Light-mediated dual phosphine-/copper-catalyzed atom transfer radical addition reaction

Article abstract of DOI:10.1021/acs.joc.9b01649

The atom transfer radical addition reaction catalyzed by triphenylphosphine and copper(I) halide is described. The reaction proceeds under irradiation with 365 nm light using a light-emitting diode and was performed in regular glassware. The proposed mech

Full text of DOI:10.1021/acs.joc.9b01649

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Article
Light mediated dual phosphine/copper
catalyzed atom transfer radical addition reaction
Oleg V. Fedorov, Sofya I Scherbinina, Vitalij V. Levin, and Alexander D. Dilman
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 14 Aug 2019
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Light mediated dual phosphine/copper catalyzed
atom transfer radical addition reaction
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Oleg V. Fedorov,† Sofya I. Scherbinina,†,‡ Vitalij V. Levin,† Alexander D. Dilman†,*
†N. D. Zelinsky Institute of Organic Chemistry, 119991 Moscow, Leninsky prosp. 47, Russian
Federation
‡D. Mendeleev University of Chemical Technology of Russia, Higher Chemical College, 125047
Moscow, Miusskaya sq. 9, Russian Federation
PPh3 (0.4 equiv)
X
Cu(I) (10 mol %)
+
R1
R1
X
R2
R2
365 nm LED
*
R1 PPh3
R1 PPh3
CuX
X
h

e
R1
X Cu X
KEYWORDS Atom Transfer, Copper Catalysis, Photocatalysis, Radical Addition
ABSTRACT The atom transfer radical addition reaction catalyzed by triphenylphosphine and
copper(I) halide is described. The reaction proceeds under irradiation with 365 nm light using a
light emitting diode, and performed in a regular glassware. The proposed mechanism involves the
formation of quaternary phosphonium salt, which undergoes single electron reduction by the
copper(I) salt via photoinduced electron transfer. The method works well for terminal alkenes and
activated organic halides such as esters of bromo- and iodoacetic acid and bromoacetonitrile. gem-
Difluorinated styrenes, for which atom transfer reactions are rare, also proved to be good substrates
for this phosphine/copper catalyzed protocol.
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INTRODUCTION
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Since the original report in 1945,1 the interaction of halocarbons with alkenes known as atom
transfer radical addition (ATRA, Kharash reaction), has evolved into an attractive strategy for
carbon-carbon bond formation.2-4 Despite significant advances in this field associated with the use
of transition metal catalysts, ATRA process has notable limitations, and, as a result, it still remains
largely underemployed in synthetic applications.
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In a typical ATRA mechanism, the radical chain process is operative (Scheme 1). The reaction
efficiency depends on two major factors: the initiation event, when a free radical is generated (step
a), and the atom transfer event (step c). Moreover, if the halide transfer is slow, the formation of
oligomers by iterative radical addition to the alkene may dominate. Both steps (initiation and halide
transfer) require cleavage of carbon-halogen bond, which may necessitate harsh conditions.
Historically, ATRA reactions were conducted at elevated temperatures in the presence of radical
initiators such as peroxides,1 organotin reagents,5 triethylborane,6 or AIBN,7 which trigger
generation of free radicals by abstraction of halogen atom from a halocarbon substrate. Homolysis
of the carbon-halogen bond by harsh UV light was also occasionally used to initiate the reaction.8
Later, transition metal salts and complexes,3 and, in particular, derivatives of copper,4 were shown
to be effective catalysts of ATRA reaction and related polymerization processes.9 The metal can
facilitate the generation of radicals, whereas formed metal-halide species can effect rapid transfer of
the halide from metal to the carbon-centered radical.10
Another step forward was achieved due to the advent of photoredox catalysis,11,12 in which the
initiation event involves the single electron reduction of the substrate by the light activated catalyst.
In this case, the reduction potential of the starting alkyl halide is an important factor. The atom
transfer event can also proceed via different mechanism involving single electron oxidation of the
radical to carbocation followed by trapping by halide anion. The latter mechanistic scenario is likely
for ruthenium-based photocatalysts.13,14 Recently, photoactive copper(I) complexes bearing diaryl-
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substituted phenanthrolines as ligands have emerged as catalysts for visible light photoredox
chemistry, and, in particular, for promoting ATRA reactions.15,16
Scheme 1. ATRA process.
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Intitiaton (a):
Peroxides
Typical mechanism:
R2
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(b)
Organotins
Et3B, AIBN
Metal salts
(a)
R1
R1
X
R1
R2
Atom transfer (c):
Direct
(c)
X
Metal mediated
R1
X
R1
R2
Photoredox:
(a) SET reduction
(c) SET oxidation + X
Herein we report a novel mechanistic pathway for performing light-mediated ATRA processes.
Our approach is based on combined use of triphenylphosphine and copper(I) halide as catalysts
(Scheme 2). The role of phosphine is to convert alkyl halide into phosphonium salt, which would
serve as a source of free radicals. Thus, the phosphonium salt could interact with Cu(I) to generate
ion pair consisting from phosphonium cation and cuprate anion (Scheme 2, bottom equation). Then,
light mediated electron transfer leads to the generation of the radical with concomitant formation of
copper(II) halide and regeneration of the phosphine. Such type of radical generation from
fluorinated phosphonium salts has recently been proposed.17 After radical addition to the double
bond, copper(II) halide would rapidly convert the radical into product 3. Back in 1983, there was a
report on ATRA reaction using copper halide and stoichiometric amount of tri(n-butyl)phosphine
by irradiation with 254 nm UV light.18 However, based on mechanistic experiments, it was
proposed that the reaction proceeds via two-electron pathway involving copper(III) intermediates
and oxidative addition/reductive elimination sequence.18
The ability of phosphonium salts to undergo fission of the C-P bond has previously been
described. In the absence of photocatalyst, this process requires harsh UV light (< 300 nm) as
evidenced by photolysis of benzyl and benzhydryl phosphonium salts.19 For reactions with visible
light, a photocatalyst is needed. In particular, phosphonium salts bearing adjacent fluorine atoms20
or a carbonyl group,21 were activated using typical iridium photocatalysts.22 It should be pointed out
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that in these reactions, phosphonium salts were employed as stoichiometric reagents thereby
wasting one equivalent of the phosphine, whereas in our approach, the phosphine may be used as
catalyst. Examples of using phosphines and phosphates as catalysts or mediators have been
reported, with P-centered radicals being proposed as reactive intermediates.23
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Scheme 2. Dual phosphine/copper catalyzed reaction.
X
h
R1
R1 PPh3
X
R2
CuX
3
R1
X
CuX2
PPh3
1
R1
R1
R2
R2
2
Generation of radicals:
*
R1 PPh3
X Cu X
R1 PPh3
X Cu X
R1 PPh3
X
h
CuX
e
R1
For successful realization of the process catalytic in phosphine, several criteria should be
satisfied. First, the phosphine must interact with substrate 1 much faster than with product 3. This,
in fact, is easy to achieve, since formation of phosphonium salts is sensitive to steric effects, and
required differentiation is realized when the substrate is a primary halide, while the product is a
secondary halide. The second issue is that the intermediate phosphonium salt should be prone to
undergo single electron reduction. Correspondingly, alkyl halides bearing adjacent
electronwithdrawing groups should be considered.
RESULTS AND DISCUSSION
For optimization studies, the interaction between methyl bromoacetate (1a) and 4-phenylbut-1-
ene (2a) was evaluated (Table 1). The reaction was performed in dichloromethane by irradiation
using 365 nm light emitting diode, and the temperature was maintained around 20 °C. In the
presence of 0.4 equiv of triphenylphosphine and 10 mol % of copper(I) bromide, the expected
product 3a was formed in 53% yield after 15 hours (entry 2). Addition of ligands led to notable
improvement, with the highest efficiency achieved with a copper salt complexed with 1,3-bis(2,4,6-
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trimethylphenyl)imidazolium carbene, IMes (entry 6). With the latter catalyst the reaction time can
be reduced to 3.5 hours. Decrease of amount of the copper catalyst and phosphine, as well as use of
tributylphosphine instead of triphenylphosphine, led to decreased yields (entries 7, 8, 10, 11). Effect
of solvent was briefly evaluated. Ethereal solvents were less efficient, apparently, because of their
ability to serve as sources of hydrogen atom, which is transferred onto intermediate radical species.
Dichloromethane (DCM) was the optimal from the point of view of solubility of reagents and
catalysts. However, in this solvent, products bearing chloride instead of bromide were occasionally
observed in minor amounts. In this cases, acetonitrile (ACN) can be successfully used as solvent.
Application of light with longer wavelengths (400 or 465 nm) gave decreased yields, while in the
dark, there was no product at all (entries 12-14).
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Table 1. Optimization studies.
O
Cu(I)
Br
O
MeO
1a PPh3 (0.4 equiv)
Ph
+
MeO
365 nm LED
Ph
2a
Br
3a
#
Solv.a Time, h
DCM 15
Cat.
