Selenium-catalyzed trifluoromethylsulfinylation/rearrangement of allylic and propargylic alcohols: Access to allylic and allenic triflones

Article abstract of DOI:10.1021/acs.orglett.0c04236

A selenium-catalyzed trifluoromethylsulfinylation/ rearrangement of allylic and propargylic alcohols for synthesizing triflones was developed for the first time. Various allylic and allenic triflones were delivered in moderate to excellent yields. After n

Full text of DOI:10.1021/acs.orglett.0c04236

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Letter
Selenium-Catalyzed Trifluoromethylsulfinylation/Rearrangement of
Allylic and Propargylic Alcohols: Access to Allylic and Allenic
Triflones
Deng Zhu, Hui-Yun Luo, and Zhi-Min Chen*
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ABSTRACT: A selenium-catalyzed trifluoromethylsulfinylation/
rearrangement of allylic and propargylic alcohols for synthesizing
triflones was developed for the first time. Various allylic and allenic
triflones were delivered in moderate to excellent yields. After
numerous control experiments were performed, it was suggested
that this transformation includes an unusual [+SCF3] group
disproportionation process that forms [+SOCF3] that is in-situ-
catalyzed by selenium, and H2O was used as an oxygen source.
This reaction features mild reaction conditions and good
compatibility of substrates, and it is transition-metal-free.
enantioselective sulfenofunctionalizations of alkenes using
llylic sulfones are an important class of compounds that
Anot only are versatile intermediates in modern synthetic chiral selenide derivatives as the catalyst,10 and Zhao and
chemistry1 but also widely exist in drug molecules.2 The
coworkers demonstrated the chiral selenide-catalyzed asym-
metric trifluoromethylthiolation of alkenes and selenide-
catalyzed oxidation reactions.11,12 Inspired by the successful
development of organoselenium catalysis, and as part of our
ongoing research to synthesize organic sulfides,13 we
envisioned that the efficient construction of allylic and allenic
triflones may be achieved by the organoselenium-catalyzed
trifluoromethylsulfinylation/rearrangement of allylic and prop-
argylic alcohols (Scheme 1b). Herein we report our
preliminary results.
In our initial study, 1,1-diphenyl-2-propen-1-ol (1a) was
selected as a model substrate and reacted with N-
trifluoromethylthiosaccharin 2a (Shen’s reagent14). After
systematically screening the reaction conditions, we found
that the desired product 3a was obtained in 84% isolated yield
when Shen’s reagent 2a was used in the presence of rac-C6
developed by Denmark10 as a catalyst and diphenyl phosphate
and H2O as additives in acetonitrile at room temperature
under air. (For details, see Table S1 of the Supporting
Information.) With the optimized reaction conditions in hand,
various allylic alcohols were tested to investigate the scope of
the reaction (Scheme 2). A series of substrates with
symmetrical substituted aryl groups were first tested, and the
development of efficient methods for the preparation of allylic
sulfones has attracted much attention, and a number of elegant
strategies have been reported.3 Among them, because of the
unique properties of the fluorine atom, the syntheses of allylic
triflones are particularly imperative, and some strategies for the
synthesis of allylic triflones have been developed.4 As shown in
Scheme 1a, in these strategies, a trifluoromethylsulfonyl group
(SO2CF3) is directly introduced into the compounds; however,
harsh reaction conditions are always required, and the reaction
temperature has to be >100 °C. Until now, modular syntheses
of allylic triflones under mild reactions have been challenging.
In like manner, allenic triflones are not only a class of universal
synthetic intermediates but also potential medical molecules.5
However, only a few examples of the formation of allenic
triflones have been reported.6 Therefore, the development of
modular and rapid methods for the formation of allylic and
allenic triflones, which could smoothly proceed under mild
reaction conditions, is in high demand. Recently, we developed
a divergent synthesis strategy for the efficient construction of
allylic and allenic trifluoromethyl sulfoxides by a [2,3]-
sigmatropic rearrangement.7 In this context, we aimed to
develop a modular route to facilely construct allylic and allenic
triflones.
Received: December 23, 2020
Published: January 14, 2021
Because of the merits of low cost, high selectivity, mild
reaction conditions, and good tolerance of functional groups,
organoselenium catalysis has attracted attention and interest
from many chemists.8 Thus numerous transformations
catalyzed by organoselenium have been explored.9 For
instance, the Denmark group reported a series of seminal
https://dx.doi.org/10.1021/acs.orglett.0c04236
© 2021 American Chemical Society
Org. Lett. 2021, 23, 1044−1048
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Scheme 1. Design of the Synthesis of Allylic Triflones
Scheme 2. Substrate Scope of Allylic Alcohols for the
a
Synthesis of Allylic Triflones
corresponding γ,γ-diarylallyl trifluoromethyl sulfones were
afforded in moderate to excellent yields (3b−m). It was
found that the position of the methyl group at the phenyl did
not clearly affect the yield (3b−d). However, the electronic
properties of the substituents obviously affected the yield. The
electron-poor substrate 1e produced product 3e in 80% yield,
whereas the electron-rich substrate 1g gave only the desired
product 3g in 47% yield. To our delight, substrates with
multiple substituted phenyls and 2-naphthalene were well
tolerated, delivering the corresponding products in moderate
to excellent yields (3h−k). A cyclic diphenyl substrate was also
suitable for the system; however, a substrate with thiophene
gave the product in only 33% yield (3l, 3m). Next, some allylic
alcohols with unsymmetrical groups were investigated. When
groups R1 and R2 were different aromatic rings, we found that
the corresponding products were obtained with a Z/E ratio.
