Visible-light-induced intermolecular atom-transfer radical addition of benzyl halides to olefins: Facile synthesis of tetrahydroquinolines

Article abstract of DOI:10.1055/s-0033-1338910

Cu(dap)₂Cl has been utilized as a visible-light photoredox catalyst for the atom-transfer radical addition (ATRA) of benzyl halides to styrenes and silyl enol ethers. The resulting ATRA products can be readily converted into tetrahydroquinoline

Full text of DOI:10.1055/s-0033-1338910

SPECIAL TOPIC
▌2689
sVpeicsiailbtopliec-Light-Induced Intermolecular Atom-Transfer Radical Addition of
Benzyl Halides to Olefins: Facile Synthesis of Tetrahydroquinolines
Photocatalytic Radical Addition of Benzyl Halides to Olefins
Suva Paria, Michael Pirtsch, Viktor Kais, Oliver Reiser*
Institut für Organische Chemie, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany
Fax +49(941)9434631; E-mail: Oliver.Reiser@chemie.uni-regensburg.de
Received: 28.02.2013; Accepted after revision: 01.05.2013
attractive alternative to ruthenium or iridium catalysts be-
Abstract: Cu(dap)2Cl has been utilized as a visible-light photore-
side the economic advantage for visible-light-mediated
dox catalyst for the atom-transfer radical addition (ATRA) of ben-
ATRA reactions.13 In this contribution, we demonstrate
zyl halides to styrenes and silyl enol ethers. The resulting ATRA
that also benzyl halides can be efficiently coupled with al-
kenes in ATRA reactions under visible-light catalysis
(Scheme 1), offering a facile method for the synthesis of
tetrahydroquinolines.
products can be readily converted into tetrahydroquinolines.
Key words: visible-light photocatalysis, atom-transfer radical ad-
dition, benzyl halide, tetrahydroquinoline
X
X
The atom-transfer radical addition (ATRA) or Kharasch
addition1 of organic halides to olefins is a versatile tool for
organic synthesis since it results in the formation of C–C
and C–X bonds simultaneously. Commonly used initia-
tors for ATRA reactions include peroxides,1 triethylbo-
ron,2 or organotin3 reagents, which are not optimal with
respect to operational safety, sensitivity, and environmen-
tal impact. Alternatively, transition-metal complexes of
copper,4 ruthenium,5 iron,6 or nickel7 can be employed,
nevertheless, the high catalyst loading necessary to
achieve good yields leaves room for improvement. One
solution to this problem has been proposed by adding re-
ducing agents to regenerate the catalysts;8 however, the
reaction conditions necessary are generally quite harsh.
Cu(dap)2Cl
(1 mol%)
R2
EWG
EWG
MeCN
green LED
12 h
R1
R1
X = Br, Cl
3
1
+
MeO
N
R2
Ar
N
2
Cu
N
Cl
N
Ar
MeO
Ar = 4-MeOC6H4
Visible-light-driven photocatalysis has been recognized
as a versatile tool for a growing number of organic trans-
formations.9 Stephenson et al. reported intermolecular
ATRA reactions between perhaloalkanes or α-halocar-
bonyl compounds and olefins using oxidative or reductive
quenching of photoredoxcatalysts based on ruthenium
and iridium complexes.10,11 Likewise, our group recently
succeeded in the use of Cu(dap)2Cl [dap = 2,9-bis(p-an-
isyl)-1,10-phenanthroline; Sauvage’s catalyst]12 as visi-
ble-light photocatalyst for the same process utilizing the
oxidative quenching pathway.13 Cu(dap)2Cl is a stronger
reductant (*Cu+/Cu2+ = –1.43 V) than commonly used pho-
tocatalysts Ru(bpy)3Cl2 or [Ir(dF(CF3)ppy)2(dtbb-
py)](PF6) no matter if the latter are utilized in the
oxidative (*Ru2+/Ru3+ = –0.86 V; *Ir3+/Ir4+ = –0.89 V) or
reductive quenching pathway (Ru+/Ru2+ = –1.33 V;
Ir2+/Ir3+ = –1.21 V). Thus, *Cu(dap)2Cl can reduce sub-
strates more effectively in the oxidative than Ru(bpy)3Cl2
or [Ir(dF(CF3)ppy)2(dtbbpy)](PF6) in the reductive
quenching pathway with the additional advantage that no
sacrificial electron donor has to be employed, making it an
Cu(dap)2Cl
Scheme 1 Intermolecular atom-transfer radical addition of benzyl
halides to styrenes
The activation of benzyl halides under visible-light pho-
toredox conditions has only been shown in a few cases.
Sauvage et al. demonstrated the dimerization of p-nitro-
benzyl bromide under irradiation (λ ≥350 nm) in the pres-
ence of triethylamine as an electron donor and
Cu(dap)2Cl,12 while MacMillan developed the α-ben-
zylation of aldehydes using fac-Ir(ppy)3 (ppy = 2-phenyl-
pyridine) as photoredox catalyst.14 ATRA reactions of
benzyl halides to alkenes under visible-light photoredox
conditions are to the best of our knowledge not known,
and only recently was it disclosed that under UV irradia-
tion in the presence of Cu(II) complexes and AIBN this
reaction proceeds, albeit only in low yields (0–35%).15
As a model system we investigated the ATRA between
p-nitrobenzyl bromide (1a) and styrene (2a, Table 1). Em-
ploying 1 mol% of Cu(dap)2Cl and irradiating with a
green light emitting diode (LED; λmax = 530 nm) the de-
sired ATRA product 3a was smoothly obtained.
SYNTHESIS 2013, 45, 2689–2698
Advanced online publication: 20.06.2013
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1338910; Art ID: SS-2013-C0169-ST
© Georg Thieme Verlag Stuttgart · New York

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S. Paria et al.
SPECIAL TOPIC
Table 1 ATRA Reaction between p-Nitrobenzyl Bromide and Styrene: Optimization of Reaction Conditions
Br
Br
Cu(dap)2Cl (1 mol%)
+
green LED
NO2
NO2
3a
2a
1a
Entry
Conditions
Yield (%)a
1
2
3
4
5
6
7
Cu(dap)2Cl (1 mol%), styrene (10 equiv), CH2Cl2, 530 nm, 24 h
Cu(dap)2Cl (1 mol%), styrene (10 equiv), MeCN, 530 nm, 24 h
Cu(dap)2Cl (1 mol%), styrene (5 equiv), MeCN, 530 nm, 12 h
[Ir(ppy)2(dtbbpy)](PF6) (1 mol%), styrene (5 equiv), MeCN, 455 nm, 12 h
Ru(bpy)3Cl2 (1 mol%), styrene (5 equiv), MeCN, 455 nm, 12 h
no photocatalyst, 530 nm light, 24 h
60
85
85
85
69
no reaction
no reaction
with Cu(dap)2Cl, no light, 24 h
a Isolated yield after purification on silica gel.
While the reaction was incomplete in dichloromethane as over Ir (cost per mol Cu/Ir = 1:10000) we decided to go
solvent after 24 hours, in acetonitrile full conversion was forward with the former. Ru(bpy)3Cl2 was less efficient to
achieved already in 12 hours, allowing the isolation of 3a give 69% of the desired product under otherwise identical
in 85% yield (Table 1, entries 1–3). Styrene was initially reaction conditions (Table 1, entry 5). Control experi-
employed in excess (5–10 equiv), but this amount can be ments established that both a photocatalyst as well as light
reduced to 2 equivalents with equally good results (Table are necessary for the reaction to proceed (Table 1, entries
2). [Ir(ppy)2(dtbbpy)](PF6)16 (dtbbpy = 4,4′-di-tert-butyl- 6, 7).
2,2′-bipyridyl, Table 1, entry 4) was also found to be a
Having established the optimum reaction conditions the
competent photocatalyst for this transformation with sim-
scope of this ATRA reaction was evaluated (Table 2).
ilar yield, but considering the economical advantage of Cu
Electron-poor benzyl bromides or chlorides are required
X
O
OSiMe3
Cu(dap)2Cl (1 mol%)
R1
O2N
R1
NO2
+
MeCN
green LED
12 h
R2
R2
X = Br, Cl
1
4
5
O
O
NO2
O
NO2
Ph
Ph
Ph
NO2
NO2
5c
5b
5a
X = Br, 90%
X = Cl, 92%
78%
87%
NO2
O
NO2
O
NO2
CO2Et
5e
5d
50%
81%
Scheme 2 ATRA reaction of benzyl halides with silyl enol ethers
Synthesis 2013, 45, 2689–2698
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
Photocatalytic Radical Addition of Benzyl Halides to Olefins
2691
calling for heteroarenes such as 4-quinolinyl (Table 2, en- On the side of the alkenes, besides various styrenes, 2-vi-
try 19) or nitro substitution in the phenyl ring of the benzyl nylnaphthalene (Table 2, entries 4, 14) and 4-vinylbiphe-
moiety (entries 1–18). 2,4-Dinitrobenzyl chloride resulted nyl (Table 2, entries 8, 15) proved to be good substrates
in moderate yield when coupled with styrene (Table 2, en- for the title transformation.
try 16), but gave excellent yields with substituted styrenes
(Table 2, entries 17, 18). Attempts to use 4-cyano (entry
Halide substitution at para (entries 2, 6, 12) or meta posi-
tion is tolerated well (entries 3, 7, 13, 17), showing no
20), 4-trifluoromethylbenzyl bromide (entry 21) or benzyl
cross reactivity with the benzyl halide. Methyl substitu-
bromide itself (entry 22) as reaction partner resulted in
tion in β-position of the styrene was possible, although a
drop in the yield is observed (entry 11), while methyl sub-
stitution in α-position was not feasible, resulting besides
complete recovery of the starting material, being probably
due to the high reduction potential of electroneutral or
partially electron-deficient benzylic system to undergo
the expected ATRA product in additional side products
the initial C–Br bond cleavage step (E1/2 = –1.85 V vs
stemming from HBr elimination.
