A Metal-Free Approach for Bronsted Acid Promoted C-H Alkylation of Heteroarenes with Alkyl Peroxides

Article abstract of DOI:10.1055/s-0037-1609965

A metal-free protocol for Minisci C-H alkylation of heteroarenes using alkyl peroxides as the alkylating reagents and internal oxidants simultaneously under promotion of Bronsted acid has been demonstrated. A series of alkyl substituted heteroarenes were readily prepared by the C-H alkylation in moderate to good yields. A possible pathway involving the addition of alkyl radical to heterocycle followed by rearomatization is described.

Full text of DOI:10.1055/s-0037-1609965

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2018, 50, A–G
paper
A
en
Y. Zeng et al.
Paper
Synthesis
A Metal-Free Approach for Brønsted Acid Promoted C–H Alkyl-
ation of Heteroarenes with Alkyl Peroxides
Yuehua Zenga,b
Bo Qian*a
Yajun Li a
O
Brønsted acid
Alkyl
+
O
Het
Het
Alkyl
O
R
metal-free
R = COAlkyl or tBu
24 examples
up to 89% yield
Hongli Bao*a
0
0
0
0
0-
0
0
3
1-
0
3
0
5-
0
8
9
a Key Laboratory of Coal to Ethylene Glycol and Its Related Technology,
Center for Excellence in Molecular Synthesis, Fujian Institute of
Research on the Structure of Matter, University of Chinese Academy
of Sciences, 155 Yangqiao Road West, Fuzhou, Fujian 350002,
People’s Republic of China
hlbao@fjirsm.ac.cn
qianbo@fjirsm.ac.cn
b College of Chemistry and Materials Science, Fujian Normal University,
Fuzhou, Fujian 350108, People’s Republic of China
Received: 28.03.2018
Accepted after revision: 16.04.2018
Published online: 29.05.2018
tential in the synthesis of drug molecules, avoiding the tox-
icity of the metal to the protein. The key challenges might
be the appropriate coupling partner of heteroarenes and
the matched oxidant under mild reaction conditions. To
further broaden the metal-free method for Minisci C–H
alkylation of heteroarenes and enhance the diversity of
alkylating reagent, we herein employed alkyl peroxides as
general alkyl groups and internal oxidants simultaneously
to construct various alkyl-substituted heteroarenes via the
promotion of a Brønsted acid.
DOI: 10.1055/s-0037-1609965; Art ID: ss-2018-h0215-op
Abstract A metal-free protocol for Minisci C–H alkylation of hetero-
arenes using alkyl peroxides as the alkylating reagents and internal oxi-
dants simultaneously under promotion of Brønsted acid has been
demonstrated. A series of alkyl substituted heteroarenes were readily
prepared by the C–H alkylation in moderate to good yields. A possible
pathway involving the addition of alkyl radical to heterocycle followed
by rearomatization is described.
Aiming at the exploration of C–H alkylation of het-
eroarenes, 2-methylquinoline (1a) and lauryl peroxide
(LPO, 2a) were used as the model substrates for the optimi-
zation of reaction conditions (Table 1). Initially, various
Brønsted acids, such as TsOH·H2O, TFA, MsOH, H2SO4, AcOH,
and TfOH, were investigated under 80 °C for 12 hours. To
our delight, 71% yield of alkylation product 3a was obtained
when using TfOH as the Brønsted acid (Table 1, entries 1–6).
Screening of solvent indicated that MeCN was the optimal
one (entries 7–10). Either increasing or decreasing the reac-
tion temperature would lead to a lower yield of the product
3a (entries 11–13). After testing for the amount of acid, one
equivalent was found to be the most suitable for this trans-
formation (entries 14–16). The control experiment suggest-
ed that Brønsted acid was essential for this alkylation (entry
17).
With the optimal reaction conditions in hand, the sub-
strate scope of alkyl peroxides was next investigated
(Scheme 1). Under the optimal conditions, the reaction of
alkyl diacyl peroxides 2 with 2-methylquinoline (1a) af-
forded linear and branched chain alkylation products 3a–g
in moderate to good yields (45–79%). The alkyl diacyl per-
oxides possessing functional groups, such as phenyl, chloro,
allyl, and ester, are smoothly transformed to the corre-
sponding products 3h–l in 43–83% yields. Except for the
Key words metal-free conditions, Brønsted acid, C–H alkylation,
heteroarenes, alkyl peroxides
Heteroarene moieties are significant structural motifs
in natural products, pharmaceutical drugs, ligands, cata-
lysts, and materials.1 Among the numerous methods for
constructing substituted heteroaromatics, direct C–H bond
functionalization is the most prevailing strategy due to the
high atom and step economy.2 Moreover, C–H alkylation of
heteroarenes has been well documented as an effective
method, extremely enriching the diversity of C–H function-
alization.3 A pioneering and classical approach for the addi-
tion of alkyl radical to electron-deficient heteroarene fol-
lowed by rearomatization is the Minisci reaction,4 which
uses alkyl carboxylic acids or halides as alkylating agents
2–
and Ag(I)/S2O8 as oxidant. Motivated by Minisci reaction,
the protocols involving radical pathway in C–H alkylation of
heteroarenes have sprung up in recent years.5 Metal-medi-
ated Minisci-type strategy has been applied for C–H alkyla-
tion of heteroarenes, where alkyl acids, alkyl alcohols, alkyl
organometallics, and olefins were used as alkyl reagents.6
Recently, photocatalysis-mediated strategies further ex-
panded the scope of Minisci alkylation of heteroaromatics
under metal catalysis.7 However, metal-free heteroaromatic
alkylation has been less developed,8 although it is more po-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

