Construction of α-Alkylated Amines by Iridium Complex-Catalyzed One-Step Transfer Hydrogenation of C=C and C=N Bonds

Article abstract of DOI:10.1055/a-1344-2126

Hydrogenation of C=C bond and reductive amination are important transformations utilized in chemistry. An environmentally friendly, efficient, and facile one-pot transfer hydrogenation of C=C bond of enones and reductive amination of C=N bond of imines are reported using iridium complex as catalysts and formic acid as hydrogen source in aqueous medium. In this catalytic system, a wide range of α-alkylated amines were obtained in excellent yields by one-pot transfer hydrogenation of C=C bond and reductive amination. The practical application of this protocol is characterized by gram-scale transformation.

Full text of DOI:10.1055/a-1344-2126

SYNTHESIS
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
2021, 53, 1821–1827
paper
1821
en
Y. Xia et al.
Paper
Synthesis
Construction of -Alkylated Amines by Iridium Complex-Cata-
lyzed One-Step Transfer Hydrogenation of C=C and C=N Bonds
Yanping Xia
O
Lu Ouyang
Jianhua Liao
Ar
Ar'
Reduction
of C=C
Reduction
of C=N
Xiao Yang
+
Ar
N
H
Renshi Luo*
0
0
0
0
-
0
0
0
1
-
8
9
6
6
-
0
3
8
7
Ar'-NH2
Reductive C=C and C=N bond in one-step Highly chemo-selectivity Scal-up to grams Wide substrate scope
School of Pharmacy, Gannan Medical University,
Ganzhou 341000, Jiangxi Province, P. R. of China
luorenshi2010@163.com
RSeMcehnaosiCohloliuroLrouferPosehpnaosrnhmdi2ian0cg1y0,A@Gua1tnh6no3ar.cnomMedical University, Ganzhou 341000, Jiangxi Province, P. R. of China
Received: 17.11.2020
Accepted after revision: 30.12.2020
Published online: 30.12.2020
tive pharmaceutical ingredients.9 On the other hand, reduc-
tive amination could be employed for the construction of
C–N bond, which is a crucial transformation in organic
chemistry.10
DOI: 10.1055/a-1344-2126; Art ID: ss-2020-g0589-op
Abstract Hydrogenation of C=C bond and reductive amination are
important transformations utilized in chemistry. An environmentally
friendly, efficient, and facile one-pot transfer hydrogenation of C=C
bond of enones and reductive amination of C=N bond of imines are re-
ported using iridium complex as catalysts and formic acid as hydrogen
source in aqueous medium. In this catalytic system, a wide range of -
alkylated amines were obtained in excellent yields by one-pot transfer
hydrogenation of C=C bond and reductive amination. The practical ap-
plication of this protocol is characterized by gram-scale transformation.
Recently, we developed highly pH-dependent chemose-
lective transfer hydrogenation of ,-unsaturated aldehydes
in water11a and transfer hydrogenation reductive amination
of aldehydes and ketones by iridium complexes ‘on
water’.11e As our continuous interest in iridium complex-
catalyzed transfer hydrogenation,11 we intended to achieve
the reduction of C=C and C=N bonds directly by one-pot
Key words transfer hydrogenation, iridium complex, reductive ami-
nation, enones
F3C
N
H
N
H
Nitrogen-containing molecules have been identified as
one of the most important synthetic target moieties in the
field of biology and medicine because of their great impor-
tance in biological activities.1 For example, calcimimetic
agent cinacalcet and the calcium channel blocker fendiline
contain -alkylated amine skeletons (Figure 1).2 Therefore,
development of successful synthetic methods of such com-
pounds has attracted great attention. Reduction of keto-
imines or enamines,3 addition to aldimines,4 and hydroami-
noalkylation are general strategies for the synthesis of -al-
kylated amines. Undoubtedly, hydroaminoalkylation of
alkenes is the most direct and effective method for the syn-
thesis of -alkylated amines and successful progress has
been made in this field by using different catalysts.5 Howev-
er, the regioselectivity of hydroaminoalkylation for the lin-
ear and branched product is still a challenging problem
(Scheme 1a).
Calcium channel blocker fendiline
Calcimimetic agent cinacalcet
Figure 1 Structure element of -alkylated amines in pharmacy
(a) Known strategy: Progress in the field of one-pot hydrogenation and reductive amination
R2
R2
R1
R2
Hydroaminoalkylation
N
R1
R3
N
R3
+
N
VS
R1
R3
H
Linear product
Branched product
(b) This work: Iridium complexes catalyzed transfer hydrogenation of C=C and C=N bond
+
H
N
N
Cl-
N
HCOOH
H2O
Cp* Ir
Cl
10 equiv
O
1 mol%
Ar
Ar
N
+
Ar-NH2
In the past few decades, the reduction of alkenes and re-
ductive amination had raised great attention and became
the main driving force for catalytic chemistry. For example,
direct hydrogenation,6 including transfer hydrogenation7
and hydride reduction,8 had been extensively explored and
utilized in manufacturing important fine chemicals and ac-
Ar
H
rt, air
Reductive C=C and C=N bonds in one step
High chemoselectivity
Scale-up to grams
Wide substrate scope
Scheme 1 Hydroaminoalkylation strategy for the synthesis of
-alkylated amines
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Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

1822
Y. Xia et al.
Paper
Synthesis
transfer hydrogenation for the synthesis of -alkylated
amines.
gradually (entries 2–4). As we predicted, product 3a was
achieved in 96% yield when HCOOH was employed as hy-
drogen donor (entry 4), which verified that acidic condition
was helpful for this transformation.
