Anodic cyclization of dimethyl 2-(5-aryl-5-oxopentyl)malonates into the corresponding dimethyl 2-aroylcyclopentane-1,1-dicarboxylates

Article abstract of DOI:10.1016/j.tetlet.2013.12.104

A wide range of dimethyl 2-(5-aryl-5-oxopentyl)malonates was electrooxidized in methanol, in the presence of catalytic amount of potassium iodide, to give the corresponding dimethyl 2-aroylcyclopentane-1,1- dicarboxylates in high yields. The reactions were carried out under extremely mild reaction conditions, in which the optimal amount of electrolytic current ranged from 2.24 to 2.35 Fmol^-1. The reaction presumably proceeded via a two-electron oxidation process, in which iodide ions played an important role as the electron carrier between the anode and the substrate.

Full text of DOI:10.1016/j.tetlet.2013.12.104

Tetrahedron Letters 55 (2014) 1299–1302
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Tetrahedron Letters
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Anodic cyclization of dimethyl 2-(5-aryl-5-oxopentyl)malonates into
the corresponding dimethyl 2-aroylcyclopentane-1,1-dicarboxylates
⇑
Mitsuhiro Okimoto , Haruki Yamamori, Masayuki Hoshi, Takashi Yoshida
Department of Biotechnology and Environmental Chemistry, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A wide range of dimethyl 2-(5-aryl-5-oxopentyl)malonates was electrooxidized in methanol, in the pres-
ence of catalytic amount of potassium iodide, to give the corresponding dimethyl 2-aroylcyclopentane-
1,1-dicarboxylates in high yields.
The reactions were carried out under extremely mild reaction conditions, in which the optimal amount
of electrolytic current ranged from 2.24 to 2.35 Fmolꢀ1. The reaction presumably proceeded via a two-
electron oxidation process, in which iodide ions played an important role as the electron carrier between
the anode and the substrate.
Received 18 October 2013
Revised 17 December 2013
Accepted 25 December 2013
Available online 3 January 2014
Keywords:
Electrooxidation
Electron transfer
Cyclization
Ó 2014 Elsevier Ltd. All rights reserved.
Ring closure
Carbon–carbon bond formation
The formation of carbon–carbon bonds, which is essential in the
syntheses of organic compounds, typically involves well-known
classical chemical reactions. In certain cases, however, carbon–car-
bon bond formation can be effectively achieved via electrooxida-
tion,1–3 which is typically carried out under very mild reaction
conditions (rt and atmospheric pressure), and without the use of
special and often harsh chemical reagents. Previously, we reported
on the successful electrooxidative synthesis of 1,2-diaroyl cyclo-
propane derivatives (Scheme 1, II, R1, R2 = Aryl, R3, R4 = H, n = 1)4
and 1,2-diaroyl cyclopentane derivatives (Scheme 1, II, R1,
R2 = Aryl, R3, R4 = H, n = 3)5 via intramolecular formation of
carbon–carbon bonds, involving iodide ions as the electron carrier.
Unfortunately, however, attempts to form the four-, six-, seven-,
or eight-membered ring versions of the 1,2-diaroyl compounds
(Scheme 1, II, R1, R2 = Aryl, R3, R4 = H, n = 2, 4, 5, or 6) using similar
electrooxidative methods proved to be unsuccessful. Interestingly,
Nikishin and co-workers have reported on the electrochemical
formation of tetramethyl cyclopropane-1,1,2,2-tetracarboxylate
derivatives starting from propyl compounds that possess two
dimethyl malonate moieties at the terminal carbons (Scheme 1, I,
R1, R2 = OCH3, R3, R4 = COOCH3, n = 1).6 Recently, in continuation
of our investigations, we were successful in converting dimethyl
2-(3-aryl-3-oxopropyl)malonates to the corresponding cyclized
dimethyl 2-aroylcyclopropane-1,1-dicarboxylates via intramolecu-
lar cyclization.7 Consequently, we reasoned that cyclopentane
derivatives can be similarly constructed from the correspond-
ing pentyl substrates (Scheme 1, I, R1 = Aryl, R2 = OCH3, R3 = H, R4 -
= COOCH3, n = 3). Although the synthesis of cyclopentane
derivatives using electrochemical means have been previously
reported,2f the electrooxidative formation of dimethyl 2-aroylcycl-
opentane-1,1-dicarboxylates (2) starting from dimethyl 2-(5-aryl-
5-oxopentyl)malonates (1), to the best of our knowledge, has yet
to be described. The cyclizations described herein significantly
differ from those of our previous reports for the following reasons:
(i) the optimal amount of KI was 3 mmol (0.6 equiv, substrate
5 mmol), whereas 5 mmol (1.0 equiv, substrate 5 mmol) was required
for the previous electrooxidations, (ii) the addition of a base, which
was essential for the previous electrooxidations, was unnecessary
for the present reactions, and (iii) the use of a glass filter as the
partition between the anolyte and catholyte, which was essential
in maximizing the yield for the previous electrooxidations, was
not required; in other words, an undivided cell was acceptable.