B
Y. Zeng et al.
Paper
Synthesis
Table 1 Optimization of the Reaction Conditionsa
Alkyl
O
TfOH
C
N
11H23
+
O
Alkyl
O
R
O
N
N
3a–l
TfOH
O
C11H23
2
1a
+
C11H23
O
R = COAlkyl
N
O
2a
3a
1a
iPr
C11H23
C5H11
C7H15
Entry
Acid (1 equiv)
Solvent
Temp (°C)
Yield (%)b
1
2
TsOH·H2O
TFA
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
toluene
80
80
80
80
80
80
80
80
80
80
100
60
40
80
80
80
80
40
N
3a, 71%
N
N
3c, 75%
N
3b, 74%
3d, 67%
trace
2
tBu
tBu
3
MsOH
H2SO4
AcOH
TfOH
TfOH
TfOH
TfOH
TfOH
TfOH
TfOH
TfOH
TfOH
TfOH
TfOH
–
Et
Ph
4
trace
trace
76 (71)c
42
5
N
N
N
N
6
3e, 45%
3f, 79%
3g, 73%
3h, 73%
7
Ph
Cl
CO2Me
8
1,4-dioxane
THF
38
9
36
N
N
N
N
10
11
12
13
14d
15e
16f
17
DMF
18
3i, 83%
3j, 62%
3k, 43%
3l, 79%
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
42
40
Alkyl
Alkyl =
Et
O
trace
50
TfOH
3m, 46%
3n, 63%
O
+
Alkyl
O
tBu
nBu
N
N
3
1a
59
4
38
–
Scheme 1 Substrate scope of the alkyl peroxides
a Reaction conditions: 1a (0.5 mmol, 1.0 equiv), 2a (0.75 mmol, 1.5 equiv)
in 2 mL of solvent for 12 h under N2 atmosphere.
b Yields are determined by 1H NMR analysis.
c Yield of the isolated product in parentheses.
d TfOH used: 1.5 equiv.
monoalkylated efficiently under the standard reaction con-
ditions (3u, 73%). Quinoxaline and pyridine are trans-
formed to the corresponding products 3v and 3w with
regioselectivity. Benzothiazole is well tolerated in the al-
kylation reaction, providing the product 3x in 61% yield.
In addition, based on our previous work on the decar-
boxylation of aliphatic acid,9 we propose a possible path-
way of the alkylation with 2-methylquinoline as an exam-
ple (Scheme 3). Protonated 2-methylquinoline I is attacked
by the alkyl radical II generated by the thermolysis of alkyl
peroxide to produce the amino-radical cation III. The oxida-
tion of intermediate III results in the rearomatization of
protonated 4-alkylheteroarene IV, which would convert
into the alkylated product following the workup.
In summary, we have developed a Brønsted acid pro-
moted C–H alkylation of heterocycles under metal-free
conditions. Alkyl peroxides are employed as general al-
kylating reagents and internal oxidants simultaneously, af-
fording a series of alkyl heteroarenes in moderate to good
yields. Besides, a plausible mechanism for the alkylation
transformation is proposed, in which a radical process is in-
volved.
e TfOH used: 0.5 equiv.
f TfOH used: 0.25 equiv.
primary alkylation product, the secondary alkyl hetero-
arenes 3m and 3n also could be prepared from alkyl perest-
ers 4 as the alkyl reagents (46% and 63% yield) because sec-
ondary alkyl peresters are relatively more stable and acces-
sible than secondary alkyl diacyl peroxides (Scheme 1,
bottom).
A variety of heteroarene compounds were next exam-
ined as shown in Scheme 2. 8-Methoxy-2-methylquinoline
and 2,6-dimethylquinoline can both be converted to the de-
sired products 3o and 3p in 89% and 70% yield, respectively.
2-Chloroquinoline gave the 4-alkyl-substituted product 3q
in 74% yield. 4-Substituted quinoline bearing methyl and
bromo groups also react with alkyl diacyl peroxide to afford
2-alkylated products 3r and 3s. Selectivity for 2- and 4-po-
sition of quinoline leads to the generation of 2-, 4-, and 2,4-
alkylation products 3t, 3t′ and 3t′′ (71%). Other heterocycles
could be compatible in the alkylation. Isoquinoline is
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

C
Y. Zeng et al.
Paper
Synthesis
Metal-Free Approach for Brønsted Acid Promoted C–H Alkylation
of Heteroarenes; 2-Methyl-4-undecylquinoline (3a); Typical Pro-
cedure (Schemes 1 and 2)
O
TfOH
Alkyl
O
Alkyl
3o–x
+
Het
Het
Alkyl
Ph
O
O
1
2
To a flame-dried Schlenk tube, 2-methylquinoline (1a; 72 mg, 0.5
mmol, 1 equiv) and lauryl peroxide (2a; 299 mg, 0.75 mmol, 1.5
equiv) were added, followed by the addition of MeCN (2 mL) under N2
atmosphere. Then TfOH (75 mg, 0.5 mmol, 1 equiv) was added se-
quentially. The reaction mixture was heated at 80 °C for 12 h, and
then cooled to r.t. The solvent was removed by rotary evaporation,
and then diluted with EtOAc, which washed with 10% aq NaOH (3 ×
15 mL). The aqueous phase extracted with EtOAc (3 × 15 mL) and the
combined organic phases were dried (MgSO4). The solvent was re-
moved by rotary evaporation under vacuum and the residue was
chromatographed on silica gel (PE/EtOAc 20:1 → 10:1) to afford 3a as
a clear liquid; yield: 105 mg (0.35 mmol, 71%).