Indeed, efforts had been devoted to one-pot reduction
of C=C and C=N bonds. For example, Fan and co-workers de-
veloped a consecutive intermolecular reductive amina-
tion/asymmetric hydrogenation of quinoline-2-carbalde-
hydes with aniline using Ir/Ru catalyst.12 Chang’s group pre-
sented an Ru-Segphos complex-catalyzed asymmetric
hydrogenation of prochiral olefins and imines.13 It needs to
be pointed out that Xiao’s group reported one example of
one-pot transfer hydrogenation of C=C bond and reductive
amination of C=N bond, using iridium complex as catalyst,
and formic acid and formate as hydrogen sources.14
Among these reported methods, transfer hydrogenation
has outstanding merits: (i) the hydrogen donors are readily
available, inexpensive, and easy to handle and (ii) the cata-
lysts are readily accessible and compatible, and the process
is operationally simple.15 Therefore, transfer hydrogenation
has been developed into one of the most practical strategies
for the reduction of C=C and C=N bonds.
To achieve the reduction of C=C and C=N bonds directly
by one-pot transfer hydrogenation for the synthesis of -al-
kylated amines, challenges are needed to be tackled. For ex-
ample, the compatibility of catalytic system for C=C and
C=N and the suppression of side-reactions of semi-reduc-
tion products. According to our previous work,11 we envi-
sioned that the Tang’s catalysts might help to solve these
problems. One is the application of Tang’s catalysts on che-
moselective transfer hydrogenation of ,-unsaturated al-
dehydes.11a The other is Tang’s catalysts realized transfer
hydrogenation reductive amination of aldehydes and ke-
tones.11e Thus, an efficient and compatible system for the
reduction of alkenes and imines in one pot would be highly
feasible.
Table 1 Optimization of the Reaction Conditionsa
+
O
H
R
N
Tang's catalyst
Ph
N
Ph
N
Ph NH2
+
Cl–
Ph
H
N
hydride donor
solvent
Cp* Ir
1a
Cl
Tang's catalyst
2a
3a
TC-1: R = H
TC-4: R = 4-OMe
TC-2: R = 4-Me TC-5: R = 6-F
TC-3: R = 4-Cl TC-6: R = 6-OMe
Entry
Catalyst
Hydrogen donor
Solvent
Yield (%)b
1
2c
3d
4
TC-1
TC-1
TC-1
TC-1
TC-2
TC-3
TC-4
TC-5
TC-6
TC-1
TC-1
TC-1
TC-1
TC-1
TC-1
HCOONa
H2O
57
HCOOH/NEt3
H2O
62
HCOOH/HCOONa
HCOOH
HCOOH
HCOOH
HCOOH
HCOOH
HCOOH
HCOOH
HCOOH
HCOOH
HCOOH
HCOOH
HCOOH
H2O
84
H2O
96 (92)e
87
5
H2O
6
H2O
84
7
H2O
88
8
H2O
76
9
H2O
80
10
11
12
13
14
15
THF
46
DMF
MeCN
toluene
Et2O
acetone
77
80
76
69
80
a Reaction conditions: 1a (0.5 mmol), 2a (0.6 mmol), solvent (2 mL), cata-
lyst (1 mol%), hydrogen donor (10 equiv) at rt under air for 12 h.
b Determined by GC-MS using dodecane as the internal standard.
c The reaction was carried out with 7.2 equiv of HCOOH, 2.8 equiv of Et3N.
d The reaction was carried out with 7.2 equiv of HCOOH, 2.8 equiv of
HCOONa.
Herein, we describe an efficient consecutive reduction
of C=C and C=N bonds by using formic acid as hydrogen
source and an iridium complex as catalyst in one pot
(Scheme 1b). This protocol relies on simple and readily
available materials to deliver useful -alkylated amines un-
der mild reaction conditions.
e Isolated yield.
With the efficient hydrogen source in hand, we further
examined different Tang’s catalysts on the reactivities of
this transformation, the results of which are summarized in
Table 1. Disappointedly, different substituents, including
electron-withdrawing or electron-donating group on the li-
gands, were only found to give moderate yields of 3a (Table
1, entries 5–9). Literature survey indicated that water may
participate in the rate determining step, which speeds up
the reaction.17 To verify this idea, further investigations on
organic solvents were also performed. For example, organic
solvents such as THF, MeCN, DMF, toluene, acetone, and
Et2O were tested in this iridium complex-catalyzed transfer
hydrogenation reaction, only to find that low to moderate
yields were obtained, which indirectly proves that water
can accelerate this type of reaction.
