Reactions of Anodically Generated Methoxystilbene Cation Radicals: The Influence of Ortho-Substituted Vinyl and Formyl Groups

Article abstract of DOI:10.1021/acs.joc.9b00939

The present investigation represents a continuation of studies on the effect of ortho′-substitution on the reactivity of anodically generated methoxystilbene cation radicals. Whereas previous studies have focused on the effect of ortho′-substituted nucleophilic groups such as OH, NH₂, CH₂OH, CH₂NH₂, and COOH, the present study extends the investigation to ortho′-substituted vinyl and formyl groups. The results show that when the ortho′-substituent is a vinyl group, the products include a bisdihydronaphthalene derivative and a doubly bridged, dibenzofused cyclononane from direct trapping of a bis carbocation intermediate. In the presence of an additional 3-methoxy substituent, the products are the tetracyclic chrysene derivatives. When the ortho′-substituent is a nonnucleophilic formyl group, the products include fused indanylnaphthalenes and indanylbenzopyran aldehydes. When an additional 3-methoxy group is present, an unusual fused benzofluorene-dibenzoannulene product is obtained. Mechanistic rationalization for the formation of the various products is presented. The results have contributed to a deeper understanding of how the reactivity of the methoxystilbene cation radicals is affected by the nature of the ortho′-substituents.

Full text of DOI:10.1021/acs.joc.9b00939

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Article
Reactions of Anodically Generated Methoxystilbene Cation Radicals:
The Influence of Ortho-Substituted Vinyl and Formyl Groups
Kam-Weng Chong, Noel F. Thomas, Yun-Yee Low, and Toh-Seok Kam
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00939 • Publication Date (Web): 06 May 2019
Downloaded from http://pubs.acs.org on May 8, 2019
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Reactions of Anodically Generated Methoxystilbene
Cation Radicals: The Influence of Ortho-Substituted
Vinyl and Formyl Groups
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Kam-Weng Chong, Noel F. Thomas, Yun-Yee Low, and Toh-Seok Kam*
Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala
Lumpur, Malaysia
Corresponding author’s e-mail address: tskam@um.edu.my
Ar1
Ar2
MeO
Ar1
Ar1
Ar1
O
Ar1
O
OR
X
Ar1
Ar1
Ar3
NHAc
X = formyl
anode
X = vinyl
anode
(2 stereoisomers)
OH
MeO
MeO
Ar2
Ar2
Ar1
Ar1
Ar3
R1
MeO
MeO
MeO
MeO
OMe
MeO
MeO
H
O
R1 = H or OMe
X = CH=CH2 or CHO
Ar1 = 4-MeOC6H4; Ar2 = 3,4-(MeO)2C6H3
Ar3 = 2-CH2=CHC6H4
Ar1 = 4-MeOC6H4; Ar2 = 2-CHOC6H4; R = H or Me
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Abstract
The present investigation represents a continuation of studies on the effect of ortho'-
substitution on the reactivity of anodically generated methoxystilbene cation radicals.
Whereas previous studies have focused on the effect of ortho'-substituted nucleophilic
groups such as OH, NH , CH OH, CH NH and COOH, the present study extends the
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investigation to ortho'-substituted vinyl and formyl groups. The results show that when
the ortho'-substituent is a vinyl group, the products include a bisdihydronaphthalene
derivative and a doubly-bridged, dibenzofused cyclononane from direct trapping of a bis
carbocation intermediate. In the presence of an additional 3-methoxy substituent, the
products are the tetracyclic chrysene derivatives. When the ortho'-substituent is a non-
nucleophilic formyl group, the products include fused indanylnaphthalenes and
indanylbenzopyran aldehydes. When an additional 3-methoxy group is present, an
unusual fused benzofluorene-dibenzoannulene product is obtained. Mechanistic
rationalization for the formation of the various products is presented. The results have
contributed to a deeper understanding of how the reactivity of the methoxystilbene cation
radicals is affected by the nature of the ortho'-substituents.
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Introduction
While less frequently employed compared to conventional reactions, electrochemically-
mediated transformations has always retained its place as a useful option in organic
synthetic methodology for the formation of C-C bonds and for functional group
transformations.1-4 This is in large part due to several inherent advantages associated with
the approach such as the use of mild conditions, the high chemoselectivity, umpolung
reactivity, and the use of green methodology.4-7 It is therefore hardly surprising that there
has been a recent revival of interest in the application of electrochemically-mediated
transformations in organic synthesis.8-17 The electrochemical method involves in essence
the removal or addition of an electron from a substrate through the application of an
electric potential. As such for organic substrates the first formed species is either the
cation radical (anodic oxidation) or the anion radical (cathodic reduction). An
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understanding of the properties and reactivity of these species would be useful in applying
electrochemical methodology to synthesis.18,19 In our systematic studies of the reactions
of anodically-generated stilbene cation radicals, we first investigated the effect of
aromatic substitution (para and meta substituents) on the nature and distribution of the
products in the oxidation of substituted stilbenes. The aromatic substituents were found to
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fall into three groups based on the type of products formed (Figure 1). This was then
followed by a study of the influence of ortho'-substituted nucleophilic groups (OH, NH2,
CH OH, CH NH CO H) on the reactivity of anodically-generated 4-methoxy- and 3,4-
2
2
2,
2
dimethoxystilbene cation radicals (Figure 2).21,22 The results showed that when ortho'-
substituted OH or NHR groups are present in the other ring, the products are the
bisbenzofurans/bisindoles or fused bisbenzopyrans/bisquinolines, formed respectively as
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a result of both direct and crossover intramolecular cation-nucleophile reactions. Bridged
oxocine/azocine products are also formed in the presence of an additional 3-methoxy
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substituent. When the ortho' substituents are hydroxymethyl, aminomethyl, and
carboxylic acid groups, the products are bisbenzopyrans, or bisisoquinolines, or bis--
lactones, respectively, a result of direct intramolecular cation-nucleophile reactions.
Crossover products (e.g., fused benzoxepanes or fused benzoazepanes) were not formed.
In the presence of an additional 3-methoxy substituent, competing Friedel-Crafts
reactions occur to give other fused polycyclic products.22
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Ar2
Ar1

