Synthesis of some cyclopentenones and crystal structure of 4-hydroxy-3,4-bis(4-methoxyphenyl)-5,5-dimethyl-2-cyclopenten-1-one

Article abstract of DOI:10.1007/s00706-009-0177-8

Sodium-hydroxide-catalyzed condensation of di-p-methyl- and di-p-methoxybenzil with acetone derivatives was investigated in methanol. Di- and trisubstituted products were obtained as cyclopentenones, while tetraaryl-substituted systems were isolated as cy

Full text of DOI:10.1007/s00706-009-0177-8

Monatsh Chem (2009) 140:1331–1336
DOI 10.1007/s00706-009-0177-8
ORIGINAL PAPER
Synthesis of some cyclopentenones and crystal structure
of 4-hydroxy-3,4-bis(4-methoxyphenyl)-5,5-dimethyl-2-
cyclopenten-1-one
Katayoun Marjani Æ Mohsen Mousavi Æ Omid Arazi Æ Akram Ashouri Æ
Samira Bourghani Æ Mohammad Rajabi
Received: 2 August 2008 / Accepted: 9 August 2009 / Published online: 1 September 2009
Ó Springer-Verlag 2009
Abstract Sodium-hydroxide-catalyzed condensation of
di-p-methyl- and di-p-methoxybenzil with acetone
derivatives was investigated in methanol. Di- and trisub-
stituted products were obtained as cyclopentenones, while
tetraaryl-substituted systems were isolated as cyclopenta-
dienones. The structures of the products were identified by
elemental analysis, infrared (IR), nuclear magnetic reso-
nance (1H NMR), and mass spectroscopy. The solid-state
structure of 4-hydroxy-3,4-bis(4-methoxyphenyl)-5,5-
dimethyl-2-cyclopenten-1-one was further studied by sin-
gle-crystal X-ray diffraction analysis. The title compound
crystallizes in an orthorhombic space group and intermo-
lecular O–HꢀꢀꢀO and C–HꢀꢀꢀO hydrogen bonds stabilize the
crystal lattice.
Among a variety of approaches available for preparation
of cyclopentenones [7–13], condensation of aromatic
a-diketones with acetone derivatives is a simple and effi-
cient method. The aldol condensation is an extremely
useful carbon–carbon bond-forming reaction in organic
chemistry and this reaction has served as a powerful tool
for synthesis of functionalized ring systems [14]. The
reactions are usually carried out under classical homoge-
neous conditions in ethanol [15–18] and catalyzed by acids
or bases [19–21].
Condensation of benzil and acetone derivatives was
frequently utilized for preparation of diphenylcyclopente-
nones [22–25]. Recently, we extended the procedure to the
synthesis of diarylcyclopentenones from di-p-bromo- and
di-p-chlorobenzils [26]. In this work, we applied the same
method to the synthesis of diarylcyclopentenones from di-
p-methyl- and di-p-methoxybenzil.
Keywords Aldol condensation ꢀ Cyclopentenone ꢀ
Hydrogen bonds ꢀ X-ray structure determination
Introduction
Results and discussion
Cyclopentenones are not only key building blocks for
organic synthesis, but possess many interesting biological
properties [1–3]. The cyclopentenone ring is present in a
wide array of natural products [4], interesting drug targets,
and commercial products [5]. Furthermore the cyclo-
pentenone structure has photochemical properties [6].
Condensations of di-p-methyl- and di-p-methoxybenzil
with five different ketones were performed in methanolic
sodium hydroxide under reflux (Scheme 1). The main
products were obtained as precipitates, after pouring the
mixtures into water. A summary of results is presented in
Table 1.
Generally, the reactions of di-p-methoxybenzil proceeded
faster than the corresponding reactions of di-p-methylbenzil.
All di- and trisubstituted products were obtained as cyclo-
pentenones (entries 1–4 and 6–9). The yields of
cyclopentenones are apparently a function of their ease of
dehydration: the cyclopentenones 3 and 8, which cannot be
dehydrated, were isolated with the highest yields. On the
other hand, 2, 4, 7, and 9, which are more susceptible to
K. Marjani ꢀ O. Arazi ꢀ A. Ashouri ꢀ S. Bourghani ꢀ M. Rajabi
Faculty of Chemistry, Tarbiat Moalem University,
49 Mofateh Avenue, 15614 Tehran, Iran
M. Mousavi (&)
Department of Chemistry, Islamic Azad University,
Saveh Branch, P.O. Box 39187/366, Saveh, Iran
e-mail: drmousavi@hotmail.com
123

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K. Marjani et al.
