An efficient procedure for the synthesis of α,β-unsaturated ketones and its application to heterocyclic systems

Article abstract of DOI:10.1055/s-0031-1289571

An efficient and room-temperature procedure is developed for high yield synthesis of novel α,β-unsaturated derivatives of thiopyran 3 directly from ketone 1 and various aldehydes in the presence of catalytic quantities of TMSNMe₂ and MgBr₂OEt₂ under solvent-free conditions. The main advantage of the procedure is that the formation of the undesired bis by-products is minimized. In addition, the procedure is applicable to other enolizable carbocyclic and acyclic ketones. Georg Thieme Verlag Stuttgart. New York.

Full text of DOI:10.1055/s-0031-1289571

PAPER
3821
An Efficient Procedure for the Synthesis of a,b-Unsaturated Ketones and Its
Application to Heterocyclic Systems
Efficient
Synthesis of
a
o
,
b
-
Unsatura
h
s
ammad M. Mojtahedi,*a M. Saeed Abaee,*a Mehdi Khakbaz,a Tooba Alishiri,a Maedeh Samianifard,a
A. Wahid Mesbah,a Klaus Harmsb
a
Department of Organic Chemistry, Chemistry & Chemical Engineering Research Center of Iran, P. O. Box 14335-186, Tehran, Iran
Fax ++98(21)44580762; E-mail: mojtahedi@ccerci.ac.ir; E-mail: abaee@ccerci.ac.ir
Fachbereich Chemie der Philipps-Universität Marburg, Hans-Meerwein-Str., 35032 Marburg, Germany
b
Received 1 September 2011; revised 28 September 2011
to study the effect of silylated amines in direct synthesis
Abstract: An efficient and room-temperature procedure is devel-
of a,b-unsaturated ketones.
oped for high yield synthesis of novel a,b-unsaturated derivatives of
thiopyran 3 directly from ketone 1 and various aldehydes in the
presence of catalytic quantities of TMSNMe2 and MgBr2·OEt2 un-
der solvent-free conditions. The main advantage of the procedure is
that the formation of the undesired bis by-products is minimized. In
addition, the procedure is applicable to other enolizable carbocyclic
and acyclic ketones.
We have an ongoing program on the synthesis of bisaryl-
methylidenes of various homo- and heterocyclic ketones.7
As part of this program, we decided to extend our experi-
ence to the synthesis of the monoarylidene counterparts.
Based on our previous studies on thiopyran system,8 we
envisaged that ketone 1 could be an appropriate probe for
evaluating possible synthesis of products 3 using silylated
amines.9 A search in the literature showed very rare previ-
ous successful examples on the preparation of products 3.
Nyberg et al., who studied the aldol reactions of various
ketones, observed no formation of 3 for proline-catalyzed
reactions of 1 under aqueous conditions.10 In two other in-
dependent attempts and under harsher conditions, only
low yields of a single product of type 3 were obtained in
each case.11 As a result of our investigation, here we
would like to report on a novel and high yield room tem-
perature procedure for the synthesis of a,b-unsaturated
derivatives of 3 (Scheme 1). The procedure is applicable
to the reactions of both homo- and heterocyclic ketones
with various aldehydes.
Key words: a,b-unsaturated ketones, thiopyran-4-one, magnesium
bromide etherate, aldol condensation
a,b-Unsaturated ketones are of great importance in syn-
thetic organic chemistry since they are found as key com-
ponents in many natural and biologically active
structures.1 In addition, they could serve as convenient
precursors for other nucleophilic synthetic transforma-
tions.2 Several strategies are reported so far for the prepa-
ration of these compounds.3 However, many of them
usually incorporate more than one-step reaction or require
the use of commercially unavailable starting materials.
