Anodic cyclization of 1,7-diarylheptane-1,7-diones to the corresponding 1,2-diaroylcyclopentanes

Article abstract of DOI:10.1055/s-0032-1317206

A range of 1,7-diarylheptane-1,7-diones were electrooxidized in the presence of iodide ions and a base in a mixture of methanol and toluene as the reaction solvents to give the corresponding cyclized 1,2-diaroylcyclopentanes in moderate to good yields. Th

Full text of DOI:10.1055/s-0032-1317206

2544▌
LETTER
lAettner odic Cyclization of 1,7-Diarylheptane-1,7-diones to the Corresponding
1,2-Diaroylcyclopentanes
Anodic Cyclization of 1,7-Diarylheptane-1,7-diones
Mitsuhiro Okimoto,* Haruki Yamamori, Kousuke Ohashi, Shinnosuke Nishikawa, Masayuki Hoshi, Takashi Yoshida
Department of Biotechnology and Environmental Chemistry, Kitami Institute of Technology, 165 Kitami, Koen-cho, Hokkaido 090-8507, Japan
Fax +81(157)247719; E-mail: okimotmt@mail.kitami-it.ac.jp
Received: 04.07.2012; Accepted after revision: 16.08.2012
Initially, the optimal reaction conditions for the anodic cy-
Abstract: A range of 1,7-diarylheptane-1,7-diones were electro-
clization were determined in methanol using 1,7-di-
phenylheptane-1,7-dione (1a, X = H) as the model
substrate. Various combinations of the supporting electro-
oxidized in the presence of iodide ions and a base in a mixture of
methanol and toluene as the reaction solvents to give the corre-
sponding cyclized 1,2-diaroylcyclopentanes in moderate to good
yields. The reactions were carried out under extremely mild reac- lytes (mediators and bases) are listed in Table 1, along
tion conditions for which the optimal amount of electrolytic current
with the yields of the resulting cyclized product 2a
(X = H) and recoveries of unreacted substrate 1a. Where-
varied from 2.05–3.17 F·mol–1 depending on the substrates. The re-
action presumably proceeds through a two-electron oxidation pro-
as the use of NaOMe was ineffective (2% yield, Table 1,
cess in which the iodide ion plays an important role as the electron
entry 2), and the use of KI gave a yield of 48% (entry 1),
carrier.
the presence of both KI and NaOMe (1.0 equivalent with
Key words: electron transfer, oxidation, cyclization, ring closure,
respect to substrate 1a) was effective in increasing the
green chemistry, iodine
yield to 60% (entry 3). Although substituting KI with NaI
gave a comparable yield (59%, entry 12), significantly
lower yields were observed when KI was substituted with
The formation of carbon–carbon bonds is indispensable
KBr (4%, entry 7) or KCl (3%, entry 8), with nearly full
for the construction of organic compounds, and typically
recoveries of 1a. These results indicate that the yield of 2a
involves well-known classical chemical reactions. In cer-
is strongly affected by the presence of the iodide ion.
tain situations, however, a more effective synthetic strate-
Lower yields were also observed with the use of a neutral
gy can be provided by the electrooxidative method.
salt such as NaClO4 (38% yield, entry 9), a weaker base
Moreover, such electrooxidations can be carried out under
such as NaOAc (42% yield, entry 10), or a strong base
such as t-BuOK (47% yield, entry 11).
very mild reaction conditions, without the use of special,
and often harsh, reagents. The use of electrooxidations for
carbon–carbon bond formations in the syntheses of vari-
During the early stages of the electrooxidation, the yield
of 2a increased in proportion to the amount of current
ous organic compounds has been described in numerous
passed (41% after 1.0 F·mol–1, then 60% after 2.1 F·mol–1).
