Effects of substituents on NMR chemical shifts and mass fragmentation patterns of 1-aryl-3-phenylpropanes

Article abstract of DOI:10.1002/bkcs.10720

The ¹H and ¹³C chemical shifts and the mass spectral fragmentation patterns of 1-aryl-3-phenylpropanes with m- or p-substituents (H, NO₂, Br, Cl, OCH₃, CH₃) were studied. The electronic effects of the substi-tuents seemed to be transmitted by the through-space as well as by a through-bond mechanism, resulting in an inverse correlation in the plot of the chemical shift values of i-C vs. the Hammett σ values. The mass spectra showed the substituted benzyl fragments as the base peaks when the substituents were electron donating, whereas the benzyl fragment was observed as the base peaks with the electron-withdrawing substituents.

Full text of DOI:10.1002/bkcs.10720

Article
DOI: 10.1002/bkcs.10720
BULLETIN OF THE
E. J. Jeong and I.-S. H. Lee
KOREAN CHEMICAL SOCIETY
Effects of Substituents on NMR Chemical Shifts and Mass
Fragmentation Patterns of 1-Aryl-3-phenylpropanes
*
Eun Jeong Jeong and In-Sook Han Lee
Department of Science Education, Kangwon National University, Chuncheon 24341, South Korea.
*E-mail: ishl@kangwon.ac.kr
Received November 16, 2015, Accepted December 28, 2015, Published online March 9, 2016
1
The H and 13C chemical shifts and the mass spectral fragmentation patterns of 1-aryl-3-phenylpropanes
with m- or p-substituents (H, NO2, Br, Cl, OCH3, CH3) were studied. The electronic effects of the substi-
tuents seemed to be transmitted by the through-space as well as by a through-bond mechanism, resulting
in an inverse correlation in the plot of the chemical shift values of i-C vs. the Hammett σ values. The
mass spectra showed the substituted benzyl fragments as the base peaks when the substituents were elec-
tron donating, whereas the benzyl fragment was observed as the base peaks with the electron-withdrawing
substituents.
Keywords: Chalcone, Reduction, 1,3-Diarylpropane, Correlation of chemical shift with Hammett σ value
Introduction
The structure of 2 can be considered as a methylene
bonded to an unsubstituted benzyl and an m- or a p-
substituted benzyl group. The substituted and the unsubsti-
tuted benzyl groups should affect each other on the physi-
cochemical properties such as the chemical shifts in the
NMR spectra and the fragmentation pattern in the mass
spectra. We report the results of our study on the effect of
the substituents on the one benzyl group to the other unsub-
stituted benzyl group that appeared in the NMR and the
mass spectra of 2.
The effect of substituents on the physical and chemical
properties of compounds is perhaps one of the most fre-
quently considered concepts in organic chemistry. A num-
ber of common and important relationships between the
substituent groups and the physicochemical properties have
been developed. Linear free energy relationship, the so-
called the Hammett equation, is probably the most widely
applied relationship. This equation was originally derived
to relate the acidities of the substituted benzoic acids with
the electronic effect of the substituents. There are countless
reports where the principle is applied in the investigation of
the organic reaction mechanism.1
The concept has been extended to rationalize the nuclear
magnetic resonance (NMR) chemical shifts. The empirical
substituent constants have been derived by relating the
observed values of chemical shift and the electronic nature
of the substituents.2 Such methodology was applied to make
comparison of the NMR properties of the five-membered
heterocyclic aromatic compounds, which led to the calcula-
tion of the aromaticity indices of the heterocycles.3
Results and Discussion
Synthesis. First we had to synthesize the compounds 2a–
k. There are, in general, two approaches to achieving the
