Effect of methoxyl groups on the NMR spectra: configuration and conformation of natural and synthetic indanic and tetralinic structures

Article abstract of DOI:10.1002/mrc.4564

Here, we studied the influence of the methoxyl groups attached at C-7 and C-2′ of natural and synthetic 1-arylindanes on the chemical shift of the signal of bibenzylic hydrogen and carbon atoms and J_1,2 coupling constants. This influence was also analysed in natural 1-aryltetralins and related compounds that possess methoxyl and/or hydroxyl groups bound at C-8 and C-2′. The methoxyl groups attached at C-7 in indanes or at C-8 in tetralins produce a deshielding signal at H-1 and shield at C-1 and a strong decrease in the value of J_1,2 due to the pseudoequatorial location adopted by the aryl group bound at C-1, avoiding an ‘A^1,3 strain’. Furthermore, compounds with hydroxyl or methoxyl groups in C-2′, in the absence of substituents of C-7 or C-8, present a strong deshielding signal at H-1, strong shield of the C-1 signal and a decrease in the value of J_1,2. This is attributed to the stereoelectronic effects of the methoxyl or hydroxyl groups, which we have called ‘Asarone effect’. NOESY experiments were conducted to confirm the configuration and conformation of some of the compounds included in this work. This study shows that both effects, A^1,3 strain and Asarone effect, must be taken into account when the structure of natural indanes and tetralins is analysed by using ¹H-NMR and ¹³C-NMR spectra. Copyright

Full text of DOI:10.1002/mrc.4564

Research article
Received: 14 November 2016
Revised: 2 December 2016
Accepted: 6 December 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/mrc.4564
Effect of methoxyl groups on the NMR spectra:
configuration and conformation of natural and
synthetic indanic and tetralinic structures
Beatriz Lantaño,a,b* José M. Aguirre,a** Eleonora V. Drago,a
Diego J. de la Faba,a Nicolás Pomiliob and Jorge D. Mufatoa
Here, we studied the influence of the methoxyl groups attached at C-7 and C-20 of natural and synthetic 1-arylindanes on the
chemical shift of the signal of bibenzylic hydrogen and carbon atoms and J1,2 coupling constants. This influence was also analysed
in natural 1-aryltetralins and related compounds that possess methoxyl and/or hydroxyl groups bound at C-8 and C-20. The
methoxyl groups attached at C-7 in indanes or at C-8 in tetralins produce a deshielding signal at H-1 and shield at C-1 and a strong
decrease in the value of J1,2 due to the pseudoequatorial location adopted by the aryl group bound at C-1, avoiding an ‘A1,3 strain’.
Furthermore, compounds with hydroxyl or methoxyl groups in C-20, in the absence of substituents of C-7 or C-8, present a strong
deshielding signal at H-1, strong shield of the C-1 signal and a decrease in the value of J1,2. This is attributed to the stereoelectronic
effects of the methoxyl or hydroxyl groups, which we have called ‘Asarone effect’. NOESY experiments were conducted to confirm
the configuration and conformation of some of the compounds included in this work. This study shows that both effects, A1,3 strain
and Asarone effect, must be taken into account when the structure of natural indanes and tetralins is analysed by using 1H-NMR
and 13C-NMR spectra. Copyright © 2016 John Wiley & Sons, Ltd.
Keywords: indans; tetralins; 1H-NMR; 13C-NMR
obtained by cyclodimerization of natural stilbenes, as resveratrol
Introduction
and ixyresveratrol, and synthetic stilbenes present remarkable
differences in the 1H-NMR and 13C-NMR spectra, with similar
Cyclodimers with indanic structure derived from natural (E)-β-
methylstyrenes (Isohomogenol and Isosafrole) and synthetic (E)-β-
methylstyrenes have been described earlier (Scheme 1).[1]
The configurational assignment of the four possible diastereo-
mers led to several controversies until 1969, when MacMillan et al.[2]
established the relative configuration of isomers α, β and γ of
Isohomogenol and Isosafrole by using 1H-NMR (Fig. 1).
This contribution has been of significant importance and is
widely mentioned in the literature for the configurational assign-
ment of these kinds of structures.[3]
structures that do not have methoxyl groups at C-7 or C-8 of
the indanic and the tetralinic rings respectively.[8] These
differences are also observed in tetralinic bisnorlignans derived
from 2,4,5-trimethoxystyrene such as pachypostaudins A and B
(Scheme 2).[9]
Herein, we studied the influence of the methoxyl groups at-
tached at C-7 and C-20 of indanes on the chemical shift of bibenzylic
hydrogen and carbon atoms and coupling constants J1,2. This anal-
ysis was extended to tetralinic structures with methoxyl groups at
C-8 and C-20. Model indanic and tetralinic structures with a different
substitution pattern at sp3 carbons and aromatic rings were synthe-
sized. We also aimed to shed light on the scopes and limitations of
NMR as a tool for the configurational assignment of natural and
synthetic indanic and tetralinic cyclodimers formed from styrene,
(E)-β-methylstyrenes and stilbenes.
However, based on works mentioned in the preceding texts,
some authors[4] have incorrectly assigned the configuration to
cyclodimers derived from (E)-β-methylstyrenes.
The γ configuration of the only indanic cyclodimer isolated
from the natural styrene Asarone (Scheme 1) has been assigned
by X-ray diffraction.[5] This compound shows low values of J1,2
and J2,3 (~4 Hz), which are not consistent with data published
by MacMillan[2] for any of the diastereomers studied. Alesso et al.[6]
reported that in cyclodimerization processes of (E)-β-
methylstyrenes, the presence of methoxyl groups at C-2 and C-5
of the aryl group is determinant for the stereoselectivity of the re-
action. The γ-diasarone has methoxyl groups at C-4, C-7 and C-20,
which influence the coupling constants of benzylic hydrogens
and the chemical shift of hydrogen and carbon atoms. On the
other hand, several stereodirected syntheses of diastereomers of
1,2,3-trisubstituted indanic structures have been developed, and
the configurational assignments have been supported by 1D
and 2D NMR studies.[7] Other indanic and tetralinic structures
*
Correspondence to: Beatriz Lantaño, Cátedra de Química Orgánica II, Facultad de
Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Ciudad de
Buenos Aires, Argentina. E-mail: lantanob@gmail.com
** Correspondence to: José M. Aguirre, Departamento de Ciencias Básicas,
Universidad Nacional de Luján, Ruta 5 y Av. Constituci, 6700, Argentina. E-mail:
jaguirre@hotmail.com
a Departamento de Ciencias Básicas, Universidad Nacional de Luján, Ruta 5 y Av.
Constituci, 6700, Argentina
b Cátedra de Química Orgánica II, Facultad de Farmacia y Bioquímica, Universidad
de Buenos Aires, Junín 956, 1113, Ciudad de Buenos Aires, Argentina
Magn. Reson. Chem. (2017)
Copyright © 2016 John Wiley & Sons, Ltd.

B. Lantaño et al.
Scheme 1. Indanic cyclodimers from natural (E)-β-methylstyrenes.
Synthesis of 1-aryltetralins
Tetralins 24 and 26–28 were obtained from the suitable substituted
1-tetralone and the arylmagnesium reagent followed by
hydrogenolysis[7,11] (Scheme 4 and Table 2). The structure was
confirmed by NMR spectroscopy.
Synthesis of 1,2,3-triaryltetralins
Figure 1. Diastereomers of 3-ethyl-2-methyl-1-aryilindanes.
Tetralins 30–32 and 36 were synthesized by dimerization catalysed
by Lewis acids, using the respective trans-stilbenes as starting
material (Scheme 5 and Table 3). The structure and the stereochem-
istry of 31 and 32 have been previously published by us.[8] The
1H-NMR data for 30 and 36 have been published by Hiscock and
Porter,[13] although the authors only assigned the configuration of
isomer 31. Based on HSQC, HMBC and NOESY experiments, we
established that the configuration for 36 is 1,2-trans-2,3-cis
(Table 4).
Scheme 2. Tetralinic cyclodimers from a natural styrene.
NMR spectroscopy of substituted indanes and tetralins
Results and Discussion
Synthesis of substituted indanes and tetralins
Synthesis of 1-arylindanes
NMR spectral analysis of 1,2-substituted indanes
The configuration of the model indanes 1–4 was supported by
NMR data. The trans arrangement was assigned, considering the
chemical shifts for the hydrogens and the carbon of the methyl
group attached at C-2, δH 1.14–1.17 p.p.m. and δC 17.1–20.0 p.p.m.
(Fig. 2 and Table 5).
Compounds 1–17 were obtained by the formal cycloaddition reac-
tion [3 + 2] (CAF [3 + 2]) from benzylic alcohols, β-methylestyrenes
and SnCl4 as catalyst[10] (Scheme 3 and Table 1).
