Synthesis of bis(arylmethylidene)thiopyranones and crystal structure of the phenyl derivative

Article abstract of DOI:10.1080/10426500701542759

A convenient method is offered for double aldol condensation of tetrahydrothiopyran-4-one with aromatic aldehydes under LiBr catalysis. An X-ray analysis verifies the proposed structures. Copyright Taylor & Francis Group, LLC.

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Synthesis of
Bis(arylmethylidene)thiopyranones
and Crystal Structure of the
Phenyl Derivative
a
a
M. Saeed Abaee , Mohammad M. Mojtahedi
,
a
a
M. Mehdi Zahedi , A. Wahid Mesbah , Nafiseh
a
b
Mohaddes Ghandchi & Werner Massa
a
Chemistry and Chemical Engineering Research
Center of Iran , Tehran, Iran
b
Fachbereich Chemie der Philipps-Universitaet
Marburg , Marburg, Germany
Published online: 03 Dec 2007.
To cite this article: M. Saeed Abaee , Mohammad M. Mojtahedi , M. Mehdi Zahedi ,
A. Wahid Mesbah , Nafiseh Mohaddes Ghandchi & Werner Massa (2007) Synthesis of
Bis(arylmethylidene)thiopyranones and Crystal Structure of the Phenyl Derivative,
Phosphorus, Sulfur, and Silicon and the Related Elements, 182:12, 2891-2895, DOI:
10.1080/10426500701542759
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Phosphorus, Sulfur, and Silicon, 182:2891–2895, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701542759
Synthesis of Bis(arylmethylidene)thiopyranones
and Crystal Structure of the Phenyl Derivative
M. Saeed Abaee
Mohammad M. Mojtahedi
M. Mehdi Zahedi
A. Wahid Mesbah
Nafiseh Mohaddes Ghandchi
Chemistry and Chemical Engineering Research Center of Iran,
Tehran, Iran
Werner Massa
Fachbereich Chemie der Philipps-Universitaet Marburg, Marburg,
Germany
A
convenient method is offered for double aldol condensation of
tetrahydrothiopyran-4-one with aromatic aldehydes under LiBr catalysis.
An X-ray analysis verifies the proposed structures.
Keywords Aldol condensation; bis(arylmethylidene)thiopyranones; lithium bromide;
thiopyranone
INTRODUCTION
Synthesis of bis(arylmethylidene)cycloalkanones is facilitated via
1
aldol condensation of homocyclic ketones with aromatic aldehydes
and several procedures are offered so far for this purpose using
2
3
4
Lewis acid catalysis, solid-supported reactions, ionic liquids,
microwave irradiation,3a and ultrasound mediation. In contrast,
similar chemistry for heterocyclic analogs is much less developed. We
recently disclosed the synthesis of several novel bisarylmethylidene
derivatives of thiopyranone5 and pyranone structures using very
3b
6
Received April 2, 2007; accepted June 5, 2007.
Partial financial support by the Ministry of Science, Research, and Technology of Iran
is greatly appreciated.
Address correspondence to Mohammad M. Mojtahedi, Chemistry and Chemical Engi-
neering Research Center of Iran, P. O. Box 14335-186, Tehran, Iran. E-mail: mojtahedi@
ccerci.ac.ir
2891

2
892
M. S. Abaee et al.
facile synthetic methods. The structures were assigned logically based
on the spectroscopic characterization of the products. However, to
distinguish between the possible isomers (Scheme 1) and verify the
proposed structures we decided to determine the crystal structure of a
representative compound by X-ray diffraction.
SCHEME 1
In the present article, a convenient and rapid procedure is offered for
the synthesis of bis(arylmethylidene)thiopyranones under catalysis of
LiBr which has found many applications as a mild Lewis-acid in recent
7
years to ease up various synthetic organic transformations. The X-ray
structure analysis of the phenyl derivative confirms the presence of
exocyclic double bonds in the products in Z-Z configuration (3).
RESULTS AND DISCUSSION
An equimolar mixture of thiopyranone 4 and an aldehyde (as listed in
Table I) was treated with LiBr (10 mol%) and Et3N in dichloromethane.
Complete conversion of the starting materials to the desired product
was observed within a few hours as reactions were monitored by TLC.
TABLE I Alodol Condensation of 4 with Aldehydes under LiBr
Catalysis
◦
Yield%a
Entry
ArCHO
benzaldehyde
(p-Me)benzaldehyde
(p-MeO)benzaldehyde
(p-CI)benzaldehyde
2-thiophenecarbaldehyde
furfural
M.P. ( C)
Product
1
2
3
4
5
6
7
142–144
186–188
174–176
126–128
155–157
156–158
186–188
3a
3b
3c
3d
3e
3f
95
91
93
95
92
88
94
3-pyridinecarbaldehyde
3g
aIsolated yields.