Surprisingly, further passage of current gradually de-
creased the yield of 2a, despite the presence of unreacted
substrate 1a; for example, after the passage of 2.6 F·mol–1
of current, the yield of 2a decreased to 53% despite the
presence of 1a (11%). Presumably, 2a underwent further
oxidation to form a tar-like material that remained at the
top of the column during the chromatographic purification
steps. The yield of 2a was not significantly affected by the
amount of KI (3.0 to 15.0 mmol), the reaction temperature
(5 to 50 °C), or the current intensity (0.2–0.4 A). Howev-
er, the yield decreased to 62% with the use of a catalytic
amount of KI (0.3 equivalents with respect to 1a, Table 1,
reports,1 including those from our laboratories.2 During
our investigations, we have discovered that 1,7-diaryl-
heptane-1,7-diones 1 can be converted through intramo-
lecular cyclization into the corresponding 1,2-di-
aroylcyclopentanes 2, as shown in Scheme 1.
Although there are a few reports that describe the conver-
sion of 1,7-diarylheptane-1,7-diones or their derivatives
into the corresponding products through classical chemi-
cal methods,3 the electrooxidative cyclization of such
compounds is, to the best of knowledge, novel. On a relat-
ed note, we have previously described the electro-
oxidative formation of 1,2-diaroylcyclopropanes.4
X
X
electrooxidation
X
X
KI, NaOMe in MeOH
or MeOH–PhMe
O
O
O
O
2
1
X = H, Alk, alkoxyl, halogen
Scheme 1 Electrooxidative formation of 1,2-diaroylcyclopentanes
SYNLETT 2012, 23, 2544–2548
Advanced online publication: 14.09.2012
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0032-1317206; Art ID: ST-2012-U0567-L
© Georg Thieme Verlag Stuttgart · New York

LETTER
Anodic Cyclization of 1,7-Diarylheptane-1,7-diones
2545
Table 1 Effect of Mediators and Bases on the Yield of 2aa
electrooxidation
in MeOH or MeOH–PhMe
O
O
O
O
1a
2a
Entry
1
Mediator and/or base
KI
mmol
5
Yield of 2a (%)b
Recovery of 1a (%)b
48
2
19
97
15
13
13
14
84
96
24
22
22
14
2
NaOMe
5
3
KI/NaOMe
KI/NaOMe
KI/NaOMe
KI/NaOMe
KBr/NaOMe
KCl/NaOMe
KI/NaClO4
KI/NaOAc
KI/t-BtOK
NaI/NaOMe
5–5
5–5
1.5–5
5–10
5–5
5–5
5–5
5–5
5–5
5–5
60
74
62
51
4
4c
5c
6c
7
8
3
9
38
42
47
59
10
11
12
a Reaction conditions: Substrate 1 (1.40 g, 5 mmol), MeOH (40 mL), constant current (0.3 A), current passed (2.1 F·mol–1), r.t. (ca. 15 °C).
b Determined by GC analysis.
c PhMe was used as the co-solvent (40 mL, MeOH–PhMe = 5:3). Current passed (2.24 F·mol–1).
entry 5), and to nearly 50% with the use of an excess mal reaction conditions described above; the results are
amount of NaOMe (2.0 equivalents with 1a, Table 1, en- listed in Table 2. During the course of the electrooxida-
try 6), Interestingly, the yield of 2a was improved to 74% tions, the composition of the reaction mixture (anolyte)
by the use of toluene as a co-solvent (methanol– was monitored by GC and/or TLC analysis to determine
PhMe = 5:3; Table 1, entry 4). As a note, the yield of 2a the endpoint of the reactions. Products 2b,c,f,i were ob-
decreased to 63% when the electrooxidation was carried tained in reasonable yields from 1b,c,f,i, respectively,
out in an undivided cell under the same reaction condi- even without the use of PhMe as a co-solvent. In the cases
tions as those presented in Table 1, entry 4.
of 1d,c,g,h, PhMe (15 mL) was required as the co-solvent
to afford products 2d,e,g,h in good yields (presumably
due to the low solubility of the substrates in methanol).