synthesis of 2 in the literature: coupling the arylpropane
derivatives with aryl derivatives, and the stepwise reduction
of the chalcones 1. However, there is no report of preparing
2a–k using one set of reaction conditions. For example, the
synthesis of the unsubstituted 1,3-diphenylpropane (2d)
was done by the reduction of the chalcone 1d with NaBH4/
5
Pd(OAc)2 in CHCl3 or with triethylsilane and trifluoroace-
Recently, we have been interested in the transmission of
the electronic effect of the substituent that should result in
the shift in the NMR spectra. For example, in our previous
report we studied the transmission of the electronic effect
of the substituent in the benzene ring on the chemical shift
tic acid,6 by the coupling of 3-phenylpropyl halides with
phenylmagnesium halides,7 by the high-pressure hydrogen-
ation of 1,3-diphenylpropene,8 or by the desulfurization of
benzo[b]thiophene derivatives.9 Other 1,3-diphenylpropane
derivatives reported in the literature are p-NO2 (2k),10 p-Br
(2g),6,11,12 m-Br (2i),13 p-OCH3 (2a),5,8,9,14 and p-CH3
(2b).6,15 The use of triethylsilane and trifluoroacetic acid in
CCl4 solution has been reported for the preparation of 2g
(82% yield), 2a (82%), and 2d (80%) with the ratio of the
substrate (1):HSiEt3:CF3CO2H = 1:3:10, and the reaction
1
of H and 13C with the system of the chalcones (1).4 The
two aryl rings are linked by the three sp2-hybridized carbon
atoms of the enone moiety. Then, it seemed natural to
investigate the transmission of the electronic effect of the
substituent in one ring to another through three sp3-
hybridized carbon atoms. The ideal system should be
the derivatives of 1-(m- or p-substituted)phenyl-3-
phenylpropane (2).
6
ꢀ
conditions of stirring at 50 C for 6 h. But we were unable
to reproduce the yields, and the major products were substi-
tuted 1,3-diphenylpropan-1-ols.
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Therefore, several attempts were made for the synthesis
of 2a–k from the chalcones (1) using one set of conditions,
employing triethylsilane and trifluoroacetic acid, as shown
in Scheme 1. After the countless trials of the reaction con-
ditions, we were able to find the most effective conditions
for the complete conversion of 1 to 2, namely heating the
mixture of 1: Et3SiH:CF3CO2H = 1:8:16 by mole for 5 h
DSP provides the information on the magnitudes of the
inductive and resonance effects of the substituent, respec-
1
tively. We have found that the correlations of the H and
13C chemical shifts vs. the Hammett σ values using SSP
analysis are fair to good, as shown in Figure 1. The slopes
(ρ) and the correlation coefficients (r) from similar plots are
listed in Table 3.
ꢀ
in a sealed tube at 80 C. The reaction time could be
As shown in Table 3, the proton chemical shift values
did not show any meaningful correlation with the σ values.
On the other hand, the values of the 13C showed a signifi-
cant correlation (r = 0.950–0.984) with 2-C, i-C, o-C, and
p-C, but no correlation was apparent with 1-C and m-C. 3-
C showed only a trend in the correlation. There was abso-
lutely no correlation with 1-C (r = 0.247), which is the
benzylic carbon atom directly bonded to the benzene ring
having the substituents. This is in contrast to the general
notion that the electronic effect would be most efficiently
transmitted to it. The observation is consistent with similar
phenomena observed in the m- or p-substituted phenethyl
compounds18 and in the benzyl esters.19
reduced to 1 h by employing a huge excess of the reagents,
but that does not seem to be economical. The isolated
yields of 2a–k were over 80% after the column chromatog-
raphy (silica gel, hexane:EtOAc = 9:1). The 1H and 13C
NMR spectroscopic data are listed in Tables 1 and 2,
respectively.
Correlations of NMR Chemical Shifts with Hammett σ.
