Oxidative fragmentation of 1-aryl-1-cycloalkenes using cerium(IV) ammonium nitrate (CAN): Some novel observations

Article abstract of DOI:10.1016/S0040-4020(02)00261-2

1-Phenyl-1-cycloalkenes undergo oxidative fragmentation in presence of CAN in methanol, affording 1,n-dicarbonyl compounds as the major products along with 1,2-dimethoxycycloalkanes. The reaction under deoxygenated conditions afforded the latter in good yields. In the presence of azide ion, fragmentation leading to the corresponding cyanoketones was observed whereas with sulfinate only the 1-methoxy-2-sulfonyl cycloalkanes were formed.

Full text of DOI:10.1016/S0040-4020(02)00261-2

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 3229±3234
Oxidative fragmentation of 1-aryl-1-cycloalkenes using
cerium(IV) ammonium nitrate (CAN): some novel observations
Vijay Nair,p Sreeletha B. Panicker, Siji Thomas, V. Santhi and Sindhu Mathai
Organic Chemistry Division, Regional Research Laboratory (CSIR), Trivandrum 695019, India
This paper is dedicated with warm personal regards and best wishes to Professor Gilbert Stork on the occasion of his 80th birthday
Received 20 August 2001; revised 6 February 2002; accepted 28 February 2002
AbstractÐ1-Phenyl-1-cycloalkenes undergo oxidative fragmentation in presence of CAN in methanol, affording 1,n-dicarbonyl
compounds as the major products along with 1,2-dimethoxycycloalkanes. The reaction under deoxygenated conditions afforded the latter
in good yields. In the presence of azide ion, fragmentation leading to the corresponding cyanoketones was observed whereas with sul®nate
only the 1-methoxy-2-sulfonyl cycloalkanes were formed. q 2002 Published by Elsevier Science Ltd.
1.Introduction
addition of malononitrile to alkenes; malononitrile is an
active methylene compound (pKa 11.2) comparable to
dimethyl malonate (pKa 12.7). With this objective, a metha-
nolic solution of 1-phenyl-1-cyclohexene and malononitrile
was treated with a solution of CAN in the same solvent. In
the event, no addition of malononitrile to phenylcyclo-
hexene occurred; instead the latter underwent a smooth
oxidative fragmentation to afford the mono acetal of
5-benzoylpentanaldimethyl acetal and 1,2-dimethoxy-1-
phenylcyclohexane (Scheme 1). It may be noted that a
similar fragmentation has been reported electrochemically
by Ojibin et al.7
Carbon±carbon bond forming reactions mediated by
radicals have found general acceptance in organic synthesis
during the last two decades, largely due to a paradigm shift
consequent on Stork's demonstration that radical method-
ology offers a powerful and unique alternative to ionic
reactions in complex carbocyclic constructions.1 The use
of one-electron oxidants such as Ce(IV) reagents in the
generation of carbon centered radicals and the addition of
the latter to alkenes was introduced independently by Heiba
and Dessau.2 Subsequent investigations carried out by a
number of groups have shown that cerium(IV) ammonium
nitrate (CAN) is an excellent one electron oxidant for
various synthetic transformations;3 special mention may
be made of the work by Baciocchi and co-workers on
CAN mediated carbon±carbon bond formation.4
Although the expected reaction did not occur, the fragmen-
tation of the alkene was quite interesting and therefore we
decided to pursue this novel reaction. In particular, the
reaction appeared very useful for the synthesis of 1,n-dicar-
bonyl compounds, which are key intermediates in the
synthesis of various heterocyclic compounds. A preliminary
report of this work has been published.8 In view of its
synthetic potential and the mechanistic implications, we
studied this reaction in some detail and the complete results
are presented here.
In recent years, we have been interested in the addition of
carbon centered radicals generated by CAN to various
alkenes. A detailed investigation carried out in this area
has shown that CAN is a superior reagent vis a vis
Mn(OAc)3 in intermolecular reactions and the CAN induced
addition of various 1,3-dicarbonyl compounds such as
dimedone and acetylacetone to alkenes offers a convenient
method for the synthesis of dihydrofuran derivatives.5 The
CAN mediated addition of dimethylmalonate to styrene in
methanol led to a mechanistically fascinating reaction yield-
ing 2-oxo-2-phenylethylpropanedioic acid dimethylester as
the major product.6 During the course of this work, we were
intrigued by the possibility of CAN mediated oxidative
Keywords: oxidative fragmentation; cycloalkenes; dicarbonyl compounds.
Corresponding author. Tel.: 191-471-490406; fax: 191-471-491712;
e-mail: gvn@csrrltrd.ren.nic.in
p
Scheme 1.
0040±4020/02/$ - see front matter q 2002 Published by Elsevier Science Ltd.