The structure and configuration of model-synthesized indanes
(1–4) were established by 1D and 2D NMR, and they all have
trans configuration. The indanes 1,2,3-trisubstituted in the
pentagonal ring were obtained as α and/or γ diastereomers,
and in those having substituents at C-4 and C-7, the predomi-
nant diastereomer is γ.
The values of these chemical shifts correspond to methyl
groups which, in this kind of structure, do not significantly
experience the influence of a substituent on a neighbour carbon
atom (low-shielding γ-gauche effect).[14] The value of the J1,2
coupling constants (9.5 and 8.5 Hz respectively) in compounds 1
and 2 are indicative of H-1-pseudoaxial/H-2-axial arrangement.
The 1H-NMR spectra of cycloadduct 2 show a deshielding of the
signal at H-1 (δ: 4.28 p.p.m.) relative to compound 1 (δ: 3.70 p.p.m.)
and a lower value of J1,2 (ΔJ = 1 Hz). This effect is due to the influ-
ence of the methoxyl group attached at C-20 of the unfused aryl
group, which produces a stereoelectronic effect on H-1. On the
other hand, the chemical shifts of C-1 and C-2 in cycloadduct 2
show a strong shielding effect [ΔδC: 6.2 (C-1) and 4.0 (C-2)] relative
to cycloadduct 1 due to the shielding γ-gauche effect.[7] This
shielding effect indicates that the aryl group attached at C-1 has a
spatial position in which the oxygen of the methoxyl group
attached at C-20 is coplanar to C-1 and that the C-20 of the aryl
Scheme 3. Synthesis of 1-arylindanes 1–17.
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Magn. Reson. Chem. (2017)

Effect of methoxyl groups on the NMR spectra of indanic and tetralinic structures
Table 1. Synthesized substituted 1-arylindanes
0
0
0
0
R5
Compound
R2
R3
R4
R4
R5
R6
R7
R
Configuration
Diast
C-1–C-2/C-2–C-3
1
H
H
OCH3
OCH3
OCH3
OCH3
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OCH3
OCH3
OCH3
OCH3
OCH2O
OCH3
OCH3
OCH2O
OCH3
OCH3
OCH3
OCH3
OCH2O
H
OCH3
OCH3
OCH3
OCH3
H
H
H
H
H
H
trans
trans
2[10]
3
OCH3
H
H
H
H
OCH3
H
trans
trans
OCH3
OCH3
H
trans
trans
4
OCH3
H
OCH3
H
trans
trans
5[2,6,10]
OCH2O
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
trans-cis
trans-cis
trans-cis
trans-cis
trans-cis
trans-cis
trans-cis
trans-cis
trans-trans
trans-trans
trans-trans
trans-trans
trans-trans
α
α
α
α
α
α
α
α
γ
γ
γ
γ
γ
6
OCH3
OCH3
OCH3
H
H
H
H
OCH3
OCH3
H
7[10]
8[6]
H
OCH3
OCH3
OCH3
OCH3
H
OCH3
OCH3
H
H
H
H
9[6]
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
H
10[6]
11
H
OCH3
OCH3
H
OCH3
OCH3
H
H
12[10]
13[6]
14[6,10,7]
15[10]
16[10]
17
H
OCH3
OCH3
H
OCH2O
OCH3
H
H
H
H
H
OCH3
OCH3
OCH3
OCH3
OCH3
H
OCH3
OCH3
H
OCH3
OCH3
OCH3
OCH3
OCH3
H
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH2O
H
H
Scheme 4. Synthesis of 1-aryltetralins 24–28.
Table 2. Synthesized substituted 1-arylitetralins
Scheme 5. Synthesis of 1,2,3-triaryltetralins 30–36.
0
Compound
R5
R8
R2´
R4
24[12]
26
H
H
H
H
H
OCH3
OCH3
H
substituted indanic structures have been collectively named
‘Asarone effect’.[15]
OCH3
H
Another observation to highlight is that indane 3 shows J1,2
4.7 Hz, which is significantly lower than that observed in
compound 1 and than that expected in a trans arrangement
(H-H-1-pseudoaxial/H-2-axial). This difference is due to the fact that
in indane 3, the conformation of the pentagonal ring locates the
aryl group attached at C-1 in the pseudoaxial position because of
the presence of the methoxyl group at C-7 (Fig. 3).
27
OCH3
OCH3
OCH3
OCH3
28
OCH3
OCH3
group and the C-2 of the pentagonal ring are in a gauche
arrangement (Table 5).
In this study, the striking unshielding effect of the bibenzylic
hydrogen atoms (H-1), the decrease in the coupling constant (J1,2
and the shielded bibenzylic carbon atoms (C-1) observed in 1-aryl
In this conformation, the ‘A1,3 strain’ is avoided.[16] This assertion
was confirmed by a NOESY experiment.
)
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B. Lantaño et al.
Table 3. Synthesized substituted 1,2,3-aryltetralins
0
0
Compound
R6
R7
R3
R4
Configuration
Diastereomer
C-1–C-2/C-2–C-3
36[13]
30[13]
31[8]
H
H
H
H
H
H
trans-cis
α
γ
γ
γ
H
H
trans-trans
trans-trans
trans-trans
OCH3
H
OCH3
OCH3
OCH3
H
OCH3
OCH3
32[8]
Table 4. NMR spectral data of compound 36 (CDCl3, 500 MHz)
Position
1H
13C
HMBC
NOESY
1
4.57 [1H, doublet (d), 2.6]
50.11
54.59
C-8, C-8a, C-10, C-1″
H-20, H-2″
H-20, H-2″, H-2‴
2
3.40 [1H, triplet (t), 3.1, 3.3]
C-8a
3
3.57 (1H, ddd, 9.7, 6.3, 3.5)
39.37
C-1″, C-1‴, C-20
H-20, H-2″
H-20, H-2″, H-2‴
4
3.08 [2H, multiplet (m)]
30.60
C-4a, C-5
—
4a
5
—
137.56
126.08
130.85
137.83
147.76
128.29
141.32
128.20
142.97
127.74
—
7.05 (1H,m)
—
—
8
6.99 (1H, m)
—
—
—
8a
10
20
1″
2″
1‴
2‴
—
—
—
—
—
7.10 (2H, m)
—
H-1, H-4
—
—
—
6.58 (2H, d, 7.0)
—
H-1, H-2, H-4
—
—
—
6.69 [2H, doublet doublet (dd), 2.0, 5.5]
—
H-3, H-4
Figure 2. Synthetic trans-1-Aryl-2-methylindanes.
Table 5. 1H-NMR and 13C-NMR spectral data of hydrogen and aliphatic
carbon atoms of 1-arylindanes
Compound δHCH3 δCCH3 δH-1 J1,2
δC-1
δC-2
δC-3
Figure 3. Conformational equilibrium of indane 3.
1
1.16
1.15
1.17
1.14
18.17 3.70 9.5 58.79
17.91 4.28 8.5 52.56 42.81 39.58
19.99 3.88 4.7 56.11 45.27 40.48
17.10 4.35 5.1 53.61 42.33 40.84
46.77 40.08
210b
3
The analysis of the data provided by NOESY experiment of 3
(Fig. 4 and Table 6) indicates that H-1 (δ 3.88 p.p.m.) correlates with
hydrogens at δ1.17 p.p.m. from the methyl group attached at C-2
4
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Effect of methoxyl groups on the NMR spectra of indanic and tetralinic structures
Figure 4. NOESY data of compound 3.
Table 6. NMR spectral data of compound 3 (CDCl3, 600 MHz)
Position
1H
13C
TOCSY
NOESY
1
3.8 7 (1H, d, 4.7)
2.39 (1H, m)
3.19 (1H, dd, 7.7, 15.6)
2.52 (1H, dd, 6.7, 15.6)
—
56.98
45.27
—
H-20, H-3α, CH3
—
H-20, H-4
2
—
3α
3β
3a
40.48
C-3a, C-7a
40.48
C-3a
—
139.08
103.44
153.29
140.83
150.38
19.99
—
—
4
6.61 [1H, singlet (s)]
—
C-3, C-5, C-6
OCH3(C-5)
5
—
—
—
6
—
—
7
—
—
—
CH3
1.17 (3H, d, 6.8)
3.88 (3H, s)
3.40 (3H, s)
3.81 (3H, s)
—
—
—
OCH3(C-5)
56.11
C-5
—
OCH3(C-6)
60.05
—
H-4
H-20
OCH3(C-7)
10
20
30
60.87
—
137.82
128.43
113.56
157.86
55.21
—
—
7.08 (2H, d, 8.6)
6.84 (2H, d, 8.6)
—
C-3, C-40
C-30, C-40
—
OCH3(C-7)
—
40
—
OCH3(C-40)
3.81 (3H, s)
C-3a
—
because H-1 and CH3(C-2) are in a cis arrangement. Furthermore,
the hydrogens of CH3(C-2) correlate with the hydrogens of the
methoxyl group attached at C-7 (δ 3.81 p.p.m.).
