A Metal-Free Approach to 1,2-Diamines via Visible Light-Driven Reductive Coupling of Imines with Perylene as a Photoredox Catalyst

Article abstract of DOI:10.1021/acs.joc.7b01838

A simple, metal-free, and versatile approach to 1,2-diamines has been developed based on reductive coupling reactions of various imines, where perylene, an aromatic hydrocarbon, was used as a photoredox catalyst under visible light irradiation using a white light-emitting diode. The use of 1 mol % perylene enabled almost complete conversion of the imines, leading to the formation of their corresponding 1,2-diamines, which were isolated in good yields. The ratios between dl and meso diamines ranged from 31:69 to 82:18 depending on the substituents of the imines.

Full text of DOI:10.1021/acs.joc.7b01838

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Article
A Metal-free Approach to 1,2-Diamines via Visible Light-driven
Reductive Coupling of Imines with Perylene as a Photoredox Catalyst
Shusuke Okamoto, Risako Ariki, Hiroki Tsujioka, and Atsushi Sudo
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b01838 • Publication Date (Web): 24 Aug 2017
Downloaded from http://pubs.acs.org on August 25, 2017
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A Metalꢀfree Approach to 1,2ꢀDiamines via Visible Lightꢀdriven Reductive Coupling of
Imines with Perylene as a Photoredox Catalyst
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Shusuke Okamoto, Risako Ariki, Hiroki Tsujioka and Atsushi Sudo*
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Department of Applied Chemistry, Faculty of Science and Engineering, Kindai
University, Kowakae 3ꢀ4ꢀ1, Higashi Osaka, Osaka 577ꢀ8502, Japan.
Eꢀmail: asudo@apch.kindai.ac.jp
Abstract
A simple, metalꢀfree, and versatile approach to 1,2ꢀdiamines has been developed based
on reductive coupling reactions of various imines, where perylene, an aromatic
hydrocarbon, was used as a photoredox catalyst under visible light irradiation using a
white LED. The use of 1 mol% perylene enabled almost complete conversion of the
imines, leading to the formation of their corresponding 1,2ꢀdiamines, which were
isolated in good yields. The ratios between dl and meso diamines ranged from 31:69 to
82:18 depending on the substituents of the imines.
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Introduction
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Reductive coupling reaction of imines is a straightforward approach to obtain
1,2ꢀdiamines,1aꢀg which are highly valuable as precursors for ligands and chiral
auxiliaries.2aꢀc These reactions have been achieved using metals, lowꢀvalent metal
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species,
and
metal
alloys
such
as
magnesium,1a,b
samarium(II),1cꢀe
titanium(III)ꢀmagnesium,1f and zincꢀcopper alloys.1g From these metal species with high
reduction potentials, one electron can be transferred efficiently to imines to transform
them into the corresponding radical anions, which then readily undergo coupling
reactions to give 1,2ꢀdiamines. Due to a lack of other efficient methods, existing
protocols have been frequently used. However, the consumption of stoichiometric
amounts of precious metals such as those listed above is becoming more problematic in
recent years from both economic and environmental perspectives. Therefore, the
development of alternative catalytic method that avoid the utilization of large amounts
of metal species is desired.
The requirement for greener and more sustainable alternative methods may be
fulfilled by utilizing visible light as an energy source to drive the reaction. Currently,
various reactions that can be promoted under irradiation of visible light have been
developed.3 In these reactions, photoredox catalysts are excited by visible light and
mediate reactions via electron transfer processes. Among the various photoredox
catalysts developed so far, ruthenium(II) and iridium(III) complexes have been the most
extensively investigated. The applications of these metal complexes include
dehalogenation,4 CꢀC bond forming,5 and Cꢀheteroatom bond forming reactions.6
Nakajima et al. reported reductive coupling of Nꢀbenzylimines under irradiation of
visible light using iridium(II) complexes as photoredox catalysts, allowing for the
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efficient synthesis of a variety of 1,2ꢀdiamines.7 Fava et al. have reported the use of an
iridium complex for visible lightꢀdriven reductive coupling of imines and
Nꢀmethylaniline derivatives.8 In addition, Rono et al. have reported the intramolecular
coupling of ketohydrazone under the irradiation of visible light using iridium(II)
complexes as a photoredox catalyst.9
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Besides such metal complexes, organic dyes with extended πꢀconjugated systems are
also attractive candidates for photoredox catalysts, due to their structural diversity and
lower cost and their nonꢀdependence of the utilization of precious metals.10 Recently,
perylene, a commercially available polycyclic aromatic hydrocarbon, has been attracted
attention as a photoredox catalyst that mediates controlled radical polymerizations.11 We
reported reductive coupling reactions of aromatic aldehydes and ketones, where
perylene acted as a photoredox catalyst effectively.12 In the mechanism postulated
therein, perylene is excited (P*) upon irradiation with visible light. The excited perylene,
P*, then abstracts one electron from a sacrificial tertiary amine, affording a perylene
radical anion (P˙−). Then, single electron transfer from P˙− to aldehydes and ketones
converts them into the corresponding ketyl radicals, which readily undergo
homoꢀcoupling reactions to afford 1,2ꢀdiols.