A routine method for the synthesis of these compounds is
the aldol condensation of ketones with aldehydes,4 which
often involves the use of strong bases and is accompanied
by competitive formation of the respective bis by-prod-
ucts. To overcome this limitation, two recent improved
approaches were introduced based on the use of dimethyl-
ammonium dimethyl carbonate and a pyrrolidine imide
catalyst,5 respectively. However, in these methods either
prolonged high temperature treatment of the reactants
were needed, workup had to be performed under an atmo-
sphere of CO2, use of a solvent or a large excess of the re-
actants was required, or the yields were low or moderate
in many cases. Thus, the development of efficient meth-
ods capable of producing the title compounds under mild-
er conditions has yet remained a great challenge.
Nevertheless, in both of the investigations a catalytic cy-
cle involving transient iminium species was suggested, fa-
cilitating the formation of the desired products. This
mechanism and the fact that silylated amines ease the for-
mation of the intermediate iminium salts,6 encouraged us
O
O
TMSNMe2
Ar
ArCHO
+
MgBr2•OEt2, r.t.
S
1
S
2
3
Scheme 1 Reaction of ketone 1 with aldehydes 2
First, 1 was subjected to react with benzaldehyde under
various conditions. In most of the experiments, formation
of 3a along with other competitive by-products was ob-
served. Better results were obtained when magnesium
based Lewis acids were used in the presence of silylated
amines leading to the formation of 3a in moderate yields.
The results were further optimized when an equimolar
solvent-free mixture of the two reactants came into con-
tact with TMSNMe2 and MgBr2·OEt2 leading to the for-
mation of the respective product 3a in high yield (Table 1)
and lowering the amounts of the side-products to mini-
mum quantities. Experiments showed that 7 mol% of
MgBr2·OEt2 is enough for the reaction to complete within
6 hours (Table 1, entry 1). Control experiments in the ab-
sence of either MgBr2·OEt2 or TMSNMe2 led to no signif-
icant process. Under optimized conditions, other
SYNTHESIS 2011, No. 23, pp 3821–3826
x
x.
x
x
.
2
0
1
1
Advanced online publication: 20.10.2011
DOI: 10.1055/s-0031-1289571; Art ID: T85811SS
© Georg Thieme Verlag Stuttgart · New York

3822
M. M. Mojtahedi et al.
PAPER
aldehydes bearing various substituents behaved similarly In all cases, reactions proceeded rapidly at room tempera-
to produce compounds 3b–l within 3–8 hours (entries 2– ture and complete disappearance of the starting materials
12) showing the generality of the method.
was observed within the time periods indicated in the
Table 1 Solvent-Free Synthesis of 3 Using MgBr2·OEt2 and TMSNMe2
Entry
Aldehyde
Product
Time (h)
6
Yield (%)a
70
O
O
1
2a
3a
S
O
O
O
2
3
4
5
6
7
2b
2c
2d
2e
2f
3b
3c
3d
3e
3f
8
8
8
3
4
4
66
65
65
80
76
77
S
O
OMe
S
OMe
O
OMe
OMe
O
O
S
O
F
S
F
O
O
O
O
Cl
S
Cl
Br
O
2g
3g
Br
S
O
8
2h
3h
3
77
NO2
S
NO2
O
O
O
9
10
11
12
2i
3i
4
8
3
3
72
68
80
80
CO2Me
S
CO2Me
O
2j
2k
2l
3j
3k
3l
S
O
S
S
O
O
S
O
O
O
S
a Isolated yields.
Synthesis 2011, No. 23, 3821–3826 © Thieme Stuttgart · New York

PAPER
Efficient Synthesis of a,b-Unsaturated Ketones
3823
1
Table 1. Analysis of the reaction mixtures by H NMR condensation procedures14 have been introduced in recent
spectroscopy showed the formation of a single mono- years to improve the synthesis of a,b-unsaturated ketones
arylidene isomer with Z-stereochemistry as the major and aldehydes. However, some of the methods still re-
product in each reaction. The structure of the products was quire more than one step reaction or employ reagents
assigned based on their spectroscopic analyses. The pro- which are not commercially available. Therefore, there is
posed Z-geometry was confirmed by X-ray still a demand for the development of more efficient pro-
crystallography12 of product 3i (Figure 1).
cedures for selective and high-yield preparation of these
compounds under milder conditions. Table 2 shows the
successful application of our method to the reactions of
three model cyclic and acyclic ketones with various alde-
hydes.