First, the optimal reaction conditions for the anodic cyclization
in methanol were investigated using dimethyl 2-(5-oxo-5-phenyl-
pentyl)malonate (1a, Aryl = C6H5) as the model substrate, with the
⇑
Corresponding author. Tel.: +81 (0157)26 9394; fax: +81 (0157)24 7719.
E-mail address: okimotmt@mail.kitami-it.ac.jp (M. Okimoto).
Scheme 1. Anodic cyclization of alkyl compounds that possess terminal carbonyl
groups.
0040-4039/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.12.104

1300
M. Okimoto et al. / Tetrahedron Letters 55 (2014) 1299–1302
Table 1
Effects of mediators and electrolytes on the yield of 2aa
Entry
Mediator (mmol)
Electrolyte (mmol)
Yield of 2ab (%)
Recovery of 1ab (%)
1c
2c
3d
4
5
6
7
8
9
10
None
KI–2
KI–3
KI–3
KI–5
KI–5
KI–5
KI–5
KCl–5
KBr–5
NaOMe–2
None
None
None
None
NaOMe–2
NaOMe–5
NaClO4–2
None
0
9 2
9 6
8 9
9 0
4 9
2 3
8 6
1 4
5 2
78
0
0
0
0
0
0
0
0
None
2 7
a
Reaction conditions: Substrate 1a (5 mmol), MeOH (40 mL), Constant current (0.3 A), Current passed (2.30 Fmolꢀ1), Temperature (ca. 15 °C), Anode (Pt net), Cathode (Ni
coil). Glass filter was used except for entry 3.
b
Determined using GC analysis.
Terminal voltage of the electrolytic cell tended to increase over 15 V.
Filter was not used.
c
d
passage of 2.30 Fmolꢀ1 of electricity, using various combinations of
mediators and supporting electrolytes (bases and/or neutral salts)
as listed in Table 1, for the formation of dimethyl 2-benzoylcycl-
opentane-1,1-dicarboxylate (2a8, Aryl = C6H5). Although the pres-
ence of NaOMe without KI was ineffective (0%, entry 1), in which
most of the substrate was recovered, the presence of KI without
NaOMe (0.4, 0.6, 0.6, and 1.0 equiv to substrate 1a) afforded high
yields of 2a (92%, 96%, 89%, and 90%, respectively; entries 2–5).
Unexpectedly, the presence of both KI (1.0 equiv) and NaOMe
(0.4 and 1.0 equiv; entries 6 and 7) was not very effective, and
afforded the products in low yields of 49% and 23%, respectively.
However, the combination of KI and neutral salt such as NaClO4
(0.4 equiv) proved to be very effective (86%, entry 8). Substitution
of KI with KCl or KBr resulted in lowered yields of 2a (14% and 52%,
respectively; entries 9 and 10); in the case of KCl, the reaction pro-
ceeded until substrate 1a was completely consumed, resulting in
the formation of not only product 2a but also various unidentifi-
able byproducts (detected by GC analysis).
Table 2
Electrochemical formation of cyclopentane derivativesa
1
Aryl
Isolated yield of 2 (%)
1a
1b
1c
1d
1e
1f
1g
1h
1i
C6H5
4-MeC6H4
8 9
8 7
8 1
8 0
8 8
8 0
9 1
8 1
7 8
4-MeOC6H4
4-ClC6H4
2-MeO-5-MeC6H3
2-MeO-5-MeOC6H3
2-MeO-5-ClC6H3
2-Furyl
3-Thienyl
a
Substrate 1 (5 mmol), KI (3 mmol), MeOH (40 mL), Constant current (0.3 A),
Current passed (2.24 Fmolꢀ1), except for 1f (2.35 Fmolꢀ1) and 1g (2.29 Fmolꢀ1), rt
ca.15 °C, Anode (Pt net), Cathode (Ni coil). Filter was not used.
The maximum yield (96%) was obtained when the electrooxida-
tion was carried out in the presence of only KI (0.6 equiv to sub-
strate, entry 3) using an undivided cell (without filter),
corresponding to a current efficiency of 77%. The yield of 2a was
not significantly affected by the amount of KI (2.0–5.0 mmol), the
reaction temperature (5–35 °C), or the constant current (0.2–0.4
A) under the undivided cell (without filter) conditions.