In this study, we expanded the scope of metalꢀfree photocatalysis using perylene for
the reductive coupling reaction of imines under visible light irradiation. Reductive
coupling reactions of Nꢀarylmethylꢀ, Nꢀtertꢀbutylꢀ, and Nꢀarylꢀsubstituted imines
derived from aromatic aldehydes were performed to demonstrate the versatility of this
photocatalytic system.
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Results and Discussion
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Coupling reaction of imine 1a using perylene as a photoredox catalyst
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First, using imine 1a obtained by the condensation of benzaldehyde and
benzylamine, conditions for the reductive coupling reaction of imines
1 were
optimized (Scheme 1, Table 1). Acetonitrile was selected as the solvent, since it
has been reported that photosensitized oxidation of tertiary amines using perylene
was successfully performed in acetonitrile.13 In addition, successful photoredox
catalysis of the reductive coupling reaction of aromatic aldehydes in acetonitrile
was successfully demonstrated in our previous report.12
Scheme 1. Reductive coupling of imine 1a
Initially, the reaction was performed under the same optimized conditions
developed for the visible lightꢀdriven reductive coupling reaction of
benzaldehyde reported in our previous work (entry 1): upon irradiating an
acetonitrile solution of 1a, perylene (12 mol%), and
N,Nꢀdiisopropylethylamine
(
i
ꢀPr2NEt; 8 eq.) with visible light using an 8.5 W white LED for 16 h, imine 1a
was consumed completely to yield the corresponding diamine 2a. Diamine 2a
was isolated by preparative TLC in 66% yield. The structure of 2a was confirmed
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1
by comparing its Hꢀ and 13CꢀNMR data with reported spectra.7 The spectra
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clarified that diamine 2a was obtained as a diastereomeric mixture with a dl:meso
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ratio of 65:35.
Table 1. Optimization of the reaction conditions for the reductive coupling of
Nꢀbenzylimine 1a
Amount of
Yield
of 2a
/%a
66
Yield of
Tertiary
Amine
Reaction
time/h
dl :
Entry
perylene
DBA
mesob
/mol%
/%c
1
2
i
ꢀPr2NEt
ꢀPr2NEt
ꢀPr2NEt
ꢀPr2NEt
Et3N
12
4
16
16
16
4
65:35
71:29
67:33
89:11
74:26
ꢀ
N.D.d
i
i
i
58
5
3
1
68
6
4
1
25
N.D.d
5
1
16
16
16
46
N.D.d
6e
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i
i
ꢀPr2NEt
ꢀPr2NEt
None
1
0
ꢀ
ꢀ
0
0
ꢀ
8
1
16
0
ꢀ
ꢀ
a
b
1
Yield of 2a isolated by preparative TLC. Determined by the H NMR
analysis of 2a isolated by preparative TLC. c Determined by the H NMR
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analysis of crude 2a before isolation. d Not determined. e Without irradiation.
Next, the influence of the amount of added perylene on the reaction efficiency was
investigated (Table 1, entries 2 and 3). Remarkably, even when the amount of perylene
was decreased to 1 mol%, the reaction proceeded efficiently to give 2a with good yields.
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The crude product obtained by the experiment in entry 3 was analyzed by 1HꢀNMR. The
spectrum is shown in Figure 1. All the major signals were attributable to the protons of
2a, implying a high conversion of imine 1a to diamine 2a. Besides, broad and multiple
signals at around 1 ppm were attributable to alkyl groups of unidentified compounds
derived from iꢀPr2NEt. A weak signal at 8.1 ppm was observed to confirm the presence
of a small amount of unconsumed imine 1a.
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The 13CꢀNMR spectrum of the crude product is also shown in Figure 1. The spectrum
confirmed that diamine 2a was fairly pure when the unidentified iꢀPr2NEtꢀderived
compounds were neglected.
The reduction of 1a into dibenzylamine (DBA) can compete with the reductive
1
coupling reaction of 1a into the diamine 2a. In the HꢀNMR spectrum of the crude
mixture (Figure 1), a singlet signal was observed at 3.8 ppm, confirming the presence of
DBA. The presence of DBA was also confirmed by 13CꢀNMR analysis of the crude
mixture. A weak signal attributable to the methylene carbons of DBA was observed at
1
53 ppm. Based on the HꢀNMR analysis, the yields of DBA in entries 2 and 3 were
calculated to be 5 and 6%, respectively.
In the experiment denoted by entry 4, irradiation of visible light was stopped at 4 h.
As a result, the yield of 2a dropped to 25%. For the experiment denoted by entry 5,
triethylamine (Et3N) was used in place of iꢀPr2NEt. The yield of 2a decreased to 46%
without influencing the diastereoselectivity. For the runs summarized in entries 6–8, the
reaction was carried out without irradiation, in the absence of perylene, and in the
absence of tertiary amine, respectively. In these cases, the reaction barely proceeded,
indicating that the presence of all of these factors were indispensable for efficient
progress of the reaction.
