Highly convenient regioselective synthesis of functionalized arylated benzene from ketene-S,S-acetal under mild conditions at room temperature

Article abstract of DOI:10.1016/j.tetlet.2008.11.098

A general, highly efficient synthesis of arylated benzenes from simple stitching of α-oxo-ketene-S,S-acetals and functionalized deoxybenzoins via a 'lactone intermediate' is described. This procedure offers easy access to highly functionalized arylated be

Full text of DOI:10.1016/j.tetlet.2008.11.098

Tetrahedron Letters 50 (2009) 680–683
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Highly convenient regioselective synthesis of functionalized arylated
benzene from ketene-S,S-acetal under mild conditions at room temperature q
*
Vijay Kumar, Fateh V. Singh, Amrita Parihar, Atul Goel
Division of Medicinal and Process Chemistry, Central Drug Research Institute, Lucknow 226001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A general, highly efficient synthesis of arylated benzenes from simple stitching of a-oxo-ketene-S,S-ace-
Received 17 September 2008
Revised 20 November 2008
Accepted 25 November 2008
Available online 30 November 2008
tals and functionalized deoxybenzoins via a ‘lactone intermediate’ is described. This procedure offers easy
access to highly functionalized arylated benzenes containing sterically demanding groups in good to
excellent yields. The advantage of the procedure lies in the fabrication of arylated benzenes with desired
conformational flexibility along the molecular axis at room temperature and in a transition metal-free
environment through easily accessible precursors.
Keywords:
Ó 2008 Elsevier Ltd. All rights reserved.
Ketene-S,S-acetal
2H-Pyran-2-one
Arylated benzene
Molecular propeller
Quinquephenyl
Over the last few decades, polyarylated propeller systems have
received a great deal of attention owing to their unique photophys-
ical and optical properties associated with them.1 These propeller
systems exhibit a geared rotation about a central, planar unit such
as a phenyl ring, which can perform as molecular rotors,1 and thus
have shown great relevance to modern carbon-nanotechnology.2
The inherent rotational isomerism associated with sterically
crowded arylated benzenes has further enhanced the importance
of these propellers with a desired degree of rotational freedom
for the development of new chiral ligands or auxiliaries for asym-
metric synthesis.3 Recently, a current interest has been focused to
fabricate useful quateraryl or quinquearyl building blocks with
electron-donor and -acceptor groups for preparing advanced elec-
troluminescent materials such as organic light emitting diodes.4
Highly arylated benzenes are difficult to be synthesized by pal-
ladium-catalyzed iterative aryl–aryl cross-coupling between the
electrophilic aromatic polyhalides and organometallic species.5
Although there are numerous synthetic strategies for di- and/or tri-
arylated benzenes,6 methods for polyarylated benzene such as
quater- or quinquephenyls remain sparse. Limited procedures are
known for the synthesis of such arylated benzene, in which one
of the phenyl rings is tagged with three or more aromatic rings
in a juxtaposed manner. The most common and popular approach
for the introduction of polyaryl groups onto the benzene skeleton
is based on the [4+2]-cycloaddition of arylated cyclopentadienones
or 2H-pyran-2-ones with functionalized alkynes at elevated tem-
peratures.7 The notable examples of various types of cycloaddition
processes involve copper-mediated cycloaddition of zirconacyclo-
pentadienes with fumaronitrile,8 through flash vacuum pyrolysis
of cyclobutane-fused sulfolanes,9 reaction of tetraphenylcyclopen-
tadienones either with allyl phenyl sulfone10 or with 7-oxanorbor-
nadienes11 or with acrylonitriles12 at high temperature. Some of
these mentioned reactions, however, are relatively limited in scope
particularly towards the tolerance of electron-donor or -acceptor
substituents or involve high reaction temperature and/or forma-
tion of undesirable side products.
