2-[(Trimethylsilyl)methyl]benzyl methanesulfonates: Useful precursors for the generation of o -quinodimethanes

Article abstract of DOI:10.1055/s-0033-1341238

2-[(Trimethylsilyl)methyl]benzyl methanesulfonates react with potassium fluoride in the presence of a catalytic amount of 18-crown-6 at room temperature to give o-quinodimethanes, which are trapped with electron-deficient olefins to afford [4+2] cycloadducts in good yields. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0033-1341238

1788▌
PAPER
p2a-p[er(Trimethylsilyl)methyl]benzyl Methanesulfonates: Useful Precursors for
the Generation of o-Quinodimethanes
2-[(Trimethylsilyl)methyl]benzyl Methanesulfonates
Hidenori Shirakawa, Hiroshi Sano*
Department of Chemistry, Graduate School of Engineering, Gunma University, Tenjin 1-5-1, Kiryu, Gunma 376-8515, Japan
Fax +81(277)301282; E-mail: sano@gunma-u.ac.jp
Received: 11.02.2014; Accepted after revision: 26.03.2014
of o-quinodimethane generated from 2 with electron-defi-
Abstract: 2-[(Trimethylsilyl)methyl]benzyl methanesulfonates re-
cient olefins could be performed to give tetrahydronaph-
act with potassium fluoride in the presence of a catalytic amount of
thalenes 3. We examined the reaction of 2 with dimethyl
18-crown-6 at room temperature to give o-quinodimethanes, which
fumarate as a typical dienophile in the presence of potas-
sium fluoride in acetonitrile at room temperature to opti-
mize the reaction conditions (Table 1).
are trapped with electron-deficient olefins to afford [4+2] cycload-
ducts in good yields.
Key words: o-quinodimethane, Diels–Alder reaction, 1,4-elimina-
tion, silicon, mesylate, fluoride
MsCl
OH
OMs
TMS
TMS
Et3N, CH2Cl2
The Diels–Alder reaction of o-quinodimethane intermedi-
ates with alkenes is a versatile method for the synthesis of
1,2,3,4-tetrahydronaphthalene structures. Various meth-
ods for the generation of o-quinodimethanes have been
developed, and these have been applied to the syntheses of
natural products such as steroids.1 Among them, 1,4-elim-
ination in α′-heterosubstituted α-silyl-o-xylenes is a useful
method for the generation of o-quinodimethanes under
mild conditions compared with other methods.2 However,
some problems remain with this type of reaction; the pre-
cursors are difficult or troublesome to prepare and some-
what harsh conditions are required to generate the o-
quinodimethane intermediate in some cases. For example,
it has been reported that 2-[(trimethylsilyl)methyl]benzyl
acetate and the corresponding phenyl carbonate can be
prepared in short steps, and the o-quinodimethane can be
generated under thermal conditions using potassium fluo-
ride (DMF, 100 °C) or potassium fluoride with an equi-
molar amount of 18-crown-6 (MeCN, 35–50 °C).2g–j We
envisioned that the silyl compound, which has a better
leaving group than the ester or carbonate group, would
generate the o-quinodimethane under milder conditions.
In this study, we aimed to develop a new precursor, which
can be prepared in short steps, and generate o-quinodi-
methane under mild conditions; we expected that 2-[(tri-
methylsilyl)methyl]benzyl methanesulfonate (2) would
meet these requirements.3
(wtihout isolation)
1
2
EWG
EWG
F–
3
o-quinodimethane
EWG = electron-withdrawing group
dimerization
+
4
5
Scheme 1
No cycloaddition took place when potassium fluoride was
used alone (entry 1), however, the reaction proceeded
when 18-crown-6 (30 mol%) was used as a catalyst to
give the desired cycloadduct 3a5 in 66% with a small
amount of 2 remaining (entry 2); a prolonged reaction
time increased the yield (87%) (entry 3). Decreasing the
catalyst loading from 30 to 10 mol% resulted in a lower
product yield (61%) with a substantial amount of recov-
ered starting 2 (entry 4). When the reaction was carried
out at a higher concentration, 2 was completely consumed
in 42 hours and the yield of the cycloadduct 3a increased
to 87% (entry 5). On the other hand, the use of potassium
chloride in place of potassium fluoride gave a trace
amount of cycloadduct 3a with complete consumption of
the precursor 2 (entry 6). In this case, chlorination of the
starting mesylate 2 predominantly occurred to give [2-
(chloromethyl)benzyl]trimethylsilane (>99%).