The correlations described are only possible in the conformation
where the aryl group attached at C-1 is in a pseudoaxial position
and the methyl group is axial.
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B. Lantaño et al.
Table 7. 1H-NMR spectral data of the aliphatic hydrogen atoms of 1-aryl-3-ethyl-2-methylindanes
Compound
H-1
H-2
H-3
CH3
CH2CH3
CH2CH3
J1,2
J2,3
α-Diisohomogenol[2]
β-Diisohomogenol[2]
γ-Diisohomogenol[2]
?-Diisoeugenol[4]
3.77
4.27
3.65
3.73
3.73
2.4
2.90
1.04
0.47
1.15
1.03
1.03
1.65
1.61
1.80
0.96
1.07
1.00
0.97
0.97
9.5
7.0
9.0
9.4
9.5
7.25
7.0
2.77
2.95
2.00
2.69
9.0
2.4–2.5
2.4–2.5
2.86–2.95
2.85–2.95
1.31–1.441.65–1.75
1.31–1.441.65–1.75
No data
No data
?-Diisoeugenol[4]
Nuclear magnetic resonance spectroscopic data indicate that
indane 4 adopts the conformation which avoids the A1,3 strain
(J1,2 5.1 Hz) and presents the Asarone effect (δH-1 4.35 p.p.m.; J1,2
5.1 Hz, δC-1: 53.6 p.p.m. and δC-2 42.3 p.p.m.; Table 5).
described in the literature and which have been broadly used for
the configurational assignment of 1-aryl-3-ethyl-2-methylindanes,
cyclodimers of β-methylestirenes.
The coupling constants J1,2 and J2,3 allow differentiating
diastereomers β and γ from the other two because H-1 and H-3
show the same configurational relationship related to H-2 (Fig. 5).
NMR spectral analysis of 1,2,3-trisubstituted indanes
Because this kind of compound can appear as four racemic diaste-
Table 9. 1H-NMR spectral data of the aliphatic hydrogen atoms of 1-
aryl-3-ethyl-2-methylindanes: diastereomer α
reomers named α, β, γ and δ (Fig. 1), the configuration of
1
cyclodimers α, β and γ was assigned by using the H-NMR data
reported by MacMillan et al.[2] The studies performed to dimerize
Isohomogenol and Isosafrole show that the main isomers are α
and γ.[2,3] Nevertheless, Angle et al.[3] reported that in CAF[3 + 2],
the main diastereomers are α and β. Through different synthetic
pathways and cyclodimerization reactions, we obtained the diaste-
reomers α, β and γ.[7,10] Tables 7 and 8 summarize the NMR data of
aliphatic hydrogens and carbons (δH, δC and JH H) of the indanes
Compound
H-1
H-2
H-3
CH3C-2
J1,2
J2,3
α-Diisohomogenol
β-Diisohomogenol
γ-Diisosafrole
5
3.77
4.27
3.57
3.70
4.33
4.33
4.31
3.95
3.90
4.36
4.33
2.11
2.77
1.99
2.46
2.44
2.43
2.51
2.47
2.46
2.35
2.36
2.90
2.95
2.65
2.90
2.90
2.91
2.90
3.04
3.00
2.91
2.93
1.04
0.47
1.14
1.00
0.99
1.02
1.03
1.02
1.01
0.96
0.97
9.5
7.0
9.3
9.4
6.7
7.9
8.4
5.1
5.1
2.5
3.6
7.2
7.0
9.3
7.3
6.9
7.2
6.8
7.1
7.2
6.9
7.2
6
7
Table 8. 13C-NMR spectral data of the aliphatic carbon atoms of
1-aryl-3-ethyl-2-methylindanes
8
9
10
11
12
Compound
C-1
C-2
C-3
CH3 CH2CH3 CH2CH3
α-Diisohomogenol[3]
56.7 49.3 48.3 13.6
9.8
22.2
21.3
24.6
22.4
22.4
12.0
12.3
10.6
12.2
12.2
β-Diisohomogenol[7d] 54.3 49.1 43.2
γ-Diisosafrole[3]
?-Diisoeugenol[4]
?-Diisoeugenol[4]
58.5 51.4 50.9 17.4
56.7 49.2 48.5 13.8
56.7 49.2 48.5 13.8
Table 10. 13C-NMR spectral data of the aliphatic carbon atoms of
1-aryl-3-ethyl-2-methylindanes: diastereomer α
Compound
C-1
C-2
C-3
CH3
α-Diisohomogenol
56.7
49.3
48.3
13.6
β-Diisohomogenol
54.3
49.1
43.2
9.8
γ-Diisosafrole
58.5
51.4
50.8
17.4
5
56.68
50.33
49.49
49.05
55.40
56.60
46.14
46.57
49.41
48.23
49.03
48.77
48.37
48.95
48.07
48.23
48.31
48.63
48.91
48.70
48.75
48.36
49.12
48.48
13.65
15.09
14.74
14.66
15.20
15.40
15.66
15.32
6
7
8
9
10
11
12
Figure 5. NMR data of diastereomers of 3-ethyl-2-methyl-1-aryilindanes.
Figure 6. Synthetic 1,2-trans-2,3-cis-3-ethyl-2methyl-1-arylindanes (α).
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Effect of methoxyl groups on the NMR spectra of indanic and tetralinic structures
Instead, in isomer α, the spatial position of H-1/H-2 is trans and
H-2/H-3 is cis, and thus the different values for J1,2 and J2,3 are ~10
and ~7 Hz respectively. Other relevant data are the chemical shifts
of the hydrogen and carbon of the methyl group attached at C-2,
which show different shielding effect due to the spatial relationship
of the groups at C-1 and at C-3 in each isomer (Fig. 4).
Recently, Kouznetsov and Merchan Arenas[4] have reported a
new and efficient stereoselective synthesis of γ-diisoeugenol and
its large-scale preparation under green conditions, and Gonzalez
de Castro and Jianliang[4] obtained the same cyclodimer to which
configuration γ was assigned by catalysed selective oxidation of
olefins to carbonyls with O2. The evaluation of NMR data published
Figure 7. NOESY data of compound 7.
Magn. Reson. Chem. (2017)
Copyright © 2016 John Wiley & Sons, Ltd.
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B. Lantaño et al.
in both cases (Tables 7 and 8) indicates that the configurational
assignment of the synthesized cyclodimers is not correct and
corresponds to diastereomer α.
moiety attached at C-3. This indicates that the H-1 and the methyl
and the ethyl groups are in a cis arrangement. On the other hand,
the correlation between H-2 (2.43 p.p.m.) and the aromatic
hydrogen atoms (6.38 p.p.m.) determines that the aromatic ring
attached at C-1 is cis related to H-2. These results are consistent to
the α configuration assigned to compound 7 and also to 6 and 8,
by comparison.
1
3-Ethyl-2-methyl-1-arylindanes: diastereomer α. The H-NMR and
13C-NMR spectroscopic data of cycloadducts 5–12 (Fig. 6) are
shown in Tables 9 and 10.
Indanes 9–12 (Fig. 8) are all diastereomers α and show the same
substitution pattern in the aromatic ring. The NMR analysis of 9 and
10 shows J1,2 values (5.1 Hz) lower than those expected for a trans
diaxial arrangement (Fig. 5). This difference is because both present
a conformation in which the unfused ring is in a pseudoaxial
position, avoiding the A1,3 strain[16] as observed in compound 4.
The spatial relationship of H-2/H-3 is gauche in any of the possible
extreme conformations. For this reason, the J2,3 values do not show
a significant variation. Moreover, compounds 11 and 12 have an
aryl group at C-1 with a methoxyl group attached at C-20 and show
chemical shift of C-1, H-1 and J1,2 consistent with the Asarone effect
(Tables 9 and 10).