Subsequently, the electrooxidations of several 1,7-diaryl-
heptane-1,7-diones (1b–i) were carried out using the opti-
Table 2 Electrooxidative Cyclizations of 1,7-Diarylheptane-1,7-dionesa,b
X
X
electrooxidation
X
X
KI, NaOMe in MeOH
or MeOH–PhMe
O
O
O
O
1
2
Substrate 1
X
H
Current passed (F·mol–1)
Isolated yield of 2 (%)
1ac
1b
1c
2.24
2.05
2.65
2.65
3.02
2.05
63
69
66
77
65
67
4-Me
4-Et
1dc
1ec
1f
4-MeO
4-EtO
4-F
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2544–2548

2546
M. Okimoto et al.
LETTER
Table 2 Electrooxidative Cyclizations of 1,7-Diarylheptane-1,7-dionesa,b (continued)
X
X
electrooxidation
X
X
KI, NaOMe in MeOH
or MeOH–PhMe
O
O
O
O
1
2
Substrate 1
X
Current passed (F·mol–1)
Isolated yield of 2 (%)
1gc
1hc
1i
4-Cl
4-Br
2.65
3.17
2.65
64
69
65
2,5-di-Me
a Reaction conditions: Substrate 1 (5 mmol), KI (0.83 g, 5 mmol), NaOMe (5 mmol), methanol (40 mL), constant current (0.3 A), r.t. (ca. 15 °C),
anode (Pt net), cathode (Ni coil).
b It was thought that the trans form of 2 was obtained exclusively.
c A mixture of methanol (25 mL) and PhMe (15 mL) was used as solvent.
J. Org. Chem. 1971, 36, 1523. (l) Chiba, K.; Arakawa, T.;
Tada, M. Chem. Commun. 1996, 1763. (m) Chiba, K.; Jinno,
M.; Nozaki, A.; Tada, M. Chem. Commun. 1997, 1403.
(n) Fry, A. J.; Porter, J. M.; Fry, P. F. J. Org. Chem. 1996,
61, 3191. (o) Mizuno, K.; Ichinose, N.; Otsuji, Y. J. Org.
Chem. 1992, 57, 1855. (p) Shundo, R.; Nishiguch, I.;
Matsubara, Y.; Hirashima, T. Tetrahedron 1991, 47, 831.
(q) Suga, S.; Okajima, M.; Yoshida, J. Tetrahedron Lett.
2001, 42, 2173. (r) Suga, S.; Suzuki, S.; Yamamoto, A.;
Yoshida, J. J. Am. Chem. Soc. 2000, 122, 10244.
(s) Yoshida, J.; Suga, S.; Suzuki, S.; Kinomura, N.;
Yamamoto, A.; Fujiwara, K. J. Am. Chem. Soc. 1999, 121,
9546. (t) Matsumoto, K.; Fuji, S.; Ueoka, K.; Suga, S.;
Yoshida, J. Angew. Chem. Int. Ed. 2008, 47, 2506.
(u) Nokami, T.; Ohata, K.; Inoue, M.; Tsuyama, H.;
Shibuya, A.; Soga, K.; Okajima, M.; Suga, S.; Yoshida, J. J.
Am. Chem. Soc. 2008, 130, 10864. (v) Kanada, Y.;
Onomura, O.; Maki, T.; Matsumura, Y. Chirality 2003, 15,
89. (w) Libendi, S. S.; Demizu, Y.; Onomura, O. Org.
Biomol. Chem. 2009, 7, 351.
Surprisingly, neither electron-withdrawing groups
(1f,g,h) nor electron-donating groups (1d,e) on the para-
position of the benzene ring of the substrate exhibited sig-
nificant substituent effects on the reaction. In all cases, the
passage of an excess amount of current resulted in lower
yields. The Rf values (silica gel TLC) of the substrate and
the product were nearly identical when using n-hexane,
ethyl acetate, diethyl ether, toluene and/or their mixtures
as the mobile phase; however, the product was successful-
ly purified by silica gel column chromatography using di-
chloromethane as the eluent.
Although details of the reaction mechanism remain un-
clear, as described above (Table 1), the iodide ion plays an
important role as the electron carrier during this indirect
electrooxidation process. As a result, substrate 1 would
lose two electrons and two protons during the formation
of product 2.
(2) (a) Chiba, T.; Okimoto, M.; Nagai, H.; Takata, Y. J. Org.