In order to study the generality of the reaction, chalcone
(1a) and aniline (2a) were chosen as model reaction part-
ners (Table 1). With Tang’s catalysts in hand, we had studied
the activities of these catalysts. According to our previous
work, the C=C bond could be reduced under weak base con-
dition.11a With this in mind, we first selected the HCOONa
as hydrogen source, using Tang’s catalyst TC-1 and water as
solvent. Encouragingly, consecutive reduction of C=C and
C=N product 3a was obtained in 57% yield (Table 1, entry 1)
and the semi-reduced product of allylic amines and by-
products of alcohols were not formed. It is known that
acidic conditions are beneficial for imine formation and
reduction.16 Based on this, we next investigated the effects
of different hydrogen donors, such as HCOOH/NEt3,
HCOOH/HCOONa, and HCOOH, by increasing the acidity
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Y. Xia et al.
Paper
Synthesis
O
TC-1 (1 mol%)
Ar'
+
Ar'-NH2
Ar
Ar
N
HCOOH (10 equiv)
H2O, rt, air
H
1
2
3
Me
F
Cl
CF3
Ph
CN
Ph
N
Ph
N
H
Ph
N
H
N
Ph
N
H
Ph
N
H
Me
H
H
3b, 94%
3c, 91%
3d, 92%
3e, 90%
3f, 95%
3g, 86%
OMe
Ph
Ph
Ph
Ph
N
H
N
N
N
Ph
N
H
H
H
H
Ph
N
H
Me
F
Cl
Cl
Me
3h, 82%
3i, 95%
3j, 88%
3k, 90%
3l, 91%
3m, 93%
Ph
N
Ph
Ph
H
N
H
Ph
N
N
H
N
H
OMe
O
3n, 90%
3o, 91%
3p, 93%
3q, 84%
Scheme 2 Substrates scope of enones and arylamines for synthesis of -alkylated amines. Reagents and conditions: A solution of 1 (0.5 mmol),
2 (0.6 mmol), TC-1 (1 mol%), and HCOOH (10 equiv) in H2O (2 mL) at rt under air for 12 h. Yields of isolated products are shown.
Having developed the effective catalytic system for this
regioselective transfer hydrogenation of C=C and C=N bonds
in one-pot, we then investigated the substrate scope by car-
rying out reactions with different enones 1 and various
arylamines 2 (Scheme 2). First, all selected arylamines, with
electron-withdrawing groups, such as fluorine atom (3b),
chlorine atom (3c), CF3 group (3d), and CN group (3e) or
electron-donating groups, such as 3f–i, reductively coupled
with enones 1 to achieve the desired transfer hydrogena-
tion of C=C and C=N bond products in 82–95% yields, show-
casing that different substituent groups were compatible
with this catalytic system. Moreover, substituents at differ-
ent positions of aniline (para-, meta, and ortho-positions)
were again tolerated in this transformation, affording the
corresponding products, such as 3f, 3g, 3h, in excellent
yields. Likewise, the scope of enones was also explored. No-
tably, desired products 3j–o were obtained in high yields
(82–95%) with different substituents at aryl such as me-
thoxy, fluoro, chloro, methyl, and N,N-dimethylamino
groups. In addition, the higher conjugation degree substrate
such as (E)-4-(naphthalen-1-yl)but-3-en-2-one performed
well to access the desired product 3p in 93% yield.
Besides, this protocol could also be applied to heterocy-
clic substrate. For example, when (E)-4-(furan-2-yl)but-3-
en-2-one was employed in this catalytic system, the desired
product 3q was obtained in 84% yield.
To further showcase the utility of this iridium complex-
catalyzed transfer hydrogenation methodology of C=C and
C=N bonds, a variety of aliphatic enones are also investigat-
ed and the results are summarized in Scheme 3. From the
results, we can see that aliphatic enones proceed smoothly
under the standard conditions. For example, when 4-cyclo-
hexylbut-3-en-2-one (1r), hept-3-en-2-one (1s) and hex-4-
en-3-one (1t) are employed in this catalytic system, the
corresponding products 3r–t could be afforded in 86–93%
yields. At the same time, cyclohepten-1-yl methyl ketone
and carvone could also be used as substrates, affording the
corresponding products in excellent yields, which indicates
the potential synthesis of broad -alkylated amines.
To explore the practical synthesis of -alkylated amines,
a gram scale transformation was investigated. As can be
seen in Scheme 4, a gram-scale reaction of 1a (10 mmol)
and 2a (12 mmol) took place smoothly under the standard
conditions, affording 2.2 g of 3a in 90% yield.
