoroform gas through a DMF solution of CuCl and tꢀBuOK with a slight variation
calling for conducting the reaction under atmospheric pressure and without any
Et3N/3HF. The resultant CuCF3 solution (1.5 mole/equivalents) was reacted with 1ꢀ
selenocyanatotetradecane
(1a),18
and
the
previously
unknown
nꢀ
tetradecyl(trifluoromethyl)selane (2a), was formed in quantitative yield after 1.5 h at
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room temperature. The progress of these type of reactions was monitored by F NMR
(vs. calibrated amount of PhCF3).
The CuCF3 solution was reacted with (3ꢀselenocyanatopropyl)benzene (1b)18 as
well, forming quantitatively (3ꢀphenylpropyl)trifluoromethylselane (2b). In order to
demonstrate the efficiency of this reaction, the doubly selenated, 1,10ꢀ
diselenocyanatodecane (1c)18 was reacted with 3 moleꢀequivalents of the fluoroform
derived CuCF3 (50% excess) for 2.5 h at room temperature yielding the previously
unknown 1,10ꢀbis(trifluoromethylseleno)decane (2c) in 95% yield.
Cyclohexyltrifluoromethylselanes are of special interest since secondary
trifluoromethylselanes in general and cyclohexyl ones in particular are not known. The
reaction of cyclohexene with KSeCN and CuCl2 in ethanol yielded mainly transꢀ1ꢀ
ethoxyꢀ2ꢀselenocyanatocyclohexane (1d) with less than 10% of the cis isomer. The
reaction of CuCF3 with 1d showed that the stereochemistry around the CꢀSe bond is
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retained
and
the
secondary
trifluoromethylseleno
ether,
transꢀ(2ꢀ
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ethoxycyclohexyl)trifluoromethylselane (2d) was formed in 80% in 4 h at R.T.
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Aromatic selenocyanates are also reactive towards the nucleophilic
trifluoromethylating reagent CuCF3. When the commercial PhSeCN (1e) was added to
this fluoroform derived agent, the reaction was completed in 3 hours and
phenyltrifluoromethylselane (2e) was formed in 85% yield. The trifluoromethylation is
also suitable for electronꢀrich aromatic selenocyanates, which are readily prepared by
electrophilic aromatic substitution. For example, treatment of N,Nꢀdimethylaniline with
selenium (IV) oxide and malononitrile gives paraꢀsubstituted N,Nꢀdimethylꢀ4ꢀ
selenocyanatoaniline (1f).19 When this compound was reacted with the CuCF3 suspension
for 4 h at R.T., the N,Nꢀdimethylꢀ4ꢀ(trifluoromethylselanyl)aniline (2f) was formed in
80% yield. The trifluoromethylation of selenocyanates with CuCF3 is also effective with
electronꢀpoor aromatics, as evident from the reaction of 8ꢀselenocyanatoquinoline (1g)20
with 1.5 equivalents of the fluoroform derived CuCF3 which led to quantitative formation
of the previously unreported 8ꢀ(trifluoromethylselanyl)quinoline (2g). In this case the
reaction rate was faster and was completed within 1.5 h, probably due to copperꢀnitrogen
interactions, which could hold the trifluoromethylating agent closer to the reaction center.
Nitrogen heterocyclic substrates such as the electron rich 1ꢀmethylꢀ3ꢀselenocyanatoꢀ1Hꢀ
indole (1h), prepared by direct electrophilic aromatic substitution, also reacted with
CuCF3 to form the new 1ꢀmethylꢀ3ꢀ(trifluoromethylselanyl)ꢀ1Hꢀindole (2h) in 80% after
4 h at room temperature (Scheme 1).