Based on the above optimal reaction conditions, the electroox-
idations of dimethyl 2-(5-aryl-5-oxopentyl)malonates 1b–i were
carried out, and the results are listed in Table 2.9 During the course
of the electrooxidations, the progress of the reaction was moni-
tored by analyzing the composition of the reaction mixture using
GC or silica-gel TLC analysis. Upon passage of 2.24 Fmolꢀ1 of the
electrolytic current, with the exception of 1f (2.35 Fmolꢀ1) and
1g (2.29 Fmolꢀ1), the corresponding cyclopentane derivatives 2b–
i were isolated in good to high yields (78–91%). It is interesting
to note that substituent effects were not observed; substituents
on the benzene ring, whether electron-withdrawing (1d) or
-donating (1c and 1f), did not significantly affect the reaction.
The cyclization could be applied to substrates that possess hetero
aromatic moiety such as 1h and 1i.
ingly, a plausible reaction mechanism featuring the iodide ions is
presented in Scheme 2. Substrate 1a would undergo keto–enol tau-
tomerism and result in the formation of anion 1a0 due to the reac-
tion with a base formed at the cathode even in the absence of any
bases as electrolytes. As a note, a filter was not used between the
anode and the cathode for the electrooxidations. Next, anion 1a0
would undergo a one-electron oxidation involving an iodonium
ion which was generated by a two-electron oxidation of iodide
ion at the anode to form radical 1a00 that would then attack the in-
tra-molecular double bond of the keto-enol moiety. The resulting
radical 1a000 would undergo further a one-electron oxidation involv-
ing iodonium ion to produce cation 1a0000 that would afford the de-
sired cyclized product 2a upon deprotonation. Essentially,
substrate 1a loses two electrons and two protons during the for-
mation of product 2a. Our results show that, although the reaction
does require the presence of a base, the use of excess amounts of
base would decrease the efficiency of the reaction with decreased
yields. Interestingly, but unfortunately, our electrooxidative cycli-
zation was ineffective in the formation of the corresponding
four-, six-, seven-, and eight-membered ring compounds; such at-
tempts resulted in the formation of unidentifiable tar-like prod-
ucts. We are currently investigating the electrochemical
Although the details of the reaction mechanism remain unclear,
the iodide ions undoubtedly play an important role as electron car-
riers during the indirect electrooxidation process (Table 1). Accord-

M. Okimoto et al. / Tetrahedron Letters 55 (2014) 1299–1302
1301
Scheme 2. Plausible reaction pathway for the anodic formation of the cyclopentane derivatives.
T. L.; Nikishin, G. I. Tetrahedron 2000, 56, 3063–3069; (e) Elison, M. N.;
Feducovich, S. K.; Nikishin, G. I. Arkivoc 2001, 31–36.
7. Okimoto, M.; Yamamori, H.; Ohashi, K.; Hoshi, M.; Yoshida, T. Synlett 2013,
1568–1571.
formation of cyclopropane and cyclopentane derivatives that
possess b-dicarbonyl compounds, such as methyl acetoacetate,
acetylacetone, and dibenzoylmethane.
8. Okuro, K.; Alper, H. J. Org. Chem. 1996, 61, 5312–5315.
In conclusion, the synthesis of dimethyl 2-aroylcyclopentane-
9. General procedures: 1-aryl-1-oxo-5-bromopentanes were prepared via typical
Friedel–Crafts acylation,10 using commercially available 5-bromopentanoyl
chloride and aromatic compounds in the presence of AlCl3 or SnCl4 at below
50 °C. Dimethyl 2-(5-aryl-5-oxopentyl)malonates 1 were prepared by refluxing
the corresponding 1-aryl-1-oxo-5-bromopentanes and dimethyl malonate
with excess amount (1.2 equiv) of NaOMe in methanol for ca. 2 h.11 Melting
points of the substrates were 1a: 54–56 °C, 1b: 47–49 °C, 1c: 53–55 °C, 1d: 51–
53 °C, 1e: 50–52 °C, 1f: 22–25 °C, 1g: 33–35 °C, 1h: 52–54 °C and 1i: 46–48 °C,
respectively.
1,1-dicarboxylate
2 via electrooxidative intramolecular ring-
formation was successfully carried out in a high yield, under very
mild reaction conditions at rt, and in the absence of any harsh
oxidants and/or special reagents.
References and notes
Preparative-scale electrooxidations were carried out in a tall 50-mL beaker
equipped with a nickel coil cathode, along with a cylindrical platinum net
anode (height: 35 mm, diameter: 30 mm, 50 mesh) without the use of any
1. For example see: (a) Andreades, S.; Zahnow, E. W. J. Am. Chem. Soc. 1969, 91,
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Org. Chem. 1996, 61, 3191–3194; (m) Mizuno, K.; Ichinose, N.; Otsuji, Y. J. Org.
