An efficient synthesis of carboxaldehyde derivatives of 4H-pyran-4-one

Article abstract of DOI:10.1139/V07-034

We developed a general method for the synthesis of various 2-mono- and 2,6-di-carboxaldehyde substituted derivatives of 3,5-diphenyl-4H-pyran-4-one and 4H-pyran-4-one. 3,5-Diphenyl-6-methyl-4-oxo-4H-pyran-2-carboxaldehyde (4a), 6-methyl-4-oxo-4H-pyran-2-c

Full text of DOI:10.1139/V07-034

352
An efficient synthesis of carboxaldehyde
derivatives of 4H-pyran-4-one
Reza Teimuri-mofrad and Fatemeh Abrishami
Abstract: We developed a general method for the synthesis of various 2-mono- and 2,6-di-carboxaldehyde substituted
derivatives of 3,5-diphenyl-4H-pyran-4-one and 4H-pyran-4-one. 3,5-Diphenyl-6-methyl-4-oxo-4H-pyran-2-
carboxaldehyde (4a), 6-methyl-4-oxo-4H-pyran-2-carboxaldehyde (4b), 3,5-diphenyl-4-oxo-4H-pyran-2,6-
dicarboxaldehyde (5a), 4-oxo-4H-pyran-2,6-dicarboxaldehyde (5b), 3,5-diphenyl-6-hydroxymethyl-4-oxo-4H-pyran-2-
carboxaldehyde (10a), and 6-hydroxymethyl-4-oxo-4H-pyran-2-carboxaldehyde (10b) were obtained from the corre-
sponding di-, tri-, and tetra-bromo derivatives of 2,6-dimethyl-3,5-diphenyl-4H-pyran-4-one (1a) and 2,6-dimethyl-4H-
pyran-4-one (1b) by treatment with silver acetate followed by hydrolysis. Compounds 4a and 4b were also obtained by
the oxidation of 10a and 10b with barium manganate.
Key words: 4H-pyran-4-one, hydroxymethyl and carboxaldehyde derivatives, acetoxylation, hydrolysis, oxidation.
Résumé : On a développé une méthode de synthèse générale pour divers 2-mono- et 2,6-di-carboxaldéhydes dérivés de
la 3,5-diphényl-4H-pyran-4-one et la 4H-pyran-4-one. On a ainsi préparé la 3,5-diphényl-6-méthyl-4-oxo-4H-pyrane-2-
carboxaldéhyde (4a), la 6-méthyl-4-oxo-4H-pyrane-2-carboxaldéhyde (4b), la 3,5-diphényl-4-oxo-4H-pyrane-2,6-
dicarboxaldéhyde (5a), la 4-oxo-4H-pyrane-2,6-dicarboxaldéhyde (5b), la 3,5-diphényl-6-hydroxyméthyl-4-oxo-4H-py-
rane-2-carboxaldéhyde (10a) et la 6-hydroxyméthyl-4-oxo-4H-pyrane-2-carboxaldéhyde (10b) en soumettant les dérivés
di-, tri- et tétra-bromés correspondants de la 2,6-diméthyl-3,5-diphényl-4H-pyran-4-one (1a) et de la 2,6-diméthyl-4H-
pyran-4-one (1b) à un traitement par de l’acétate d’argent suivi par une hydrolyse. Les composés 4a et 4b ont aussi été
obtenus par oxydation des produits 10a et 10b par le manganate de baryum.
Mots-clés : 4H-pyran-4-one, dérivés hydroxyméthyles et carboxaldéhydes, acétoxylation, hydrolyse, oxydation.
[Traduit par la Rédaction] Teimuri-mofrad and Abrishami 357
Introduction
4H-pyran-4-one with benzaldehyde, followed by the oxida-
tion of the corresponding mono- and di-styryl derivatives in
the presence of osmium tetroxide and potassium periodate
(Scheme 1) (16).
4H-Pyran-4-one and its derivatives have been the subject
of intensive research because of their importance in various
applications and their widespread biological significance (1–
3). They are widely distributed in nature (4–6), and conse-
quently, have become accessible in laboratories by a variety
of synthetic methods (7–9). These compounds are useful as
fungicides, herbicides, and in the treatment of hypersensitiv-
ity conditions, such as asthma and allergies (10, 11).