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(a) 1H-NMR
Ph
CHCl3
b
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a
b'
HN H
Ph
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a'
Ph
Ph
N
H
Ph
HN H
a
b
DBA
Ph
c
dl-2a
Ph
Ph
H NH
Ph
Ph
HN H
4.0
3.5
3.0
a'
b'
Ph
meso-2a
imine
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ppm
Figure 1. 1Hꢀ and 13CꢀNMR spectra of crude diamine 2a
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Reductive coupling reactions of imines 1b-m
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Under the optimized conditions for the reductive coupling reaction of 1a, those of the
other imines 1b–1m were performed to expand the substrate scope of the photoredox
catalyst under study (Scheme 2, Table 2). Imine conversion was determined by
1HꢀNMR analysis of reaction mixtures before isolation of the corresponding diamines.
The reactions of Nꢀ(arylmethyl)imines 1b–1g gave the corresponding diamines 2b–
2g in moderate to good yields. Diamines 2b–2g were obtained as mixtures of dlꢀ and
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mesoꢀdiastereomers and their ratios were determined by HꢀNMR. It is noteworthy that
the coupling reaction of imine 1c bearing a 4ꢀmethoxyphenyl group gave diamine 2c
with a higher yield of its dlꢀdiastereomer over that of its mesoꢀdiastereomer (Table 2,
entry 3). Such a dominant formation of the dlꢀdiastereomer was observed also in the
reductive pinacol coupling reaction of 4ꢀmethoxybenzaldehyde.12
The protocol using perylene as the photoredox catalyst was extended to the reductive
coupling reactions of several Nꢀ(tertꢀbutyl)imines 1h–1k (Table 2, entries 8–11). In all
1
cases, excellent reactivity was revealed by HꢀNMR analysis of the crude reaction
1
product. Figure S2 shows the Hꢀ and 13CꢀNMR spectra of the crude product obtained
by the coupling reaction of imine 1h, demonstrating the high efficiency of the reaction.
In these reactions, the amounts of meso isomers were slightly higher than those of dl
isomers. Nꢀarylꢀtype imines 1l and 1m were also converted into the corresponding
diamines 2l and 2m. In these reactions, higher mesoꢀselectivity was observed than in the
reactions of Nꢀ(tertꢀbutyl)imines 1h–1k.
The conversions of imines 1c and 1m bearing a 4ꢀmethoxyphenyl group were lower
than those of the other imines. The lower reaction efficiencies may be due to the higher
electron densities of these substrates, which can hinder the approach of a radical anion
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of perylene to the substrates.
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Scheme 2. Reductive coupling of imines 1
Table 2. Reductive coupling reactions of imines
Conversion
of 1/%a
Yield
/%b
dl :
mesoc
Entry
R1
R2
1
2
1
2
PhCH2
PhCH2
PhCH2
PhCH2
PhCH2
Ph
4ꢀMeC6H4
4ꢀMeOC6H4
4ꢀCF3C6H4
4ꢀClC6H4
Ph
98
100
53
68
69
32
80
70
55
75
64
77
73
75
70
41
67 : 33
69 : 31
82 : 18
54 : 46
65 : 35
66 : 34
59 : 41
45 : 55
41 : 59
48 : 52
44 : 56
39 : 61
31 : 69
1a
1b
1c
1d
1e
2a
2b
2c
2d
2e
2f
3
4
100
100
100
100
100
100
100
100
99
5
6
1f (4ꢀMeOC6H4)CH2
7
(4ꢀCF3C6H4)CH2
Ph
1g
1h
1i
2g
2h
2i
8
tꢀBu
tꢀBu
tꢀBu
tꢀBu
Ph
Ph
9
4ꢀMeC6H4
4ꢀFC6H4
4ꢀCF3C6H4
Ph
10
11
12
13
1j
2j
1k
1l
2k
2l
4ꢀMeOC6H4
Ph
67
1m
2m
a Determined by HꢀNMR analysis of crude product. b Isolated by silica gel column
1
chromatography. c Determined by 1HꢀNMR of isolated product.
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Reaction mechanism
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In our previous report, a plausible mechanism for the photoredox catalysis of
reductive coupling reactions of aromatic aldehydes and ketones by perylene was
postulated,12 based on the ability of perylene to mediate the oxidation of tertiary amines
by absorbing visible light.13 By analogy, a mechanism for the present photoredox
catalysis of the reductive coupling reaction of imines was postulated (Scheme 3).
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Scheme 3. Plausible mechanism for the reductive coupling using perylene as the
photoredox catalyst
First, excited perylene (P*) generated by the irradiation of perylene (P) with
visible light abstracts one electron from a tertiary amine. Second, single electron
transfer (SET) from the resulting radical anion of perylene (P.ꢀ) to imine
1 takes
place to convert into the corresponding radical anion. Third, the radical anions
1
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undergo a homoꢀcoupling reaction to achieve carbonꢀcarbon bond formation.