Ph
Ph
N
OMe
N
N
Cl
3o, 89%
3p, 70%
3q, 74%
Br
Ph
Ph
Ph
N
N
N
3t, 2-alkyl: 48%
3t' (4-alkyl) +
3t'' (2,4-dialkyl): 23%
1H NMR (400 MHz, CDCl3): δ = 8.02 (d, J = 8.3 Hz, 1 H), 7.97 (d, J = 8.2
Hz, 1 H), 7.69–7.59 (m, 1 H), 7.51–7.42 (m, 1 H), 7.11 (s, 1 H), 3.04–
2.95 (t, J = 7.6 Hz, 2 H), 2.70 (s, 3 H), 1.78–1.67 (m, 2 H), 1.46–1.38 (m,
2 H), 1.33–1.22 (m, 14 H), 0.88 (t, J = 6.8 Hz, 3 H).
3s, 77%
3r, 72%
N
N
Ph
C11H23
Ph
13C NMR (100 MHz, CDCl3): δ = 157.77, 147.85, 147.23, 128.50,
128.09, 125.03, 124.48, 122.55, 120.73, 31.34, 31.09, 29.29, 28.93,
28.83, 28.80, 28.75, 28.65, 28.52, 24.48, 21.87, 13.30.
Ph
N
N
3u, 73%
3v (2-alkyl) +
3w (2-alkyl) +
3v' (2,3-dialkyl): 75%
3w' (4-alkyl): 43%
S
HRMS (ESI): m/z [M + H+] calcd for [C21H32N]+: 298.2535; found:
Ph
N
298.2529.
3x, 61%
2-Methyl-4-pentylquinoline (3b)10
Scheme 2 Substrate scope of the heteroarenes
Yellow oil; yield: 78.8 mg (74%).
1H NMR (400 MHz, CDCl3): δ = 8.02 (d, J = 8.4 Hz, 1 H), 7.98 (d, J = 8.2
Hz, 1 H), 7.67–7.63 (m, 1 H), 7.52–7.46 (m, 1 H), 7.13 (s, 1 H), 3.05–
2.98 (m, 2 H), 2.71 (s, 3 H), 1.80–1.71 (m, 2 H), 1.46–1.35 (m, 4 H),
0.92 (t, J = 7.0 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 158.63, 148.68, 148.07, 129.34,
128.92, 125.86, 125.31, 123.3, 121.58, 32.13, 31.91, 29.81, 25.32,
22.52, 14.01.
Alkyl
N
O
O
Alkyl
Alkyl
O
N
O
Δ
TfOH
CO2
Alkyl
Alkyl II
Alkyl
[O]
4-Heptyl-2-methylquinoline (3c)11
N
H
N
N
H
–OTf
H
–OTf
I
Yellow oil; yield: 90 mg (75%).
–OTf
IV
III
1H NMR (400 MHz, CDCl3): δ = 8.03 (d, J = 8.2 Hz, 1 H), 7.96 (d, J = 8.3
Hz, 1 H), 7.64 (t, J = 7.6 Hz, 1 H), 7.47 (t, J = 7.6 Hz, 1 H), 7.11 (s, 1 H),
2.99 (t, J = 7.8 Hz, 2 H), 2.70 (s, 3 H), 1.73 (pent, J = 7.6 Hz, 2 H), 1.45–
1.25 (m, 8 H), 0.88 (t, J = 6.8 Hz, 3 H).
Scheme 3 Proposed reaction mechanism
All reactions were carried out under an atmosphere of N2 in a flame-
dried glassware with magnetic stirring, unless otherwise indicated.
Commercially obtained reagents were used directly as received. Sol-
vents were dried by Innovative Technology Solvent Purification Sys-
tem. Liquids and solutions were transferred via syringe. All reactions
were monitored by TLC. GC-MS data were recorded on Thermo ISQ
QD. 1H and 13C NMR spectra were recorded on Bruker BioSpin Avance
III HD spectrometer. Data for 1H NMR spectra are reported relative to
CHCl3 as an internal standard (7.26 ppm) and are reported as follows:
chemical shift (ppm), multiplicity, coupling constant (Hz), and inte-
gration. Data for 13C NMR spectra are reported relative to CHCl3 as an
internal standard (77.23 ppm) and are reported in terms of chemical
shift (ppm). HRMS data were recorded on Waters Micromass GCT Pre-
mier or Thermo Fisher Scientific LTQ FT Ultra. Alkyl peroxides were
prepared according to our previous work.9
13C NMR (100 MHz, CDCl3): δ = 158.75, 148.91, 148.14, 129.41,
129.11, 126.02, 125.49, 123.54, 121.74, 32.32, 31.95, 30.28, 29.88,
29.30, 25.39, 22.82, 14.26.
4-Isobutyl-2-methylquinoline (3d)12
Yellow oil; yield: 67 mg (67%).
1H NMR (400 MHz, CDCl3): δ = 8.01 (d, J = 8.4 Hz, 1 H), 7.92 (d, J = 8.3
Hz, 1 H), 7.63 (t, J = 7.8 Hz, 1 H), 7.45 (t, J = 7.2 Hz, 1 H), 7.04 (s, 1 H),
2.86–2.80 (m, 2 H), 2.70–2.67 (s, 3 H), 2.04 (m, 1 H), 0.96–0.91 (d, J =
6.6 Hz, 6 H).
13C NMR (100 MHz, CDCl3): δ = 158.49, 148.29, 147.66, 129.43,
129.06, 126.29, 125.39, 123.81, 122.80, 41.66, 29.43, 25.40, 22.92.
2-Methyl-4-neopentylquinoline (3e)
Yellow oil; yield: 79 mg (45%).
