Cerium(IV) ammonium nitrate induced dimerization of methoxystyrenes

Article abstract of DOI:10.1016/S0040-4020(00)00054-5

4-Methoxystyrene 1 underwent dimerization to 1,4-diphenylbutane derivatives 5 and 6 in presence of CAN in methanol. But in ethanol the same reaction afforded a tetralone derivative along with 5 and 6.3,4- Dimethoxystyrene 10 underwent dimerization in pres

Full text of DOI:10.1016/S0040-4020(00)00054-5

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 2461–2467
Cerium(IV) Ammonium Nitrate Induced
Dimerization of Methoxystyrenes
a
a
a
a
Vijay Nair,a, V. Sheeba, Sreeletha B. Panicker, Tesmol G. George, Roshini Rajan,
*
Lakshmi Balagopal,a M. Vairamanib and S. Prabhakarb
aOrganic Chemistry Division, Regional Research Laboratory [CSIR], Trivandrum, 695 019, India
bIndian Institute of Chemical Technology, Hyderabad, 500 007, India
Received 26 May 1999; revised 4 January 2000; accepted 13 January 2000
Abstract—4-Methoxystyrene 1 underwent dimerization to 1,4-diphenylbutane derivatives 5 and 6 in presence of CAN in methanol. But in
ethanol the same reaction afforded a tetralone derivative along with 5 and 6. 3,4-Dimethoxystyrene 10 underwent dimerization in presence of
CAN in methanol to afford acyclic as well as cyclic products. 3,4,5-Trimethoxystyrene 12 in presence of CAN in methanol afforded only the
cyclized dimers, the tetralone 21 and the tetralin derivative 22. ᭧ 2000 Elsevier Science Ltd. All rights reserved.
Introduction
use in C–C bond forming reactions via radicals.10–13
However, there is very little information available on its
use in generating cation radicals.14–16 During our investi-
gations on CAN mediated addition of 1,3-dicarbonyl
compounds to alkenes, we uncovered a novel reaction of
malonate and styrene17 resulting in a ketone and a lactone
as the major products. The reaction was found to occur with
various substituted styrenes. However, 4-methoxystyrene 1,
when exposed to CAN and malonate did not afford the
expected products. Instead products arising from the dimeri-
zation of 1 and further transformations of the dimer were
obtained. There was no evidence for the participation of
malonate in this reaction (Scheme 1).
In recent years, electron transfer mediated reactions have
come to the fore due to their potential to trigger transforma-
tions that are not easily accomplished by any other method.1
Various procedures involving chemical,2 electrochemical3
and photochemical4 methods can bring about electron
transfer. Of the three, chemical electron transfer (CET)
reactions have come to prominence only recently. The
CET mediated dimerization of N-vinyl carbazole5 and the
recent work on carbon–carbon bond forming reactions
involving cation radicals generated from alkoxy arenes6–8
and bicyclo [2.1.0] pentanes9 are representatives of the
limited investigations in this area.
Intrigued by the ease and novelty of the process, we investi-
gated the CAN mediated dimerization of 4-methoxystyrene
Cerium(IV) ammonium nitrate (CAN) has found extensive
Scheme 1. Arˆ4-methoxyphenyl, EˆCO2Me.
Keywords: chemical electron transfer (CET); CAN; alkoxystyrene; dimerization.
* Corresponding author. Tel.: ϩ91-471-490406; fax: ϩ91-471-491712; e-mail: gvn@csrrltrd.ren.nic.in
0040–4020/00/$ - see front matter ᭧ 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00054-5

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V. Nair et al. / Tetrahedron 56 (2000) 2461–2467
Table 2.
Entry
Reaction conditions (0ЊC)
7 (%)
8 (%)
9 (%)
1
2
3
CAN/EtOH, air
CAN/EtOH, oxygen
CAN/EtOH, argon
48
10
74
–
13
–
26
70
8
Scheme 2. Arˆ4-methoxyphenyl.
Table 1.