SCE for benzyl bromide in MeCN).17
Table 2 Substrate Scope of the ATRA Reaction between Nitrobenzyl Halides and Styrenesa
X
Cu(dap)2Cl (1 mol%)
R
Ar1
X
Ar2
Ar1
Ar2
+
MeCN
R
green LED, 12 h
1
2
3
Entry
Ar1
X
Product
Ar2
Yield (%)b
Br
1
2
3
4
Ph (3a)
85c
90
4-BrC6H4 (3b)
3-ClC6H4 (3c)
2-naphthyl (3d)
Ar2
4-O2NC6H4
2-O2NC6H4
Br
87 (84)c
85 (83)c
NO2
Br
NO2
NO2
5
6
7
8
Ph (3e)
91 (80)d
87
4-BrC6H4 (3f)
3-ClC6H4 (3g)
biphenyl (3h)
Ar2
Br
80 (79)c
82
Br
Ar2
9
4-EtO2C-2-O2NC6H3
2,4-(O2N)2C6H3
Br
Br
Ph (3i)
70
CO2Et
10
11
12
13
14
15
Ph (3j, R = H)
Ph (3k, R = Me)
4-BrC6H4 (3l, R = H)
3-ClC6H4 (3m, R = H)
2-naphthyl (3n, R = H)
biphenyl (3o, R = H)
89
Br
NO2
35c,e,f
86
Ar2
95
81
90
R
NO2
Cl
Br
NO2
16
17
18
Ph (3p)
3-ClC6H4 (3q)
4-MeC6H4 (3r)
51
92
93
Ar2
2,4-(O2N)2C6H3
4-quinolinyl
Cl
Br
NO2
Cl
Ar2
19
2-naphthyl (3s)
66
N
20
21
22
4-NCC6H4
4-F3CC6H4
Ph
Br
Br
Br
Ph
Ph
Ph
no reaction
no reaction
no reaction
a Benzyl halide (0.2 mmol, 1 equiv), styrene (2-5 equiv), Cu(dap)2Cl (1 mol%) in degassed MeCN (1.0 mL), external irradiation at 530 nm for
12 h.
b Yield of isolated product.
c Benzyl bromide: 1 mmol.
d Benzyl bromide (2 mmol) with 0.5 mol% of catalyst loading.
e Internal irradiation at 60 °C for 20 h (see experimental section for details).
f Combined yield of two diastereoisomers (dr = 1.3:1).
© Georg Thieme Verlag Stuttgart · New York
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SPECIAL TOPIC
visible light
*Cu(dap)2
Cu(dap)2
8
10
Ph
Ar
Br
Ar
15
1
Ar
Br
2+
Cu(dap)2
O
N
Br
Ar
9
TEMPO
12
Br
Ar
Ph
Ar
Ph
H2C
3
Ph
14
11
13
2
1
11
Scheme 3 Mechanistic discussion
Silyl enol ethers 4 also proved to be valuable coupling The product formation is consistent with an oxidative
partners for the benzyl halides, affording the correspond- quenching cycle of the copper catalyst (Scheme 3). Excit-
+
ing ketones 5 (Scheme 2). Excellent results were obtained ed *Cu(dap)2 (8) is transformed to its Cu+2 state 9 by
when 4 contained an aromatic substituent (products 5a– transferring an electron to the benzyl halide 1, thus gener-
d), but also the silyl enol ether derived from cyclopenta- ating a benzyl radical 11, which adds to the alkene 2 to
none gave the ATRA product 5e in acceptable yield. give radical intermediate 14. Product 3 can be formed by
Cu(dap)2Cl was necessary for those transformations irre- two possible pathways: through carbocation 15, which is
spective of the solvent used, contrasting the trifluorometh- generated by a back electron transfer from 14 to
+2
ylation of enolsilanes with trifluoromethyl iodide that was Cu(dap)2 (9) (radical polar crossover), thus closing the
recently reported to proceed by visible-light irradiation catalytic cycle and regenerating the catalyst. This mecha-
only when carried out in DMF.18
nistic proposal calls for the reaction of two components, 9
Table 3 Application of ATRA Products to the Synthesis of Tetrahydroquinolines
Br
NO2
FeCl3 (3 equiv)
Zn (10 equiv)
N
R2
R2
H
DMF–H2O (1:1)
100 °C, 1 h
3e–g
6
Starting material
Product
Yield (%)a
Br
NO2
N
H
75
3e
6a
6b
Br
NO2
N
H
72
70
Br
Br
3f
Br
NO2
N
H
Cl
Cl
3g
6c
a Yield of isolated product.
Synthesis 2013, 45, 2689–2698
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SPECIAL TOPIC
Photocatalytic Radical Addition of Benzyl Halides to Olefins
2693
sponding benzyl halide (1.0 equiv). The flask was purged with a
stream of N2 and MeCN (1.0 mL) was added. The resultant mixture
was degassed for 5 min by N2 sparging and the respective styrene
(2–5 equiv) or silyl enol ether (3 equiv) was added to the vial. The
vial was placed at a distance of 0.5–1.0 cm from a green LED lamp
(530 nm) and stirred for 12 h. After the completion of the reaction
(monitored by TLC), the mixture was directly concentrated in vac-
uo. The residue was purified by chromatography on silica gel, using
hexane–EtOAc as the solvent system.
and 14, that are present only in low concentrations. Alter-
natively, a chain process can be initiated through electron
transfer from 14 to 1, which regenerates 11 (radical prop-
agation). While both mechanistic pathways are viable,
Stephenson et al. have elegantly shown that radical-polar
crossover must clearly play a significant role in photore-
dox induced ATRA processes.10 When the ATRA reac-
tion was carried out in the presence of 2,2,6,6-
tetramethylpiperidinoxyl (12, TEMPO), adduct 13 was
detected by mass spectrometry, which supports the overall
radical mechanism by either pathway of the process re-
ported here (see Supporting Information for more details).
Bromide to Methoxide Transformation; General Procedure B
(GP-B)
Since some of the ATRA products did not give molecular ion peaks
in the MS analysis, they were converted into their corresponding
methoxides for analytical purposes: The purified bromide (0.10
The ATRA products derived from o-nitrobenzyl bromide mmol) was dissolved in MeOH (1 mL) and refluxed at 60 °C for 2
h. After completion of the reaction (monitored by TLC), MeOH was
removed in vacuo. The residue was purified by chromatography on
silica gel, using hexane–EtOAc as the solvent system to afford the
methoxides 3′ corresponding to the ATRA products 3.
are valuable precursors for the synthesis of tetrahydro-
quinolines. Treatment of 3e–g with FeCl3/Zn in DMF–
H2O (1:1)19 under reflux conditions smoothly resulted in
the reduction of the nitro to the amino functionality with
concurrent cyclization to 2-substituted tetrahydroquino-
lines 6 (Table 3).
Tetrahydroquinolines;19 General Procedure C (GP-C)
In a round-bottomed flask, FeCl3·6H2O (3 equiv) and Zn dust (10
equiv) were added to the ATRA product (0.46 mmol) in 1:1 DMF
Alternatively, 5 can be subjected to a catalytic hydrogena-
tion with palladium/carbon,20 to give tetrahydroquinolines
6 as exemplified for the transformation of 5b to 6a
(Scheme 4).
and H2O (2.5 mL). The mixture was heated for 1 h in an oil bath at
100 °C. After completion of the reaction (monitored by TLC), the
reaction mixture was filtered and the filtrate was diluted with H2O
(5 mL) and basified with sat. aq Na2CO3. It was then extracted with
CH2Cl2 (3 × 10 mL). The combined organic layers were dried
(Na2SO4), the solvent was removed in vacuo, and the residue was
subjected to column chromatography on silica gel, using hexane–
EtOAc as solvent system to obtain the pure product.
O
NO2
Pd/C, H2
N
H
1-(3-Bromo-3-phenylpropyl)-4-nitrobenzene (3a)
According to general procedure GP-A, 4-nitrobenzyl bromide
(0.216 g, 1.00 mmol, 1 equiv), Cu(dap)2Cl (8.8 mg, 1 mol%), and
styrene (0.520 g, 5.00 mmol, 5 equiv) afforded 3a (0.272 g, 85%) as
a colorless liquid after column purification on silica gel; Rf = 0.45
(EtOAc–hexane, 1:9).