In our preliminary experiment, we found that 2, which
was derived from the corresponding alcohol 1,2f reacts
with two equivalents of potassium fluoride in the presence
of 30 mol% of 18-crown-6 to give spiro-di-o-xylylene 4 in
68% yield (NMR) with a small amount of [4+4] cycload-
duct of o-quinodimethane 5 (6%),4 indicating that 2 works
as a precursor of o-quinodimethane in the presence of a
fluoride source (Scheme 1). Intermolecular cycloaddition
Cycloadditions with a variety of dienophiles were con-
ducted under the optimized conditions (Table 2). The re-
action was performed with electron-deficient olefins other
than dimethyl fumarate; benzylideneacetone, methyl ac-
SYNTHESIS 2014, 46, 1788–1792
Advanced online publication: 13.05.2014
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1341238; Art ID: ss-2014-f0098-op
© Georg Thieme Verlag Stuttgart · New York

PAPER
2-[(Trimethylsilyl)methyl]benzyl Methanesulfonates
1789
rylate, and acrylonitrile afforded 3d, 3e, and 3f in high
yields, respectively (entries 4–6). The use of methyl cin-
namate and methyl methacrylate as dienophiles also gave
good yields (entries 2 and 7). No cycloaddition with di-
enophiles proceeded when poor dienophiles such as sty-
rene and dimethyl maleate were employed.6 In contrast to
our expectations, we found that the use of fumaronitrile
resulted in a complex mixture.7 It is noteworthy that the
reagent system of potassium fluoride and 18-crown-6 as a
fluoride source was found to be superior to tetrabutylam-
monium fluoride for cycloadditions with dienophiles with
relatively low reactivity6 (entries 3 and 7). In these cases,
the use of tetrabutylammonium fluoride gave substantial
amounts of dimer 4 (>50%) together with the cycload-
ducts 3c and 3g, suggesting that the predominant dimer-
ization is due to the high concentration of o-
quinodimethane, which was rapidly generated by tetrabu-
tylammonium fluoride.8 That is, it is conceivable that the
dimerization competes with the cycloaddition when di-
enophiles with low reactivity are employed. On the other
hand, slow generation of o-quinodimethane by potassium
fluoride and 18-crown-6 seems to suppress the dimeriza-
tion to give the cycloadducts predominantly.
Table 1 Reaction of 2 with Dimethyl Fumarate under Various Con-
ditionsa
MeO2C
CO2Me
CO2Me
CO2Me
2
KF
r.t.
3a
Entry
Promoter Catalyst (mol%)
Time (h) Yieldb (%)
1
2
3
4
5c
6
KF
KF
KF
KF
KF
KCl
none
30
30
42
42
42
42
0
66
87
61
87
<1
18-crown-6 (30)
18-crown-6 (30)
18-crown-6 (10)
18-crown-6 (10)
18-crown-6 (30)
a Reaction conditions: 2 (0.5 mmol), dimethyl fumarate (1 mmol), KF
(1 mmol), MeCN (5 mL, 0.1 M with respect to 2), r.t., unless other-
wise specified.
b Determined by 1H NMR analysis.
c MeCN (1 mL, 0.5 M with respect to 2) was used.
We also demonstrated the superiority of precursor 2 com-
pared to other precursors that have different leaving
groups such as ester and carbonate groups. Thus, both 6
Table 2 Cycloaddition of o-Quinodimethane with Dienophilesa
Entry Dienophile
Product
Yieldb (%)
CN
(2 equiv)
MeO2C
CO2Me
OMs
TMS
1
3a
81 (92)c
KF (2 equiv)
18-crown-6 (10 mol%)
MeCN, r.t., 42 h
CO2Me
CO2Me
Ph
CN
CN
3f
2
86%
Ph
2
3b
3c
3d
67d
CO2Me
CO2Me
3f
CN
(2 equiv)
3
4
49 (trace)c
74
not observed
OAc
TMS
CO2Me
CO2Me
Ph
+
KF (2 equiv)
18-crown-6 (10 mol%)
MeCN, r.t., 42 h
Ph
OAc
6
COMe
COMe
CO2Me
CN
99%
MeO2C
5
6
7
3e
3f
80 (74)c
86 (65)c
66 (20)c
CO2Me
CO2Me
CO2Me
CO2Me
(2 equiv)
OMs
TMS
CN
KF (2 equiv)
18-crown-6 (10 mol%)
MeCN, r.t., 42 h
3a
81%
2
3g
MeO2C
CO2Me
CO2Me
O
a Conditions: 2 (0.5 mmol), dienophile (1 mmol), KF (1 mmol), 18-
crown-6 (0.05 mmol), MeCN (1 mL), r.t., 42 h, unless otherwise
specified.