Entry
Reaction conditions (0ЊC)
5 (%)
6 (%)
1
2
3
CAN/MeOH, air
CAN/MeOH, oxygen
CAN/MeOH, argon
10
16
60
53
62
8
Figure 1.
and a preliminary report of our results has been published.18
The reaction appeared interesting both from the mechanistic
and synthetic standpoints. In order to assess the generality
and synthetic potential of the reaction, we have carried out a
systematic study involving some alkoxy styrenes and the
results of our expanded investigation are presented here.
Results and Discussion
Scheme 4. Arˆ3,4-dimethoxyphenyl.
The starting point of our investigations was the reaction of
4-methoxystyrene 1 with CAN in methanol resulting in two
products, 5 and 6 (Scheme 2).
Table 3.
Entry Reaction conditions (0ЊC) 13 (%) 14 (%) 15 (%) 16 (%)
Presumably 5 and 6 arise by the dimerization of the styrene
via a cation radical followed by the incorporation of metha-
nol. The keto group in 6 can be considered to arise from the
oxygen in the air as evidenced from the predominance of
this product when the experiment was carried out in an
atmosphere of O2. Under deoxygenated conditions 5 was
found to be the predominant product (Table 1).
1
2
3
CAN/MeOH, air
CAN/MeOH, oxygen
CAN/MeOH, argon
15
–
36
12
–
–
59
65
–
8
10
37
Similarly when the reaction was carried out in ethanol, 15,
16 and 17 were obtained (Scheme 5 and Table 4). No ethoxy-
butanone derivative was observed in this reaction. The C-8
proton of tetralone 15 gave a characteristic signal at d 7.59
In ethanol, the reaction took a slightly different course
leading to 7, 8 and 9 (Scheme 3). Here too, participation
of the solvent was observed though to a lesser extent (Table
2). The product 9 was characterized by the usual spectral
and analytical methods. The proton bonded to the C-8
appeared as a doublet at d 8.06 with a J value of 8.7 Hz
in the proton NMR spectrum. The IR spectrum of 9 revealed
the carbonyl stretching at 1667 cmϪ1 and the carbonyl
carbon appeared at 196.38 in the 13C NMR spectrum.
1
in the H NMR spectrum.
3,4-Methylenedioxystyrene 11, when subjected to CAN in
methanol at 0ЊC afforded a complex mixture of products.
However, under deoxygenated conditions it afforded 18 in
77% yield (Scheme 6). Similarly in ethanol the diethoxy-
butane derivative 19 was obtained in 60% yield (Scheme 6).
In oxygen saturated solvents the reaction of 11 led to a
complex mixture of products.
To study the generality of the reaction, the following
styrenes were included in the investigation (Fig. 1).
3,4,5-Trimethoxystyrene 12, when treated with CAN in
methanol afforded 20 and 21 in 25 and 20% yields respec-
tively. It is noteworthy that none of the products obtained
are acyclic dimers. Similarly, the reaction in ethanol
afforded 21 and 22 in 15 and 29% yields respectively
(Scheme 7). Here 20 and 22 appear to be isomeric mixtures
(according to 13C NMR). These reactions were carried out
3,4-Dimethoxystyrene 10 when treated with CAN in metha-
nol afforded 13, 14, 15 and 16 (Scheme 4 and Table 3). The
enhanced reactivity of the dimethoxybenzene ring predis-
poses it to electrophilic closure and this may account for the
preferential formation of tetralone 15 and the naphthalene
derivative 16.
Scheme 3. Arˆ4-methoxyphenyl.

V. Nair et al. / Tetrahedron 56 (2000) 2461–2467
2463
Scheme 5. Arˆ3,4-dimethoxyphenyl.
under various conditions and the results are summarized in
Table 5.
Table 4.