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Scheme 1: From selenocyanates to trifluoromethyl selenoethers
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CuCF3 (1.5 eq.)/ DMF
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R SeCF3
R SeCN
CHF3/ tꢀBuOK/ CuCl
1
2
a
R = nꢀC14H29
> 95%
1.5h, R.T
1.5h, R.T
2.5h, R.T
b
R = Ph(CH2)3
> 95%
95%a
(CH2)10
c R =
d
4h, R.T
R =
80%
OEt
R = Ph
e
85%
80%
3h, R.T
4h, R.T
4ꢀMe2NꢀC6H4
N
R =
R =
f
g
>95%
80%
1.5h, R.T
4h, R.T
h
R =
N
Me
(a) using 3 mol/eq of CuCF3
While selenocyanates are probably the best starting point for the synthesis of
trifluoromethylselenides, occasionally diselenides (RSeꢀSeR) could be more readily
available, or prepared by air oxidation of the corresponding selenols (RSeH) and hence
from the corresponding Cu or K salts. These diselenides21 could also serve as substrates
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for trifluoromethyl selenides by using almost the same procedure as with selenocyanates,
and the reactions are even somewhat faster as shown for 2e and 2i.17 Although mole per
mole the yields were about 90%, when based on the Se atoms they are around 45% only
with the balance being the corresponding selenide salts – RSeCu/K ejected as the leaving
group. These salts, of course, are easy to protonate by acidic workup to the corresponding
selenols, RSeH, which in their turn could be oxidized by air to the parent diselenides, 3.
As the recovery is a simple, high – yield process, the recovered diselenides can be reused
to form trifluoromethyl selenides, and thus increasing the yield and minimizing the waste
(Scheme 2).
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Scheme 2: From diselenides to trifluoromethyl
selenoethers
a
CuCF3
RSeSeR
RSeCF3 + RSeCu/K
CHF3
2
4
3
90%b
90%b
e R = Ph
45%
45%
i
R = nꢀC8H17
a) 1.5 mol/eq; 1h; R.T.; b) when calculated
mole per mole. 45% when based on the Se atom.
Conclusion
In conclusion, a diverse series of trifluoromethylseleno derivatives was prepared
from the corresponding alkyl, aryl or heterocyclic selenocyanates. As these
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trifluoromethylseleno compounds are expected to be highly lipophilic, their popularity is
on the rise and it was important to find a general and simple procedure that combines an
easily accessible selenium source coupled with an attractive trifluoromethylating agent.
These requirements are satisfied in the reaction of selenocyanates and fluoroform derived
CuCF3. It was also shown that similar conditions are compatible for the reaction with
diselenides serving as starting materials, resulting again in the corresponding
trifluoromethylseleno compounds.
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Experimental
General Procedures:
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The fluoroform cylinder was purchased from commercial sources. H, F, and
13C NMR spectra were obtained with CDCl3 as a solvent at 400, 376, and 100 MHz,
1
13
respectively, with Me4Si as an internal standard for the H and C NMR and CFCl3 for
the 19F NMR spectra. HRMS samples of 2f and 2g were measured under ASAP
conditions. In all other cases this method could not detect any molecular ion, so we have
used successfully the unique Amirav’s supersonic GCꢀMS technique which without
practically any exceptions could reveal such ions. In these cases, the isotope abundance
analysis provided very satisfactory results, as shown for the specific compounds. This
type of analysis confirmed the proposed elemental formulas as it ranked them in first
place and hence as the best choice, with very good matching factors of better than 940
(out of 999).22
Selenocyanates formation:
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We have referenced the known selenocyanates. In particular, we have prepared the
primary selenocyanates 1a and 1b via the substitution of 1ꢀbromotetradecane and 1ꢀ
bromoꢀ3ꢀphenylpropane with 1.2 equivalent potassium selenocyanate in a refluxing
ethanolic solution for 1 h (>95% yields). Bis–selenocyanate 1c was similarly prepared
using 2.5 equivalent potassium selenocyanate and 1,10ꢀdibromodecane in 90% yield. The
cyclic selenocyanate 1d was prepared by the reaction of cyclohexene with 2 equiv.
copper(II) chloride and potassium selenocyanate each in refluxing ethanol in 60% yield.23
Selenocyanate 1g was prepared by the diazotation of 8ꢀaminoquinoline, followed by
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o
substitution with potassium selenocyanate at 0 C (60% yield). The preparations of the
electronꢀrich selenocyanates 1f and 1h were achieved by electrophilic aromatic
substitutions using selenium(IV) oxide and malononitrile in DMSO as described in
reference 19 in 85% and 90% yield respectively.