O
TC-1 (1 mol%)
Ph
+
Ph-NH2
Alkyl
N
Alkyl
H
HCOOH (10 equiv)
H2O, rt, air
1
2
3
Product 3
Entry
Yield
Substrate 2
Ph
HN
O
3r, 93%
1
2
3
Ph
HN
Ph
O
3s, 86%
3t, 89%
HN
O
H
N
Ph
3u, 90%
3v, 82%
4
5
O
O
Ph
N
H
Scheme 3 Substrate scope of aliphatic enones and arylamines for the
synthesis of -alkylated amines. Reagents and conditions: a solution of 1
(0.5 mmol), 2 (0.6 mmol), TC-1 (1 mol%) and HCOOH (10 equiv) in H2O
(2 mL) at rt under air for 12 h. Yields of isolated products are shown.
© 2020. Thieme. All rights reserved. Synthesis 2021, 53, 1821–1827

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Y. Xia et al.
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Synthesis
according to standard abbreviations. GC analyses were performed on
a GC-7900 chromatograph with an FID and equipped with an AT.SE-
30 capillary column (internal diameter: 0.32 mm, length: 30 m).
+
H
N
Cl–
N
N
O
Cp* Ir
(1 mol%)
Ph
Cl
+
Ph-NH2
Ph
N
Ph
H
-Alkylated Amines; General Procedure
HCOOH (10 equiv), rt, air, H2O
1a, 10 mmol
2a, 12 mmol
3a, 2.2 g
To a 25.0 mL Schlenk tube was added successively the respective
enone 1 (0.5 mmol), the corresponding amine 2 (0.6 equiv), Ir catalyst
(1.0 mol%), and HCOOH (10.0 equiv) in H2O (2.0 mL). The mixture was
stirred at rt for 12 h under air. After completion of the reaction, the
mixture was diluted with H2O (15.0 mL), neutralized with NaHCO3,
and extracted with EtOAc (3 × 10.0 mL). The combined organic ex-
tracts were washed with brine (3 × 10.0 mL) and dried (MgSO4). After
removal of the EtOAc under vacuum, the crude product was purified
by column chromatography on silica gel with hexanes or PE/EtOAc
(10:1 to 50:1) to give the desired product.
Scheme 4 Large-scale synthesis of 3a
On the basic of experimental results, a mechanism is
proposed, which is summarized in Scheme 5. First, [Ir]-H
(Int-II) is formed by decarboxylation of the formate ion.18
The carbonyl group and arylamine react to form the imine
via dehydration condensation,19 which subsequently coor-
dinates with Int-II to generate Int-III via 1,4-addition, af-
fording allylic amine intermediate. Isomerization of allylic
amine intermediate can take place to imine, thus allowing
for 1,2-addition of imine to achieve the respective target
product via Int-IV.20
In conclusion, an environmentally friendly, efficient,
and facile one-pot transfer hydrogenation of C=C bond of
enones and reductive amination of C=N bond of imines
have been established by using iridium complex as the cat-
alyst, and formic acid as hydrogen source in aqueous medi-
um, affording a wide range of -alkylated amines in excel-
lent yields. A gram scale transformation was also realized
by this iridium complex catalytic system. Deuterium exper-
iments show that HCOOH is the hydrogen donor. Improve-
ment of the catalysts activities and further asymmetric
studies are in progress.
N-(4-Phenylbutan-2-yl)aniline (3a)21a
Light yellow oil; yield: 103.5 mg (92%).
1H NMR (400 MHz, CDCl3):  = 7.42 (t, J = 7.5 Hz, 2 H), 7.31 (dt, J = 7.6,
4.4 Hz, 5 H), 6.82 (t, J = 7.4 Hz, 1 H), 6.67 (d, J = 8.0 Hz, 2 H), 3.71–3.32
(m, 2 H), 2.86 (t, J = 7.9 Hz, 2 H), 2.01 (td, J = 14.1, 7.5 Hz, 1 H), 1.89 (td,
J = 14.0, 7.9 Hz, 1 H), 1.34 (d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 147.7, 142.1, 129.4, 128.6, 128.5,
126.0, 117.1, 113.3, 48.0, 39.0, 32.6, 21.0.
4-Fluoro-N-(4-phenylbutan-2-yl)aniline (3b)14
Light yellow oil; yield: 110.5 mg (94%).
1H NMR (400 MHz, CDCl3):  = 7.36 (t, J = 7.4 Hz, 2 H), 7.27 (dd, J =
11.5, 7.2 Hz, 3 H), 6.98–6.87 (m, 2 H), 6.56–6.48 (m, 2 H), 3.46 (dt, J =
12.6, 6.3 Hz, 1 H), 2.78 (q, J = 7.3 Hz, 2 H), 1.99–1.77 (m, 2 H), 1.27 (d,
J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 156.6 (d, J = 233 Hz), 143.9 (d, J = 2
Hz), 142.0, 128.5 (d, J = 2 Hz), 126.0, 115.7 (d, J = 22 Hz), 114.1 (d, J = 7
Hz), 48.7, 38.8, 32.5, 20.8.