e
anode
R2'
H
Ar1
Ar1'
R2'
Ar2
Ar2'
Ar2
Ar2'
H
Ar1
Ar1
Ar2'
Ar2
H
Ar2
H
H
Ar1
Ar1'
Ar1
Ar1'
H
Ar1'
O
O
H
Ar1'
NHAc
NHAc
H
R2
Ar1'
Ar1'
R2'
Ar1'
Ar1
Ar2'
Ar2'
Ar1'
H
H
H
Ar1
Ar2' Ar1
Ar1
Ar2 Ar1
Ar2
H
H
Ar2
H
Ar1'
R2
R2'
H
H
R2
Figure 1. Effect of aromatic substitution (p- and m-substituents) on the distribution of
products in the anodic oxidation of stilbenes.
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Ar1
X
O
O
X
X
O
O
X
Ar1
Ar1
Ar1
Ar1
Ar1
(
3 stereoisomers)
(
3 stereoisomers)
Ar1
Ar1
Ar1
1
1
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Ar2
(
H)MeO
MeO
X
X
X = CH OH or
2
X
2
O
O
Ar1
Ar1
CH NHR or
X
2
X = OH or NHR2
anode
CO2H
(
2 stereoisomers)
Ar1
Ar1
anode
Ar2
MeO
MeO
MeO
MeO
Ar1 Ar1
R1
O
OMe
O
O
R1 = H or OMe
Ar2
Ar1
Ar1
Ar2
Ar2
X
MeO
MeO
MeO
MeO
N
N
Ar1
R2
Ar1 = 4-MeOC H  or
Ar1 = 4-MeOC H  or
6
4
6 4
3
,4-(MeO) C H ;
3,4-(MeO) C H ;
2 6 3
2
6
3
Ar2 = 2-R C H ;
3
2
3
6
4
2
Ar = 2-R C H ;
6 4
R3 = OH or NHR ;
R3 = CH OH or CH NHR ;
2
2
2
X = O or NR2
X = O or NR2
Figure 2. Effect of ortho-substituted nucleophilic groups on the distribution of products
in the anodic oxidation of methoxystilbenes.
In this final part of the study, we propose to investigate the effect of ortho-
substituted vinyl and formyl groups and herein report our results.
RESULTS AND DISCUSSION
Stilbenes were synthesized by coupling (Heck) of the appropriate aryl halide and
styrene precursors. The choice of the appropriate potential for carrying out controlled
potential electrolysis (CPE) was based on a preliminary cyclic voltammogram.
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Preparative electrolyses were carried out at the first anodic wave until consumption of ca.
0
.91 F, after which the products were separated by preparative radial chromatography
and/or HPLC.
We first investigated the anodic oxidation (0.98 V, Pt gauze anode, Pt cathode,
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MeCN/0.2 M LiClO ) of methoxystilbene 1 in which the ortho-substituent is a vinyl
4
group, in order to determine whether and how efficiently the -electrons of the vinyl
moiety can engage the benzylic cation in an cation-olefin cyclization process. A
preliminary cyclic voltammogram of 1 (Pt anode, MeCN/0.2 M LiClO ) showed the
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presence of two irreversible waves at 0.89 V and 1.13 V versus Ag/AgNO . Controlled
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potential electrolysis at the first anodic wave (0.98 V, Pt-gauze anode, Pt cathode;
MeCN/0.2 M LiClO ) gave a product mixture comprising the C symmetric
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bisdihydronaphthalene 1a (27%), the unusual, doubly-bridged, dibenzofused cyclononane
b (6%), and the stereoisomeric tetraaryltetrahydrofurans 1c (15%) and 1d (12%)
1
2
0
1
13
1
(
Scheme 1). The H and C{ H} NMR spectra of 1a (C H O ) can be assigned by
3
4
30
2
analogy to the related C symmetric compounds such as the bisbenzopyran,
2
2
2
bisisoquinolines, and bis--lactones obtained in the previous study. The presence of the
C-15C-16 double bond is indicated by the olefinic resonances at    130.1) and
H
C
  ( 130.0).
H
C
1
The H NMR data of the cyclononane derivative 1b (C H NO ) showed
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resonances due to 16 aromatic hydrogens, 2 methoxy groups, 7 methines, one methylene,
and one methyl of an acetamide group. A distinctly deshielded doublet at δ 5.31 (δ
H
C
4
8.1) is assigned to an aminomethine (H-15a), while the NH resonance is observed at δH
4
.52. The presence of an amide group is also indicated by the IR bands at 1655 (C=O)
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-1
and 3305 (NH) cm in addition to the amide carbonyl resonance at δ 168.5. The
C
aromatic resonances are attributed to two 1,4-disubstituted (two p-methoxyphenyl) and
two 1,2-disubstituted aromatic moieties, corresponding to rings A, A, B and B. The
COSY data (Figure 3) showed the presence of a −NHCHCHCHCHCHCHCHCH− partial
structure, corresponding to NH−C-15a−C-16a−C-7a−C-8a−C-8b−C-7b−C-16b−C-15b,
with C-15b linked to C-16a to forge a substituted seven-membered ring. Examination of
the HMBC data permitted assembly of the complete structure of 1b, revealing a doubly-
bridged, dibenzofused cyclononane derivative. The acetamido side chain is linked to the
cyclononane core at C-15a from the H-15a/C-17 three bond correlation in the HMBC
spectrum. The strong NOE interaction between H-15a and H-16-b (Figure 3) requires the
methano (C-7a) and ethano (C-7bC16-b) bridges to be oriented anti to each other
resulting in these hydrogens being proximate and pointing towards each other (the same
NOE would be impossible for the alternative structure with a syn disposition of the
methano and ethano bridges). With the geometry of the methano (C-7a) and ethano (C-
7bC16b) bridges fixed, the orientation of H-8a, H-8b, H-15b, and H-16a can be
accordingly assigned, while the orientations of H-7a and H-7b are assigned from the H-2a
1
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(