The wide-ranging applications and high demand of arylated
benzenes and paucity of mild synthetic methodologies prompted
us to develop a simple, general and efficient route that could offer
flexibility of substituent variations on benzene scaffold. In this Let-
ter, we report a highly convenient and commercially viable syn-
thetic route for arylated benzenes through simple stitching of
a-
oxo-ketene-S,S-acetals and deoxybenzoin in just two steps via
six-membered lactone intermediate. The versatility and generality
of the procedure lies in the creation of a central benzene ring with
optionally functionalized tetraaryl moieties in a controlled fashion
at room temperature.
q
C.D.R.I. Communication No. 7254.
During our recent studies13 on the chemistry of arylated 2H-
pyran-2-ones, we observed that the nature of an electron-with-
drawing group such as nitrile or ester group at position 3 of 2H-
pyran-2-one dictates the Michael addition of a conjugate base of
* Corresponding author at present address: Institut für Organische Chemie,
Universität Würzburg, Am Hubland, 97074 Würzburg, Germany. Tel.: +49 931 888
5393; fax: +49 931 8884755.
E-mail addresses: goela@chemie.uni-wuerzburg.de, agoel13@yahoo.com (A.
Goel).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.11.098

V. Kumar et al. / Tetrahedron Letters 50 (2009) 680–683
681
conditions furnished 5,6-diaryl-2H-pyran-2-ones4e,13 8a–d in
excellent yields (Scheme 2). The 5,6-diaryllactones 8a–d generated
from a-cyano-ketene-S,S-acetal 6 possess a methylsulfanyl group,
which may be replaced by a secondary amine. In general, when a
secondary amine reacts with 4-methylsulfanyl-2H-pyran-2-ones
in the presence of methanol at reflux temperature, the correspond-
ing 4-amino-2H-pyran-2-ones are formed very easily with
excellent yields. Accordingly when we performed a reaction of
R4
SMe
R3
4
R2
R1
3
X
R4
O
O
KOH / DMF
X=COOMe
5
R2
R1
O
+
2
O
R3
6
O1
1
O
2
O
5
KOH / DMF
R4
X=CN
(64-84%)
SMe
3-cyano-5,6-diaryl-4-methylsulfanyl-2H-pyran-2-ones
and
a
R3
R2
R1
CN
R4
secondary amine such as dimethyl amine or piperidine under sim-
ilar conditions, to our surprise, no desired lactone 10 was obtained
(Scheme 2).
O
R2
R1
+
R3
O
3
O
Interestingly, when we tried reaction of 8a–d with a primary al-
kyl amine such as methyl amine or isopropyl amine, we observed a
clean reaction leading to the formation of 5,6-diaryl-4-alkylamino-
2-oxo-2H-pyran-3-carbonitriles 9a–e in good yield.16 Further, 5,6-
diaryl-4-alkylamino-2-oxo-2H-pyran-3-carbonitriles 9a–e were
methylated to 5,6-diaryl-4-(N-alkyl,N-methylamino)-2-oxo-2H-
pyran-3-carbonitriles 10a–e by CH3I in the presence of cesium car-
bonate in dry acetone under reflux conditions.17
4
(29-40%)
(51-62%)
Scheme 1.
deoxybenzoin onto the lactone either at position 4 and/or position
6 of 5,6-diaryl-2H-pyran-2-ones (Scheme 1). The reaction of 3-cy-
ano-5,6-diaryl-2H-pyran-2-ones (1, X = CN) with functionalized
deoxybenzoins (2) led to the formation of 4-(2-oxo-1,2-diaryleth-
yl)-5,6-diaryl-pyran-2-ones (3) through an unusual decyanation
as a major product and tetraarylbenzene (4) as a minor product.
A characteristic feature of 3-cyano-5,6-diaryl-2H-pyran-2-ones 1
revealed that C4 and C6 positions are susceptible to nucleophilic
attack in a competitive manner depending upon the nature of
nucleophile used. In order to prepare donor–acceptor arylated ben-
zene exclusively, the change of electron density at position 4 of 2H-
pyran-2-one 1 was desirable.