CO2Me
(2 equiv)
CO2Me
CO2Me
OCOMe
TMS
KF (2 equiv)
18-crown-6 (10 mol%)
MeCN, r.t., 42 h
b Isolated yield.
3a
26%
7
c Yield in parenthesis is for the reaction conducted for 2 h using
TBAF·3H2O in place of KF without 18-crown-6.
d The reaction was conducted for 96 h.
Scheme 2
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 1788–1792

1790
H. Shirakawa, H. Sano
PAPER
for a few months and in CH2Cl2 solution at r.t. for at least several
weeks.
IR (neat): 3000, 1620, 1375, 1270, 1195, 990, 940, 870 cm–1.
1H NMR (300 MHz, CDCl3): δ = 7.31 (d, J = 7.8 Hz, 1 H), 7.24 (t,
J = 7.5 Hz, 1 H), 7.09 (t, J = 7.5 Hz, 1 H), 7.03 (d, J = 7.8 Hz, 1 H),
5.19 (s, 2 H), 2.85 (s, 3 H), 2.21 (s, 2 H), –0.01 (s, 9 H).
13C NMR (75.3 MHz, CDCl3): δ = 140.6, 130.7, 129.7, 129.5(2 C),
124.6, 70.0, 38.3, 23.1, –1.56 (3 C).
HRMS (ESI-TOF): m/z [M + Na]+ calcd for C12H20NaO3SSi:
295.0795; found: 295.0796.
and 7 gave unsatisfactory results under the same condi-
tions as shown in Scheme 2.
The present reaction can be applied to the generation of an
α-alkyl-substituted o-quinodimethane. Thus, the precur-
sor 9, which has a methyl group in the α-position of the si-
lyl group, was found to generate α-methyl-o-
quinodimethane under similar conditions, which reacted
with acrylonitrile to give the corresponding cycloadduct
10 in 69% as a mixture of stereo- and regioisomers
(Scheme 3).9
2-[1-(Trimethylsilyl)ethyl]benzyl Methanesulfonate (9)
MsCl
1) BuLi
2) MeI
OH
OH
2-[1-(Trimethylsilyl)ethyl]benzyl Alcohol (8)
TMS
TMS
To a solution of 2-[(trimethylsilyl)methyl]benzyl alcohol2f (1, 0.92
g, 4.7 mmol) in Et2O (7 mL) was added slowly n-BuLi in n-hexane
solution (6.0 mL, 9.6 mmol) and the resulting solution was refluxed
overnight. The solution was then cooled to r.t., MeI (0.30 mL, 4.8
mmol) was added, and the resulting mixture was stirred for 1 h at
r.t. The mixture was worked up by the addition of H2O (20 mL) and
extracted with Et2O (3 × 20 mL). The combined organic layers were
dried (Na2SO4) and concentrated in vacuo. The crude oil was then
purified by column chromatography (silica gel; hexane–EtOAc,
10:1) to give 2-[1-(trimethylsilyl)ethyl]benzyl alcohol10 (8, 0.38 g,
39%) as a colorless oil.
Et3N, CH2Cl2
1
8
39%
CN
OMs
TMS
CN
KF
18-crown-6 (10 mol%)
MeCN, r.t., 72 h
9
10
69%
(wtihout isolation)
1H NMR (300 MHz, CDCl3): δ = 7.04–7.30 (m, 4 H), 4.57 (d, J =
12.6 Hz, 1 H), 4.47 (d, J = 12.6 Hz, 1 H), 2.45 (q, J = 7.5 Hz, 1 H),
1.36 (dd, J = 4.8, 7.2 Hz, 3 H), –0.04 (s, 9 H).
