Efficient method for the synthesis of, ′-bis(arylmethylidene) cycloalkanones catalyzed by bromodimethylsulfonium bromide

Article abstract of DOI:10.1080/00397911.2013.834362

Bromodimethylsulfonium bromide (BDMS)-catalyzed crossed aldol condensation between aromatic aldehydes and ketones is reported to access ′-bis(arylmethylidene) cycloalkanones at room temperature in good yields within 3-10 min. The salient features of this method are the simplicity of the procedure, the ready accessibility of the catalyst, and greater yields in relatively short reaction times. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications for the following free supplemental resource(s): Full experimental and spectral details.]

Full text of DOI:10.1080/00397911.2013.834362

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Efficient Method for the Synthesis
of α,α′-Bis(arylmethylidene)
Cycloalkanones Catalyzed by
Bromodimethylsulfonium Bromide
Cong-Ying Zhao a , Ju-Yan Liu a , Ying Wang a , Xiao-Jun Zhao a , Bin
Yuan a & Min-Min Yue a
a College of Chemistry, Tianjin Key Laboratory of Structure
and Performance for Functional Molecule, Key Laboratory of
Inorganic–Organic Hybrid Functional Material Chemistry , Ministry of
Education, Tianjin Normal University , Tianjin , China
Published online: 20 Feb 2014.
To cite this article: Cong-Ying Zhao , Ju-Yan Liu , Ying Wang , Xiao-Jun Zhao , Bin Yuan & Min-Min
Yue (2014) Efficient Method for the Synthesis of α,α′-Bis(arylmethylidene) Cycloalkanones Catalyzed
by Bromodimethylsulfonium Bromide, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 44:6, 827-835, DOI: 10.1080/00397911.2013.834362
To link to this article: http://dx.doi.org/10.1080/00397911.2013.834362
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Synthetic Communications1, 44: 827–835, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.834362
EFFICIENT METHOD FOR THE SYNTHESIS
OF a,a’-BIS(ARYLMETHYLIDENE) CYCLOALKANONES
CATALYZED BY BROMODIMETHYLSULFONIUM
BROMIDE
Cong-Ying Zhao, Ju-Yan Liu, Ying Wang, Xiao-Jun Zhao,
Bin Yuan, and Min-Min Yue
College of Chemistry, Tianjin Key Laboratory of Structure and
Performance for Functional Molecule, Key Laboratory of Inorganic–Organic
Hybrid Functional Material Chemistry, Ministry of Education,
Tianjin Normal University, Tianjin, China
GRAPHICAL ABSTRACT
Abstract Bromodimethylsulfonium bromide (BDMS)–catalyzed crossed aldol condensation
between aromatic aldehydes and ketones is reported to access a,a0-bis(arylmethylidene)
cycloalkanones at room temperature in good yields within 3–10 min. The salient features
of this method are the simplicity of the procedure, the ready accessibility of the catalyst,
and greater yields in relatively short reaction times.
[Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 for the following free supplemental resource(s):
Full experimental and spectral details.]
Keywords a,a0-Bis(arylmethylidene) cycloalkanones; bromodimethylsulfonium bromide
(BDMS); crossed aldol condensation; solvent-free
INTRODUCTION
The a,a0-bis(arylmethylidene) cycloalkanones are very important precursors to
potentially bioactive pyrimidine derivates;[1] intermediates of agrochemical, perfumes,
and pharmaceuticals;[2] new organic material for nonlinear optical applications;[3]
cytotoxic analogs;[4] and the units of liquid-crystalline polymers.[5] The crossed-aldol
Received March 6, 2013.
Address correspondence to Ju-Yan Liu, College of Chemistry, Tianjin Normal University, Tianjin
300387, China. E-mail: hxxyljy@mail.tjnu.edu.cn
827