G
G
G
G
G
O
O
HO
O
-OH
R3
R1
+
C
CH
R2
R3
R2
-H2O
-H2O
H2
O
R1
R3
R1
G
O
5 : G = CH3, R1 = R3= Ph
10 : G = OCH3, R1 = R3= Ph
1 : G = CH3, R1 = R2 = R3 = H
2 : G = CH3, R1 = CH3, R2 = R3 = H
3 : G = CH3, R1 = H, R2 = R3 = CH3
4 : G = CH3, R1 = Ph, R2 = R3 = H
6 : G = OCH3, R1 = R2 = R3 = H
7 : G = OCH3, R1 = CH3, R2 = R3 = H
8 : G = OCH3, R1 = H, R2 = R3 = CH3
9 : G = OCH3, R1 = Ph, R2 = R3 = H
Scheme 1
Table 1 Summary of results
Cpd. Substituents
Time (min) Yielda (%)
G
R1
R2
R3
1
2
3
4
5
6
7
8
9
10
a
CH3
CH3
CH3
CH3
CH3
OCH3
H
H
H
H
H
180
300
225
75
78b
45b
85b
42b
86c
35b
45b
80b
41b
87c
CH3
H
CH3 CH3
C6H5
C6H5
H
H
H
H
H
H
C6H5 120
Scheme 2
H
H
90
150
150
240
75
OCH3 CH3
OCH3
previously reported values for 2-cyclopentenone deriva-
tives [29]. In cyclopentadienones, these bands are shifted to
1,725 and 1,618 cm-1, respectively.
H
CH3 CH3
OCH3 C6H5
OCH3 C6H5
H
H
H
C6H5
1
In the H NMR spectra of 1, 2, 4, 6, 7, and 9, two dou-
Isolated yields
blets near 2.7 and 2.9 ppm are assigned to the methylene
moiety of the cyclopentenone rings. The corresponding
J constants are in the range 12–18 Hz. The presence of
these doublets in the 1H NMR spectra of 2, 4, 7, and 9, along
with the absence of vinyl signals near 6.7 ppm, indicates the
preferred formation of 2-substituted cyclopentenones
(Scheme 2).
b
c
The product is a cyclopentenone derivative
The product is a cyclopentadienone derivative
dehydration, were obtained in relatively lower yields. The
condensation of benzils with 1,3-diphenyl-2-propanone
(entries 5 and 10), which were expected to form tetraaryl-
cyclopentenones, led to the formation of cyclopentadienones
5 and 10 as the main products. The presence of four aryl
groups is known to stabilize the cyclopentadienone system,
which is inherently unstable. The preparations of 5, 10, and
some other tetraarylcyclopentadienones have been previ-
ously reported [27, 28].
1
The H NMR spectra of all compounds show doublets
with coupling constants of about 9 Hz in the aromatic
region, which are representative of p-disubstituted benzene
1
rings. The simplicity of the H NMR spectra of cyclo-
pentadienones 5 and 10 is consistent with their symmetric
structures.
Spectroscopy
Crystal structure of 8
The IR spectra of all cyclopentenones exhibit tOH as a
broad band around 3,400 cm-1. This band is absent in the
IR spectra of cyclopentadienones 5 and 10. The spectra of
the cyclopentenones present also two bands around 1,690
(tC=O) and 1,605 cm-1 (tC=C), in accordance with
Figure 1 shows an ORTEP view and atom numbering of 8.
The structure of the title compound is composed of two
aromatic rings attached to a central cyclopentenone ring.
The cyclopentenone ring has an envelope conformation
with C(1), C(3), C(4), and C(5) lying in a plane, and C(2)
123

Synthesis of some cyclopentenones
1333
The internal bond angles of the five-membered ring
range from 102.25(13)° to 111.07(15)°. The bond distances
˚
vary according to the bond character: 1.347(2) A for the
˚
C(4)–C(5) double bond to 1.578(2) A for the C(2)–C(3)
single bond. These values are very close to the values
reported for similar structures [30, 31].