(For details, see the SI.) The electronic effect could improve
the ratio, whereas the steric effect did not obviously affect the
ratio (3n, 3o). When R1 is a phenyl group and R2 is
phenylacetylene, a single product, 3p, was obtained in 50%
yield, the relative configuration of which was determined by X-
ray crystallography. To our delight, the products (E)-3q and 3r
were also solely obtained when R1 was a phenyl group and R2
was an alkyl group. (For details, see the SI.) It is a pity that no
reaction occurred when substrate 1s with a symmetrical
substituted alkyl group was investigated. Furthermore, the
secondary allylic alcohol 1t was relevant to this system,
furnishing the desired product (E)-3t in 71% yield. It is of note
that an array of 2,2-disubstituted alkene substrates were also
applicable in this reaction (3u−x). Two tetra-substituted
alkene products were rapidly produced in moderate yields (3w,
3x). The relative configuration of 3v was assigned by X-ray
crystallography. Finally, the nonterminal alkene substrate 1y
was tested under the standard conditions, and the product 3y
was obtained in 80% yield. To evaluate the practicability of this
a
Reaction conditions: Unless otherwise noted, the reaction was
conducted with 1 (0.1 mmol), 2a (0.3 mmol), rac-C6 (0.1 equiv),
diphenyl phosphate (0.1 equiv), and H2O (10 equiv) in CH3CN (2
b
mL) at room temperature under air. Isolated yield. Reaction was
c
d
performed at 10 °C. Ratio was determined by 1H NMR. Yield of 1
mmol scale.
transformation, a 1 mmol scale of 1a was carried out under
standard conditions. Satisfactorily, trifluoromethyl sulfone 3a
was obtained in 85% yield.
Subsequently, we turned our attention to develop a method
for the synthesis of allenic triflones. We speculated that
propargylic alcohols may be used as substrates for the
formation of allenic triflones under the above optimized
reaction conditions. To examine our hypothesis, 1,1-
diphenylbut-2-yn-1-ol (4a) was first subjected to the standard
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reaction conditions. To our delight, the desired allenic triflone
5a was obtained in 86% yield. Next, various propargylic
alcohols were tested to study the generality of this system
(Scheme 3). Similarly, it was found that an electron-deficient
Scheme 4. Some Control Experiment Results
Scheme 3. Substrate Scope of Propargylic Alcohols for the
a
Synthesis of Allenic Triflones
a
Reaction conditions: Unless otherwise noted, the reaction was
conducted with 4 (0.1 mmol), 2a (0.3 mmol), rac-C6 (0.1 equiv),
diphenyl phosphate (0.1 equiv), and H2O (10 equiv) in CH3CN (2
b
mL) at room temperature under air. Isolated yield. Yield of 1 mmol
scale.
substrate (4c) gave a higher yield than an electron-rich
substrate (4d). To our satisfaction, substrates containing 2-
naphthalene and cyclic diphenyl groups were well tolerated,
delivering the corresponding products in 75 and 91% yields,
respectively (5e, 5f). To our delight, the thiophene substrate
was also tested, affording the product 5g in 64% yield. It
should be noted that product 5g is not stable at room
temperature. Next, two compounds with unsymmetrical aryl
moieties were also suitable for this transformation, and the
corresponding products were produced in satisfactory yields
(5h, 5i). Furthermore, a compound with methyl and phenyl
groups (4j) was also subjected to the reaction. Satisfactorily,
product 5j was obtained in 73% yield. To further broaden the
scope of this reaction, two secondary propargylic alcohols 4k
and 4l were investigated. It was found that the transformations
smoothly occurred, and the desired products were obtained in
moderate yields. Next, the phenylacetylene-type substrate 4m
was tested, furnishing the product 5m in 66% yield. Finally,
product 5n was obtained in 54% yield using terminal
propargylic alcohol 4n as the substrate, and the configuration
of 5n was determined by X-ray crystallography. Likewise, to
evaluate the utility of the reaction of propargylic alcohols, a 1
mmol scale of 4a was carried out, and product 5a was obtained
in a maintained yield (85%).