Table 2 Application of the Present Method to Other Ketones
O
MgBr2•OEt2
O
R2
R1
Ar
R1
TMSNMe2
ArCHO
R2
Figure 1 Crystal structure of 3i; displacement ellipsoids at 50%
probability level
R1, R2
Ar
Time (h)
Yield (%)
-(CH2)4-
-(CH2)4-
Ph
16
14
18
5
93
85
94
90
82
92
80
64
71
Based on the results, a mechanistic pathway could be pro-
posed, as depicted in Scheme 2. Initially, in the presence
4-ClC6H4
4-MeOC6H4
Ph
of the TMSNMe2, the starting aldehyde is converted to its -(CH2)4-
respective iminium salt. Then, the trimethylsilanolate an-
ion, resulting from this conversion, facilitates the
-(CH2)3-
MgBr2·OEt2-catalyzed enolization of the ketone 1. Final-
ly, addition of the enol to the iminium ion results in the
formation of 3. Similar mechanisms involving iminium
ions in aldol condensations have also been offered by oth-
ers.5
-(CH2)3-
-(CH2)3-
Ph, H
4-ClC6H4
4-MeOC6H4
Ph
4
7
16
14
24
Ph, H
4-O2NC6H4
4-MeOC6H4
Ph, H
+NMe2
O
ArCHO
+
Ar
Ar
+
TMSNMe2
In conclusion, we have presented a convenient and effi-
cient protocol for the synthesis of monoarylidenes of var-
ious cyclic ketones. Products are prepared in one pot, the
method involves mild reaction conditions, and the workup
is easy. More importantly, the procedure is applicable to
both homo- and heterocyclic ketones, the use of expensive
and commercially unavailable reagents is avoided, and re-
actions are conducted with equimolar quantities of the
starting materials. We can reach at a better conclusion by
the comparison of the present method with some selected
recent reports, as summarized in Table 3 for the synthesis
of monoarylidenes of cyclohexanone. The same compari-
sons can be made for other cyclic and acyclic systems,
which would end up with similar conclusions.3,15
S
3
O
– OTMS
O–
– HNMe2
S
1
O
NMe2
Ar
H
S
S
Scheme 2 Proposed mechanism for the synthesis of 3
With these results in hand, we were encouraged to extend
the procedure to the synthesis of a,b-unsaturated deriva-
tives of homocyclic and acyclic systems as well. The clas-
sical approach for the synthesis of these compounds
involves the use of aldol condensation of ketones with al-
dehydes.4 However, the method suffers from the use of
relatively strong bases and is limited by competitive for-
mation of side products. Alternative methods such as de-
hydration of b-hydroxy ketone products of Mukaiyama
reaction,13 tandem ring expansion–aldol condensation of
tert-trihalomethyl carbinols,3f coupling of alkenyl trichlo-
roacetates with aldehydes,1c and organocatalyzed aldol
We are currently working on the reactions involving the
use of aliphatic aldehydes and other similar heterocyclic
systems, for which the products shown in Figure 2 are al-
ready synthesized in our laboratory. Utilization of the
products in other synthetic reactions is also under investi-
gation.
Melting points are uncorrected. IR spectra were recorded using KBr
disks on a Bruker Vector-22 IR spectrometer. NMR spectra were
obtained on a FT-NMR Bruker Ultra ShieldTM (500 MHz) as CDCl3
Synthesis 2011, No. 23, 3821–3826 © Thieme Stuttgart · New York

3824
M. M. Mojtahedi et al.
PAPER
(Z)-3-Benzylidenedihydro-2H-thiopyran-4(3H)-one (3a)
Table 3 Comparison of the Present Method with Related Proce-
dures for the Synthesis of Monoarylidenes of Cyclohexanone
Yield: 70%; cream-colored solid; mp 63–64 °C.
IR (KBr): 1717, 1668, 1587 cm–1.
