Oxidative Hydro-, Bromo-, and Chloroheptafluoroisopropylation of Unactivated Alkenes with Heptafluoroisopropyl Silver

Article abstract of DOI:10.1021/acs.orglett.9b03705

Oxidant-induced three-component hydro-, bromo-, and chloroheptafluoroisopropylation of unactivated alkenes are disclosed. In these reactions, the CF(CF₃)₂ radical was generated from the oxidation of AgCF(CF₃)₂.

Full text of DOI:10.1021/acs.orglett.9b03705

Letter
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Oxidative Hydro‑, Bromo‑, and Chloroheptafluoroisopropylation of
Unactivated Alkenes with Heptafluoroisopropyl Silver
†
†
,†,‡
Chao-Lai Tong, Xiu-Hua Xu, and Feng-Ling Qing*
†Key Laboratory of Organofluorine Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic
Chemistry, University of Chinese Academy of Science, Chinese Academy of Science, 345 Lingling Lu, Shanghai 200032, China
‡
Key Laboratory of Science and Technology of Eco-Textiles, Ministry of Education, College of Chemistry, Chemical Engineering
and Biotechnology, Donghua University, 2999 North Renmin Lu, Shanghai 201620, China
*
S Supporting Information
ABSTRACT: Oxidant-induced three-component hydro-, bromo-,
and chloroheptafluoroisopropylation of unactivated alkenes are
disclosed. In these reactions, the CF(CF ) radical was generated
3
2
from the oxidation of AgCF(CF ) . Then the addition of this
3
2
perfluorinated radical to alkenes, followed by hydrogenation,
bromination, or chlorination, gave the corresponding difunctional-
ized CF(CF ) -containing products in high yields.
3
2
5
lkenes are versatile feedstocks and intermediates in
organic synthesis. Hydrofunctionalization of alkenes is a
recently been incorporated into bioactive compounds, chiral
6 7 8
A
catalysts, ligands, and functional materials. While numerous
methods have been developed for the heptafluoroisopropyla-
tion of arenes and alkenes, until now, the hydrohepta-
fluoroisopropylation reaction was limited to the electron-
deficient alkenes, including α,β-unsaturated acyl-oxazolidino-
The hydroheptafluoroisopropylation of
these electron-deficient alkenes with ICF(CF3)2 in the
presence of a radical initiator using H O as the H source
gave the hydroheptafluoroisopropylated products in low yields
(Scheme 1b).
Very recently, our group developed an oxidative hydro-
trifluoromethylation of unactivated alkenes with HCF -derived
AgCF3. Inspired by this work, we envisioned that the
analogous oxidative hydroheptafluoroisopropylation of unac-
tivated alkenes with AgCF(CF ) would provide a comple-
mentary approach to CF(CF ) -containing alkanes. Herein, we
disclose our investigation of this reaction (Scheme 1c), which
is following our long-standing interest in hydrofluoroalkylation
fundamentally important transformation of the efficient
synthesis of high-value alkanes for a broad spectrum of
applications. Due to the unique properties of fluoroalkyl
groups such as metabolic stability, lipophilicity, and electron-
withdrawing properties and thus the increasing importance of
fluoroalkyl substitution in pharmaceuticals, agrochemicals, and
9
10
11a
11b
ne
and ketone.
1
2
materials, recently, much effort has been devoted to the
hydrofluoroalkylation of alkenes, particularly radical hydro-
2
3
trifluoromethylation and hydrodifluoroalkylation reactions
Scheme 1a). Despite this impressive progress, the develop-
(
3
ment of a new hydrofluoroalkylation reaction for the
incorporation of other fluoroalkyl groups into alkenes is highly
desirable.
2j
3
2
The heptafluoroisopropyl [(CF ) CF] group serves as a
3
2
3 2
strong electron-withdrawing and highly lipophilic substituent
4
like the trifluoromethyl (CF ) group. Furthermore, (CF ) CF
3
3 2
2a,j,3c,d,g,h,12
is bulkier than CF . Consequently, the (CF ) CF group has
3
3 2
reactions.
Furthermore, the unprecedented oxida-
tive bromo- and chloroheptafluoroisopropylation of unacti-
vated alkenes are also described.