Chem. 1992, 57, 1855–1860; (n) Shundo, R.; Nishiguch, I.; Matsubara, Y.;
Hirashima, T. Tetrahedron 1991, 47, 831–840; (o) Chiba, K.; Arakawa, T.; Tada,
M. Chem. Commun. 1996, 1763–1764; (p) Chiba, K.; Jinno, M.; Nozaki, A.; Tada,
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Yoshida, J. J. Am. Chem. Soc. 2000, 122, 10244–10245; (s) Yoshida, J.; Suga, S.;
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9546–9549; (t) Matsumoto, K.; Fuji, S.; Ueoka, K.; Suga, S.; Yoshida, J. Angew.
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Onomura, O. Org. Biomol. Chem. 2009, 7, 351–356.
partition such as glass filter. Typical procedures:
a solution of 1a (1.46 g,
5 mmol) in methanol (40 mL) and containing KI (0.50 g, 3.0 mmol) was
electrooxidized under a constant current (0.3 A) at ca. 15 °C with magnetic
stirring. During the course of the electrooxidation, the composition of the
reaction mixture was monitored using GC (SE-30, 0.5 m) and/or TLC analyses.
Passage of the electric current was maintained until the formation of the
product was no longer detected. The reaction mixture was concentrated in
vacuo at approximately 60 °C to near dryness. The resulting residue was
treated with brine (ca. 40 mL), then extracted with diethyl ether three times
(60, 50, 40 mL). The combined ether solution was washed with sodium
thiosulfate aqueous solution (20 wt%, 30 mL), and dried overnight over sodium
sulfate. After removal of the solvent in vacuo, the crude product was purified
using silica-gel column chromatography (height, 200 mm; diameter, 15 mm)
with dichloromethane as the eluent to afford product 2a as a viscous oil (1.29 g,
89%). Products were solidified after the column chromatography purification in
the cases of 2e, 2f, and 2g. The electrooxidation products were characterized
using IR, 1H and 13C NMR, and high-resolution MS.
Dimethyl 2-benzoylcyclopentane-1,1-dicarboxylate (2a9): Yield: 1.29 g (89%);
Viscous oily liquid; Rf = 0.58 (Silica-gel, Diethyl ether:n-Hexane = 2:1). IR
(neat): 2954, 1738 (vs), 1732 (vs), 1682 (vs), 1448 (s), 1434 (s), 1266 (vs),
1157, 1090, 702 cmꢀ1 1H NMR (400 MHz, CDCl3): d = 1.64–1.75 (m, 1H,
.
0.5 ꢁ CH2), 1.83–1.98 (m, 2H, CH2), 2.24–2.34 (m, 2H, CH2), 2.65–2.74 (m, 1H,
0.5 ꢁ CH2), 3.56 (s, 3H, OCH3), 3.75 (s, 3H, OCH3), 4.70 (dd, J = 8.9 Hz, J = 4.6 Hz,
1H, CH), 7.40–7.58 (m, 3H, Arom), 7.95–8.03 (m, 2H, Arom). 13C NMR
(100 MHz, CDCl3): d = 23.60 (CH2), 30.86 (CH2), 34.11(CH2), 51.93 (OCH3),
52.33 (OCH3), 53.07 (CH), 63.91 (C), 128.60 (CH), 128.66 (CH), 133.17 (CH),
136.13 (C), 170.76 (CO), 172.33 (CO), 200.51 (CO). MS (EI, 70 eV): m/z (relative
intensity %) = 290 [M+] (1), 259 [M+ꢀOCH3] (34), 236 (12), 199 (86), 198 (35),
153 (15), 137 (25), 126 (70), 105 [C6H5CO] (100), 77 [C6H5] (49). HRMS: m/z
[M+] calcd for C16H18O5: 290.1154; found: 290.1159. Anal. Calcd for C16H18O5
(290.30): C, 66.19; H, 6.25. Found: C, 66.28; H, 6.39.
2. Reports from our laboratory: (a) Chiba, T.; Okimoto, M. J. Org. Chem. 1992, 57,
1375–1379; (b) Chiba, T.; Okimoto, M. Chem. Lett. 1993, 22, 521–524; (c) Chiba,
T.; Okimoto, M.; Nagai, H.; Takata, Y. J. Org. Chem. 1979, 44, 3519–3523; (d)
Okimoto, M.; Chiba, T. J. Org. Chem. 1990, 55, 1070–1076; (e) Okimoto, M.;
Yoshida, T.; Hoshi, M.; Hattori, K.; Komata, M.; Numata, K.; Tomozawa, K.
Synlett 2006, 1753–1755; (f) Okimoto, M.; Takahashi, Y. Synthesis 2002, 2215–
2219; (g) Okimoto, M.; Numata, K.; Takahashi, Y.; Hoshi, M.; Tomozawa, K.;
Shigemoto, T. Synlett 2005, 2507–2509.
3. As some general references on the review of the electroorganic chemistry: (a)
Moeller, K. D. Tetrahedron 2000, 56, 9527–9554; (b) Lund, H. J. Electrochem. Soc.