In the crystal lattice two molecules of 8 are linked to
each other by hydrogen bonds. One hydrogen bond is
formed from the hydroxyl group of one molecule to the
carbonyl group of its next neighbor, O(2)–H(2O)ꢀꢀꢀO(1), to
form a chain along the b crystallographic axis (Fig. 2;
Table 2). A second intermolecular hydrogen bond forms a
link between the chains, forming a three-dimensional
structure, C(21)–H(21A)ꢀꢀꢀO(3) (Table 2). The molecules
are further stabilized by intramolecular C–HꢀꢀꢀO hydrogen
bonds (Fig. 3).
Conclusion
The condensation of aromatic a-diketones with acetone
derivatives leads to the formation of cyclopentenones, via
two aldol reactions followed by a single dehydration. When
nonsymmetric ketones are used, the dehydration proceeds
regioselectively to form the more stable cyclopentenones,
according to Saytzeff’s rule. Dehydration of cyclopente-
none to cyclopentadienones may occur in tetraarylated
systems.
Fig. 1 An ORTEP view and atom numbering of 8 (thermal ellipsoids
˚
are drawn at 50% probability level). Selected bond lengths (A) and
angles (°): O(1)–C(1): 1.231(2), C(1)–C(5): 1.451(2), C(3)–C(4):
1.538(2), O(2)–C(3): 1.424(2), C(1)–C(2): 1.526(2), C(4)–C(5):
1.347(2), C(2)–C(3): 1.578(2), C(1)–C(2)–C(3): 102.25(13), C(4)–
C(3)–C(2): 103.59(12), O(2)–C(3)–C(4): 112.95(12), C(5)–C(4)–
C(3): 110.81(14), C(5)–C(1)–C(2): 108.80(14), O(2)–C(3)–C(2):
112.25(13), C(4)–C(5)–C(1): 111.07(15)
Experimental
All chemicals were obtained from commercial sources
(Merck or Fluka), and used without further purification.
Melting points were measured on an Electrothermal 9100
apparatus. IR spectra were measured on a Shimadzu IR-
˚
located 0.303 A out of the plane. The conjugated p-
methoxyphenyl, C(15)–C(20), is coplanar with the enone
moiety of cyclopentenone. The other p-methoxyphenyl,
C(8)–C(13), is orthogonal to the plane of the main conju-
gated system (dihedral angle is 88.41°).
1
460 spectrometer. H NMR spectra were obtained on a
Bruker Avance 300 MHz instrument using TMS as internal
Fig. 2 Fragment of a
supramolecular chain formed by
intermolecular O–HꢀꢀꢀO
hydrogen bonds in the solid
state of 8
123

1334
K. Marjani et al.
(s, 1H, OH), 6.69 (s, 1H, CH), 7.08 (d, J = 8.3 Hz, 4H,
C6H4), 7.35 (d, J = 8.3 Hz, 2H, C6H4), 7.67 (d,
J = 8.3 Hz, 2H, C6H4) ppm; MS (70 eV): m/z
(%) = 278 (M?, 28), 129 (59), 119 (100), 115 (88), 91(59).
Table 2 Hydrogen-bond geometry for 8
D–HꢀꢀꢀA
d(D–H) d(HꢀꢀꢀA) d(DꢀꢀꢀA)
\(DHA)
(°)
´
˚
´
˚
´
˚
(A)
(A)
(A)
O(2)–H(2O)ꢀꢀꢀO(1)a
C(9)–H(9A)ꢀꢀꢀO(2)
C(20)–H(20A)ꢀꢀꢀO(2)
0.94
0.95
0.95
1.87
2.32
2.44
2.54
2.792 (2) 165
2.685 (2) 102
3.025 (2) 119
3.412 (2) 148
4-Hydroxy-5-methyl-3,4-di-p-tolyl-2-cyclopenten-1-one
(2, C20H20O2)
C(21)–H(21A)ꢀꢀꢀO(3)b 0.98
Yellow solid recrystallized from toluene. M.p.: 105–
107°C; IR (KBr): vꢀ ¼ 3;400 (OH), 1,690 (C=O), 1,619
Symmetry transformations used to generate equivalent atoms: a1/2 -
b
x, -1/2 ? y, z; 1/2 ? x, 3/2 - y,-z
1
(C=C) cm-1; H NMR (300 MHz, acetone-d6): d = 1.83
(s, 3H, CH3), 2.21 (s, 3H, CH3), 2.23 (s, 3H, CH3), 2.81 (d,
J = 18.3 Hz, 1H, methylene), 2.91 (d, J = 18.3 Hz, 1H,
methylene), 5.15 (s, 1H, OH), 7.07 (d, J = 8.2 Hz, 4H,
C6H4), 7.27 (d, J = 8.2 Hz, 4H, C6H4) ppm; MS (70 eV):
m/z (%) = 292 (M?, 20), 129 (59), 119 (100), 115 (88), 91
(59).