PII: S0040-4020(02)00261-2

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V. Nair et al. / Tetrahedron 58 (2002) 3229±3234
alkenes (vide infra) invokes the participation of oxygen in
the reaction. It is then reasonable to assume that in the
absence of oxygen the benzylic radical may undergo further
oxidation to the cation which in turn will be quenched by
methanol leading to the dimethoxy compound. In order to
verify these assumptions, the reactions were done under
deoxygenated conditions. Interestingly, when phenylcyclo-
hexene was treated with CAN in dry methanol in an argon
atmosphere, the dimethylether 5b was formed as the major
product (72% yield). Only a trace amount of the fragmenta-
tion product was observed. The reaction under deoxy-
genated conditions has been studied with other
phenylcycloalkenes also and the results are presented in
Table 1.
Scheme 2.
2.Results and discussion
As already reported,8 studies were initiated by treating a
methanolic solution of 1-phenyl-1-cyclohexene with a
solution of CAN in methanol at 08C. A facile reaction
occurred and the absence of the starting material after
30 min indicated the completion of the reaction. The
products 4b and 5b were isolated in 69 and 18% yields,
respectively (Scheme 2). In order to explore the scope of
the reaction, a number of aryl cycloalkenes were treated
with CAN in methanol. The results are summarized in the
following scheme
2.2. Reactions of cycloalkenes in presence of azide and
sul®nate ions
In view of our recent observation of facile CAN mediated
oxidative addition of azide and sul®nate to styrenic double
bonds it was of interest to examine the reaction of CAN with
arylcycloalkene in presence of these anions.9 Interestingly,
while the above work was in progress, a photochemical
cleavage of phenyl cycloalkenes with azide in the presence
of copper ions in an atmosphere of oxygen affording the
corresponding keto nitriles was reported.10
When 1-naphthyl-1-cyclohexene was treated with a metha-
nolic solution of CAN, the expected fragmentation occurred
and the product was obtained in 72% yield; surprisingly no
dimethoxy compound was isolated in this case (entry 4,
Table 1). 1-Phenyl-3,4-dihydronaphthalene 6 under the
usual reaction conditions afforded the keto acetal 7 and
the dimethoxycompound 8 in 35 and 30% yields,
respectively (Scheme 3).
An experiment was carried out in which a mixture of
phenylcyclohexene, sodium azide and methanol was treated
with CAN at ice temperature. As expected, the keto-nitrile
was obtained. Similar reactivity was observed in the case of
phenylcyclopentene and phenylcycloheptene (Scheme 4).
Subsequent to the above studies, we attempted the addition
of sul®nate in presence of CAN. Narasaka has extensively
studied the addition of sul®nate radical to electron rich
ole®ns using CAN and other Ce(IV) reagents.11 Phenyl-
cyclohexene on treatment with CAN and phenylsul®nic
acid sodium salt in methanol, led to the formation of the
addition product 10 (Scheme 5). Interestingly, no fragmen-
tation product was observed in this case. Phenylcyclo-
pentene and phenylcycloheptene also gave similar results,
Although the mechanistic details of the reaction are not fully
understood a rationalization involving the intermediacy of a
cation radical may be invoked to account for the formation
of the products (vide infra for a detailed discussion).
2.1. Reaction of phenylcycloalkenes under deoxygenated
conditions
The mechanism for the fragmentation of phenylcyclo-
Table 1. Reaction of phenylcycloalkenes with CAN in methanol under
deoxygenated conditions
Entry
Alkene
Product
Yield (%)
1
2
3
4
5
1a
1b
1c
1d
6
5a
5b
5c
5d
8
72
72
80
69
65
Scheme 4.
Reaction conditions: CAN, dry MeOH, argon, 1 h, 08C.
Scheme 3.
Scheme 5.

V. Nair et al. / Tetrahedron 58 (2002) 3229±3234
3231
when treated with phenylsul®nic acid sodium salt and CAN
in methanol.
may be due to the competing reaction of the latter and/or
sulfonyl radical with oxygen. A schematic representation is
shown in Scheme 8.
2.3. Mechanistic aspects
Although it cannot be said with certainty, it is likely that
both pathways (a and b) may be operating in these reactions.
Mechanistically it is not clear if all the above reactions
follow the same pathway; the initial event, however may
be considered to be the formation of the cation radical I
from the arylcycloalkene. The involvement of the latter in
further transformations may be invoked to explain the
formation of the different products. Reaction of I with
methanol can lead to the benzylic radical II which can
trap molecular oxygen leading to a peroxyradical III and
the latter can abstract hydrogen from the solvent to form the
hydroperoxide IV. The hydroperoxide can undergo frag-
mentation and ultimately lead to the keto acetal as outlined
in Scheme 6.
In conclusion, we have uncovered some novel reactions of
phenyl cycloalkenes in presence of CAN affording products
which are of importance both from mechanistic and
synthetic standpoints. It is worthy of note that in view of
the experimental simplicity and mild reaction conditions,
the present method offers a convenient alternative to the
existing methods for oxidative fragmentation. Since the
products can serve as important intermediates for a variety
of compounds, it is conceivable that these reactions will ®nd
application in organic synthesis.