Entry
Reaction conditions (0ЊC)
15 (%)
16 (%)
17 (%)
Even though the mechanistic details of the reactions
described herein are not known, a rationalization along the
following lines may be made. The reaction of 3,4-dimethoxy-
styrene 10 can be taken as a representative example
(Scheme 8). Styrene 10 in the presence of Ce(IV) under-
goes oxidative electron transfer to afford the cation radical I.
This in turn would add to another styrene molecule to
generate a distonic radical cation II. Nucleophilic solvents
such as methanol and ethanol can trap this cation radical II
to generate the radical intermediate III This can react with
oxygen from the atmosphere21 to afford the product 14. The
radical III on further oxidation by Ce(IV) to a cation IV and
subsequent trapping of the latter by solvents can afford the
products 13 and 17.
1
2
3
CAN/EtOH, air
CAN/EtOH, oxygen
CAN/EtOH, argon
20
63
13
10
8
27
15
10
40
Scheme 6. Arˆ3,4-methylenedioxyphenyl.
The 1,4-cation radical II can also undergo 1,6-cyclization to
give a substituted hexatriene radical cation V, which on
losing a proton yields the radical intermediate VI that can
eventually transform to the tetralone 15. The hexatriene
cation radical V can also aromatize to afford the naphtha-
lene derivative 16 (Scheme 9).
The tetralin derivatives 20 and 22 obtained in case of 3,4,5-
trimethoxystyrene can be presumably arise from the cation
radical Va, which is analogous to V. This on losing a proton
generates a radical VIa which undergoes oxidation to a
cation and the latter gets quenched by the solvent methanol
or ethanol to afford the tetralin derivatives 20 and 22 respec-
tively (Scheme 10).
Scheme 7. Arˆ3,4,5-trimethoxyphenyl.
Table 5.
Entry
Reaction conditions (0ЊC)
20 (%)
21 (%)
22 (%)
It may be noted that an analogous mechanistic postulation
1
2
3
4
5
6
CAN/MeOH, air
25
12
78
–
–
–
20
60
–
15
55
–
–
–
–
29
15
70
CAN/MeOH, oxygen
CAN/MeOH, argon
CAN/EtOH, air
CAN/EtOH, oxygen
CAN/EtOH, argon
Scheme 9. Arˆ3,4-Dimethoxyphenyl.
Scheme 8. Arˆ3,4-Dimethoxyphenyl.
Scheme 10. Arˆ3,4,5-Trimethoxyphenyl.

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V. Nair et al. / Tetrahedron 56 (2000) 2461–2467
has been made for the PET mediated dimerization of 4-
methoxystyrene.19,20,22 Bauld24 and Lewis23 have given
evidence for the formation of a long bond cyclobutane cation
radical. This long bond cyclobutane cation radical can
undergo a 1,3-sigmatropic shift to give the hexatriene radi-
cal cation V. Also Bauld et al.24 have concluded on the basis
of MNDO calculations that the cyclic dimer of the ethylene
cation radical is ca. 5 kcal/mol more stable than the acyclic
dimer. As shown, our results here are consistent with the
mechanism proposed and proven for the PET process.
(1.5 mmol) in the same solvent (20 mL) was added drop-
wise while the reaction mixture was continuously being
purged with oxygen. The reaction mixture, on completion
of the reaction, was processed as described in the general
procedure given above.
CAN mediated oxidation of alkoxystyrenes in the
absence of oxygen
General procedure: To an ice cooled deoxygenated (purged
with argon) solution of alkoxystyrene (1 mmol) in the
appropriate solvent (20 mL), a deoxygenated solution of
CAN (1.5 mmol) in same solvent (20 mL) was added drop-
wise while the reaction mixture was continuously being
purged with argon. The reaction mixture, on completion
of the reaction, was processed as described in the general
procedure given above.
In conclusion we have uncovered a number of fascinating
reactions of alkoxystyrenes initiated by the CAN mediated
dimerization. These are synthetically attractive and mecha-
nistically interesting carbon–carbon bond forming processes.