Y., %b
53
1
2
CuBr (10%)
DCM 15
25
O
O
N
N
N
CuBr (10%),
(11%)
(11%)
3
4
DCM 15
DCM 15
65
N
N
N
N
N
CuBr (10%),
CuBr (10%),
97 (90)c
N
N
N
N
(11%)
NMe2
5
DCM 15
DCM 3.5
69
N
Me2
N
NMe2
CuBr (10%),
Mes
(11%)
6
96 (89)c
N
CuBr
N
Mes
(IMes·CuBr) (10%)
7d
8e
9
DCM 3.5
DCM 3.5
ACN 3.5
IMes·CuBr (10%)
22
6
IMes·CuBr (10%)
IMes·CuBr (10%)
quant.
(91)c
55
76
24
10
-
10f ACN 3.5
11 ACN 3.5
12g ACN 3.5
13h ACN 3.5
14i ACN 3.5
15 ACN 15
IMes·CuBr (10%)
IMes·CuBr (5%)
IMes·CuBr (10%)
IMes·CuBr (10%)
IMes·CuBr (10%)
-
2
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a DCM, dichloromethane; ACN, acetonitrile
b Determined by GC analysis.
c Isolated yield.
d Bu3P instead of PPh3.
e No PPh3.
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f 0.2 equiv of PPh3.
g 400 nm LED.
h 465 nm LED.
i In the dark.
To confirm intermediacy of phosphonium salt in the reaction, the salt prepared from 1a and
triphenylphosphine was combined with 4-phenylbut-1-ene 2a in acetonitrile under standard
conditions (Scheme 3, upper equation). Thus, a quite fast reaction was observed, with the
meaningful yields of product 3a achieved even in 20 minutes. To support the radical character of
the process, a radical clock experiment was carried out using isopropenylcyclopropane as alkene
counterpart, and only ring-opened product (3-open) was formed (Scheme 3, bottom equation).
Though this experiment favors radical mechanism, the light absorbing species remains unclear.
Indeed, the intermediate phosphonium salt, the copper catalyst, the phosphine, as well as their
mixtures, do not absorb light at wavelengths greater than 320 nm (see Supporting Information for
the absorption spectra). This phenomenon is similar to that observed in our previous work.17
Scheme 3. Mechanistic experiments.
O
Br
MeO
O
IMes·CuBr (10%)
365 nm LED
PPh3
Ph
+
MeO
Ph
3a
Br
2a
20 min, 45%; 1.5 h, 96%
O
IMes·CuBr (10%)
PPh3 (0.4 equiv)
Br
MeO
O
1a
+
MeO
365 nm LED
O
O
MeO
3-
Br
MeO
open, 70%
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Under the optimized conditions, a series of alkenes 2 were subjected to the atom transfer reaction
with bromoacetic esters (Table 2, entries 1-19). These reactions were performed on 2 mmol scale of
the alkene. Though for some alkenes the process was complete within few hours, in many cases
longer time was needed. The reaction between bromoacetates and terminal alkenes proceeded
cleanly and with high yields. Unactivated alkyl-substituted linear and branched alkenes proved to be
excellent substrates for this atom transfer reaction. Allylic and homoallylic ethers and esters were
successfully employed. While cyclohexene was poorly effective, a more reactive alkene,
norbornene, gave addition product in good yield (entries 17 and 18). Bromoacetonitrile was also
successfully used, though for good conversion, slightly increased amount of bromide (1.6 equiv)
was employed (entries 20-23).
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Table 2. Reactions of alkenes.
PPh3 (0.4 equiv)
R2
IMes·CuBr (10 mol %)
R2
R1
R1 Br
+
365 nm LED, rt
Br
1
2
3
(1.4 equiv)
#
Solv.
Time,
Bromide
Alkene
Product
Yield, %a
81
h
2
O
Ph
O
1
ACN
ACN
ACN
ACN
ACN
3b
3c
3d
3e
3f
Br
Br
Br
Br
Br
Ph
MeO
MeO
Br
Br
Br
Br
Br
O
2
3
4
5
6
O
85 (94b)
79 (90b)
87
MeO
MeO
O
O
3.5
6
SiMe3
SiMe3
MeO
MeO
O
O
MeO
MeO
O
15
81
O
O
O
N
O
MeO
MeO
N
O
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O
6
DCM
DCM
DCM
ACN
ACN
15
15
15
15
15
O
O
O
3g
3h
3iс
3j
84
88
72
71
77
Br
Br
Br
Br
Br
MeO
BnO
MeO
MeO
MeO
O
O
MeO
Ph
O
Br
O
O
O
7
O
O
O
Br
9
O
O
O
O
O
O
8
Ph
10
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Ph
Br OMEM
MeO
MeO
MeO
OMEM
9d
OMEM
OMEM
Br
Br
10e
3kc
O
O
O
O
O
O
O
OAc
11
DCM
DCM
15
20
3l
72
83
OAc
Br
Br
MeO
MeO
MeO
Br
12f
OMe
3m
OMe
O
O
O
MeO
MeO
MeO
O
O
Br
Br
Br
13e
14
15
DCM
DCM
ACN
20
5
OEt
OEt
OEt
OEt
3n
3o
3p
61
87
67
O
O
Br
Br
MeO
MeO
EtO
O
O
O
15
O
O
O
Br
N
N
EtO
O
O
Br
Cl
Cl
O
O
16
DCM
15
3q
80
O
Br
O
O
EtO
EtO
O
Br
O
17
DCM
ACN
15
6
3rg
3sg
35
87
EtO2C
Br
Br
EtO
Br
18h
O
CO2Me
MeO
Br
19e
DCM
15
O O
S
O
3t
59
O
O O
S
Br
Ph
EtO
EtO
Ph
Br
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DCM
DCM
DCM
30
15
15
Ph
NC
NC
Ph
3u
3v
3w
49
97
61
NC
NC
NC
Br
Br
Br
Br
Br
4
5
21f
Ph
O
Ph
O
6
7
8
22f,i
9
NC
NC
10
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Br
Br
23e
DCM
30
3x
72
NC
Br
O
O
O
O
a Isolated yield
b Yield determined by NMR with dibromomethane as internal standard.
c Mixture of isomers, ratio 1:1.
d
As catalyst, a combination of CuBr (10%) and bis(3,5-dimethyl-1H-pyrazol-1-yl)methane (11%)
was used.
e PPh3 (1 equiv), R1-Br (2.25 equiv), IMes·CuBr (15%).
f 1.6 equiv of R1-Br was used.
g Mixture of isomers, ratio 1.5:1.
h As catalyst, a combination of CuBr (15%) and bis(3,5-dimethyl-1H-pyrazol-1-yl)methane (16%)
i
As catalyst, a combination of CuBr (10%) and bis(3,5-diphenyl-1H-pyrazol-1-yl)methane (11%)
was used.
Of special note is that in reaction of styrene we were able to isolate benzylic bromide 3b in
relatively good yield (entry 1). Indeed, benzylic halides are prone to elimination under the
conditions of atom transfer, and, typically, even slightly basic medium can cause
dehydrohalogenation with the formation of alkene.24,25 This was the case with 2,2-dimethyl-3-
methylenenorbornene, which afforded alkene 4 (Scheme 4).
Scheme 4. Formation of alkene product.
OEt
PPh3
O
O
cat. IMes·CuBr
+
EtO
1a
365 nm LED, 5 h
Br
4
, 76%
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However, the method is inapplicable to the coupling of unactivated alkyl bromide with Michael
acceptors, as shown for attempted reaction of ethyl bromide with tert-butyl acrylate, in which the
desired product was not detected. Similarly, the interaction of benzyl bromide with either tert-butyl
acrylate or 4-phenylbut-1-ene 2a did not furnish expected ATRA products.
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Addition of carbon-centered radicals to 1,1-difluorinated alkenes is a rare process. Indeed, two
fluorine atoms exert notable deactivating effect on the radical addition. While atom transfer
reactions of perfluorinated alkenes with polyhalogenated hydrocarbons have been reported,26,27 the
use of 1,1-difluoroalkenes is rare.28,29 At the same time, these alkenes can be readily prepared from
carbonyl compounds by a Wittig-type process.30 When 1,1-difluoroalkenes were subjected to our
standard conditions, conversions did not exceed 70%. Higher loading of the reagents and longer
times were needed to obtain good yields in reactions with ethyl bromoacetate. However, the
reaction with bromoacetonitrile gave the product in moderate yield (Scheme 5).
Scheme 5. Reactions of 1,1-difluoroalkenes.