Alternatively, the benzylic radical II undergoes oxidation to
the cation V and the latter on quenching by methanol will
lead to the formation of the dimethoxy compound
(Scheme 7). Exclusive formation of the dimethoxy
compound under deoxygeneated conditions indirectly
supports this suggestion.
3.Experimental
All reactions were carried out in oven dried glassware.
Melting points were recorded on Toshniwal or Buchi-530
melting point apparatus and are uncorrected. The IR spectra
were recorded on Nicolet Impact 400D FT-IR or Bomem
MB series FT-IR spectrophotometers. The NMR spectra
were recorded at 300 MHz on a Bruker 300 MHz
FT-NMR spectrometer using chloroform-d as the solvent.
Chemical shifts are reported on d scale with TMS as the
internal standard. Elemental analyses were carried out on a
Perkin±Elmer 2400 Series II CHNSO analyser. Products
were puri®ed by gravity column chromatography using
silica gel (100±200 mesh) in hexane or hexane±ethyl
acetate mixtures as eluent. All the solvents were distilled
prior to use. CAN used for the reaction was purchased from
Aldrich Co. and was used without puri®cation.
In reactions involving the addition of anions to phenyl
cycloalkenes, either a mechanism involving the addition
of the anion to the cation radical of phenylcycloalkene lead-
ing to a benzylic radical (path a) or the addition of the azide/
sul®nate radical generated by the oxidation of the corre-
sponding anion by CAN leading to the benzylic radical
(path b) can be conceived. In the case of azide, the benzylic
radical traps molecular oxygen forming a hydroperoxide
and subsequent transformations of the hydroperoxide lead
to the ketonitrile. However in the reaction involving the
addition of sul®nate, the benzylic radical undergoes oxida-
tion by CAN, followed by methanol quenching. The
absence of fragmentation product in the reaction of sul®nate
3.1. Synthesis of phenylcycloalkenes: general procedure
All the cycloalkenes were prepared from the corresponding
cycloalkanones and bromobenzene or bromonaphthalene by
Grignard reaction, followed by acid catalyzed dehydration.
3.2. Synthesis of monoacetals of 1,n-dicarbonyl com-
pounds from phenyl cycloalkenes: general procedure
To a solution of the phenylcycloalkene (1 mmol) in metha-
nol (10 mL) was added dropwise a solution of CAN
(2.3 mmol) in methanol (15 mL) at ice temperature. When
the starting material was fully consumed as shown by tlc,
the reaction mixture was diluted with water (100 mL) and
extracted with dichloromethane (3£30 mL). The combined
organic extracts were washed with brine and dried over
sodium sulfate. The solvent was removed on a rotary
evaporator and the residue was subjected to column chro-
matography on silica gel. Elution with an appropriate
mixture of hexane and ethyl acetate afforded the products.
Scheme 6.
Scheme 7.
3.3. Synthesis of dimethylethers under deoxygenated
conditions: general procedure
To a deoxygenated solution of the phenylcycloalkene
(1 mmol) in methanol (10 mL), a deoxygenated solution
Scheme 8.

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V. Nair et al. / Tetrahedron 58 (2002) 3229±3234
of CAN (2.3 mmol) in methanol (15 mL) was added drop-
wise at ice temperature. When the starting material was
fully consumed as shown by TLC, the reaction mixture
was diluted with water (100 mL) and extracted with
dichloromethane (3£30 mL). The combined organic
extracts were washed with brine and dried over sodium sul-
fate. The solvent was removed on a rotary evaporator and
the residue was subjected to column chromatography on
silica gel. Elution with an appropriate mixture of hexane
and ethyl acetate afforded the products.
NMR: 7.69±7.28 (m, 5H, ArH), 3.30 (s, 3H, OMe), 3.14 (m,
1H, CHOMe), 3.09 (s, 3H, OMe), 1.67±1.01 (m, 6H, CH2);
13C NMR: 142.81, 128.14, 127.88, 126.69, 86.24, 80.58,
59.18, 49.04, 36.64, 29.99, 23.16.
3.5.2. 5-Benzoylpentanaldimethylacetal (4b)7 and 1,2-
dimethoxy-1-phenylcyclohexane (5b).12 To a solution of
1-phenyl-1-cyclohexene (156 mg, 1 mmol) in methanol
(10 mL) a solution of CAN (1.26 g, 2.3 mmol) in methanol
(15 mL) was added at ice temperature and stirred for
30 min. On completion of the reaction, the mixture was
processed as described in the general procedure. The residue
on column chromatography on silica gel using hexane±
ethyl acetate mixture (98:2) afforded 39 mg of 4b as color-
less viscous liquid (18%) and on further elution using
hexane±ethyl acetate mixture (95:5) afforded 162 mg of
5b as colorless viscous liquid (69%).