Bis(arylmethylidene)thiopyranones and Crystal Structure
2893
FIGURE 1 Structure of 3a at 193 K in the crystal. Displacement ellipsoids at
5
0% probability level. C1–C2 1.495(2), C2–C3 1.498(2), C2–C6 1.344(2), C3–S1
˚
1.802(2), S1–C4 1.799(2), C4–C5 1.499(2), C5–C1 1.503(2), C5–C13 1.331(2) A.
Control experiments confirmed the combined promoting and catalytic
effects of LiBr; an alternative reaction in the absence of the catalyst led
to formation of less than 10% of 3a after 24 h.
The structure of the products was assigned with spectroscopic meth-
5
,8
ods and compared with the literature data. In order to verify this
structure, a single crystal of 3a was prepared and investigated by X-ray
diffraction. The result, as depicted in the Figure 1, clearly supports the
proposed structure with exocyclic double bonds C2–C6 and C5–C13.
The experimental data and crystal parameters are given in the
Table II.
The atoms of the central moiety C1, O1, C2, C3, C4, C5, C6, C7,
C13, and C14 are almost coplanar (maximum deviation from the best
˚
plane 0.065(2) A). The folding angle of this main plane and the C3,
◦
S1, C4 plane is 122.8(6) . The planes of the phenyl rings are rotated
out of the main plane as documented in torsion angles C5-C13-C14-
◦
◦
C15 –143.0(2) and C2-C6-C7-C12 147.3(2) , resulting in a molecule
conformation resembling a landing bird (Fig. 2).
In summary, a LiBr promoted aldol condensation of thiopyran 4 with
various aldehydes was carried out within few hours. Reactions pro-
ceeded with catalytic amounts of the Lewis acid, and the use of harsh
conditions and tedious work up procedures were avoided. High yields
of the products and rapid completion of the reactions are among other
advantages of this methodology. The proposed structure was confirmed
for the first time by single crystal X-ray diffraction analysis.
EXPERIMENTAL
Typical Procedure for the Synthesis of 3a
A mixture of 4 (5.0 mmol), benzaldehyde (5.0 mmol), LiBr (0.5 mmol),
and Et3N (10.0 mmol) in CH2Cl2 (15 mL) was stirred in a flask.
The course of the reaction was monitored by TLC and complete

2
894
M. S. Abaee et al.
TABLE II Crystal and Experimental Data for the Structure
Determination of 3a
Empirical formula
C19 H16 O S
Formula weight
Habitus, color
Crystal size
Crystal system
Space group
292.38
column, colorless
0.33 × 0.15 × 0.12 mm
monoclinic
3
P21/n, Z = 4
˚
Unit cell dimensions
a = 10.035(1) A
˚
◦
b = 9.540(1) A β = 95.32(1) .
˚
3
c = 15.595(1) A
˚
Volume
Wavelength
1486.55(15) A
˚
0.71073 A
Temperature
193(2) K
3
Density (calculated)
Absorption coefficient
F(000)
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 25.87
Refinement method
Treatment of hydrogen atoms
Data / restraints / parameters
1.306 Mg/m
0.213 mm 1, no correction
−
616
2.32 to 25.87 .
◦
−12<=h<=12, −11<=k<=11, −19<=l<=19
14181
2870 [R(int) = 0.0308]
◦
99.6 %
2
Full-matrix least-squares on F
refined with isotropic displacement parameters
2870 / 0 / 254
2
Goodness-of-fit on F
0.715
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 = 0.0307, wR2 = 0.0758
R1 = 0.0505, wR2 = 0.0828
˚
−3
0.185 and −0.159 e.A
disappearance of the starting materials was observed within few
hours. The mixture was diluted by dichloromethane (20 mL) and
washed twice by water (20 mL portions). The organic phase was
dried over Na2SO4, the solvent was removed at reduced pressure
and the product was precipitated after removal of the volatile por-
tion. The NMR, and IR spectra and melting point of the product
were obtained and compared perfectly with those existing in the
5
,8
literature.
(
3Z,5Z)-3,5-Dibenzylidene-tetrahydrothiopyran-4-one (3a)
◦
Yellow crystals were obtained in 95% yield. M.p. 142–144 C; IR (KBr,
−
1
1
cm ) 1599, 1444, 1269; H NMR (CDCl3)δ 3.84 (s, 4H), 7.30 (s, 10H),
7
1
1
3
.72 (s, 2H); C NMR (CDCl3)δ0.0, 128.4, 128.7, 129.8, 133.7, 134.9,
+
36.6, 188.6; MS (70 eV) m/z (%) 292 (M ), 147, 115.

Bis(arylmethylidene)thiopyranones and Crystal Structure
2895
FIGURE 2 Side views of the structure of 3a in the crystal showing the molec-
ular conformation.
X-Ray Crystal Structure Analysis of 3a
A crystal of 3a, grown from hexane, was investigated on an IPDS
◦
area detector system (Stoe) at −80 C using MoKα-radiation. Crystal
and experimental data are given in the Table II. The structure was
solved by direct methods and refined using the SHELX97 programs.
Crystallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
Crystallographic Data Center as supplementary publication no.
CCDC-637988. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:
int. Code +44(1223)336-033; E-mail: deposit@ccdc.cam.ac.uk or via
www.ccdc.cam.ac.uk/conts/retrieving.html]
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