The configurational assignment of 1,2-trans-2,3-cis, diastereomer
α, was performed, considering the descriptions mentioned in the
preceding texts, especially δH and δC of the methyl group attached
at C-2. Nevertheless, it is necessary to study the differences
observed from the spectroscopic data with the data previously
published. The coupling constants J2,3 of compounds 6, 7 and 8
(7.2, 6.9 and 6.8 Hz respectively) are similar to those of indane 5,
which indicate a H-2/H-3 cis arrangement but differ in the chemical
shift of H-1, unshielded in ~0.6 p.p.m., and in the value of J1,2 (7.9,
6.7 and 8.4 Hz), which is lower than that found in 5 (~9.5 Hz). The
three indanes also show that C-1 is remarkably shielded (~7 p.p.m.;
Table 10). These differences are similar to those described for
compound 2 and are related to the Asarone effect. In addition, a
NOESY experiment of 7 was performed (Fig. 7 and Table 11) and
showed that the H-1 at δ 4.33 p.p.m. correlates to the hydrogen
at δ 1.55 p.p.m., which belongs to the methylene group of the ethyl
3-Ethyl-2-methyl-1-arylindanes: diastereomer γ
Indanes 13 (diisosafrole), 14 (diasarone) and 15–17 are diastereo-
mers γ (Fig. 9). In all of them, the methyl group attached at C-2
Table 11. NMR spectral data of compound 7 (CDCl3, 400 MHz)
Position
1H
13C
NOESY
1
4.33 (1H, d, 7.9)
49.49
49.03
H-α, H-4, CH3(C-2)
H-3, H-6´, CH3(C-2)
2
2.43 (1H, m, 7.2, 7.9, 6.9)
3
2.91(1H, m)
48.91
H-α, H-β, H-4, CH2CH3
3a
—
140.21
108.66
143.82
148.18
108.77
138.57
22.76
H-α, H-2, CH2CH3
H-α, H-2, CH2CH3, OCH3(C-5)
—
4
6.79 (1H, s)
5
—
6
—
6.45 (1H, s)
—
—
7
OCH3(C-6)
7a
—
CH-Hα
CH-Hβ
CH2CH3
CH3(C-2)
OCH3(C-5)
OCH3(C-6)
10
20
30
40
50
1.55 (1H, m, 7.4, 7.7, 13.6)
1.75 (1H, m, 6.9, 7.4, 13.6)
0.96 (3H, t, 7.4)
1.02 (3H, d, 7.2)
3.90 (3H, s)
3.74 (3H, s)
—
—
22.76
—
12.95
—
14.74
—
57.46
—
56.61
—
124.94
152.98
98.39
—
—
—
6.59 (1H, s)
—
OCH3(C-40)
148.41
148.66
112.94
56.67
—
—
—
60
6.36 (1H, s)
3.91 (3H, s)
3.84 (3H, s)
3.65 (3H, s)
OCH3(C-50)
OCH3(C-20)
OCH3(C-40)
OCH3(C-50)
—
—
—
56.75
57.19
Figure 8. Synthetic 1,2-trans-2,3-cis-3-ethyl-2-methyl-1-aryl-7-methoxyindanes (α).
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Effect of methoxyl groups on the NMR spectra of indanic and tetralinic structures
Figure 9. Synthetic 1,2-trans-2,3-trans-3-ethyl-2-methyl-1-arylindanes (γ).
shows close values of chemical shift of hydrogen and carbon atoms
(Tables 12 and 13).
stable conformer possesses H-1 and H-3 in pseudoequatorial posi-
tion and H-2 in equatorial, avoiding the A1,3 strain, as informed for
the γ-diasarone. On the other hand, the differences of the chemical
shifts observed in H-1 and C-1 in the two cycloadducts show that
indane 15 does not present the Asarone effect due to the absence
of the methoxyl group in C-20. Instead, this effect is observed in
cycloadducts 16 and 17.
These data indicate a 1,2-trans-2,3-trans arrangement. Com-
pounds 14 and 15 have the same substitution pattern at the aro-
matic ring of the indanic frame and show low and similar values
of J1,2 and J2,3 (Table 12). This indicates that the presence of
methoxyl groups at C-4 and C-7 in 15 determines that the most
Table 12. 1H-NMR spectral data of the aliphatic carbon atoms of
1-aryl-3-ethyl-2-methylindanes: diastereomers γ
NMR spectral analysis of 1-aryltetralins
Natural bisnorlignans, pachypostaudins A and B[9] (18 and 19),
derived from cyclodimerization of 2,4,5-trimethoxyestyrene
(Scheme 2), have a methoxyl group at C-8 and C-20 in their
structures. It is therefore interesting to study if the size of the
non-aromatic ring and the substitution pattern in the tetralinic
structures have the same influence as those observed in NMR
Compound
H-1
H-2
H-3
CH3
J1,2
J2,3
γ-Diisosafrole
γ-Diasarone
3.57
4.30
3.55
4.27
3.88
4.23
4.19
1.99
2.08
2.02
2.07
2.12
2.05
2.10
2.65
2.69
2.67
2.65
2.75
2.65
2.67
1.14
1.18
1.12
1.17
1.19
1.15
1.16
9.3
4.1
9.4
4.3
5.3
8.6
9.0
9.3
4.1
9.4
4.2
5.5
8.1
9.0
13
14
15
16
17
Table 14. 1H-NMR and 13C-NMR spectral data of the hydrogen and al-
iphatic carbon atoms of tetralinic structures
Compound δH-1
J1,2
δC-1
δC-2
δC-3
δC-4
20[17,18]
21[19]
22[17,20]
23[21]
24[12]
25[22]
26
2.73
2.74
2.75
4.12
4.07
4.44
4.52
4.41
4.66
4.78
4.28
4.90
m
m
29.3
23.3
22.9
22.9
29.8
29.7
30.1
23.3
23.5
23.1
21.0
20.9
26.9
20.62
16.84
17.13
17.5
—
29.3
30.2
29.7
33.3
33.3
33.5
30.62
23.45
23.51
22.9
—
Table 13. 13C-NMR spectral data of the aliphatic carbon atoms of
1-aryl-3-ethyl-2-methylindanes: diastereomers γ
25,9
6.1 (t)
6.4
22.9
45.6
44.5
42.2
Compound
C-1
C-2
C-3
CH3
6.0(t)
γ-Diisosafrole
γ-Diasarone
13
58.5
51.4
50.8
52.3
50.8
52.4
52.9
50.8
50.4
17.4
6.8
49.8
47.6
22.0
7.0 (t)
3.4 (t)
3.2 (d)
4.8 (m)
8.7 (t)
2.8 (dd)
37.52 29.83
38.54 31.17
31.46 28.20
58.37
49.91
57.49
51.54
50.80
51.25
47.73
49.66
51.03
50.75
17.28
22.01
22.04
18.97
18.65
27
1415
28
18[9]
29[23]
19[9]
31.9
43.9
28.4
29.1
32.0
29.8
16
17
121.2
123.5
Figure 10. Synthetic and natural 1-aryltetralins.
Magn. Reson. Chem. (2017)
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B. Lantaño et al.
spectra for the indanic structures. The Asarone effect and the A1,3
strain were analysed on the basis of the tetralinic structures shown
in Fig. 10, and the NMR data are summarized in Table 14.
The NMR analysis of 21 and 22 compared with that of 20 shows
that the ethyl and the methoxyl groups attached at C-8 present a
shielding effect on C-1 (ΔδC ~3 and 7 p.p.m.) due to steric and
stereoelectronic factors respectively. In 1-aryltetralins, the presence
of these groups attached at C-20 has an effect on C-1 and H-1 similar
to that shown in compounds 25 and 26 compared with 23 and 24
respectively (ΔδC ~3 and 7 p.p.m. and ΔδH ~0.3 and 0.5 p.p.m.).
Tetralin 27, which has a methoxyl group at C-8, presents a marked
decrease in J1,2 and a shielding effect in carbons sp3 due to a
conformational change regarding the monosubstituted tetralins
analysed before, in which the aryl group is located in a pseudoaxial
position to avoid the A1,3 strain. The chemical shift of C-1, H-1 and
J
1,2 of compound 28 clearly shows the Asarone effect and the A1,3
strain as in the natural bisnorlignan pachypostaudin 18.
The NMR spectra of 29 and pachypostaudin B (19) were
identically analysed to assess the effects on this kind of
dihydronaphthalene (Fig. 11 and Table 14).
The NMR data of H-1 and C-1 (δH and J1,2) of the natural product
19 (δH 4.90 p.p.m.; J1,2 2.8 Hz and δC 28.4 p.p.m.) compared with the
corresponding 29 (δH 4.28 p.p.m.; J1,2 8.7 Hz and δC 43.9 p.p.m.)
show the same effects as those discussed in the preceding texts
and that, in this case, the sp2 carbons do not exert appreciable
influence.
Figure 11. Synthetic and natural 1-aryldihydronaphthalenes.
NMR spectral analysis of 1,2,3-triaryltetralinic structures
Natural tetralinic cyclodimers with hydroxyl groups and/or
methoxyl groups and whose biosynthetic origin are stilbene,
resveratrol, oxyresveratrol and isorhapontigenin (Fig. 12) have
attracted strong interest for their antioxidant properties in the
preservation of fruits and durability of wood.[8]
Tetralins derived from these natural stilbenes have hydroxyl or
methoxyl groups at C-8 and C-20, as is the case of bisnorlignans
Figure 12. Natural stilbenes.