SI.) Because the reaction of 1a with trifluoromethanesulfinyl
chloride could produce product 3a in 38% yield (eq 2, Scheme
4), we proposed that path 1 is feasible (eq 6, Scheme 4): After
the substrate reacts with the trifluoromethanesulfinyl cation
generated in situ, the [2,3]-sigmatropic rearrangement of 8
subsequently occurs to deliver the product 3. Additionally, we
found that adding acid and water to this reaction system could
increase the yield, so we proposed a possible path 2 (eq 7,
Scheme 4): After the substrate is rearranged to form a primary
alcohol 9 under acidic conditions (for more details, see the SI),
it will interact with the trifluoromethanesulfinyl cation
generated in situ. The intermediate 10 is produced at the
same time, and the product is obtained after the rearrangement
process of int-10.15 To verify the hypothetical path 2, 9a was
subjected to standard reaction conditions, and 3a was obtained
in 40% yield (eq 3, Scheme 4). Thus both paths 1 and 2 may
concurrently exist in this transformation. To further verify the
main pathway, we conducted 18O-labeling experiments. (See
the SI for details.) The ordinary water (H216O) of the reaction
system was replaced with heavy oxygen water (H218O) to
produce 3a in 87% yield, of which the ratio was 3ab/3ac 1:5
(eq 4, Scheme 4). Meanwhile, we conducted an experiment
under argon conditions, and 3a was obtained in 81% yield (eq
5, Scheme 4), further eliminating the possible oxidation of
[SCF3] by oxygen in the air. On the basis of these results, we
found that H2O was used as an oxygen source and that path 2
was the main pathway. Next, we focused on the possible
process of generating a trifluoromethanesulfinyl cation in situ
in the reaction and conducted a series of experiments. (For
details, see the SI.) It was found that a trifluoromethanesulfinyl
Next, we started to investigate the possible mechanism of
this reaction. To gain more mechanistic insights into the
reaction, a series of control experiments were carried out. First,
trifluoromethyl sulfoxide 7a was reacted with 2a under
standard conditions (eq 1, Scheme 4), and only a trace
amount of 3a was formed within 16 h, which could rule out the
notion that sulfone 3 oxidated from sulfoxide, which was
obtained from the trifluoromethylthiolation/[2,3]-sigmatropic
rearrangement of allylic alcohols 7. (For more details, see the
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cation [+SOCF3] was generated from an unconventional
[+SCF3] group disproportionation process catalyzed by
selenium.
On the basis of our experimental results and combined with
previous works,15,16 we propose a plausible mechanism in
Scheme 5a. First, the trifluoromethylsulfenic ion is transferred
Accession Codes
CCDC 2008975, 2040878, and 2040880 contain the
supplementary crystallographic data for this paper. These
data can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
Scheme 5. Proposed Mechanism
AUTHOR INFORMATION
Corresponding Author
■
Zhi-Min Chen − School of Chemistry and Chemical
Engineering, Shanghai Key Laboratory for Molecular
Engineering of Chiral Drugs, Shanghai Jiao Tong University,
Shanghai 200240, P. R. China; orcid.org/0000-0002-
6988-8955; Email: chenzhimin221@sjtu.edu.cn
Authors
Deng Zhu − School of Chemistry and Chemical Engineering,
Shanghai Key Laboratory for Molecular Engineering of
Chiral Drugs, Shanghai Jiao Tong University, Shanghai
200240, P. R. China
Hui-Yun Luo − School of Chemistry and Chemical
Engineering, Shanghai Key Laboratory for Molecular
Engineering of Chiral Drugs, Shanghai Jiao Tong University,
Shanghai 200240, P. R. China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c04236
from Shen’s reagent 2a to Lewis base rac-C6 under the
activation of diphenyl phosphate to form an active species 13.
Second, the trifluoromethylsulfenic ion undergoes a dispro-
portionation, as shown in Scheme 5b, in the presence of water,
generating species 14. Third, the trifluoromethylsulfinyl ion is
attacked by compound 9, which is rearranged from substrate 1
in the presence of acid and water, forming the intermediate 10,
which undergoes a further rearrangement process,15 leading to
the delivery of the desired trifluoromethyl sulfone 3 along with
reproduction of rac-C6 and diphenyl phosphate. Meanwhile,
the trifluoromethylsulfinyl ion can be directly attacked by
substrate 1, forming the intermediate 8, which undergoes a
further [2,3]-sigmatropic rearrangement to produce trifluor-
omethyl sulfone 3.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the NSFC (nos. 21871178, 22071149, 21702135)
and the STCSM (19JC1430100) for the financial support.
This research was also supported by The Program for
Professor of Special Appointment (Eastern Scholar) at
Shanghai Institutions of Higher Learning. We thank Prof.
Yong-Qiang Tu (Shanghai Jiao Tong University) and Prof.
Qing-Wei Zhang (University of Science and Technology of
China) for helpful discussions on this paper.
In summary, we successfully developed an efficient and
modular method for the synthesis of allylic and allenic triflones
under mild reaction conditions via the selenium-catalyzed
trifluoromethylsulfinylation/rearrangement of allylic and prop-
argylic alcohols. A variety of allylic and allenic triflones were
obtained in moderate to excellent yields. Interestingly, we
found that this tandem reaction includes an unusual [+SCF3]
group disproportionation process to form [+SOCF3] in situ,
and H2O was used as an oxygen source. This reaction avoided
the previous high-temperature reaction conditions and the use
of a dangerous oxidizing agent for the synthesis of allylic and
allenic triflones.
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ASSOCIATED CONTENT
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* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c04236.
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