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

D
Y. Zeng et al.
Paper
Synthesis
1H NMR (400 MHz, CDCl3): δ = 8.05 (d, J = 8.1 Hz, 1 H), 8.01 (d, J = 8.4
Hz, 1 H), 7.68–7.59 (m, 1 H), 7.45 (m, 1 H), 7.08 (s, 1 H), 2.96 (s, 2 H),
2.72 (s, 3 H), 0.98 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 158.03, 148.45, 146.21, 129.44,
128.99, 127.31, 125.17, 124.87, 124.58, 44.49, 33.07, 30.33, 25.51.
1H NMR (400 MHz, CDCl3): δ = 8.02 (d, J = 8.4 Hz, 1 H), 7.93 (d, J = 8.3
Hz, 1 H), 7.64 (t, J = 8.1 Hz, 1 H), 7.47 (t, J = 7.6 Hz, 1 H), 7.10 (s, 1 H),
3.57 (t, J = 7.2 Hz, 2 H), 3.01 (t, J = 7.2 Hz, 2 H), 2.69 (s, 3 H), 1.92–1.85
(m, 4 H).
13C NMR (100 MHz, CDCl3): δ = 158.67, 148.07, 147.72, 129.42,
129.16, 125.74, 125.61, 123.24, 121.65, 44.68, 32.40, 31.30, 27.20,
25.32.
HRMS (ESI): m/z [M + H+] calcd for [C15H20N]+: 214.1596; found:
214.1590.
HRMS (ESI): m/z [M + H+] calcd for [C14H17ClN]+: 234.1050; found:
234.1043.
2-Methyl-4-(2-methylbutyl)quinoline (3f)
Yellow oil; yield: 84 mg (79%).
4-(But-3-en-1-yl)-2-methylquinoline (3k)
1H NMR (400 MHz, CDCl3): δ = 8.02 (d, J = 8.4 Hz, 1 H), 7.96 (d, J = 8.3
Hz, 1 H), 7.64 (t, J = 7.1 Hz, 1 H), 7.47 (t, J = 7.6 Hz, 1 H), 7.08 (s, 1 H),
3.07 (dd, J = 8.4 Hz, 1 H), 2.70 (s, 3 H), 1.87–1.80 (m, 1 H), 1.52–1.41
(m, 1 H), 1.35–1.23 (m, 2 H), 0.96 (t, J = 7.4 Hz, 3 H), 0.89 (d, J = 6.6 Hz,
3 H).
13C NMR (100 MHz, CDCl3): δ = 158.50, 148.36, 147.77, 129.50,
129.08, 126.3, 125.42, 123.84, 122.98, 39.78, 35.84, 29.99, 25.46,
19.47, 11.68.
Brown liquid; yield: 43 mg (43%).
1H NMR (400 MHz, CDCl3): δ = 8.03 (d, J = 8.4 Hz, 1 H), 7.97 (d, J = 8.3
Hz, 1 H), 7.65 (t, J = 7.6 Hz, 1 H), 7.51 (t, J = 7.4 Hz, 1 H), 7.12 (s, 1 H),
5.96–5.84 (m, 1 H), 5.12–5.01 (m, 2 H), 3.11 (t, J = 7.8 Hz, 2 H), 2.70 (s,
3 H), 2.54–2.47 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 158.78, 148.21, 147.71, 137.49,
129.54, 129.19, 125.91, 125.63, 123.39, 121.82, 115.72, 34.07, 31.61,
25.46.
HRMS (ESI): m/z [M + H+] calcd for [C15H20N]+: 214.1596; found:
214.1590.
HRMS (ESI): m/z [M + H+] calcd for [C14H16N]+: 198.1283; found:
198.1277.
2-Methyl-4-(2,4,4-trimethylpentyl)quinoline (3g)
Methyl 3-(2-Methylquinolin-4-yl)propanoate (3l)
Yellow oil; yield: 93 mg (73%).
Brown oil; yield: 90 mg (79%).
1H NMR (400 MHz, CDCl3): δ = 8.03 (d, J = 8.4 Hz, 1 H), 7.97 (d, J = 8.3
Hz, 1 H), 7.64 (t, J = 7.6 Hz, 1 H), 7.47 (t, J = 7.6 Hz, 1 H), 7.08 (s, 1 H),
3.04–2.94 (m, 1 H), 2.71 (s, 3 H), 2.05–1.94 (m, 1 H), 1.45–1.34 (m, 1
H), 1.23 (dd, J = 13.8, 6.5 Hz, 2 H), 0.92 (d, J = 6.6 Hz, 3 H), 0.85 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 158.36, 148.22, 147.73, 129.41,
129.07, 126.35, 125.44, 123.77, 123.00, 51.52, 42.22, 31.18, 30.69,
30.12, 25.32, 22.84.
1H NMR (400 MHz, CDCl3): δ = 8.02 (d, J = 8.3 Hz, 1 H), 7.95 (d, J = 7.9
Hz, 1 H), 7.65 (t, J = 7.7 Hz, 1 H), 7.49 (t, J = 7.6 Hz, 1 H), 7.12 (s, 1 H),
3.68 (s, 3 H), 3.35 (t, J = 7.8 Hz, 2 H), 2.75 (t, J = 7.8 Hz, 2 H), 2.69 (s, 3
H).
13C NMR (100 MHz, CDCl3): δ = 172.99, 158.88, 148.13, 146.33,
129.57, 129.37, 125.93, 125.56, 123.06, 121.64, 51.99, 34.11, 27.18,
25.40.
HRMS (ESI): m/z [M + H+] calcd for [C18H26N]+: 256.2065; found:
256.2058.