828
C.-Y. ZHAO ET AL.
condensation reaction is suitable for these preparations and can be carried out using
strong acid or base catalysts.[6]
Different complexes of metal (II) ions have also been used as catalysts for this cross
reaction but the yields (<38%) were not satisfactory.[7] Improved approaches have been
reported for the synthesis of a,a0-bis(arylmethylidene) cycloalkanones including
KF-supported reagents,[8,9] Yb(OTf)3,[10] iodotrimethylsilane,[11] TiCl3(SO3CF3),[12]
RuCl3,[13] Pd=C-Me3SiCl,[14] SOCl2,[15] SmI3,[16] LiOH,[17] KOH,[18,19] TMSCl,[20]
LiClO4-TMSNEt2,[21] 2,4,6-trichloro-1,3,5-triazine (TCT),[22] FeCl3,[23] Cp2TiPh2,[24]
bis(p-ethoxyphenyl)telluroxide,[25] Cp2ZrH2,[26] BF3 ꢀ OEt2,[27] InCl3,[28] and animal bone
meal (ABM)[29] as catalysts or activators. A good yield of the corresponding products,
however, can be obtained only at elevated temperature, and the purification operations
are always complicated. The cross-aldol reaction has also been operated at room tempera-
ture using I2 as catalyst but the reaction time is long.[30] Thus, the development of new
catalytic methods is highly desirable.
Bromodimethylsulfonium bromide (BDMS) is a readily accessible, cheap, and
highly effective reagent[31] as well as a catalyst for various organic transforma-
tions.[32] Recently, Yadav et al. reported the efficiency of BDMS in Beckmann
rearrangement (BKR).[33] In addition, very recently they have demonstrated the
virtue of this catalyst for multicomponent synthesis of 3-aminoalkylated indoles.[34]
In continuation of our work on the development of new synthetic methodologies,[35]
we sought to explore the advantages of this reagent further for other important
transformations. Here we report an efficient, convenient, and facile method for the
condensation of aldehydes with cycloalkanones leading to the corresponding
a,a0-bis(arylmethylidene) cycloalkanones in the presence of BDMS as a catalyst
Scheme 1.
RESULTS AND DISCUSSION
The condensation reaction of benzaldehyde (2 mmol) with cyclohexanone
(1 mmol) was carried out at room temperature. In the study of catalyst loading, 0,
1, 5, 10, and 15 mol% of BDMS were tested. Reactions with both 10% and 15% cat-
alysts both gave quantitative yields in 4 min (Table 1, entries 4 and 5), while the reac-
tion with 5 mol% loading only gave 85% yield even after a long reaction time of
25 min. In the absence of catalyst, the reaction did not yield any product at room
temperature even after a long reaction time. This result suggests that BDMS plays
a critical role in this reaction.
Scheme 1. Crossed-aldol condensation catalyzed by BDMS.