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Finally, target diamine
2 can be obtained via abstraction of protons from proton
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donors such as the radical cation of the tertiary amine. Another possibility is that
the radical anions abstract protons, and then the formed radicals undergo coupling
reactions to form the corresponding diamines.
Because the important step in this reaction is SET from P.ꢀ to imine, density
functional theory (DFT) calculations were conducted to estimate the SOMO energy
level of the perylene radical anion (P.ꢀ) and the LUMO energy level of imine 1a (Figure
2). For comparison, the LUMO energy level of benzaldehyde was calculated in a similar
manner. The LUMO energy level of 1a (–1.21 eV) was higher than that of benzaldehyde
(–1.73 eV) and thus closer to the SOMO level of P.ꢀ (–0.69 eV), implying that the SET
from P.ꢀ to 1a would be less exothermic and less efficient than that to benzaldehyde. On
the other hand, the amount of perylene required for the efficient reductive coupling of
imine 1a was 1 mol%, while the amount of perylene required for the coupling reaction
of benzaldehyde was 12 mol%,12 implying that the efficiency of the SET from P.ꢀ to 1a
would be higher than that of the SET to benzaldehyde. The combination of these two
considerations leads to an assumption that the interactions of the SOMO of P.ꢀ and the
LUMO of an acceptor (imine or aldehyde) govern the SET process to some extent.
Because perylene is an aromatic compound with high planarity that allows πꢀπ
interaction with the substrates, such SOMOꢀLUMO interactions can be significantly
enhanced.
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Figure 2. Energy levels of SOMO and HOMO of the perylene radical anion, LUMO of
imine 1a, and LUMO of benzaldehyde
Conclusions
A highly efficient visible lightꢀdriven system for reductive coupling reactions to
transform imines to their corresponding 1,2ꢀdiamines has been developed using
perylene, a simple polycyclic aromatic hydrocarbon, as a photoredox catalyst. The
coupling reactions gave the corresponding 1,2ꢀdiamines as mixtures of their dlꢀ and
mesoꢀdiastereomers, and the selectivity depended on the substituents on the nitrogen
atom of imines. 1) Coupling reactions of Nꢀarylmethyl imines gave the corresponding
diastereomeric mixtures of diamines, where the dlꢀdiastereomers dominated over the
mesoꢀdiastereomers. 2) In coupling reactions of Nꢀtertꢀbutyl imines, no clear
diastereoselectivity was observed. 3) In coupling reactions of Nꢀaryl imines, the
formation of mesoꢀdiamines dominated over that of dlꢀdiamines. The present
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photoredox catalytic method using perylene under irradiation of visible light allows for
the synthesis of 1,2ꢀdiamines without the use of stoichiometric amounts of precious
metal reagents and is thus considered to be more cost effective and environmentally
friendly.
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EXPERIMENTAL SECTION
General methods and materials
Acetonitrile was distilled from calcium hydride and stored over 4 Å molecular sieves
in an argon atmosphere. The aldehydes were also distilled under an argon atmosphere.
The primary amines and diisopropylethyamine were distilled and stored over sodium
1
hydroxide in argon. NMR spectra (400 MHz for H; 100 MHz for 13C) were recorded
with a JEOL NMR spectrometer (JNMꢀAL400) as solutions in CDCl3 using TMS as the
internal standard. Chemical shifts, δ, and coupling constants, J, are expressed in ppm
and Hz, respectively. IR spectra were obtained using a JASCO FT/IRꢀ470 spectrometer,
and wavenumbers, ν, are given in cm−1. Highꢀresolution mass spectroscopic analyses
were performed using a JEOL mass spectrometer (JMSꢀT100LP AccuTOF LCꢀplus) in
a direct analysis in real time (DART) mode and detected by the timeꢀofꢀflight (TOF)
method. For irradiation, a HOZAN LED (model L–711) was used.
General procedure for the preparation of imines 1
To a solution of an aldehyde (5.0–20.0 mmol) and a primary amine (1.0–1.3 eq) in
dichloromethane (10–40 mL), molecular sieves 4 Å (1.0–4.0 g) were added. The
resulting mixture was stirred vigorously at room temperature for 16 h. The mixture was
passed through a Celite pad, and the filtrate was concentrated under reduced pressure
and dried under vacuum to obtain the corresponding imines. The imines were purified
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by Kugelrohr distillation.
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N-Benzylbenzaldimine (1a)
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According to the general procedure, 1a was obtained as a colourless oil (1.11 g, 57%
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yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.14 HRMS (DART) m/z:
[M+H]+ Calcd for C14H14N 196.1126; Found: 196.1132.
N-Benzyl-4-methylbenzaldimine (1b)
According to the general procedure, 1b was obtained as a pale yellow oil (604 mg,
1
58% yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.14 HRMS (DART)
m/z: [M+H]+ Calcd for C15H16N 210.1283; Found: 210.1277.