Figure 13. Synthetic and natural 1,2-trans-2,3-trans-1,2,3-triaryltetralins: diastereomer γ.
Figure 14. Synthetic and natural 1,2-trans-2,3-cis-1,2,3-triaryltetralins: diastereomer α.
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Effect of methoxyl groups on the NMR spectra of indanic and tetralinic structures
18 and 19. This substitution pattern is of interest for a comparative
analysis of 1H-NMR and 13C-NMR spectra of 1,2,3-triarylsubstituted
tetralins, which do not have substituents at those positions. In this
study, synthetic tetralins (31–32 and 36) and natural tetralins:
isorhaformicol A (33),[8] resformicol A (34),[25] epialboctalol (35),[8]
Table 17. 1H-NMR and 13C-NMR spectral data of the hydrogen
and aliphatic carbon atoms of trans-1,2,3-triarylsubstituted
dihydronaphthalenes
Compound
δH-1
δH-2
J1,2
δC-1
δC-2
[24]
isorhaformicol B (37),[8] resformicol B (38),[8] alboctalol (39)
40 Restrytisol C
41[27]
42[27]
4.62
4.12
4.20
4.79
4.12
4.78
4.4 (d)
(sa)
54.0
52.0
49.0
49.8
51.0
45.6
and restrytisol C (40)[26] were used (Figs 13 and 14).
(sa)
Synthetic compounds 30–32 are diastereomers γ (1,2-trans-2,3-
trans) that do not have substituents at C-8 and C-20 unlike 33–35.
The NMR data of the latter three show A1,3 strain due to the
decrease in J1,2 and smaller chemical shift of H-1 and C-1, as
observed in tetralins 27. Besides, compound 35 presents Asarone
effect on H-1 and C-1 and on H-3 and C-3 due to the hydroxyl group
at C-20 of the aryl groups attached at C-1 and C-3 (Table 15).
The comparative analysis of the NMR spectroscopic data of
diastereomer α (1,2-trans-2,3-cis) 36 regarding 37–39 (Fig. 14 and
Table 16), which have substituents at C-8 or C-8 and C-20 (hydroxyl
or methoxyl group), shows effects similar to those observed in
diastereomers γ (Fig. 13).
Lastly, the NMR spectra of restrytisol C (40), a natural
dihydronaphthalene produced by grapes (Vitis spp)[26] compared
with 41, show values that indicate that the trisubstituted ring
adopts a conformation that avoids the A1,3 strain due to the
presence of the hydroxy group attached at C-8. In the
dihydronaphthalene 42, the Asarone effect is observed at H-2 and
C-2 (Fig. 15 and Table 17). However, the presence of four sp2
carbons in the triarylsubstituted cycle does not show the same
trends as in the monosubstituted dihydronaphthalenes and
triarylsubstituted tetralins.
NMR spectral analysis of other indanic and tetralinic structures
In 1976, Deshpande et al.[28] assigned a 1,2-diaryl-2-benzylindane
structure to alboctalol, the cyclodimer of oxyresveratrol, on the
basis of spectroscopic data and biogenetic considerations, without
indicating the stereochemistry (43). Later, the same researchers
published the revised structure of alboctalol 39[24] (Fig. 16).
With the aim of confirming the proposed structure and assigning
the configuration, Alesso et al.[7] conducted the stereodirected
synthesis of the frame of 43. In an exploratory study, the two
diastereomers of 1,2-diphenyl-2-benzylindane (44a and 44b) were
obtained, and then the respective octamethylderivatives of 43[11]
were synthesized (Fig. 17).
The 1H-NMR and 13C-NMR spectroscopic data of 44 and 45
(Table 18) are indicative of Asarone effect in positions 1 and 2
of diastereomers 45a and 45b. This effect is due to the 2,4-
dimethoxyphenyl groups attached at C-1 and C-2 (δH-1 4.60
and 4.57 p.p.m. in 44a and 44b vs δH-1 4.94 and 4.93 p.p.m. in
45a and 45b), and the δC-1 and δC-2 show the consequent
protection.
Table 15. 1H-NMR and 13C-NMR spectral data of the hydrogen and ali-
phatic carbon atoms of 1,2,3-triarylsubstituted tetralins: diastereomer γ
Compound
δH-1 δH-3
J1,2
δC-1 δC-2 δC-3 δC-4
30
31
32
4.25 3.25 10.5 (d) 55.39 56.19 46.82 40.04
4.16 3.36 10.3 (d) 54.1 55.4 45.8 38.9
4.19 3.37 10.3(d) 54.4 55.0 45.4 39.0
33 Isorhaformicol A 4.23 3.01 8.1 (d) 50.3 59.9 48.0 41.0
34 Resformicol A
35 Epialboctalol
4.26 3.04 6.9 (d) 49.8 60.0 47.9 41.0
4.42 3.51 8.2 (d) 44.1 56.2 40.3 40.1
Figure 16. Proposed structures for alboctalol.
Table 16. 1H-NMR and 13C-NMR spectral data of the hydrogen and aliphatic carbon atoms of 1,2,3-triarylsubstituted tetralins: diastereomer α
Compound
δH-1
δH-3
J1,2
δC-1
δC-2
δC-3
δC-4
3613
4.57
4.42
4.36
4.84
3.57
3.32
3.23
3.72
2.7(d)
50.11
45.9
45.4
37.9
54.59
56.2
56.4
48.0
39.37
38.7
30.60
32.3
31.4
29.9
37 Isorhaformicol B
38 Resformicol B
39 Alboctalol
Broad singlet (brs)
(s)
(s)
37.3
31.0
Figure 15. Synthetic and natural 1,2-trans-1,2,3-triaryldihydronaphthalenes.
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B. Lantaño et al.
Figure 17. Synthetic 2-benzyl-1-diarylindanes.
These two effects, A1,3 strain and Asarone effect, are significant
and must be taken into account when using monodimensional
NMR data for the configurational assignment of these structures,
which are very common in products derived from natural styrenes
and stilbenes.
Table 18. 1H-NMR and 13C-NMR spectral data of the hydrogen and
aliphatic carbon atoms of 1,2-diaryl-2-benzylindanes
Compound δH-1
δH-3
δCH2Ph δC-1 δC-2 δC-3 δCH2Ph
44a
44b
45a
45b
4.60 3.21/3.56 3.05/3.32 63.2 57.7 40.0
48.4
43.0
53.4
44.9
4.57 3.20/3.36 2.62/2.97 64.2 57.3 39.3
4.94 3.39/**
3.07/** 60.5 55.9 44.6
Experimental
4.93 3.20/3.33 2.62/3.02 60.6 56.0 41.6
General
Nuclear magnetic resonance spectra were recorded on a 7.05 Tesla
Criomagnet Bruker-Oxford BZH 300/89 with a resonance frequency
of 300.130 MHz 1H and 13C 75.468 MHz. Probe multinuclear
Z3150/0006 (5 mm). Data acquisition system and control Bruker
Avance III. Administration and process software Bruker TOPSPIN 3.2,
a 400.13-MHz 1H and 100.61-MHz 13C Ultra Shield NMR Spectrome-
1
ter, a 500.13-MHz H-NMR and 125.76-MHz 13C-NMR Bruker and
14.1 Tesla magnet Bruker Ultra Shield with shim system BOSS II
resonance frequency of 600.13 MHz 1H and 13C 150.91 MHz. Probe
multinuclear Bruker SmartProbe BBFO (5 mm). Data acquisition
system and control Bruker Avance III. Chemical shifts (δ) are quoted
in parts per million and are reference to the residual solvent peak
CDCl3, δ = 7.28 p.p.m. (1H), δ = 77.4 p.p.m. (13C). Spin multiplicities
as s, brs, d, dd, t, quadruplet (q) and m. Coupling constant (J) is
given in Hz.
Figure 18. Synthetic and natural 1-aryltetralones.
Table 19. 1H-NMR and 13C-NMR spectral data of the hydrogen and
aliphatic carbon atoms of 4-aryltetralones
The HMBC spectra were measured with a pulse sequence
hmbcgplpndqf (standard sequence pulse Bruker catalogue).
The HSQC spectra were measured with a pulse sequence
hsqcgpph (standard sequence pulse Bruker catalogue).
Nuclear overhauser spectra were recorded on Bruker Ultra
Shield spectrometer, operating at 600 MHz, with a spectral width
of 10.013 p.p.m. (6.009615 kHz) in both F2 and F1 domains (TD
F1: 2048, F2: 256 points), acquired with 16 scans per increment
and relaxation delays of 1.0 s. The mixing time in NOESY
experiments was 0.5 s. Data processing was performed on a
2 × 2 K data matrix.