Quantitative analysis of the electronic effects of the substi-
tuents on the benzene ring on the rate or equilibrium con-
stants that take place at the side chain has usually been
made by the Hammett correlation. Such an approach can
also be applied to the variation of the chemical shift
values.16 The analysis is typically done by the single sub-
stituent parameter (SSP) and dual substituent parameter
(DSP) approaches, which are represented by Eqs. (1) and
(2), respectively.17
One of the notable phenomena is that the 13C correlation
has the negative ρ values for 2-C and i-C. Similar observa-
tions were made in the m- and p-substituted chalcones (1)
in our previous report,1 and the values are listed in Table 3
for the purpose of comparison. The three carbon atoms that
connect the two benzene rings in the chalcone system are
sp2-hybridized, which is striking contrast to the present sys-
tem of sp3-hybridized carbon atoms. Apparently, the elec-
tronic effect of the substituent seems to transmit more
efficiently through the sp2-C, which is evidenced by the lar-
ger absolute ρ values (−121.42 for α-C of 1 vs. –64.60 for
2-C of 2). The negative ρ value observed in 1 was
explained by the π polarization mechanism.19 Obviously,
such mechanism cannot be applied to the present system in
which the linkers are all sp3-hybrized.
δZ – δH = ρσ
ð1Þ
ð2Þ
δZ – δH = ρIσI + ρRσR
O
β
3
1
2'
5'
i
2
1'
i
3'
Z
4'
Et iH
3S
α
Z
o
o
F H
C 3CO2
p
p
6'
m
m
1
2
The inverse correlation of 2-C in 2 may be explained by
the transmission of the electronic effect alternating like a
wave.20 The alternation of substituent-induced charges was
suggested as a general phenomenon for carbon atoms in π
Z :a, p-OCH3; b, p-CH3; c, m-CH3; d, H; e, m-OCH
f, p-Cl; g, p-Br; h, m-Cl; i, m-Br; j, m-NO2, k, p-NO2
3,
Scheme 1. Synthesis of 1-aryl-3-phenylpropanes.
Table 1. 1H-NMR chemical shift values of 2a–2k in chloroform-d (in δ).
1-H
2-H
3-H
o-H
m-H
p-H
20-H
3-H
40-H
50-H
60-H
a
a
a
d
a
f
g
h
i
2.60
2.64
2.64
2.67
2.65
2.65
2.52
2.55
2.63
2.60
2.67
1.95
1.96
1.98
1.99
1.97
1.97
1.85
1.87
1.96
1.93
1.92
2.66
2.67
2.68
2.67
2.67
2.67
2.56
2.57
2.66
2.68
2.59
7.20
7.21
7.21
7.21
7.19
7.21
7.09
7.10
7.19
7.11
7.10
7.30
7.30
7.30
7.30
7.29
7.32
7.21
7.21
7.30
7.22
7.22
7.19
7.20
7.19
7.20
7.23
7.22
7.11
7.09
7.20
7.13
7.13
7.12
7.12
7.01
7.21
6.75
7.14
6.97
7.09
7.35
7.96
7.25
6.85
7.09
6.85
7.09
7.19
7.30
7.29
7.28
7.31
7.11
7.15
7.36
8.06
7.12
7.12
7.01
7.21
7.19
7.14
6.97
6.97
7.11
7.43
7.25
7.01
7.20
6.75
7.30
7.28
7.31
7.12
7.33
7.97
j
k
8.06
aCH3 signal in δ: 2a 3.87; 2b 2.34; 2c 2.31; 2e 3.82.
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Table 2. 13C-NMR chemical shift values of 2a–2k in chloroform-d (in ppm).