Our approach to prepare 60-(N-alkyl,N-methylamino)-[1,10;20,
100;30,1000;4’,10000]quinquephenyl-50-carbonitriles 11a–i is based on
the ring transformation of 5,6-diaryl-4-(N-alkyl,N-methylamino)-
2-oxo-2H-pyran-3-carbonitriles 10a–e using functionalized deoxy-
benzoins 7a–d as a carbanion source. Unfortunately, reaction of
10a with a deoxybenzoin containing an electron-withdrawing ni-
tro group (7, R5 = NO2, R6 = OMe) resulted in a mixture of decom-
posed products. The 2H-pyran-2-ones 10a–e have three
electrophilic centres; C2, C4 and C6 in which the position C6 is
highly susceptible to nucleophilic attack due to the extended con-
jugation and the presence of an electron-withdrawing substituent
at position 3 of the pyranone ring. Thus, stirring an equimolar mix-
ture of 5,6-diaryl-4-(N-alkyl,N-methylamino)-2-oxo-2H-pyran-3-
carbonitriles 10a–e and functionalized deoxybenzoins 7a–d in
the presence of KOH in dry DMF for 2–4 h at room temperature
afforded 60-(N-alkyl,N-methylamino)-[1,10;20,100;30,1000;40,10000]-quin-
Our aim to prepare 5,6-diaryl-2H-pyran-2-ones 8a–d was
achieved by preparing a key intermediate a-cyano-ketene-S,S-ace-
tal 6 from easily accessible precursors methyl cyanoacetate, carbon
disulfide and methyl iodide through modified procedure.4e,14 The
a
-cyano-ketene-S,S-acetal 6 on Michael addition–cyclization reac-
tion with various substituted deoxybenzoins15 7a–d under alkaline
R1
R1
R2
SMe
SMe
SMe
CN
OH
DMSO
KOH
CN
CN
O
MeS
+
COOMe
O
7
R3
O
R1
COOMe
O
6
OMe
R2
R3
R2
R3
Me R4
N
H
-CH3OH
X
CH3OH
R1
R1
Me
R4
R1
NHR4
CN
N
O
SMe
CN
CH3I
CN
O
R4 NH2
CH3OH
Cs2CO3
acetone
O
O
O
O
R2
R3
10
R2
R3
9
R3
R2
R3
8
Entry
R1
R2
R4
Yield (%)
9
10
H
H
OMe
Cl
H
H
H
H
H
OMe
H
Me
Me
Me
Me
i-Pr
71
88
90
83
79
90
91
89
94
86
a
b
c
d
e
OMe
OMe
OMe
H
Scheme 2.

682
V. Kumar et al. / Tetrahedron Letters 50 (2009) 680–683
O
R4
N
CN
O
R1
Me
R4
O
Me
R2
R6
N
O
CN
O
R1
DMF
KOH
+
R3
O
R6
R5
7
R2
R3
10
R5
R4
O
R1
Me
R3
R4
CN
R4
N
N
Me
CN
Me
N
O
O
CN
O
R6
R1
R1
H+
-H2O
-CO2
R6
R3
R3
R2
R6
R5
R2
R2
R5
11
R5
11
a
b
c
d
e
R1
R2
H
H
OMe
H
OMe
OMe
R3
H
H
H
H
H
H
H
R4
R5
H
H
H
OMe
H
OMe
OMe
H
R6
H
Cl
H
Yield (%)
H
H
H
H
H
H
Me
Me
Me
Me
Me
Me
Me
Me
i-Pr
92
89
87
88
90
92
89
56
73
OMe
OMe
OMe
OMe
H
f
g
h
i
OMe OMe
Cl
H
OMe
H
OMe
H
OMe
OMe
Scheme 3.