H-6a)/H-16a and H-2b (H-6b)/H-16b NOEs. The resulting relative configuration of 1b is
in perfect agreement with the NOESY data (Figure 3). Other observations which are
consistent with the structure include the observation that H-15a and H-16a are orthogonal
(
J15a-16a = 0) consistent with the -orientation of H-15a, and the observation of long-range
W-coupling (3.2 Hz) between H-8a and H-16a.
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Scheme 1. Products from the Anodic Oxidation of Stilbene 1
12a
12b
OMe
10a
10b
MeO 4b
12a
10a
12b
10b
4a
1
5a
15b
16b
9a
9b
8b
H
H
8a
16a
H
9a
8a
9b
8b
CPE at +0.98 V, 1 F
ACN, 0.2 M LiClO4
H
8b
0
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7
a
7b
1b
1b
9b
1a
8a
H
H
15b
1b
1a
9a
16a
4a
15a
1a
16b
4b
H
12a
7b
7a
16b
0b
H
7a
7b
12b
1
6a
15a
10a
O
O
1
15b
MeO
OMe MeO
OMe
4a
4b
NHAc
H H
H
OMe
MeO
OMe
1
1a
27%
1b
1c
15%
1d
12%
Total yield = 60%
6%
Scheme 2. Products from the Anodic Oxidation of Stilbene 2
OMe
OMe
4b
MeO
MeO
3b
12b
1b
9
b
CPE at +0.87 V, 0.9 F
ACN, 0.2 M LiClO4
7b
MeO 4a
6a
8b
10b
MeO
MeO
15b
8a
16b
9a
3a
1a
7a
MeO
OMe
16a
12a
10a
15a
OMe
2
2a
28%
2b
14%
Total yield = 42%
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OMe
OMe
4a
MeO 4b
MeO 4b
4
a
A
A'
H
H
1
b
1a
7a
8b
8a 1a
9a
8
b
8a
1
b
9
b
9b
9a
H
H
12a
12a
7b
6b
7a
15a
B
7b
16b
10b
B'
1
12b
10a
12b
10a
1
0b
16a
15b
15b
16a 15a
O
1
1
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5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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8
9
0
1
2
3
4
5
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7
8
9
0
NHAc
HN
H H
H
Me
1
2b
9
b
8
b
7
a
4b
4a
7b
1
6b
1b
9a
16a
5a
1
12a
Figure 3. COSY, selected HMBCs, and selected NOEs of 1b
Anodic oxidation of the dimethoxystilbene 2 gave two products which are
derivatives of the polyaromatic hydrocarbon, chrysene, viz., the dihydrochrysene 2a
1
13
1
(28%) and the tertrahydrochrysene 2b (14%) (Scheme 2). The H and C{ H} NMR data
of 2a (C H O ) can be readily assigned with the aid of the 2-D data. The resonances of
3
6
32
4
H-7b and H-8b (constituting the CHCH fragment linked to C-6a) are singlets indicating
that they are orthogonal, which has been noted previously in related dehydrotetralin
20
derivatives. The benzylic C-7b is linked to a 1,2-dimethoxyphenyl group while the
adjacent C-8b is linked to a vinyl substituted aromatic moiety (Figure 4). The hydrogens
of the vinyl group are seen at  5.65, 5.92, and 7.69. Compound 2b is readily identified as
1
13
1
the dihydro derivative of 2a from the HRMS (C H O ) and the H and C{ H} NMR
3
6
34
4
1
data. The H spectrum of 2b is generally similar to that of 2a except for the observation
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1
1
1
1
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1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
of a CHCHCHCHCH=CH fragment (in place of a CHCH and CH=CH fragment in 2a)
corresponding to C-7bC-8bC-8aC-7aC-16aC-15a, as a consequence of C-8a and
2
C-7a (quarternary sp carbons in 2a) being methines in 2b (Figure 5). This change is also
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
3
1
shown in the C{ H} NMR spectrum of 2b in which C-8a and C-7a appear as methines
( 44.3, 41.0) instead of as olefinic carbons in 2a ( 130.9, 132.5).
OMe
4b
4b
3b
MeO3b
16b
15b
1b
1
b
b
7b
6a
9b
7
6a
4a
8b
8a
9b
MeO 4a
10b
5b
8b
8a
1
7a
3a
16b
3a
1
a
9
a
1a
MeO
7a
16a
15a
1
0a
16a
10a
15a
COSY
HMBC
NOE
Figure 4. COSY, selected HMBCs, and selected NOEs of 2a
OMe
4b
3b
MeO3b
4b
1b
10b
1
b
b
4a
7b
6a
9b
8b
15b
9b
7
16b
MeO 4
a
6a
10b
5b
8b
8a
1
8a
3a
16b
3a
1a
7a
9a
9
a
1a
MeO
7a
6a
16a
15a
10a
1
1
0a
15a
COSY
HMBC
NOE
Figure 5. COSY, selected HMBCs, and selected NOEs of 2b
The choice of a vinyl group as the ortho'-substituent is to test whether, and to
what extent, the -electrons of a vinyl group can efficiently trap the benzylic cations. The
1
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results showed that although intramolecular cation trapping products are formed (1a, 1b;
3
3%), the products of competing intermolecular cation trapping are also obtained (1c, 1d;
2
0
27%). The proposed mechanism leading to the formation of the products is shown in
Scheme 3. The bisdihydronaphthalene 1a is a result of direct trapping of the dication 8
from cation radical dimerization, followed by deprotonation (path a). The doubly-
bridged, dibenzofused cyclononane 1b is a result of further reaction of the cationic
intermediate 9, formed after the second direct cation trapping step. Instead of
deprotonation to 1a, the benzylic cation in 9 is trapped in a ‘crossover’ manner by the -
electrons of the conjugated double bond associated with the first formed
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
dihydronaphthalene moiety (path b). Subsequent capture of the resulting cation
intermediate 10 by acetonitrile, followed by hydrolysis (Ritter reaction) gave 1b.
Scheme 3. Proposed Mechanism for the Formation of Products in the Anodic
Oxidation of Stilbene 1 in MeCN/LiClO4
1
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
B
B
B'
B
B'