Scheme 1. Hydrofluoroalkylation of Alkenes
On the basis of our previous hydrotrifluoromethylation of
2j
unactivated alkenes with AgCF , we initially investigated the
3
hydroheptafluoroisopropylation of model substrate hex-5-enyl
benzoate (1a) with a AgCF(CF ) solution, in situ generated
3
2
13
from hexafluoropropylene (HFP) and AgF in MeCN (Table
). The desired product 2a was detected in only 11% yield
1
using phenyliodine diacetate (PIDA) as the oxidant and 1,4-
cyclohexadiene (1,4-CHD) as the H source, while most of 1a
and AgCF(CF ) were not converted (entry 1). Different
3
2
Received: October 19, 2019
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b03705
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Table 1. Optimization of Reaction Conditions
Scheme 2. Substrate Scope of
a
Hydroheptafluoroisopropylation of Unactivated Alkenes
b
entry
oxidant
PIDA
Selectfluor
BPO
H source
yield (%)
1
2
3
4
5
6
7
8
9
1,4-CHD
1,4-CHD
1,4-CHD
1,4-CHD
1,4-CHD
1,4-CHD
11
18
30
39
Na S O
2
2
8
c
NBS
7
PIFA
PIFA
PIFA
PIFA
92
28
25
29
Et SiH
3
1,3-dioxolane
n-Bu SnH
3
a
Reaction conditions: 1a (0.2 mmol), AgF (0.6 mmol), HFP (excess,
ballon, 1 atm), oxidant (0.4 mmol), H source (0.4 mmol), MeCN
b
19
(
2.0 mL), N , rt, 18 h. Yields determined by F NMR spectroscopy
2
c
using trifluoromethoxybenzene as an internal standard. Bromohepta-
fluoroisopropylated byproduct formed in 10% yield.
oxidants were then screened. Selectfluor, benzoyl peroxide
(
2
BPO), and Na S O gave 2a in slightly higher yields (entries
−4, respectively), whereas N-bromosuccinimide (NBS)
2 2 8
afforded 2a along with the unexpected bromoheptafluoroiso-
propylated product in low yields (entry 5). Gratifyingly, 2a was
formed in 92% yield when phenyliodine bis(trifluoroacetate)
(
PIFA) was used as the oxidant (entry 6). These results
indicated that a proper strong oxidant was beneficial for this
reaction. Further screening of the H sources demonstrated that
1
,4-CHD was far superior to other common H sources,
including Et SiH, 1,3-dioxolane, and n-Bu SnH (entries 7−9,
respectively).
3
3
With the optimal reaction conditions in hand, the substrate
scope of this hydroheptafluoroisopropylation reaction was then
examined. As shown in Scheme 2, a wide range of unactivated
alkenes (1a−1ab) underwent this transformation smoothly to
give the corresponding products in moderate to excellent
yields. The reaction also proceeded readily on a 1.0 mmol scale
to afford 2a in 82% yield. The common functional groups,
including ether (1c), aldehyde (1k), ester (1e and 1n),
sulfonate (1p), amide (1o), sulfonamide (1f), cyano (1d),
chloride (1m), bromide (1l), iodide (1g), and boronate (1h),
were all well tolerated. Substrates bearing heterocycles, such as
benzo[d][1,3]dioxole (1q), furan (1r), thiophene (1s),
pyridine (1t), phthalimide (1u), and coumarin (1v), readily
participated in the reaction, leading to the desired products in
high yields. 1,1-Disubstituted terminal alkenes (1w−1y) were
also compatible with the reaction conditions. Finally, bio-
logically relevant compounds derived from estrone (1z),
menbutone (1aa), and dicamba (1ab) were successfully
converted to the heptafluoroisopropylated derivatives, thus
demonstrating the potential utility of this protocol in late-stage
functionalization. However, the hydroheptafluoroisopropyla-
tion of internal alkenes and styrenes afforded the desired
products in low yields.
a
Reaction conditions: 1 (0.6 mmol), AgF (1.8 mmol), HFP (excess,
ballon, 1 atm), PIFA (1.2 mmol), 1,4-CHD (1.2 mmol), MeCN (6.0
mL), N , rt, 18 h, isolated yields. Reaction performed on a 1.0 mmol
scale.
b
2
bromoheptafluoroisopropylation reaction because organobro-
mides are frequently used as intermediates in organic synthesis.
To the best of our knowledge, the bromoheptafluoroisopro-
pylation of alkenes is previously unknown. After a simple
screening of the brominating reagents (Scheme 3), we were
fortunate to find that 1,3-dibromo-5,5-dimethylhydantoin
(DBDMH) efficiently promoted the reaction of 1a and
AgCF(CF ) , furnishing 3a in 95% yield. Other evaluated
Encouraged by the formation of the bromoheptafluoroiso-
propylated product (3a) using NBS as the oxidant (Table 1,
entry 5), we subsequently focused our attention on the
3
2
B
DOI: 10.1021/acs.orglett.9b03705
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 3. Screening of Brominating Reagents
Selectfluor as the oxidant and fluorine source; however, this
reaction was complex, and the desired fluoroheptafluoroiso-
propylated product was formed in very low yield.
To gain insight into the reaction mechanism, several
experiments were conducted. The hydroheptafluoroisopropy-
lation of 1a in the presence of 2,2,6,6-tetramethylpiperidin-1-
oxyl (TEMPO) did not yield the desired product.