Chem. 1979, 44, 3519. (b) Okimoto, M.; Chiba, T. J. Org.
Chem. 1990, 55, 1070. (c) Chiba, T.; Okimoto, M. J. Org.
Chem. 1992, 57, 1375. (d) Chiba, T.; Okimoto, M. Chem.
Lett. 1993, 22, 521. (e) Okimoto, M.; Takahashi, Y.
Synthesis 2002, 2215. (f) Okimoto, M.; Numata, K.;
Takahashi, Y.; Hoshi, M.; Tomozawa, K.; Shigemoto, T.
Synlett 2005, 2507. (g) Okimoto, M.; Yoshida, T.; Hoshi,
M.; Hattori, K.; Komata, M.; Numata, K.; Tomozawa, K.
Synlett 2006, 1753.
(3) (a) Gao, J. Y.; Chen, W. X.; Jiang, K. Acta Chim. Sinica
1982, 40, 91. (b) Baumstark, A. L.; McCloskey, C. J.; Witt,
K. E. J. Org. Chem. 1978, 43, 3609. (c) Gong, Y. D.;
Tanaka, H.; Iwasawa, N.; Narasaka, K. Bull. Chem. Soc. Jpn.
1998, 71, 2181. (d) Nakamura, M.; Miki, M.; Majima, T. J.
Chem. Soc., Perkin Trans. 1 2000, 415.
In conclusion, the electrochemical method developed here
was successfully applied to the oxidative formation of
novel 1,2-diaroylcyclopentanes 2.5 This electrooxidative
intramolecular ring formation can be carried out at room
temperature, under mild conditions, and in the absence of
any harsh oxidants and/or special reagents. Further inves-
tigations of the electrochemical cyclizations of 1,6-diaryl-
hexane-1,6-diones and 1,8-diaryl-octane-1,8-diones are
underway.
References
(1) See for example: (a) Longchamp, M. S.; Caullet, C.; Libert,
M. Bull. Soc. Chim. Fr. 1974, 353. (b) Nilsson, A.;
(4) Okimoto, M.; Takahashi, Y.; Kakuchi, T. Bull. Chem. Soc.
Jpn. 2003, 76, 207; Note: At present, cyclobutane and
cyclohexane derivatives could not be obtained from the
corresponding aromatic diketones by the electrooxidation
method.
(5) 1,7-Diarylheptane-1,7-diones were prepared by using
standard Friedel–Crafts acylation conditions between
pimeloyl dichloride and aromatic compounds in the
presence of AlCl3.6 Preparative-scale electrooxidations were
carried out in a tall 50-mL beaker equipped with a
cylindrical fine frit cup (height: 45 mm, diameter: 12 mm) as
Palmquist, U.; Ronlán, A.; Parker, V. D. J. Am. Chem. Soc.
1975, 97, 3540. (c) Sainsbury, M.; Watt, J. J. Chem. Soc.,
Perkin Trans. 1 1979, 108. (d) Andreades, S.; Zahnow, E.
W. J. Am. Chem. Soc. 1969, 91, 4181. (e) Nilsson, A.; Rolan,
A.; Park, V. D. Tetrahedron Lett. 1975, 1107. (f) Richard, J.
A.; Evans, D. H. J. Electroanal. Chem. 1977, 81, 171.
(g) Nyberg, K. Acta Chem. Scand. 1973, 27, 503.
(h) Yoshida, K.; Fueno, T. J. Org. Chem. 1972, 37, 4145.
(i) Miyashi, T.; Nishizawa, Y.; Sugiyama, T.; Mukai, T.