1-C
2-C
3-C
i-C
o-C
m-C
p-C
a
b
c
d
e
f
g
h
i
34.93
35.41
35.81
35.86
35.84
35.14
35.19
35.48
35.46
35.66
35.68
10-C
33.60
33.47
33.40
33.37
33.23
33.25
33.18
33.10
33.12
32.97
32.85
20-C
35.80
35.86
35.94
35.86
35.88
35.71
35.70
35.74
35.74
35.38
35.65
30-C
142.79
142.80
142.67
142.71
142.68
142.11
142.40
142.36
142.06
141.94
141.91
40-C
128.71
128.70
128.71
128.72
128.72
130.19
128.77
128.78
128.78
128.81
128.81
50-C
128.86
128.87
128.87
128.87
128.86
128.81
128.84
128.84
128.84
128.86
128.86
60-C
126.12
126.12
126.14
126.15
126.16
126.25
126.26
126.27
126.28
126.42
126.44
j
k
a
a
a
d
a
f
g
h
i
134.78
139.62
142.78
142.71
160.03
141.11
141.63
144.74
142.34
144.65
150.61
129.72
128.74
129.69
128.72
114.63
130.19
130.63
128.98
131.90
123.65
129.61
114.14
129.41
138.25
128.87
144.36
128.81
131.77
134.48
122.82
148.75
124.05
158.14
135.56
126.90
126.15
111.43
131.85
119.67
127.06
129.30
121.45
146.76
114.14
129.41
128.62
128.87
129.66
128.81
131.77
129.96
130.28
129.58
124.05
129.72
128.74
125.86
128.72
121.30
130.19
130.63
126.37
127.52
135.15
129.61
j
k
aCH3 signal in ppm 2a 55.67; 2b 21.42; 2c 21.84; 2e 55.55.
0.4
ρ value of i-C (−90.31) is the largest in spite of the separa-
tion of the two rings by CH2CH2CH2 chain. The obser-
vation may be explained by the mode of the transmission
of substituent electronic effect not only through bonding
but also through space, as shown in Figure 2. The two ben-
zene rings may be partially stacked by the π–π interaction,
as shown in the Newman projection like I.
Such an arrangement in space may facilitate the trans-
mission of the substituent effect through the interaction of
the p orbitals. The largest magnitude of the ρ and the good
correlation coefficient values for the i-C may be the result
of such an interaction.
The close array of the two rings may also be the cause
for the negative ρ value for 3-C, although the value of
r (0.745) may only imply a trend. The H atom bonded to 3-
C and the ortho carbon atom of the benzene ring having the
substituents may be close comprising a six-membered ring,
as shown in II. If this is the case, the meta substituents
may be considered para to the carbon atom and the para
substituents should become meta. In order to examine the
plausibility of such a rationale, the values of σm and σp for
each substituent were replaced with the values of σp and
σm, respectively. The results of calculations after the
exchange are listed in Table 3 in italic.
p-OCH3
0.2
2-C
i-C
m-CH3
H
m-OCH3
p-
CH3
0
-0.2
-0.4
-0.6
-0.8
-1
p-Cl
m-Cl
m-NO2
p-Br
m-
Br
p-NO2
-0.4
-0.2
0
0.2
0.4
0.6
0.8
σ
Figure 1. Correlation between σ and 13C chemical shift differ-
ences δZ – δH of 2-C and i-C in 2 in 0.1 M-chloroform-d.
systems.21 Apparently, such a phenomenon also seems to
take place through the sp3-hybridized carbon skeleton, as
shown by a negative ρ and the best r (0.984) value
observed in the present system.
Such a rationale should raise a question as to why the ρ
value of i-C is negative. Furthermore, the magnitude of the
It is interesting to note that the correlation coefficient for
3-H was improved dramatically from 0.135 to 0.773 after
exchange of σp and σm. Furthermore, the correlation for 3-
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C was also improved from 0.745 to 0.896. On the other
hand, 2-C showed a decreased correlation, changing the
r value from 0.984 to 0.727.