2002, 149, S21–S33; (c) Sperry, J. B.; Wright, D. L. Chem. Soc. Rev. 2006, 35, 605–
621; (d) Yoshida, J.; Kataoka, K.; Horcajada, R.; Nagai, A. Chem. Rev. 2008, 108,
2265–2299.
4. Okimoto, M.; Takahashi, Y.; Kakuchi, T. Bull. Chem. Soc. Jpn. 2003, 76, 207–208.
5. Okimoto, M.; Yamamori, H.; Ohashi, K.; Nishikawa, S.; Hoshi, M.; Yoshida, T.
Synlett 2012, 2544–2548.
6. (a) Elinson, M. N.; Feducovich, S. K.; Bushuev, S. G.; Zakharenkov, A. A.;
Pashchenko, D. V.; Nikishin, G. I. Mendeleev Commun. 1998, 8, 15–16; (b)
Elinson, M. N.; Feducovich, S. K.; Starikova, Z. A.; Olessova, O. S.; Vereshchagin,
A. N.; Nikishin, G. I. Tetrahedron Lett. 2000, 41, 4937–4941; (c) Elinson, M. N.;
Fedukovich, S. K.; Zaimovskaya, T. A.; Vereshchagin, A. N.; Nikishin, G. I. Russ.
Chem. Bull. 2003, 52, 2241–2246; (d) Elinson, M. N.; Feducovich, S. K.; Lizunova,
Dimethyl 2-(4-methylbenzoyl)cyclopentane-1,1-dicarboxylate (2b): Yield: 1.32 g
(87%); Viscous oily liquid; Rf = 0.60 (Silica-gel, Diethyl ether: n-Hexane = 2:1).
IR (neat): 2953, 1738 (vs), 1732 (vs), 1682 (vs), 1607, 1454, 1434 (s), 1267 (vs),
1155, 1089 cmꢀ1
.
1H NMR (400 MHz, CDCl3): d = 1.62–1.75 (m, 1H, 0.5 ꢁ CH2),
1.82–1.97 (m, 2H, CH2), 2.20–2.33 (m, 2H, CH2), 2.65–2.74 (m, 1H, 0.5 ꢁ CH2),
2.41 (s, 3H, CH3), 3.56 (s, 3H, OCH3), 3.72 (s, 3H, OCH3), 4.67 (dd, J = 8.9 Hz,
J = 4.6 Hz, 1H, CH), 7.24–7.30 (m, 2H, Arom), 7.87–7.92 (m, 2H, Arom). 13C NMR
(100 MHz, CDCl3): d = 21.64 (CH3), 23.57 (CH2), 30.96 (CH2), 34.14 (CH2), 51.84
(OCH3), 52.32 (OCH3), 53.04 (CH), 63.88 (C), 128.81 (CH), 129.28 (C), 133.63
(CH), 143.99 (C), 170.83 (CO), 172.43 (CO), 200.12 (CO). MS (EI, 70 eV): m/z
(relative intensity %) = 304 [M+] (3), 273 [M+ꢀOCH3] (8), 245 [M+ꢀCO2CH3] (5),
213 (16), 112 (6), 185 (6), 120 (22), 119 [CH3C6H4CO] (100), 91 [CH3C6H4] (38),
65 (11). HRMS: m/z [M+] calcd for C17H20O5: 304.1311; found: 304.1300. Anal.
Calcd for C17H20O5 (304.33): C, 67.09; H, 6.62. Found: C, 67.00; H, 6.48.

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M. Okimoto et al. / Tetrahedron Letters 55 (2014) 1299–1302
Dimethyl 2-(4-methoxybenzoyl)cyclopentane-1,1-dicarboxylate (2c): Yield: 1.30 g
(81 %); Viscous oily liquid; Rf = 0.45 (Silica-gel, Diethyl ether : n-Hexane = 2:1).
(CH), 127.88 (C), 152.92 (C), 153.46 (C), 171.24 (CO), 172.47 (CO), 202.10 (CO).
MS (EI, 70 eV): m/z (relative intensity %) = 350 [M+] (11), 252 (20), 236 (17),
219 (13), 166 (20), 165 [CH3O, CH3OC6H3CO] (100), 150 (9), 107 (12), 77 (13),
44 (14). HRMS: m/z [M+] calcd for C18H22O7: 350.1366; found: 350.1327. Anal.
Calcd for C18H22O7 (350.36): C, 61.70; H, 6.33. Found: C, 61.55; H, 6.19.