1H and 13C NMR spectra were recorded on a Bruker DRX-400 spec-
trometer (400 MHz for 1H; 100 MHz for 13C) using CDCl3 as solvent
and TMS as an internal standard. The chemical shifts are referenced
to signals at 7.26 and 77.0 ppm, respectively. Chemical shifts () are
reported in ppm and quoted to the nearest 0.01 ppm relative to the
residual protons in CDCl3 (7.26 ppm for 1H) or TMS (0 ppm for 1H)
and CDCl3 (77.0 ppm for 13C). Data are reported as follows: Chemical
shift (number of protons, multiplicity, coupling constants). Coupling
constants were quoted to the nearest 0.1 Hz and multiplicity reported
4-Chloro-N-(4-phenylbutan-2-yl)aniline (3c)14
Light yellow oil; yield: 117.8 mg (91%).
1H NMR (400 MHz, CDCl3):  = 7.28 (t, J = 7.3 Hz, 2 H), 7.18 (dd, J =
15.3, 7.2 Hz, 3 H), 7.10–7.05 (m, 2 H), 6.46–6.38 (m, 2 H), 3.41 (dd, J =
12.7, 6.3 Hz, 1 H), 2.70 (t, J = 7.4 Hz, 2 H), 1.88–1.72 (m, 2 H), 1.20 (d,
J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 146.0, 141.7, 129.0, 128.4, 125.9,
121.4, 114.2, 48.01, 38.5, 32.4, 20.6.
1a
+
+
2a
Ph
Ph
N
HN
N
N
CO2
Cp*
H
Ph
Ir
Ph
N
H+
H
1,4-addition
int-II
HN
+
+
+
+
HN
N
N
HN
N
N
N
N
HN
N
N
Cp*
Ir
O
Cp*
Cp*
Cp*
HCO2H
O
Ir
Ph
Ir
Ph
Ir
TC-1
N
H
N
H
Ph
int-I
int-IV
Ph
1,2-addition
Ph
HCO2H
int-III
Ph
N
Ph
N
Ph
H
Scheme 5 Mechanistic investigations
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Y. Xia et al.
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Synthesis
N-(4-Phenylbutan-2-yl)-4-(trifluoromethyl)aniline (3d)14
13C NMR (100 MHz, CDCl3):  = 152.0, 142.2, 141.8, 128.5, 128.5,
125.9, 115.0, 114.9, 55.9, 49.0, 38.9, 32.6, 20.9.
Light yellow oil; yield: 134.8 mg (92%).
1H NMR (400 MHz, CDCl3):  = 7.35 (t, J = 7.3 Hz, 2 H), 7.26 (dd, J =
13.5, 7.1 Hz, 3 H), 7.06 (d, J = 8.3 Hz, 2 H), 6.54–6.48 (m, 2 H), 3.49 (dd,
J = 12.7, 6.3 Hz, 2 H), 2.78 (t, J = 7.7 Hz, 2 H), 1.96–1.80 (m, 2 H), 1.27
(d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 146.3, 141.7, 139.9, 128.4, 128.4,
125.9, 122.4, 121.3 (q, J = 254 Hz), 113.1, 48.0, 38.6, 32.4, 20.6.
N-[4-(4-Fluorophenyl)butan-2-yl]aniline (3j)
Light yellow oil; yield: 106.9 mg (88%).
1H NMR (400 MHz, CDCl3):  = 7.23–7.13 (m, 4 H), 7.01 (dd, J = 12.1,
5.3 Hz, 2 H ), 6.72 (t, J = 7.3 Hz, 1 H), 6.58 (d, J = 8.0 Hz, 2 H), 3.52 (dd,
J = 12.7, 6.3 Hz, 2 H), 2.74 (t, J = 7.8 Hz, 2 H), 1.93–1.74 (m, 2 H), 1.25
(d, J = 6.3 Hz, 3 H).
4-[(4-Phenylbutan-2-yl)amino]benzonitrile (3e)21b
13C NMR (100 MHz, CDCl3):  = 161.3 (d, J = 242 Hz), 147.5, 137.6 (d,
J = 2 Hz), 129.8 (d, J = 8 Hz), 129.4, 117.1, 115.1 (d, J = 21 Hz), 113.2,
47.8, 39.0, 31.7, 20.9.
Yellow oil; yield: 112.5 mg (90%).
1H NMR (400 MHz, CDCl3):  = 7.42–7.37 (m, 2 H), 7.35–7.29 (m, 2 H),
7.27–7.17 (m, 3 H), 6.50–6.44 (m, 2 H), 4.10 (d, J = 6.8 Hz, 1 H), 3.61–
3.45 (m, 1 H), 2.74 (dd, J = 11.4, 4.7 Hz, 2 H), 1.96–1.80 (m, 2 H), 1.27
(d, J = 6.4 Hz, 3 H).
HRMS-ESI: m/z calcd for C16H19FN [M
+
H]+: 244.1502; found:
244.1501.
N-[4-(4-Chlorophenyl)butan-2-yl]aniline (3k)
13C NMR (100 MHz, CDCl3):  = 150.7, 141.4, 133.8, 128.54, 128.4,
Light yellow oil; yield: 116.5 mg (90%).