3.4. Reaction of phenylcycloalkenes with CAN in
presence of sodium azide: general procedure
To a solution of the phenylcycloalkene (1 mmol) and
sodium azide (1 mmol) in methanol (10 mL) was added
dropwise a solution of CAN (2.3 mmol) in the same solvent
(15 mL) at ice temperature. On completion, the reaction
mixture was diluted with water (50 mL) and extracted
with dichloromethane (3£30 mL). The organic extracts
were pooled, washed with brine and dried over sodium sul-
fate. The solvent was removed on a rotary evaporator and
the residue was subjected to column chromatography on
silica gel. Elution with an appropriate mixture of hexane
and ethyl acetate afforded the products.
4b: IR (neat) nmax: 2959, 1681, 1593, 1482, 1202, 1128,
1
1067, 960, 703 cm21; H NMR: 7.94±7.91 (m, 2H, ArH),
7.53±7.43 (m, 3H, ArH), 4.36 (t, 1H, CH(OMe)2,
Jˆ5.4 Hz), 3.29 (s, 6H, OMe), 2.90 (t, 2H, CH2,
Jˆ7.2 Hz), 1.99±1.39 (m, 6H, CH2); 13C NMR: 200.15,
137.01, 132.90, 128.55, 127.93, 104.93, 52.75, 38.42,
32.41, 24.34, 24.07.
5b: IR (neat) nmax: 2897, 1647, 1448, 1108, 1202, 1074,
3.5. Reaction of phenylcycloalkenes with CAN in
presence of phenyl sul®nic acid sodium salt: general
procedure
1
966, 717 cm21; H NMR: 7.46±7.26 (m, 5H, ArH), 3.15
(s, 3H, OMe), 3.06±3.01 (m, 1H, CHOMe), 2.98 (s, 3H,
OMe), 2.10±1.25 (m, 8H, CH2); 13C NMR: 142.35,
127.73, 127.14, 126.67, 85.92, 80.03, 57.82, 50.12, 31.86,
26.86, 26.52, 24.52, 24.69, 20.92. Anal. Calcd for C14H20O2:
C 76.33, H 9.15; Found C 76.12, H 8.97.
To a solution of the phenylcycloalkene (1 mmol) and phenyl
sul®nic acid sodium salt (1 mmol) in methanol (10 mL) was
added dropwise a solution of CAN (2.3 mmol) in the same
solvent (15 mL) at ice temperature. On completion, the
reaction mixture was diluted with water (50 mL) and
extracted with dichloromethane (3£30 mL). The organic
extracts were pooled, washed with brine and dried over
sodium sulfate. The solvent was removed on a rotary
evaporator and the residue was subjected to column chro-
matography on silica gel. Elution with an appropriate
mixture of hexane and ethyl acetate afforded the products.
3.5.3. 6-Benzoylhexanal dimethylacetal (4c)7 and 1,2-
dimethoxy-1-phenylcycloheptane (5c).12 To a solution of
1-phenyl-1-cycloheptene (172 mg, 1 mmol) in methanol
(10 mL) was added a solution of CAN (1.26 g, 2.3 mmol)
in methanol (15 mL) at ice temperature and stirred for
30 min. On completion of the reaction, the mixture was
processed as described in the general procedure. The residue
on column chromatography on silica gel using a mixture of
hexane±ethyl acetate (98:2) as eluent afforded 75 mg of 5c
as colorless viscous liquid (32%) and on further elution with
a mixture of hexane±ethyl acetate (95:5) afforded 140 mg of
4c as colorless viscous liquid (56%).
3.5.1. 4-Benzoylbutanal dimethylacetal (4a)7 and 1,2-
dimethoxy-1-phenylcyclopentane (5a).12 To a solution of
1-phenyl-1-cyclopentene (144 mg, 1 mmol) in methanol
(10 mL) was added a solution of CAN (1.26 g, 2.3 mmol)
in methanol (15 mL) at ice temperature and stirred for
30 min. On completion of the reaction, the mixture was
processed as described in the general procedure. The residue
on column chromatography on silica gel using a mixture of
hexane±ethyl acetate (98:2) as eluent afforded 41 mg of 5a
as colorless viscous liquid (20%) and on further elution with
hexane±ethyl acetate (95:5) afforded 106 mg of 4a as color-
less viscous liquid (48%).
4c: IR (neat) nmax: 2956, 1681, 1593, 1482, 1450, 1359,
1273, 1091 cm21; 1H NMR: 7.96±7.94 (m, 2H, ArH), 7.54±
7.42 (m, 3H, ArH), 4.36 (t, 1H, CH(OMe)2, Jˆ5.5 Hz), 3.31
(s, 6H, OMe), 2.97 (t, 2H, CH2, Jˆ7.1 Hz), 1.76±1.25 (m, 8H,
CH2); 13C NMR: 200.15, 137.15, 133.90, 128.67, 128.15,
104.61, 52.79, 38.56, 32.48, 29.29, 24.57, 24.35.