J. Am. Chem. Soc. 1977, 99, 6111. (j) Chiba, T.; Takata, Y.
J. Org. Chem. 1977, 42, 2973. (k) Yoshida, K.; Fueno, T.
Synlett 2012, 23, 2544–2548
© Georg Thieme Verlag Stuttgart · New York

LETTER
the cathode compartment with a nickel coil cathode (length:
Anodic Cyclization of 1,7-Diarylheptane-1,7-diones
2547
Cyclopentane-1,2-diylbis[(4-methoxyphenyl)methanone]
(2d): Yield: 1.30 g (77%); colorless, fine cubic crystals; mp
130–131 °C (MeOH); Rf = 0.43 (CH2Cl2). IR (KBr): 3013
(w), 2959, 1665 (s), 1600 (s), 1575, 1331, 1261, 1215, 1166
(s), 1018, 1004, 838 cm–1. 1H NMR (400 MHz, CDCl3): δ =
1.76–1.91 (m, 4 H, 2 × CH2), 2.15–2.27 (m, 2 H, CH2), 3.85
(s, 6 H, 2 × CH3O), 4.30–4.38 (m, 2 H, 2 × CH), 6.91 (d, J =
280 mm, diameter: 1 mm), along with a cylindrical platinum
net anode (height: 35 mm, diameter: 30 mm, 50 mesh).
Typical Procedure: A solution of 1,7-diphenylheptane-1,7-
dione 1a (1.40 g, 5 mmol) in a mixture of MeOH (25 mL)
and toluene (15 mL) containing KI (0.83 g, 5.0 mmol) and
NaOMe (2.70 g, 5.0 mmol) was electrooxidized under a
constant current (0.3 A) at r.t. (ca. 15 °C) with magnetic
stirring. During the course of the electrooxidation, the
composition of the reaction mixture was monitored by GC
and/or TLC analyses. Passage of the electric current was
continued until the increase in the amount of the product was
no longer detected (2.24 F·mol–1). The reaction mixture was
concentrated in vacuo at approximately 60 °C to near
dryness. The resulting residue was treated with brine (ca. 30
mL), then extracted with diethyl ether or chloroform (3 × 40
mL), and dried overnight over sodium sulfate. After removal
of the solvent in vacuo, the crude product was purified by
silica gel column chromatography (height: 350 mm,
diameter: 25 mm) using dichloromethane as the eluent, to
afford the pure cyclized product 2a (0.88 g, 63%). The
electrooxidation products were characterized by using IR,
1H and 13C NMR analyses, and by HRMS.
Cyclopentane-1,2-diylbis(phenylmethanone) (2a): Yield:
0.88 g (63%); colorless, fine cubic crystals; mp 88–89 °C
(MeOH); Rf = 0.64 (CH2Cl2). IR (KBr): 3061 (w), 2965,
1675 (s), 1595, 1450, 1322, 1284, 1194, 987, 781, 702 (s)
cm–1. 1H NMR (400 MHz, CDCl3): δ = 1.75–1.92 (m, 4 H,
2 × CH2), 2.18–2.31 (m, 2 H, CH2), 4.38–4.46 (m, 2 H,
2 × CH), 7.45–7.57 (m, 6 H, 6 × CH), 7.97–8.03 (m, 4 H,
4 × CH). 13C NMR (100 MHz, CDCl3): δ = 26.29 (CH2),
32.06 (CH2), 48.67 (CH), 128.58 (CH), 128.68 (CH), 133.06
(CH), 136.41 (C), 201.74 (CO). MS (EI, 70 eV): m/z
(%) = 278 (6) [M+], 260 (7), 174 (25), 173 (98) [M+ –
C6H5CO], 106 (19), 105 (100) [C6H5CO], 95 (10), 77 (61)
[C6H5], 67 (7), 51 (15). HRMS: m/z [M+] calcd for C19H18O2:
278.1307; found: 278.1310.