The idea that the substituent effect of one ring can be
transmitted by the through-space mechanism may be sup-
ported by examining the substituent chemical shift correc-
tions for the arylpropyl group. Such a calculation is
possible by averaging the values for the series. The results
are listed in Table 4 along with the values reported in the
downfield except p-C. Especially, the magnitude of the
shift for the i-C (14.08 ppm) is far greater than that for the
alkyl groups (9.2–11.7 ppm). Comparison of the magni-
tudes of the values for the arylpropyl and phenyl groups is
more striking because the benzene ring separated by the
three sp3-hybridized carbon atoms shows a much larger
H
H
literature for CH3
,
CH3CH2
,
CH3CH2CH2
and
H
H
C6H5 groups.22 In general, phenyl group is considered as
an electron-withdrawing substituent, which causes down-
H
H
H
Z
H
Z
1
field shift of H and 13C signals in the benzene ring to
H
which it is linked with some minor exceptions of p-H and
o-C. On the other hand, alkyl groups are known to cause
upfield shift of all H and C signals except i-C, as shown in
Table 4. Table 4 clearly shows that the signals of the pro-
tons in the phenyl ring of 2a–2k shift upfield with a minor
exception (Δδ 0.01) of m-H, and those of the 13C shift to
I
II
Figure 2. Illustration of the through-space transmission of the sub-
stituent effect.
Table 3. Slopes ρ (in Hz) and the correlation coefficients r for the plots of the chemical shift difference values δZ – δH vs. the Hammett
substituent constants σ.a,b
1c
2
From 1H-NMR data
From 13C-NMR data
ρ
r
ρ
r
ρ
r
C O
α-C
β-C
i-C
−142.66
0.573
1-H
2-H
3-H
43.52
27.90
13.39
9.95
1.90
17.52
0.731
0.507
0.515
0.306
0.135
0.773
1-C
2-C
3-C
i-C
22.73
−20.07
−64.60
−47.73
−33.35
−40.12
−90.31
−83.65
11.87
0.247
0.218
0.984
0.727
0.745
0.896
0.975
0.904
0.950
0.894
0.357
0.367
0.976
0.914
−121.42
268.96
−77.66
35.99
0.844
0.994
0.993
0.995
0.986
0.993
o-C
m-C
p-C
a
o-H
m-H
p-H
−9.25
−8.78
1.25
1.22
4.91
0.777
0.738
0.330
0.324
0.598
0.102
o-C
m-C
p-C
11.17
19.42
1.34
−1.37
33.11
31.01
89.04
0.839
The numbers in italic indicate the values obtained by exchanging σm and σp.
The σ values are taken from Ref. 16.
b
c
The values are taken from Ref. 4.
Table 4. Calculated substituent parameters for m- and p-substituted 3-arylpropyl group on the chemical shifts of the protons and carbons
in the benzene ring.
Substituent
o-H
m-H
0.01
−0.12
−0.05
b
p-H
i-C
o-C
0.38
0.7
−0.6
−0.2
−1.6
m-C
0.35
−0.1
−0.1
0.1
p-C
Z-C6H4CH2CH2CH2-
CH3-a
−0.09
−0.20
−0.14
b
−0.09
−0.21
−0.18
b
14.08
9.2
11.7
10.3
9.6
−2.26
−3.0
−2.8
−2.7
0.5
a
CH3CH2
a
CH3CH2CH2
a
C6H5
0.22
0.06
−0.04
0.5
a
From Ref. 22.
Data unavailable.
b
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effect than the ring itself. The observation can be best
explained by the mechanism of the through-space transmis-
sion of the electronic effect of the benzene ring having a
substituent to the unsubstituted benzene ring that is sepa-
because the substituent would make the benzyl cation more
stable.
In conclusion, the 1-aryl-3-phenylpropane system is an
excellent model for the support of the through-space trans-
mission of the electronic effect of a substituent. Such phe-
nomenon, in addition to the through-bond transmission,
should play an important role in the correlation of the 13C
chemical shift with the Hammett σ values and the mass
spectral fragmentation.
rated by the
Figure 2.
CH2CH2CH2
moiety, as shown in
Mass Spectral Fragmentation Patterns. The through-
space transmission of the substituent effect seems to be
consistent with the fragmentation pattern in the mass spec-
tra of 2. The m/z values of the major fragments and their
relative intensities are listed in Table 5.