The experimental simplicity and mild reaction conditions are
noteworthy. It is anticipated that the processes described will
find applications in organic synthesis especially in the synth-
esis of lignans, since most of the products reported in this
paper incorporate structural frameworks present in lignans. It
is noteworthy that several compounds in the lignan family are
found to possess antiplatelet,25 antiviral,26 antitumor,27 anti-
depressant28 and insect antifeedant29 activities.
1,4-Bis(40-methoxyphenyl)-1,4-dimethoxybutane (5) and
1,4-bis(4-methoxyphenyl)-4-methoxybutan-1-one (6). To
an ice-cooled solution of 1 (300 mg, 2.24 mmol) in metha-
nol (20 mL), a solution of CAN (1.5 g, 2.69 mmol) in
methanol (20 mL) was added dropwise. The mixture, on
completion of the reaction, was processed as described in
the general procedure. Column chromatography on silica
gel using hexane: ethylacetate mixture as eluent afforded
5 (37 mg, 10%) and 6 (185 mg 53%).
Experimental
General
(5) Colorless crystals recrystallized from hexane-dichloro-
NMR spectra were recorded at 300 (1H) and 75 (13C) MHz.
Chemical shifts are reported (d) relative to TMS (1H) and
CDCl3 (13C) as the internal standards. Mass spectra were
recorded under EI/HRMS (at 5000 resolution) using Auto
Spec. M mass spectrometer. Gravity column chroma-
tography was performed on silica gel (100–200 mesh) in
hexane-ethyl acetate mixtures as the eluent. Solvents were
distilled prior to use. The CAN used for the reactions was
purchased from Aldrich Co. and was used without purifi-
cation. The styrenes used were prepared from the correspond-
ing aldehydes using the Wittig procedure. Commercially
available ethanol and methanol were distilled prior to use.
methane. Mp 98–100ЊC; IR (KBr): 2961, 1615, 1150 cmϪ1
;
1H NMR: d 7.04 (d, Jˆ8.6 Hz, 4H, ArH), 6.74 (d,
Jˆ8.6 Hz, 4H ArH), 3.87 (m, 2H CHOMe), 3.69 (s, 6H,
ArOMe), 3.03 (s, 6H CHOMe), 1.61 (m, 4HCH2); 13C
NMR: d 159.28, 134.53, 128.12, 113.99, 83.83, 56.59,
55.47, 34.83; GC–MS (m/z) 298 (m/z) [MϩϪHOCH3] (5),
266 (4), 227 (5), 166 (25), 151 (100), 135(15); Anal. Calcd
for C20H26O4: C, 72.7; H, 7.93%. Found: C, 72.64; H, 8.15%.
(6) Pale yellow crystals recrystallized from hexane-
dichloromethane. Mp 107–108ЊC; IR (KBr): 2954, 1676,
1
1604, 1258 cmϪ1; H NMR: d 7.83 (m, 2H, ArH), 7.16
(m, 2H, ArH), 4.10 (dd, Jˆ7.7, 5.5 Hz, 1H, –CHOCH3),
3.12 (s, 3H, –CHOCH3), 3.69 (s, 6H, ArOCH3), 2.89 (t,
Jˆ7.2 Hz, 2H, –CH2), 2.05 (m, 2H, –CH2); 13C NMR: d
198.83, 163.6, 159.39, 134.14, 130.52, 130.47, 128.06,
114.09, 113.89, 82.74, 56.68, 55.66, 55.49, 34.55, 32.82;
Anal. Calcd for C19H22O4: C, 72.59; H, 7.05%. Found: C,
72.38; H, 7.02%.
CAN mediated oxidation of alkoxystyrenes
General procedure: A solution of CAN (1.5 mmol) in the
appropriate solvent (20 mL) was added dropwise to an ice
cold solution of alkoxystyrene (1 mmol) in the same solvent
(20 mL). When the starting material was fully consumed
(15 min), as observed by tlc, the reaction mixture was
diluted with water (150 mL) and extracted with dichloro-
methane (3×30 mL). The combined organic extracts were
pooled, washed with water, brine and dried over sodium
sulfate. The solvent was removed on a rotary evaporator
and the residue was subjected to column chromatography
on silica gel. Elution with a mixture of ethyl acetate and
petroleum ether afforded the products.