a,a0-BIS(ARYLMETHYLIDENE) CYCLOALKANONES
829
Table 1. BDMS-catalyzed reactions of benzaldehyde with cyclohexanonea
Entry
BDMS (mol%)
Time (min)
Yieldb (%)
1
2
3
4
5
0
1
120
40
25
4
0
76
85
98
98
5
10
15
4
aRoom temperature.
bIsolated yield.
To demonstrate the generality and scope of this method, various aromatic
aldehydes such as 4-nitrobenzaldehyde, 4-methoxybenzaldehyde, and 4-chloroben-
zaldehyde were treated with cycloalkanones in the presence of catalytic amounts
of BDMS (10 mol%) under solvent-free conditions, and the obtained results are sum-
marized in Table 2. All the yields were excellent, including the heteroaromatic alde-
hydes such as 2-furaldehyde and 2-thiophenecarboxaldehyde. Aromatic aldehydes
containing both electron-donating (Me, MeO, OH) and electron-withdrawing
(NO2, Cl) groups underwent the conversion smoothly. Both cyclopentanone and
cyclohexanone showed similar activity toward the condensation with aromatic alde-
hydes. All the reactions were free from by-products usually found in classical reac-
tion conditions.[6] The purification of these compounds was easily performed by
simple filtration and recrystallization with alcohol.
The EE geometry of the double bonds in these compounds (3a–t) was based on
earlier literature reports.[36–38] It is reported that the vinylic protons are in close prox-
imity to the carbonyl group, which exerted an anisotropic effect, resulting in the
downfield shifting and overlapping of the vinylic protons with the aromatic protons
and the appearance of vinylic protons in the region of d 7.15–7.95 ppm is an indi-
cation of such compounds with E-configuration and in the region of d 6.8 ppm indi-
cates Z-configuration.[36,37] For example, the olefinic protons of Z-2-phenyl
methylenecyclohexanones and Z-2-phenyl methylene-6,6-diphenyl cyclohexanones
are generally observed at d 6.27 and 6.22 ppm.[38]
We used BDMS as a source of HBr to catalyze this reaction and found it to be an
excellent catalyst for preparation of a,a0-bis(arylmethylidene) cycloalkanones. A plaus-
ible mechanism is shown in Scheme 2. Accordingly, BDMS (10 mol%) reacts with the
aromatic aldehyde and releases 2 mol of HBr and 1 mol of DMSO (removable by wash-
ing with water) as the by-products. The in situ–generated HBr acts as a protic acid and
activates the carbonyl oxygen to promote the condensation to give the products.
Some critical mechanistic information for the reaction of benzaldehyde with cyclo-
pentanone was collected by experimental investigations (Scheme 3). The benzaldehyde
could efficiently react with cyclopentanone with the aid of HBr (20 mol%) as catalyst,

830
C.-Y. ZHAO ET AL.
Table 2. Preparation of a,a0-bis(arylmethylidene) cycloalkanones catalyzed by BDMS at room
temperature under solvent-free conditionsa
Entry
n
Ar
Product
Time (min)
Yield (%)b
Mp (ꢁC) (lit.)[ref]
1
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
Ph
3a
3b
3c
3d
3e
3f
3
3
96
94
93
93
95
85
88
85
93
92
98
95
93
95
90
85
85
87
93
94
191–192 (188–190)[10]
210–212 (211–212)[10]
240–242 (243–244)[10]
230–231 (228–229)[10]
204–205 (206–207)[10]
231–233 (229–231)[10]
220–222 (222–224)[10]
>300 (>300)[10]
217–219 (215–216)[10]
166–168 (163–164)[10]
115–117 (117–118)[10]
163–165 (161–163)[10]
161–162 (164–165)[10]
147–148 (147–148)[13]
162–164 (163–164)[10]
162–163 (161–162)[10]
251–253 (250–252)[10]
294–296 (290–292)[10]
178–179 (177–178)[10]
140–142 (142–143)[10]
4-OCH3C6H4
4-CH3C6H4
4-ClC6H4
3
4
4
8
5
2,4-Cl2C6H3
4-NO2C6H4
3-pyridyl
5
6
10
8
7
3g
3h
3i
8
4-OHC6H4
=
C6H4CH CH
10
5
9
10
11
12
13
14
15
16
17
18
19
20
2-furyl
Ph
3j
4
3k
3l
4
4-OCH3C6H4
4-CH3C6H4
4-ClC6H4
4
3m
3n
3o
3p
3q
3r
4
3
2,4-Cl2C6H3
4-NO2C6H4
4-N(CH3)2C6H4
4-OHC6H4
=
C6H4CH CH
2-Thienyl
8
10
10
10
5
3s
3t
4
aRoom temperature.
bIsolated yield.
giving the corresponding product 3a in 95% yield. This result suggests that HBr plays the
critical role in this reaction.
In comparison with other catalysts such as Yb(OTf)3, Cp2TiPh2, RuCl3, I2,
ABM, Na=animal bone meal (Na=ABM), and TCT, which were recently used in
the synthesis of a,a0-bis(arylmethylidene) cycloalkanones, BDMS employed here
exhibits more effective catalytic activity than those previously reported in terms of
the reaction temperature, yields, and reaction time (Table 3). All the products
obtained were fully characterized by infrared (IR), 1H NMR, 13C NMR, and
elemental analyses. The spectral data were also compared with the reported values.
EXPERIMENTAL
All chemicals were purchased from Aldrich Co. and used as received. Melting
points were measured using a X-4 apparatus and are uncorrected. IR spectra were
obtained using Shimadzu FTIR-8900 spectrometer instrument. NMR spectra were