126.1, 120.7, 112.4, 98.1, 47.50, 38.4, 32.3, 20.6.
1H NMR (400 MHz, CDCl3):  = 7.31 (d, J = 8.4 Hz, 2 H), 7.23 (t, J = 7.8
Hz, 2 H), 7.16 (d, J = 8.3 Hz, 2 H), 6.75 (t, J = 7.3 Hz, 1 H), 6.60 (d, J = 8.0
Hz, 2 H), 3.53 (dd, J = 12.7, 6.3 Hz, 2 H), 2.75 (t, J = 7.9 Hz, 2 H), 1.85
(dtd, J = 19.9, 13.9, 6.3 Hz, 2 H), 1.27 (d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 147.5, 140.5, 131.6, 129.9, 129.4,
128.5, 117.1, 113.2, 47.8, 38.8, 31.9, 20.9.
4-Methyl-N-(4-phenylbutan-2-yl)aniline (3f)14
Light yellow oil; yield: 113.5 mg (95%).
1H NMR (400 MHz, CDCl3):  = 7.42–7.35 (m, 2 H), 7.30 (t, J = 6.6 Hz, 3
H), 7.08 (d, J = 8.3 Hz, 2 H), 6.58 (d, J = 8.3 Hz, 2 H), 3.56 (dd, J = 12.6,
6.3 Hz, 1 H), 2.83 (t, J = 7.9 Hz, 2 H), 2.35 (s, 3 H), 1.98 (dd, J = 14.3, 6.7
Hz, 1 H), 1.85 (dd, J = 13.9, 6.1 Hz, 1 H), 1.31 (d, J = 6.3 Hz, 3 H).
HRMS-ESI: m/z calcd for C16H19ClN [M + H]+: 260.1206; found:
13C NMR (100 MHz, CDCl3):  = 145.4, 142.2, 129.9, 128.6, 128.5,
260.1205.
126.3, 125.9, 113.6, 48.3, 39.0, 32.6, 21.0, 20.5.
N-[4-(2-Chlorophenyl)butan-2-yl]aniline (3l)
3-Methyl-N-(4-phenylbutan-2-yl)aniline (3g)
Light yellow oil; yield: 117.8 mg (91%).
1H NMR (400 MHz, CDCl3):  = 7.41 (d, J = 7.4 Hz, 1 H), 7.29–7.18 (m, 5
H), 6.75 (t, J = 7.3 Hz, 1 H), 6.64 (d, J = 8.2 Hz, 2 H), 3.81–3.31 (m, 2 H),
2.99–2.82 (m, 2 H), 1.97–1.81 (m, 2 H), 1.31 (d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 147.6, 139.7, 133.9, 130.5, 129.6,
129.4, 127.5, 126.9, 117.0, 113.2, 48.2, 37.1, 30.5, 20.9.
Light yellow oil, yield: 102.8 mg (86%).
1H NMR (400 MHz, CDCl3):  = 7.45–7.39 (m, 2 H), 7.32 (d, J = 7.9 Hz, 3
H), 7.17 (dd, J = 11.7, 4.4 Hz, 1 H), 6.64 (d, J = 7.5 Hz, 1 H), 6.48 (d, J =
6.2 Hz, 2 H), 3.61 (dd, J = 12.6, 6.3 Hz, 2 H), 2.85 (t, J = 7.8 Hz, 2 H), 2.39
(s, 3 H), 2.05–1.83 (m, 2 H), 1.33 (d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 147.6, 142.1, 139.1, 129.2, 128.5,
HRMS-ESI: m/z calcd for C16H19ClN [M + H]+: 260.1206; found:
128.4, 125.9, 117.9, 114.0, 110.3, 47.9, 38.9, 32.5, 21.7, 20.9.
260.1204.
HRMS-ESI: m/z calcd for C17H22
N [M +
H]+: 240.1752; found:
240.1752.
N-[4-(p-Tolyl)butan-2-yl]aniline (3m)
Light yellow oil; yield: 111.1 mg (93%).
2-Methyl-N-(4-phenylbutan-2-yl)aniline (3h)
1H NMR (400 MHz, CDCl3):  = 7.30 (t, J = 7.7 Hz, 2 H), 7.27–7.18 (m, 4
H), 6.82 (t, J = 7.3 Hz, 1 H), 6.68 (d, J = 7.7 Hz, 2 H), 3.61 (dt, J = 12.6, 6.3
Hz, 2 H), 2.83 (t, J = 7.8 Hz, 2 H), 2.47 (s, 3 H), 2.04–1.85 (m, 2 H), 1.34
(d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 147.7, 139.0, 135.4, 129.4, 129.2,
128.5, 117.0, 113.3, 48.0, 39.1, 32.2, 21.2, 21.0.
Light yellow oil; yield: 98.0 mg (82%).