Cyclopentane-1,2-diylbis(p-tolylmethanone) (2b): Yield:
1.06 g (69%); colorless, column crystals; mp 92–93 °C
(MeOH); Rf = 0.65 (CH2Cl2). IR (KBr): 3066 (w), 2949,
1667 (s), 1607 (s), 1412, 1335, 1222, 1178, 1016, 843, 825
cm–1. 1H NMR (400 MHz, CDCl3): δ = 1.75–1.89 (m, 4 H,
2 × CH2), 2.15–2.27 (m, 2 H, CH2), 2.38 (s, 6 H, 2 × CH3),
4.34–4.42 (m, 2 H, 2 × CH), 7.22 (d, J = 8 Hz, 4 H, 4 × CH),
7.90 (d, J = 8 Hz, 4 H, 4 × CH). 13C NMR (100 MHz,
CDCl3): δ = 21.59 (CH3), 26.32 (CH2), 32.14 (CH2), 48.56
(CH), 128.81 (CH), 129.25 (CH), 133.93 (C), 143.79 (C),
201.42 (CO). MS (EI, 70 eV): m/z (%) = 306 (4) [M+], 289
(8), 288 (35), 188 (27), 187 (86) [M+ – CH3C6H4CO], 120
(30), 119 (100) [CH3C6H4CO], 95 (13), 91 (70), [CH3C6H4],
65 (29). HRMS: m/z [M+] calcd for C21H22O2: 306.1619;
found: 306.1602.
Cyclopentane-1,2-diylbis[(4-ethylphenyl)methanone]
(2c): Yield: 1.10 g (66%); colorless, cubic crystals; mp 56–
57 °C (MeOH); Rf = 0.72 (CH2Cl2). IR (KBr): 3057 (w),
2966, 2933, 1665 (s), 1606 (s), 1416, 1330, 1218, 1181,
1006, 848 cm–1. 1H NMR (400 MHz, CDCl3): δ = 1.23 (t,
J = 8 Hz, 6 H, 2 × CH3), 1.76–1.91 (m, 4 H, 2 × CH2), 2.18–
2.28 (m, 2 H, CH2), 2.67 (q, J = 8 Hz, 4 H, 2 × CH2), 4.35–
4.43 (m, 2 H, 2 × CH), 7.26 (d, J = 8 Hz, 4 H, 4 × CH), 7.93
(d, J = 8 Hz, 4 H, 4 × CH). 13C NMR (100 MHz, CDCl3): δ=
15.16 (CH3), 26.33 (CH2), 28.91 (CH2), 32.15 (CH2), 48.61
(CH), 128.07 (CH), 128.94 (CH), 134.16 (C), 149.96 (C),
201.47 (CO). MS (EI, 70 eV): m/z (%) = 334 (3) [M+], 316
(15), 202 (22), 201 (76) [M+ – CH3CH2C6H4CO], 134 (23),
133 (100) [CH3CH2C6H4CO], 105 (26) [CH3CH2C6H4], 103
(13), 79 (19), 77 (13). HRMS: m/z [M+] calcd for C23H26O2:
334.1933; found: 334.1937.
9 Hz, 4 H, 4 × CH), 7.98 (d, J = 9 Hz, 4 H, 4 × CH). 13
C
NMR (100 MHz, CDCl3): δ = 26.39 (CH2), 32.28 (CH2),
48.46 (CH), 55.45 (OCH3), 113.72 (CH), 129.48 (C), 130.98
(CH), 163.46 (C), 200.50 (CO). MS (EI, 70 eV): m/z
(%) = 338 (2) [M+], 320 (7), 204 (9), 203 (66) [M+ –
CH3OC6H4CO], 136 (11), 135 (100) [CH3OC6H4CO], 118
(4), 107 (10) [CH3OC6H4], 92 (8), 77 (11). HRMS: m/z [M+]
calcd for C21H22O4: 338.1518; found: 338.1473.