PPh3 (1 equiv)
F
F
F
IMes·CuBr (15 mol %)
Y
Ar
Y
Br
+
Ar
F
365 nm LED, rt, 15-30 h
Br
2.3 equiv
5
6
6a,
6b,
6c,
Y = CO2Me, Ar = Ph, 82%
Y = CO2Me, Ar = 4-MeOC6H4, 87%
Y = CN, Ar = 4-MeOC6H4, 21%
It was also interesting to evaluate iodides in the ATRA process. Owing to higher reactivity of the
C-I bond compared to the C-Br bond, the iodide products are expected to be prone to
dehydrohalogenation. On the other hand, higher reactivity of iodides makes them more attractive
for further transformations. In the literature, a complex between CuI and IMes ligand has not been
described. Our attempts to prepare it were unsuccessful, leading to species bearing two NHC
ligands at copper,31 which were inactive in the ATRA reaction. Screening of ligands allowed to
identify dm-Pybox [2,6-bis(4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl)pyridine], which was
successfully used to promote addition of iodoacetates to alkenes (Table 3). The expected products 8
were obtained in good yields, though for tert-butylethylene, increased amounts of the phosphine
and copper iodide were required.
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Table 3. Reactions iodoacetates.
4
5
6
7
8
9
PPh3 (0.4 equiv)
CuI (10 mol %)
O
O
dm-Pybox (11 mol %)
R2
R2
O
O
R1O
R1O
+
N
365 nm LED, CH2Cl2, rt, 15 h
N
N
I
I
8
2
7
dm-Pybox
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Alekene
Product
Yield, %a
73
Ph
O
8a
8b
8c
8d
Ph
MeO
I
I
O
83
I
MeO
I
SiMe3
O
87
SiMe3
EtO
I
O
72b
EtO
I
a Isolated yield
b Ethyl iodoacetate (1.6 equiv), PPh3 (1.0 equiv), CuI (15 mol %), dm-Pybox (16 mol %).
In summary, a method for performing light mediated ATRA reaction catalyzed by the phosphine
and copper(I) salt is described. The formation of quaternary phosphonium salts, which are able to
undergo single electron reduction from copper(I), is believed to be the key feature of the process.
The reaction is applicable for a wide variety of alkenes leading to alkyl bromides and iodides in
good yields.
EXPERIMENTAL SECTION
General methods. All reactions were performed under an argon atmosphere. Acetonitrile was
distilled from CaH2 and stored over MS 4Å. DMF was distilled under vacuum from P2O5 and stored
over MS 4Å. Dichloromethane (DCM) was distilled from CaH2 prior to use. Column
chromatography was carried out employing silica gel (230−400 mesh). Precoated silica gel plates F-
254 were used for thin-layer analytical chromatography visualizing with UV and/or acidic aq.
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KMnO4 solution. NMR spectra were recorded in CDCl3 (distilled from CaH2) using a Bruker AV-
300 instrument. High-resolution mass spectra (HRMS) were measured using electrospray ionization
(ESI) and time-of-flight (TOF) mass analyzer (Bruker MicrOTOF II). For preparative HPLC,
reversed phase column (C18-kromasil, 5 µm, 21.2×250 mm) and UV-HPLC grade
acetonitrile/water as a mobile phase were used. All photochemical reactions were performed in
regular borosilicate glassware. As a light source, 100W LED chip (BLD-HP100UV2-E45 operated
at 32 V, 2.2 A) was used, the distance from light source to the reaction vessel was 5 mm. For the
reaction set-up, see Supporting Information. 1,3-Bis(2,4,6-trimethylphenyl)imidazolium carbene-
copper (I) bromide complex (IMes·CuBr),32 2,6-bis(4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-
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yl)pyridine
(dm-Pybox),33
(2,2-difluorovinyl)benzene
(5a),34
1-(2,2-difluorovinyl)-4-
methoxybenzene (5b),30 isopropenylcyclopropane.35
{1-[(2-Methoxyethoxy)methoxy]but-3-en-1-yl}benzene (2i).36 MEMCl (934 mg, 7.5 mmol, 1.5
equiv) was added portionwise to a solution of 1-phenyl-3-buten-1-ol (741 mg, 5 mmol, 1 equiv) and
EtN(i-Pr)2 (840 mg, 6.5 mmol, 1.3 equiv) in dichloromethane (8 mL). The reaction was stirred at
room temperature for 2.5 h, then quenched with water (5 mL) and extracted with hexane (4×5 mL).
The combined organic layers were filtered through Na2SO4, concentrated under vacuum, and the
residue was purified by flash chromatography. Rf 0.19 (hexane/EtOAc, 10/1). Yield 1.02 g (87%).
Colorless oil. 1H NMR (300 MHz, CDCl3), δ: 7.37–7.22 (m, 5H), 5.78 (ddt, J = 17.2, 10.2, 7.0 Hz,
1H), 5.15–4.97 (m, 2H), 4.73–4.56 (m, 3H), 3.89–3.74 (m, 1H), 3.62–3.42 (m, 3H), 3.37 (s, 3H),
2.60 (dt, J = 14.6, 7.4 Hz, 1H), 2.53–2.38 (m, 1H). 13C{1H} NMR (75 MHz, CDCl3), δ: 42.4, 59.1,
67.1, 71.9, 78.0, 93.4, 117.3, 127.1, 127.8, 128.4, 134.9, 141.7.
5-[(2-Methoxyethoxy)methoxy]pent-1-ene (2j).37 MEMCl (934 mg, 7.5 mmol, 1.5 equiv) was
added portionwise to a solution of 4-penten-1-ol (430 mg, 5 mmol, 1 equiv) and EtN(i-Pr)2 (840
mg, 6.5 mmol, 1.3 equiv) in dichloromethane (5 mL), The reaction was stirred at room temperature
for 2.5 h, then quenched with water (5 mL) and extracted with hexane (4×5 mL). The combined
organic layers were filtered through Na2SO4 and concentrated under vacuum. The residue was
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purified distillation using the Hickman distillation head (40 mbar, bath temperature 110-125 C).
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5
1
Yield: 644 mg (74%). Colorless oil. H NMR (300 MHz, CDCl3), δ: 5.73 (ddt, J = 16.9, 10.2, 6.6
6
7
8
9
Hz, 1H), 4.99–4.82 (m, 2H), 4.63 (s, 2H), 3.61 (dd, J = 5.7, 3.6 Hz, 2H), 3.52–3.42 (m, 4H), 3.31
(s, 3H), 2.13–1.98 (m, 2H), 1.68–1.52 (m, 2H). 13C{1H} NMR (75 MHz, CDCl3), δ: 28.9, 30.3,
58.9, 66.6, 67.1, 71.8, 95.4, 114.7, 138.0.
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General procedure 1 (synthesis of compounds 3a-j,l,m,o-s,u-w, 4). A 25 ml vial equipped with a
magnetic stirrer and a screw cap with septum was charged with triphenylphosphine (210 mg, 0.8
mmol, 0.4 equiv), and a copper (I) catalyst [for 3a-i,l,m,o-r,u,v, 4, IMes·CuBr (44 mg, 0.2 mmol,
0.1 equiv); for 3j, CuBr (29 mg, 0.2 mmol, 0.1 equiv) and bis(3,5-dimethyl-1H-pyrazol-1-
yl)methane (45 mg, 0.22 mmol, 0.11 equiv); for 3s, CuBr (43 mg, 0.3 mmol, 0.15 equiv) and
bis(3,5-dimethyl-1H-pyrazol-1-yl)methane (66 mg, 0.32 mmol, 0.16 equiv); for 3w, CuBr (29 mg,
0.2 mmol, 0.1 equiv) and bis(3,5-diphenyl-1H-pyrazol-1-yl)methane (100 mg, 0.44 mmol, 0.11
equiv).] The vial was evacuated and filled with argon, and 2.5 mL of a solvent (for 3a-f,j,p,s,
acetonitrile; for 3g-i,l,m,o,r,t-w, 4, dichloromethane) was added by gastight syringe. The reaction
mixture was cooled to –20 °C, and with stirring evacuated at about 12 Torr for 2 min followed by
filling the vial with argon. Organic bromide 1 (for bromoacetates, RO2CCH2Br, 2.8 mmol, 1.4
equiv and 3.2 mmol, 1.6 equiv for 3m; for bromoacetonitrile, NCCH2Br, 3.2 mmol, 1.6 equiv) and
alkene 2 (2 mmol, 1 equiv) were successively added by gastight syringe. The reaction vessel was
put into water-filled beaker (water temperature 20 C) with transparent bottom (Figure S2, (d)), and
was irradiated with 365 nm LED until full conversion of the starting alkene (verified by GC
analysis of aliquots), while maintaining the reaction temperature around 20 C (reaction time is
given in Table 2). For the workup, water (8 mL) was added, and the mixture was extracted with
pentane (4×5 mL). The combined organic layers were filtered through Na2SO4, concentrated under
reduced pressure, and the residue purified by flash chromatography on silica gel.