EtOH
3 h
5b
6a
67%
Scheme 4
1H NMR (300 MHz, CDCl3): δ = 8.20–8.11 (m, 2 H), 7.42–7.27 (m,
7 H), 4.87 (dd, J = 8.6, 6.1 Hz, 1 H), 2.95 (ddd, J = 14.4, 9.1, 5.7 Hz,
1 H), 2.88–2.74 (m, 1 H), 2.71–2.55 (m, 1 H), 2.51–2.37 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 148.27, 146.67, 141.42, 129.38,
128.90, 128.69, 127.23, 123.85, 53.96, 40.79, 34.20.
In conclusion, we have successfully developed the so far
elusive visible-light-mediated ATRA between different
electron deficient benzyl halides and styrenes or silyl enol
ethers, applying Cu(dap)2Cl as an economic and highly
efficient photoredox catalyst. The ATRA products de-
rived from o-nitrobenzyl halides can be directly converted
into 2-substituted tetrahydroquinolines.
MS (EI, 70 eV): m/z = 319 [M]+, 275.1, 239.2, 44.1.
1-(3-Methoxy-3-phenylpropyl)-4-nitrobenzene (3a′)
General procedure GP-B afforded 3a′ (0.025 g, 74%) as a colorless
liquid after column purification on silica gel; Rf = 0.53 (EtOAc–
hexane, 1:9).
All reactions were performed using common dry, inert atmosphere
techniques. Reactions were monitored by TLC and visualized by a
dual short/long wave UV lamp and stained with an ethanolic solu-
tion of vanillin. Column flash chromatography was performed using
230–400 mesh silica gel. NMR spectra were recorded on 300 MHz
spectrometer. Chemical shifts for 1H NMR were reported as δ (parts
per million) relative to the signal of CDCl3 at 7.26 ppm. Chemical
shifts for 13C NMR were reported as δ (parts per million) relative to
the center line signal of the CDCl3 triplet at 77 ppm. Proton and car-
bon assignments were established using spectral data of similar
compounds. Standard abbreviations were used to denote signal mul-
tiplicities. Some of the ATRA products (3a, 3d, 3e, 3h, 3j, 3l, 3m,
3n, 3o) were unstable under mass spectrometric analysis. So HRMS
of the corresponding methoxides has been obtained by converting
the ATRA bromides into methoxides.
1H NMR (300 MHz, CDCl3): δ = 8.16–8.10 (m, 2 H), 7.40–7.22 (m,
7 H), 4.07 (dd, J = 8.1, 5.1 Hz, 1 H), 3.22 (s, 3 H), 2.91–2.70 (m, 2
H), 2.21–2.05 (m, 1 H), 2.02–1.87 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 149.99, 141.59, 129.94, 129.26,
128.56, 127.84, 126.61, 123.67, 82.74, 56.68, 39.24, 32.01.
HRMS (ESI): m/z calcd for C16H17NO3 [M]+: 271.1208; found:
271.1207.
1-[3-Bromo-3-(4-bromopropyl)propyl]-4-nitrobenzene (3b)
According to general procedure GP-A, 4-nitrobenzyl bromide
(0.050 g, 0.23 mmol, 1 equiv), Cu(dap)2Cl (2 mg, 1 mol%), and 4-
bromostyrene (0.126 g, 0.69 mmol, 3 equiv) afforded 3b (0.082 g,
90%) as a colorless oil after column purification on silica gel; Rf =
0.45 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.21–8.13 (m, 2 H), 7.52–7.44 (m,
2 H), 7.38–7.29 (m, 2 H), 7.29–7.20 (m, 2 H), 4.80 (dd, J = 8.7, 6.1
Hz, 1 H), 2.94 (ddd, J = 14.4, 9.0, 5.7 Hz, 1 H), 2.87–2.75 (m, 1 H),
2.67–2.52 (m, 1 H), 2.47–2.31 (m, 1 H).
Photoredox Catalysis of ATRA Reaction; General Procedure A
(GP-A)
An oven dried 10 mL vial equipped with a plastic septum and mag-
netic stir bar was charged with Cu(dap)2Cl (1 mol%) and the corre-
© Georg Thieme Verlag Stuttgart · New York
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S. Paria et al.
SPECIAL TOPIC
13C NMR (75 MHz, CDCl3): δ = 147.96, 146.73, 140.48, 132.07,
129.36, 128.90, 123.91, 122.56, 52.67, 40.65, 34.09.
HRMS (ESI): m/z calcd for C15H13Br2NO2 [M]+: 396.9313; found:
396.9310.
Large-Scale Reaction with Low Catalyst Loading: According to
general procedure GP-A, 2-nitrobenzyl bromide (0.432 g, 2.0
mmol, 1 equiv), Cu(dap)2Cl (8.8 mg, 0.5 mol%), and styrene (1.04
g, 10.0 mmol, 5 equiv) in MeCN (5 mL) was irradiated for 12 h to
obtain 3e (0.510 g, 80%) as a yellow liquid after column purifica-
tion on silica gel.
1-[3-Bromo-3-(3-chlorophenyl)propyl]-4-nitrobenzene (3c)
According to general procedure GP-A, 4-nitrobenzyl bromide
(0.216 g, 1.00 mmol, 1 equiv), Cu(dap)2Cl (8.8 mg, 1 mol%), and
3-chlorostyrene (0.415 g, 3.00 mmol, 3 equiv) afforded 3c (0.298 g,
84%) as a colorless oil after column purification on silica gel; Rf =
0.30 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.21–8.11 (m, 2 H), 7.40–7.31 (m,
3 H), 7.31–7.19 (m, 3 H), 4.79 (dd, J = 8.8, 5.9 Hz, 1 H), 3.03–2.89
(m, 1 H), 2.88–2.75 (m, 1 H), 2.67–2.48 (m, 1 H), 2.48–2.29 (m, 1
H).
13C NMR (75 MHz, CDCl3): δ = 147.93, 146.74, 143.38, 134.63,
130.17, 129.36, 128.82, 127.45, 125.44, 123.90, 52.44, 40.63,
34.08.
HRMS (ESI): m/z calcd for C15H13BrClNO2 [M]+: 352.9818; found:
352.9817.
1-(3-Methoxy-3-phenylpropyl)-2-nitrobenzene (3e′)
General procedure GP-B afforded 3e′ (0.030 g, 89%) as a colorless
oil after column purification on silica gel; Rf = 0.42 (EtOAc–
hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 7.93–7.85 (m, 1 H), 7.50 (t,
J = 7.5 Hz, 1 H), 7.41–7.23 (m, 7 H), 4.14 (dd, J = 8.1, 5.1 Hz, 1 H),
3.23 (s, 3 H), 3.11–2.98 (m, 1 H), 2.98–2.84 (m, 1 H), 2.19–1.92 (m,
2 H).
13C NMR (75 MHz, CDCl3): δ = 149.44, 141.74, 137.09, 132.87,
131.99, 128.48, 127.72, 127.00, 126.62, 124.71, 83.23, 56.67,
38.85, 29.56.
HRMS (ESI): m/z calcd for C16H17NO3 [M]+: 271.1208; found:
271.1201.
1-[3-Bromo-3-(4-bromophenyl)propyl]-2-nitrobenzene (3f)
According to general procedure GP-A, 2-nitrobenzyl bromide
(0.040 g, 0.18 mmol, 1 equiv), Cu(dap)2Cl (1.5 mg, 1 mol%), and
4-bromostyrene (0.098 g, 0.54 mmol, 3 equiv) afforded 3f (0.064 g,
87%) as a colorless liquid after column purification on silica gel;
Rf = 0.44 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 7.95 (dd, J = 8.1, 1.2 Hz, 1 H),
7.59–7.43 (m, 3 H), 7.42–7.33 (m, 2 H), 7.31–7.27 (m, 2 H), 4.93
(dd, J = 8.4, 6.5 Hz, 1 H), 3.10 (ddd, J = 13.3, 9.9, 5.3 Hz, 1 H), 2.92
(ddd, J = 13.3, 9.7, 6.1 Hz, 1 H), 2.66–2.41 (m, 2 H).
2-[1-Bromo-3-(4-nitrophenyl)propyl]naphthalene (3d)
According to general procedure GP-A, 4-nitrobenzyl bromide
(0.216 g, 1.00 mmol, 1 equiv), Cu(dap)2Cl (8.8 mg, 1 mol%), and
2-vinylnapthalene (0.308 g, 2.00 mmol, 2 equiv) afforded 3d (0.307
g, 83%) as a colorless liquid after column purification on silica gel;
Rf = 0.30 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.20–8.12 (m, 2 H), 7.90–7.73 (m,
4 H), 7.58–7.47 (m, 3 H), 7.35 (d, J = 8.7 Hz, 2 H), 5.05 (dd, J = 8.1,
6.5 Hz, 1 H), 3.04–2.91 (m, 1 H), 2.90–2.66 (m, 2 H), 2.62–2.46 (m,
1 H).
13C NMR (75 MHz, CDCl3): δ = 140.55, 135.56, 133.28, 132.19,
131.99, 128.97, 127.65, 125.09, 122.23, 53.28, 40.37, 32.10.