As mentioned earlier, the unique structural characteristic
of 2 is the presence of the substituted benzyl and the unsub-
stituted benzyl groups linked by a CH2 group. Therefore,
the notable fragments should be those listed in Scheme 2.
The nitro compounds 2j and 2k showed very similar
fragmentation patterns. Because of the strong electron-
withdrawing nature of the nitro group, the major bond
cleavage is expected to take place between 2-C and 3-C,
resulting in the formation of III and IX.
Scheme 2. Mass fragmentation patterns of 2.
Similarly, the base peak was III when the electron-
withdrawing groups were present at the meta position as
for 2i and 2h. On the other hand, 2e and 2c showed the
base peaks derived from the McLafferty rearrangement.
The cleavage of 1-C–2-C bond may be facilitated by the
electron-donating substitution at the meta position, as
shown in Scheme 3.
The position to which the proton transfers for the
McLafferty rearrangement is para from the substituents in
2e and 2c. The m-OCH3 group is electron withdrawing (σ
0.12). But the rearrangement should take place at the para
position from the OCH3 group, as shown in Scheme 4.
Apparently, the through-space interaction of the elec-
tronic effect of the substituent seems to be parallel in trend
to the chemical shift and the fragmentation pattern. Then, it
is understandable that the rearrangement takes place from
the substituted benzylic proton to the unsubstituted benzyl
ring forming IX in case of the presence of the electron-
withdrawing group (2f–k). When the electron-donating
group is at the para position (2a, 2b), the base peak is VI
δδ+
CH2
+
H
H2C
EWG
EDG
EWG
III
V
IV
H
EDG
-
H
δδ
+
H
H2C
VIII
EDG
EDG
CH2
+
H
δ-
H2C
VI
X
VII
CH2
EWG
EWG
δ+
+
H
H
H
IX
Scheme 3. Dependence of the mass fragmentation on the elec-
tronic nature of the substituent.
Table 5. Mass spectral data of 2a–2k, m/z (%).
M+
III
IV
V
VI
VIII
IX
(6)
(61)
(26)
(100)
(7)
(100)
(100)
(66)
a
b
c
d
e
f
g
h
i
226 (55)
210 (100)
210 (62)
196 (65)
226 (39)
230 (74)
274 (51)
230 (87)
274 (58)
241 (100)
241 (51)
(14)
(46)
(43)
(53)
(19)
(60)
(63)
(100)
(100)
(100)
(100)
135 (4)
(7)
121 (100)
105 (100)
105 (35)
91 (53)
122 (13)
106 (71)
106 (100)
92 (100)
122 (100)
126 (13)
170 (7)
126 (61)
170 (42)
137 (41)
137 (31)
119 (42)
119 (21)
105 (49)
135 (4)
139 (16)
183 (15)
139 (14)
183 (8)
(81)
(35)
(49)
(7)
(43)
(49)
(39)
(44)
(100)
(100)
121 (9)
125 (29)
169 (18)
125 (13)
169 (7)
136 (12)
136 (1)
(79)
(100)
(100)
j
k
150 (83)
150 (49)
Bull. Korean Chem. Soc. 2016, Vol. 37, 538–543
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
542

BULLETIN OF THE
Article
Effects of Substituents on NMR and Mass Spectra
KOREAN CHEMICAL SOCIETY
H
H
H
OC
H
3
H
OC
H
OC
+
3
3
+
H
H
H
H
-
:
2C
2C
m z
/
122 100
%
)
(
Scheme 4. McLafferty cleavage observed in 2e.
4. For example,H. S. H. Lee, H. J. Jeon, J. S. Yu, C. K. Lee,
Bull. Korean Chem. Soc. 2010, 31, 1689.