N-Benzyl-4-methoxybenzaldimine (1c)
According to the general procedure, 1c was obtained as a pale yellow oil (629 mg,
1
56% yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.14 HRMS (DART)
m/z: [M+H]+ Calcd for C15H15NO 226.1228; Found: 226.1232.
N-Benzyl-4-trifluoromethylbenzaldimine (1d)
According to the general procedure, 1d was obtained as a white solid (2.45 g, 93%
1
yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.15 HRMS (DART) m/z:
[M+H]+ Calcd for C15H12F3N 264.1000; Found: 264.0994.
N-Benzyl-4-chlorobenzaldimine (1e)
According to the general procedure, 1e was obtained as a colourless oil (2.10 g, 92%
1
yield). Its HꢀNMR data agreed with those reported.16 13CꢀNMR (CDCl3, r.t.) δ 160.7,
139.2, 136.8, 134.7, 129.6, 129.0, 128.7, 128.4, 128.1, 127.2, 65.1. IR: 3061, 3028,
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2839, 1644, 751, 697 cm−1. HRMS (DART) m/z: [M+H]+ Calcd for C14H12ClN
230.0737; Found: 230.0736.
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N-Benzylidene-4-methoxybenzylamine (1f)
According to the general procedure, 1f was obtained as a white solid (1.86 g, 83%
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yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.17 HRMS (DART) m/z:
[M+H]+ Calcd for C15H15NO 226.1232; Found: 226.1230.
N-Benzylidene-4-trifluoromethylbenzylamine (1g)
According to the general procedure, 1g was obtained as pale a pale yellow oil (2.53 g,
96% yield): 1HꢀNMR (CDCl3, r.t.) δ 8.40 (s, 1H), 7.78 (d, J = 5.4 Hz, 2H), 7.58 (d, J =
8.3 Hz, 2H), 7.46ꢀ7.41 (m, 5H), 4.84 (s, 2H); 13CꢀNMR (CDCl3, r.t.) δ 162.8, 143.7,
136.0, 131.1, 129.5, 129.2, 128.8, 128.4, 128.2, 125.8, 125.6, 125.5, 125.5, 125.4, 123.1,
64.5; IR (KBr) ν 3064, 3029, 2846, 1646, 761, 693 cm−1. HRMS (DART) m/z: [M+H]+
Calcd for C15H13F3N 264.1000; Found: 264.0996.
N-tert-Butylbenzaldimine (1h)
According to the general procedure, 1h was obtained as a colourless oil (2.43 g, 75%
1
yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.18 HRMS (DART) m/z:
[M+H]+ Calcd for C11H16N 162.1283; Found: 162.1269.
N-tert-Butyl-4-methylbenzaldimine (1i)
According to the general procedure, 1i was obtained as a colourless oil (1.30 g, 74%
1
yield). Its HꢀNMR data agreed with those reported.19 13CꢀNMR (CDCl3, r.t.) δ 155.2,
140.4, 129.3, 128.0, 114.0, 57.2, 29.9, 21.6. HRMS (DART) m/z: [M+H]+ Calcd for
C12H18N 176.1439; Found: 176.1422.
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N-tert-Butyl-4-fluorobenzaldimine (1j)
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According to the general procedure, 1j was obtained as a colourless oil (0.77 g, 43%
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yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.18 HRMS (DART) m/z:
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[M+H]+ Calcd for C11H15FN 180.1189; Found: 180.1170.
N-tert-Butyl-4-trifluoromethylbenzaldimine (1k)
According to the general procedure, 1k was obtained as a colourless oil (0.85 g, 74%
1
yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.18 HRMS (DART) m/z:
[M+H]+ Calcd for C12H15F3N 230.1157; Found: 230.1152.
N-Phenylbenzaldimine (1l)
According to the general procedure, 1l was obtained as a pale yellow oil (1.68 g, 93%
1
yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.14 HRMS (DART) m/z:
[M+H]+ Calcd for C13H12N 182.0970; Found: 182.0962.
N-(4-Methoxyphenyl)benzaldimine (1m)
According to the general procedure, 1m was obtained as a brown solid (2.09 g, 99%
1
yield). Its Hꢀ and 13CꢀNMR data agreed with those reported.20 HRMS (DART) m/z:
[M+H]+ Calcd for C14H14NO 212.1075; Found: 212.1074.
General Procedure for the reductive coupling reaction of imines
Imine 1 (1.00 mmol), perylene (2.5 mg; 10 ꢁmol), iꢀPr2EtN (1.40 mL, 8.00 mmol),
and acetonitrile (50 mL) were added to a 100 mL flask under argon. The resulting
solution was irradiated using a LED light under stirring at room temperature. After 16 h,
the solution was concentrated under reduced pressure. The resulting residue was
purified by a silica gel column chromatography (eluent: hexane / ethyl acetate /
triethylamine = 400~1000 / 50 / 1) and preparative TLC (eluent: hexane / ethyl acetate /
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triethylamine = 500~1000 : 50 : 1) to afford the corresponding diamine 2 as a mixture of
dlꢀ and mesoꢀdiastereomers.