Compound
δH-1
J1,2
δC-1 δC-2 δC-3
δC-4
46[29]
47[30]
48[31]
5.03
4.31
4.5–4.6 (m)
(m)
7.9, 4.6 (dd) 45.6
33.9
32.5 27.6 35.9 197.6
32.1
31.0
37.0
38.4
198.3
198.5
Another example is the tetralone 46 isolated from Peperomia
pellucida,[29] which shows the two effects discussed in this paper
with reference to tetralones 47 and 48 (Fig. 18 and Table 19).
Microanalyses were performed by Elemental Analyser Carlo Erba.
Preparative thin-layer chromatography (p-TLC) was done on Merck
Silica Gel 60 GF254, and analytical TLC was performed on Merck alu-
minium sheets Silica Gel 60 GF254. Commercial compounds were
purchased from Aldrich Chemical Co. Tetrahydrofuran and CH2Cl2
were distilled from sodium/benzophenone and CaH2 respectively.
Melting points are uncorrected and were determined in a Thomas
Hoover apparatus. In cases where synthetic intermediates or prod-
ucts were isolated by ‘aqueous workup (aqueous solution, organic
solvent)’, the procedure was to quench the reaction mixture with
the indicated aqueous solution, dilute with the indicated organic
solvent, separate the organic layer, extract the aqueous layer
several times with the organic solvent, dry the combined organic
extracts over Na2SO4 and remove the solvent under reduced
pressure (water aspirator) with a Büchi Rotavapor.
Conclusions
This study evaluated the effect exerted by the methoxyl groups at
C-7 and C-20 on the chemical shift of bibenzylic hydrogen and car-
bon atoms as well as on J1,2 in indanic structures and was extended
to tetralinic structures with methoxyl groups in C-8 and C-20.
In both indanic and tetralinic structures, the presence of a
methoxyl group at C-20 produces a stereoelectronic effect that we
called Asarone effect. The presence of a methoxyl group attached
at C-7 in indanes or to C-8 in tetralins determines that the most
favoured conformation for the pentagonal or hexagonal ring is
the one that decreases the A1,3 strain because the aryl group takes
the pseudoaxial position.
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Effect of methoxyl groups on the NMR spectra of indanic and tetralinic structures
General procedure for the formal [3 + 2] cycloaddition of an
alcohol and an alkene in the presence of SnCl4
0.95 (t, J = 7.4, 3H, CH2-CH3) p.p.m. 13C-NMR (75.468 MHz, CDCl3)
δ = 158.54, 148.68, 148.36, 140.22, 138.16, 133.62, 128.81, 127.71,
121.15, 110.89, 109.09, 108.39, 56.64, 56.62, 56.18, 50.33, 48.64,
48.23, 22.61, 15.09, 13.05 p.p.m. Anal. Calcd. for C21H26O3: C, 77.27,
H, 8.03. Found: C, 77.31, H, 7.95.
r-1-(4-Methoxyphenyl)-t-2-methyl-5,6-dimethoxyindane (1)
(E)-4-methoxyphenyl-β-methylstyrene (0.07 g, 0.48 mmol) and
SnCl4 (0.156 g, 0.60 mmol) were sequentially added to a solution
of (3,4-dimethoxyphenyl)methanol (0.108 g, 0.46 mmol) in CH2Cl2
(10 ml) at 0 °C. The resulting solution was stirred for 30 min at
0 °C and then poured into a rapidly stirred solution of NaCO3H
5%. Aqueous workup (NaCO3H, CH2Cl2) followed by p-TLC (95 : 5,
hexane/isopropanol) afforded 0.057 g (30%) of 1 (white solid),
t-3-Ethyl-t-2-methyl-r-1-(2-methoxyphenyl)-5,6,7-trimethoxyindane (11)
General procedure was carried out with 1-(3,4,5-trimethoxyphenyl)
propan-1-ol (0.113 g, 0.5 mmol), (E)-2-methoxyphenyl-β-
methylstyrene (0.074 g, 0.50 mmol) and SnCl4 (0.166 g, 0.64 mmol).
1
p-TLC (CH2Cl2) afforded 0.093 g (53%) of 11 (clear oil). H-NMR
1
mp: 82–83 °C. H-NMR (300.130 MHz, CDCl3) δ = 7.11 (d, J = 8.7,
(300.130 MHz, CDCl3) δ = 7.13 (t, J = 7.4, 1H, Ar), 6.86 (d, J = 8.2,
1H, Ar), 6.72 (t, J = 7.4, 1H, Ar), 6.54 (s, 1H, Ar), 6.52 (d, J = 7.4, 1H,
Ar), 4.36 (d, J = 2.5, 1H, CH-Ar), 3.88 (s, 3H, OCH3), 3.87 (s, 3H,
OCH3), 3.86 (s, 3H, OCH3), 3.80 (s, 3H, OCH3), 2.91 (m, 1H, CH-
CH2CH3), 2.35 (m, J = 2.5, 6.9, 7.4, 1H, CH-CH3), 1.72 (m, 1H, CH2),
1.46 (m, 1H, CH2), 0.96 (d, J = 7.2, 3H, CH-CH3), 0.91 (t, J = 7.4, 3H,
CH2-CH3) p.p.m. 13C-NMR (75.468 MHz, CDCl3) δ = 157.95, 153.76,
151.07, 143.96, 133.54, 129.61, 129.48, 127.82, 127.60, 120.72,
110.84, 103.54, 61.56, 60.86, 56.80, 56.16, 49.12, 48.07, 46.14,
21.97, 15.66, 13.05 p.p.m. Anal. Calcd. for C22H28O4: C, 74.13, H,
7.92. Found: C, 74.35, H, 7.80.
2H, Ar), 6.87 (d, J = 8.7, 2H, Ar), 6.40 (s, 1H,Ar), 3.88 (s, 3H, OCH3),
3.81 (s, 3H, OCH3), 3.72 (s, 3H, OCH3), 3.70 (d, J = 9.5, 1H, ArCHAr),
3.06 (dd, J = 7.4, 14.9 1H, CH2Ar), 2.55 (dd, J = 9.5, 14.9, 1H, CH2Ar),
2.35 (m, 1H, CHCH3), 1.16 (d, J = 6.7, 3H, CHCH3) p.p.m. 13C-NMR
(75.468 MHz, CDCl3) δ = 158.22, 148.14, 148.01, 138.73, 136.46,
135.13, 129.48, 113.76, 108.04, 107.32, 58.85, 56.02, 55.91, 55.24,
46.87, 40.06, 18.32, p.p.m. Anal. Calcd. for C19H22O3: C, 76.48, H,
7.43. Found: C, 76.50, H, 7.45.
r-1-(4-Methoxyphenyl)-t-2-methyl-5,6,7-trimethoxyindane (3)
General procedure was carried out with (3,4,5-trimethoxyphenyl)
methanol (0.129 g, 0.66 mmol), (E)-4-methoxyphenyl-β-
methylstyrene (0.097 g, 0.66 mmol) and SnCl4 (0.23 g, 0.90 mmol).
p-TLC (70 : 30, hexane/ethylacetate) afforded 0.14 g (65%) of 3
(clear oil). 1H-NMR (600.13 MHz, CDCl3) δ = 7.08 (d, J = 8.6, 2H, Ar),
6.84 (d, J = 8.6, 2H, Ar), 6.61 (s, 1H, Ar), 3.88 (s, 3H, OCH3), 3.37 (d,
J = 4.7, 1H, CHAr), 3.81 (s, 3H, OCH3), 3.80 (s, 3H, OCH3), 3.40 (s, 3H,
OCH3), 3.19 (dd, J = 7.7, 15.6, 1H, CH2), 2.52 (dd, J = 6.7, 15.6, 1H,
CH2), 2.39 (m, J = 6.8, 1H, CHCH3), 1.17 (d, J = 6.8, 3H, CH3) p.p.m.