Functionalized heterocycles are often used for the synthe-
sis of the target organic compounds. Some 4H-pyran-4-ones,
containing a carboxaldehyde group, may be prepared by the
oxidation of hydroxymethyl group in derivatives of kojic
acid (12–14) and by the formylation of pyrones in the
presence of trifluoroacetic acid (15). Recently, Ghandi and
co-workers prepared some mono- and di-carboxaldehyde de-
rivatives of 4H-pyran-4-one, substituted at positions 2 and 6
by the condensation of mono- and dimethyl derivatives of
It is important to explore an efficient method for the syn-
thesis of carboxaldehyde derivatives of 4H-pyran-4-ones be-
cause these compounds are potentially useful and carry out a
wide range of reactions that would make them suitable for
the synthesis of a number of 4H-pyran-4-one derivatives. For
example, host macrocycles, such as azacrown ethers, could
be obtained from their dicarboxaldehyde derivatives.
We report a novel method for the synthesis of mono- and
di-carboxaldehyde derivatives of 4H-pyran-4-one, substi-
tuted at positions 2 and 6, from the acetoxylation and hydro-
lysis of the corresponding di-, tri-, and tetra-bromo
derivatives of 4H-pyran-4-one.
Results and discussion
2-Dibromomethyl-6-methyl-4H-pyran-4-one (6b), 6-
bromomethyl-2-dibromomethyl-4H-pyran-4-one (7b), 2,6-
bis(dibromomethyl)-4H-pyran-4-one (8b), and 3,5-dibromo-
2,6-bis(dibromomethyl)-4H-pyran-4-one (8c) were first pre-
pared in 1997 by Lowe and co-workers through the
bromination of 2,6-dimethyl-4H-pyran-4-one (1b) with
2.1 equiv. of N-bromosuccinimide in 10%, 3.1%, 3.4%, and
0.3% yields, respectively, (17). As a result, we tried to syn-
thesize 2-dibromomethyl-3,5-diphenyl-6-methyl-4H-pyran-
Received 28 November 2006. Accepted 14 March 2007.
Published on the NRC Research Press Web site at
canjchem.nrc.ca on 12 May 2007.
R. Teimuri-mofrad1 and F. Abrishami. Department of
Chemistry, Faculty of Materials, Malek-ashtar University of
Technology, Tehran, P.O. Box 16765–3454, Iran.
1Corresponding author (e-mail: teimuri@mut.ac.ir).
Can. J. Chem. 85: 352–357 (2007)
doi:10.1139/V07-034
© 2007 NRC Canada

Teimuri-mofrad and Abrishami
353
Scheme 1. (i) PhCHO, NaOMe, 1,4-Dioxane; (ii) OsO4, KIO4.
mono- and 2,6-di-carboxaldehyde derivatives of 4H-pyran-
4-one, 6-methyl-4-oxo-4H-pyran-2-carboxaldehyde (4b), 6-
acethoxymethyl-4-oxo-4H-pyran-2-carboxaldehyde
(9b),
and 4-oxo-4H-pyran-2,6-dicarboxaldehyde (5b) in 73%,
66%, and 70% yields, respectively.
Acidic hydrolysis (hydrochloric acid, water, tetrahydro-
furan) of 9a and 9b produced 3,5-diphenyl-6-hydroxy-
methyl-4-oxo-4H-pyran-2-carboxaldehyde (10a) and 6-
hydroxymethyl-4-oxo-4H-pyran-2-carboxaldehyde (10b) in
89% and 81% yields, respectively.
In addition, we decided to oxidize the monohydroxy-
methyl derivatives of 4H-pyran-4-one, 10a and 10b, to the
corresponding dicarboxaldehyde derivatives, 5a and 5b, with
barium manganate in dichloromethane and tetrahydrofuran
at room temperature. Compounds 5a and 5b were obtained
in 91% and 82% yields, respectively, (Scheme 2).