1H NMR (CDCl3): d = 2.94–2.98 (m, 2 H), 3.06–3.08 (m, 2 H), 3.87
(s, 2 H), 7.38–7.40 (m, 3 H), 7.43–7.46 (m, 2 H), 7.57 (s, 1 H).
13C NMR (CDCl3): d = 26.4, 29.1, 41.8, 129.0, 129.3, 130.2, 134.8,
135.2, 136.2, 199.2.
Conditions
Substrate
ketones
ketones
Reference
a
TMSNMe2, MgBr2·OEt2
present work
Kreher et al.5a
Me2NCO2H·Me2NH,b 50 °C
MS (70 eV): m/z = 204 (M+), 147, 115, 89.
OH
CrCl2,b THF, HMPA
Falck et al.3f
Anal. Calcd for C12H12OS: C, 70.55; H, 5.92. Found: C, 70.43; H,
6.00.
CCl3
OCOCl3
OTMS
O
Bu2Sn(OMe)2,a THF, MeOH
SnCl2,a AcCl,b CH2Cl2
Yanagisawa et al.1c
(Z)-3-(4-Methylbenzylidene)dihydro-2H-thiopyran-4(3H)-one
(3b
Yield: 66%; yellow solid; mp 103–105 °C.
IR (KBr): 1710, 1511 cm–1.
1H NMR (CDCl3): d = 2.40 (s, 3 H), 2.92–2.95 (m, 2 H), 3.03–3.05
(m, 2 H), 3.86 (s, 2 H), 7.23 (d, J = 7.5 Hz, 2 H), 7.28 (d, J = 7.5 Hz,
2 H), 7.54 (s, 1 H).
13C NMR (CDCl3): d = 21.8, 26.4, 29.2, 41.7, 129.8, 130.4, 132.3,
134.0, 136.5, 139.7, 199.1.
Oriyama et al.16a
Enholm et al.16b
n-Bu3SnH, AIBN, toluene, 80 °C
MS (70 eV): m/z = 218 (M+), 145, 119, 91.
Anal. Calcd for C13H14OS: C, 71.52; H, 6.46. Found: C, 71.12; H,
6.53.
a Catalytic.
b Excess.
(Z)-3-(4-Methoxybenzylidene)dihydro-2H-thiopyran-4(3H)-
one (3c)
Yield: 65%; yellow solid; mp 83–85 °C.
IR (KBr) 1684, 1601, 1511 cm–1.
1H NMR (CDCl3): d = 2.90–2.92 (m, 2 H), 3.02–3.03 (m, 2 H), 3.85
(s, 3 H), 3.87 (s, 2 H), 6.95 (d, J = 7.0 Hz, 2 H), 7.35 (d, J = 7.0 Hz,
2 H), 7.53 (s, 1 H).
13C NMR (CDCl3): d = 26.3, 29.2, 41.6, 55.7, 114.5, 127.6, 132.3,
132.8, 136.4, 160.7, 198.9.
O
O
O
O
Ph
Ph
N
X
Me
3m; X = S; 60%
4m; X = CH2; 70%
5m; X = none; 68%
6a; 85%
7a; 79%
Figure 2 Additional compounds prepared using aliphatic aldehydes
and other systems
MS (70 eV): m/z = 234 (M+), 134, 55, 43.
Anal. Calcd for C13H14O2S: C, 66.64; H, 6.02. Found: C, 67.03; H,
6.10.
solutions using TMS as internal standard reference. Elemental anal-
yses were performed using a Thermo Finnigan Flash EA 1112 in-
strument. MS spectra were obtained on a Fisons 8000 Trio
instrument at ionization potential of 70 eV. TLC experiments were
carried out on precoated silica gel plates using PE–EtOAc (4:1) as
the eluent. Compound 117 and MgBr2·OEt218 were prepared accord-
ing to known methods. TMSNMe2, solvents, and all other starting
materials were purchased from commercial sources. Aldehydes
were redistilled or recrystallized before being used. Petroleum ether
(PE) refers to the fraction boiling in the range 40–60 °C.