4-Hydroxy-5,5-dimethyl-3,4-di-p-tolyl-2-cyclopenten-1-
one (3, C21H22O2)
Colourless solid recrystallized from toluene. M.p.: 146–
148°C; IR (KBr): vꢀ ¼ 3;356 (OH), 1,678 (C=O), 1,605
1
(C=C) cm-1; H NMR (300 MHz, acetone-d6): d = 0.52
(s, 3H, CH3), 1.26 (s, 3H, CH3), 2.21 (s, 3H, CH3), 2.22 (s,
3H, CH3), 5.02 (s, 1H, OH), 6.70 (s, 1H, CH), 7.09 (d,
J = 8 Hz, 4H, C6H4), 7.60 (d, J = 8 Hz, 4H, C6H4) ppm;
MS (70 eV): m/z (%) = 306 (M?, 20), 129 (40), 119 (100),
115 (99), 59 (18).
Fig. 3 Intramolecular C–HꢀꢀꢀO hydrogen bonds in 8; distances are
4-Hydroxy-2-phenyl-3,4-di-p-tolyl-2-cyclopenten-1-one
(4, C25H22O2)
˚
shown in A
Slightly yellow solid recrystallized from toluene. M.p.:
163–165°C; IR (KBr): vꢀ ¼ 3;439 (OH), 1,697 (C=O),
standard. Mass spectra were recorded on a Shimadzu GC/
MS QP1100 EX model. Elemental analyses for C and H
were conducted using a Perkin-Elmer 2400 series II ana-
lyzer; their results were compatible with the calculated
values.
1,605 (C=C) cm-1 1H NMR (300 MHz, acetone-d6):
;
d = 2.18 (s, 3H, CH3), 2.27 (s, 3H, CH3), 2.91 (d,
J = 18.2 Hz, 1H, methylene), 3.07 (d, J = 18.2 Hz, 1H,
methylene), 5.37 (s, 1H, OH), 6.90 (d, J = 8 Hz, 2H,
C6H4), 7.06 (d, J = 8 Hz, 2H, C6H4), 7.13 (d, J = 8 Hz,
2H, C6H4), 7.26–7.31 (m, 5H, Ph), 7.40 (d, J = 8 Hz, 2H,
C6H4) ppm; MS (70 eV): m/z (%) = 354 (M?, 20), 295
(26), 189 (100), 91(56).
General synthetic procedure
A magnetically stirred mixture of the substituted benzil
(0.3 mmol) and the appropriate ketone (2 mmol) in 2 cm3
methanolic sodium hydroxide (10%) was heated under
reflux. After completion of the reaction, which was moni-
tored by thin-layer chromatography (TLC), the mixture
was poured into 200 cm3 cold water. The precipitate was
then filtered off, washed successively with water and a
mixture of n-hexane/ether, and dried in vacuo.
2,5-Diphenyl-3,4-di-p-tolyl-2,4-cyclopentadien-1-one
(5)
Deep red solid recrystallized from methanol. M.p.: 220–
222°C (221.8–222°C [28]); IR (KBr): vꢀ ¼ 1;725 (C=O),
1618 (C=C) cm-1 1H NMR (300 MHz, acetone-d6):
;
d = 2.28 (s, 6H, 2 CH3), 6.87 (d, J = 8 Hz, 4H, C6H4),
7.03 (d, J = 8 Hz, 4H, C6H4), 7.22–7.23 (m, 10H, Ph)
ppm.