1
The data obtained from Mass spectrometry, IR, H and
4-one (6a), 6-bromomethyl-2-dibromomethyl-3,5-diphenyl-
4H-pyran-4-one (7a), and 2,6-bis(dibromomethyl)-3,5-
diphenyl-4H-pyran-4-one (8a) from 2,6-dimethyl-3,5-
diphenyl-4H-pyran-4-one (1a) by means of Wohl–Ziegler
bromination (18, 19). Bromination of 1a with 5 equiv. of N-
bromosuccinimide in the presence of dibenzoyl peroxide in
tetrachloromethane produced a mixture of 6a, 7a, and 8a, as
major products, and other minor products. The crude prod-
uct was chromatographed on silica gel and eluted with ethyl
acetate – petroleum ether (1:9) to yield 8a, 7a, and 6a as the
first, second, and third fractions in 43%, 32%, and 17%
yields, respectively. The mixture of other minor products
was obtained as the fourth fraction (Scheme 2).
13C NMR spectra, and elemental analyses are fully consis-
tent with the proposed structures.
In conclusion, we developed a new efficient method for
the preparation of mono- and di-carboxaldehyde derivatives
of 3,5-diphenyl-4H-pyran-4-one and 4H-pyran-4-one, substi-
tuted at positions 2 and 6, resulting in the compounds 4a,
4b, 5a, 5b, 9a, 9b, 10a, and 10b. Our method offers some
advantages over the previous one. For instance, it uses
cheaper reagent and has higher total yields. Some of these
compounds can be used as precursors to synthesize the host
molecules. This work is now under investigation.
As a second result, we attempted to synthesize 6b, 7b,
and 8b, in accordance with Lowe and co-workers report
(17), by means of Wohl–Ziegler bromination in the presence
of excess N-bromosuccinimide. Since Lowe and co-workers
were looking to obtain 2,6-bis(bromomethyl)-4H-pyran-4-
one, they merely used 2.1 equiv. of N-bromosuccinimide, but
they further got 6b, 7b, and 8b as well. Therefore, to in-
crease the yields of compounds 6b, 7b, and 8b, we tried to
use excess amount of N-bromosuccinimide, longer reaction
time, and sun lamps during the reaction. Bromination of 1b
(20) with 8 equiv. of N-bromosuccinimide in presence of
dibenzoyl peroxide in tetrachloromethane under radiation of
IR lamps produced a mixture of 6b, 7b, and 8b, as major
products, and other minor products. The crude product was
chromatographed on silica gel and eluted with ethyl acetate
– petroleum ether (4:1). The first fraction was 8c in 0.8%
yield, which was produced from further bromination of the
nuclear 4H-pyran-4-one positions in 8b (17). The com-
pounds 8b, 7b, and 6b were obtained as the second, third,
and fourth fractions in 31%, 23%, and 9% yields, respec-
tively. Additionally, the mixture of other minor products was
afforded as the fifth fraction (Scheme 2).
Treatment of 6a, 7a, and 8a with silver acetate in
refluxing glacial acetic acid, followed by the reaction with
aq. acetic acid (21), produced 2-mono- and 2,6-di-car-
boxaldehyde derivatives of 3,5-diphenyl-4H-pyran-4-one, 6-
methyl-3,5-diphenyl-4-oxo-4H-pyran-2-carboxaldehyde (4a),
6-acethoxymethyl-3,5-diphenyl-4-oxo-4H-pyran-2-carboxalde-
hyde (9a), and 3,5-diphenyl-4-oxo-4H-pyran-2,6-dicarbox-
aldehyde (5a) in 86%, 71%, and 75% yields, respectively.
Under the same conditions, 6b, 7b, and 8b produced 2-
Experimental
Melting points were determined with an Electrothermal
Instrument model 9100 and are uncorrected. IR spectra were
run on a Shimadzu FTIR-4300 Spectrophotometer as KBr
disks or as smears between salt plates. The 1H and 13C NMR
spectra were recorded on a FT-NMR Bruker 300 MHz spec-
trometer. Chemical shifts (δ) were reported in ppm using
TMS as internal standard. Mass spectra were recorded on a
Shimadzu MS-QP 1100 EX mass spectrometer. Elemental
analyses were performed on a Heareus, CHN-O-RAPID, an-
alyzer.