a,a0-BIS(ARYLMETHYLIDENE) CYCLOALKANONES
831
Scheme 2. Plausible mechanistic illustration of BDMS-catalyzed crossed-aldol condensation reaction.
Scheme 3. Crossed-aldol condensation of benzaldehyde with cyclopentanone catalyzed by HBr.
taken with a Varian 400 spectrometer. Elemental analyses were carried out on MT-3
analyzer. Physical and spectral characterization of the products was confirmed by
comparison with available literature data.[10,13]
Table 3. Comparison of the effect of catalysts for the synthesis of product 3k
Catalyst=solvent
Temperature (ꢁC)
Time
Yield (%)
Ref.
Yb(OTf)3
Cp2TiPh2
RuCl3
90
120
120
rt
6 h
94
73
95
92
76
96
90
98
10
25
13
31
30
30
23
—
6 h
6 h
I2
Animal bone meal (ABM)
4.5 h
100
100
90
1.25 h
20 min
20 min
4 min
Na=animal bone meal (Na=ABM)
TCT
BDMS
rt

832
C.-Y. ZHAO ET AL.
General Procedure for the Synthesis of a,a’-Bis(Arylmethylidene)
Cycloalkanone Derivatives
A mixture of aromatic aldehyde (2.0 mmol), cycloalkanone (1.0 mmol), and
bromodimethylsulfonium bromide (0.1 mmol) was stirred at room temperature for
an appropriate time (Table 2). After completion of the reaction as indicated by
thin-layer chromatography (TLC), the mixture was diluted with water (10 mL),
which precipitated the solid product. The product obtained was pure as found by
TLC and 1H and 13C NMR spectroscopy. However, the products were further
purified by recrystallization from ethanol.
a,a’-Bis(Benzylidene) Cyclohexanone 3k
IR (KBr): 3024, 2926, 1657, 1609, 1570, 1440, 1268, 1144, 773 cmꢂ1. 1H NMR
(CDCl3): d ¼ 7.81 (s, 2 H), 7.33–7.48 (m, 10 H), 2.96 (t, J ¼ 6.4 Hz, 4 H), 1.83–1.76
(m, 2 H). 13C NMR (CDCl3): d ¼ 187.2, 144.3, 141.5, 134.7, 128.6, 127.5, 27.8. Anal.
calcd. for C20H18O: C, 87.56; H, 6.61; Found: C, 87.61; H, 6.74.
CONCLUSION
In conclusion, we have developed an expeditious, novel, and efficient method
for the synthesis of a,a0-bis(arylmethylidene) cycloalkanones from aromatic alde-
hydes with ketones using a catalytic amount of bromodimethylsulfonium bromide
at room temperature. The advantages of the current protocol include experimentally
operational ease, mild reaction conditions, ready accessibility of the catalyst, and
high efficiency, all of which make it a useful and attractive strategy for the prep-
aration of various a,a0-bis(arylmethylidene) cycloalkanone derivatives simply by
changing different substrates.
SUPPORTING INFORMATION
1
Full experimental detail and H and 13C NMR data can be found via the
Supplementary Content section of this article’s Web page.
ACKNOWLEDGMENTS
This work was supported financially by Tianjin Normal University (Grant No.
5RL090), the Natural Science Foundation of Tianjin (Grant, Nos. 12JCZDJC34300,
11JCYBJC03600), and the Young Scientist Fund (Grant No.21001080).
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