Dimethyl 2-(2-methoxy-5-chlorobenzoyl)cyclopentane-1,1-dicarboxylate (2g):
Yield: 1.63 g (91 %); White powder, mp 75–77 °C, Rf = 0.46 (Silica-gel, Diethyl
ether: n-Hexane = 2:1). IR (KBr): 2953, 1738 (vs), 1732 (vs), 1680 (s), 1485 (vs),
IR (neat): 2954, 1738 (s), 1732 (s), 1674 (s), 1601 (vs), 1574, 1512, 1435, 1258
(vs), 1171 cmꢀ1
.
1H NMR (400 MHz, CDCl3): d = 1.62–1.75 (m, 1H, 0.5 ꢁ CH2),
1.84–1.96 (m, 2H, CH2), 2.20–2.31 (m, 2H, CH2), 2.65–2.74 (m, 1H, 0.5 ꢁ CH2),
3.56 (s, 3H, OCH3), 3.75 (s, 3H, OCH3), 3.87 (s, 3H, OCH3), 4.65 (dd, J = 8.9 Hz,
J = 4.6 Hz, 1H, CH), 6.94 (d, J = 12 Hz, 2H, Arom), 7.98 (d, J = 12 Hz, 2H, Arom).
13C NMR (100 MHz, CDCl3): d = 23.62 (CH2), 31.04 (CH2), 34.17(CH2), 51.60
(OCH3), 52.30 (OCH3), 53.03 (CH), 55.47 (OCH3), 63.93 (C), 113.75 (CH), 129.13
(C), 131.00 (CH), 163.58 (C), 170.86 (CO), 172.48 (CO), 199.03 (CO). MS (EI,
70 eV): m/z (relative intensity%) = 320 [M+] (9), 289 [M+ꢀOCH3] (13), 247 (7),
229 (21), 163 (7), 136 (36), 135 [CH3OC6H4CO] (100), 107 [CH3OC6H4] (19), 92
(18), 77 (24). HRMS: m/z [M+] calcd for C17H20O6: 320.1260; found: 320.1221.
Anal. Calcd for C17H20O6 (320.33): C, 63.74; H, 6.29. Found: C, 63.58; H, 6.42.
Dimethyl 2-(4-chlorobenzoyl)cyclopentane-1,1-dicarboxylate (2d): Yield: 1.30 g
(80 %); Viscous oily liquid, Rf = 0.64 (Silica-gel, Diethyl ether : n-Hexane = 2:1).
IR (neat): 2955, 1738 (vs), 1732 (vs), 1683 (s), 1590, 1435, 1266 (vs), 1157,
1463, 1435, 1270 (vs), 1178, 1021 cmꢀ1 1H NMR (400 MHz, CDCl3): d = 1.62–
.
1.76 (m, 1H, 0.5 ꢁ CH2), 1.78–1.97 (m, 2H, CH2), 2.15–2.27 (m, 2H, CH2), 2.58–
2.69 (m, 1H, 0.5 ꢁ CH2), 3.64 (s, 3H, OCH3), 3.72 (s, 3H, OCH3), 3.91 (s, 3H,
OCH3), 4.61 (dd, J = 8.9 Hz, J = 4.6 Hz, 1H, CH), 6.91 (d, J = 8.9 Hz, 1H, Arom),
7.37–7.58 (m, 2H, Arom). 13C NMR (100 MHz, CDCl3): d = 23.10 (CH2), 29.88
(CH2), 34.34 (CH2), 52.40 (OCH3), 52.90 (OCH3), 56.03 (OCH3), 56.69 (CH), 63.95
(C), 113.12 (CH), 125.94 (C), 129.12 (C), 130.25 (CH), 132.94 (CH), 156.81 (C),
171.02 (CO), 172.29 (CO), 201.44. (CO). MS (EI, 70 eV): m/z (relative intensity
%) = 356 [M+, 37Cl] (2), 354 [M+, 35Cl] (6), 325 [M+, 37Cl- OCH3] (2), 323 [M+, 35Cl-
OCH3] (6), 265 (5), 263 (15), 171 [CH3O, 37ClC6H3CO], (83), 170 (31), 169 [CH3O,
35ClC6H3CO] (100), 128 (8), 126 (24), 113 (8), 111 (24), 59 [CO2CH3], (11).
HRMS: m/z [M+] calcd for C17H1935ClO6: 354.0870; found: 354.0818. HRMS: m/
z [M+] calcd for C17H1937ClO6: 356.0841; found: 356.0879. Anal. Calcd for
1092 (s), 1012 cmꢀ1 1H NMR (400 MHz, CDCl3): d = 1.63–1.76 (m, 1H,
.
0.5 ꢁ CH2), 1.83–1.96 (m, 2H, CH2), 2.18–2.31 (m, 2H, CH2), 2.62–2.73 (m,
1H, 0.5 ꢁ CH2), 3.56 (s, 3H, OCH3), 3.76 (s, 3H, OCH3), 4.63 (dd, J = 8.0 Hz,
J = 4.6 Hz, 1H, CH), 7.44 (d, J = 9.0 Hz, 2H, Arom), 7.94 (d, J = 9.0 Hz, 2H, Arom).