5c: IR (neat) nmax: 2989, 1730, 1632, 1272, 1074, 766,
1
696 cm21. H NMR: 7.44±7.23 (m, 5H, ArH), 3.14 (s, 3H,
4a: IR (neat) nmax: 2978, 1742, 1684, 1607, 1364, 1128,
1074, 960 cm21 1H NMR: 7.93±7.90 (m, 2H, ArH),
;
OMe), 3.08±3.01 (m, 1H, CHOMe), 2.99 (s, 3H, OMe),
2.07±1.42 (m, 10H, CH2); 13C NMR: 144.15, 128.02,
127.62, 127.33, 126.54, 89.57, 82.23, 57.78, 50.91, 33.75,
27.00, 26.21, 23.67, 20.47.
7.52±7.40 (m, 3H, ArH), 4.38 (t, 1H, CH(OMe)2,
Jˆ5.6 Hz), 3.30 (s, 6H, OMe), 3.01 (t, 2H, CH2, Jˆ7 Hz),
1.82±1.63 (m, 4H, CH2); 13C NMR: 200.51, 136.85, 132.90,
128.51, 127.93, 104.67, 52.51, 38.01, 32.26, 23.53, 21.67.
3.5.4. 7-Benzoylheptanal dimethylacetal (4d)7 and 1,2-
dimethoxy-1-phenylcyclooctane (5d).12 To a solution of
1
5a: IR (neat) nmax: 1621, 1508, 1206, 1169, 721 cm21. H

V. Nair et al. / Tetrahedron 58 (2002) 3229±3234
3233
1
1-phenyl-1-cyclooctene (196 mg, 1 mmol) in methanol
(10 mL) was added a solution of CAN (1.26 g, 2.3 mmol)
in methanol (15 mL) at ice temperature and stirred for
30 min. On completion of the reaction, the mixture was
processed as described in the general procedure. The residue
on column chromatography on silica gel using a mixture of
hexane±ethyl acetate (98:2) as eluent afforded 84 mg of 5d
as colorless viscous liquid (37%) and on further elution with
a mixture of hexane±ethyl acetate (95:5) afforded 118 mg of
4d as colorless viscous liquid (45%).
8: IR (neat) nmax: 1632, 1486, 1438, 1280, 1115 cm21. H
NMR: 7.17±7.04 (m, ArH, 9H), 3.59 (m, 2H, PhCH2), 3.09
(s, 3H, OMe), 3.03 (s, 3H, OMe), 2.78 (m, 2H, CH2), 2.12 (m,
2H, CH2); 13C NMR: 142.80, 138.73, 136.09, 129.39, 128.78,
127.04, 126.97, 83.49, 80.49, 57.77, 50.83, 26.91, 23.69.
HRMS Calcd for C18H20O2, 268.1463. Found 268.1459.
3.5.7. 4-Benzoylbutanenitrile (9a). A solution of CAN
(1.26 g, 2.3 mmol) in methanol (15 mL) was added to a
solution of 1-phenyl-1-cyclopentene (144 mg, 1 mmol)
and sodium azide (65 mg, 1 mmol) in the same solvent
(10 mL) at ice temperature and stirred for 30 min. On
completion of the reaction, the mixture was processed as
described in the general procedure. The residue on column
chromatography on silica gel using hexane±ethyl acetate
mixture (95:5) afforded 112 mg of 9a as colorless viscous
liquid (60%). IR (neat) nmax: 2932, 2106, 1725, 1447,
4d: IR (neat) nmax: 2987, 1681, 1596, 1442, 1202, 1181,
715 cm21; H NMR: 7.95±7.92 (m, 2H, ArH), 7.53±7.41
1
(m, 3H, ArH), 4.34 (t, 1H, CH(OMe)2, Jˆ5.4 Hz), 3.28 (s,
6H, OMe), 2.95 (t, 2H, CH2, Jˆ7.2 Hz), 1.73±1.22 (m, 8H,
CH2); 13C NMR: 199.18, 136.95, 132.63, 128.35, 128.10,
104.25, 52.25, 42.29, 32.21, 29.15, 24.31, 24.05, 20.74.
1
1265 cm21. H NMR: 7.95±7.93 (m, 2H, ArH), 7.59±7.43
5d: IR (neat) nmax: 1647, 1448, 1108, 1202, 1074, 966,
(m, 3H, ArH), 3.15 (t, 2H, CH2, Jˆ7 Hz), 2.50 (t, 2H, CH2,
Jˆ7 Hz), 2.13±2.04 (m, 2H, CH2); 13C NMR: 197.74,
136.71, 133.14, 128.64, 127.96, 119.22, 37.27, 25.03,
23.06, 17.18. HRMS Calcd for C11H11NO, 174.0841.