quephenyl-50-carbonitriles 11a–i in 56–92% yields (Scheme 3). The
reaction was monitored by TLC, which showed an intense blue spot
when exposed to short-wave UV radiation at 254 nm. After com-
pletion, the reaction mixture was poured into ice water and neu-
tralized with dilute HCl. The precipitate was filtered, dried over
CaCl2 and the crude product thus obtained was purified by neutral
alumina column chromatography using chloroform/hexane (1:4)
as the eluent. All the compounds were characterized by the spec-
troscopic analysis.18
The plausible reaction mechanism for the formation of donor–
acceptor arylated benzenes 11a–i from 2H-pyran-2-ones 10a–e
is depicted in Scheme 3. The transformation of 5,6-diaryl-2-oxo-
2H-pyran-3-carbonitriles 10a–e into quinquephenyls 11a–i is
possibly initiated by Michael addition of conjugate base of deoxy-
benzoin 7 at position C6 of lactone 10, followed by intramolecular
cyclization involving the carbonyl functionality of 7 and C3 of the
pyranone ring followed by elimination of carbon dioxide and water
to yield quinquephenyls 11a–i in excellent yields.
Industrial Research, New Delhi, for research fellowships. Authors
are thankful to SAIF, CDRI, Lucknow for providing spectroscopic
analysis.
References and notes
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In summary, we have demonstrated highly convenient ring
transformation approach to access functionally congested arylated
benzenes at room temperature in excellent yields. This protocol of-
fers in a transition metal-free environment, the flexibility of intro-
ducing the electron-donor or -acceptor groups in the molecular
architecture of arylated benzene scaffolds.
Acknowledgements
9. Aitken, R. A.; Cadogan, J. I. G.; Gosney, I.; Humphries, C. M.; AcLaughlin, L. M.;
Wyse, S. J. J. Chem. Soc., Perkin Trans. 1 1999, 605–614.
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391.
A.G. is grateful to Professor G. Bringmann for his encourage-
ments and kind support and Alexander von Humboldt Foundation
for research fellowship. This work is supported by the Indian Coun-
cil of Medical Research, and Department of Science and Technol-
ogy, New Delhi. V.K. and F.V.S. thank Council of Scientific and
12. Oku, A.; Hasegawa, H.; Shimazu, H.; Nishimura, J.; Harada, T. J. Org. Chem. 1981,
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V. Kumar et al. / Tetrahedron Letters 50 (2009) 680–683
683
13. Singh, F. V.; Dixit, M.; Chaurasia, S.; Raghunandan, R.; Maulik, P. R.; Goel, A.
Tetrahedron Lett. 2007, 48, 8998–9002.
14. Tominaga, Y. Trends Heterocycl. Chem. 1991, 2, 43–83.
15. Allen, C. F. H.; Barker, W. E.. In Deoxybenzoins, Organic Syntheses; Blatt, A. H.,
Ed.; John Wiley and Sons: New York, 1943; Vol. 2, pp 156–158.
J = 8.4 Hz, 2H, Ar); IR (KBr) 1716 (CO), 2214 cmꢀ1 (CN); MS (ESI) 411 (M++1).
Compound 10e: White solid; mp 178–180 °C; 1H NMR (300 MHz, CDCl3) d 1.00
(d, J = 6.6 Hz, 6H, 2Me), 2.78 (s, 3H, NMe), 3.96–4.09 (m, 1H, CH), 7.02–7.25 (m,
7H, ArH), 7.27–7.33 (m, 3H, ArH); IR (KBr) 1709 (CO), 2217 cmꢀ1 (CN); MS (ESI)
345 (M++1).
16. General procedure for the synthesis of 5,6-diaryl-4-alkylamino-2-oxo-2H-pyran-3-
carbonitrile (9a–e): A mixture of a respective compound 8a–d (1 mmol) and
methyl amine or isopropyl amine (1.2 mmol) was refluxed in methanol
(10 mL) for 1–2 h. After completion, the solvent was evaporated under
vacuum, and the residue was treated with water and extracted with
chloroform. The crude product was purified on a silica gel column using
chloroform as the eluent. Compound 9a: White solid; mp 160–162 °C; 1H NMR
(300 MHz, CDCl3) d 3.41 (d, J = 5.6 Hz, 3H, NMe), 5.25 (br s, 1H, NH), 7.10–7.31
(m, 7H, ArH), 7.42–7.48 (m, 3H, ArH); IR (KBr) 1716 (CO), 2218 cmꢀ1 (CN); MS
(FAB) 303 (M++1); HRMS calcd for C19H14O2N2: 302.1055, found: 302.1042.