Scheme 3
13C NMR (75.3 MHz, CDCl3): δ = 144.7, 137.2, 128.1, 127.8,
126.8, 124.4, 63.3, 23.6, 16.2, –2.84 (3 C).
In summary, we have developed a new and convenient
method for the generation of o-quinodimethane interme-
diates from 2 and 9, which are prepared in short steps from
commercially available compounds. The combination of
potassium fluoride with a catalytic amount of 18-crown-6
was effective for the induction of 1,4-elimination of the
mesyloxy and trimethylsilyl groups from the precursors,
leading to the generation of o-quinodimethanes at room
temperature, which underwent cycloaddition with elec-
tron-deficient olefins to afford tetrahydronaphthalenes.
2-[1-(Trimethylsilyl)ethyl]benzyl Methanesulfonate (9)
To a solution of 2-[1-(trimethylsilyl)ethyl]benzyl alcohol (8, 104
mg, 0.50 mmol) in CH2Cl2 (4.0 mL) were added Et3N (84 μL, 0.60
mmol) and MsCl (47 μL, 0.60 mmol) at 0 °C and the resulting solu-
tion was stirred for 1 h at 0 °C. The mixture was worked up by the
addition of sat. NaHCO3 solution (40 mL) and extracted with
CH2Cl2 (3 × 30 mL). The combined organic layers were dried
(Na2SO4) and concentrated in vacuo to give 9 (143 mg, 100%) as a
pale-yellow oil. The product was used for the next reaction without
further purification. This compound is stable in a freezer for a few
months and in CH2Cl2 solution at r.t. for at least several weeks.
1H NMR (300 MHz) and 13C NMR (75.3 MHz) spectra were record-
ed on a FT-NMR Jeol JNM-AL 300 spectrometer relative to TMS
(δ = 0.0 ppm) as the internal standard or the residual signal of deu-
terated solvent. IR spectra were recorded on a Hitachi 270-50 infra-
red spectrophotometer. HRMS were recorded on an AB Sciex
Triple TOF 4600 mass spectrometer. TLC analysis used Merck pre-
coated TLC plates (silica gel 60 GF254, 0.25 mm). Column chro-
matography used silica gel 60 N (spherical, neutral, 63–210 μm;
Kanto Chemical Co., Inc.). All reactions were carried out under an
argon atmosphere in dried glassware. All solvents were distilled pri-
or to use. The other simple chemicals were purchased and used as
such.
IR (neat): 3000, 1622, 1376, 1274, 1196, 990, 940, 870 cm–1.
1H NMR (300 MHz, CDCl3): δ = 7.29–7.34 (m, 2 H), 7.07–7.17 (m,
2 H), 5.30 (d, J = 8.7 Hz, 1 H), 5.16 (d, J = 8.7 Hz, 1 H), 2.86 (s, 3
H), 2.46 (q, J = 7.2 Hz, 1 H), 1.36 (d, J = 7.2 Hz, 3 H), –0.04 (s, 9 H).
13C NMR (75.3 MHz, CDCl3): δ = 146.6, 130.8, 129.8, 129.7,
127.3, 124.6, 70.2, 38.3, 24.1, 16.2, –2.97 (3 C).
HRMS (ESI-TOF): m/z [M + Na]+ calcd for C13H22NaO3SSi:
309.0956; found: 309.0949.
Dimethyl (2S*,3S*)-1,2,3,4-Tetrahydronaphthalene-2,3-dicar-
boxylate (3a);5 Typical Procedure
To a solution of 2 (136 mg, 0.50 mmol) in MeCN (1.0 mL) were
added dimethyl fumarate (144 mg, 1.0 mmol), KF (58 mg, 1.0
mmol), and 18-crown-6 (13 mg, 0.050 mmol). The mixture was
stirred for 42 h at r.t. and then it was poured into H2O (40 mL), ex-
tracted with CH2Cl2 (3 × 30 mL), dried (anhyd Na2SO4), and con-
centrated in vacuo. The crude oil was purified by column
chromatography (silica gel; hexane–EtOAc, 10:1; Rf = 0.20) to pro-
vide 3a (101 mg, 81%) as a colorless oil.