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1,2-Diphenyl-N,N'-bis(phenylmethyl)-1,2-ethanediamine (2a)
According to the general procedure, 2a was obtained as a pale yellow solid (133 mg,
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68%, dl : meso = 67 : 33). Its Hꢀ and 13CꢀNMR data agreed with those reported.7,12
HRMS (DART) m/z: [M+H]+ Calcd for C28H29N2 393.2331; Found: 393.2314.
1,2-Bis(4-methylphenyl)-N,N'-bis(phenylmethyl)-1,2-ethanediamine (2b)
According to the general procedure, 2b was obtained as a pale yellow solid (146 mg,
69% yield, dl : meso = 69 : 31): 1HꢀNMR (CDCl3, r.t.) δ 7.30ꢀ7.12 (m, 28H), 6.97ꢀ6.93
(m, 8H), 3.69 (s, 2H, dl), 3.67 (s, 2H, meso), 3.64 (d, J = 13.7 Hz, 2H, meso), 3.52 (d, J
= 14.2 Hz, 2H, dl), 3.47 (d, J = 13.7 Hz, 2H, meso), 3.28 (d, J = 13.7 Hz, 2H), 2.35 (s,
6H, dl), 2.25 (s, 6H, meso), 1.92 (brs, 4H, dl and meso); 13CꢀNMR (CDCl3, r.t.) δ 140.6,
140.6, 137.9, 137.3, 129.3, 129.3, 128.8, 128.8, 128.6, 128.4, 128.3, 128.2, 128.0, 126.8,
126.7, 68.0, 67.1, 51.4, 51.0, 21.3, 21.3. IR (KBr) ν 3308, 3061, 2963, 2922, 2825, 1454,
738, 695. cm−1. HRMS (DART) m/z: [M+H]+ Calcd for C30H33N2 421.2644; Found:
421.2631.
1,2-Bis(4-methoxyphenyl)-N,N'-bis(phenylmethyl)-1,2-ethanediamine (2c)
According to the general procedure, 2c was obtained as a pale yellow solid (72.7 mg,
32% yield, dl : meso = 82 : 18). Its 1Hꢀ and 13CꢀNMR data agreed with those reported.7
HRMS (DART) m/z: [M+H]+ Calcd for C30H33N2O2 453.2542; Found: 453.2527.
1,2-Bis(4-trifluoromethylphenyl)-N,N'-bis(phenylmethyl)-1,2-ethanediamine (2d)
According to the general procedure, 2d was obtained as a pale yellow solid (211 mg,
80% yield, dl : meso = 54 : 46): 1HꢀNMR (CDCl3, r.t.) 7.55 (d, J = 7.8 Hz, 4H), 7.43 (d,
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J = 8.3 Hz, 4H), 7.30 (d, J = 8.3 Hz, 4H), 7.27ꢀ7.18 (m, 16H), 7.14 (d, J = 7.8 Hz, 4H),
7.01 (d, J = 7.8 Hz, 4H), 3.85 (s, 2H, dl), 3.75 (s, 2H, meso), 3.65 (d, J = 13.2 Hz, 2H,
dl), 3.56 (d, J = 13.7 Hz, 2H, meso), 3.46 (d, J = 13.7 Hz, 2H, dl), 3.32 (d, J = 13.7 Hz,
2H, meso), 2.03 (brs, 4H, dl and meso); 13CꢀNMR (CDCl3, r.t.) δ145.2, 144.6, 140.0,
139.9, 130.6, 130.3, 129.9, 129.8, 129.6, 129.5, 129.0, 128.6, 128.5, 128.3, 128.2, 128.0,
127.2, 127.2, 125.7, 125.6, 125.4, 125.4, 125.3, 125.3, 125.2, 125.2, 123.0, 122.9, 67.9,
66.6, 51.4, 51.2. IR (KBr) ν 3274, 3020, 2927, 2861, 1327, 1121, 748, 699 cm−1. HRMS
(DART) m/z: [M+H]+ Calcd for C30H27F6N2 529.2078; Found: 529.2053.
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1,2-Bis(4-chlorophenyl)-N,N'-bis(phenylmethyl)-1,2-ethanediamine (2e)
According to the general procedure, 2e was obtained as a pale yellow solid (162 mg,
70% yield, dl : meso = 65 : 35): 1HꢀNMR (CDCl3, r.t.) 7.31ꢀ7.17 (m, 16H), 7.14 (d, J =
8.3 Hz, 8H), 7.00 (d, J = 6.3 Hz, 8H), 6.94 (d, J = 8.3 Hz, 4H), 3.72 (s, 2H, dl),
3.65ꢀ3.61 (m, 4H, dl and meso), 3.55 (d, J = 13.7 Hz, 2H, dl), 3.46 (d, J = 13.7 Hz, 2H,
meso), 3.30 (d, J = 13.7 Hz, dl), 1.80 (brs, 4H, dl and meso); 13CꢀNMR (CDCl3, r.t.)