Compound 9b: Yellow solid; mp 224–226 °C; 1H NMR (300 MHz, CDCl3) d 3.35
(d, J = 5.6 Hz, 3H, NMe), 3.75 (s, 3H, OMe), 5.18 (br s, 1H, NH), 6.66 (d, J = 9.0 Hz,
2H, ArH), 7.14 (d, J = 9.0 Hz, 2H, ArH), 7.16–7.24 (m, 2H, ArH), 7.43–7.51 (m,
3H, ArH); IR (KBr) 1702 (CO), 2215 cmꢀ1 (CN); MS (ESI) 333 (M++1). Compound
18. General procedure for the synthesis of 60-N-alkyl,N-methylamino-
[1,10;20,100;30,1000;40,10000]-quinquearyl-50-carbonitrile (11a–i):
A
mixture of
a
respective compound 10a–e (1 mmol), functionalized deoxybenzoins
7
(1.2 mmol) and powdered KOH (1.2 mmol) in dry DMF (5 mL) was stirred at
room temperature for 2–5 h. At the end, reaction mixture was poured into ice
water with vigorous stirring and finally neutralized with dilute HCl. The solid
thus obtained was filtered and purified on a neutral alumina column using
chloroform–hexane (1:4) as the eluent. Compound 11a: White solid; mp 174–
176 °C; 1H NMR (300 MHz, CDCl3) d 2.67 (s, 6H, NMe2), 6.67–6.76 (m, 4H, ArH),
6.80–6.87 (m, 6H, ArH), 6.97–7.04 (m, 2H, ArH), 7.14–7.22 (m, 8H, ArH); IR
(KBr) 2215 cmꢀ1 (CN); MS (ESI) 451 (M++1); HRMS calcd for C33H26N2:
450.2096, found: 450.2093. Compound 11b: White solid; mp 188–190 °C; 1H
NMR (200 MHz, CDCl3) d 2.66 (s, 6H, NMe2), 6.64–6.77 (m, 4H, ArH), 6.79–6.90
(m, 6H, ArH), 6.94–7.03 (m, 2H, ArH), 7.07–7.23 (m, 7H, ArH); IR (KBr)
2218 cmꢀ1 (CN); MS (ESI) 485 (M++1); HRMS calcd for C33H25ClN2: 484.1706,
found: 484.1706. Compound 11c: White solid; mp 224–226 °C; 1H NMR
(200 MHz, CDCl3) d 2.66 (s, 6H, NMe2), 3.59 (s, 3H, OMe), 6.38 (d, J = 8.6 Hz, 2H,
ArH), 6.59 (d, J = 8.6 Hz, 2H, ArH), 6.67–6.74 (m, 2H, ArH), 6.81–6.88 (m, 3H,
ArH), 7.00 (d, J = 8.6 Hz, 2H, ArH), 7.07–7.18 (m, 8H, ArH); IR (KBr) 2214 cmꢀ1
(CN); MS (ESI) 481 (M++1). Compound 11d: White solid; mp 182–184 °C; 1H
NMR (200 MHz, CDCl3) d 2.65 (s, 6H, NMe2), 3.60 (s, 3H, OMe), 3.76 (s, 3H,
OMe), 6.39 (d, J = 8.6 Hz, 2H, ArH), 6.61 (d, J = 8.6 Hz, 2H, ArH), 6.64–6.80 (m,
4H, ArH), 6.81–6.91 (m, 3H, ArH), 6.93–7.02 (m, 2H, ArH), 7.05–7.20 (m, 5H,
ArH); IR (KBr) 2214 cmꢀ1 (CN); MS (ESI) 511 (M++1). Compound 11e: White
solid; mp 144–146 °C; 1H NMR (200 MHz, CDCl3) d 2.65 (s, 6H, NMe2), 3.59 (s,
3H, OMe), 3.74 (s, 3H, OMe), 6.38 (d, J = 8.8 Hz, 2H, ArH), 6.58 (d, J = 8.8 Hz, 2H,
ArH), 6.67–6.76 (m, 4H, ArH), 6.82–6.93 (m, 3H, ArH), 6.95–7.02 (m, 2H, ArH),
7.04–7.22 (m, 5H, ArH); IR (KBr) 2216 cmꢀ1 (CN); MS (ESI) 511 (M++1).