1H NMR (300 MHz, CDCl3): δ = 7.07–7.15 (m, 4 H), 3.73 (s, 6 H),
2.89–3.17 (m, 6 H).
13C NMR (75.3 MHz, CDCl3): δ = 175.0 (2 C), 133.8 (2 C), 128.7
2-[(Trimethylsilyl)methyl]benzyl Methanesulfonate (2)
To a solution of 2-[(trimethylsilyl)methyl]benzyl alcohol2f (1; 97
mg, 0.50 mmol) in CH2Cl2 (4.0 mL) was added Et3N (84 μL, 0.60
mmol) and MsCl (47 μL, 0.60 mmol) at 0 °C and the resulting solu-
tion was then stirred for 1 h at 0 °C. The mixture was worked up by
the addition of sat. NaHCO3 solution (40 mL) and extracted with
CH2Cl2 (3 × 30 mL). The combined organic layers were dried
(Na2SO4) and concentrated in vacuo to give 2 (136 mg, 100%) as a
pale-yellow oil. The product was used for the next reaction without
further purification, since 2 was decomposed by distillation or by
chromatography on silica gel. This compound is stable in a freezer
(2 C), 126.4 (2 C), 52.1 (2 C), 42.1 (2 C), 31.8 (2 C).
Synthesis 2014, 46, 1788–1792
© Georg Thieme Verlag Stuttgart · New York

PAPER
2-[(Trimethylsilyl)methyl]benzyl Methanesulfonates
1791
Methyl (2S*,3S*)-3-Phenyl-1,2,3,4-tetrahydronaphthalene-2-
carboxylate (3b)11
column chromatography (silica gel; hexane–EtOAc, 20:1; Rf =
0.38) to provide 3g (67 mg, 66%) as a colorless oil.
Following the typical procedure using methyl cinnamate (162 mg,
1.0 mmol) for 96 h at r.t. gave a crude mixture. After Kugelrohr dis-
tillation (160 °C/9.3 mbar) of the mixture to remove excess methyl
cinnamate, the residue was purified by column chromatography
(silica gel; hexane–EtOAc, 10:1; Rf = 0.48) to provide 3b (89 mg,
67%) as a colorless solid.
1H NMR (300 MHz, CDCl3): δ = 7.05–7.12 (m, 4 H), 3.66 (s, 3 H),
3.24 (d, J = 16.5 Hz, 1 H), 2.82 (t, J = 6.6 Hz, 2 H), 2.66 (d, J = 16.5
Hz, 1 H), 2.15 (m, 1 H), 1.72 (m, 1 H), 1.27 (s, 3 H).
13C NMR (75.3 MHz, CDCl3): δ = 178.0, 135.1, 135.0, 129.3,
128.8, 125.9 (2 C), 52.0, 41.8, 38.7, 31.9, 26.3, 24.2.
1H NMR (300 MHz, CDCl3): δ = 7.07–7.33 (m, 9 H), 3.43 (s, 3 H),
3.00–3.29 (m, 6 H).
13C NMR (75.3 MHz, CDCl3): δ = 175.2, 143.6, 135.7, 134.4, 128.8
(2 C), 128.6 (2 C), 127.5(2 C), 126.9, 126.3, 126.2, 51.6, 47.0, 43.7,
37.4, 33.2.
2-Cyano-1-methyl-1,2,3,4-tetrahydronapthalene (10)2c
Following the typical procedure using 9 (143 mg, 0.5 mmol) and ac-
rylonitrile (53 mg, 1.0 mmol) gave a crude mixture. The mixture
was purified by column chromatography (silica gel; hexane–EtO-
Ac, 20:1; Rf = 0.2) to provide 10 (59 mg, 69%) as a colorless oil con-
taminated with ca. 15% of stereo- and regioisomers.
1H NMR (300 MHz, CDCl3): δ = 7.07–7.30 (m, 4 H), 2.66–3.23 (m,
4 H), 2.00–2.42 (m, 2 H), 1.48 (d, J = 7.2 Hz, 3 H).
13C NMR (75.3 MHz, CDCl3): δ = 138.2, 134.4, 129.1, 128.2,
Methyl (2S*,3S*)-3-Methyl-1,2,3,4-tetrahydronaphthalene-2-
carboxylate (3c)5
Following the typical procedure using methyl crotonate (100 mg,
1.0 mmol) gave a crude mixture. The mixture was purified by col-
umn chromatography (silica gel; hexane–EtOAc, 20:1; Rf = 0.38) to
provide 3c (50 mg, 49%) as a colorless oil.