δ140.3, 140.1, 139.6, 139.0, 133.7, 133.4, 130.1, 130.0, 129.4, 128.6, 128.6, 128.5,
128.5, 128.4, 128.4, 128.3, 128.2, 128.2, 128.0, 128.0, 127.1, 127.0, 126.9, 67.7, 66.4,
51.4, 51.1. IR (KBr) ν 3279, 3062, 3026, 2961, 2859, 1455, 747, 697 cm−1. HRMS
(DART) m/z: [M+H]+ Calcd for C28H27Cl2N2 461.1551; Found: 461.1530.
N,N'-Bis[(4-methoxyphenyl)methyl]-1,2-diphenyl-1,2-ethanediamine (2f)
According to the general procedure, 2f was obtained as a pale yellow solid (125 mg,
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55% yield, dl : meso = 66 : 34): HꢀNMR (CDCl3, r.t.) 7.33ꢀ7.25 (m, 12H), 7.15ꢀ7.11
(m, 8H), 7.03 (d, J = 6.8 Hz, 4H), 6.88 (d, J = 8.8 Hz, 4H), 6.82 (d, J = 8.3 Hz, 4H),
6.74 (d, J = 8.8 Hz, 4H), 3.78 (s, 6H, meso), 3.76 (s, 6H, dl), 3.73 (s, 2H, dl), 3.68 (s,
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2H, meso), 3.58 (d, J = 12.7 Hz, 2H), 3.46 (d, J = 13.7 Hz, 2H), 3.40 (d, J = 13.2 Hz,
2H), 3.23 (d, J = 13.2 Hz, 2H), 1.92 (brs, 4H, dl and meso); 13CꢀNMR (CDCl3, r.t.)
δ158.6, 158.5, 141.4, 141.0, 132.9, 132.6, 129.4, 129.1, 128.7, 128.4, 128.1, 128.0,
127.7, 127.0, 113.8, 113.7, 68.3, 67.2, 55.4, 55.3, 50.8, 50.4. IR (KBr) ν 3446, 3029,
2954, 2834, 1457, 753, 702 cm−1. HRMS (DART) m/z: [M+H]+ Calcd for C30H33N2O2
453.2542; Found: 453.2520.
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N,N'-Bis[(4-trifluoromethylphenyl)methyl]-1,2-diphenyl-1,2-ethanediamine (2g)
According to the general procedure, 2g was obtained as a pale yellow solid (198 mg,
75% yield, dl : meso = 59: 41): 1HꢀNMR (CDCl3, r.t.) 7.52 (d, J = 7.8 Hz, 8H), 7.44 (d,
J = 7.8 Hz, 8H), 7.36ꢀ7.29 (m, 12H), 7.21ꢀ7.14 (m, 8H), 7.05 (d, J = 7.8 Hz, 8H),
3.73ꢀ3.70 (m, 6H), 3.56 (t, J = 13.7 Hz, 4H), 3.35 (d, J = 14.2 Hz, 2H), 2.02 (brs, 4H, dl
and meso); 13CꢀNMR (CDCl3, r.t.) δ144.7, 144.6, 140.8, 140.6, 129.4, 129.3, 129.1,
128.9, 128.7, 128.6, 128.5, 128.4, 128.4, 128.3, 128.2, 128.1, 128.0, 127.3, 125.8, 125.7,
125.4, 125.3, 125.3, 125.2, 125.2, 125.2, 123.1, 123.0, 68.4, 67.5, 50.9, 50.5. IR (KBr) ν
3278, 3061, 2854, 2825, 1454, 1119, 753, 697 cm−1. HRMS (DART) m/z: [M+H]+
Calcd for C30H27F6N2 529.2078; Found: 529.2054.
N,N'-Bis(1,1-dimethylethyl)-1,2-diphenyl-1,2-ethanediamine (2h)
According to the general procedure, 2h was obtained as a pale yellow solid (104 mg,
64% yield, dl : meso = 45 : 55). Its 1Hꢀ and 13CꢀNMR data agreed with those reported.21
HRMS (DART) m/z: [M+H]+ Calcd for C22H33N2 325.2644; Found 325.2647.
N,N'-Bis(1,1-dimethylethyl)-1,2-bis(4-methylphenyl)-1,2-ethanediamine (2i)
According to the general procedure, 2i was obtained as a pale yellow solid (135 mg,
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77% yield, dl : meso = 41 : 59): HꢀNMR (CDCl3, r.t.) δ 7.26 (d, J = 5.9 Hz, 4H),
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7.11ꢀ7.08 (m, 8H), 6.96 (d, J = 7.8 Hz, 4H), 3.65(s, 2H, dl), 3.64 (s, 2H, meso), 2.32 (s,
6H, meso), 2.25 (s, 6H, dl) 0.80 (s, 18H, dl), 0.69 (s, 18H, meso). 13CꢀNMR (CDCl3,
r.t.) δ dl: 142.8, 142.0, 136.5, 135.5, 128.8, 128.5, 128.4, 127.7, 63.8, 63.7, 50.9, 50.9,
30.0, 30.0, 21.3, 21.2. IR (KBr) ν 3335, 2955, 2924, 2854, 1457, 758, 691 cm−1. HRMS
(DART) m/z: [M+H]+ Calcd for C24H37N2 353.2957; Found 353.2957.