(Z)-3-(2-Methoxybenzylidene)dihydro-2H-thiopyran-4(3H)-
one (3d)
Yield: 65%; yellow solid; mp 92–94 °C.
IR (KBr): 1679, 1599, 1487 cm–1.
1H NMR (CDCl3): d = 2.92–2.95 (m, 2 H), 3.03–3.06 (m, 2 H), 3.77
(s, 2 H), 3.88 (s, 3 H), 6.90 (d, J = 8.0 Hz, 1 H), 6.98 (dd, J = 6.5,
7.5 Hz, 1 H), 7.22 (dd, J = 1.5, 7.5 Hz, 1 H), 7.35 (ddd, J = 1.5, 7.5,
8.0 Hz, 1 H), 7.69 (s, 1 H).
13C NMR (CDCl3): d = 26.5, 29.3, 42.0, 55.9, 111.2, 120.6, 124.2,
130.0, 130.7, 131.0, 132.5, 158.6, 199.2.
a,b-Unsaturated Ketones 3; General Procedure
A mixture of an aldehyde 2 (3 mmol), ketone 1 (348 mg, 3.00
mmol), MgBr2·OEt2 (7 mol%, 54 mg), and TMSNMe2 (176 mg, 237
mL, 1.5 mmol) was stirred at r.t. under inert atmosphere for the giv-
en period of time (Table 1). The progress of the reaction was mon-
itored by TLC (eluent: PE–EtOAc, 4:1). At the end, H2O (5 mL)
was added to the mixture and the product was extracted with Et2O
(2 × 5 mL). The combined organic layers were dried (Na2SO4).
Evaporation of the solvent led to a residue, which was purified by
column chromatography using silica gel and PE–EtOAc (4:1) as the
eluent. Isolated yields of products were 60–80% (Table 1). The
structure of the new products was determined by their physical and
spectroscopic specifications and their purity was confirmed by ele-
mental analyses.
MS (70 eV): m/z = 234 (M+), 173, 131, 116.
Anal. Calcd for C13H14O2S: C, 66.64; H, 6.02. Found: C, 66.92; H,
6.12.
(Z)-3-(4-Fluorobenzylidene)dihydro-2H-thiopyran-4(3H)-one
(3e)
Yield: 80%; cream colored solid; mp 55–56 °C.
IR (KBr): 1697, 1594, 1517 cm–1.
1H NMR (CDCl3): d = 2.93–2.96 (m, 2 H), 3.05–3.07 (m, 2 H), 3.83
(s, 2 H), 7.14 (d, J = 8.0 Hz, 2 H), 7.36 (dd, J = 5.5, 8.0 Hz, 2 H),
7.51 (s, 1 H).
Synthesis 2011, No. 23, 3821–3826 © Thieme Stuttgart · New York

PAPER
Efficient Synthesis of a,b-Unsaturated Ketones
3825
13C NMR (CDCl3): d = 26.3, 28.9, 41.7, 116.1, 116.3, 131.2, 131.3,
IR (KBr): 1717, 1601, 1468 cm–1.
132.2, 132.3, 134.6, 135.1, 163.2, 164.3, 199.0.
1H NMR (CDCl3): d = 2.97–2.99 (m, 2 H), 3.08–3.10 (m, 2 H), 3.96
(s, 2 H), 7.48 (dd, J = 1.5, 8.5 Hz, 1 H), 7.54–7.58 (m, 2 H), 7.72 (s,
1 H), 7.86–7.90 (m, 4 H).
13C NMR (CDCl3): d = 26.4, 29.2, 41.8, 127.1, 127.4, 127.5, 128.2,
128.7, 128.8, 130.1, 132.7, 133.4, 133.6, 135.0, 136.4, 199.2.
MS (70 eV): m/z = 222 (M+), 133, 82.
Anal. Calcd for C12H11FOS: C, 64.84; H, 4.99. Found: C, 64.73; H,
4.89.