126.6, 126.4, 122.1, 34.1, 31.9, 27.4, 22.9, 19.7.
1H NMR (300 MHz, CDCl3): δ = 7.03–7.23 (m, 4 H), 3.72 (s, 3 H),
3.06 (dd, J = 11.1, 16.2 Hz, 1 H), 2.95 (dd, J = 5.1, 16.2 Hz, 1 H),
2.87 (dd, J = 5.4, 16.8 Hz, 1 H), 2.50 (dd, J = 11.1, 16.8 Hz, 1 H),
2.43 (dt, J = 5.4, 10.8 Hz, 1 H), 2.05–2.34 (m, 1 H), 1.05 (d, J = 6.3
Hz, 3 H).
Acknowledgment
We thank Prof. Tatsuya Nabeshima and Prof. Masaki Yamamura
(Tsukuba University) for their kind help with measuring HRMS.
We are also grateful to Prof. Hideki Amii (Gunma University) for
his helpful suggestions.
13C NMR (75.3 MHz, CDCl3): δ = 176.2, 135.7, 134.7, 128.7,
128.6, 126.0, 125.9, 51.7, 47.7, 37.4, 32.7, 31.8, 19.9.
(2S*,3S*)-2-Acetyl-3-phenyl-1,2,3,4-tetrahydronaphthalene
(3d)11
Following the typical procedure using benzalacetone (146 mg, 1.0
mmol) gave a crude mixture. The mixture was purified by column
chromatography (silica gel; hexane–EtOAc, 10:1; Rf = 0.33) to pro-
vide 3d (92 mg, 74%) as a colorless solid.
1H NMR (300 MHz, CDCl3): δ = 7.07–7.34 (m, 9 H), 2.95–3.27 (m,
6 H), 1.89 (s, 3 H).
13C NMR (75.3 MHz, CDCl3): δ = 211.4, 143.8, 135.8, 134.6, 128.9
(2 C), 128.7 (2 C), 127.5 (2 C), 127.0, 126.3, 126.2, 53.9, 43.5, 37.7,
32.7, 30.1.
Supporting Information for this article is available online
at
http://www.thieme-connect.com/products/ejournals/journal/
10.1055/s-00000084.SunogIpimrfiantoSuIpg
n
fonirtat
ori
References
(1) Reviews: (a) Oppolzer, W. Synthesis 1978, 793.
(b) Charlton, J. L.; Alauddin, M. M. Tetrahedron 1987, 43,
2873. (c) Martin, N.; Seoane, C.; Hanak, M. Org. Prep.
Proced. Int. 1991, 23, 237. (d) Segura, J. L.; Martin, N.
Chem. Rev. 1999, 99, 3199. (e) Sano, H.; Nishimura, J.
Science of Synthesis; Vol. 45a; Georg Thieme Verlag:
Stuttgart, 2009, 483.
(2) (a) Ito, Y.; Nakatsuka, M.; Saegusa, T. J. Am. Chem. Soc.
1980, 102, 863. (b) Djuric, S.; Sarkar, T.; Magnus, P. J. Am.
Chem. Soc. 1980, 102, 6885. (c) Ito, Y.; Nakatsuka, M.;
Saegusa, T. J. Am. Chem. Soc. 1982, 104, 7609. (d) Ito, Y.;
Amino, Y.; Nakatsuka, M.; Saegusa, T. J. Am. Chem. Soc.
1983, 105, 1586. (e) Beard, A. R.; Hazell, S. J.; Mann, J.;
Palmer, C. J. Chem. Soc., Perkin Trans. 1 1993, 1235.
(f) Lenihan, B. D.; Schechter, H. J. Org. Chem. 1998, 63,
2072. (g) Kuwano, R.; Shige, T. Chem. Lett. 2005, 728.
(h) Yoshida, H.; Nakano, S.; Yamaryo, M.; Ohshita, J.;
Kunai, A. Org. Lett. 2006, 8, 4157. (i) Yoshida, H.; Nakano,
S.; Mukae, M.; Ohshita, J. Org. Lett. 2008, 10, 4319.