HRMS (ESI): m/z calcd for C15H13Br2NO2 [M]+: 396.9313; found:
13C NMR (75 MHz, CDCl3): δ = 148.23, 146.68, 138.56, 133.28,
133.02, 129.39, 129.06, 128.05, 127.76, 126.74, 126.69, 126.10,
124.85, 123.87, 54.35, 40.68, 34.22.
396.9314.
MS (EI, 70 eV): m/z = 370.0 [M + H]+, 330.1, 290.1, 162.0, 141.0.
1-[3-Bromo-3-(3-chlorophenyl)propyl]-2-nitrobenzene (3g)
According to general procedure GP-A, 2-nitrobenzyl bromide
(0.216 g, 1.00 mmol, 1 equiv), Cu(dap)2Cl (8.8 mg, 1 mol%), and
3-chlorostyrene (0.415 g, 3.00 mmol, 3 equiv) afforded 3g (0.280 g,
79%) as a colorless liquid after column purification on silica gel;
Rf = 0.48 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 7.95 (dd, J = 7.8, 1.6 Hz, 1 H),
7.63–7.46 (m, 1 H), 7.44–7.33 (m, 3 H), 7.32–7.22 (m, 3 H), 4.91
(dd, J = 8.6, 6.2 Hz, 1 H), 3.13 (ddd, J = 13.4, 9.8, 5.2 Hz, 1 H), 2.93
(ddd, J = 13.3, 9.6, 6.1 Hz, 1 H), 2.66–2.39 (m, 2 H).
2-[1-Methoxy-3-(4-nitrophenyl)propyl]naphthalene (3d′)
General procedure GP-B afforded 3d′ (0.027 g, 78%) as a yellow
liquid after column purification on silica gel; Rf = 0.43 (EtOAc–hex-
ane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.17 (m, 2 H), 7.91–7.78 (m, 3 H),
7.70 (s, 1 H), 7.58–7.38 (m, 3 H), 7.38–7.23 (m, 2 H), 4.24 (dd,
J = 7.9, 5.3 Hz, 1 H), 3.25 (s, 3 H), 2.96–2.70 (m, 2 H), 2.33–2.14
(m, 1 H), 2.13–1.95 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 149.92, 146.35, 138.96, 133.21,
129.27, 128.60, 127.80, 127.77, 127.69, 126.29, 126.00, 125.94,
124.17, 123.68, 82.88, 56.76, 39.05, 32.00.
HRMS (ESI): m/z calcd for C20H19NO3 [M]+: 321.1365; found:
321.1367.
13C NMR (75 MHz, CDCl3): δ = 149.12, 143.48, 135.53, 134.56,
133.29, 132.20, 130.12, 128.73, 127.68, 127.52, 125.51, 125.09,
53.08, 40.35, 32.07.
HRMS (ESI): m/z calcd for C15H13BrClNO2 [M]+: 352.9818; found:
352.9818.
1-(3-Bromo-3-phenylpropyl)-2-nitrobenzene (3e)
According to general procedure GP-A, 2-nitrobenzyl bromide
(0.050 g, 0.23 mmol, 1 equiv), Cu(dap)2Cl (2.0 mg, 1 mol%), and
styrene (0.119 g, 1.15 mmol, 5 equiv) afforded 3e (0.067 g, 91%) as
a yellow liquid after column purification on silica gel; Rf = 0.44
(EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 7.98–7.90 (m, 1 H), 7.54 (td,
J = 7.7, 1.3 Hz, 1 H), 7.46–7.28 (m, 7 H), 4.99 (dd, J = 8.5, 6.4 Hz,
1 H), 3.12 (ddd, J = 13.4, 9.8, 5.3 Hz, 1 H), 2.93 (ddd, J = 13.3, 9.6,
6.1 Hz, 1 H), 2.71–2.44 (m, 2 H).
1-[3-Bromo-3-(biphenyl)propyl]-2-nitrobenzene (3h)
According to general procedure GP-A, 2-nitrobenzyl bromide
(0.030 g, 0.13 mmol,1 equiv), Cu(dap)2Cl (1.1 mg, 1 mol%), and 4-
vinylbiphenyl (0.046 g, 0.26 mmol, 2 equiv) afforded 3h (0.045 g,
82%) as a colorless oil after column purification on silica gel; Rf =
0.36 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 7.95 (dd, J = 8.5, 1.4 Hz, 1 H),
7.63–7.30 (m, 12 H), 5.05 (dd, J = 8.5, 6.5 Hz, 1 H), 3.21–3.08 (m,
1 H), 2.98 (ddd, J = 13.3, 9.5, 6.2 Hz, 1 H), 2.74–2.49 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 141.51, 135.78, 133.20, 132.20,
128.83, 128.60, 127.54, 127.29, 125.83, 125.02, 54.59, 40.49,
32.10.
13C NMR (75 MHz, CDCl3): δ = 141.52, 140.47, 140.42, 135.78,
133.71, 133.23, 132.24, 129.63, 128.84, 127.74, 127.57, 127.13,
125.53, 125.05, 54.40, 40.41, 32.18.
MS (EI, 70 eV): m/z = 321.0 [M + H]+, 319.1, 239.2, 115.1, 44.1.
MS (EI, 70 eV): m/z = 315.0 [M – HBr]+, 281.1, 167.1, 133.1, 77.1.
Synthesis 2013, 45, 2689–2698
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
Photocatalytic Radical Addition of Benzyl Halides to Olefins
2695
1-(3-Methoxy-3-(biphenyl)propyl)-2-nitrobenzene (3h′)
General procedure GP-B afforded 3h′ (0.022 g, 63%) as a yellow
gummy liquid after column purification on silica gel; Rf = 0.40
(EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 7.90 (d, J = 8.2 Hz, 1 H), 7.64–
7.54 (m, 4 H), 7.48 (m, 3 H), 7.35 (m, 5 H), 4.20 (dd, J = 8.2, 5.0
Hz, 1 H), 3.27 (s, 3 H), 3.14–3.02 (m, 1 H), 3.02–2.92 (m, 1 H),
2.24–1.95 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 149.45, 140.86, 140.82, 140.63,
137.08, 132.89, 132.02, 128.77, 127.28, 127.24, 127.09, 127.07,
127.02, 124.73, 82.99, 56.74, 38.83, 29.61.
HRMS (ESI): m/z calcd for C22H21ClNO3 + Na [M + Na]+:
370.1414; found: 370.1412.
Cu(dap)2Cl (8.8 mg, 1 mol%). The flask was purged with a stream
of N2 and MeCN (10.0 mL) was added. The resultant mixture was
degassed using freeze–pump–thaw cycles (5 ×) and flushed with
N2. The reaction mixture was internally irradiated using blue LED
rods at 530 nm. After 20 h of irradiation, the solvent was evaporated
under reduced pressure, and the crude reaction mixture was purified
by chromatography on flash silica gel to afford 3k (0.133 g, 35%)
as a colorless oil in a diastereomeric ratio of 1.3:1; Rf = 0.63
(EtOAc–hexane, 1:3).
1H NMR (400 MHz, CDCl3): δ = 8.78* (d, J = 2.3 Hz, 1 H), 8.74 (d,
J = 2.4 Hz, 1 H), 8.39–8.33 (m, 2 H), 7.60 (d, J = 8.5 Hz, 1 H),
7.55* (d, J = 8.5 Hz, 1 H), 7.34 (m, 10 H), 4.93* (d, J = 5.8 Hz, 1
H), 4.89 (d, J = 8.1 Hz, 1 H), 3.78 (dd, J = 13.5, 3.7 Hz, 1 H), 3.19*
(dd, J = 13.4, 5.5 Hz, 1 H), 2.89 (dd, J = 12.3, 7.6 Hz, 1 H), 2.83
(dd, J = 12.4, 9.2 Hz, 1 H), 2.62–2.51 (m, 1 H), 2.43–2.35* (m, 1
H), 1.05* (d, J = 6.6 Hz, 3 H), 0.76 (d, J = 6.8 Hz, 2 H); * major
diastereomer.
Ethyl 4-(3-Bromo-3-phenylpropyl)-3-nitrobenzoate (3i)
According to general procedure GP-A, ethyl 4-(bromomethyl)-3-
nitrobenzoate (0.10 g, 0.34 mmol, 1 equiv), Cu(dap)2Cl (3 mg, 1
mol%), and styrene (0.176 g, 1.7 mmol, 5 equiv) afforded 3i (0.093
g, 70%) as a light yellow liquid after column purification on silica
gel; Rf = 0.67 (EtOAc–hexane, 1:8).
13C NMR (100 MHz, CDCl3): δ = 146.67, 146.53, 142.30, 142.08,
140.05,139.96, 134.23, 133.98, 128.72, 128.58, 128.52, 128.37,
128.02, 127.86, 126.72, 126.58, 120.53, 120.30, 61.93, 61.59,
42.58, 42.25, 38.70, 37.80, 17.23, 16.61.
HRMS (ESI): m/z calcd for C16H16BrN2O [M]+: 379.0288; found:
379.0278.
FT-IR (neat): 2981, 2360, 1720, 1532, 1455, 1262, 755 cm–1.