General procedure 2 (synthesis of compounds 3k,n,t,x,6a-c). A 25 ml vial equipped with a
magnetic stirrer and a screw cap with septum was charged with triphenylphosphine (525 mg, 2
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mmol, 1 equiv) and IMes·CuBr (for 3k,n,t,x,6a,b, 66 mg, 0.3 mmol, 0.15 equiv; for 6c, 44 mg, 0.2
mmol, 0.2 equiv). The vial was evacuated and filled with argon, and 2.5 mL of dichloromethane (or
acetonitrile for 3k) was added by gastight syringe. The reaction mixture was cooled to –20 °C, and
evacuated at about 12 Torr for 2 min followed by filling the vial with argon. Organic bromide 1 (for
3k,n,t,x, 6a,b, 4.5 mmol, 2.25 equiv; for 6c, 3.6 mmol, 1.8 equiv) and alkene 2 (2 mmol, 1 equiv)
were successively added by gastight syringe. The reaction vessel was put into water-filled beaker
(water temperature 20 C) with transparent bottom (Figure S2, (d)), and was irradiated with 365 nm
LED until full conversion of the starting alkene (verified by GC analysis of aliquots), while
maintaining the reaction temperature around 20 C (for 3k,n,t,x reaction time is given in Table 2;
for 6a,c, reaction time 30 h; for 6b, reaction time 15 h). The workup is the same as in General
procedure 1.
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General procedure 3 (synthesis of compounds 8a-d). A 25 ml vial equipped with a magnetic
stirrer and a screw cap with septum was charged with triphenylphosphine (PPh3, 210 mg, 0.8 mmol,
0.4 equiv), CuI (38 mg, 0.2 mmol, 0.1 equiv), and dm-Pybox (60 mg, 0.44 mmol, 0.11 equiv). The
vial was evacuated and filled with argon, and dichloromethane (2.5 mL) was added by gastight
syringe. The reaction mixture was cooled to –20 °C, and evacuated at about 12 Torr for 2 min
followed by filling the vial with argon. Iodoacetate 7 (2.8 mmol, 1.4 equiv) and alkene 2 (2 mmol, 1
equiv) were successively added to reaction mixture by gastight syringe. The reaction vessel was put
into water-filled beaker (water temperature 20 C) with transparent bottom (Figure S2, (d)), and
was irradiated with 365 nm LED until full conversion of the starting alkene, while maintaining the
reaction temperature around 20 C. The conversion was monitored by capillary GC of aliquots, and
the reaction was complete within 15 hours, unless stated otherwise. The workup is the same as in
General procedure 1.
Methyl 4-bromo-6-phenylhexanoate (3a).
O
Ph
MeO
Br
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Following General procedure 1, the reaction was carried out in acetonitrile, and irradiated for 3.5
4
5
1
hours. Yield 517 mg (91%). Colorless oil. Rf 0.34 (hexane/EtOAc, 5/1). H NMR (300 MHz,
6
7
CDCl3), δ: 7.56–7.04 (m, 5H), 4.00 (dtd, J = 13.1, 8.7, 4.2 Hz, 1H), 3.67 (s, 3H), 2.91 (ddd, J =
8
9
13
14.1, 8.6, 5.7 Hz, 1H), 2.84–2.70 (m, 1H), 2.69–2.43 (m, 2H), 2.31–1.99 (m, 4H). C{1H} NMR
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(75 MHz, CDCl3), δ: 32.2, 33.8, 34.2, 40.9, 51.8, 56.2, 126.3, 128.6, 140.9, 173.3. HRMS (ESI):
calcd C13H1779BrNaO2 (M + Na) 307.0304, found 307.0288; calcd C13H1781BrNaO2 (M + Na)
309.0284, found 309.0269.
Methyl 4-bromo-4-phenylbutanoate (3b).
O
Ph
MeO
Br
Following the General procedure 1, the reaction was carried out in acetonitrile, and irradiated for
2 hours. Yield 415 mg (81%). Colorless oil. Rf 0.18 (hexane/EtOAc, 15/1). 1H NMR (300 MHz,
CDCl3), δ: 7.49–7.15 (m, 5H), 5.20–4.91 (m, 1H), 3.66 (s, 3H), 2.71–2.31 (m, 4H). 13C{1H} NMR
(75 MHz, CDCl3), δ: 32.4, 34.9, 51.6, 54.2, 127.1, 128.4, 128.6, 141.3, 172.5. HRMS (ESI): calcd
C11H1379BrNaO2 (M + Na) 278.9991, found 278.9990; calcd C11H1381BrNaO2 (M + Na) 280.9971,
found 280.9967.
Methyl 4-bromononanoate (3c).
O
MeO
Br
Following the General procedure 1, the reaction was carried out in acetonitrile, and irradiated for
6 hours. Yield 426 mg (85%). Colorless oil. Rf 0.32 (hexane/EtOAc, 15/1). 1H NMR (300 MHz,
CDCl3), δ: 4.04 (tt, J = 8.9, 5.2 Hz, 1H), 3.67 (s, 3H), 2.71–2.40 (m, 2H), 2.31–2.10 (m, 1H), 2.10–
13
1.93 (m, 1H), 1.93–1.69 (m, 2H), 1.69–1.15 (m, 6H), 0.89 (t, J = 6.5 Hz, 3H). C{1H} NMR (75
MHz, CDCl3), δ: 14.1, 22.6, 27.3, 31.3, 32.3, 34.1, 39.4, 51.8, 57.3, 173.4. HRMS (ESI): calcd for
C10H1979BrNaO2 (M + Na) 273.0461, found 273.0455; calcd for C10H1981BrNaO2 (M + Na)
275.0440, found 275.0432.
Methyl 4-bromo-4-(trimethylsilyl)butanoate (3d).
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O
SiMe3
3
MeO
4
Br
5
6
7
8
9
Following the General procedure 1, the reaction was carried out in acetonitrile, and irradiated for
3.5 hours. Yield 399 mg (79%). Colorless oil. Rf 0.35 (hexane/EtOAc, 15/1). 1H NMR (300 MHz,
CDCl3), δ: 3.67 (s, 3H), 3.23 (dd, J = 12.3, 2.3 Hz, 1H), 2.70 (ddd, J = 16.3, 8.2, 4.9 Hz, 1H), 2.60–
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2.38 (m, 1H), 2.19 (dt,J = 17.7, 7.8 Hz, 1H), 2.04–1.78 (m, 1H), 0.13 (s, 9H). C{1H} NMR (75
MHz, CDCl3), δ: -3.0, 28.7, 33.8, 44.0, 51.7, 173.6. HRMS (ESI): calcd for C8H1779BrNaO2Si (M +
Na) 275.0073, found 275.0081 ; calcd for C8H1781BrNaO2Si (M + Na) 277.0053, found 277.0055.
Methyl 4-bromo-5,5-dimethylhexanoate (3e).
O
MeO
Br
Following the General procedure 1, the reaction was carried out in acetonitrile, and irradiated for
6 hours. Yield 410 mg (87%). Colorless oil. Rf 0.33 (hexane/EtOAc, 15/1). 1H NMR (300 MHz,
CDCl3), δ: 3.82 (dd, J = 11.7, 1.8 Hz, 1H), 3.62 (s, 3H), 2.64 (ddd, J = 16.7, 8.1, 5.1 Hz, 1H), 2.51–
2.36 (m, 1H), 2.22 (dtd, J = 9.5, 8.0, 1.8 Hz, 1H), 1.85 (dddd, J = 14.7, 11.7, 8.0, 5.1 Hz, 1H), 1.02
(s, 9H). 13C{1H} NMR (75 MHz, CDCl3), δ: 27.5, 29.4, 33.3, 36.1, 51.6, 70.8, 173.4. HRMS (ESI):
calcd for C9H1879BrO2 (M + H) 237.0485, found 237.0491; calcd for C9H1881BrO2 (M + H)
239.0465, found 239.0472.
Methyl 4-bromo-5-(1,3-dioxoisoindolin-2-yl)pentanoate (3f).
O
O
MeO
N
Br
O
Following the General procedure 1, the reaction was carried out in acetonitrile, and irradiated for
1
15 hours. Yield 549 mg (81%). White crystals. Mp 97-99 °C. Rf 0.12 (hexane/EtOAc, 4/1). H
NMR (300 MHz, CDCl3), δ: 7.80 (s, 2H), 7.69 (s, 2H), 4.52–4.20 (m, 1H), 4.06 (dd, J = 13.8, 7.9
Hz, 1H), 3.90 (dd, J = 13.8, 6.3 Hz, 1H), 3.60 (s, 3H), 2.69–2.54 (m, 1H), 2.47 (dt, J = 16.2, 7.4
Hz, 1H), 2.32–2.09 (m, 1H), 2.09–1.75 (m, 1H). C{1H} NMR (75 MHz, CDCl3), δ: 20.6, 30.2,
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31.5, 50.1, 51.6, 67.3, 170.1, 172.7. HRMS (ESI): calcd for C14H1479BrNNaO4 (M + Na) 361.9998,
found 361.9991; calcd for C14H1481BrNNaO4 (M + Na) 363.9979, found 363.9969.