2e
2
2
H
A
A
A'
A
A'
OMe
OMe
MeO
OMe
MeO
OMe
1
8
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
H

H2O H (c)
B
B'
B
B'
15a
MeO
O
OMe
1
6b
H
1
c
H
A
A'
A
A'
OMe
MeO
O
H
OMe
MeO
OMe
MeO
9
O
OMe
(a) H
MeO
1d
OR
OMe
H
H
MeO
H
H
B
H
H
H2O
H
B
R
16b
B'
R
H
H
H
R
B'
R
H
H
(b)
15a

H
H
15b
16a
MeCN
R = 4-OMe-C6H4
NHAc
H H
MeO
OMe
1
b
10
9
1a
Scheme 4. Proposed Mechanism for the Formation of Products in the Anodic
Oxidation of Stilbene 2 in MeCN/LiClO4
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OMe
OMe
MeO
MeO
B
A'

2e
H

2
MeO
MeO
6a
MeO
MeO
2
A
(a)
A
OMe
OMe
OMe
OMe
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
b) H
H
(
OMe
OMe
MeO
MeO
H
MeO
MeO
MeO
MeO
2b

H2
OMe
MeO
MeO
MeO
2a
The formation of the chrysene derivatives in the oxidation of the
dimethoxystilbene 2 is a consequence of additional methoxy substitution in the meta-
position, resulting in enhanced nucleophilicity of the aromatic carbon para to the m-
methoxy substituent (e.g., C-6a, ring A), and the consequent activation of the dimethoxy-
substituted ring towards electrophilic substitution (Friedel-Crafts reaction). As shown in
Scheme 4, two different order of the events can be envisaged viz., cation trapping by the
vinyl group followed by Friedel-Crafts reaction (path a), or, cyclization followed by
cation trapping (path b). Both lead to the same chrysene products, 2b, and then 2a.
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2
2
2
2
2
2
2
2
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3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
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5
5
5
5
5
5
5
5
5
6
A notable departure was observed in the oxidation of methoxystilbenes where the
ortho-substituent is a formyl group (37). The product mixture obtained in the case of 3
comprises the tetracylic fused indanylnaphthalene 3a (7%), the epimeric
0
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6
7
8
9
0
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7
8
9
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5
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7
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7
8
9
0
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2
3
4
5
6
7
8
9
0
indanylbenzopyran aldehydes (3b 23%, 3c 10%), in addition to the
tetraaryltetrahydrofuran 3d (24%) (Scheme 5). The products obtained for the oxidation of
4 include 3a, 3b, 3c, 3d, and 4a, while oxidation of 5 gave in addition to 3a, 3b, 3c, and
3
d, the indene aldehyde 5a (Scheme 5). The acetal protected stilbene aldehyde 4 gave the
best overall yield (87%).
The molecular formula of 3a (C H O ) established from HRMS indicated loss of
3
2
24
3
1
H O from the dimerization of the two starting stilbenes (3). The H NMR spectrum
2
showed the presence of 15 aromatic resonances, 2 aromatic methoxy groups, an isolated
benzylic methylene ( 4.28,  35.8), and an aldehyde-H ( 9.81,  191.8). The
H
C
H
C
aromatic resonances correspond to a 1,3,4-trisubstituted aryl, a 1,2-disubstituted aryl, a 4-
methoxyaryl, and a 2-formylaryl moiety. These partial structures can be linked by the
COSY and HMBC data (Figure 6) to give the structure shown in 3a, which received
further confirmation by X-ray analysis (Figure 6).
The HRMS of 3b (C H O ) showed that it is derived from dimerization of two
3
2
28
5
1
starting stilbenes with addition of H O. The H NMR data showed the presence of 16
2
aromatic resonances, 2 aromatic methoxy groups, 4 methine hydrogens, an aldehyde-H
(
 9.31,  197.6), and a hemiacetal OH ( 3.51, exchanged with D O). The aromatic
H
C
H
2
resonances are due to two 4-methoxyaryl and two 1,2-disubstituted aryl moieties.
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Scheme 5. Products from the Anodic Oxidation of Stilbenes 35
OMe
b
MeO 4b
MeO
12a
MeO
MeO
4
1
2a
12b
4b
R
4a
OMe
1
2b
1b 7b
9
a
10a
15b
9a
8a
9b
8b
CPE, 1 F
1b
1b
7b
H
H
H
H
1a
1
0a
10b
8
b
H
9b
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9b
7b
8a
8b
MeO 4a
6a
1a
8b
7a
O
O
OHC 1a
CHO
1b
10b
1a
9a
15a
12a
ACN, 0.2 M LiClO4
9b
8a
7a
7b
8a
CHO
12b
4a
O
4b
O
OR
O
OH
10b
10a
9a
10b
15b
7a
MeO
OMe
4a
15a
H
10a
MeO
O
OMe
12b
12a
3 R = CHO
Total yield = 64%
Total yield = 87%
3a
3b R = H
23%
3c
3d
24%
7%
10%
4
R = CH(OMe)2
3a
8%
3b R = H
25%
3c
3d
14%
23%
4a R = Me
17%
5
R = CH(OCH CH O) Total yield = 68%
3a
3b R = H
3c
5a
5%
3d
20%
2
2
6%
24%
13%
Scheme 6. Product from the Anodic Oxidation of Stilbenes 6 and 7
OH
MeO 4b
1
5b
12b
6
b
10b
R
MeO 3b
CPE at +1.10 V, 1 F
ACN, 0.2 M LiClO4
1b
7
9b
8b
8a 9a
b
6a
4a
MeO
12a
1a
7a
3
a
10a
15a
OMe
MeO
OMe
6a
6
7
R = CHO
Total yield = 20%
Total yield = 30%
20%
R = CH(OMe)2
30%
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2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
The two 4-methoxyaryl groups are linked to the same carbon ( 52.9, C-7b) from the
HMBC data (Figure 7), while the hemiacetal H and C resonances, are observed at  5.93
H
(
H-15a) and  91.9 (C-15a), respectively. Examination of the 2-D NMR data (Figure 7),
C
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2
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6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
leads to the structure shown in 3b, which also received confirmation from X-ray analysis
(Figure 7).
1
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1
Compound 3c is an isomer of 3b from the MS data. The H and C{ H} NMR
data of the two compounds are very similar, except for small differences in chemical
shifts, suggesting a stereoisomeric relationship. In particular, noticeable differences are
1
seen for the resonances of H-13a, 14a, and 15b in the H NMR spectra and C-8b in the
1
3
1
C{ H} NMR spectra. The large carbon chemical shift difference (10 ppm) for C-8b
suggests that C-8b could be the epimeric center, which was confirmed by the NOESY
data (Figure 8). Comparison of the NOESY data for 3c (Figure 8) with that of 3b (Figure
7
), readily establish 3c as the C-8b epimer of 3b (H-7a/H-7b and H-15a/H-14b NOEs
observed for 3c but not 3b, whereas, H-7a/H-8b and H-15a/H-8b NOEs observed for 3b
but not 3c). The acetal 4a is readily identified from comparison of the spectroscopic data
(NMR and MS) with that of the precursor hemiacetal 3b. The molecular formula of 4a
differs from that of 3b (and 3c) by 14 mass units or replacement of H with CH . In
3
addition, the hemiacetal OH ( 3.51), H-15a ( 5.93), and C-15a ( 91.9) resonances
H
H
C
in 3b have been replaced by the acetal OMe ( 3.71,  55.9), H-15a ( 5.50), and C-
H
C
H
1
5a ( 98.5) resonances, respectively, in 4a.
C
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4
b
OMe
4b
12b
10b
1
b
1
2b
9
b
15b
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
b
4
a
7b
7a
8
b
7b
9b
8b
MeO4
a
1
0b
8a
9a
15b
3a
8a
CHO
1
a
3a
1
a
9a
7
a
15a
10a
12a
1
5a
10a
1
2a
COSY
HMBC
NOE
Figure 6. COSY, selected HMBCs, selected NOEs, and X-ray structure of 3a
12b
MeO
12b
4
b
9
b
10b
15b
4b
9b
10b
15b
1b
8b
1b
8a
1
5a
8
b
7
b
7a
9a
O
8a
1a
7b
1a
7
a
1
5a
10a
9a
4a
O
OH
1
0a
4a
12a
MeO
12a
COSY
HMBC
NOE
Figure 7. COSY, selected HMBCs, selected NOEs, and X-ray structure of 3b
1
2b
4b
1
2b
9
b
10b
4b
1
5b
1b
10b
9b
8a
1
5b
1b
15a
7b
8b
8b
7a
9a
7b
1a
8a
15a
1a
1
0a
7
a
9a
4
a
10a
4a
1
2a
12a
NOE
3c
NOE
4a
Figure 8. Selected NOEs of 3c and 4a
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
MeO
4b
4
b
4
a
1b
OMe
4a
1
a
1b
7
b
1a
7
b
9b
8b
8
a
9a
8b
12a
9b
1
2b
12b
10b
10a
5a
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1
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8
9
0
9a
15b
10a
8a
1
1
2a
O15a
10b
15b
H
COSY
HMBC
NOE
Figure 9. COSY, selected HMBCs, and selected NOEs of 5a
The HRMS data of 5a (C H O ) indicated loss of a formic acid moiety when
3
1
26
3
compared to 3b and 3c. The NMR data showed the presence of two 1,2-disubstituted
aromatic moieties, and two 4-methoxyaryl groups which are linked to the same carbon (
5
0.0, C-7b, HMBC, Figure 9). This carbon (C-7b) is in turned linked to the benzylic
methine (C-8b) of an indene moiety from the observed vicinal (J7b-8b) coupling of 6 Hz.
The presence of the trisubstituted indene double bond was consistent with the observed
NMR resonances at  6.56, H-15b;  135.8, C-15b;  146.1, C-8a. The NMR and IR