Found 174.0832.
1
717 cm21. H NMR: 7.46±7.26 (m, 5H, ArH), 3.15 (s, 3H,
OMe), 3.06±3.01 (m, 1H, CHOMe), 2.98 (s, 3H, OMe),
2.10±1.25 (m, 12H, CH2); 13C NMR: 142.35, 127.73,
127.14, 126.67, 85.92, 80.03, 57.12, 31.86, 26.86, 26.52,
24.69, 20.92.
3.5.8. 5-Benzoylpentanenitrile (9b).13 A solution of CAN
(1.26 g, 2.3 mmol) in methanol (15 mL) was added to a
solution of 1-phenyl-1-cyclohexene (156 mg, 1 mmol) and
sodium azide (65 mg, 1 mmol) in the same solvent (10 mL)
at ice temperature and stirred for about 30 min. On comple-
tion of the reaction, the mixture was processed as described
in the general procedure. The residue on column chromato-
graphy on silica gel using hexane±ethyl acetate mixture
(95:5) afforded 115 mg of 9b (52%). IR (neat) nmax: 2950,
1679, 1449, 1411 cm21. 1H NMR: 7.94±7.91 (m, 2H, ArH),
7.43±7.32 (m, 3H, ArH), 3.06 (t, 2H, CH2, Jˆ6.9 Hz), 2.40
(t, 2H, CH2, Jˆ7 Hz), 1.93±1.65 (m, 4H, CH2); 13C NMR:
197.74, 136.35, 133.26, 128.58, 127.84, 119.09, 36.16,
19.63, 16.47.
3.5.5. 5-Naphthoylpentanaldimethylacetal (4e). To a
solution of 1-naphthyl-1-cyclohexene (208 mg, 1 mmol) in
methanol (10 mL) was added a solution of CAN (1.26 g,
2.3 mmol) in methanol (15 mL) at ice temperature and stir-
red for 30 min. On completion of the reaction, the mixture
was processed as described in the general procedure. The
residue on column chromatography on silica gel using a
mixture of hexane±ethyl acetate (95:5) as eluent afforded
205 mg of 4e as colorless viscous liquid (72%). IR (neat)
n
max: 2942, 1681, 1593, 1482, 1128, 1067, 960, 703 cm21
.
1H NMR: 8.53 (d, 1H, ArH, Jˆ8.2 Hz), 7.94 (d, 1H, ArH,
Jˆ8.2 Hz), 7.84 (t, 1H, ArH, Jˆ8.1 Hz), 7.59±7.45 (m, 4H,
ArH), 4.36 (t, 1H, CH (OMe)2, Jˆ7.5 Hz), 3.30 (s, 6H,
OMe), 3.05 (t, 2H, CH2, Jˆ7.3 Hz), 2.03±1.42 (m, 6H,
CH2); 13C NMR: 200.15, 137.01, 132.90, 128.55, 127.93,
104.43, 52.75, 38.42, 32.41, 24.34, 24.07. HRMS cald for
C18H22O3, 287.1569. Found 287.1579.
3.5.9. 6-Benzoylhexanenitrile (9c). A solution of CAN
(1.26 g, 2.3 mmol) in methanol (15 mL) was added to a
solution of 1-phenyl-1-cycloheptene (172 mg, 1 mmol)
and sodium azide (65 mg, 1 mmol) in the same solvent
(10 mL) at ice temperature and stirred for 30 min. On
completion of the reaction, the reaction mixture was
processed as described in the general procedure. The residue
on column chromatography on silica gel using hexane±
ethyl acetate mixture (95:5) afforded 122 mg of 9c as color-
less viscous liquid (62%). IR (neat) nmax: 2932, 2101, 1725,
1686, 1447, 1336 cm21; 1H NMR: 7.94±7.91 (m, 2H, ArH),
7.57±7.42 (m, 3H ArH), 2.98 (t, 2H, CH2, Jˆ7 Hz), 2.35 (t,
2H, CH2, Jˆ6.9 Hz), 1.80±1.57 (m, 4H, CH2), 1.56±1.52
(m, 2H, CH2); 13C NMR: 199.12, 136.66, 132.80, 128.38,
127.75, 119.24, 37.74, 28.08, 25.11, 22.96, 16.75; HRMS
Calcd for C13H15NO, 201.1154. Found 201.1154
3.5.6. 2-(3,3-Dimethoxy) propylbenzophenone (7) and
1,2-dimethoxy-1-phenyl tetralin (8). To a solution of
1-phenyl-3,4-dihydro naphthalene (206 mg, 1 mmol) in
methanol (10 mL) was added a solution of CAN (1.26 g,
2.3 mmol) in methanol (15 mL) at ice temperature and stir-
red. On completion of the reaction, the mixture was
processed as described in the general procedure. The residue
on column chromatography on silica gel using a mixture of
hexane±ethyl acetate (98:2) as eluent afforded 30% of 8 as
colorless viscous liquid and on further elution using a
mixture of hexane±ethyl acetate (95:5) afforded 99 mg of
7 as colorless viscous liquid (35%).