Methyl 5-acetoxy-4-bromopentanoate (3g).
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9
O
O
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MeO
O
Br
Following the General procedure 1, the reaction was carried out in dichloromethane, and
irradiated for 15 hours. Yield 424 mg (84%). Rf 0.25 (hexane/EtOAc, 6/1). 1H NMR (300 MHz,
CDCl3), δ: 4.38–4.00 (m, 3H), 3.59 (s, J = 15.7 Hz, 3H), 2.63–2.32 (m, 2H), 2.18 (dtd, J = 15.1,
8.1, 7.6, 3.4 Hz, 1H), 2.00 (s, 3H), 2.10–1.82 (m, 1H). C{1H} NMR (75 MHz, CDCl3), δ: 20.6,
13
30.2,31.5, 50.1, 51.6, 67.3, 170.1, 172.7. HRMS (ESI): calcd for C8H1479BrO4 (M + H) 253.0070,
found 253.0060; calcd for C8H1481BrO4 (M + H) 255.0050, found 255.0038.
Benzyl 5-acetoxy-4-bromopentanoate (3h).
O
O
Ph
O
O
Br
Following the General procedure 1, the reaction was carried out in dichloromethane, and
irradiated for 15 hours. Yield 578 mg (88%). Colorless oil. Rf 0.12 (hexane/EtOAc, 10/1). 1H NMR
(300 MHz, CDCl3), δ: 7.45–7.28 (m, 5H), 5.14 (s, 2H), 4.42–4.22 (m, 2H), 4.22–4.11 (m, 1H),
2.78–2.45 (m, 2H), 2.30 (dddd, J = 15.3, 8.3, 7.2, 3.5 Hz, 1H), 2.14–1.95 (m, 1H), 2.09 (s, 3H).
13C{1H} NMR (75 MHz, CDCl3), δ: 20.84, 30.36, 31.97, 50.12, 66.65, 67.59, 128.37, 128.46,
128.73, 135.84, 170.44, 172.34. HRMS (ESI): calcd for C14H1779BrNaO4 (M + Na) 351.0202, found
351.0210; calcd for C14H1781BrNaO4 (M + Na) 353.0183, found 353.0188.
Methyl 4-bromo-6-[(2-methoxyethoxy)methoxy]-6-phenylhexanoate (3i).
O
Ph
MeO
Br
O
O
OMe
Following the General procedure 1, the reaction was carried out in dichloromethane, and
irradiated for 15 hours. Yield 560 mg (72%). Colorless oil. Mixture of diastereoisomers, ratio 1:1.
1
Rf 0.23 (hexane/EtOAc, 4/1). H NMR (300 MHz, CDCl3), δ: 7.41–7.11 (m, 5H), 4.92 (dd, J =
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10.2, 2.6 Hz) and 4.84 (t, J = 7.0 Hz) (1H), 4.68–4.48 (m, 2H), 4.43–4.30 (m) and 3.86–3.66 (m)
(1H), 3.86–3.66 (m, 1H), 3.63 (s) and 3.58 (s) (3H), 3.55–3.35 (m, 3H), 3.31 (s) and 3.31 (s) (3H),
2.68–2.30 (m) and 2.25–1.90 (m) (6H). 13C{1H} NMR (75 MHz, CDCl3), δ: 32.0, 33.7, 34.4, 46.7,
47.9, 51.6, 51.6, 52.2, 53.4, 58.9, 67.1, 67.2, 71.7, 71.7, 75.9, 76.4, 93.1, 93.3, 126.7, 127.1, 127.8,
128.1, 128.5, 128.5, 140.3, 141.4, 172.9, 173.0. HRMS (ESI): calcd for C17H2579BrNaO5 (M + Na)
411.0778, found 411.0772; calcd for C17H2581BrNaO5 (M + Na) 413.0758, found 413.0752.
Methyl 4-bromo-7-[(2-methoxyethoxy)methoxy]heptanoate (3j).
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O
OMe
MeO
O
O
Br
Following the General procedure 1, reaction was carried out in acetonitrile with 10 mol. % CuBr
(29 mg, 0.2 mmol, 0.1 equiv) and 11 mol. % bis(3,5-dimethyl-1H-pyrazol-1-yl)methane (45 mg,
0.22mmol, 0.11 equiv) and irradiated for 15 hours. Yield 463 mg (71%). Colorless oil. Rf 0.35
(hexane/EtOAc, 3/1). Further purification was performed via preparative HPLC (flow rate 12
1
mL·min−1, mobile phase: isocratic, 10% water in acetonitrile, retention time 9.1 min). H NMR
(300 MHz, CDCl3), δ: 4.65 (s, 2H), 4.03 (dddd, J = 8.9, 8.1, 4.7, 3.7 Hz, 1H), 3.69–3.58 (m, 5H),
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3.57–3.46 (m, 4H), 3.34 (s, 3H), 2.64–2.38 (m, 2H), 2.30–1.57 (m, 6H). C{1H} NMR (75 MHz,
CDCl3), δ: 27.8, 32.1, 34.1, 36.0, 51.7, 56.7, 59.0, 66.8, 66.9, 71.8, 95.5, 173.2. HRMS (ESI): calcd
for C12H2379BrNaO5 (M + Na) 349.0621, found 349.0625; calcd for C12H2381BrNaO5 (M + Na)
351.0601, found 351.0606.
Methyl 4-bromo-6-[(tetrahydro-2H-pyran-2-yl)oxy]hexanoate (3k).
O
O
O
MeO
Br
Following the General procedure 2, the reaction was carried out in acetonitrile, and irradiated for
15 hours. Yield 475 mg (77%). Colorless oil. Mixture of diastereoisomers, ratio 1:1. Rf 0.32
1
(hexane/EtOAc, 10/1). H NMR (300 MHz, CDCl3), δ: 4.58–4.40 (m, 1H), 4.23–4.04 (m, 1H),
3.90–3.66 (m, 2H), 3.57 (s, 3H), 3.52–3.34 (m, 2H), 2.58–2.33 (m, 2H), 2.22–1.84 (m, 4H), 1.77–
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1.31 (m, 6H). C{1H} NMR (75 MHz, CDCl3), δ: 19.2, 19.5, 25.3, 30.5, 30.5, 32.0, 32.0, 34.0,
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34.1, 39.0, 39.1, 51.5, 53.3, 53.5, 61.8, 62.3, 64.7, 65.1, 98.2, 99.3, 172.9. HRMS (ESI): calcd for
C12H2179BrNaO4 (M + Na) 331.0515, found 331.0527; calcd for C12H2181BrNaO4 (M + Na)
333.0495, found 333.0508.
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Methyl 5-(2-acetoxyphenyl)-4-bromopentanoate (3l).
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O
OAc
MeO
Br
Following the General procedure 1, the reaction was carried out in dichloromethane, and
irradiated for 15 hours. Yield 473 mg (72%). Colorless oil. Rf 0.13 (hexane/EtOAc, 10/1). 1H NMR
(300 MHz, CDCl3), δ: 7.37–7.24 (m, 2H), 7.24–7.15 (m, 1H), 7.12–7.03 (m, 1H), 4.25 (ddt, J =
13.5, 7.2, 3.6 Hz, 2H), 3.66 (s, 3H), 3.24–3.02 (m, 2H), 2.63 (ddd, J = 16.7, 8.3, 5.6 Hz, 1H), 2.57–
2.44 (m, 1H), 2.35 (s, 3H), 2.21 (tdd, J = 10.8, 7.8, 3.2 Hz, 1H), 2.10–1.89 (m, 1H). 13C{1H} NMR
(75 MHz, CDCl3), δ: 21.1, 32.2, 33.5, 40.7, 51.8, 54.5, 122.7, 126.2, 128.4, 130.1, 131.4, 149.2,
169.3, 173.1. HRMS (ESI): calcd for C14H1879BrO4 (M + H) 329.0383, found 329.0384; calcd for
C14H1881BrO4 (M + H) 331.0363, found 331.0366.
Methyl 4-bromo-5-(4-methoxyphenoxy)pentanoate (3m).
OMe
O
MeO
O
Br
Following the General procedure 1, the reaction was carried out in dichloromethane using 1.6
equiv of methyl bromoacetate, and irradiated for 20 hours. Yield 518 mg (83%). Colorless oil. Rf
1
0.21 (hexane/EtOAc, 8/1). H NMR (300 MHz, CDCl3), δ: 6.89–6.73 (m, 4H), 4.32–4.12 (m, 2H),
4.06 (dd, J = 10.0, 6.9 Hz, 1H), 3.72 (s, 3H), 3.64 (s, 3H), 2.71–2.30 (m, 3H), 2.19–2.01 (m, 1H).