C
C
-
data also indicated that in 5a, an aromatic aldehyde group ( 8.90,  192.6; IR 1686 cm
H
C
1)
has replaced the formyl group present in 3b ( 9.31,  197.6; IR 1720 cm ). This
-1
H
C
aromatic aldehyde is part of the other 1,2-disubstituted aryl group, and linking the partial
structures by reference to the HMBC data (Figure 9) gave the structure shown in 5a.
Anodic oxidation of the ortho-formyl substituted 3,4-dimethoxystilbenes (67)
gave only one product, viz., the fused benzofluorene-dibenzoannulene alcohol 6a
(
Scheme 6). The acetal protected stilbene 7 gave the better yield (30% vs 20%), although
in both cases the reactions were accompanied by formation of a significant quantity of
1
polymeric products. The H NMR data of 6a (C H O from HRMS) showed the
34 28
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presence of 12 aromatic resonances, 4 methoxy groups, two hydrogens of a benzylic
methylene which is part of an indene moiety ( 4.14, 4.34), an oxymethine H ( 5.71),
and an OH group ( 2.51, exchanged with D O). The aromatic resonances are due to two
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
,2-disubstituted and two 1,2,4-5-tetrasubstituted aromatic moieties (each substituted by
aromatic OMe groups). In addition to the two quaternary olefinic carbons of the indene
unit at  134.7 and 139.7, two additional quaternary carbons are seen at  130.1 and
C
C
1
33.3. In view of the many quaternary centers, further elucidation of the structure
requires HMBC data (Figure 10), which led to the structure shown in 6a. The structure of
6
a was also confirmed by X-ray analysis (Figure 10).
OH
MeO 4
b
15b
6b
10b
12b
3b
A'
B'
MeO
1
b
9b
8b
8a
7
b
6
a
9a
4
a
B
MeO
A
12a
1a
7a
3a
15a
10a
MeO
COSY
HMBC
Figure 10. COSY, selected HMBCs, and X-ray structure of 6a
An overall mechanism which accounts for the formation of the products from the
anodic oxidation of the formyl substituted stilbenes 35 is shown in Scheme 7. Formation
of the spirocyclic cation 11 via a Friedel-Crafts reaction, followed by ring-expansion and
deprotonation as described previously20,22 leads to the dehydrotetralin 12. A concerted
deprotonation-Prins-type cyclization leads to the tetracyclic carbinol 13, which on
1
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Scheme 7. Proposed Mechanism for the Formation of Products in the Anodic
Oxidation of Stilbenes 35 in MeCN/LiClO4
R
R
R
R

2e
H2O
H
d)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
OHC
CHO
H
OHC
CHO

(
MeO
O
H
OMe
MeO
O
OMe
OMe
OMe
MeO
OMe
3
R = CHO
14
3d
4 R = CH(OMe)2
H (a)

5
R = CH(OCH2CH2O)
OR
MeO
OMe
MeO
OHC
CHO
MeO
MeO
O
MeO
O
(b)
O
O
O
H
O
MeO
OMe
H
O
O
11
15
H (b)
H

OMe
OMe
OMe
OMe
H
MeO
MeO
O
O
MeO
MeO
H
H
H
O
O
O
O
O
O
H
HO
O
12
13
17
16

H2O
OMe
OMe
MeO
MeO
OMe
[1,5]
H2O
H
H
HO
MeO
MeO
OH
OH
O
O
(c)
O
O
HO
O
MeO
3a
18
19
(b)
HCO2H
MeO
H2O
MeO
MeO
MeO
MeO
MeO
OMe
H
O
H
O
MeOH
H
H
H
H
H
H
O
O
OMe
O
OH
O
OH
H
MeO
O
4a
3b
3c
5a
dehydration, followed by a [1,5] hydrogen shift, gives the indanylnaphthalene 3a.
Friedel-Crafts cyclization of the cationic intermediate 14 on the other hand, leads to the
spirocyclic alcohol 15, which on ring opening as described before20,22 gives the aldehyde
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6. Formation of the enol 17 followed by an aldol addition gives the hydroxyaldehyde 18.
A Grob-like fragmentation from the aldehyde hydrate 19 with elimination of formic acid
and water, gives the indene aldehyde 5a. Alternatively, cyclization of the
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
hydroxyaldehyde 18 leads to the epimeric hemiacetals 3b and 3c, and thence to the acetal
4
a.
Scheme 8. Proposed Mechanism for the Formation of 6a in the Anodic Oxidation of
Stilbenes 6 and 7 in MeCN/LiClO4
OMe
MeO
R
R
R
R

2e
H
2
2
MeO
MeO
O
OMe
OMe
MeO
OMe
OMe
OMe
MeO
OMe
O
6
R = CHO
7 R = CH(OMe)2
OMe
H
OMe
OMe
MeO
OMe
MeO
MeO
MeO