General Trifluoromethylation Procedure:
To a two necked flask equipped with a glass pipette inlet for argon, 40 ml of dry
DMF were inserted and the solvent was degassed for 5 minutes followed by addition of
4.7 g of finely ground potassium tertꢀbutoxide. The suspension was stirred for about 5
minutes until most of the solid was dissolved. Two g of copper (I) chloride were added,
the suspension turned black within a minute and was vigorously stirred while argon was
passed through for 1 h at room temperature. The argon inlet was replaced with a
fluoroform inlet and this gas was bubbled through the black solution for 5 minutes at a
rate of about 600 ml per minute (about 6 moleꢀequivalents, based of Cu). This procedure
produced about 16 mmol CuCF3 (calibrated using 19F NMR with PhCF3 as a standard). A
measured volume was added to the DMF solution of the selenocyanate ensuring about
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50% excess of CuCF3 over the starting selenocyanate, and the suspension was stirred
under argon atmosphere for 3 – 5 hours till completion (monitored by TLC or UV for 2e
– 2h). The suspension was added to cold water and extracted with ether. The ethereal
solution was passed through a short pad of celite to remove inorganic salts and
evaporated. The product was purified by flash column chromatography using pentane
(compounds 2a, b, c, e) or pentane/ether mixtures (compounds 2d, f, g, h). Specific
amounts of selenocyanates, CuCF3 suspension, reaction times and temperatures are
specified herein. As these reactions were conducted in small scale, excess fluoroform was
not destroyed, for large scale applications a continuous flow process for preparation and
reactions of CuCF3 was reported.16
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Tetradecyl(trifluoromethyl)selane (2a). Prepared from selenocyanate 1a (0.80
g, 2.9 mmol) and about 4.0 mmol CuCF3 as described in the general procedure.
Quantitative yield; 0.91 g, clear oil, 1H NMR 2.98 (2 H, t, J = 7.6 Hz), 1.78 (2 H, quin, J
= 7.6 Hz), 1.40 (2 H, m), 1.26 (20 H, m), 0.88 (3 H, t, J = 6.4 Hz) ppm. 13C NMR 122.8
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(q, J = 328 Hz), 32.0, 30.3, 29.7ꢀ29.4 (8 C), 29.0, 25.9, 22.8, 14.2 ppm. F NMR ꢀ39.5
ppm (3 F, s). The common MS methods failed to show any molecular peak. Amirav’s
supersonic GCꢀMS revealed a strong molecular ion peak of m/z 340.1 (M)+ with an
isotope abundance analysis matching factor of 998 out of 999. Anal. calc. for C15H29F3Se:
C, 52.17; H, 8.46; F, 16.5. Found: C, 51.95; H, 8.45; F, 16.11.
(3-Phenylpropyl)(trifluoromethyl)selane (2b).12 Prepared from selenocyanate
1b (0.55 g, 2.4 mmol) and fluoroform derived CuCF3 (about 3.7 mmol) as described in
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the general procedure, in quantitative yield: 0.65 g, clear oil, H NMR 7.30 ꢀ 7.32 (2 H,
m), 7.18 ꢀ 7.24 (3 H, m), 2.99 (2 H, t, J = 7.2 Hz), 2.75 (2 H, t, J = 7.6 Hz), 2.14 (2 H,
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quin, J = 7.2 Hz), ppm. 13C NMR 141.6, 128.6, 128.5, 126.3, 122.7 (q, J = 328 Hz), 35.5,
31.8, 25.2 ppm. 19F NMR ꢀ32.7 ppm (3 F, s).