13C{1H} NMR (75 MHz, CDCl3), δ: 30.4, 31.6, 50.9, 51.6, 55.5, 72.5, 114.6, 115.8, 152.1, 154.3,
172.8. HRMS (ESI): calcd for C13H1779BrNaO4 (M + Na) 339.0202, found 339.0204; calcd for
C13H1781BrNaO4 (M + Na) 341.0183, found 341.0185.
Methyl 4-bromo-5,5-diethoxypentanoate (3n).
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O
OEt
OEt
MeO
4
Br
5
6
7
8
9
Following the General procedure 2, the reaction was carried out in dichloromethane using 1.6
equiv of methyl bromoacetate, and irradiated for 20 hours. Yield 344 mg (61%). Colorless oil. Rf
0.28 (hexane/EtOAc, 9/1). 1H NMR (300 MHz, CDCl3), δ: 4.49 (d, J = 5.2 Hz, 1H), 3.99 (ddd, J =
10.0, 5.2, 3.2 Hz, 1H), 3.77–3.59 (m, 2H), 3.63 (s, 3H), 3.59–3.45 (m, 2H), 2.58 (ddd, J = 16.3, 8.6,
5.5 Hz, 1H),2.45 (dt, J = 16.3, 7.7 Hz, 1H), 2.31 (dddd, J = 15.5, 8.7, 7.1, 3.2 Hz, 1H), 2.06–1.88
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(m, 1H), 1.18 (t, J = 7.0 Hz, 6H). C{1H} NMR (75 MHz, CDCl3), δ: 15.2, 28.1,31.9, 51.6, 54.4,
63.7, 63.4, 104.1, 173.2. HRMS (ESI): calcd for C10H1979BrNaO4 (M + Na) 305.0359, found
305.0351; calcd for C10H1981BrNaO4 (M + Na) 307.0339, found 307.0332.
Methyl 4-bromo-7-oxooctanoate (3o).
O
O
MeO
Br
Following the General procedure 1, the reaction was carried out in dichloromethane and irradiated
for 5 hours. Yield 443 mg (87%). Сolorless oil. Rf 0.23 (hexane/EtOAc, 5/1). 1H NMR (300 MHz,
CDCl3), δ: 4.03 (tt, J = 9.4, 3.8 Hz, 1H), 3.64 (s, 3H), 2.76–2.60 (m, 2H), 2.60–2.39 (m, 2H), 2.23–
13
1.84 (m, 4H), 2.13 (s, 3H). C{1H} NMR (75 MHz, CDCl3), δ: 30.1, 32.1,32.7, 34.3, 41.4, 51.8,
56.3, 173.1, 207.3. HRMS (ESI): calcd for C9H1579BrNaO3 (M + Na) 273.0097, found 273.0094;
calcd for C9H1581BrNaO3 (M + Na) 275.0077, found 275.0074.
Ethyl 4-bromo-6-(1,3-dioxoisoindolin-2-yl)hexanoate (3p).
O
O
N
EtO
O
Br
Following the General procedure 1, the reaction was carried out in acetonitrile, and irradiated for
1
15 hours. Yield 490 mg (67%). White crystals. Mp 45-46 °C. Rf 0.11 (hexane/EtOAc, 4/1). H
NMR (300 MHz, CDCl3), δ: 7.80 (dd, J = 5.5, 3.1 Hz, 2H), 7.68 (dd, J = 5.5, 3.1 Hz, 2H), 4.08 (q,
J = 7.1 Hz, 2H), 4.09–3.97 (m, 1H), 3.96–3.72 (m, 2H), 2.65–2.36 (m, 2H), 2.32–1.94 (m, 4H),
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1.20 (t, J = 7.1 Hz, 3H). C{1H} NMR (75 MHz, CDCl3), δ: 14.2, 32.2, 34.0, 36.4, 37.7, 52.8,
60.6, 123.3, 132.1, 134.1, 168.2, 172.5. HRMS (ESI): calcd for C16H1879BrNNaO4 (M + Na)
390.0311, found 390.0323; calcd for C16H1881BrNNaO4 (M + Na) 392.0291, found 392.0304.
3-Bromo-6-ethoxy-6-oxohexyl 4-chlorobenzoate (3q).
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Cl
O
O
EtO
Br
O
Following the General procedure 1, the reaction was carried out in dichloromethane, and
1
irradiated for 15 hours. Yield 605 mg (80%). Сolorless oil. Rf 0.27 (hexane/EtOAc, 8/1). H NMR
(300 MHz, CDCl3), δ: 7.91 (dm, J = 8.6 Hz, 2H), 7.35 (dm, J = 8.6 Hz, 2H),4.51 (dt, J = 11.3, 5.7
Hz, 1H), 4.42 (ddd, J = 11.3, 7.9, 5.7 Hz, 1H), 4.18 (ddd, J = 13.3, 9.2, 3.9 Hz, 1H), 4.08 (q, J =
7.1 Hz, 2H), 2.66–2.40 (m, 2H), 2.39–1.99 (m, 4H), 1.20 (t, J = 7.1 Hz, 3H). C{1H} NMR (75
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MHz, CDCl3), δ: 14.3, 32.3, 34.2, 38.1, 52.3, 60.7, 63.1, 128.5, 128.8, 131.1, 139.6, 165.5, 172.6.
HRMS (ESI): calcd for C15H1879BrClKO4 (M + K) 414.9709, found 414.9699; C15H1881BrClKO4
(M + K) 416.9688, found 416.9674.
Ethyl 2-(2-bromocyclohexyl)acetate (3r).
EtO2C
Br
Following the General procedure 1, the reaction was carried out in dichloromethane, and
irradiated for 15 hours. Yield 174 mg (35%). Colorless oil. Mixture of diastereoisomers, ratio 3:2.
(Rf 0.11 (hexane). 1H NMR (300 MHz, CDCl3), δ: 4.62 (dd, J = 3.1, 2.6 Hz, major) and 3.86 (td, J
= 11.0, 4.1 Hz, minor) (1H), 4.12 (q, J = 7.1 Hz, 2H), 2.88 (dd, J = 15.0, 2.9 Hz minor), 2.51–2.03
(m, 3H), 2.02–1.80 (m, 2H), 1.79–1.63 (m, 2H), 1.24 (t, J = 7.1 Hz, 3H), 1.59–1.01 (m, 3H).
13C{1H} NMR (75 MHz, CDCl3), δ: Major: 14.4, 20.8, 25.3, 27.3, 35.0, 39.2, 40.4, 60.5, 61.0,
172.5; Minor: 14.4, 25.4, 27.5, 32.6, 38.7, 40.5, 43.4, 58.7, 60.4, 172.5. HRMS (ESI): calcd for
C10H1779BrNaO2 (M + Na) 271.0304, found 271.0306; calcd for C10H1781BrNaO2 (M + Na)
273.0284, found 273.0287.
Methyl 2-(3-bromobicyclo[2.2.1]heptan-2-yl)acetate (3s).
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CO2Me
4
5
Br
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Following the General procedure 1, the reaction was carried out in acetonitrile with 15 mol %
CuBr (43 mg, 0.3mmol, 0.15 equiv) and 16 mol % bis(3,5-dimethyl-1H-pyrazol-1-yl)methane (66
mg, 0.32 mmol, 0.16 equiv), and irradiated for 6 hours. Yield 427 mg (87%). Colorless oil. Mixture
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of diastereoisomers, ratio 3:2. Rf 0.26 (hexane/EtOAc, 10/1). H NMR (300 MHz, CDCl3), δ: 4.26
(dd, J = 7.2, 1.8 Hz, minor) and 3.86–3.77 (m, major) (1H), 3.67 (s, major) and 3.67 (s, minor)
(3H), 2.70–2.47 (m, 1H), 2.47–2.15 (m, 2H), 2.30–2.16 (m, minor, 1H),2.07–1.89 (m, 2H), 1.83 (dt,
J = 10.4, 1.7 Hz, minor, 1H), 1.73–1.11 (m, 5H). 13C{1H} NMR (75 MHz, CDCl3), δ: Major: 23.6,
29.71, 34.8, 38.9, 40.5, 41.8, 44.6, 51.8, 59.0, 172.3. Minor: 27.4, 29.67, 33.6, 42.6, 43.8, 48.2,
50.1, 51.8, 61.4, 173.5. HRMS (ESI): calcd for C10H1579BrNaO2 (M + Na) 269.0148, found
269.0157; calcd for C10H1581BrNaO2 (M + Na) 271.0127, found 271.0136.
Ethyl 4-bromo-4-(phenylsulfonyl)butanoate (3t).