Cyclopentane-1,2-diylbis[(4-ethoxyphenyl)methanone]
(2e): Yield: 1.17 g (64%); colorless, cubic crystals; mp 109–
110 °C (MeOH); Rf = 0.49 (CH2Cl2). IR (KBr): 3075 (w),
2930, 1662 (s), 1600 (s), 1573, 1509, 1321, 1260, 1190,
1169 (s), 1038, 846 cm–1. 1H NMR (400 MHz, CDCl3): δ =
1.42 (t, J = 7 Hz, 6 H, 2 × CH3), 1.76–1.90 (m, 4 H,
2 × CH2), 2.16–2.26 (m, 2 H, CH2), 4.07 (q, J = 7 Hz, 4 H,
2 × CH2O), 4.30–4.38 (m, 2 H, 2 × CH), 6.88 (d, J = 9 Hz,
4 H, 4 × CH), 7.97 (d, J = 9 Hz, 4 H, 4 × CH). 13C NMR
(100 MHz, CDCl3): δ = 14.65 (CH3), 26.39 (CH2), 32.28
(CH2), 48.44 (CH), 63.70 (OCH2), 114.14 (CH), 129.30 (C),
130.97 (CH), 162.89 (C), 200.50 (CO). MS (EI, 70 eV): m/z
(%) = 366 (2) [M+], 348 (15), 319 (13), 218 (15), 217 (85)
[M+ – CH3CH2OC6H4CO], 150 (15), 149 (100)
[CH3CH2OC6H4CO], 121 (55) [CH3CH2OC6H4], 93 (13), 65
(8). HRMS: m/z [M+] calcd for C23H26O4: 366.1831; found:
366.1824.
Cyclopentane-1,2-diylbis[(4-fluorophenyl)methanone]
(2f): Yield: 1.05 g (67%); colorless, fine cubic crystals; mp
84–86 °C (MeOH); Rf = 0.69 (CH2Cl2). IR (KBr): 3060 (w),
2960, 1672 (s), 1596 (s), 1504, 1320, 1303, 1231 (s), 1205,
1150, 1007, 853 cm–1. 1H NMR (400 MHz, CDCl3): δ =
1.75–1.90 (m, 4 H, 2 × CH2), 2.16–2.31 (m, 2 H, CH2),
4.30–4.39 (m, 2 H, 2 × CH), 7.06–7.16 (m, 4 H, 4 × CH),
7.99–8.07 (m, 4 H, 4 × CH). 13C NMR (100 MHz, CDCl3):
δ = 26.29 (CH2), 32.08 (CH2), 48.70 (CH), 115.74 (d,
JC–F = 21 Hz, CH), 131.35 (d, JC–F = 10 Hz, CH), 132.80 (d,
J
C–F = 3 Hz, C), 165.79 (d, JC–F = 254 Hz, C), 200.09 (CO).
MS (EI, 70 eV): m/z (%) = 314 (3) [M+], 192 (21), 191 (76)
[M+ – FC6H4CO], 164 (7), 124 (22), 123 (100) [FC6H4CO],
96 (7), 95 (54) [FC6H4], 75 (19), 67 (9). HRMS: m/z [M+]
calcd for C19H16O2F2: 314.1118; found: 314.1167.
Cyclopentane-1,2-diylbis[(4-chlorophenyl)methanone]
(2g): Yield: 1.12 g (64%); colorless, fine needle-like
crystals; mp 97–99 °C (MeOH); Rf = 0.75 (CH2Cl2). IR
(KBr): 3062 (w), 2950, 1666 (s), 1588 (s), 1568, 1400, 1331,
1211 (s), 1089, 1005, 848, 839 cm–1. 1H NMR (400 MHz,
CDCl3): δ = 1.76–1.88 (m, 4 H, 2 × CH2), 2.16–2.30 (m,
2 H, CH2), 4.30–4.38 (m, 2 H, 2 × CH), 7.42 (d, J = 9 Hz,
4 H, 4 × CH), 7.93 (d, J = 9 Hz, 4 H, 4 × CH). 13C NMR
(100 MHz, CDCl3): δ = 26.24 (CH2), 31.98 (CH2), 48.66
(CH), 128.93 (CH), 130.09 (CH), 134.63 (C), 139.60 (C),
200.33 (CO). MS (EI, 70 eV): m/z (%) = 350 (< 1) [M+,
37Cl2], 348 (2) [M+, 37Cl, 35Cl], 346 (3) [M+, 35Cl2], 209 (32)
[M+ – ClC6H4CO], 208 (15), 207 (83) [M+ – ClC6H4CO],
141 (35) [37ClC6H4CO], 140 (12), 139 (100) [35ClC6H4CO],
113 (12) [37ClC6H4], 111 (35) [35ClC6H4]. HRMS: m/z [M+]
calcd for C19H16O237Cl2: 350.0468; found: 350.0462.