1H NMR (400 MHz, CDCl3):  = 7.43 (dd, J = 14.6, 7.5 Hz, 2 H), 7.34 (s, 3
H), 7.29–7.18 (m, 2 H), 6.78 (dd, J = 15.4, 7.6 Hz, 1 H), 6.68 (t, J = 7.9
Hz, 1 H), 3.70 (dt, J = 12.0, 6.0 Hz, 1 H), 3.44 (s, 1 H), 2.89 (dd, J = 15.2,
7.5 Hz, 2 H), 2.25 (d, J = 7.5 Hz, 3 H), 2.02 (ddd, J = 43.3, 13.7, 6.7 Hz, 2
H), 1.40 (t, J = 6.8 Hz, 3 H).
HRMS-ESI: m/z calcd for C17H22
N [M +
H]+: 240.1752; found:
13C NMR (100 MHz, CDCl3):  = 145.5, 142.1, 130.4, 128.6, 127.3,
240.1753.
126.0, 121.8, 116.5, 110.2, 47.9, 39.0, 32.7, 21.2, 17.7.
HRMS-ESI: m/z calcd for C17H22
N
[M
+
H]+: 240.1752; found:
N-[4-(2-Methoxyphenyl)butan-2-yl]aniline (3n)
240.1755.
Light yellow oil; yield: 114.7 mg (90%).
1H NMR (400 MHz, CDCl3):  = 7.22–7.10 (m, 4 H), 6.87 (dd, J = 17.4,
7.8 Hz, 2 H), 6.66 (t, J = 7.3 Hz, 1 H), 6.55 (d, J = 8.5 Hz, 2 H), 3.80 (s, 3
H), 3.49 (dd, J = 12.6, 6.3 Hz, 1 H), 2.80–2.65 (m, 2 H), 1.90–1.70 (m, 2
H), 1.60 (s, 1 H), 1.24 (d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 157.4, 147.7, 130.4, 129.8, 129.2,
127.1, 120.4, 116.7, 113.1, 110.2, 55.2, 48.3, 37.1, 27.0, 20.8.
4-Methoxy-N-(4-phenylbutan-2-yl)aniline (3i)14
Light yellow oil; yield: 121.1 mg (95%).
1H NMR (400 MHz, CDCl3):  = 7.41–7.33 (m, 2 H), 7.28 (t, J = 6.7 Hz, 3
H), 6.89–6.82 (m, 2 H), 6.60 (d, J = 8.9 Hz, 2 H), 3.82 (d, J = 5.2 Hz, 3 H),
3.48 (dt, J = 12.6, 6.3 Hz, 1 H), 3.02 (s, 1 H), 2.85–2.76 (m, 2 H), 1.95
(td, J = 13.9, 7.3 Hz, 1 H), 1.82 (td, J = 14.0, 7.6 Hz, 1 H), 1.28 (d, J = 6.3
Hz, 3 H).
© 2020. Thieme. All rights reserved. Synthesis 2021, 53, 1821–1827

1826
Y. Xia et al.
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Synthesis
HRMS-ESI: m/z calcd for C17H22NO [M + H]+: 256.1701; found:
13C NMR (100 MHz, CDCl3):  = 147.7, 129.2, 116.7, 113.0, 48.4, 37.1,
256.1705.
31.9, 25.8, 22.6, 20.7, 14.0.
N,N-Dimethyl-4-[3-(phenylamino)butyl]aniline (3o)
N-(Hexan-3-yl)aniline (3t)21d
Light yellow oil; yield: 121.9 mg (91%).
Light yellow oil; yield: 78.8 mg (89%).
1H NMR (400 MHz, CDCl3):  = 7.26 (t, J = 7.6 Hz, 2 H), 7.17 (d, J = 8.2
Hz, 2 H), 6.79 (dd, J = 19.3, 7.8 Hz, 3 H), 6.65 (d, J = 7.9 Hz, 2 H), 3.59
(dd, J = 12.6, 6.3 Hz, 1 H), 3.25 (s, 1 H), 3.01 (s, 6 H), 2.74 (t, J = 7.8 Hz,
2 H), 1.95 (td, J = 14.2, 7.3 Hz, 1 H), 1.82 (td, J = 14.3, 7.4 Hz, 1 H), 1.31
(d, J = 6.3 Hz, 3 H).
1H NMR (400 MHz, CDCl3):  = 7.23–7.15 (m, 2 H), 6.68 (tt, J = 7.4, 1.0
Hz, 1 H), 6.63–6.58 (m, 2 H), 3.44 (s, 1 H), 3.33 (dd, J = 11.8, 5.9 Hz, 1
H), 1.65–1.41 (m, 6 H), 0.96 (td, J = 7.2, 2.0 Hz, 6 H).
13C NMR (100 MHz, CDCl3):  = 148.3, 129.3, 116.5, 112.9, 53.8, 36.7,
27.3, 19.2, 14.3, 10.1.
13C NMR (100 MHz, CDCl3):  = 149.2, 147.8, 130.3, 129.4, 129.1,
N-Phenylcycloheptanamine (3u)21e
116.9, 113.3, 113.2, 48.0, 41.1, 39.2, 31.5, 20.9.