O
O O
S
EtO
Ph
Br
Following the General procedure 2, the reaction was carried out in dichloromethane, and
irradiated for 15 hours. Yield 391 mg (59%). Colorless oil. Rf 0.28 (hexane/EtOAc, 2/1). 1H NMR
(300 MHz, CDCl3), δ: 7.94 (d, J = 7.5 Hz, 2H), 7.69 (t, J = 7.4 Hz, 1H), 7.57 (t, J = 7.5 Hz, 2H),
4.96 (dd, J = 10.5, 3.0 Hz, 1H), 4.10 (q, J = 7.1 Hz, 2H), 2.76–2.44 (m, 3H), 2.24–2.06 (m, 1H),
1.21 (t, J = 7.1 Hz, 3H). C{1H} NMR (75 MHz, CDCl3), δ: 14.2, 27.1, 31.2, 60.9, 64.6, 129.2,
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130.0,134.7, 135.2, 171.6. HRMS (ESI): calcd for C12H1579BrNaO4S (M + Na) 356.9767, found
356.9770; calcd for C12H1581BrNaO4S (M + Na) 358.9746, found 358.9745.
4-Bromo-4-phenylbutanenitrile (3u).
NC
Ph
Br
Following the General procedure 1, the reaction was carried out in dichloromethane using 1.6
equiv of bromoacetonitrile, and irradiated for 30 hours. Yield 220 mg (49%). Colorless oil. Rf 0.30
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(hexane/EtOAc, 5/1). Further purification was performed via preparative HPLC (flow rate 12
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5
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mL·min−1, mobile phase: isocratic, 25% water in acetonitrile, retention time 19.3 min.) H NMR
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(300 MHz, CDCl3), δ: 7.47–7.28 (m, 5H), 5.04 (m, 1H), 2.66–2.33 (m, 4H). 13C{1H} NMR (75
MHz, CDCl3), δ: 16.6, 35.5, 52.3, 118.4, 127.3, 129.2,140.3. HRMS (ESI): calcd for
C10H1079BrNNa (M + Na) 245.9889, found 245.9889; calcd for C10H1081BrNNa (M + Na) 247.9869,
found 247.9865.
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4-Bromo-6-phenylhexanenitrile (3v).
NC
Ph
Br
Following the General procedure 1, the reaction was carried out in dichloromethane using 1.6
equiv of bromoacetonitrile, and irradiated for 15 hours. Yield 487 mg (97%). Colorless oil. Rf 0.25
(hexane/EtOAc, 10/1). 1H NMR (300 MHz, CDCl3), δ: 7.41–7.31 (m, 2H), 7.30–7.20 (m, 3H), 4.05
(tt, J = 8.8, 4.2 Hz, 1H), 2.97 (ddd, J = 14.1, 8.7, 5.6 Hz, 1H), 2.89–2.74 (m, 1H), 2.72–2.48 (m,
2H), 2.34–2.02 (m, 4H). 13C{1H} NMR (75 MHz, CDCl3), δ:16.0, 33.6, 34.6, 40.5, 54.2, 118.7,
126.4, 128.5, 128.6, 140.3. HRMS (ESI): calcd for C12H1479BrNNa (M + Na) 274.0202, found
274.0209; calcd for C12H1481BrNNa (M + Na) 276.0182, found 276.0191..
4-Bromo-7-oxooctanenitrile (3w).
O
NC
Br
Following the General procedure 1, reaction was carried out in dichloromethane with 10 mol%
CuBr (29 mg, 0.2 mmol, 0.1 equiv), 11 mol% bis(3,5-diphenyl-1H-pyrazol-1-yl)methane (99 mg,
0.22 mmol, 0.11 equiv), bromoacetonitrile (384 mg, 3.2 mmol, 1.6 equiv), and irradiated for 15
1
hours. Yield 266 mg (61%). Pale yellow oil. Rf 0.18 (hexane/EtOAc, 3/1). H NMR (300 MHz,
CDCl3), δ: 4.04 (tt, J = 9.7, 3.6 Hz, 1H), 2.77–2.62 (m, 2H), 2.62–2.48 (m, 2H), 2.23–1.86 (m, 4H)
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2.13 (s, 3H). C{1H} NMR (75 MHz, CDCl3), δ: 16.0, 30.1,32.3, 34.8, 41.2, 54.3, 118.6, 207.0.
HRMS (ESI): calcd for C8H1279BrNNaO (M + Na) 239.9994, found 239.9999; calcd for
C8H1281BrNNaO (M + Na) 241.9974, found 241.9978.
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Cyclohexyl 4-bromo-6-cyanohexanoate (3x).
4
5
O
NC
O
6
7
Br
8
9
Following the General procedure 2, the reaction was carried out in dichloromethane and irradiated
for 30 hours. After column chromatography (Rf 0.35, hexane/EtOAc, 3/1), further purification was
performed by preparative HPLC (flow rate 12 mL·min−1, mobile phase: isocratic, 10% water in
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acetonitrile, retention time 8.1 min). Yield 436 mg (72%). Colorless oil. H NMR (300 MHz,
CDCl3), δ: 4.70 (td, J = 8.6, 3.9 Hz, 1H), 4.06 (tt, J = 9.5, 3.6 Hz, 1H), 2.72–2.32 (m, 4H), 2.32–
13
1.90 (m, 4H), 1.90–1.56 (m, 4H), 1.56–1.05 (m, 6H). C{1H} NMR (75 MHz, CDCl3), δ: 16.0,
23.6, 25.3, 31.5, 32.4, 33.8, 34.5, 53.8, 72.9, 118.5,171.6. HRMS (ESI): calcd for
C13H2179BrNO2(M + H) 302.0750, found 302.0751; calcd for C13H2181BrNO2(M + H) 304.0730,
found 304.0731.
Ethyl 3-(3,3-dimethylbicyclo[2.2.1]heptan-2-ylidene)propanoate (4).
OEt
O
Following the General procedure 1, the reaction was carried out in dichloromethane, and
irradiated for 5 hours. Yield 316 mg (76%). Colorless oil. Rf 0.64 (hexane/EtOAc, 10/1). Mixture of
isomers, ratio ~11.5:1. 1H NMR (300 MHz, CDCl3), δ: 5.26 (t, J = 7.5 Hz, minor) and 5.04 (t, J =
7.2 Hz, major) (1H), 4.10 (q, J = 7.1 Hz, 2H), 3.05 (d, J = 7.5 Hz, minor) and 2.99 (d, J = 7.2 Hz,
major) (2H), 2.87 (d, J = 3.8 Hz, major) and 2.57 (d, J = 4.2 Hz, minor) (1H), 1.87 (d, J = 2.5 Hz,
1H), 1.70–1.52 (m, 3H), 1.45–1.28 (m, 1H), 1.28–1.05 (m, 2H), 1.22 (t, J = 7.1 Hz, 3H), 1.01 (s,
13
3H), 0.98 (s, 3H). C{1H} NMR (75 MHz, CDCl3), δ, Major: 14.3, 23.8, 26.0, 28.0, 29.3, 34.9,
37.3, 41.6, 42.2, 48.1, 60.4, 107.0, 159.4, 172.7. Minor: 25.0, 27.0, 29.1, 34.1, 37.0, 48.6, 50.8,
108.7. HRMS (ESI): calcd for C14H22NaO2 (M + Na) 245.1512, found 245.1518.
Methyl 4-bromo-3,3-difluoro-4-phenylbutanoate (6a).
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MeO2C
Ph
4
Br
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8
9
Following the General procedure 2, the reaction was carried out in dichloromethane, and
irradiated for 30 hours. Yield 478 mg (82%). Colorless oil. Rf 0.30 (hexane/EtOAc, 10/1). 1H NMR
(500 MHz, CDCl3), δ: 7.58–7.46 (m, 2H), 7.42–7.31 (m, 3H), 5.62 (dd, J = 15.7, 11.7 Hz, 1H), 3.73
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(s, 3H), 3.21 (td, J = 16.3, 10.6 Hz, 1H), 2.88 (ddd, J = 19.6, 16.4, 10.1 Hz, 1H). F NMR (471
MHz, CDCl3), δ: –98.4 (dtd, J = 251.6, 16.0, 10.1 Hz), –96.5 (ddt, J = 251.6, 19.6, 11.1 Hz).
13C{1H} NMR (126 MHz, CDCl3), δ: 39.8 (t, J = 28.3 Hz), 51.6 (t, J = 26.2 Hz), 52.4, 119.1 (t, J =
248.3 Hz), 128.8, 129.6 (d, J = 1.6 Hz), 135.0 (d, J = 3.6 Hz), 167.0 (dd, J = 8.9, 6.5 Hz). HRMS
(ESI): calcd for C11H1179BrF2NaO2 (M + Na) 314.9803, found 314.9803; calcd for
C11H1181BrF2NaO2 (M + Na) 316.9783, found 316.9787.
Methyl 4-bromo-3,3-difluoro-4-(4-methoxyphenyl)butanoate (6b).