Reaction of 1a with excessive N-bromosuccinimide —
Synthesis of di-, tri-, and tetra-bromo derivatives 6a,
7a, and 8a
2,6-Dimethyl-3,5-diphenyl-4H-pyran-4-one (1a) was pre-
pared according to a published procedure (18). A mixture of
1a (5.52 g, 0.02 mol), N-bromosuccinimide (17.8 g, 0.1
mol), and dibenzoyl peroxide (0.4 g) in tetrachloromethane
(60 mL) was refluxed for 96 h. After cooling, the reaction
mixture was filtered. The filtrate was concentrated in vac-
uum, and then dichloromethane (150 mL) was added to the
residue. The mixture was washed with several portions of
satd. sodium hydrogen carbonate and then water (3 ×
50 mL). The organic layer was dried over magnesium sulfate
and concentrated in vacuum. The resulting solid was purified
by column chromatography on silica gel with ethyl acetate –
petroleum ether (1:9) as eluent. Compounds 6a, 7a, and 8a
were obtained as major products in 0.4:0.74:1 molar ratio,
respectively. Specific details are given for each compound.
© 2007 NRC Canada

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Can. J. Chem. Vol. 85, 2007
Scheme 2. (i) NBS (for 1a: 5 equiv. and for 1b: 8 equiv.), BPO, CCl4 (for 1a: reflux, 96 h and for 1b: reflux under IR lamps radia-
tion (3 × 400 W), 96 h); (ii) AgOAc, AcOH (reflux, 16 h); (iii) HCl – THF – H2O (0.03:2:1) (reflux, 15 h); (iv) BaMnO4, CH2Cl2 –
THF (1:1) (RT, 2 h).
(br, phenyl C), 157.3 (pyran C-2,-6), 175.7 (pyran C-4). MS
m/z: 596, 594, 592, 590, 588 [M+]. Anal. calcd. for
C19H12Br4O2 (591.918) %: C 38.55, H 2.04; found: C 38.70,
H 2.0.
2-Dibromomethyl-3,5-diphenyl-6-methyl-4H-pyran-4-one
(6a)
Light-brown crystals (1.48 g, 17%); mp 211.2–212.8 °C.
1
IR υ (cm–1): 1250, 1395, 1640, 3025. H NMR (CDCl3):
2.19 (3H, s, –CH3), 6.33 (1H, s, –CHBr2), 7.15–7.55
(10H, m, phenyl H). 13C NMR (CDCl3): 16.0 (–CH3), 31.1
(–CHBr2), 122.4 (pyran C-5), 127.2 (pyran C-3), 128.2–
131.3 (m, phenyl C), 157.2 (pyran C-6), 159.3 (pyran C-2),
176.5 (pyran C-4). MS m/z: 436, 434, 432 [M+]. Anal. calcd.
for C19H14Br2O2 (434.126) %: C 52.57, H 3.25; found: C
52.83, H 3.33.
Reaction of 1b with excessive N-bromosuccinimide —
Synthesis of di-, tri- and tetra-bromo derivatives 6b, 7b,
and 8b
2,6-Dimethyl-4H-pyran-4-one (1b) was prepared accord-
ing to a published procedure (20). A mixture of 1b (2.48 g,
0.02 mol), N-bromosuccinimide (28.48 g, 0.16 mol), and
dibenzoyl peroxide (0.5 g) in tetrachloromethane (80 mL)
was refluxed under the radiation of IR lamps for 96 h. After
cooling, the reaction mixture was filtered. The filtrate was
concentrated in vacuum, and then dichloromethane
(180 mL) was added to the residue. The mixture was washed
with several portions of satd. sodium hydrogen carbonate
and then water (3 × 50 mL). The organic layer was dried
over magnesium sulfate and concentrated in vacuum. The re-
sulting solid was purified by column chromatography on sil-
ica gel with ethyl acetate – petroleum ether (4:1) as eluent.
Compounds 6b, 7b, 8b, and 8c were obtained in
0.29:0.74:1:0.026 molar ratio, respectively. Specific details
are given for each compound.
6-Bromomethyl-2-dibromomethyl-3,5-diphenyl-4H-pyran-
4-one (7a)
Light-brown crystals (3.28 g, 32%); mp 219.7–221.3 °C.