13C NMR (100 MHz, CDCl3): d = 23.66 (CH2), 30.79 (CH2), 34.16(CH2), 51.79
(OCH3), 52.39 (OCH3), 53.11 (CH), 64.03 (C), 128.92 (CH), 130.10 (CH), 134.57
(C), 139.66 (C), 170.61 (CO), 172.25 (CO), 199.43 (CO). MS (EI, 70 eV): m/z
(relative intensity%) = 326 [M+, 37Cl] (1), 324 [M+, 35Cl] (3), 295 [M+, 37ClꢀOCH3]
(9), 293 [M+, 35ClꢀOCH3] (27), 265 (20), 251 (20), 233 (56), 232 (20), 185 (33),
141 [37ClC6H4CO] (77), 140 (42), 139 [35ClC6H4CO] (100), 113 [37ClC6H4] (33),
111 [35ClC6H4] (71), 75 (31), 59 [CO2CH3] (25). HRMS: m/z [M+] calcd for
C17H19ClO6 (354.78): C, 57.55; H, 5.40. Found: C, 57.71; H, 5.63.
Dimethyl 2-(furan-2-carbonyl)cyclopentane-1,1-dicarboxylate (2h): Yield: 1.13 g
(81 %); Viscous oily liquid; Rf = 0.40 (Silica-gel, Diethyl ether: n-Hexane = 2:1).
IR (neat): 2955, 1738 (vs), 1732 (vs), 1682 (vs), 1568, 1470 (s), 1268 (s), 1158,
1088, 770 cmꢀ1
.
1H NMR (400 MHz, CDCl3): d = 1.63–1.78 (m, 1H, 0.5 ꢁ CH2),
1.87–2.03 (m, 2H, CH2), 2.16–2.29 (m, 2H, CH2), 2.60–2.72 (m, 1H, 0.5 ꢁ CH2),
3.60 (s, 3H, OCH3), 3.75 (s, 3H, OCH3), 4.45 (dd, J = 8.9 Hz, J = 4.6 Hz, 1H, CH),
6.55–6.57 (m, 1H, Arom), 7.27–7.30 (m, 1H, Arom), 7.61–7.63 (m, 1H, Arom).
13C NMR (100 MHz, CDCl3): d = 23.69 (CH2), 30.65 (CH2), 34.31 (CH2), 52.15
(OCH3), 52.49 (OCH3), 53.06 (C), 63.73 (CH), 112.33 (CH), 118.27 (CH), 146.86
(CH), 152.05 (C), 170.57 (CO), 172.20 (CO), 189.14 (CO). MS (EI, 70 eV): m/z
(relative intensity %) = 280 [M+] (8), 249 [M+- OCH3] (26), 239 (27), 221
[M+ꢀCO2CH3] (26), 207 (46), 189 (37), 158 (21), 123 (21), 95 [C4H3OCO] (100),
67 [C4H3O] (26). HRMS: m/z [M+] calcd for C14H16O6: 280.0947; found:
280.0963. Anal. Calcd for C14H16O6 (280.27): C, 59.99; H, 5.75. Found: C, 59.68;
H, 5.63.
C
C
16H1735ClO5: 324.0764; found: 324.0725. HRMS: m/z [M+] calcd for
16H1737ClO5: 326.0735; found: 326.0717. Anal. Calcd for C16H17ClO5
(324.76): C, 59.17; H, 5.28. Found: C, 66.30; H, 5.08.
Dimethyl 2-(2-methoxy-5-methylbenzoyl)cyclopentane-1,1-dicarboxylate (2e):
Yield: 1.47 g (88 %); White powder, mp 65–67 °C. Rf = 0.45 (Silica-gel, Diethyl
ether : n-Hexane = 2:1). IR (KBr): 2959, 1759 (s), 1741 (vs), 1667 (s), 1497,
1284, 1255 (vs), 1214, 1179, 1155 cmꢀ1 1H NMR (400 MHz, CDCl3): d = 1.62–
.
1.74 (m, 1H, 0.5 ꢁ CH2), 1.77–1.96 (m, 2H, CH2), 2.17–2.26 (m, 2H, CH2), 2.62–
2.70 (m, 1H, 0.5 ꢁ CH2), 2.29 (s, 3H, CH3), 3.63 (s, 3H, OCH3), 3.72 (s, 3H, OCH3),
3.88 (s, 3H, OCH3), 4.68 (dd, J = 8.8 Hz, J = 4.6 Hz, 1H, CH), 6.85 (d, J = 8.5 Hz, 1H,
Arom), 7.21–7.45 (m, 2H, Arom). 13C NMR (100 MHz, CDCl3): d = 20.26 (CH3),
23.09 (CH2), 30.10 (CH2), 34.28 (CH2), 52.30 (OCH3), 52.83 (OCH3), 55.73
(OCH3), 56.84 (CH), 63.78 (C), 111.65 (CH), 127.39 (C), 129.87 (CH), 131.00 (C),
134.04 (CH), 156.41 (C), 171.23 (CO), 172.51 (CO), 202.67 (CO). MS (EI, 70 eV):
m/z (relative intensity %) = 334 [M+] (7), 303 [M+ꢀOCH3] (6), 243 (10), 236 (7),
219 (5), 150 (34), 149 [CH3, CH3OC6H3CO] (100), 134 (5), 106 (10), 91 (32).