OMe
F
F
MeO2C
Br
Following the General procedure 2, the reaction was carried out in dichloromethane and irradiated
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for 15 hours. Yield 560 mg (87%). Colorless oil. Rf 0.26 (hexane/EtOAc, 10/1). H NMR (300
MHz, CDCl3), δ: 7.43 (d, J = 8.7 Hz, 2H), 6.87 (d, J = 8.7 Hz, 2H), 5.58 (dd, J = 16.3, 11.3 Hz,
1H), 3.79 (s, 3H), 3.71 (s, 3H), 3.17 (td, J = 16.0, 10.6 Hz, 1H), 2.87 (ddd, J = 19.7, 16.3, 10.6 Hz,
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1H). F NMR (376 MHz, CDCl3), δ: –96.35 (ddt, J = 250.9, 19.7, 10.9 Hz, 1F), –98.76 (dtd, J =
250.9, 16.0, 10.6 Hz, 1F). C{1H} NMR (75 MHz, CDCl3), δ: 39.8 (t, J = 28.4 Hz), 51.6 (t, J =
13
26.2 Hz), 52.3, 55.3, 114.2, 119.2 (t), 127.0 (d, J = 3.8 Hz), 130.8, 160.4, 167.0 (dd, J = 9.3, 5.9
Hz). HRMS (ESI): calcd for C12H1379BrF2NaO3 (M + Na) 344.9908, found 344.9909; calcd for
C12H1381BrF2NaO3 (M + Na) 346.9888, found 346.9884.
4-Bromo-3,3-difluoro-4-(4-methoxyphenyl)butanenitrile (6c).
OMe
F
F
NC
Br
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Following the General procedure 2, reaction was carried out with 20 mol % IMes·CuBr (176 mg,
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0.4 mmol, 0.20 equiv), and bromoacetonitrile (3.6 mmol, 1.8 equiv), and irradiated for 30 hours.
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Yield 121 mg (21%). Colorless oil. Rf 0.16 (hexane/EtOAc, 5/1). H NMR (300 MHz, CDCl3), δ:
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7.43 (d, J = 8.7 Hz, 2H), 6.91 (dm, J = 8.7 Hz, 2H), 5.17 (dd, J = 13.5, 11.9 Hz, 1H), 3.82 (s, 3H),
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3.19 (ddd, J = 17.0, 14.3, 11.4 Hz, 1H), 2.96 (dt, J = 17.0, 13.7 Hz, 1H). F NMR (282 MHz,
CDCl3), δ: –97.71 (dq, J = 245.8, 12.3 Hz, 1F), –99.88 (dq, J = 245.8, 12.5 Hz, 1F). 13C{1H} NMR
(75 MHz, CDCl3), δ: 25.8 (t, J = 31.2 Hz), 50.8 (t, J = 26.1 Hz), 55.5, 112.8 (t, J = 6.3 Hz), 114.6,
117.0 (t, J = 251.7 Hz), 125.4 (d, J = 3.1 Hz), 130.7, 160.9. HRMS (ESI): calcd for
C11H1079BrF2NNaO (M + Na) 311.9806, found 311.9804; calcd for C11H1081BrF2NNaO (M + Na)
313.9786, found 313.9784.
Methyl 4-iodo-6-phenylhexanoate (8a).
O
Ph
MeO
I
Following the General procedure 3. Yield 484 mg (73%). Colorless oil. Rf 0.25 (hexane/EtOAc,
10/1). 1H NMR (300 MHz, CDCl3), δ: 7.41–7.31 (m, 2H), 7.31–7.19 (m, 3H), 4.12 (tt, J = 8.8, 4.5
Hz, 1H), 3.72 (s, 3H), 2.96 (ddd, J = 13.9, 9.2, 5.1 Hz, 1H), 2.79 (dt, J = 13.9, 8.0 Hz, 1H), 2.72–
2.59 (m, 1H), 2.52 (dt, J = 16.3, 7.6 Hz, 1H), 2.37–1.97 (m, 4H). 13C{1H} NMR (75 MHz, CDCl3),
δ: 34.1, 35.5,37.1, 42.3, 51.7, 126.2, 128.5, 140.6, 172.9. HRMS (ESI): calcd for C13H17INaO2(M +
Na) 355.0165, found 355.0158.
Methyl 4,8-diiodooctanoate (8b).
O
I
MeO
I
Following the General procedure 3. Yield 678 mg (83%). Colorless oil. Rf 0.14 (hexane/EtOAc,
25/1). 1H NMR (300 MHz, CDCl3), δ: 4.05 (ddd, J = 13.2, 8.4, 4.9 Hz, 1H), 3.62 (s, 3H), 3.14 (t, J
= 6.9 Hz, 2H), 2.61–2.32 (m, 2H), 2.09–1.92 (m, 2H), 1.92–1.36 (m, 6H). 13C{1H} NMR (75 MHz,
CDCl3), δ: 6.3, 30.4, 32.5, 34.0, 35.3, 37.2, 39.5, 51.7,172.8. HRMS (ESI): calcd for C9H16I2NaO2
(M + Na) 432.9132, found 432.9128.
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Ethyl 4-iodo-4-(trimethylsilyl)butanoate (8c).
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O
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SiMe3
EtO
I
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Following the General procedure 3. Yield (546 mg, 87%). Colorless oil Rf 0.12 (hexane/EtOAc,
25/1). 1H NMR (300 MHz, CDCl3), δ: 4.11 (q, J = 7.1 Hz, 2H), 3.10 (dd, J = 12.0, 3.0 Hz, 1H),
2.65 (ddd, J = 16.4, 8.2, 5.0 Hz, 1H), 2.50–2.33 (m, 1H), 2.06–1.69 (m, 2H), 1.23 (t, J = 7.1 Hz,
3H), 0.14 (s, 9H). 13C{1H} NMR (75 MHz, CDCl3), δ: –2.1, 14.3,22.5, 29.2, 36.6, 60.5, 172.9.
HRMS (ESI): calcd for C9H19INaO2Si (M + Na) 337.0091, found 337.0085.
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Ethyl 4-iodo-5,5-dimethylhexanoate (8d).
O
EtO
I
Following the General procedure 3, the reaction was carried out with 15 mol % CuI (57 mg, 0.3
mmol, 0.15 equiv), 16 mol% dm-PyBOX (87 mg, 0.32 mmol, 0.16 equiv), ethyl iodoacetate (685
mg, 3.2 mmol, 1.6 equiv), and irradiated for 20 hours. Yield 429 mg (72%). Colorless oil. Rf 0.14
1
(hexane/EtOAc, 25/1). H NMR (300 MHz, CDCl3), δ: 4.12 (q, J = 7.1 Hz, 2H), 4.01 (d, J = 11.4
Hz, 1H), 2.67 (ddd, J = 16.7, 7.8, 5.3 Hz, 1H), 2.51–2.36 (m, 1H), 2.18–1.85 (m, 2H), 1.24 (t, J =
13
7.1 Hz, 3H), 1.09 (s, 9H). C{1H} NMR (75 MHz, CDCl3), δ: 14.4, 28.6,31.3, 35.8, 36.1, 57.0,
60.5, 172.9. HRMS (ESI): calcd for C10H19NaIO2 (M + Na) 321.0322, found 321.0324.
Radical clock experiment. Methyl 7-bromo-5-methylhept-4-enoate (3-open).
O
MeO
Br
Following the General procedure 1 using methyl bromoacetate 1a and isopropenylcyclopropane, the
reaction was carried out in acetonitrile, and irradiated for 3.5 hours. Desired product was obtained
as colorless oil (329 mg, 70%). Rf= 0.33 (hexane/EtOAc, 10/1). Mixture of isomers 2:1. 1H NMR
(300 MHz, CDCl3), δ: Major isomer 1.62 (s, 3H), 2.23–2.45 (m, 4H), 2.46–2.62 (m, 2H), 3.31 (t, J
= 7.3 Hz, 1H), 3.65 (s, 3H), 5.15 (t, J = 6.4 Hz, 1H). Minor isomer 1.69 (s, 3H), 3.32 (t, J = 7.1 Hz,
1H), 3.65 (s, 3H), 5.18 (d, J = 5.7 Hz, 1H). 13C{1H} NMR (75 MHz, CDCl3), δ: Both isomers: 16.2,
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22.9, 27.3, 31.6, 32.8, 34.6, 51.5, 121.8, 136.8, 173.6. Minor isomer: 31.4, 32.5, 51.6, 123.2, 136.6,
173.5. HRMS (ESI): calcd C9H1579BrO2Na (M + Na) 257.0148, found 257.0138; calcd
C9H1581BrO2Na (M + Na) 259.0127, found 259.0117.
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ASSOCIATED CONTENT
Supporting Information. Reaction set-up and copies of NMR spectra for all compounds (PDF).
The Supporting Information is available free of charge on the ACS Publications website.
AUTHOR INFORMATION
Corresponding Author
* E-mail: adil25@mail.ru
Author Contributions
All authors have given approval to the final version of the manuscript.
ACKNOWLEDGEMENTS
This work was supported by the Russian Foundation for Basic Research (project 18-33-20015).
REFERENCES
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