HRMS (ESI): m/z [M + H+] calcd for [C14H16NO2]+: 230.1181; found:
230.1173.
2-Methyl-4-phenethylquinoline (3h)12
4-(Heptan-3-yl)-2-methylquinoline (3m)
Yellow oil; yield: 84 mg (73%).
Yellow oil; yield: 55 mg (46%).
1H NMR (400 MHz, CDCl3): δ = 8.08 (d, J = 8.4 Hz, 1 H), 8.01 (d, J = 8.3
Hz, 1 H), 7.68 (t, J = 7.6 Hz, 1 H), 7.50 (t, J = 7.5 Hz, 1 H), 7.32 (t, J = 7.3
Hz, 2 H), 7.23 (t, J = 6.1 Hz, 3 H), 7.08 (s, 1 H), 3.33 (t, J = 8.2 Hz, 2 H),
3.05 (t, J = 8.0 Hz, 2 H), 2.70 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 158.76, 148.16, 147.48, 141.22,
129.53, 129.19, 128.65, 128.48, 126.42, 125.78, 125.69, 123.26,
121.84, 36.33, 34.19, 25.37.
1H NMR (400 MHz, CDCl3): δ = 8.05 (t, J = 7.9 Hz, 2 H), 7.65 (t, J = 7.7
Hz, 1 H), 7.48 (t, J = 7.6 Hz, 1 H), 7.14 (s, 1 H), 3.40–3.32 (m, 1 H), 2.73
(s, 3 H), 1.87–1.68 (m, 4 H), 1.30–1.20 (m, 4 H), 0.80 (q, J = 7.2 Hz, 6
H).
13C NMR (100 MHz, CDCl3): δ = 158.71, 152.82, 148.36, 129.61,
129.05, 126.75, 125.43, 123.2, 119.23, 35.61, 34.13, 29.90, 29.13,
25.66, 23.05, 14.15, 12.20.
2-Methyl-4-(3-phenylpropyl)quinoline (3i)13
HRMS (ESI): m/z [M + H+] calcd for [C17H24N]+: 242.1909; found:
242.1904.
Yellow oil; yield: 108 mg (83%).
1H NMR (400 MHz, CDCl3): δ = 8.03 (d, J = 8.3 Hz, 1 H), 7.89 (d, J = 8.3
Hz, 1 H), 7.65 (t, J = 8.3 Hz, 1 H), 7.46 (t, J = 7.6 Hz, 1 H), 7.32 (d, J = 7.6
Hz, 2 H), 7.24–7.20 (m, 3 H), 7.12 (s, 1 H), 3.05–3.02 (t, J = 7.8 Hz, 2 H),
2.77 (t, J = 7.6 Hz, 2 H), 2.71 (s, 3 H), 2.15–2.06 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 158.79, 148.30, 148.22, 141.80,
129.51, 129.19, 128.63, 128.62, 126.21, 125.95, 125.60, 123.45,
121.79, 35.96, 31.70, 29.89, 25.46.
4-Cyclohexyl-2-methylquinoline (3n)12
Yellow oil; yield: 71 mg (63%).
1H NMR (400 MHz, CDCl3): δ = 8.02 (d, J = 8.5 Hz, 2 H), 7.63 (t, J = 7.7
Hz, 1 H), 7.47 (t, J = 7.2 Hz, 1 H), 7.15 (s, 1 H), 3.32–3.23 (m, 1 H), 2.71
(s, 3 H), 2.04–1.81 (m, 5 H), 1.57–1.47 (m, 4 H), 1.38–1.23 (m, 1 H).
13C NMR (100 MHz, CDCl3): δ = 158.95, 153.45, 148.31, 129.70,
128.92, 125.41, 125.32, 122.98, 118.46, 38.96, 33.74, 27.11, 26.50,
25.69.
4-(4-Chlorobutyl)-2-methylquinoline (3j)
Yellow oil; yield: 72 mg (62%).
8-Methoxy-2-methyl-4-(3-phenylpropyl)quinoline (3o)
Yellow solid; yield: 129.5 mg (89%); mp 96.3–96.8 °C.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

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1H NMR (400 MHz, CDCl3): δ = 7.46 (d, J = 9.4 Hz, 1 H), 7.34 (t, J = 8.2
Hz, 1 H), 7.33–7.27 (m, 2 H), 7.23–7.18 (m, 3 H), 7.15 (s, 1 H), 7.01 (d,
J = 7.1 Hz, 1 H), 4.06 (s, 3 H), 2.75 (t, J = 7.8 Hz, 2 H), 2.78–2.71 (m, 5
H), 2.13–2.04 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 156.82, 154.48, 147.19, 140.84,
139.11, 127.63, 127.60, 126.05, 125.18, 124.48, 121.42, 114.36,
106.39, 55.18, 34.97, 31.16, 30.65, 24.83.
2-(3-Phenylpropyl)quinoline (3t)14
Yellow oil; yield: 60 mg (48%).
1H NMR (400 MHz, CDCl3): δ = 8.06 (t, J = 7.2 Hz, 2 H), 7.78 (d, J = 8.0
Hz, 1 H), 7.69 (t, J = 7.7 Hz, 1 H), 7.49 (t, J = 7.8 Hz, 1 H), 7.35–7.27 (m,
3 H), 7.20–7.18 (m, 3 H), 3.07–3.00 (m, 2 H), 2.79–2.72 (m, 2 H), 2.17
(pent, J = 7.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 162.52, 147.96, 142.12, 136.25,
129.38, 128.86, 128.51, 128.34, 127.50, 126.75, 125.81, 125.72,
121.37, 38.84, 35.72, 31.59.