1H NMR (300 MHz, CDCl3): δ = 8.56 (d, J = 1.7 Hz, 1 H), 8.18 (dd,
J = 8.0, 1.7 Hz, 1 H), 7.49–7.27 (m, 6 H), 4.98 (dd, J = 8.5, 6.3 Hz,
1 H), 4.41 (q, J = 7.13 Hz, 2 H), 3.17 (ddd, J = 13.4, 9.9, 5.2 Hz, 1
H), 2.98 (ddd, J = 13.3, 9.7, 6.1 Hz, 1 H), 2.70–2.44 (m, 2 H), 1.41
(t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 164.41, 149.14, 141.28, 140.33,
133.61, 132.44, 130.35, 128.89, 128.70, 127.26, 126.11, 125.79,
61.84, 54.26, 40.27, 32.20, 14.29.
1-[3-Bromo-3-(4-bromophenyl)propyl]-2,4-dinitrobenzene (3l)
According to general procedure GP-A, 2,4-dinitrobenzyl bromide
(0.040 g, 0.15 mmol, 1 equiv), Cu(dap)2Cl (1.3 mg, 1 mol%), and
4-bromostyrene (0.082 g, 0.45 mmol, 3 equiv) afforded 3l (0.057 g,
86%) as a colorless oil after column purification on silica gel; Rf =
0.17 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.81 (d, J = 2.3 Hz, 1 H), 8.39 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.61 (d, J = 8.5 Hz, 1 H), 7.55–7.45 (m, 2 H),
7.29 (m, 2 H), 4.93 (dd, J = 8.6, 6.2 Hz, 1 H), 3.23 (ddd, J = 13.4,
10.1, 5.2 Hz, 1 H), 3.03 (ddd, J = 13.3, 10.0, 6.0 Hz, 1 H), 2.67–2.41
(m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 149.04, 146.72, 142.52, 140.05,
133.53, 132.13, 128.88, 127.28, 122.74, 120.65, 52.66, 40.06,
32.26.
HRMS (ESI): m/z calcd for C18H18BrNO4 [M]+: 391.0419; found:
391.0417.
1-(3-Bromo-3-phenylpropyl)-2,4-dinitrobenzene (3j)
According to general procedure GP-A, 2,4-dinitrobenzyl bromide
(0.130 g, 0.5 mmol, 1 equiv), Cu(dap)2Cl (4.4 mg, 1 mol%), and sty-
rene (0.260 g, 2.50 mmol, 5 equiv) afforded 3j (0.162 g, 89%) as a
yellow liquid after column purification on silica gel; Rf = 0.51
(EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.79 (s, 1 H), 8.38 (dd, J = 8.5, 2.2
Hz, 1 H), 7.61 (d, J = 8.5 Hz, 1 H), 7.47–7.27 (m, 5 H), 4.98 (dd,
J = 8.5, 6.3 Hz, 1 H), 3.25 (ddd, J = 13.5, 10.0, 5.2 Hz, 1 H), 3.05
(ddd, J = 13.4, 9.9, 6.1 Hz, 1 H), 2.72–2.45 (m, 2 H).
MS (EI, 70 eV): m/z = 444.0 [M]+, 422.0, 364.9, 350.2, 283.2.
1-[3-Methoxy-3-(4-bromophenyl)propyl]-2,4-dinitrobenzene
(3l′)
General procedure GP-B afforded 3l′ (0.029 g, 82%) as a yellow oil
after column purification on silica gel; Rf = 0.46 (EtOAc–hexane,
2:8).
1H NMR (300 MHz, CDCl3): δ = 8.76 (d, J = 2.4 Hz, 1 H), 8.35 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.56 (d, J = 8.5 Hz, 1 H), 7.52–7.45 (m, 2 H),
7.20–7.13 (m, 2 H), 4.12 (dd, J = 8.2, 4.7 Hz, 1 H), 3.21 (s, 3 H),
3.18–2.96 (m, 2 H), 2.14–1.92 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 149.23, 146.34, 144.14, 140.31,
133.33, 131.79, 128.21, 126.93, 121.76, 120.35, 82.33, 56.78,
38.46, 29.69.
13C NMR (75 MHz, CDCl3): δ = 149.06, 146.64, 142.78, 141.00,
133.54, 128.96, 128.84, 128.73, 127.22, 120.58, 53.92, 40.17,
32.27.
MS (EI, 70 eV): m/z = 285.0 [M – HBr]+, 193.1, 179.0, 91.0.
1-(3-Methoxy-3-phenylpropyl)-2,4-dinitrobenzene (3j′)
General procedure GP-B afforded 3j′ (0.026 g, 75%) as a light yel-
low liquid after column purification on silica gel; Rf = 0.51 (EtOAc–
hexane, 2:8).
1H NMR (300 MHz, CDCl3): δ = 8.75 (d, J = 2.4 Hz, 1 H), 8.34 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.56 (d, J = 8.5 Hz, 1 H), 7.47–7.19 (m, 5 H),
4.15 (dd, J = 8.2, 4.8 Hz, 1 H), 3.21 (s, 3 H), 3.20–3.11 (m, 1 H),
3.11–2.96 (m, 1 H), 2.20–1.94 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 149.24, 146.28, 144.39, 141.19,
133.32, 128.63, 127.97, 126.86, 126.52, 120.30, 82.93, 56.69,
38.53, 29.75.
HRMS (ESI): m/z calcd for C16H16N2O5 + Na [M + Na]+: 339.0951;
found: 339.0952.
HRMS (ESI): m/z calcd for C16H15BrN2O5 [M]+: 394.0164; found:
394.0150.
1-[3-Bromo-3-(3-chlorophenyl)propyl]-2,4-dinitrobenzene
(3m)
According to general procedure GP-A, 2,4-dinitrobenzyl bromide
(0.040 g, 0.15 mmol, 1 equiv), Cu(dap)2Cl (1.3 mg, 1 mol%), and
3-chlorostyrene (0.062 g, 0.45 mmol, 3 equiv) afforded 3m (0.058
g, 95%) as a very light yellow oil after column purification on silica
gel; Rf = 0.63 (EtOAc–hexane, 2:8).
1H NMR (300 MHz, CDCl3): δ = 8.81 (d, J = 2.3 Hz, 1 H), 8.40 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.62 (d, J = 8.5 Hz, 1 H), 7.37 (d, J = 15.3 Hz,
1 H), 7.34–7.27 (m, 3 H), 4.91 (dd, J = 8.7, 6.0 Hz, 1 H), 3.26 (ddd,
1-(3-Bromo-2-methyl-3-phenylpropyl)-2,4-dinitrobenzene (3k)
An oven-dried Schlenk flask equipped with magnetic stir bar was
charged with 2,4-dinitrobenzyl bromide (0.261 mg 1.00 mmol, 1.0
equiv), trans-β-methylstyrene (0.590 mg, 5.0 mmol, 5.0 equiv), and
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2689–2698

2696
S. Paria et al.
SPECIAL TOPIC
MS (EI, 70 eV): m/z = 361.1 [M – HBr]+, 280.2, 242.2.
J = 13.4, 10.0, 5.1 Hz, 1 H), 3.05 (ddd, J = 13.3, 9.9, 6.1 Hz, 1 H),
2.69–2.40 (m, 2 H).
2-(1-Methoxy-3-(biphenyl)propyl]-2,4-dinitrobenzene (3o′)
General procedure GP-B afforded 3o′ (0.021 g, 59%) as a yellow oil
after column purification on silica gel; Rf = 0.42 (EtOAc–hexane,
2:8).
1H NMR (300 MHz, CDCl3): δ = 8.76 (d, J = 2.3 Hz, 1 H), 8.35 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.59 (dd, J = 8.3, 2.6 Hz, 5 H), 7.49–7.39 (m,
2 H), 7.39–7.31 (m, 3 H), 4.21 (dd, J = 8.2, 4.8 Hz, 1 H), 3.26 (s, 3
H), 3.24–3.15 (m, 1 H), 3.14–3.01 (m, 1 H), 2.25–1.96 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 149.28, 146.29, 144.38, 140.92,
140.69, 140.22, 133.34, 128.82, 127.39, 127.37, 127.08, 126.97,
126.87, 120.32, 82.69, 56.77, 38.52, 29.80.
HRMS (ESI): m/z calcd for C22H20N2O5 + Na [M + Na]+: 415.1264;
found: 415.1266.
13C NMR (75 MHz, CDCl3): δ = 149.04, 146.73, 142.95, 142.50,
134.72, 133.53, 130.25, 128.97, 127.45, 127.27, 125.43, 120.65,
52.43, 40.03, 32.23.
MS (EI, 70 eV): m/z = 362.1 [M – HCl]+, 358.0.
1-[3-Methoxy-3-(3-chlorophenyl)propyl]-2,4-dinitrobenzene
(3m′)
General procedure GP-B afforded 3m′ (0.027 g, 77%) as a yellow
gummy liquid after column purification on silica gel; Rf = 0.58
(EtOAc–hexane, 2:8).
1H NMR (300 MHz, CDCl3): δ = 8.76 (d, J = 2.3 Hz, 1 H), 8.35 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.56 (d, J = 8.5 Hz, 1 H), 7.32–7.24 (m, 3 H),
7.19–7.13 (m, 1 H), 4.13 (dd, J = 8.1, 4.8 Hz, 1 H), 3.23 (s, 3 H),
3.20–2.98 (m, 2 H), 2.18–1.92 (m, 2 H).