Compound 11f: White solid; mp 138–140 °C; 1H NMR (300 MHz, CDCl3) d 2.60
(s, 6H, NMe2), 3.56 (s, 3H, OMe), 3.57 (s, 3H, OMe), 3.72 (s, 3H, OMe), 6.32–6.44
(m, 4H, ArH), 6.50–6.62 (m, 4H, ArH), 6.70 (d, J = 8.6 Hz, 2H, ArH), 6.90–6.98
(m, 2H, ArH), 7.00–7.19 (m, 5H, ArH); IR (KBr) 2217 cmꢀ1 (CN); MS (ESI) 541
(M++1); HRMS calcd for C36H32N2O3: 540.2413, found: 540.2400. Compound
11g: White solid; mp 214–216 °C; 1H NMR (200 MHz, CDCl3) d 2.65 (s, 6H,
NMe2), 3.62 (s, 6H, 2OMe), 3.76 (s, 6H, 2OMe), 6.41 (d, J = 8.6 Hz, 4H, ArH),
6.54–6.64 (m, 4H, ArH), 6.66–6.78 (m, 4H, ArH), 6.88 (d, J = 8.6 Hz, 2H, ArH),
7.07 (d, J = 8.6 Hz, 2H, ArH); IR (KBr) 2213 cmꢀ1 (CN); MS (ESI) 571 (M++1).
Compound 11h: White solid; mp 140–142 °C; 1H NMR (300 MHz, CDCl3) d 2.68
(s, 6H, NMe2), 3.46 (s, 3H, OMe), 3.61 (s, 3H, OMe), 5.96 (d, J = 2.2 Hz, 1H, ArH),
6.05 (dd, J = 8.4, 2.2 Hz, 1H, ArH), 6.47 (d, J = 8.4 Hz, 1H, ArH), 6.65–6.68 (m, 1H,
ArH), 6.78–6.88 (m, 4H, ArH), 6.89–7.05 (m, 2H, ArH), 7.11–7.22 (m, 7H, ArH);
IR (KBr) 2214 cmꢀ1 (CN); MS (ESI) 545 (M++1). Compound 11i: White solid; mp
136–138 °C; 1H NMR (300 MHz, CDCl3) d 0.82 (d, J = 6.5 Hz, 6H, 2Me), 2.86 (s,
3H, NMe), 3.14–3.22 (m, 1H, CH), 3.60 (s, 3H, OMe), 3.76 (s, 3H, OMe), 6.39 (d,
J = 8.8 Hz, 2H, ArH), 6.62 (d, J = 8.5 Hz, 2H, ArH), 6.67–6.71 (m, 2H, ArH), 6.75
(d, J = 8.8 Hz, 2H, ArH), 6.80–6.88 (m, 3H, ArH), 6.96–7.02 (m, 2H, ArH), 7.04–
7.15 (m, 5H, ArH); IR (KBr) 2218 cmꢀ1 (CN); MS (ESI) 539 (M++1).