1
IR υ (cm–1): 1253, 1392, 1638, 3031. H NMR (CDCl3):
4.21 (2H, s, –CH2Br), 6.32 (1H, s, –CHBr2), 7.35 (10H, s,
phenyl H). 13C NMR (CDCl3): 26.0 (–CH2Br), 31.1 (–CHBr2),
122.8 (pyran C-5), 127.6 (pyran C-3), 128.4, 128.7, 129.1,
129.3, 129.5, and 130.2 (phenyl-C), 157.0 (pyran C-6),
158.9 (pyran C-2), 177.0 (pyran C-4). MS m/z: 516, 514,
512, 510 [M+]. Anal. calcd. for C19H13Br3O2 (513.022) %: C
44.48, H 2.55; found: C 44.81, H 2.63.
2,6-Bis(dibromomethyl)-3,5-diphenyl-4H-pyran-4-one (8a)
2-Dibromomethyl-6-methyl-4H-pyran-4-one (6b)
Light-brown crystals (5.09 g, 43%); mp 228.1–230.0 °C.
1
IR υ (cm–1): 1250, 1396, 1650, 3028. H NMR (CDCl3):
Light-yellow crystals (0.51 g, 9%); mp 131.2–132.8 °C
(lit. 132 °C) (17). IR υ (cm–1): 1248, 1655. 1H NMR
(DMSO-d6): 2.36 (3H, s, –CH3), 6.28 (1H, s, –CHBr2), 6.37
6.35 (2H, s, –CHBr2), 7.10–7.60 (10H, m, phenyl H). 13C
NMR (CDCl3): 31.1 (–CHBr2), 122.7 (pyran C-3,-5), 129.2
© 2007 NRC Canada

Teimuri-mofrad and Abrishami
355
(1H, s, pyran CH-5), 7.22 (1H, s, pyran CH-3). 13C NMR
(DMSO-d6): 17.0 (–CH3), 32.2 (–CHBr2), 111.5 (pyran C-
5), 116.1 (pyran C-3), 158.5 (pyran C-6), 163.8 (pyran C-2),
180.1 (pyran C-4). MS m/z: 284, 282, 280 [M+]. Anal. calcd.
for C7H6Br2O2 (281.930) %: C 29.82, H 2.1; found: C
29.94, H 2.21.
183.9 (pyran C-4), 202.0 (–CHO). MS m/z: 290 [M+]. Anal.
calcd. for C19H14O3 (290.317) %: C 78.60, H 4.86; found: C
77.93, H 4.93.
3,5-Diphenyl-4-oxo-4H-pyran-2,6-dicarboxaldehyde (5a)
From 0.89 g of 8a, pale-yellow crystals (0.34 g, 75%)
were obtained; mp 195.9–196.8 °C (lit. 196.9 °C) (16). IR υ
6-Bromomethyl-2-dibromomethyl-4H-pyran-4-one (7b)
Colorless crystals (1.66 g, 23%); mp 85.1–85.9 °C (lit.
85 °C) (17). IR υ (cm–1): 1250, 1400, 1648. 1H NMR
(DMSO-d6): 4.61 (2H, s, –CH2Br), 6.42 (1H, s, –CHBr2),
6.68 (1H, s, pyran CH-5), 7.22 (1H, s, pyran CH-3). 13C
NMR (DMSO-d6): 26.5 (–CH2Br), 31.9 (–CHBr2), 112.8
(pyran C-5), 116.5 (pyran C-3), 158.2 (pyran C-6), 163.5
(pyran C-2), 179.8 (pyran C-4). MS m/z: 364, 362, 360, 358
[M+]. Anal. calcd. for C7H5Br3O2 (360.826) %: C 23.30, H
1.40; found: C 23.82, H 1.48.
1
(cm–1): 1650, 1710, 2880, 3030. H NMR (acetone-d6): 7.35
(10H, s, phenyl H), 9.59 (2H, s, –CHO). 13C NMR (acetone-
d6): 128.5, 129.0, 130.2, 132.0, and 134.1 (phenyl C), 136.0
(pyran C-3,-5), 152.5 (pyran C-2,-6), 185.0 (pyran C-4),
205.7 (–CHO). MS m/z: 304 [M+]. Anal. calcd. for C19H12O4
(304.300) %: C 74.99, H 3.98; found: C 75.15, H 4.09.