(Z)-3-(4-Chlorobenzylidene)dihydro-2H-thiopyran-4(3H)-one
(3f)
Yield: 76%; oil.
IR (KBr): 1707, 1604, 1488 cm–1.
MS (70 eV): m/z = 254 (M+), 197, 165, 135.
Anal. Calcd for C16H14OS: C, 75.55; H, 5.55. Found: C, 75.30; H,
5.62.
1H NMR (CDCl3): d = 2.93–2.95 (m, 2 H), 3.04–3.08 (m, 2 H), 3.81
(s, 2 H), 7.30 (d, J = 8.5 Hz, 2 H), 7.41 (d, J = 8.5 Hz, 2 H), 7.48 (s,
1 H).
(Z)-3-(Thiophen-2-ylmethylene)dihydro-2H-thiopyran-4(3H)-
one (3k)
Yield: 80%; yellow solid; mp 94–96 °C.
13C NMR (CDCl3): d = 26.4, 29.0, 41.8, 129.3, 131.5, 133.6, 134.8,
IR (KBr): 1717, 1668, 1587 cm–1.
135.2, 135.3, 198.9.
1H NMR (CDCl3): d = 2.92–2.96 (m, 2 H), 3.00–3.05 (m, 2 H), 3.98
(s, 2 H), 7.17–7.20 (m, 1 H), 7.38 (d, J = 5.0 Hz, 1 H), 7.58 (d,
J = 5.0 Hz, 1 H), 7.83 (s, 1 H).
MS (70 eV): m/z = 238 (M+), 181, 147, 115, 91.
(Z)-3-(4-Bromobenzylidene)dihydro-2H-thiopyran-4(3H)-one
(3g)
Yield: 77%; brown solid; mp 112–114 °C.
IR (KBr): 1712, 1485, 1421 cm–1.
1H NMR (CDCl3): d = 2.98–3.00 (m, 2 H), 3.04–3.07 (m, 2 H), 3.80
(s, 2 H), 7.23 (d, J = 8.5 Hz, 2 H), 7.45 (s, 1 H), 7.56 (d, J = 8.5 Hz,
2 H).
13C NMR (CDCl3): d = 26.4, 29.0, 41.8, 123.6, 131.7, 132.3, 134.0,
134.8, 135.4, 198.9.
13C NMR (CDCl3): d = 26.3, 29.4, 41.4, 128.25, 129.7, 130.3, 130.6,
134.3, 138.4, 197.9.
MS (70 eV): m/z = 210 (M+), 118, 116, 88.
Anal. Calcd for C10H10OS2: C, 57.11; H, 4.79. Found: C, 57.43; H,
4.70.
(Z)-3-(Furan-2-ylmethylene)dihydro-2H-thiopyran-4(3H)-one
(3l)
Yield: 80%; oil (80%).
MS (70 eV): m/z = 281 (M+), 194, 115, 45.
IR (KBr): 1711, 1607 cm–1.
Anal. Calcd for C12H11BrOS: C, 50.90; H, 3.92. Found: C, 50.59; H,
3.99.
1H NMR (CDCl3): d = 2.90–2.93 (m, 2 H), 3.03–3.06 (m, 2 H), 4.15
(s, 2 H), 6.55 (dd, J = 1.5, 3.5 Hz, 1 H), 6.72 (d, J = 3.5 Hz, 1 H),
7.33 (s, 1 H), 7.60 (d, J = 1.5 Hz, 1 H).
(Z)-3-(4-Nitrobenzylidene)dihydro-2H-thiopyran-4(3H)-one
(3h)
Yield: 77%; brown solid; mp 112–114 °C.
IR (KBr): 1697, 1594, 1517 cm–1.
13C NMR (CDCl3): d = 26.2, 29.3, 39.2, 112.7, 118.3, 122.4, 130.1,
145.2, 151.9, 198.3.
MS (70 eV): m/z = 194 (M+), 165, 107, 97.