9c: Yellow solid; mp 176–178 °C; 1H NMR (200 MHz, CDCl3)
d 3.35 (d,
J = 5.6 Hz, 3H, Me), 3.75 (s, 3H, OCH3), 3.85 (s, 3H, OCH3), 5.32 (br s, 1H, NH),
6.67 (d, J = 9.0 Hz, 2H, ArH), 6.99 (d, J = 9.0 Hz, 2H, ArH), 7.07–7.19 (m, 4H,
ArH); IR (KBr) 1707 (CO), 2210 cmꢀ1 (CN); MS (FAB) 363 (M++1); 13C NMR
(50.0 MHz) 32.56, 55.69, 55.82, 110.41, 113.85, 116.21, 117.39, 122.06, 124.14,
131.31, 133.24, 158.14, 160.73, 160.91, 161.40. Compound 9d: Yellow solid;
mp 240–242 °C; 1H NMR (200 MHz, CDCl3) d 3.36 (d, J = 5.6 Hz, 3H, NMe), 3.57
(s, 3H, OMe), 3.75 (s, 3H, OMe), 5.31 (br s, 1H, NH), 6.21 (d, J = 2.0 Hz, 1H, ArH),
6.32 (dd, J = 2.0, 8.8 Hz, 1H, ArH), 6.97–7.08 (m, 3H, ArH), 7.31 (d, J = 8.3 Hz, 2H,
ArH); IR (KBr) 1717 (CO), 2215 cmꢀ1 (CN); MS (ESI) 397 (M++1). Compound 9e:
White solid; mp 174–176 °C; 1H NMR (300 MHz, DMSO-d6) d 1.17 (d, J = 6.6 Hz,
6H, 2Me), 4.46–4.61 (m, 1H, CH), 5.82 (d, J = 8.2 Hz, 1H, NH), 7.13–7.34 (m, 7H,
ArH), 7.38–7.48 (m, 3H, ArH); IR (KBr) 1712 (CO), 2208 cmꢀ1 (CN); MS (ESI)
331 (M++1); HRMS calcd for C21H18O2N2: 330.1368, found: 330.1374.
17. General procedure for the synthesis of 4-(N-alkyl,N-methylamino)-2-oxo-5,6-
diaryl-2H-pyran-3-carbonitrile (10a–e): A mixture of a respective compound
9a–e (1 mmol) and methyl iodide (1.5 mmol) was refluxed in dry acetone
(10 mL) in the presence of Cs2CO3 (2 mmol) for 1–2 h. After completion, the
unreacted Cs2CO3 was filtered and washed with acetone. The filtrate was
evaporated under vacuum. Crude product was purified on a silica gel column
using chloroform as the eluent. Compound 10a: White solid; mp 216–218 °C;
1H NMR (300 MHz, CDCl3) d 2.89 (s, 6H, NMe2), 7.05–7.35 (m, 10H, ArH); IR
(KBr) 1716 (CO), 2227 cmꢀ1 (CN); MS (FAB) 317 (M++1). Compound 10b:
Yellow solid; mp 232–234 °C; 1H NMR (300 MHz, CDCl3) d 2.87 (s, 6H, NMe2),
3.75 (s, 3H, OMe), 6.65 (d, J = 9.0 Hz, 2H, ArH), 7.02 (d, J = 9.0 Hz, 2H, ArH),
7.08–7.19 (m, 2H, ArH), 7.29–7.38 (m, 3H, ArH); IR (KBr) 1716 (CO), 2216 cmꢀ1
(CN); MS (ESI) 347 (M++1). Compound 10c: Yellow solid; mp 212–214 °C; 1H
NMR (300 MHz, CDCl3) d 2.88 (s, 6H, NMe2), 3.76 (s, 3H, OCH3), 3.82 (s, 3H,
OCH3), 6.67 (d, J = 8.8 Hz, 2H, ArH), 6.87 (d, J = 8.8 Hz, 2H, ArH), 6.97–7.08 (m,
4H, ArH); IR (KBr) 1704 (CO), 2208 cmꢀ1 (CN); MS (FAB) 377 (M++1).
Compound 10d: Yellow solid; mp 226–228 °C; 1H NMR (300 MHz, CDCl3) d
2.90 (s, 6H, NMe2), 3.59 (s, 3H, OMe), 3.75 (s, 3H, OMe), 6.23 (d, J = 2.0 Hz, 1H,
ArH), 6.31 (d, J = 2.0, 8.4 Hz, 1H, ArH), 6.86 (d, J = 8.4 Hz, 2H, ArH), 7.19 (d,