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1,10-Bis(trifluoromethylseleno)decane (2c). Prepared from selenocyanate 1c18
(0.80 g, 2.3 mmol) and the fluoroform derived CuCF3 (about 5.7 mmol) as described in
the general procedure, in 95% yield: 0.95 g, clear oil, 1H NMR 2.98 (4 H, t, J = 7.2 Hz),
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1.78 (2 H, quin, J = 7.6 Hz), 1.37 ꢀ 1.401 (4 H, m), 1.25 ꢀ 1.37 (8 H, m) ppm. C NMR
122.8 (q, J = 330 Hz), 30.3, 29.6, 29.3, 28.9, 25.9 ppm. 19F NMR ꢀ32.8 ppm (3 F, s). The
common MS methods failed to show any molecular peak. Amirav’s supersonic GCꢀMS
revealed a strong molecular ion peak of m/z 426.0 (M)+ with an isotope abundance
analysis matching factor of 940 out of 999.
Trans-(2-ethoxycyclohexyl)(trifluoromethyl)selane (2d). Prepared from
selenocyanate 1d23 (1.0 g, 4.1 mmol) and the fluoroform derived CuCF3 (about 6.5
1
mmol) as described in the general procedure, in 80% yield: 0.95 g, clear oil, H NMR
3.28 ꢀ 3.68 (2 H, m), 2.04 ꢀ 2.35 (1 H, m), 1.60 ꢀ 1.79 (2 H, m), 1.18 ꢀ 1.43 (7 H, m), 0.83
13
ꢀ 0.91 (3 H, m) ppm. C NMR 123.2 (q, J = 329 Hz), 96.2, 80.1, 64.5, 47.6, 31.2, 25.8,
19
23.2, 15.4 ppm. F NMR ꢀ30.2 ppm (3 F, s). The common MS methods failed to show
any molecular peak. Amirav’s supersonic GCꢀMS revealed a strong molecular ion peak
of m/z 270.0 (M)+ with an isotope abundance analysis matching factor of 980 out of 999.
Phenyl(trifluoromethyl)selane (2e).11 Prepared from commercial selenocyanate
1e (3.00 g, 16.4 mmol) the fluoroform derived CuCF3 (about 24.7 mmol) as described in
the general procedure, in 85% yield: 3.15 g, clear oil, 1H NMR 7.74 ꢀ 7.77 (2 H, m), 7.46
ꢀ 7.50 (1 H, m), 7.38 ꢀ 7.42 (2 H, m) ppm. 13C NMR 137.1, 130.4, 129.6, 122.6, 122.6 (q,
J = 330 Hz) ppm. 19F NMR ꢀ34.8 ppm (3 F, s).
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N,N-Dimethyl-4-(trifluoromethylselanyl)aniline
(2f).
Prepared
from
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selenocyanate 1f19 (1.00 g, 4.4 mmol) and the fluoroform derived CuCF3 (about 6.7
mmol) as described in the general procedure, in 80% yield: 0.95 g, pinkish solid, m.p. 58
– 59 oC. 1H NMR 7.56 (2 H, d, J = 9.2 Hz), 6.66 (2 H, d, J = 8.8 Hz), 3.00 (6 H, s) ppm.
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13CNMR 152.3, 139.4, 123.3 (q, J = 332 Hz), 113.3, 107.7, 40.8 ppm. FNMR ꢀ36.7
ppm (3 F, s). HRMS (ASAP): calcd. for C9H11NF3Se (M+H)+ 266.0036; found 266.0047.
Anal. calc. for C9H10NF3Se: C, 40.31; H, 3.76; F, 21.26; N, 5.22. Found: C, 40.11; H,
3.63; F, 20.83; N, 4.71.