HRMS: m/z [M+] calcd for C19H16O235Cl/37Cl: 348.0498;
found: 348.0438. HRMS: m/z [M+] calcd for C19H16O235Cl2:
346.0527; found: 346.0577.
Cyclopentane-1,2-diylbis[(4-bromophenyl)methanone]
(2h): Yield: 1.51 g (69%); colorless, fine needle-like
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2544–2548

2548
M. Okimoto et al.
LETTER
viscous oily liquid; bp 206–208 °C/1.2 mbar; Rf = 0.72
crystals; mp 107–109 °C (MeOH); Rf = 0.75 (CH2Cl2). IR
(KBr): 3069 (w), 2946, 1666 (s), 1584 (s), 1565, 1397, 1330,
1210 (s), 1068, 1004, 844, 837 cm–1. 1H NMR (400 MHz,
CDCl3): δ= 1.73–1.87 (m, 4 H, 2 × CH2), 2.16–2.30 (m, 2 H,
CH2), 4.30–4.37 (m, 2 H, 2 × CH), 7.59 (d, J = 9 Hz, 4 H,
4 × CH), 7.86 (d, J = 9 Hz, 4 H, 4 × CH). 13C NMR (100
MHz, CDCl3): δ= 26.22 (CH2), 31.94 (CH2), 48.59 (CH),
128.36 (C), 130.18 (CH), 131.91 (CH), 134.98 (C), 200.51
(CO). MS (EI, 70 eV): m/z (%) = 438 (1) [M+, 81Br2], 436 (2)
[M+, 81Br, 79Br], 434 (1) [M+, 79Br2], 253 (89) [M+ –
BrC6H4CO], 251 (90) [M+ – BrC6H4CO], 185 (99)
[81BrC6H4CO], 183 (100) [79BrC6H4CO], 157 (32)
[81BrC6H4], 155 (31) [79BrC6H4], 76 (11). HRMS: m/z [M+]
calcd for C19H16O281Br2: 437.9476; found: 437.9411.
HRMS: m/z [M+] calcd for C19H16O281Br/79Br: 435.9497;
found: 435.9491. HRMS: m/z [M+] calcd for C19H16O279Br2:
433.9517; found: 433.9495.
(CH2Cl2). IR (neat): 3020 (w), 2959 (s), 2926, 1678, 1495,
1449, 1294, 1244, 1169, 1006, 817 cm–1. 1H NMR (400
MHz, CDCl3): δ = 1.71–1.84 (m, 4 H, 2 × CH2), 2.02–2.14
(m, 2 H, CH2), 2.32 (s, 6 H, 2 × CH3), 2.38 (s, 6 H, 2 × CH3),
4.16–4.25 (m, 2 H, 2 × CH), 7.03–7.17 (m, 4 H, 4 × CH),
7.36–7.41 (m, 2 H, 2 × CH). 13C NMR (100 MHz, CDCl3):
δ = 20.45 (CH3), 20.91 (CH3), 26.02 (CH2), 31.14 (CH2),
51.62 (CH), 128.96 (CH), 131.53 (CH), 131.71 (CH), 134.63
(C), 135.19 (C), 138.08 (C), 206.06 (CO). MS (EI, 70 eV):
m/z (%) = 334 (7) [M+], 265 (12), 201 (36) [M+ –
(CH3)2C6H3CO], 134 (24), 133 (100) [(CH3)2C6H3CO], 105
(44) [(CH3)2C6H3], 103 (19), 95 (7), 79 (24), 77 (22).
HRMS: m/z [M+] calcd for C23H26O2: 334.1933; found:
334.1904
(6) Fuson, R. C.; Walker, J. T. Org. Synth. Coll. Vol. II; John
Wiley & Sons: New York, 1943, 169.
Cyclopentane-1,2-diylbis[(2,5-dimethylphenyl)-
methanone] (2i): Yield: 1.09 g (65%); slightly yellowish
Synlett 2012, 23, 2544–2548
© Georg Thieme Verlag Stuttgart · New York

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