(j) Yoshida, H.; Mukae, M.; Ohshita, J. Chem. Commun.
2010, 46, 5253.
Methyl 1,2,3,4-Tetrahydronaphthalene-2-carboxylate (3e)12
Following the typical procedure using methyl acrylate (86 mg, 1.0
mmol) gave a crude mixture. The mixture was purified by column
chromatography (silica gel; hexane–EtOAc, 20:1; Rf = 0.33) to pro-
vide 3e (77 mg, 80%) as a colorless oil.
1H NMR (300 MHz, CDCl3): δ = 7.05–7.12 (m, 4 H), 3.71 (s, 3 H),
2.99–3.02 (m, 2 H), 2.78–2.87 (m, 2 H), 2.68–2.77 (m, 1 H), 2.16–
2.24 (m, 1 H), 1.73–1.92 (m, 1 H).
13C NMR (75.3 MHz, CDCl3): δ = 175.9, 135.7, 134.9, 129.1,
128.9, 126.0, 125.9, 51.8, 40.0, 31.7, 28.6, 26.0.
2-Cyano-1,2,3,4-tetrahydronaphthalene (3f)12
Following the typical procedure using acrylonitrile (53 mg, 1.0
mmol) gave a crude mixture. The mixture was purified by column
chromatography (silica gel; hexane–EtOAc, 10:1; Rf = 0.45) to pro-
vide 3f (67 mg, 86%) as a colorless oil.
(3) The choice of the leaving group is important. Thus, our
preliminary examination showed that the corresponding
triflate, which possesses an excellent leaving group, is too
labile to use as a precursor of o-quinodimethane.
(4) Errede, L. A. J. Am. Chem. Soc. 1961, 83, 949.
(5) Inaba, S-i.; Wehmeyer, R. M.; Forkner, M. W.; Rieke, R.
J. Org. Chem. 1988, 53, 339.
1H NMR (300 MHz, CDCl3): δ = 7.06–7.24 (m, 4 H), 2.94–3.15 (m,
4 H), 2.84 (ddd, J = 6.3, 8.1, 17.1 Hz, 1 H), 2.14–2.23 (m, 1 H), 2.07
(ddt, J = 5.7, 8.7, 14.1 Hz, 1 H).
13C NMR (75.3 MHz, CDCl3): δ = 134.6, 132.4, 129.2, 129.0,
126.8, 126.3, 122.2, 32.4, 27.1, 26.3, 25.6.
(6) Carruthers, W. In Some Modern Methods of Organic
Synthesis, 2nd ed.; Elmore, D. T.; Leadbetter, A. J.;
Schofield, K., Eds.; Cambridge University Press:
Cambridge, 1978, 161.
Methyl 2-Methyl-1,2,3,4-tetrahydronaphthalene-2-carboxylate
(3g)13
Following the typical procedure using methyl methacrylate (100
mg, 1.0 mmol) gave a crude mixture. The mixture was purified by
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 1788–1792

1792
H. Shirakawa, H. Sano
PAPER
(7) Some examples of cycloadditions of o-quinodimethanes
with fumaronitrile are known; see ref. 5 and: Sano, H.;
Ohtsuka, H.; Migita, T. J. Am. Chem. Soc. 1988, 110, 2014.
(8) The crude NMR indicated that 2 was completely consumed
within 2 h.
(10) Cho, I. S.; Chang, S. S. S.; Ho, D.; Lee, C. P.; Ammon, H.
L.; Mariano, P. S. Heterocycles 1991, 32, 2161.
(11) Kuwano, R.; Shige, T. J. Am. Chem. Soc. 2007, 129, 3802.
(12) Mills, R. J.; Taylor, N. J.; Snieckus, V. J. J. Org. Chem.
1998, 63, 2072.
(9) NMR analysis showed that the cycloadduct 10 consisted of
4 isomers in a ratio of about 85:12.5:2:0.5.
(13) Eru, E.; Hawkes, G. E.; Utley, J. H. P.; Wyatt, P. B.
Tetrahedron 1995, 51, 303.
Synthesis 2014, 46, 1788–1792
© Georg Thieme Verlag Stuttgart · New York