HRMS-ESI: m/z calcd for C18H25N2 [M
+
H]+: 269.2018; found:
Light yellow oil; yield: 85.0 mg (90%).
269.2013.
1H NMR (400 MHz, CDCl3):  = 7.24 (t, J = 7.8 Hz, 2 H), 6.74 (t, J = 7.3
Hz, 1 H), 6.62 (d, J = 8.3 Hz, 2 H), 3.90–3.29 (m, 2 H), 2.13–2.03 (m, 2
H), 1.78–1.51 (m, 10 H).
N-[4-(Naphthalen-1-yl)butan-2-yl]aniline (3p)
Light yellow oil; yield: 127.9 mg (93%).
13C NMR (100 MHz, CDCl3):  = 147.3, 129.2, 116.7, 113.1, 53.5, 34.7,
1H NMR (400 MHz, CDCl3):  = 8.11–8.05 (m, 1 H), 7.97–7.89 (m, 1 H),
7.79 (d, J = 8.1 Hz, 1 H), 7.58–7.51 (m, 2 H), 7.49–7.43 (m, 1 H), 7.39
(d, J = 6.9 Hz, 1 H), 7.24 (t, J = 7.8 Hz, 2 H), 6.77 (t, J = 7.3 Hz, 1 H), 6.65
(d, J = 8.1 Hz, 2 H), 3.67 (dd, J = 12.6, 6.3 Hz, 1 H), 3.55 (s, 1 H), 3.31–
3.20 (m, 2 H), 2.08–1.97 (m, 2 H), 1.34 (d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 147.7, 138.2, 134.0, 131.9, 129.4,
128.9, 126.8, 126.1, 125.9, 125.7, 125.6, 123.8, 117.1, 113.4, 48.4, 38.1,
29.6, 21.0.
28.3, 24.3.
N-[2-Methyl-5-(prop-1-en-2-yl)cyclohexyl]aniline (3v)21f
Light yellow oil; yield: 93.9 mg (82%).
1H NMR (400 MHz, CDCl3):  = 7.18 (t, J = 7.8 Hz, 2 H), 6.66 (dd, J =
14.0, 7.6 Hz, 3 H), 4.69 (s, 2 H), 3.68 (d, J = 3.1 Hz, 1 H), 2.10 (ddd, J =
10.5, 9.1, 2.8 Hz, 2 H), 1.86–1.76 (m, 2 H), 1.70 (s, 3 H), 1.64 (ddd, J =
15.4, 9.3, 6.5 Hz, 2 H), 1.41–1.27 (m, 3 H), 0.99 (d, J = 6.9 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 150.0, 148.2, 129.3, 116.5, 112.9,
108.6, 52.7, 38.6, 35.5, 35.3, 31.3, 29.2, 21.1, 18.9.
HRMS-ESI: m/z calcd for
C20H22N [M +
H]+: 276.1752; found:
276.1756.
N-[4-(Furan-2-yl)butan-2-yl]aniline (3q)
Brown oil; yield: 90.3 mg (84%).
Funding Information
1H NMR (400 MHz, CDCl3):  = 7.39 (s, 1 H), 7.24 (dd, J = 8.0, 7.6 Hz, 2
H), 6.76 (t, J = 7.3 Hz, 1 H), 6.63 (d, J = 7.8 Hz, 2 H), 6.36 (d, J = 1.7 Hz, 1
H), 6.09–6.04 (m, 1 H), 3.63–3.34 (m, 2 H), 2.82 (t, J = 7.7 Hz, 2 H),
2.00–1.85 (m, 2 H), 1.28 (d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3):  = 155.8, 147.6, 141.0, 129.4, 117.1,
113.2, 110.3, 105.1, 48.0, 35.4, 24.9, 20.8.
The authors thank the National Natural Science Foundation of China
(21962004, 21562004), Jiangxi Provincial Department of Science and
Technology (20192BAB203004), the Emergency Research Project for
Gannan Medical University (YJ202027), and the Fundamental Re-
search Funds for Gannan Medical University (QD201810) for financial
support.
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HRMS-ESI: m/z calcd for C14H18NO [M + H]+: 216.1388; found:
216.1391.
Supporting Information
N-(4-Cyclohexylbutan-2-yl)aniline (3r)
Supporting information for this article is available online at
Light yellow oil; yield: 107.4 mg (93%).
https://doi.org/a-1344-2126.
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1H NMR (400 MHz, CDCl3):  = 7.18 (t, J = 7.9 Hz, 2 H), 6.68 (t, J = 7.3
Hz, 1 H), 6.59 (d, J = 7.9 Hz, 2 H), 3.47–3.41 (m, 2 H), 1.75–1.57 (m, 6
H), 1.44 (ddd, J = 10.1, 6.6, 4.3 Hz, 1 H), 1.32–1.17 (m, 9 H), 0.91 (ddd,
J = 19.6, 9.4, 6.1 Hz, 2 H).
References
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