HRMS (ESI): m/z [M + H+] calcd for [C20H22NO]+: 292.1701; found:
292.1697.
4-(3-Phenylpropyl)quinoline (3t′)15 and 2,4-Bis(3-phenylpro-
pyl)quinoline (3t′′)
2,6-Dimethyl-4-(3-phenylpropyl)quinoline (3p)
Yellow liquid; yield: 96 mg (70%).
1H NMR (400 MHz, CDCl3): δ = 7.93 (d, J = 8.6 Hz, 1 H), 7.59 (s, 1 H),
7.48 (d, J = 10.4 Hz, 1 H), 7.36–7.30 (m, 2 H), 7.26–7.20 (m, 3 H), 7.08
(s, 1 H), 3.01 (t, J = 8.0 Hz, 2 H), 2.77 (t, J = 7.5 Hz, 2 H), 2.69 (s, 3 H),
2.50 (s, 3 H), 2.09 (pent, J = 7.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 157.69, 147.55, 146.66, 141.83,
135.18, 131.28, 129.13, 128.65, 128.57, 126.16, 125.80, 122.43,
121.73, 35.86, 31.62, 31.50, 25.28, 21.94.
Yellow oil; 3t′ + 3t′′ yield: 34 mg (23%).
1H NMR (400 MHz, CDCl3): δ = 8.82 (d, J = 4.5 Hz, 2.32 H), 8.15–8.13
(m, 2.4 H), 7.94–7.92 (m, 2.39 H), 7.70–7.67 (m, 2.37 H), 7.54–7.52 (m,
2.35 H), 7.38–7.26 (m, 6 H), 7.27–7.12 (m, 14.6 H), 3.15–3.02 (m, 4.88
H), 2.75–2.73 (m, 5.25 H), 2.72–2.70 (m, 1.81 H), 2.43–2.40 (m, 1.93
H), 2.13–2.07 (m, 5.17 H), 2.05–1.96 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 149.71, 148.89, 147.74, 141.51,
129.63, 129.30, 128.57, 128.49, 128.47, 128.37, 127.57, 126.49,
126.10, 125.89, 123.55, 120.83.
HRMS (ESI): m/z [M + H+] calcd for [C20H22N]+: 276.1752; found:
276.1745.
3t′
2-Chloro-4-(3-phenylpropyl)quinoline (3q)
HRMS (ESI): m/z [M + H+] calcd for [C18H18N]+: 248.1439; found:
Yellow oil; yield: 104 mg (74%).
248.1433.
1H NMR (400 MHz, CDCl3): δ = 8.00 (d, J = 8.4 Hz, 1 H), 7.85 (d, J = 8.0
Hz, 1 H), 7.67 (t, J = 7.7 Hz, 1 H), 7.50 (t, J = 8.2 Hz, 1 H), 7.30 (t, J = 7.3
Hz, 2 H), 7.24–7.17 (m, 4 H), 3.01 (t, J = 7.8 Hz, 2 H), 2.74 (t, J = 7.5 Hz,
2 H), 2.06 (pent, J = 7.7 Hz, 2 H).
3t′′
HRMS (ESI): m/z [M + H+] calcd for [C27H28N]+: 366.2222; found:
366.2215.
13C NMR (100 MHz, CDCl3): δ = 151.81, 150.73, 148.14, 141.35,
130.28, 129.45, 128.64, 128.57, 126.80, 126.31, 126.29, 123.65,
121.56, 35.75, 31.49, 31.33.
1-(3-Phenylpropyl)isoquinoline (3u)16
HRMS (ESI): m/z [M + H+] calcd for [C18H17ClN]+: 282.1045; found:
Yellow oil; yield: 90 mg (73%).
1H NMR (400 MHz, CDCl3): δ = 8.42 (d, J = 5.7 Hz, 1 H), 8.01 (d, J = 8.4
Hz, 1 H), 7.76 (d, J = 8.2 Hz, 1 H), 7.61 (t, J = 8.0 Hz, 1 H), 7.52 (t, J = 7.7
Hz, 1 H), 7.46 (d, J = 5.7 Hz, 1 H), 7.30–7.24 (m, 2 H), 7.23–7.15 (m, 3
H), 3.31 (t, J = 8 Hz, 2 H), 2.79 (t, J = 7.7 Hz, 2 H), 2.24–2.15 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 161.94, 142.19, 141.99, 136.37,
129.89, 128.65, 128.46, 127.50, 127.10, 127.03, 125.96, 125.33,
119.38, 36.06, 34.96, 31.25.
282.1045.
4-Methyl-2-(3-phenylpropyl)quinoline (3r)13
Yellow oil; yield: 94 mg (72%).
1H NMR (400 MHz, CDCl3): δ = 8.04 (d, J = 8.4 Hz, 1 H), 7.91 (d, J = 7.5
Hz, 1 H), 7.65 (t, J = 7.0 Hz, 1 H), 7.47 (t, J = 7.6 Hz, 1 H), 7.30–7.24 (m,
2 H), 7.22–7.14 (m, 3 H), 7.09 (s, 1 H), 2.96 (t, J = 7.8 Hz, 2 H), 2.73 (t,
J = 7.4 Hz, 2 H), 2.63 (s, 3 H), 2.14 (pent, J = 7.8 Hz, 2 H).
2-(3-Phenylpropyl)quinoxaline (3v) and 2,3-Bis(3-phenylpro-
pyl)quinoxaline (3v′)
13C NMR (100 MHz, CDCl3): δ = 162.30, 147.91, 144.36, 142.31,
129.51, 129.18, 128.64, 128.46, 126.95, 125.93, 125.60, 123.73,
122.19, 38.88, 35.92, 31.72, 18.80.