8-(Trifluoromethylselanyl)quinoline (2g). Prepared from selenocyanate 1g20
(0.61 g, 2.6 mmol) and the fluoroform derived CuCF3 (about 3.9 mmol) as described in
the general procedure, in quantitative yield: 0.72 g, clear oil, 1H NMR 8.88 (1 H, dd, J1 =
4.3 Hz, J2 = 1.7 Hz), 8.15 (1 H, dd, J1 = 8.3 Hz, J2 = 1.6 Hz), 7.99 (1 H, t, J = 7.4 Hz),
7.76 (1 H, dd, J1 = 8.2 Hz, J2 = 1.1 Hz), 7.51 (1 H, t, J = 8.0 Hz), 7.45 (1 H, dd, J1 = 8.3
Hz, J2 = 4.3 Hz) ppm. 13C NMR 150.5, 146.5, 137.2, 131.3, 130.2, 129.1, 128.1, 124.2 (q,
J = 330 Hz), 122.9 ppm 19F NMR ꢀ35.2 ppm (3 F, s). HRMS (ASAP): calcd. for
C10H7F3NSe (M + H)+ 273.9723; found 273.9727.
1-methyl-3-(trifluoromethylselanyl)-1H-indole
(2h).
Prepared
from
selenocyanate 1h19 (0.52 g, 2.2 mmol) and the fluoroform derived CuCF3 (about 3.3
mmol) as described in the general procedure, in 80% yield: 0.49 g, beige solid, m.p = 59
oC. H NMR 7.75 (1 H, d, J = 7.6 Hz), 7.26ꢀ7.39 (4 H, m), 3.85 (3 H, s) ppm. C NMR
1
13
19
137.3, 137.1, 130.9, 122.9, 122.3 (q, J = 333 Hz), 121.2, 120.2, 109.8, 33.3 ppm. F
NMR ꢀ36.7 ppm (3 F, s). The common MS methods failed to show any molecular peak.
Amirav’s supersonic GCꢀMS revealed a strong molecular ion peak of m/z 273.0 (M)+
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with an isotope abundance analysis matching factor of 999 out of 999. Anal. calc. for
C10H8NF3Se: C, 43.18; H, 2.90; F, 20.49; N, 5.04. Found: C, 43.17; H, 2.79; F, 20.94; N,
4.76.
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Octyl(trifluoromethyl)selane (2i)17. Prepared from diselenide 3i (2.69 gr, 7.0
mmol) and about 10.5 mmol CuCF3, whose preparation was described in the general
procedure. The suspension was stirred under argon atmosphere for one hour (monitoring
by TLC) then added to cold 2% aqueous HCl, stirred for 5 minutes and extracted with
pentane. The organic solution was passed through a short pad of celite to remove
inorganic salts and evaporated. The product was purified by flash column
chromatography using pentane. The product was isolated in 90% yield (45% based on Se
atoms): 1.65 g, 6.3 mmol, clear oil. 1H NMR 2.98 (2 H, t, J = 7.2 Hz), 1.78 (2 H, quin, J =
7.6 Hz), 1.43 ꢀ 1.22 (10 H, m), 0.88 (3 H, t, J = 6.4 Hz) ppm. 13C NMR 123.4 (q, J = 332
Hz), 32.5, 30.9, 30.3, 29.8, 29.6, 26.6, 23.3, 14.7 ppm. 19F NMR ꢀ32.9 ppm (3 F, s).
ASSOCIATED CONTENT
Supporting Information. 1H NMR and 13C NMR spectra for all new compounds. This
material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Fax: +972 3 640 9293. Tel: +972 3 640 8378. Eꢀmail: rozens@post.tau.ac.il.
Acknowledgement: This work was supported by the Israel Science Foundation.
Notes and References
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1.
(a) Nishiumi, H.; Sato, K.; Kato, R. Advances in Fluorine Science, 2006. (b)
Filler, R.; Kirk, K. Biological properties of fluorinated compounds. In Chemistry
of Organic Fluorine Compounds II: A Critical Review; Hudlicky, M.; Pavlath, A.
E., Eds.; ACS Monograph 187; American Chemical Society: Washington, DC,
1995.
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Hansch, C. ; Leo, A.; Hoekman, D. H. Exploring QSAR: Hydrophobic, electronic
and steric constants. 1995, American Chemical Society, Washington, D.C.