1,4-Bis(40-methoxyphenyl)-1,4-diethoxybutane (7) and
4-(40-methoxyphenyl)-6-methoxy-1-tetralone (9). To an
ice-cooled solution of 1 (300 mg, 2.24 mmol) in ethanol
(20 mL), a solution of CAN (1.5 g, 2.69 mmol) in ethanol
(20 mL) was added dropwise. The mixture, on completion
of the reaction, was processed as described in the general
procedure. Column chromatography on silica gel using
hexane: ethylacetate mixture as eluent afforded 7 (192 mg,
48%) and 9 (82 mg, 26%).
CAN mediated oxidation of alkoxystyrenes in presence
of oxygen
1
(7) Colorless oil IR: 2971, 2931, 1611, 1247 cmϪ1; H
General procedure: To an ice cooled solution of alkoxy-
styrene (1 mmol) in the appropriate solvent (20 mL) satu-
rated with oxygen, an oxygenated solution of CAN
NMR: d 7.16 (d, 4H, Jˆ8.54 Hz, ArH), 6.83 (d, 4H, Jˆ
8.58 Hz, ArH), 4.07 (bs, 2H, CHOEt), 3.79 (s, 6H,
ArOCH3), 3.25 (m, 4H, OCH2CH3), 1.70 (m, 4H,

V. Nair et al. / Tetrahedron 56 (2000) 2461–2467
2465
CHCH2), 1.11 (t, 6H, Jˆ6.98 Hz, CH2CH3); 13C NMR: d
159.01, 135.24, 127.79, 113.81, 81.91, 63.90, 55.23, 35.17,
15.48; HRMS Calcd for C22H30O4: [MϩϪHOEt] 312.1725.
Found: [MϩϪHOEt] 312.1742
153.71, 153.48, 147.97, 141.20, 135.44, 133.76, 129.77,
119.87, 111.07, 56.07, 56.02, 55.96, 53.99, 44.78, 36.19,
32.44; GC–MS (m/z) (Mϩ) 374(26), 342(100), 343(30),
329(32), 315(65), 314(30), 283(35), 255(100), 205(32),
165(32), 115(15), 77(12), 59(15).
(9) Colorless crystals recrystallized from hexane-dichloro-
methane. Mp 116–117ЊC; IR (KBr): 2953, 1667,
1
(15) Colorless oil. IR: 3002, 2942, 2847, 1681 cmϪ1; H
1596 cmϪ1
;
1H NMR: d 8.06 (d, 1H, Jˆ8.7 Hz, ArH),
NMR: d 7.59 (s, 1H, ArH), 6.82 (d, 1H, Jˆ8.1 Hz, ArH),
6.66 (s, 1H, ArH), 6.63 (d, 1H, Jˆ8.2 Hz, ArH), 6.44 (s, 1H,
ArH), 4.19 (dd, 1H, Jˆ4.5, 7 Hz, CHCH2), 3.95 (s, 3H,
ArOCH3), 3.88 (s, 3H, ArOCH3), 3.83 (s, 3H, ArOCH3),
3.76 (s, 3H, ArOCH3), 2.63 (m, 2H, COCH3), 2.47 (m,
1H, CHCH2), 2.24 (m, 1H, CHCH2); 13C NMR: d 196.64,
153.61, 149.15, 148.22, 147.92, 140.99, 136.19, 126.21,
120.72, 111.55, 111.16, 110.90, 108.30, 55.90, 55.86,
55.82, 44.75, 36.08, 32.42; HRMS Calcd for C20H22O5:
342.1467. Found: 342.1463.
7.01 (d, 2H, Jˆ8.55 Hz, ArH), 6.84 (d, 3H, Jˆ8.66 Hz,
ArH), 6.41 (d, 1H, Jˆ1.66 Hz, ArH), 4.11 (dd, 1H,
Jˆ4.36, 7.44 Hz, CHCH2), 3.79 (s, 3H, ArOCH3), 3.73 (s,
3H, ArOCH3), 2.61 (m, 2H, –COCH2), 2.41 (m, 1H,
CHCH2), 2.29 (m, 1H, CHCH2); 13C NMR: d 196.39,
163.58, 158.36, 148.92, 135.39, 129.56, 129.37, 126.49,
113.96, 113.49, 113.18, 55.13, 55.04, 44.82, 36.33, 31.95;
HRMS Calcd for C18 H18 O3: 282.1256. Found: 282. 1267.
1,4-Bis(4-methoxyphenyl)-4-ethoxybutan-1-one (8). The
same reaction when carried out in an atmosphere of oxygen
afforded 8 (83 mg, 13%) along with 7 and 9, which were
obtained in 10 and 70% yields, respectively.
(16) Amorphous powder. IR (KBr): 2937, 2834, 1601 cmϪ1
;
1H NMR: d 7.69 (d, 1H, Jˆ7.98 Hz, ArH), 7.35 (t, 1H,
Jˆ7.5 Hz, ArH), 7.25 (m, 2H, ArH), 7.15 (s, 1H, ArH),
7.01 (m, 3H, ArH), 4.01 (s, 3H, –OCH3), 3.96 (s, 3H,
OCH3), 3.89 (s, 3H, OCH3), 3.82 (s, 3H, OCH3); 13C
NMR: d 149.50, 149.37, 138.64, 133.98, 129.81, 125.84,
125.36, 123.90, 122.01, 113.24, 111.25, 106.71, 104.89,
55.98, 55.88, 55.74; HRMS Calcd for C20H20O4:
324.1361. Found: 324. 1354.
1
(8) Colorless oil. IR: 2959, 1674, 1604 cmϪ1; H NMR: d
7.91 (d, 2H, Jˆ8.72 Hz, ArH), 7.22 (d, 2H, Jˆ8.5 Hz, ArH),
6.90 (d, 2H, Jˆ8.8 Hz, ArH), 6.85 (d, 2H, Jˆ8.5 Hz, ArH),
4.27 (dd, 1H, Jˆ5.6, 7.5 Hz, CHOEt), 3.86 (s, 3H, ArOMe),
3.80 (s, 3H, ArOMe), 3.30 (m, 2H, –OCH2CH3), 2.96 (t, 2H,
Jˆ7 Hz, –CH2CH2–), 2.09 (m, 2H, –CH2CH2–), 1.14 (t,
3H, Jˆ7 Hz, –OCH2CH3); 13C NMR: d 198.35, 163.21,
158.93, 134.61, 130.21, 127.57, 113.70, 113.53, 80.42,
63.817, 55.24, 55.06, 34.22, 32.81, 15.28; GC–MS (m/z)
(Mϩ) 284 (2), 282 (20), 265 (15), 178 (10), 165 (8), 147
(10), 135 (100), 107 (8), 92 (5), 77 (10).
4-(30,40-Dimethoxyphenyl)-6,7-dimethoxy-1-tetralone (15),
1-(30,40-dimethoxyphenyl)-6,7-dimethoxynaphthalene (16)
and 1,4-bis(30,40-dimethoxyphenyl)-1,4-diethoxybutane (17).
To an ice-cooled solution of 38 (300 mg, 1.83 mmol) in
ethanol (20 mL), a solution of CAN (1.2 g, 2.19 mmol) in
ethanol (20 mL) was added dropwise. The mixture, on
completion of the reaction was processed as described in
the general procedure. Column chromatography on silica
gel using hexane:ethylacetate mixture as the eluent afforded
17 (60 mg, 15%) along with 15 (62 mg, 20%) and 16
(30 mg, 10%).