6-Acethoxymethyl-3,5-diphenyl-4-oxo-4H-pyran-2-
carboxaldehyde (9a)
From 1.03 g of 7a, pale-yellow crystals (0.5 g, 71%) were
obtained; mp 211 °C. IR υ (cm–1): 1631, 1700, 1745, 3054.
1H NMR (CDCl3): 2.05 (3H, s, –OOCCH3), 4.91 (2H, s,
–CH2O–), 7.35 (10H, s, phenyl H), 9.60 (1H, s, –CHO). 13C
NMR (CDCl3): 20.5 (–OOCCH3), 62.3 (–CH2OOC–), 127.8,
128.2, 130.0, 130.8, 132.1, and 132.8 (phenyl C), 133.9
(pyran C-5), 138.1 (pyran C-3), 151.0 (pyran C-6), 155.5
(pyran C-2), 169.8 (–OOCCH3), 184.2 (pyran C-4), 204.5
(–CHO). MS m/z: 348 [M+]. Anal. calcd. for C21H16O5
(348.352) %: C 72.41, H 4.63; found: C 73.60, H 4.52.
2,6-Bis(dibromomethyl)-4H-pyran-4-one (8b)
Colorless crystals (2.73 g, 31%); mp 159.2–161.3 °C (lit.
161 °C) (17). IR υ (cm–1): 1250, 1396, 1655. 1H NMR
(DMSO-d6): 6.50 (2H, s, –CHBr2), 7.30 (2H, s, pyran CH-
3,-5). 13C NMR (DMSO-d6): 31.2 (–CHBr2), 116.1 (pyran
C-3,-5), 158.3 (pyran C-2,-6), 179.7 (pyran C-4). MS m/z:
444, 442, 440, 438, 436 [M+]. Anal. calcd. for C7H4Br4O2
(439.723) %: C 19.12, H 0.92; found: C 19.33, H 0.89.
3,5-Dibromo-2,6-bis(dibromomethyl)-4H-pyran-4-one (8c)
Light-yellow crystals (0.095 g, 0.8%); mp 206.7–207.8 °C
(lit. 207.0 °C) (17). IR υ (cm–1): 1251, 1396, 1658. 1H NMR
(DMSO-d6): 7.46 (2H, s, –CHBr2). Anal. calcd. for
C7H2Br6O2 (597.515) %: C 14.07, H 0.34; found: C 14.15,
H 0.32.
Reaction of 6b, 7b, and 8b with silver acetate —
Synthesis of 4b, 9b, and 5b
A mixture of 6b (1.5 mmol), 7b (1 mmol) or 8b
(0.75 mmol), and silver acetate (0.585 g, 3.45 mmol) in gla-
cial acetic acid (10 mL) was refluxed for 16 h. After cool-
ing, the mixture was filtered, and the precipitate was washed
with dichloromethane (40 mL). Then, cold water (20 mL)
was added to the filtrate, and the mixture was stirred and
separated. The aqueous layer was concentrated under re-
duced pressure, and the residue, after complete drying, was
extracted with dichloromethane (3 × 20 mL). The combined
organic layer was washed with cold aqueous solution of
satd. sodium chloride (2 × 5 mL) and concentrated in vac-
uum. A solution of acetic acid (10 mL) and water (10 mL)
was added to the residue. The mixture was refluxed for 4 h
and then concentrated in reduced pressure. The residue, after
complete drying, was extracted with acetone (3 × 10 mL).
The combined organic solution was concentrated in vacuum
after drying over sodium sulfate. Specific details are given
for each compound.
Reaction of 6a, 7a, and 8a with silver acetate —
Synthesis of 4a, 9a, and 5a
A mixture of 6a (3 mmol), 7a (2 mmol) or 8a (1.5 mmol),
and silver acetate (1.17 g, 6.9 mmol) in glacial acetic acid
(20 mL) was refluxed for 16 h. After cooling, the mixture
was filtered, and the precipitate was washed with dichloro-
methane (30 mL). Then, cold water (30 mL) was added to
the filtrate, and the mixture was stirred and separated. The
aqueous layer was extracted with dichloromethane (2 ×
20 mL). The combined organic layer was washed with cold
water (4 × 20 mL) and then concentrated in vacuum. A solu-
tion of acetic acid (20 mL) and water (20 mL) was added to
the residue. The mixture was refluxed for 3 h and then con-
centrated in reduced pressure. Dichloromethane (30 mL)
was added to the residue, and the mixture was washed with
water (3 × 20 mL). Organic layer was dried over magnesium
sulfate, and the solvent was evaporated in vacuum. Specific
details are given for each compound.