1-(3-Chloro-3-phenylpropyl)-2,4-dinitrobenzene (3p)
According to general procedure GP-A, 2,4-dinitrobenzyl chloride
(0.049 g, 0.23 mmol, 1 equiv), Cu(dap)2Cl (2.0 mg, 1 mol%), and
styrene (0.119 g, 1.15 mmol, 5 equiv) afforded 3p (0.038 g, 51%)
as a light yellow liquid after column purification on silica gel; Rf =
0.32 (EtOAc–hexane, 1:9).
13C NMR (75 MHz, CDCl3): δ = 149.25, 146.36, 144.11, 143.53,
134.63, 133.34, 129.98, 128.12, 126.92, 126.56, 124.67, 120.35,
82.36, 56.91, 38.49, 29.68.
HRMS (ESI): m/z calcd for C16H15ClN2O5 + Na [M + Na]+:
373.0562, found: 373.0561.
1H NMR (300 MHz, CDCl3): δ = 8.79 (d, J = 2.3 Hz, 1 H), 8.38 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.62 (m, 1 H), 7.48–7.28 (m, 5 H), 4.91 (dd,
J = 8.3, 5.9 Hz, 1 H), 3.26 (ddd, J = 13.5, 9.5, 5.7 Hz, 1 H), 3.07
(ddd, J = 13.4, 9.4, 6.6 Hz, 1 H), 2.59–2.30 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 149.10, 146.62, 142.98, 140.61,
133.53, 128.89, 128.75, 127.17, 126.86, 120.57, 62.63, 40.22,
31.12.
2-[1-Bromo-3-(2,4-dinitrophenyl)propyl]naphthalene (3n)
According to general procedure GP-A, 2,4-dinitrobenzyl bromide
(0.040 g, 0.15 mmol, 1 equiv), Cu(dap)2Cl (1.3 mg, 1 mol%), and
2-vinylnaphthalene (0.082 g, 0.30 mmol, 2 equiv) afforded 3n
(0.064 g, 81%) as a yellow liquid after column purification on silica
gel; Rf = 0.23 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.79 (d, J = 2.4 Hz, 1 H), 8.36 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.91–7.76 (m, 4 H), 7.64–7.46 (m, 4 H), 5.17
(dd, J = 8.3, 6.6 Hz, 1 H), 3.28 (ddd, J = 13.4, 10.0, 5.2 Hz, 1 H),
3.06 (ddd, J = 13.3, 9.8, 6.2 Hz, 1 H), 2.82–2.56 (m, 2 H).
HRMS (ESI): m/z calcd for C18H13ClN2O4 [M]+: 320.0522; found:
320.0524.
1-[3-Chloro-3-(3-chlorophenyl)propyl]-2,4-dinitrobenzene (3q)
According to general procedure GP-A, 2,4-dinitrobenzyl chloride
(0.040 g, 0.18 mmol, 1 equiv), Cu(dap)2Cl (1.5 mg, 1 mol%), and
3-chlorostyrene (0.074 g, 0.54 mmol, 3 equiv) afforded 3q (0.060 g,
92%) as a light yellow oil after column purification on silica gel;
Rf = 0.70 (EtOAc–hexane, 2:8).
1H NMR (300 MHz, CDCl3): δ = 8.80 (d, J = 2.3 Hz, 1 H), 8.39 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.61 (d, J = 8.5Hz, 1 H), 7.39 (s, 1 H), 7.34–
7.22 (m, 3 H), 4.87 (dd, J = 8.1, 6.0 Hz, 1 H), 3.27 (ddd, J = 13.4,
9.3, 6.0 Hz, 1 H), 3.08 (ddd, J = 13.4, 9.1, 6.9 Hz, 1 H), 2.48–2.37
(m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 149.08, 146.70, 142.68, 142.56,
134.73, 133.54, 130.18, 128.89, 127.24, 127.12, 125.06, 120.63,
61.62, 40.13, 31.05.
HRMS (ESI): m/z calcd for C15H12Cl2N2O4 + Na [M + Na]+:
377.0778; found: 377.0777.
13C NMR (75 MHz, CDCl3): δ = 149.04, 146.61, 142.74, 138.12,
133.54, 133.31, 132.99, 129.13, 128.08, 127.76, 127.16, 126.83,
126.75, 126.17, 124.74, 120.58, 54.25, 40.05, 32.34.
MS (EI, 70 eV): m/z = 300.1, 254.2, 178.0, 156.1, 127.1.
2-[1-Methoxy-3-(2,4-dinitrophenyl)propyl]naphthalene (3n′)
General procedure GP-B afforded 3n′ (0.025 g, 71%) as a light yel-
low liquid after column purification on silica gel; Rf = 0.53 (EtOAc–
hexane, 2:8).
1H NMR (300 MHz, CDCl3): δ = 8.70 (d, J = 2.4 Hz, 1 H), 8.28 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.87–7.72 (m, 3 H), 7.67 (s, 1 H), 7.54–7.33
(m, 4 H), 4.28 (dd, J = 8.2, 4.9 Hz, 1 H), 3.21 (s, 3 H), 3.20–3.10
(m, 1 H), 3.02 (ddd, J = 13.4, 9.5, 6.3 Hz, 1 H), 2.25–1.99 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 148.20, 145.23, 143.30, 137.52,
132.29, 132.19, 127.63, 126.79, 126.73, 125.81, 125.29, 125.04,
124.85, 122.98, 121.16, 119.27, 82.05, 55.74, 37.30, 28.77.
HRMS (ESI): m/z calcd for C20H18N2O5 [M]+: 366.1216; found:
366.1215.
1-(3-Chloro-3-p-tolylpropyl)-2,4-dinitrobenzene (3r)
According to general procedure GP-A, 2,4-dinitrobenzyl chloride
(0.030 g, 0.13 mmol, 1 equiv), Cu(dap)2Cl (1.1 mg, 1 mol%), and
4-methylstyrene (0.046 g, 0.39 mmol, 3 equiv) afforded 3r (0.043
g, 93%) as a light yellow oil after column purification on silica gel;
Rf = 0.25 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.79 (d, J = 2.4 Hz, 1 H), 8.38 (dd,
J = 8.4, 2.3 Hz, 1 H), 7.60 (d, J = 8.5 Hz, 1 H), 7.31–7.24 (m, 2 H),
7.21–7.14 (m, 2 H), 4.89 (dd, J = 8.3, 6.0 Hz, 1 H), 3.24 (ddd,
J = 13.5, 9.6, 5.6 Hz, 1 H), 3.12–2.99 (m, 1 H), 2.51–2.38 (m, 2 H),
2.38–2.30 (m, 3 H).
13C NMR (75 MHz, CDCl3): δ = 149.11, 146.59, 143.05, 138.71,
137.66, 133.53, 129.54, 127.15, 126.78, 120.55, 62.62, 40.13,
31.15, 21.18.
HRMS (ESI): m/z calcd for C16H16ClN2O4 [M + H]+: 335.0793;
found: 335.0797.
2-[1-Bromo-3-(biphenyl)propyl]-2,4-dinitrobenzene (3o)
According to general procedure GP-A, 2,4-dinitrobenzyl bromide
(0.040 g, 0.15 mmol, 1 equiv), Cu(dap)2Cl (1.3 mg, 1 mol%), and
4-vinylbiphenyl (0.055 g, 0.30 mmol, 2 equiv) afforded 3o (0.061
g, 90%) as a light yellow liquid after column purification on silica
gel; Rf = 0.38 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.81 (d, J = 2.3 Hz, 1 H), 8.39 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.68–7.52 (m, 6 H), 7.51–7.31 (m, 6 H), 5.04
(dd, J = 8.5, 6.3 Hz, 1 H), 3.28 (ddd, J = 13.3, 10.0, 5.2 Hz, 1 H),
3.09 (ddd, J = 13.3, 9.8, 6.1 Hz, 1 H), 2.76–2.50 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 149.07, 146.66, 142.77, 141.79,
140.23, 139.93, 133.57, 128.89, 127.67, 127.60, 127.35, 127.22,
127.11, 120.62, 53.72, 40.10, 32.34.
Synthesis 2013, 45, 2689–2698
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
Photocatalytic Radical Addition of Benzyl Halides to Olefins
2697
4-[3-Bromo-3-(naphthalen-6-yl)propyl]-2-chloroquinoline (3s)
According to general procedure GP-A, 4-(bromomethyl)-2-chloro-
quinoline (0.040 g, 0.11 mmol, 1 equiv), Cu(dap)2Cl (0.98 mg, 1
mol%), and 2-vinylnaphthalene (0.033 g, 0.22 mmol, 2 equiv) af-
forded 3s (0.030 g, 66%) as a colorless oil after column purification
on silica gel; Rf = 0.28 (EtOAc–hexane, 1:9).