1,4-Bis(30,40-dimethoxyphenyl)-1,4-dimethoxybutane (13),
1,4-bis(30,40-dimethoxyphenyl)-4-methoxybutan-1-one (14),
4-(30,40-dimethoxyphenyl)-6,7-dimethoxy-1-tetralone (15),
and 1-(30,40-dimethoxyphenyl)-6,7-dimethoxynaphthalene
(16). To an ice-cooled solution of 10 (300 mg, 1.83 mmol)
in methanol (20 mL), a solution of CAN (1.2 g, 2.19 mmol)
in methanol (20 mL) was added dropwise. The reaction
mixture, on completion, was processed as described in the
general procedure. Column chromatography on silica gel
using hexane: ethylacetate mixture as eluent afforded 13
(25 mg, 10%), 14 (185 mg, 15%), 15 (185 mg, 59%) and
16 (40 mg, 12%).
1
(17) Colorless oil. IR: 2943 1513, 1251, 1026 cmϪ1; H
NMR: d 6.69 (m, 4H, ArH), 6.24 (s, 2H, ArH), 4.40 (m,
1H, –CHOEt), 4.32 (m, 1H, CHOEt), 3.82 (s, 3H, ArOCH3),
3.80 (s, 3H, ArOCH3), 3.78 (s, 3H, ArOCH3), 3.72 (s, 3H,
ArOCH3), 3.59 (m, 4H, OCH2CH3), 1.96 (m, 2H, –CH2CH2),
1.72 (m, 1H, –CH2CH2), 1.63 (m, 1H, –CH2CH2–), 1.22 (t,
3H, Jˆ6.9 Hz, –OCH2CH3); 13C NMR: d 148.35, 148.65,
147.68, 147.45, 139.45, 121.02, 111.54, 111.00, 75.29,
75.16, 63.49, 55.77, 55.65, 29.68, 26.14, 15.86; GC–MS
(m/z) [MϩϪ2OEt] 326 (100), 295 (25), 165 (52).
(13) Colorless oil. IR: 2935, 1509, 1260 cmϪ1; 1H NMR d:
6.72 (m, 4H, ArH), 6.30 (s, 2H, ArH), 3.93 (m, 2H,
CHOMe), 3.7 (s, 6H, ArOMe), 3.71 (s, 6H, ArOMe), 3.11
(s, 6H, OMe), 1.65 (m, 4H, CH2); 13C NMR: d 148.55,
148.89, 146.69, 146.55, 138.78, 120.13, 111.74, 111.01,
82.45, 56.72, 55.23, 35.93; GC–MS (m/z) [MϩϪ2OMe]
326 (100), 295 (25), 165 (52).
1,4-Bis(30,40-methylenedioxyphenyl)-1,4-dimethoxybutane
(18). To an ice cooled deoxygenated (purged with argon)
solution of 11 (300 mg, 2.03 mmol) in methanol (20 mL), a
deoxygenated solution of CAN (1.33 g, 2.43 mmol) in metha-
nol (20 mL) was added dropwise while the reaction mixture
was continuously being purged with argon. The reaction
mixture, on completion was processed as described in the
general procedure. Column chromatography using hexane:
ethylacetate mixture as the eluent afforded 18 (279 mg, 77%).