Experimental
5. K. A. De Castro, S. Oh, J. Yun, J. K. Lim, G. An, D. K. Kim,
H. Rhee, Synth. Commun. 2009, 39, 3509.
6. D. N. Kursanov, N. M. Loim, V. A. Baranova,
L. V. Moiseva, L. P. Zalukaev, Z. N. Parnes, Synthesis 1973,
7, 420.
NMR spectra were recorded on a Bruker DPX-400 FT
NMR spectrometer (Rheinstetten, Germany) in the Central
Lab of Kangwon National University at 400 MHz for H
1
and 100 MHz for 13C and were referenced to tetramethylsi-
lane. Mass spectra were obtained using a JEOL JMS-700
mass spectrometer (Akishima, Japan) at 20 eV. The solu-
tion for the NMR spectrum was prepared by dissolving the
appropriate amount of 2 in a 1-mL volumetric flask to
make the concentration 0.1 M in chloroform-d. A portion
(0.6 mL) of the solution was transferred inꢀto a 5-mm NMR
tube, and the spectrum was obtained at 20 C.
7. K. Nakata, C. Feng, T. Tojo, Y. Kobayashi, Tetrahedron Lett.
2014, 55, 5774.
8. S. Kumar, L. C. S. Reddy, Y. Kumar, A. Kumar,
B. K. Singh, V. Kumar, S. Malhotra, M. K. Pandey, R. Jain,
R. Thimmulappa, S. K. Sharma, A. K. Prasad, S. Biswal,
E. V. Eycken, A. L. DePass, S. V. Malhotra, B. Ghosh,
V. S. Parmar, Arch. Pharm. Chem. Life Sci. 2012, 345, 368.
9. R. Royer, P. Demerseman, J.-P. Lechartier, A. Cheutin,
J. Org. Chem. 1962, 27, 3808.
10. G. A. Molander, C.-S. Yun, Tetrahedron 2002, 58, 1465.
11. C. Matthias, D. Kuck, Croat. Chem. Acta 2009, 82, 7.
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Chem. 2009, 1, 494.
13. B. A. Ellsworth, W. Meng, M. Patel, R. N. Girotra, G. Wu,
P. M. Sher, D. L. Hagan, M. T. Obermeier,
W. G. Humphreys, J. G. Robertson, A. Wang, S. Han,
T. L. Waldron, N. N. Morgan, J. M. Whaley,
W. N. Washburn, Bioorg. Med. Chem. Lett. 2008, 18, 4770.
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Lett. 2010, 12, 5783.
Preparations of m- or p-substituted chalcones (1) were
carried out from the commercially available benzaldehydes
and acetophenones by following the procedures in the
literature.23
Reduction of m- and p-substituted chalcones (1) to 1,3-
diarylpropanes (2). An illustrative procedure for the conver-
sion of 1d to 2d is as follows: A mixture of 1d (110 mg,
0.53 mmoles), Et3SiH (0.70 mL, 4.38 mmoles), and
CF3CO2H (0.65 mL, 8.53 mmoles) in a sealed tube was
ꢀ
stirred at 80 C for 5 h. The resulting liquid was poured
into dichloromethane (50 mL) and washed with 1M NaOH
(3 × 20 mL) and water (10 mL), successively. The organic
layer was dried over MgSO4 and then evaporated, yielding
a viscous liquid, which was chromatographed (silica gel,
EtOAc:hexane = 1:9) to obtain the pure product 2d in 70%
yield.
15. H. Pines, J. Shabtai, J. Org. Chem. 1961, 26, 4220.
16. H.-O. Kalinowski, S. Berger, S. Braun, Carbon-13 NMR
Spectroscopy, John Wiley
1984, p. 311.
& Sons, New York, NY,
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1983, 14, 1.
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Acknowledgments. We thank Dr. Gary Kwong for help in
preparing the manuscript. This research was supported by
2015 Research Grant from the Kangwon National Univer-
sity (No. 520150200).
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Bull. Korean Chem. Soc. 2016, Vol. 37, 538–543
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
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