13C-NMR (150.91 MHz, CDCl3) δ = 157.86, 153.29, 150.38, 140.83,
139.08, 137.82, 130.70, 128.43, 113.52, 103.44, 60.87, 60.05, 56.98,
56.11, 55.21, 45.27, 40.48, 19.99 p.p.m. Anal. Calcd. for C20H24O4: C,
73.15, H, 7.37. Found: C, 73.18, H, 7.35.
c-3-Ethyl-t-2-methyl-r-1-(2,4,5-trimethoxyphenyl)-5,6-methylenedioxyindane
(17)
General
procedure
was
carried
out
with
1-(3,4-
methylenedioxyphenyl)propan-1-ol (0.09 g, 0.5 mmol), (E)-2,4,5-
trimethoxyphenyl-β-methylstyrene (0.104 g, 0.50 mmol) and SnCl4
(0.169 g, 0.65 mmol). p-TLC (80 : 20, hexane/ethylacetate) afforded
0.018 g (10%) of 17 (clear oil). 1H-NMR (300.130 MHz, CDCl3) δ = 6.72
(s, 1H, Ar), 6.59 (s, 1H, Ar), 6.56 (s, 1H, Ar), 6.33 (s, 1H, Ar), 5.93 (d, J:
1.5, 1H, OCH2O), 5.89 (d, J: 1.5, 1H, OCH2O), 4.19 (d, J = 9.0, 1H,
CH-Ar), 3.93 (s, 3H, OCH3), 3.82 (s, 3H, OCH3), 3.75 (s, 3H, OCH3),
2.67 (m, J = 5.3, 5.8, 9.0, 1H, CH-CH2), 2.10 (m, 1H, CH-CH3), 1.85
(m, 2H, CH2CH3), 1.16 (d, J = 6.8, 3H, CH-CH3), 0.99 (t, J = 7.4, 3H,
CH2-CH3), p.p.m. 13C-NMR (75.468 MHz, CDCl3) δ = 152.98, 148.51,
147.02, 146.93, 143.92, 142.31, 140.27, 124.97, 113.29, 105.64,
104.46, 100.89, 98.45, 57.51, 57.01, 56.23, 50.80, 50.75, 50.43,
25.57, 18.65, 11.47 p.p.m. Anal. Calcd. for C22H26O5: C, 71.33, H,
7.07. Found: C, 71.12, H, 7.10.
r-1-(2,4,5-Trimethoxyphenyl)-t-2-methyl-5,6,7-trimethoxyindane (4)
General procedure was carried out with (3,4,5-trimethoxyphenyl)
methanol (0.129 g, 0.66 mmol), (E)-2,4,5-trimethoxyphenyl-β-
methylstyrene (0.137 g, 0.66 mmol) and SnCl4 (0.23 g, 0.90 mmol).
p-TLC (70 : 30, hexane/ethylacetate) afforded 0.145 g (57%) of 4
1
(clear oil). H-NMR (300.130 MHz, CDCl3) δ = 6.61 (s, 1H, Ar), 6.58
(s, 1H, Ar), 6.33 (s, 1H, Ar), 4.35 (d, J = 5.0, 1H, CHAr), 3.89 (s, 3H,
OCH3), 3.88 (s, 3H, OCH3), 3.86 (s, 3H, OCH3), 3.79 (s, 3H, OCH3),
3.66 (s, 3H, OCH3), 3.49 (s, 3H, OCH3), 3.13 (dd, J = 8.0, 15.6, 1H,
CH2), 2.47 (dd, J = 5.3, 15.6, 1H, CH2), 2.35 (m, 1H, CHCH3), 1.16 (d,
J = 6.8, 3H, CH3) p.p.m. 13C-NMR (75.468 MHz, CDCl3) δ = 158.76,
152.08, 150.56, 145.99, 145.28, 140.16, 136.74, 126.40, 126.30,
113.28, 105.58, 99.48, 60.81, 60.56, 57.91, 56.13, 56.10, 55.83,
53.61, 42.33, 40.84, 19.80 p.p.m. Anal. Calcd. for C22H28O6: C, 68.02,
H, 7.27. Found: C, 68.01, H, 7.25.
General procedure for obtained 1-aryltetralins
1-(2,4-Dimethoxyphenyl)-1,2,3,4-tetrahydronaphthalene (26)
A solution of 2,4-dimethoxy bromobenzene (1.4 ml, 9.16 mmol) and
1,2-dibromoethane (0.76 ml, 9.16 mmol) in dry ether (10 ml) was
added dropwise over a period of 5 h to magnesium turnings
(474 mg, 19.75 mmol) under refluxing conditions, then the mixture
was cooled to room temperature. A solution of 1-tetralone (250 mg,
1.86 mmol) in dry benzene (15 ml) was added dropwise during
35 min. The mixture was stirred for 4 h at reflux. After cooling at
room temperature, the mixture was hydrolysed with saturated
aqueous NH4Cl. The organic layer was separated, and the aqueous
layer was extracted with chloroform (2 × 20 ml). Then, the
organic extracts were dried and the solvent evaporated in vacuo.
p-TLC (80 : 20, hexane/ethyl acetate) afforded 0.343 g (65%; clear
t-3-Ethyl-t-2-methyl-r-1-(2-methoxyphenyl)-5,6-dimethoxyindane (6)
General procedure was carried out with 1-(3,4-dimethoxyphenyl)
propan-1-ol (0.098 g, 0.5 mmol), (E)-2-methoxyphenyl-β-
methylstyrene (0.074 g, 0.50 mmol) and SnCl4 (0.166 g, 0.64 mmol).
p-TLC (CH2Cl2) afforded 0.090 g (55%) of 6 (clear oil). 1H-NMR
(300.130 MHz, CDCl3) δ = 7.16 (dt, J = 1.6, 8.2, 1H, Ar), 6.90 (d,
J = 8.2, 1H, Ar), 6.76 (s, 1H, Ar), 6.74 (m, 2H, Ar), 6.48 (s, 1H, Ar),
4.33 (d, J = 6.7, 1H, CH-Ar), 3.87 (s, 3H, OCH3), 3.84 (s, 3H, OCH3),
3.72 (s, 3H, OCH3), 2.90 (m, 1H, CH-CH2CH3), 2.44 (m, J = 6.7, 7.2,
7.9, 1H, CH-CH3), 1.59 (m, 2H, CH2), 0.99 (d, J = 7.2, 3H, CH-CH3),
oil)
1-(2,4-dimethoxyphenyl)-1,2,3,4-tetrahydronaphthalen-1-ol.
1H-NMR (300.130 MHz, CDCl3) δ = 7.33 (m, 1H, Ar), 7.19 (m, 3H,
Ar), 6.70 (d, J = 8.5, 1H, Ar), 6.51 (d, J = 2.4, 1H, Ar), 6.36 (dd,
J = 2.4, 8.5, 1H, Ar), 3.79 (s, 6H, OCH3), 4.16 (s, 1H, OH), 2.84 (m, 2H,
CH2), 2.48 (ddd, J = 2.8, 8.8, 12.7, 1H, CH2), 2.07 (ddd, J = 2.8, 10.1,
Magn. Reson. Chem. (2017)
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc

B. Lantaño et al.
12.9, 1H, CH2), 1.89 (m, 1H, CH2), 1.61 (m, 1H, CH2), p.p.m. 13C-NMR
(75.468 MHz, CDCl3) δ = 159.81, 157.33, 141.53, 137.41, 130.12,
128.37, 128.21, 127.01, 126.07, 124.87, 103.39, 99.61, 75.58, 55.43,
55.31, 38.05, 29.64, 20.08 p.p.m. Anal. Calcd. for C18H20O3: C, 76.03,
OH), 3.79 (s, 3H, OCH3), 3.53 (s, 3H, OCH3), 3.41 (s, 3H, OCH3), 2.87
(td, J = 5.4, 5.5, 17.1 Hz, 1H, CH2), 2.55 (ddd, J = 5.1, 8.4, 17.0, 1H,
CH2), 2.33 (m, 1H, CH2), 2.02 (m, 1H, CH2), 1.78 (m, 1H, CH2), 1.66
(m, 1H, CH2) p.p.m. 13C-NMR (75.468 MHz, CDCl3) δ = 159.28,
157.06, 151.74, 151.45, 132.68, 130.51, 128.84, 128.10, 109.81,
108.54, 103.59, 99.88, 73.82, 56.19, 55.91, 55.57, 55.24, 37.92,
24.05, 19.45 p.p.m. Anal. Calcd. for C20H24O5: C, 69.75; H, 7.02.
Found: C, 69.73, H, 7.04. General procedure was carried out with
0.46 ml of TFA, 28.78 mg (0.76 mmol) of NaBH4 and 26.3 mg
(0.076 mmol) of 1-(2,4-dimethoxyphenyl)-5,8-dimethoxy-1,2,3,4-
tetrahydro naphthalene-1-ol. p-TLC (80 : 20, hexane/ethyl acetate)
H, 7.09. Found: C, 76.1, H, 7.10.