Brown solid; 3v + 3v′ yield: 111 mg (75%).
1H NMR (400 MHz, CDCl3): δ = 8.70 (s, 1 H), 8.09–8.02 (m, 2 H), 8.02–
7.99 (m, 1 H), 7.76–7.68 (m, 2 H), 7.67–7.64 (m, 1 H), 7.30–7.28 (m, 4
H), 7.22–7.15 (m, 5 H), 3.06–3.01 (m, 2 H), 2.96–2.90 (m, 1 H), 2.77–
2.73 (m, 4 H), 2.25–2.15 (m, 2 H), 2.15–2.07 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 157.16, 156.09, 145.81, 142.23,
141.86, 141.60, 141.25, 140.97, 129.98, 129.20, 129.01, 128.89,
128.80, 128.55, 128.51, 128.44, 128.42, 126.01, 125.97, 35.82, 35.70,
35.54, 34.57, 30.84, 30.09, 29.74.
4-Bromo-2-(3-phenylpropyl)quinoline (3s)
Yellow oil; yield: 125 mg (77%).
1H NMR (400 MHz, CDCl3): δ = 8.03 (d, J = 8.4 Hz, 1 H), 7.87 (d, J = 9.3
Hz, 1 H), 7.69 (t, J = 7.6 Hz, 1 H), 7.54 (t, J = 7.0 Hz, 1 H), 7.36–7.30 (m,
3 H), 7.26–7.19 (m, 3 H), 3.03 (t, J = 7.6 Hz, 2 H), 2.77 (t, J = 7.5 Hz, 2
H), 2.09 (pent, J = 7.7 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 151.33, 148.85, 142.20, 141.38,
130.30, 129.60, 128.69, 128.62, 126.95, 126.54, 126.34, 125.06,
123.82, 35.81, 31.44, 31.41.
3v
HRMS (ESI): m/z [M + H+] calcd for [C17H17N2]+: 249.1392; found:
249.1383.
HRMS (ESI): m/z [M + H+] calcd for [C18H17BrN]+: 326.0544; found:
326.0535.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

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3v′
Res. 2012, 45, 826. (c) Hartwig, J. F. J. Am. Chem. Soc. 2016, 138,
2. (d) Wei, Y.; Hu, P.; Zhang, M.; Su, W. Chem. Rev. 2017, 117,
8864. (e) Yi, H.; Zhang, G.; Wang, H.; Huang, Z.; Wang, J.; Singh,
A. K.; Lei, A. Chem. Rev. 2017, 117, 9016. (f) Shang, R.; Ilies, L.;
Nakamura, E. Chem. Rev. 2017, 117, 9086. (g) Murakami, K.;
Yamada, S.; Kaneda, T.; Itami, K. Chem. Rev. 2017, 117, 9302.
(3) Selected reviews on C–H alkylation: (a) Schönherr, H.; Cernak,
T. Angew. Chem. Int. Ed. 2013, 52, 12256. (b) Yang, L.; Huang, H.
Chem. Rev. 2015, 115, 3468. (c) Dong, Z.; Ren, Z.; Thompson, S.
J.; Xu, Y.; Dong, G. Chem. Rev. 2017, 117, 9333.
(4) Selected examples of Minisci reaction: (a) Minisci, F.; Galli, R.;
Cecere, M.; Malatesta, V.; Caronna, T. Tetrahedron Lett. 1968,
5609. (b) Minisci, F.; Bernardi, R.; Bertini, F.; Galli, R.;
Perchinummo, M. Tetrahedron 1971, 27, 3575. (c) Castaldi, G.;
Minisci, F.; Tortelli, V.; Vismara, E. Tetrahedron Lett. 1984, 25,
3897. (d) Minisci, F.; Giordano, C.; Vismara, E.; Levi, S.; Tortelli,
V. J. Am. Chem. Soc. 1984, 106, 7146. (e) Minisci, F.; Vismara, E.;
Fontana, F.; Morini, G.; Serravalle, M.; Giordano, G. J. Org. Chem.
1986, 51, 4411. (f) Minisci, F.; Vismara, E.; Fontana, F. J. Org.
Chem. 1989, 54, 5224. (g) Minisci, F.; Fontana, F.; Pianese, G.;
Yan, Y. M. J. Org. Chem. 1993, 58, 4207.
HRMS (ESI): m/z [M + H+] calcd for [C26H27N2]+: 367.2174; found:
367.2168.
2-Phenyl-6-undecylpyridine (3w) and 2-Phenyl-4-undecylpyri-
dine (3w′)
Yellow oil; 3w + 3w′ yield: 87 mg (43%).
1H NMR (400 MHz, CDCl3): δ = 8.70 (m, 1 H), 8.57 (d, J = 5.0 Hz, 1 H),
8.02–7.97 (m, 4 H), 7.75–7.71 (m, 2 H), 7.54 (s, 1 H), 7.50–7.45 (m, 3.3
Hz, 4 H), 7.44–7.37 (m, 2 H), 7.23–7.21 (m, 1 H), 7.06–7.05 (m, 1 H),
2.70–2.61 (m, 2 H), 1.73–1.62 (m, 2 H), 1.43–1.22 (m, 25 H), 0.92–0.83
(m, 5 H).
13C NMR (100 MHz, CDCl3): δ = 157.50, 157.4, 152.52, 149.67, 149.48,
139.68, 139.42, 136.71, 128.94, 128.76, 128.73, 128.66, 126.97,
126.92, 122.42, 122.07, 120.84, 120.54, 35.52, 31.92, 30.44, 29.65,
29.62, 29.54, 29.44, 29.34, 29.25, 22.69, 14.12.