1H NMR (CDCl3): d = 2.98–3.00 (m, 2 H), 3.08–3.11 (m, 2 H), 3.79
(s, 2 H), 7.51 (s, 1 H), 7.53 (d, J = 8.5 Hz, 2 H), 8.31 (d, J = 8.5 Hz,
2 H).
(Z)-3-(3-Methylbutylidene)dihydro-2H-thiopyran-4(3H)-one
(3m)
Yield: 60%; yellow solid, mp 76–78 °C.
13C NMR (CDCl3): d = 26.4, 29.0, 41.9, 124.3, 130.8, 132.8, 137.7,
IR (KBr): 1710, 1424 cm–1.
141.8, 147.9, 198.7.
1H NMR (CDCl3): d = 0.96 (d, J = 6.5 Hz, 6 H), 1.80–1.84 (m, 1 H),
2.06–2.09 (m, 2 H), 2.82–2.85 (m, 2 H), 2.98 (t, J = 6.0 Hz, 2 H),
3.56 (s, 2 H), 6.68–6.71 (m, 1 H).
13C NMR (CDCl3): d = 23.0, 26.3, 27.6, 28.7, 37.3, 41.8, 135.3,
139.1, 198.7.
MS (70 eV): m/z = 249 (M+), 147, 115, 60.
Anal. Calcd for C12H11NO3S: C, 57.82; H, 4.45. Found: C, 57.62; H,
4.32.
Methyl (Z)-4-[(4-oxo-2H-thiopyran-3(4H,5H,6H)-ylid-
ene)methyl]benzoate (3i)
Yield: 72%; brown solid; mp 96–98 °C.
IR (KBr): 1714, 1608, 1434 cm–1.
MS (70 eV): m/z = 184 (M+), 129, 115.
Anal. Calcd for C10H16OS: C, 65.17; H, 8.75. Found: C, 64.77; H,
8.73.
1H NMR (CDCl3): d = 2.96–2.98 (m, 2 H), 3.07–3.10 (m, 2 H), 3.83
(s, 2 H), 3.97 (s, 3 H), 7.41 (d, J = 8.0 Hz, 2 H), 7.54 (s, 1 H), 8.11
(d, J = 8.0 Hz, 2 H).
13C NMR (CDCl3): d = 26.4, 30.5, 41.9, 52.7, 130.0, 130.2, 130.6,
134.6, 136.4, 139.7, 166.9, 198.9.
(E)-3-Benzylidenedihydro-2H-pyran-4(3H)-one (7a)
Yield: 79%; yellow solid; mp 103–104 °C.
IR (KBr): 1678, 1450, 983 cm–1.
1H NMR (CDCl3): d = 2.61 (t, J = 6.0 Hz, 2 H), 4.00 (t, J = 6.0 Hz,
2 H), 4.77 (d, J = 2.0 Hz, 2 H), 7.19–7.21 (m, 2 H), 7.27–7.35 (m, 3
H), 7.55 (t, J = 2.0 Hz, 1 H).
MS (70 eV): m/z = 262 (M+), 247, 204, 147, 115.
Anal. Calcd for C14H14O3S: C, 64.10; H, 5.38. Found: C, 63.73; H,
5.26.
13C NMR (CDCl3): d = 40.1, 65.9, 69.1, 129.1, 129.8, 130.9, 133.7,
134.7, 136.4, 196.5.
MS (70 eV): m/z = 188 (M+), 159, 131, 115.
(Z)-3-(Naphthalen-2-ylmethylene)dihydro-2H-thiopyran-
4(3H)-one (3j)
Yield: 68%; yellow solid; mp 82–84 °C.
Anal. Calcd for C12H12O2: C, 76.57; H, 6.43. Found: C, 76.12; H,
6.54.
Synthesis 2011, No. 23, 3821–3826 © Thieme Stuttgart · New York

3826
M. M. Mojtahedi et al.
PAPER
Supporting Information for this article is available online at
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(12) Crystallographic data for 3i have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-846075. Copies of these data can be
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK [Fax: +44(1223)336033; E-
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Acknowledgment
The authors would like to thank the Iran National Science Founda-
tion (INSF-88002468) for financial support of this work.
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