H2O
H
H
H
MeO
MeO
MeO
MeO
MeO
MeO
MeO
O
O
MeO
O
O
HO
O
O
20
[1,5]
OMe
MeO
MeO
MeO
OH
OH
MeO
MeO
H
MeO
MeO
O
H
H
MeO
MeO
MeO
MeO
O
MeO
MeO
MeO
MeO
21
6a
2
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2
2
2
2
2
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2
3
3
3
3
3
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3
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3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
A mechanism which accounts for the formation of the fused benzofluorene-
dibenzoannulene 6a in the oxidation of the dimethoxystilbenes 6 and 7 is shown in
Scheme 8. The pathway follows essentially the same route as in path a Scheme 7 via the
dication to the dehydrotetralin 20, and thence to the indanylnaphthalene 21, except that in
the case of the dimethoxystilbenes 6 and 7, a further aromatic substitution (Friedel-
Crafts) reaction is possible due to the presence of the 3-methoxy substituent, which leads
to the fused benzofluorene-dibenzoannulene 6a as the final product. It is noteworthy that
in the case of the dimethoxystilbene 2 where the ortho-substituent is vinyl, a similar
reaction from the chrysene derivatives (2a or 2b, Scheme 4) is not possible, since unlike
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
the carbonyl of the formyl group, the corresponding sp carbon of the vinyl group is not
electrophilic.
The primary objective of the current study was to evaluate the effect of two
different types of ortho-substituents of the reactivity of methoxystilbene cation radicals
generated by anodic oxidation. In the first instance, the choice of an ortho-vinyl
substituent was to assess how efficiently the -electrons of the vinyl group can effectively
trap the benzylic cations. The results showed that although intramolecular cation trapping
products are formed (33%), the products of competing intermolecular cation trapping are
also obtained (27%). The doubly-bridged, dibenzofused cyclononane 1b is an unusual
and unexpected product formed as a result of a further reaction of the cationic
intermediate (9, Scheme 3) formed after the second direct cation trapping step (crossover-
type cation trapping by the -electrons of the first formed conjugated double bond). In
contrast to ortho-substituted nucleophilic groups, the choice of a formyl group as the
ortho-substituent was to test whether the electrophilic carbonyl carbon of the formyl
2
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group can interact with aromatic carbons in the other ring, rendered nucleophilic by 4-
methoxy or 3-methoxy substituents. The results showed that this was indeed the case with
the reactions producing a variety of surprising and unexpected products reflecting the
varied and rich chemistry of stilbene cation radicals.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
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5
5
5
5
5
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5
6
0
1
2
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4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Experimental Section
General Experimental Procedures. Melting points were measured on a Mel-Temp
melting point apparatus and an Electrothermal IA9100 digital melting point apparatus and
are uncorrected. UV spectra were obtained on a Shimadzu UV-3101PC and UV-2600
spectrophotometers. IR spectra were recorded on a PerkinElmer Spectrum 400 FT-IR/FT-
1
13
1
FIR spectrophotometer. H and C{ H} NMR spectra were recorded in CDCl using
3
TMS as internal standard on JEOL JNM-ECA 400 or Bruker Avance III 400 and 600
spectrometers. ESIMS and HRESIMS were obtained on an Agilent 6530 Q-TOF
spectrometer and HRDARTMS were recorded on a JEOL Accu TOF-DART mass
spectrometer. X-ray diffraction analysis was carried out on a Bruker APEX II CCD area
detector system equipped with a graphite monochromator and using Mo K radiation (
=
0.71073 Å) or a Rigaku Oxford (formerly Agilent Technologies) SuperNova Dual
diffractometer with Cu K radiation ( = 1.54184 Å). Electrochemical experiments
cyclic voltammetry and controlled potential electrolysis) were performed on a Metrohm-
(
Autolab electrochemical workstation PGSTAT100. All reactions were carried out under
Ar or N , in oven-dried glassware. THF was distilled from Na/benzophenone under N .
2
2
CH Cl and MeCN were distilled from CaH , while MeOH was distilled from Mg under
2
2
2
N .
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2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Synthesis of 3 and 6 (Heck Coupling). Stilbenes 3 and 6 were synthesized
following procedures which have been described previously.20-23
Microwave Irradiation Experiments. General procedure for microwave
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
irradiation experiments have been described previously.20-22
Synthesis of Stilbenes 1 and 2 from 3 and 6, respectively. A solution of
the corresponding stilbene (3 and 6, 0.2 mmol) in THF was added to a suspension
of methyltriphenylphosphonium bromide (85.7 mg, 0.24 mmol) and NaH (21.6
mg, 0.9 mmol) in THF (10 mL) at 0 °C under Ar. The reaction mixture was
refluxed with TLC monitoring. The reaction was cooled in an ice bath and cold
distilled water was slowly added. The mixture was then extracted with CH Cl (3
2
2
× 20 ml), and the combined organic layer was then washed with H O, dried
2
(
Na SO ) and concentrated under reduced pressure. The resulting residue was
2
4
then fractionated by preparative radial chromatography to yield the
corresponding stilbene.
Synthesis of Stilbenes 4 and 7 from 3 and 6, respectively. A mixture of
the corresponding stilbene (3 and 6, 0.2 mmol), trimethylorthoformate (66 µL, 0.6
mmol), and PTSA (1.9 mg, 0.01 mmol) in MeOH was microwave irradiated (with the
heating program starting at 100 W) at 60 °C for 25 min. Triethylamine (1.4 µL, 0.01
mmol) was added to neutralize the reaction mixture. The mixture was then
extracted with CH Cl (3 × 20 ml), and the combined organic layer was then
2
2
washed with H O, dried (Na SO ) and concentrated under reduced pressure. The
2
2
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resulting residue was then fractionated by preparative radial chromatography to
yield the corresponding stilbene.
Synthesis of Stilbene 5 from 3. Ethylene glycol (22 µL, 0.4 mmol) and
PTSA (1.9 mg, 0.01 mmol) were added separately to a solution of the
corresponding stilbene (3, 0.2 mmol) in toluene (5 ml) at room temperature. The
reaction mixture was microwave irradiated (with the heating program starting at 120
W) at 100 °C for 45 min. NaOH (5%) was added and the mixture was extracted
with CH Cl (3 × 20 ml). The combined organic layer was then washed with H O,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
2
dried (Na SO ) and concentrated under reduced pressure. The resulting residue
2
4
was then fractionated by preparative radial chromatography to yield the
corresponding stilbene.
1
(E)-1-(4-methoxystyryl)-2-vinylbenzene (1). Colorless oil; (26.9 mg, 57%); H
NMR (CDCl , 400 MHz) δ 3.79 (3H, s), 5.34 (1H, d, J = 10.8 Hz), 5.63 (1H, d, J = 17.2
3
Hz), 6.88 (2H, d, J = 8.4 Hz), 6.91 (1H, d, J = 15.6 Hz), 7.09 (1H, dd, J = 17.2, 10.8 Hz),
7.23 (3H, m), 7.43 (2H, d, J = 8.4 Hz), 7.44 (1H, d, J = 15.6 Hz), 7.53 (1H, d, J = 7.2
13
1
Hz); C{ H} NMR (CDCl , 100MHz) δ 55.5, 114.3, 116.5, 124.5, 126.2, 126.7, 127.5,
3
127.97, 128.00, 130.5, 130.7, 135.2, 136.0, 136.4, 159.5; HRMS (DART-TOF) m/z: [M