7: IR (neat) nmax: 2976, 1667, 1596, 1470, 1289, 798 cm21
;
3.5.10. 2-Benzenesul®nyl-1-methoxy-1-phenyl-1-cyclo-
pentene (10a). To a solution of the 1-phenyl-1-cyclo-
pentene (144 mg, 1 mmol) and phenyl sul®nic acid
sodium salt (164 mg, 1 mmol) in methanol (10 mL) was
added dropwise a solution of CAN (1.26 g, 2.3 mmol) in
the same solvent (15 mL) at ice temperature. On comple-
tion, the reaction mixture was diluted with water (50 mL)
1H NMR: 7.22±7.17 (m, 9H, ArH), 4.43 (t, 1H, CH (OMe)2,
Jˆ5.5 Hz), 3.16 (s, 6H, OMe), 2.65 (m, 2H, CH2), 1.77 (brs,
2H, CH2); 13C NMR: 198.07, 140.88, 138.30, 137.88,
130.28, 130.18, 128.70, 128.38, 127.51, 125.34, 103.64,
52.47, 34.27, 28.50; HRMS Calcd for C18H20O3,
284.1412. Found 284.1425.

3234
V. Nair et al. / Tetrahedron 58 (2002) 3229±3234
and extracted with dichloromethane (3£30 mL). The
combined organic extracts were washed with brine and
dried over sodium sulfate. The solvent was removed on a
rotary evaporator and the residue on crystallization using
dichloromethane±petroleum ether as solvent afforded the
product as colorless crystals (205 mg, 65%), mp 115±
1178C. 10a: IR (neat) nmax: 1632, 1486, 1438, 1280,
Acknowledgements
S. B. P., S. T., S. V. and S. M. thank the CSIR, Government
of India, New Delhi for Research Fellowships. Thanks are
also due to Dr M. Vairamani, Indian Institute of Chemical
Technology, Hyderabad for HRMS data, Ms Soumini
Mathew for NMR spectral data and Mrs S. Viji for
elemental analyses.
1115 cm21 1H NMR: 7.38±6.96 (m, 10H, ArH), 3.81
.
(uneven doublet, 1H, CHSO2Ph), 2.78 (s, 3H, OMe),
2.74±2.60 (m, 2H, CH2), 2.46±2.34 (m, 1H, CH2), 2.18±
2.12 (m, 1H, CH2), 2.02±1.86 (m, 1H, CH2), 1.83±1.77 (m,
1H, CH2). 13C NMR: 139.98, 136.29, 131.99, 128. 68,
128.55, 127.93, 127.66, 127.45, 80.76, 76. 58, 48.68,
29.23, 25.01, 20.29. Anal. Calcd for C18H20O3S: C 68.33,
H 6.37, S 10.13; Found C 68.28, H 6.62, S 10.23.
References
1. (a) Stork, G.; Baine, N. H. J. Am. Chem. Soc. 1982, 104, 2321.
(b) Stork, G.; Sher, P. M. J. Am. Chem. Soc. 1983, 105, 6765.
(c) Stork, G.; Baine, N. H. Tetrahedron Lett. 1985, 26, 5927.
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93, 995. (c) Heiba, E. I.; Dessau, R. M. J. Am. Chem. Soc.
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3.5.11. 2-Benzenesul®nyl-1-methoxy-1-phenyl-1-cyclo-
hexene (10b). To a solution of the 1-phenyl-1-cyclohexene
(156 mg, 1 mmol) and phenyl sul®nic acid sodium salt
(164 mg, 1 mmol) in methanol (10 mL) was added dropwise
a solution of CAN (1.26 g, 2.3 mmol) in the same solvent
(15 mL) at ice temperature. On completion, the reaction
mixture was diluted with water (50 mL) and extracted
with dichloromethane (3£30 mL). The combined organic
extracts were washed with brine and dried over sodium sul-
fate. The solvent was removed on a rotary evaporator and
the residue on crystallization using dichloromethane±
petroleum ether as solvent afforded the product as colorless
3. For reviews on CAN mediated reactions see: (a) Molander,
G . A.Chem. Rev. 1992, 92, 29. (b) Ho, T. L. Organic
Synthesis by Oxidation with Metal Compounds; Plenum:
New York, 1986 and references cited therein. (c) Imamoto,
T. Lanthanide Reagents in Organic Synthesis; Academic:
London, 1994; p 119. (d) Nair, V.; Mathew, J.; Prabhakaran
J. Chem. Soc. Rev. 1997, 127.
4. (a) Baciocchi, E.; Ruzziconi, R. Synth. Commun. 1988, 18,
1841. (b) Baciocchi, E.; Ruzziconi, R. J. Org. Chem. 1986,
51, 1645. (c) Baciocchi, E.; Ruzziconi, R. Gazz. Chim. Ital.