Furthermore, treatment of 1,6-diene 5 under the standard
conditions afforded the cyclic hydro- and bromoheptafluor-
oisopropylated products (6 and 7, respectively) (Scheme 5).
Scheme 5. Radical Clock Experiments
brominating reagents, including NBS and 2-bromoisoindoline-
1
,3-dione, were less effective. DBDMH acted as both an
oxidant for the generation of CF(CF ) radical and a Br source
3
2
for bromoheptafluoroisopropylation.
Next, the substrate scope of the bromoheptafluoroisopro-
pylation reaction was investigated (Scheme 4). Like hydro-
Scheme 4. Substrate Scope of Bromo- and
Chloroheptafluoroisopropylation of Unactivated Alkenes
a
These results clearly demonstrated that these reactions
proceeded through radical processes. Notably, the dr of
products 6 and 7 was observed to be higher than that of the
similar trifluoromethylated compound formed from the
2
a,14
hydrotrifluoromethylation of 5 with AgCF3,
because
(
CF ) CF is bulkier than CF .
On the basis of the results presented above, as well as our
3 2 3
2a,j,3c,d,g,h,12
experiences in hydrofluoroalkylation reactions
other previous reports, a plausible mechanism was proposed
and
15
(
Scheme 6). Initially, the oxidation of AgCF(CF ) with PIFA,
3 2
Scheme 6. Proposed Reaction Mechanism
DBDMH, or DCDMH generates the CF(CF ) radical. Then,
3
2
a
the resulting CF(CF ) radical adds onto the double bond of
Reaction conditions: 1 (0.6 mmol), AgF (1.2 mmol), HFP (excess,
3 2
ballon, 1 atm), DXDMH (0.6 mmol), MeCN (6.0 mL), N , rt, 4 h,
isolated yields.
alkenes 1 to give radical intermediate A. Finally, intermediate
A abstracts the H, Br, or Cl atom from 1,4-CHD, DBDMH, or
DCDMH, respectively, furnishing difunctionalized product 2,
2
3
, or 4.
heptafluoroisopropylation, the mild reaction exhibited broad
functional group tolerance, providing a range of structurally
diverse bromoheptafluoroisopropylated products 3 in high
yields. Notably, the analogous chloroheptafluoroisopropylation
with 1,3-dichloro-5,5-dimethylhydantoin (DCDMH) leading
to chloroheptafluoroisopropylated products 4 was also
successful (Scheme 4). In contrast, the analogous iodohepta-
fluoroisopropylation of 1a with 1,3-diiodo-5,5-dimethylhydan-
toin (NIH) gave the iodoheptafluoroisopropylated product in
moderate yield (see the Supporting Information). We also
attempted the reaction of 1a and AgCF(CF3)2 using
In conclusion, we have developed the first oxidative
hydroheptafluoroisopropylation of unactivated alkenes with
AgCF(CF ) in the presence of PIFA and 1,4-CHD. The
3
2
reaction proceeded under mild conditions to provide CF-
CF ) -containing alkanes in high yields. Using DBDMH or
(
3
2
DCDMH as both an oxidant and a Br or Cl source, the
oxidative bromo- and chloroheptafluoroisopropylation of
alkenes were also accomplished. We anticipate that these
transformations will facilitate the incorporation of the
CF(CF ) group in organic synthesis and drug discovery.
3 2
C
DOI: 10.1021/acs.orglett.9b03705
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(
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The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b03705.
B.; Sedlak, D.; Dracínsky, M.;
́ ́ ̌
́
Experimental procedures, characterization data, and
̊
̌
1
19
13
copies of H, F, and C NMR spectra (PDF)
AUTHOR INFORMATION
Corresponding Author
E-mail: flq@mail.sioc.ac.cn.
■
*
(
6) (a) Guin, J.; Rabalakos, C.; List, B. Angew. Chem., Int. Ed. 2012,
51, 8859. (b) Silvi, M.; Verrier, C.; Rey, Y. P.; Buzzetti, L.;
ORCID
Melchiorre, P. Nat. Chem. 2017, 9, 868.
Xiu-Hua Xu: 0000-0002-0759-2286
Feng-Ling Qing: 0000-0002-7082-756X
Notes
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J. B.; Larson, B. W.; Chen, Y.-S.; Dunsch, L.; Seppelt, K.; Popov, A.
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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The National Natural Science Foundation of China (21421002
and 21332010), the Strategic Priority Research Program of the
Chinese Academy of Sciences (XDB20000000), and the Youth
Innovation Promotion Association CAS (2016234) are
gratefully acknowledged for funding this work.
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DOI: 10.1021/acs.orglett.9b03705
Org. Lett. XXXX, XXX, XXX−XXX