1H NMR (300 MHz, CDCl3): δ = 8.06–8.01 (m, 1 H), 7.95 (d,
J = 8.4 Hz, 1 H), 7.91–7.67 (m, 6 H), 7.61–7.47 (m, 4 H), 5.19 (dd,
J = 8.5, 6.2 Hz, 1 H), 3.43–3.30 (m, 1 H), 3.17–3.04 (m, 1 H), 2.91–
2.75 (m, 1 H), 2.64 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 150.61, 149.90, 148.13, 138.41,
133.32, 133.02, 130.44, 129.51, 129.11, 128.09, 127.77, 127.03,
126.79, 126.73, 126.18, 125.98, 124.81, 123.42, 121.86, 54.65,
39.66, 30.72.
afforded 5c (0.040 g, 90%) as a yellow liquid after column purifica-
tion on silica gel; Rf = 0.46 (EtOAc–hexane, 2:8).
FT-IR (neat): 3080, 2361, 1686, 1604, 1531, 1348, 748 cm–1.
1H NMR (300 MHz, CDCl3): δ = 8.79 (d, J = 2.4 Hz, 1 H), 8.36 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.92 (dd, J = 5.2, 3.4 Hz, 2 H), 7.76 (d, J = 8.5
Hz, 1 H), 7.56 (ddd, J = 6.6, 3.8, 1.2 Hz, 1 H), 7.44 (dd, J = 10.4,
4.7 Hz, 2 H), 3.44 (s, 4 H).
13C NMR (75 MHz, CDCl3): δ = 197.54, 149.28, 146.57, 143.64,
136.20, 134.26, 133.61, 128.79, 128.05, 127.09, 120.42, 38.71,
27.54.
HRMS (ESI): m/z calcd for C15H12N2O5 [M]+: 300.0746; found:
300.0751.
Ethyl 3-Nitro-4-(3-oxo-3-phenylpropyl)benzoate (5d)
MS (EI, 70 eV): m/z = 300.9, 222.0, 140.1, 44.0.
According to general procedure GP-A, ethyl 4-(bromomethyl)-3-
nitrobenzoate (0.050 g, 0.17 mmol, 1 equiv), Cu(dap)2Cl (1.5 mg, 1
mol%), and (1-phenylvinyloxy)trimethylsilane (0.098 g, 0.51
mmol, 3 equiv) afforded 5d (0.046 g, 81%) as a yellow liquid after
column purification on silica gel; Rf = 0.20 (EtOAc–hexane, 1:9).
4-[3-Methoxy-3-(naphthalen-6-yl)propyl]-2-chloroquinoline
(3s′)
General procedure GP-B afforded 3s′ (0.018 g, 83%) as a colorless
oil after column purification on silica gel; Rf = 0.71 (EtOAc–
hexane, 2:8).
FT-IR (neat): 2927, 2360, 1721, 1686, 1449, 1263, 743 cm–1.
1H NMR (300 MHz, CDCl3): δ = 8.02 (dd, J = 8.4, 0.6 Hz, 1 H),
7.98–7.91 (m, 1 H), 7.90–7.80 (m, 3 H), 7.76–7.66 (m, 2 H), 7.56–
7.42 (m, 4 H), 7.24 (s, 1 H), 4.33 (dd, J = 8.0, 4.9 Hz, 1 H), 3.30 (s,
3 H), 3.27–3.18 (m, 1 H), 3.18–3.03 (m, 1 H), 2.40–2.23 (m, 1 H),
2.22–2.06 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 151.59, 150.64, 148.07, 138.82,
133.23, 130.23, 129.34, 128.64, 127.84, 127.78, 126.75, 126.32,
126.26, 126.04, 125.97, 124.14, 123.69, 121.68, 82.95, 56.85,
38.02, 28.22.
1H NMR (300 MHz, CDCl3): δ = 8.54 (d, J = 1.7 Hz, 1 H), 8.13 (dd,
J = 8.0, 1.8 Hz, 1 H), 7.94–7.88 (m, 2 H), 7.56–7.49 (m, 2 H), 7.45–
7.37 (m, 2 H), 4.37 (q, J = 7.1 Hz, 2 H), 3.42–3.29 (m, 4 H), 1.37 (t,
J = 7.13 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 198.04, 164.46, 149.33, 141.19,
136.41, 133.62, 133.40, 132.95, 130.25, 128.72, 128.07, 126.01,
61.79, 39.09, 27.72, 14.30.
HRMS (ESI): m/z calcd for C18H18NO5 [M + H]+: 328.1179; found:
328.1184.
HRMS (ESI): m/z calcd for C23H21ClNO [M + H]+: 362.1306;
found: 362.1309.
2-(2,4-Dinitrobenzyl)cyclopentanone (5e)
According to general procedure GP-A, 2,4-dinitrobenzyl bromide
(0.050 g, 0.19 mmol, 1 equiv), Cu(dap)2Cl (1.6 mg, 1 mol%), and
(cyclopentenyloxy)trimethylsilane (0.089 g, 0.57 mmol, 3 equiv)
afforded 5e (0.025 g, 50%) as a yellow liquid after column purifica-
tion on silica gel; Rf = 0.21 (EtOAc–hexane, 2:8).
3-(4-Nitrophenyl)-1-phenylpropan-1-one (5a)21
According to general procedure GP-A, 4-nitrobenzyl bromide
(0.040 g, 0.18 mmol, 1 equiv), Cu(dap)2Cl (1.5 mg, 1 mol%), and
(1-phenylvinyloxy)trimethylsilane (0.103 g, 0.54 mmol, 3 equiv)
afforded 5a (0.041 g, 87%) as a yellow solid after column purifica-
tion on silica gel; mp 157–159 °C (Lit.21 mp 161–163 °C); Rf = 0.30
(EtOAc–hexane, 1:9).
FT-IR (neat): 3104, 2362, 1685, 1604, 1531, 1209, 835 cm–1.
1H NMR (300 MHz, CDCl3): δ = 8.78 (d, J = 2.3 Hz, 1 H), 8.37 (dd,
J = 8.5, 2.4 Hz, 1 H), 7.65 (d, J = 8.5 Hz, 1 H), 3.47 (dd, J = 13.8,
6.1 Hz, 1 H), 2.99 (dd, J = 13.8, 7.6 Hz, 1 H), 2.59–2.25 (m, 2 H),
2.25–1.99 (m, 3 H), 1.91–1.70 (m, 1 H), 1.70–1.47 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 218.27, 149.29, 146.57, 142.45,
134.17, 126.88, 120.38, 49.90, 37.48, 32.61, 29.62, 20.44.
1H NMR (300 MHz, CDCl3): δ = 8.15 (dd, J = 8.9, 2.2 Hz, 2 H),
7.95 (dd, J = 8.4, 1.3 Hz, 2 H), 7.60–7.41 (m, 5 H), 3.37 (dd,
J = 10.8, 4.0 Hz, 2 H), 3.19 (t, J = 7.2 Hz, 2 H).
13C NMR (75 MHz, CDCl3): δ = 198.14, 149.21, 136.51, 133.42,
129.39, 128.74, 128.01, 124.34, 123.80, 39.42, 29.74.
HRMS (ESI): m/z calcd for C12H13N2O5 [M + H]+: 265.0819; found:
265.0819.
MS (EI, 70 eV): m/z = 255.1 (24.7, [M]+), 105.1 (100.0).
3-(2-Nitrophenyl)-1-phenylpropan-1-one (5b)21
1,2,3,4-Tetrahydro-2-phenylquinoline (6a)22
According to general procedure GP-A, 2-nitrobenzyl bromide
(0.216 g, 1.00 mmol, 1 equiv), Cu(dap)2Cl (8.8 mg, 1 mol%), and
(1-phenylvinyloxy)trimethylsilane (0.576 g, 3.00 mmol, 3 equiv)
afforded 5b (0.198 g, 78%) as a light yellow solid after column pu-
rification on silica gel; mp 104–106 °C (Lit.21 mp 111–112 °C);
Rf = 0.40 (EtOAc–hexane, 1:9).
According to general procedure GP-C, ATRA product 3e (0.150 g,
0.46 mmol, 1 equiv), FeCl3·6H2O (0.379 g, 1.40 mmol, 3 equiv),
and Zn dust (0.305 g, 4.68 mmol, 10 equiv) afforded 6a (0.075 g,
75%) as a colorless liquid after column purification on silica gel.
1H NMR (300 MHz, CDCl3): δ = 7.45–7.24 (m, 5 H), 7.02 (t,
J = 7.0 Hz, 2 H), 6.67 (td, J = 7.4, 1.0 Hz, 1 H), 6.60–6.53 (m, 1 H),
4.45 (dd, J = 9.3, 3.3 Hz, 1 H), 4.16 (br, 1 H), 2.94 (ddd, J = 16.2,
10.5, 5.5 Hz, 1 H), 2.75 (dt, J = 16.4, 4.8 Hz, 1 H), 2.20–1.93 (m, 2
H).
13C NMR (75 MHz, CDCl3): δ = 144.65, 144.51, 129.33, 128.60,
127.49, 126.93, 126.60, 121.05, 117.36, 114.16, 56.30, 30.93,
26.39.
1H NMR (300 MHz, CDCl3): δ = 8.20–7.92 (m, 3 H), 7.75–7.36 (m,
6 H), 3.65–3.27 (m, 4 H).
13C NMR (75 MHz, CDCl3): δ = 198.54, 149.34, 136.59, 136.57,
133.33, 133.27, 132.66, 128.67, 128.10, 127.49, 124.93, 39.46,
27.79.