1986, 116, 671.
crystals (229 mg, 70%.), mp 143±1458C. 10b: IR (KBr)
n
1
max: 1643, 1254, 1232, 1181 cm21; H NMR: 7.31±7.26
(m, 2H, ArH), 7.16±7.11 (m, 5H, ArH), 7.04±6.96 (m, 3H,
ArH), 3.68 (brs, 1H, CHSO2Ph), 2.94 (m, 1H, CH2), 2.75 (s,
3H), 2.64 (d, 1H, Jˆ14.1 Hz, CH2), 2.38±2.27 (m, 1H), 2.08
(d, 1H, Jˆ14.3 Hz, CH2), 1.90±1.56 (m, 4H, CH2); 13C
NMR: 141.80, 140.34, 131.61, 128.36, 128.18, 127.81,
127.90, 127.04, 77.25, 70.25, 48.22, 25.19, 22.91, 21.21,
20.91. Anal. Calcd for C19H22O3S: C 69.01, H 6.88, S
10.20; Found C 69. 06, H 6.71, S 9.78.
5. (a) Nair, V.; Mathew, J. J. Chem. Soc., Perkin Trans. 1 1995,
187. (b) Nair, V.; Mathew, J.; Alexander, S. Synth. Commun.
1995, 25, 3981. (c) Nair, V.; Mathew, J.; Radhakrishnan, K. V.
J. Chem. Soc., Perkin Trans. 1 1996, 1487. (d) Nair, V.;
Mathew, J.; Nair, L. G. Synth. Commun. 1996, 26, 4531.
(e) Nair, V.; Nair, L. G.; Balagopal, L.; Mathew, J. Ind. J.
Chem. 2000, 39B, 352.
6. Nair, V.; Mathew, J. J. Chem. Soc., Perkin Trans. 1 1995,
1881.
3.5.12.
2-Benzenesul®nyl-1-methoxy-1-phenylcyclo-
7. Ojibin, Y. N.; Ilavoisky, A. I.; Nikishin, G. I. Russ. Chem.
Bull. 1996, 45, 1939 and references cited therein.
8. Nair, V.; Panicker, S. B. Tetrahedron Lett. 1999, 40, 563.
9. (a) Nair, V.; Nair, L. G.; George, T. G.; Augustine, A.
Tetrahedron 2000, 56, 7607. (b) Nair, V.; George, T. G.
Tetrahedron Lett. 2000, 41, 3199. (c) Nair, V.; George,
T. G.; Nair, L. G.; Panicker, S. B. Tetrahedron Lett. 1999,
40, 1195.
heptane (10c). To a solution of the 1-phenyl-1-cyclo-
heptene (172 mg, 1 mmol) and phenyl sul®nic acid
sodium salt (164 mg, 1 mmol) in methanol (10 mL) was
added dropwise a solution of CAN (1.26 g, 2.3 mmol) in
the same solvent (15 mL) at ice temperature. On comple-
tion, the reaction mixture was diluted with water (50 mL)
and extracted with dichloromethane (3£30 mL). The
combined organic extracts were washed with brine and
dried over sodium sulfate. The solvent was removed on a
rotary evaporator and the residue on crystalliztaion using
dichloromethane±petroleum ether as solvent afforded the
product as colorless crystals (233 mg, 68%), mp 148±
1508C. 10c: IR (neat) nmax: 1624, 1431, 1297, 1142, 1067;
1H NMR: 7.78±7.76 (m, 2H, ArH), 7.52±7.38 (m, 3H,
ArH), 7.25±7.18 (m, 5H, ArH), 3.74 (uneven doublet, 1H,
CHSO2Ph), 3.06 (s, 3H, OMe), 2.36±2. 04 (m, 5H, CH2),
1.91±1.53 (m, 5H, CH2); 13C NMR: 143.64, 142.65, 132.36,
128.91, 128.13, 128.06, 127.18, 126.49, 76.40, 50.49, 35.64,
27.43, 25.59, 24.02, 21.54; Anal. Calcd for C20H24O3S: C
69.73, H 7.02, S 9.31; Found C 70.09, H 7.11, S 9.33.
10. Shimizu, I.; Fujita, M.; Nakajima, T.; Sato, T. Synlett 1997,
888.
11. (a) Narasaka, K.; Mochizuki, T.; Hayakawa, S. Chem. Lett.
1994, 1705. (b) Mochizuki, T.; Hayakawa, S.; Narasaka, K.
Bull. Chem. Soc. Jpn 1996, 69, 2317.
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1996, 61, 3256±3258.
13. Zbiral, E.; Nestler, G. Tetrahedron 1970, 26, 2945.