4-Hydroxy-3,4-di-p-tolyl-2-cyclopenten-1-one
(1, C19H18O2)
Colorless solid recrystallized from toluene. M.p.: 158–
160°C; IR (KBr): vꢀ ¼ 3;394 (OH), 1,678 (C=O), 1,609
4-Hydroxy-3,4-bis(4-methoxyphenyl)-2-cyclopenten-1-one
(6, C19H18O4)
1
(C=C) cm-1; H NMR (300 MHz, acetone-d6): d = 2.26
Yellow solid recrystallized from toluene. M.p.: 220–
222°C; IR (KBr): vꢀ ¼ 3;390 (OH), 1,678 (C=O), 1,600
(s, 3H, CH3), 2.27 (s, 3H, CH3), 2.70 (d, J = 18.3 Hz, 1H,
methylene), 2.88 (d, J = 18.3 Hz, 1H, methylene), 5.49
1
(C=C) cm-1; H NMR (300 MHz, acetone-d6): d = 2.88
123

Synthesis of some cyclopentenones
1335
(d, J = 18 Hz, 1H, methylene), 2.91 (d, J = 18 Hz, 1H,
methylene), 3.71 (s, 3H, OCH3), 3.73 (s, 3H, OCH3), 5.27
(s, 1H, OH), 6.64 (s, 1H, CH), 6.82 (d, J = 9 Hz, 4H,
C6H4), 7.41 (d, J = 9 Hz, 2H, C6H4), 7.81 (d, J = 9 Hz,
2H, C6H4) ppm.
unique reflections (Rint = 0.0537). The structure was
solved by direct methods, and refined on F2 using all data
by full-matrix least-square procedures using SHELXTL
ver. 5.1 software [32]. The hydrogen atoms of OH groups
were found in the difference Fourier synthesis. The H(C)
atom positions were calculated.
4-Hydroxy-3,4-bis(4-methoxyphenyl)-2-methyl-2-cyclo-
penten-1-one (7, C20H20O4)
Crystallographic data for 8 are as follows: C21H22O4,
molecular weight 338.39, orthorhombic, Pbca, a =
Yellow solid recrystallized from toluene. M.p.: 108–
110°C; IR (KBr): vꢀ ¼ 3;396 (OH), 1,688 (C=O), 1,601
˚
15.869(4) A, b = 11.470(2) A, c = 19.548(3) A, V =
˚
˚
3
˚
3558.2(13) A , Z = 8, T = 120(2) K, F(000) = 1,440,
1
(C=C) cm-1; H NMR (300 MHz, acetone-d6): d = 1.89
l = 0.087 mm-1, Dcalc = 1.263 Mg m-3, 2hmax = 58.00°,
230 parameters, goodness of fit = 0.999, wR(F2) = 0.1265
(all data), wR(F2) = 0.1154 [1,634 data with I [ 2r(I)],
R = 0.0889 (all data), R = 0.0534 [1634 data with
I [ 2r(I)].
(s, 3H, CH3), 2.69 (d, J = 18 Hz, 1H, methylene), 2.89 (d,
J = 18 Hz, 1H, methylene), 3.73 (s, 3H, OCH3), 3.76 (s,
3H, OCH3), 5.16 (s, 1H, OH), 6.83 (d, J = 8.9 Hz, 4H,
C6H4), 7.32 (d, J = 8.9 Hz, 2H, C6H4), 7.39 (d,
J = 8.9 Hz, 2H, C6H4) ppm; MS: m/z (%) = 324 (M?,
14), 149 (34), 112 (64), 57 (100), 43 (88).
CCDC 692901 contains the supplementary crystallo-
graphic data for 8. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK (Fax: 44-1223-
336033 or e-mail: deposit@ccdc.cam.ac.uk).
4-Hydroxy-3,4-bis(4-methoxyphenyl)-5,5-dimethyl-2-
cyclopenten-1-one (8, C21H22O4)
Colourless solid recrystallized from toluene. M.p.: 143–
145°C; IR (KBr): vꢀ ¼ 3;356 (OH), 1,678 (C=O), 1,605
1
(C=C) cm-1; H NMR (300 MHz, acetone-d6): d = 0.52
Acknowledgments We wish to thank the Tarbiat Moalem Univer-
sity of Tehran for financial support.
(s, 3H, CH3), 1.25 (s, 3H, CH3), 3.76 (s, 3H, OCH3), 3.78
(s, 3H, OCH3), 5.01 (s, 1H, OH), 6.64 (s, 1H, CH), 6.83 (d,
J = 9 Hz, 4H, C6H4), 7.69 (d, J = 9 Hz, 4H, C6H4) ppm;
MS (70 eV): m/z (%) = 338 (M?, 95), 251 (55), 135 (100),
77 (30).
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chromated Mo-Ka radiation (k = 0.71073 A). A total of
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