3w and 3w′
HRMS (ESI): m/z [M + H+] calcd for [C22H32N]+: 310.2535; found:
310.2529.
(5) For selected reviews on the Minisci reaction, see: (a) Minisci, F.
Synthesis 1973, 1. (b) Minisci, F.; Citterio, A.; Giordano, C. Acc.
Chem. Res. 1983, 16, 27. (c) Minisci, F.; Vismara, E.; Fontana, F.
Heterocycles 1989, 28, 489. (d) Minisci, F.; Fontana, F.; Vismara,
E. J. Heterocycl. Chem. 1990, 27, 79. (e) Harrowven, D. C.; Sutton,
B. J. Prog. Heterocycl. Chem. 2005, 16, 27. (f) Punta, C.; Minisci, F.
Trends Heterocycl. Chem. 2008, 13, 1.
2-(3-Phenylpropyl)benzo[d]thiazole (3x)17
Yellow oil; yield: 77 mg (61%).
1H NMR (400 MHz, CDCl3): δ = 7.97 (d, J = 7.8 Hz, 1 H), 7.83 (d, J = 8.0
Hz, 1 H), 7.47–7.42 (m, 1 H), 7.35 (d, J = 8.1 Hz, 1 H), 7.33–7.26 (m, 2
H), 7.21 (q, J = 9.0 Hz, 3 H), 3.13 (t, J = 7.8 Hz, 2 H), 2.76 (t, J = 7.8 Hz, 2
H), 2.21 (pent, J = 7.6 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 171.78, 153.29, 141.32, 135.14,
128.54, 128.47, 126.07, 125.94, 124.72, 122.57, 121.52, 35.22, 33.74,
31.19.
(6) Selected examples of metal-mediated Minisci-type C–H alkyla-
tion of heteroarenes: (a) Cowden, C. J. Org. Lett. 2003, 5, 4497.
(b) Palde, P. B.; McNaughton, B. R.; Ross, N. T.; Gareiss, P. C.;
Mace, C. R.; Spitale, R. C.; Miller, B. L. Synthesis 2007, 2287.
(c) Duncton, M. A. J.; Estiarte, M. A.; Johnson, R. J.; Cox, M.;
O’Mahony, D. J. R.; Edwards, W. T.; Kelly, M. G. J. Org. Chem.
2009, 74, 6354. (d) Molander, G. A.; Colombel, V.; Braz, V. A. Org.
Lett. 2011, 13, 1852. (e) Correia, C. A.; Yang, L.; Li, C.-J. Org. Lett.
2011, 13, 4581. (f) Fujiwara, Y.; Dixon, J. A.; O’Hara, F.; Funder, E.
D.; Dixon, D. D.; Rodriguez, R. A.; Baxter, R. D.; Herlé, B.; Sach,
N.; Collins, M. R.; Ishihara, Y.; Baran, P. S. Nature 2012, 492, 95.
(g) Presset, M.; Fleury-Brégeot, N.; Oehlrich, D.; Rombouts, F.;
Molander, G. A. J. Org. Chem. 2013, 78, 4615. (h) Xia, R.; Xie, M.-
S.; Niu, H.-Y.; Qu, G.-R.; Guo, H.-M. Org. Lett. 2014, 16, 444.
(i) Zhao, W.-M.; Chen, X.-L.; Yuan, J.-W.; Qu, L.-B.; Duan, L.-K.;
Zhao, Y.-F. Chem. Commun. 2014, 50, 2018. (j) Ma, X.; Herzon, S.
B. J. Am. Chem. Soc. 2016, 138, 8718. (k) Mai, D. N.; Baxter, R. D.
Org. Lett. 2016, 18, 3738. (l) Bordi, S.; Starr, J. T. Org. Lett. 2017,
19, 2290. (m) Ma, X.; Dang, H.; Rose, J. A.; Rablen, P.; Herzon, S.
B. J. Am. Chem. Soc. 2017, 139, 5998.
Funding Information
We thank NSFC (Grant Nos. 21502191 and 21672213), Strategic Prior-
ity Research Program of the Chinese Academy of Sciences (Grant No.
XDB20000000), The 100 Talents Program, ‘The 1000 Youth Talents
Program’, Natural Science Foundation of Fujian Province (Grant No.
2016J01081) and Haixi Institute of CAS (CXZX-2017-P01) for financial
support.
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Supporting Information
Supporting information for this article is available online at
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(7) Selected examples of photoredox Minisci-type C–H alkylation of
heteroarenes via metal catalysis: (a) McNally, A.; Prier, C. K.;
MacMillan, D. W. C. Science 2011, 334, 1114. (b) DiRocco, D. A.;
Dykstra, K.; Krska, S.; Vachal, P.; Conway, D. V.; Tudge, M.
Angew. Chem. Int. Ed. 2014, 53, 4802. (c) Jin, J.; MacMillan, D. W.
C. Angew. Chem. Int. Ed. 2015, 54, 1565. (d) Jin, J.; MacMillan, D.
W. C. Nature 2015, 525, 87. (e) Li, G.-X.; Morales-Rivera, C. A.;
Wang, Y.; Gao, F.; He, G.; Liu, P.; Chen, G. Chem. Sci. 2016, 7,
6407. (f) Klauck, F. J. R.; James, M. J.; Glorius, F. Angew. Chem. Int.
Ed. 2017, 56, 12336. (g) Liu, W.; Yang, X.; Zhou, Z.-Z.; Li, C.-J.
Chem 2017, 2, 688. (h) Cheng, W.-M.; Shang, R.; Fu, Y. ACS Catal.
2017, 7, 907.
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G