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N,N’-Bis(1,1-dimethylethyl)-1,2-bis(4-fluorophenyl)-1,2-ethanediamine (2j)
According to the general procedure, 2j was obtained as a pale yellow solid (131 mg,
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73% yield, dl : meso = 48 : 52): HꢀNMR (CDCl3, r.t.) δ 7.27 (m, 4H), 7.10 (m, 4H),
6.97 (t, J = 8.5 Hz, 4H), 6.84 (t, J = 8.5 Hz, 4H), 3.65 (s, 2H, meso), 3.61 (s, 2H, dl),
1.50 (brs, 4H, dl and meso), 0.83 (s, 18H, dl), 0.72 (s, 18H, meso). 13CꢀNMR (CDCl3,
r.t.) δ 163.3, 162.8, 160.8, 160.3, 141.3, 141.3, 140.7, 140.6, 129.9, 129.8, 129.1, 129.0,
114.9, 114.7, 114.7, 114.5, 63.7, 63.1, 51.0, 51.0, 30.1, 30.0. IR (KBr) ν 3395, 3032,
2954, 2924, 2854, 1457, 758, 690 cm−1. HRMS (DART) m/z: [M+H]+ Calcd for
C22H31F2N2 361.2455; Found: 361.2445.
N,N'-Bis(1,1-dimethylethyl)-1,2-bis(4-trifluoromethylphenyl)-1,2-ethanediamine
(2k)
According to general procedure, the reductive coupling reaction of imine 1k (1.00
mmol) was performed to obtain 2k as a mixture of mesoꢀ and dlꢀdiastereomers. IR
(KBr) ν 3336, 3033, 2954, 2924, 2854, 1457, 758, 701 cm−1. HRMS (DART) m/z:
[M+H]+ Calcd for C24H31F6N2 461.2391; Found: 461.2382.
Silica gel column chromatography (eluent: hexane / ethyl acetate / triethylamine =
2500 / 50 / 1) gave mesoꢀ2k as a pale yellow solid (96.5 mg; 42%) and dlꢀ2k as a pale
yellow solid (76.6 mg; 33%).
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mesoꢀ2k: 1HꢀNMR (CDCl3, r.t.) δ 7.51 (d, J = 7.81 Hz, 4H, meso), 7.35 (d, J = 8.3 Hz,
4H, meso), 3.81 (s, 2H, meso), 1.29 (brs, 2H, meso), 0.77 (s, 18H, meso). 13CꢀNMR
(CDCl3, r.t.) δ 149.8, 149.0, 131.4, 129.5, 129.2, 129.1, 128.9, 128.8, 128.8, 128.5,
128.3, 128.0, 127.9, 126.7, 125.8, 125.6, 125.1, 124.9, 124.8, 124.5, 123.1, 123.0, 120.4,
63.9, 63.2, 51.2, 30.0, 30.0.
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dlꢀ2k: 1HꢀNMR (CDCl3, r.t.) δ 7.42 (d, J = 7.8 Hz, 4 H, dl), 7.30 (d, J = 7.8 Hz, 4H,
dl), 3.71 (s, 2H, dl), 1.83 (brs, 2H, dl), 0.82 (s, 18H, dl). 13CꢀNMR (CDCl3, r.t.) δ 149.7,
129.1, 128.8, 128.0, 128.0, 125.7, 124.9, 124.9, 124.8, 124.8, 123.0, 63.9, 51.2, 30.0.
N,N'-1,2-Tetraphenyl-1,2-ethanediamine (2l)
According to the general procedure, 2l was obtained as a pale yellow solid (128 mg,
70% yield, dl : meso = 39 : 61). Its 1Hꢀ and 13CꢀNMR data agreed with those reported.21
HRMS (DART) m/z: [M+H]+ Calcd for C26H25N2 365.2018; Found: 365.2017.
N,N'-Bis(4-methoxyphenyl)-1,2-diphenyl-1,2-ethanediamine (2m)
According to the general procedure, 2m was obtained as a pale yellow solid (86 mg,
41% yield, dl : meso = 31 : 69). Its 1Hꢀ and 13CꢀNMR data agreed with those reported.22
HRMS (DART) m/z: [M+H]+ Calcd for C28H29N2O2 425.2229; Found: 425.2211.
Acknowledgements
We gratefully acknowledge the financial support of the MEXTꢀsupported
Program for the Strategic Research Foundation at Private Universities 2014–2018
(no. 26410059), a subsidy from MEXT and Kindai University.
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Supporting Information. Copies of Hꢀ and 13CꢀNMR spectra of crude diamine 2h
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isolated diamines 2.
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