A mixture of 1-(2,4-
dimethoxyphenyl)-1,2,3,4-tetrahydronaphthalen-1-ol 63.4 mg,
(0.22 mmol) in CHCl3 (1 ml) and powdered sodium borohydride
83.3 mg (19 mmol) was added in portions over 2 min to
trifluoroacetic acid (TFA; 1.33 ml) in a 50-ml three-neck flask at 0°
under of nitrogen with vigorous stirring. After stirring the mixture
for 5 min at 0°, the bulk of the TFA was removed in vacuo and the
residue was treated with ice water (5 ml) and then 30% aqueous
sodium hydroxide solution and extracted with 20-ml CHCl3. The
extracted was washed with water, dried over sodium sulfate and
1
afforded 0.0163 g (65%; clear oil) of 28. H-NMR (300.130 MHz,
CDCl3) δ = 7.14 (m, 2H, Ar), 7.06 (m, 1H, Ar), 6.88 (d, J = 7.6, 1H,
Ar), 6.65 (d, J = 8.4, 1H, Ar), 6.52 (d, J = 2.4, 1H, Ar), 6.38 (dd,
J = 2.4, 8.4, 1H, Ar), 4.50 (t, J = 6.0, 1H, CH-Ar), 3.86 (s, 3H, OCH3),
3.81 (s, 3H, OCH3), 2.88 (m, 2H, CH2), 2.05 (m, 1H, CH2), 1.88 (m,
3H, CH2) p.p.m. 13C-NMR (75.468 MHz, CDCl3) δ = 158.53, 157.40,
151.53, 151.36, 129.98, 129.83, 129.43, 128.48, 127.83, 107.85,
107.03, 102.86, 98.40, 56.19, 55.56, 55.55, 55.17, 31.46, 28.20,
23.51, 17.13 p.p.m. Anal. Calcd. for C18H20O2: C, 80.56, H, 7.51.
Found: C, 80.55, H, 7.50.
1
evaporated in vacuo to provide 73.55 mg (78%) of 26. H-NMR
(300.130 MHz, CDCl3) δ = 7.14 (m, 2H, Ar), 7.06 (m, 1H, Ar), 6.88 (d,
J = 7.6, 1H, Ar), 6.65 (d, J = 8.4, 1H, Ar), 6.52 (d, J = 2.4, 1H, Ar),
6.38 (dd, J = 2.4, 8.4, 1H, Ar), 4.50 (t, J = 6.0, 1H, CH-Ar), 3.86 (s, 3H,
OCH3), 3.81 (s, 3H, OCH3), 2.88 (m, 2H, CH2), 2.05 (m, 1H, CH2), 1.88
(m, 2H, CH2) p.p.m. 13C-NMR (75.468 MHz, CDCl3) δ = 158.93,
157.84, 139.97, 137.97, 130.55, 130.06, 128.83, 128.30, 125.57,
125.54, 103.71, 98.34, 55.45, 55.29, 37.52, 30.62, 29.83, 20.62 p.p.m.
Anal. Calcd. for C18H20O2: C, 80.56, H, 7.51. Found: C, 80.55, H, 7.50.
General procedure for obtained 1,2,3-triphenyltetralins
5,8-Dimethoxy-1-phenyl-1,2,3,4-tetrahydronaphthalene (27)
General procedure employed by Hiscock et al.13 was carried out
with trans-stilbene (1 g) and SbCl3 (5 g). p-TLC (80 : 20,
hexane/ethyl acetate) afforded 150 mg of 30 (mp: 113–115 °C)
and 132 mg of 36 (mp: 144–146 °C).
General procedure was carried out with bromobenzene (0.2 ml,
1.95 mmol), magnesium turnings (47.0 mg, 1.95 mmol) and 5,8-
dimetethoxy-1-tetralone (80.0 mg, 0.39 mmol). p-TLC (80 : 20,
hexane/ethylacetate) afforded 0.067 g (61%) of 5,8-dimethoxy-1-
phenyl-1,2,3,4-tetrahydronaphthalen-1-ol (clear oil). 1H-NMR
(300.130 MHz, CDCl3) δ = 7.38 (m, 1H, Ar), 7.24 (m, 4H, Ar), 6.74 (d,
J = 8.8, 1H, Ar), 6.72 (d, J = 8.8, 1H, Ar), 4.80 (s, 1H, OH), 3.85 (s, 3H,
OCH3), 3.48 (s, 3H, OCH3), 2.85 (td, J = 4.4, 4.4, 17.7, 1H, CH2), 2.67
(ddd, J = 5.7, 10.2, 17.7, 1H, CH2), 2.20 (m, 1H, CH2), 2.03 (m, 1H,
CH2), 1.77 (m, 1H, CH2), 1.52 (m, 1H, CH2) p.p.m. 13C-NMR
(75.468 MHz, CDCl3) δ = 151.54, 150.25, 131.27, 128.67, 128.49,
127.57, 127.47, 126.54, 126.27, 125.66, 109.57, 108.70, 75.50, 55.93,
55.69, 40.36, 24.05, 18.59 p.p.m. Anal. Calcd. for C19H23O2: C, 80.53;
H, 8.18. Found: C, 80.51, H, 8.16. General procedure was carried
out with 1.4 ml of TFA, 87.1 mg (2.3 mmol) of NaBH4 and 67 mg
(1R/S,2R/S,3S/R)-1,2,3-triphenyl-1,2,3,4-tetrahydronaphthalene (30)
Proton nuclear magnetic resonance (300.130 MHz, CDCl3) δ = 7.25–
6.85 (m, 19H, Ar), 4.42 (d, J = 10.7, H-1), 3.56 (ddd, J = 4.2, 10.9, 11.5,
H-2), 3.43 (dd, J = 12.7, 16.0, H-4a), 3.40 (dd, J = 10.9, 11.1, H-3), 3.25
(dd, J = 4.0, 16.2, H-4b). 13C-NMR (75.468 MHz, CDCl3) δ = 145.40,
144.20, 142.56, 139.86, 136.84, 130.06, 129.32, 128.40, 128.25,
128.03, 127.92, 127.69, 127.59, 126.11, 125.91, 126.61, 56.19, 55.39,
46.82, 40.04.
(1R/S,2R/S,3R/S)-1,2,3-Triphenyl-1,2,3,4-tetrahydronaphthalene (36)
Proton nuclear magnetic resonance (500 MHz, CDCl3) δ = 7.31–7.02
(m, 15H, Ar), 6.69 (dd, J = 2.0, 5.5, 2H, Ar), 6.58 (d, J = 7.0, 2H, Ar), 4.57
(d, J = 2.6, H-1), 3.57 (ddd, J = 2.8, 3.5, 9.9, H-3), 3.40 (t, J = 3.3, H-2),
3.08 (m, 2H, CH2). 13C-NMR (125 MHz, CDCl3) δ = 147.76, 142.97,
141.32, 137.83, 137.56, 130.85, 129.10, 129.04, 128.95, 128.29,
128.20, 127.47, 126.36, 126.32, 126.26, 126.17, 126.08, 54.59, 50.11,
39.37, 30.60.
(0.23
mmol)
of
5,8-dimethoxy-1-phenyl-1,2,3,4-
tetrahydronaphthalen-1-ol. p-TLC (80 : 20, hexane/ethyl acetate)
afforded 0.34 g (54%; clear oil) of 27. 1H-NMR (300.130 MHz, CDCl3)
δ = 7.23 (t, J = 7.1, 2H, Ar), 7.14 (t, J = 7.1, 1H, Ar), 7.00 (d, J = 7.1, 1H,
Ar), 6.73 (d, J = 8.7, 1H, Ar), 6.64 (d, J = 8.7, 1H, Ar), 4.41 (t, J = 4.3, 1H,
CH-Ar), 3.85 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 2.90 (td, J = 1.9, 5.5,
17.6, 1H, CH2), 2.55 (ddd, J = 4.4, 6.7, 17.6, 1H, CH2), 1.98 (m, 2H,
CH2), 1.63 (m, 2H,CH2) p.p.m. 13C-NMR (75.468 MHz, CDCl3)
δ = 151.62, 151.43, 147.23, 128.91, 128.17, 128.04, 127.66, 125.23,
107.84, 107.36, 55.92, 55.63, 38.54, 31.17, 23.45, 16.84 p.p.m. Anal.
Calcd. for C19H23O2: C, 80.53; H, 8.18. Found: C, 80.51, H, 8.16.
Acknowledgement
This study was supported by Universidad Nacional de Luján and
Universidad de Buenos Aires.
1-(2,4-Dimethoxyphenyl)-5,8-dimethoxy-1,2,3,4-tetrahydronaphthalene (28)
General procedure was carried out with 2,4-dimethoxy
bromobenzene (1.0 ml, 6.91 mmol), 1,2-dibromoethane (0.57 ml,
6.91 mmol) magnesium turnings (165.84 mg, 6.91 mmol) and 5,8-
dimetethoxy-1-tetralone (0.25 mg, 1.21 mmol). p-TLC (80 : 20,
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Copyright © 2016 John Wiley & Sons, Ltd.
Magn. Reson. Chem. (2017)

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