MS (EI, 70 eV): m/z = 255.1 (24.7) [M]+), 105.1 (100.0).
MS (ESI): m/z calcd for C16H17N [M + H]+: 210.1; found: 210.0
3-(2,4-Dinitrophenyl)-1-phenylpropan-1-one (5c)
According to general procedure GP-A, 2,4-dinitrobenzyl bromide
(0.040 g, 0.15 mmol, 1 equiv), Cu(dap)2Cl (1.3 mg, 1 mol%), and
(1-phenylvinyloxy)trimethylsilane (0.086 g, 0.45 mmol, 3 equiv)
2-(4-Bromophenyl)-1,2,3,4-tetrahydroquinoline (6b)22
According to general procedure GP-C, ATRA product 3f (0.053 g,
0.13 mmol, 1 equiv), FeCl3·6H2O (0.107 g, 0.39 mmol, 3 equiv),
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2689–2698

2698
S. Paria et al.
SPECIAL TOPIC
and Zn dust (0.086 g, 1.32 mmol, 10 equiv) afforded 6b (0.027 g,
72%) as a colorless liquid after column purification on silica gel.
M.-H.; Spleterz, E.; Seong, C. M.; Chang, C.-T. J. Am.
Chem. Soc. 1989, 111, 8872. (d) Curran, D. P.; Seong, C. M.
J. Am. Chem. Soc. 1990, 112, 9401. (e) Curran, D. P.;
Tamine, J.
J. Org. Chem. 1991, 56, 2746. (f) Curran, D. P.; Kim, D.
Tetrahedron 1991, 47, 6171.
1H NMR (300 MHz, CDCl3): δ = 7.52–7.44 (m, 2 H), 7.27 (d,
J = 8.6 Hz, 2 H), 7.02 (t, J = 7.8 Hz, 2 H), 6.68 (t, J = 7.4 Hz, 1 H),
6.56 (d, J = 7.9 Hz, 1 H), 4.41 (dd, J = 9.1, 3.3 Hz, 1 H), 3.03–2.82
(m, 1 H), 2.72 (dt, J = 16.5, 4.9 Hz, 1 H), 2.22–2.04 (m, 1 H), 2.04–
1.86 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 141.02, 143.58, 131.64, 129.31,
128.33, 126.98, 121.13, 121.03, 117.73, 114.33, 55.69, 30.78,
26.06.
(4) Clark, A. J. Chem. Soc. Rev. 2002, 31, 1.
(5) Kameyama, M.; Kamigata, N.; Kobayashi, M. J. Org. Chem.
1987, 52, 3312; and references cited therein.
(6) Forti, L.; Ghelfi, F.; Libertini, E.; Pagnoni, U. M.; Soragni,
E. Tetrahedron 1991, 53, 17761.
MS (ESI): m/z calcd for C15H15BrN [M + H]+: 288.0; found: 288.0.
(7) Gossage, R. A.; Van De Kuil, L. A.; Van Koten, G. Acc.
Chem. Res. 1998, 31, 423.
2-(3-Chlorophenyl)-1,2,3,4-tetrahydroquinoline (6c)23
(8) (a) Matyjaszewski, K.; Jakubowski, W.; Min, K.; Tang, W.;
Huang, J.; Braunecker, W. A.; Tsarevsky, N. V. Proc. Natl.
Acad. Sci. U.S.A. 2006, 103, 15309. (b) Pintauer, T.;
Matyjaszewski, K. Chem. Soc. Rev. 2008, 37, 1087.
(c) Tsarevsky, N. V.; Matyjaszewski, K. Chem. Rev. 2007,
107, 2270. (d) Wang, J. S.; Matyjaszewski, K. J. Am. Chem.
Soc. 1995, 117, 5614.
(9) For recent reviews, see: (a) Teply, F. Collect. Czech. Chem.
Commun. 2011, 76, 859. (b) Narayanam, J. M. R.;
Stephenson, C. R. J. Chem. Soc. Rev. 2011, 40, 102.
(c) Yoon, T. P.; Ischay, M. A.; Du, J. Nat. Chem. 2010, 2,
527. (d) Zeitler, K. Angew. Chem. Int. Ed. 2009, 48, 9785.
(e) Ravelli, D.; Dondi, D.; Fagnoni, M.; Albini, A. Chem.
Soc. Rev. 2009, 38, 1999. (f) Fagnoni, M.; Dondi, D.;
Ravello, D.; Albini, A. Chem. Rev. 2007, 107, 2725.
(10) Nguyen, J. D.; Tucker, J. W.; Konieczynska, M. D.;
Stephenson, C. R. J. J. Am. Chem. Soc. 2011, 133, 4160.
(11) Wallentin, C. J.; Nguyen, J. D.; Finkbeiner, P.; Stephenson,
C. R. J. J. Am. Chem. Soc. 2012, 134, 8875.
(12) Kern, J. M.; Sauvage, J. P. J. Chem. Soc., Chem. Commun.
1987, 546.
(13) Pirtsch, M.; Paria, S.; Matsuno, T.; Isobe, H.; Reiser, O.
Chem. Eur. J. 2012, 18, 7336.
(14) Shih, H. W.; Vander Wal, M. N.; Grange, R. L.; MacMillan,
D. W. C. J. Am. Chem. Soc. 2010, 132, 13600.
(15) Balili, M. N. C.; Pintauer, T. Dalton Trans. 2011, 40, 3060.
(16) Slinker, J. D.; Gorodetsky, A. A.; Lowry, M. S.; Wang, J.;
Parker, J. S.; Rohl, R.; Bernhard, S.; Malliaras, G. G. J. Am.
Chem. Soc. 2004, 126, 2763.
According to general procedure GP-C, ATRA product 3g (0.038 g,
0.10 mmol, 1 equiv), FeCl3·6H2O (0.086 g, 0.30 mmol, 3 equiv),
and Zn dust (0.069 g, 1.0 mmol, 10 equiv) afforded 6c (0.018 g,
70%) as a yellow oil after column purification on silica gel.
1H NMR (300 MHz, CDCl3): δ = 7.36 (s, 1 H), 7.27–7.18 (m, 3 H),
6.98 (m, 2 H), 6.65 (t, J = 7.4 Hz, 1 H), 6.54 (d, J = 7.8 Hz, 1 H),
4.38 (dd, J = 9.1, 3.4 Hz, 1 H), 2.87 (ddd, J = 16.0, 10.4, 5.5 Hz, 1
H), 2.68 (dt, J = 16.4, 4.9 Hz, 1 H), 2.08 (ddd, J = 10.1, 8.6, 5.1 Hz,
1 H), 2.02–1.86 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 146.79, 144.07, 134.45, 129.87,
129.34, 127.61, 127.02, 126.77, 124.80, 120.99, 117.69, 114.30,
55.82, 30.86, 26.12.
MS (ESI): m/z calcd for C15H15ClN [M + H]+: 244.0; found: 244.0.
Procedure for the Reduction of Ketone with Pd/C20
Ketone 5b (150 mg, 0.58 mmol, 1 equiv) was dissolve in EtOH (3
mL) and of 5% Pd/C (23.2 mg) was added. H2 gas was passed
through the solution for 5 min and the mixture was stirred at r.t. for
3 h under H2 atmosphere. After completion of the reaction (moni-
tored by TLC), the mixture was filtered through a Celite bed, the fil-
trate was concentrated in vacuo, and the residue was subjected to
column chromatography to obtain 6a (81 mg, 67%) as a colorless
liquid. For physical and spectral data see above.
Acknowledgment
This work was supported by the Deutsche Forschungsgemeinschaft
(Graduiertenkolleg Photocatalysis 1626).
(17) Benzyl bromide (E1/2 = –1.85 V vs SCE in MeCN):
(a) Koch, D. A.; Henne, B. J.; Bartak, D. E. J. Electrochem.
Soc. 1987, 134, 3062. (b) Lawless, J. G.; Bartak, D. E.;
Hawley, M. D. J. Am. Chem. Soc. 1969, 91, 7121.
(18) Pham, P. V.; Nagib, D. A.; MacMillan, D. W. C. Angew.
Chem. Int. Ed. 2011, 50, 6119.
(19) Desai, D. G.; Swami, S. S.; Hapase, S. B. Synth. Commun.
1999, 29, 1033.
(20) Zhang, F.; Jin, J.; Zhong, X.; Li, S.; Niu, J.; Li, R.; Ma, J.
Green Chem. 2011, 13, 1238.
(21) Cromwell, N. H.; Mercer, G. D. J. Am. Chem. Soc. 1957, 79,
3815.
(22) Guo, Q.-S.; Du, D.-M.; Xu, J. X. Angew. Chem. Int. Ed.
2008, 47, 759.
(23) Wang, T.; Zhuo, L. G.; Li, Z.; Chen, F.; Ding, Z.; He, Y.;
Fan, Q. H.; Xiang, J.; Yu, Z. X.; Chan, A. S. C. J. Am. Chem.
Soc. 2011, 133, 9878.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnuIomprifgtooatrinSugpIoi
n
nfomartit
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Synthesis 2013, 45, 2689–2698
© Georg Thieme Verlag Stuttgart · New York