H] Calcd for C H O, 237.1279; Found 237.1282.
17 17
1
(
E)-1,2-dimethoxy-4-(2-vinylstyryl)benzene (2). Colorless oil; (33.0 mg, 62%); H
NMR (CDCl , 400 MHz) δ 3.90 (3H, s), 3.94 (3H, s), 5.37 (1H, dd, J = 11.2, 1.6 Hz),
3
5.66 (1H, dd, J = 17.6, 1.6 Hz), 6.86 (1H, d, J = 9.2 Hz), 6.91 (1H, d, J = 16.0 Hz), 7.05
2
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2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
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5
5
5
5
5
5
5
6
(
1H, s), 7.06 (1H, m), 7.10 (1H, dd, J = 18.0, 11.6 Hz), 7.25 (3H, m), 7.47 (1H, d, J = 7.2
1
3
1
Hz), 7.54 (1H, d, J = 7.2 Hz); C{ H} NMR (CDCl , 100 MHz) δ 56.0, 56.1, 109.1,
3
1
1
11.4, 116.5, 120.0, 124.7, 126.3, 126.7, 127.5, 128.0, 130.8, 131.0, 135.2, 135.9, 136.3,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
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1
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3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0

49.1, 149.2; HRMS (DART-TOF) m/z: [M  H] Calcd for C H O , 267.1385;
18 19
2
Found 267.1382.
2
4
(
E)-2-(4-methoxystyryl)benzaldehyde (3). Yellow solid (42.9 mg, 90%); mp
1
116118 ˚C; H NMR (CDCl , 400 MHz) δ 3.84 (3H, s), 6.92 (2H, d, J = 8.8 Hz), 7.01
3
(1H, d, J = 16.2 Hz), 7.41 (1H, t, J = 7.8 Hz), 7.51 (2H, d, J = 8.8 Hz), 7.56 (1H, t, J =
7
1
.8 Hz), 7.70 (1H, d, J = 7.8 Hz), 7.83 (1H, d, J = 7.8 Hz), 7.91 (1H, d, J = 16.2 Hz),
1
3
1
0.33 (1H, s); C{ H} NMR (CDCl , 100 MHz) δ 55.4, 114.2, 122.5, 127.0, 127.2,
3
1
28.3, 129.8, 132.2, 132.8, 133.7, 140.4, 159.9, 192.7; HRMS (DART-TOF) m/z: [M


H] Calcd for C H O , 239.1072; Found 239.1069.
1
6
15
2
(E)-1-(dimethoxymethyl)-2-(4-methoxystyryl)benzene (4). Yellowish oil (54.6 mg,
1
9
6%); H NMR (CDCl , 400 MHz) δ 3.33 (6H, s), 3.80 (3H, s), 5.59 (1H, s), 6.89 (2H, d,
3
J = 8.8 Hz), 6.94 (1H, d, J = 16.2 Hz), 7.25 (1H, t, J = 7.7 Hz), 7.31 (1H, t, J = 7.7 Hz),
1
3
1
7
.46 (2H, d, J = 8.8 Hz), 7.58 (1H, d, J = 7.7 Hz), 7.61 (1H, d, J = 7.7 Hz); C{ H} NMR
(CDCl , 100 MHz) δ 53.0, 55.3, 101.7, 114.2, 123.7, 125.8, 126.8, 127.0, 128.0, 128.7,
3

1
30.4, 130.4, 134.6, 136.6, 159.4; HRMS (DART-TOF) m/z: [M  H] Calcd for
C H O , 285.1491; Found 285.1496.
1
8
21
3
(E)-2-(2-(4-methoxystyryl)phenyl)-1,3-dioxolane (5). Yellowish oil (45.2 mg,
1
8
0%); H NMR (CDCl , 400 MHz) δ 3.80 (3H, s), 4.04 (2H, m), 4.15 (2H, m), 6.09 (1H,
3
s), 6.88 (2H, d, J = 8.8 Hz), 6.96 (1H, d, J = 16.0 Hz), 7.26 (1H, t, J = 7.6 Hz), 7.34 (1H,
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t, J = 7.6 Hz), 7.40 (1H, d, J = 16.0 Hz), 7.45 (2H, d, J = 8.8 Hz), 7.59 (1H, d, J = 7.6
1
3
1
Hz), 7.60 (1H, d, J = 7.6 Hz); C{ H} NMR (CDCl , 100 MHz) δ 55.4, 65.4, 101.9,
3
1
14.1, 123.5, 126.0, 126.1, 127.1, 128.0, 129.2, 130.4, 130.9, 134.4, 137.0, 159.4; HRMS
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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4
4
4
4
4
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5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0

(
DART-TOF) m/z: [M  H] Calcd for C H O , 283.1334; Found 283.1340.
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8
19
3
(E)-2-(3,4-dimethoxystyryl)benzaldehyde (6). Yellow solid (51.0 mg, 95%); mp
1
1
8
25127 ˚C; H NMR (CDCl , 400 MHz) δ 3.90 (3H, s), 3.95 (3H, s), 6.86 (1H, d, J =
3
.0 Hz), 6.99 (1H, d, J = 16.0 Hz), 7.10 (1H, dd, J = 8.0, 2.4 Hz), 7.11 (1H, s), 7.40 (1H,
t, J = 7.6 Hz), 7.55 (1H, t, J = 7.6 Hz), 7.69 (1H, d, J = 7.6 Hz), 7.81 (1H, d, J = 7.6 Hz),
13
1
7
.91 (1H, d, J = 16.0 Hz), 10.31 (1H, s); C{ H} NMR (CDCl , 100 MHz) δ 55.99,
3
5
1
6.04, 109.2, 111.3, 120.7, 122.8, 127.1, 127.4, 130.1, 132.4, 132.8, 133.8, 134.0, 140.3,

49.3, 149.6, 192.9; HRMS (DART-TOF) m/z: [M  H] Calcd for C H O ,
1
7
17
3
2
69.1178; Found 269.1170.
(E)-4-(2-(dimethoxymethyl)styryl)-1,2-dimethoxybenzene (7). Yellowish oil (59.1
1
mg, 94%); H NMR (CDCl , 400 MHz) δ 3.34 (6H, s), 3.88 (3H, s), 3.93 (3H, s), 5.60
3
(1H, s), 6.85 (1H, d, J = 8.4 Hz), 6.93 (1H, d, J = 16.0 Hz), 7.06 (1H, d, J = 2.0 Hz), 7.08
(1H, dd, J = 8.4, 2.0 Hz), 7.26 (1H, t, J = 7.6 Hz), 7.32 (1H, t, J = 7.6 Hz), 7.42 (1H, d, J
13
1
=
16.0 Hz), 7.59 (1H, d, J = 7.6 Hz), 7.60 (1H, d, J = 7.6 Hz); C{ H} NMR (CDCl , 100
3
MHz) δ 53.2, 55.95, 55.99, 101.7, 109.4, 111.3, 119.9, 124.1, 125.9, 126.8, 127.0, 128.7,