HRMS: m/z [M+] calcd for C18H22O6: 334.1416; found: 334.1386. Anal. Calcd for
Dimethyl 2-(thiophene-3-carbonyl)cyclopentane-1,1-dicarboxylate (2i): Yield:
1.16 g (78 %); Viscous oily liquid
Hexane = 2:1). IR (neat): 2954, 1738 (vs), 1732 (vs), 1660 (s), 1434, 1416 (s),
1266 (s), 1157, 1089, 731 cmꢀ1 1H NMR (400 MHz, CDCl3): d = 1.63–1.76 (m,
; Rf = 0.60 (Silica-gel, Diethyl ether: n-
.
1H, 0.5 ꢁ CH2), 1.88–2.06 (m, 2H, CH2), 2.17–2.30 (m, 2H, CH2), 2.64–2.73 (m,
1H, 0.5 ꢁ CH2), 3.57 (s, 3H, OCH3), 3.75 (s, 3H, OCH3), 4.45 (dd, J = 8.8 Hz,
J = 4.6 Hz, 1H, CH), 7.13–7.17 (m, 1H, Arom), 7.65–7.67 (m, 1H, Arom), 7.81–
7.85 (m, 1H, Arom). 13C NMR (100 MHz, CDCl3): d = 23.83 (CH2), 31.20 (CH2),
34.29 (CH2), 52.43 (OCH3), 52.98 (OCH3), 53.09 (C), 64.09 (CH), 128.22 (CH),
132.75 (CH), 134.21 (CH), 143.80 (C), 170.47 (CO), 172.24 (CO), 193.42 (CO). MS
(EI, 70 eV): m/z (relative intensity %) = 296 [M+] (9), 265 [M+ꢀOCH3] (19), 255
(16), 237 [M+ꢀCO2CH3] (20), 223 (24), 205 (22), 185 [M+ꢀC4H3SCO], 112 (14),
111 [C4H3SCO] (100), 83 [C4H3S] (13). HRMS: m/z [M+] calcd for C14H16O5S:
296.0718; found: 296.0705. Anal. Calcd for C14H16O5S (296.35): C, 56.74; H,
5.44. Found: C, 56.58; H, 5.40.
C
18H22O6 (290.30): C, 64.65; H, 6.63. Found: C, 64.82; H, 6.80.
Dimethyl 2-(2,5-dimethoxybenzoyl)cyclopentane-1,1-dicarboxylate (2f): Yield:
1.40 g (80 %); White powder, mp 64–66 °C. Rf = 0.41 (Silica-gel, Diethyl ether
: n-Hexane = 2:1). IR (neat): 2954, 1738 (vs), 1732 (vs), 1673 (s), 1459 (vs),
1463, 1278 (vs), 1227 (s), 1168 (s), 1040 cmꢀ1 1H NMR (400 MHz, CDCl3):
.
d = 1.61–1.74 (m, 1H, 0.5 ꢁ CH2), 1.75–1.98 (m, 2H, CH2), 2.18–2.40 (m, 2H,
CH2), 2.60–2.72 (m, 1H, 0.5 ꢁ CH2), 3.64 (s, 3H, OCH3), 3.72 (s, 3H, OCH3), 3.78
(s, 3H, OCH3), 3.88 (s, 3H, OCH3), 4.71 (dd, J = 8.0 Hz, J = 4.6 Hz, 1H, CH), 6.91 (d,
J = 8.9 Hz, 1H, Arom), 6.99–7.23 (m, 2H, Arom). 13C NMR (100 MHz, CDCl3):
d = 23.09 (CH2), 30.10 (CH2), 34.30(CH2), 52.32 (OCH3), 52.87 (OCH3), 55.79
(OCH3), 56.23 (OCH3), 56.88 (CH), 63.82 (C), 113.25 (CH), 114.49 (CH), 120.06
10. Fuson, R. C.; Walker, J. T. In Organic Syntheses Collect; John Wiley & Sons: New
York, 1943; Vol. II,; p 169
11. Adams, R.; Kamm, R. M. In Organic Syntheses Collect; John Wiley & Sons: New
York, 1941; Vol. I,; p 250