1
(14) Colorless oil. IR: 1707, 1613 cmϪ1; H NMR: d 7.52
(d, 1H, Jˆ8.2 Hz, ArH), 7.18 (d, 1H, Jˆ8 Hz, ArH), 6.82 (d,
1H, Jˆ8.1 Hz, ArH), 6.66 (s, 1H, ArH), 6.63 (d, 1H,
Jˆ8.3 Hz, ArH), 6.44 (s, 1H, ArH), 4.19 (m, 1H,
CHOCH3), 3.97 (s, 3H, ArOCH3), 3.95 (s, 3H, ArOCH3),
3.88 (s, 3H, ArOCH3), 3.82 (s, 3H, ArOCH3), 3.76 (s, 3H,
–OCH3), 2.62 (m, 2H, –COCH2–), 2.44 (m, 1H, –CHCH2–),
2.25 (m, 1H, –CHCH2–); 13C NMR: d 197.06, 161.62,
(18) Colorless crystals recrystallized from hexane-dichloro-
methane. Mp 154–156ЊC; IR (KBr): 2922, 1483, 1242 cmϪ1
;

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V. Nair et al. / Tetrahedron 56 (2000) 2461–2467
1H NMR: d 6.69 (m, 6H, ArH), 5.94 (s, 4H, –OCH2O–),
3.94 (brs, 2H, CHOMe), 3.14 (s, 6H, OCH3), 1.68 (brs, 4H,
CH2CH2); 13C NMR: d 147.83, 146.90, 136.19, 120.24,
107.89, 106.63, 100.90, 83.76, 83.57, 56.39, 34.58, 34.09;
HRMS Calcd for C20H22O6: 358.1416. Found: 358.1412.
reaction mixture on completion was processed as described
in the general procedure. Column chromatography afforded
21 (78 mg, 25%) and 22 (65 mg, 20%).
1
(22) Colorless oil. IR: 2942, 1596, 1507, 1235 cmϪ1; H
NMR: d 6.69 (s, 2H, ArH), 6.16 (s, 1H, ArH), 4.34 (brs,
1H, CHAr), 4.25 (m, 1H, CHOCH2CH3), 3.90 (s, 3H,
ArOCH3), 3.79 (s, 3H, ArOCH3), 3.77 (s, 3H, ArOCH3),
3.75 (s, 3H, ArOCH3), 3.37 (s, 3H, ArOCH3), 2.33 (m,
1H, –CH2CH2), 1.79 (m, 3H, –CH2CH2), 1.27 (m, 3H,
OCH2CH3); 13C NMR: d 14.52, 22.68, 28.11, 38.16,
54.74, 54.93, 59.13, 59.46, 62.86, 74.72, 104.08, 104.58,
106.67, 124.11, 132.56, 134.84, 142.73, 142.24, 151.04,
151.81; HRMS Calcd for C24H32O7: 432.2148. Found:
432. 2140.
1,4-Bis(30,40-dioxymethylenephenyl)-1,4-diethoxybutane
(19). To an ice cooled deoxygenated (purged with argon)
solution of 11 (300 mg, 2.03 mmol) in ethanol (20 mL), a
deoxygenated solution of CAN (1.33 g, 2.43 mmol) in
ethanol (20 mL) was added dropwise while the reaction
mixture was continuously being purged with argon. The reac-
tion mixture, on completion was processed as described in the
general procedure. Column chromatography using hexane:
ethylacetate mixture as the eluent afforded 19 (235 mg, 60%).
1
(19) Colorless oil IR: 2978, 2872, 1487, 1244 cmϪ1; H
NMR: d 6.69m, 6H, ArH), 5.91 (s, 4H, –OCH2O–), 4.04
(m, 1H, –CHOEt), 3.96 (m, 1H, –CHOEt), 3.66 (m, 4H,
–OCH2CH3), 2.05 (m, 2H, –CH2CH2), 1.83 (m, 1H,
–CH2CH2), 1.69 (m, 1H, –CH2CH2), 1.27 (m, 6H,
–OCH2CH3); 13C NMR: d 148.95, 146.49, 136.28,
121.52, 107.98, 106.72, 100.77, 80.35, 63.57, 32.57,
15.93; GC–MS (m/z) [MϩϪ2OEt] 296 (2), 294 (100), 267
(15), 172 (20), 135 (50), 115 (12), 89 (8).
Acknowledgements
V. S., S. B. P., T. G. G., R. R. and L. B. thank the CSIR, New
Delhi for research fellowships. Thanks are also due to Dr
Basavaiah, University of Hyderabad for the elemental
analyses.
References
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dropwise. The reaction mixture on completion was
processed as described in the general procedure. The
column chromatography afforded 20 (80 mg, 25%) and 21
(62 mg, 20%).
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