(a) BenꢀDavid, I.; Rechavi, D.; Mishani, E.; Rozen, S. J. Fluorine Chem. 1999,
97, 75ꢀ78. (b) Cohen, O.; Mishani, E.; Rozen, S. Tetrahedron 2010, 65, 3579ꢀ
3582. (c) Rozen, S. Acc. Chem. Res. 2005, 38, 803ꢀ812.
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(a) Prakash, G. K. S.; Panja, C.; Vaghoo, H.; Surampudi, V.; Kultyshev, R.;
Mandal, M.; Rasul, G.; Mathew, T.; Olah, G. A. J. Org. Chem. 2006, 71, 6806ꢀ
6813. (b) Chen, M.; Buchwald S. L. Angew. Chem. 2013, 52, 11628ꢀ11631.
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Chem. Int. Ed. 2012, 51, 7767ꢀ7770. (e) Zanardi A.; Novikov M. A.; Martin E.;
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Wirth, T. (Ed.), Organoselenium Chemistry: Synthesis and Reactions, Weinheim,
WileyꢀVCH, 2012.
6.
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As SCF3 compounds were measured to be more lipophilic than the corresponding
OCF3 and CF3 derivatives, the less electronegative SeCF3 compounds are
expected to even more lipophilic. See also reference 2.
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(a) Back, T. G. (Ed.), Organoselenium Chemistry: A Practical Approach, Oxford
University Press, Oxford, 1999. (b) Freudendahl, D. M.; Santoro, S.; Shahzad, S.
A.; Santi, C.; Wirth, T. Angew. Chem. Int. Ed. 2009, 48, 8409ꢀ8411. (c) Potash,
S.; Rozen, S. Eur. J. Org. Chem. 2013, 5574ꢀ5579.
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Kondratenko, N. V.; Kolomeytsev, A. A.; Popov, V. I.; Yagupolskii, L. M.
Synthesis 1985, 667ꢀ669.
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Haas, A. J. Fluorine Chem. 1986, 32, 415ꢀ439.
(a) Cherkupally, P.; Beier, P. Tetrahedron Lett. 2010, 51, 252ꢀ255. (b) Pooput, C.;
Dolbier, W. R. Jr.; Medebielle, M. J. Org. Chem. 2006, 71, 3564ꢀ3568. (c) Large,
S.; Roques, N.; Langlois, B. R. J. Org. Chem. 2000, 65, 8848ꢀ8856.
(a) Chen, C.; Ouyang, L.; Lin, Q.; Liu, Y. Hou, C.; Yuan, Y.; Weng, Z. Chem.
Eur. J. 2014, 20, 657ꢀ661. (b) Zhu, P.; He, X.; Chen, X.; You, Y.; Yuan, Y.;
Weng, Z. Tetrahedron 2014, 70, 672ꢀ677.
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Prakash, G. K. S.; Jog, P. V.; Batamack, P. T. D.; Olah, G. A. Science 2012, 338,
1324.
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Han, W.; Li, Y.; Tang, H.; Liu, H. J. Fluorine Chem. 2012, 140, 7ꢀ16.
LargeꢀRadix, S.; Billard, T.; Langlois, B. R. J. Fluorine Chem. 2003, 124,
147ꢀ149.
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Mazloomi, Z.; Bansode, A.; Benavente, P.; Lishchynskyi, A.; Urakawa, A.;
Grushin, V. V. Org. Process Res. Dev. 2014, 18, 1020−1026.
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Billard, T.; Large, S.; Langlois, B. R. Tetrahedron Lett. 1997, 38, 65ꢀ68.
(a) Huang, Y.; Chen, R. Y. Synth. Commun. 2000, 30, 377ꢀ381. (b) Rebane, E.
Acta Chem. Scand. 1967, 21, 652ꢀ656.
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Sekido, E.; Fujiwara, I. Talanta, 1972, 19, 647–655.
Diselenides are easy to observe during column chromatography as they are
generally more polar than the trifluoromethylated products and produce yellow
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