1
30.7, 130.8, 134.6, 136.5, 149.0, 149.1; HRMS (DART-TOF) m/z: [M  H] Calcd
for C H O , 315.1596; Found 315.1591.
1
9
23
4
Cyclic Voltammetry. Cyclic voltammetry experiments were carried out as
described previously.20-22
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General Procedure for Electrochemical Oxidation (Controlled Potential
Electrolysis). General procedure for controlled potential electrolysis has been described
previously.20-22
0
1
2
3
4
5
6
7
8
9
0
1
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Anodic oxidation of 1 in MeCN/ 0.2 M LiClO . Controlled potential electrolysis
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of 1 (0.99 V, 1.0 F) yielded a mixture, which on preparative radial chromatography
(Chromatotron) (SiO , n-hexane/CH Cl , 2/1 to 5% MeOH/CH Cl ), followed by HPLC
2
2
2
2
2
(
Luna Phenyl-Hexyl column, 10% H O/MeCN, 10 mL/min), gave 1a (12.7 mg, 27%), 1b
2
(3.2 mg, 6%), 1c (7.3 mg, 15%), and 1d (5.9 mg, 12%).
Bisdihydronaphthalene (1a). Colorless oil. UV (EtOH) λmax (log ε) 227 (4.54),
2
71 (4.08), and 285 (3.91) nm; IR (dry film) νmax 1607, 1507, 1244, 1175, 1033, and 750

1 1
cm ; H NMR (CDCl , 400 MHz) δ 3.16 (2H, s), 3.60 (2H, d, J = 6.0 Hz), 3.67 (6H, s),
3
6.01 (2H, dd, J = 9.5, 6.0 Hz), 6.62 (4H, d, J = 8.8 Hz), 6.67 (4H, d, J = 8.8 Hz), 6.68
13
1
(
4H, m), 6.99 (2H, m), and 7.16 (4H, m); C{ H} NMR (CDCl , 100 MHz) δ 39.7, 52.2,
3
55.1, 113.8, 125.7, 126.7, 126.9, 127.5, 128.2, 130.0, 130.1, 133.8, 134.0, 135.9, and

1
58.0; HRMS (DART-TOF) m/z: [M  H] Calcd for C H O , 471.2324; Found
3
4
31
2
4
71.2322.
Doubly-bridged-dibenzofused-cyclononane (1b). Colorless oil. UV (EtOH) λmax
log ε) 226 (4.26), 267 (3.72), 286 (3.54), and 311 (3.12) nm; IR (dry film) νmax 3305,
(

1 1
1
655, 1609, 1248, 1179, 1034, and 754 cm ; H NMR (CDCl , 400 MHz) δ 1.49 (3H, s),
3
1.62 (1H, m), 2.18 (1H, dd, J = 15.6, 10.4 Hz), 2.52 (1H, ddd, J = 10.4, 4.0, 1.6 Hz), 2.75
(
1H, br t, J = 3.2 Hz), 2.81 (1H, dt, J = 8.4, 3.2 Hz), 3.30 (1H, dd, J = 9.6, 1.6 Hz), 3.66
4H, m), 3.68 (4H, m), 4.52 (1H, d, J = 9.2 Hz), 5.31 (1H, d, J = 9.2 Hz), 6.19 (2H, d, J =
(
8.8 Hz), 6.50 (2H, d, J = 8.8 Hz), 6.64 (2H, d, J = 8.4 Hz), 6.80 (1H, d, J = 7.6 Hz), 6.86
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(
2H, d, J = 8.4 Hz), 7.08 (1H, br s), 7.15 (1H, t, J = 7.6 Hz), 7.31 (3H, m), and 7.45 (2H,
1
3
1
m); C{ H} NMR (CDCl , 100 MHz) δ 23.3, 30.9, 39.2, 40.5, 41.6, 42.0, 45.1, 48.1,
3
5
1
2.6, 55.1, 55.3, 113.0, 113.6, 125.9, 126.9, 127.3, 127.6, 128.5, 128.6, 128.7, 129.4,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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3
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5
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5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
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7
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4
5
6
7
8
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0
29.9, 130.6, 135.6, 135.8, 139.4, 140.0, 140.3, 141.3, 157.5, and 168.5; HRMS (DART-

TOF) m/z: [M  H] Calcd for C H NO , 530.2695; Found 530.2699.
3
6
36
3
Tetraaryltetrahydrofuran (1c). Colorless oil. UV (EtOH) λmax (log ε) 229 (4.58),
54 (3.99), 276 (3.42), and 284 (3.31) nm; IR (dry film) νmax 1612, 1511, 1247, 1172,
2

1 1
1032, and 771 cm ; H NMR (CDCl , 400 MHz) δ 3.78 (6H, s), 4.08 (2H, dd, J = 6.0,
3
2
6
.8 Hz), 4.93 (2H, dd, J = 11.2, 1.6 Hz), 5.08 (2H, dd, J = 17.6, 1.6 Hz), 5.38 (2H, dd, J =
.0, 2.8 Hz), 6.33 (2H, dd, J = 17.6, 11.2 Hz), 6.82 (4H, d, J = 8.8 Hz), 7.10 (2H, t, J =
7.6 Hz), 7.17 (2H, d, J = 7.6 Hz), 7.21 (4H, d, J = 8.8 Hz), 7.22 (2H, t, J = 7.6 Hz), and
1
3
1
7
.49 (2H, d, J = 7.6 Hz); C{ H} NMR (CDCl , 100 MHz) δ 55.3, 58.5, 87.8, 113.8,
3
116.7, 126.5, 126.7, 126.8, 127.0, 127.9, 133.6, 134.8, 135.3, 138.8, and 159.1; HRMS

(DART-TOF) m/z: [M  H] Calcd for C H O , 489.2430; Found 489.2437.
3
4
33
3
Tetraaryltetrahydrofuran (1d). Colorless oil. UV (EtOH) λmax (log ε) 228 (4.71),
254 (4.11), 276 (3.59), and 283 (3.47) nm; IR (dry film) νmax 1612, 1512, 1248, 1175,

1 1
1
1
4
7
033, and 772 cm ; H NMR (CDCl , 400 MHz) δ 3.79 (6H, s), 4.16 (2H, dd, J = 4.8,
3
.6 Hz), 5.04 (2H, dd, J = 10.8, 1.2 Hz), 5.25 (2H, dd, J = 17.6, 1.2 Hz), 5.59 (2H, dd, J =
.8, 1.6 Hz), 6.58 (2H, dd, J = 17.6, 10.8 Hz), 6.86 (4H, d, J = 8.8 Hz), 7.08 (6H, m),
1
3
1
.17 (2H, m), and 7.35 (4H, d, J = 8.8 Hz); C{ H} NMR (CDCl , 100 MHz) δ 51.9,
3
5
5.2, 84.9, 113.8, 116.5, 126.3, 126.6, 127.1, 127.5, 128.0, 133.9, 134.6, 135.5, 138.6,

and 159.0; HRMS (DART-TOF) m/z: [M  H] Calcd for C H O , 489.2430; Found
3
4
33
3
489.2438.
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