6-Methyl-4-oxo-4H-pyran-2-carboxaldehyde (4b)
From 0.42 g of 6b, white crystals (0.15 g, 73%) were ob-
tained; mp 117.9–118.6 °C (lit. 118.4 °C) (16). IR υ (cm–1):
1285, 1560, 1640, 1710, 2990. 1H NMR (CDCl3): 2.40
(3H, s, –CH3), 6.30 (1H, s, pyran CH-3), 6.65 (1H, s, pyran
CH-5), 9.65 (1H, s, –CHO). 13C NMR (CDCl3): 20.5
(–CH3), 118.0 (pyran C-5), 121.5 (pyran C-3), 157.2 (pyran
C-6), 168.0 (pyran C-2), 179.1 (pyran C-4), 187.0 (–CHO).
MS m/z: 138 [M+]. Anal. calcd. for C7H6O3 (138.121) %: C
60.87, H 4.38; found: C 60.61, H 4.29.
3,5-Diphenyl-6-methyl-4-oxo-4H-pyran-2-carboxaldehyde (4a)
From 1.3 g of 6a, pale-yellow crystals (0.75 g, 86%) were
obtained; mp 188.6–189.7 °C (lit. 189.6 °C) (16). IR υ (cm–1):
1
800, 980, 1260, 1640, 1700, 2820, 2920, 3010. H NMR
(CDCl3): 2.40 (3H, s, –CH3), 7.40 (10H, m, phenyl H), 9.80
(1H, s, –CHO). 13C NMR (CDCl3): 21.1 (–CH3), 128.3,
128.6, 130.2, 132.0, and 133.0 (phenyl C), 134.5 (pyran C-
5), 138.9 (pyran C-3), 149.0 (pyran C-6), 153.0 (pyran C-2),
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Can. J. Chem. Vol. 85, 2007
tion of dichloromethane–tetrahydrofuran in vacuum gave a
pale-yellow residue. Specific details are given for each com-
pound.
4-Oxo-4H-pyran-2,6-dicarboxaldehyde (5b)
From 0.33 g of 8b, yellow oil (0.08 g, 70%) was obtained.
IR υ (cm–1): 1100, 1280, 1425, 1615, 1675, 1720, 3010. H
1
NMR (acetone-d6): 7.05 (2H, s, pyran CH-3,-5), 9.75 (2H, s,
–CHO). 13C NMR (acetone-d6): 123.5 (pyran C-3,-5), 168.0
(pyran C-2,-6), 181.0 (pyran C-4), 188.0 (–CHO). MS m/z:
152 [M+]. Anal. calcd. for C7H4O4 (152.105) %: C 55.28, H
2.65; found: C 55.19, H 2.73.
Compound 5a
From 0.092 g of 10a, 0.09 g pale-yellow residue was ob-
tained, which recrystallized from ethylacetate and petroleum
ether. Pale-yellow crystals (0.083 g, 91%) were obtained; mp
195.7–197.1 °C (lit. 196.9 °C) (16). The physical and spec-
tral properties were identical to that of 5a reported earlier.
6-Acethoxymethyl-4-oxo-4H-pyran-2-carboxaldehyde (9b)
From 0.36 g of 7b, colorless oil (0.13 g, 66%) was ob-
tained. IR υ (cm–1): 1635, 1705, 1750, 2990. 1H NMR
(CDCl3): 2.10 (3H, s, –OOCCH3), 4.90 (2H, s, –CH2O–),
6.32 (1H, s, pyran CH-3), 6.62 (1H, s, pyran CH-5), 9.68
(1H, s, –CHO). 13C NMR (CDCl3): 20.0 (–OOCCH3), 61.9
(–CH2OOC–), 118.5 (pyran C-5), 122.1 (pyran C-3), 158.0
(pyran C-6), 167.2 (pyran C-2), 180.1 (pyran C-4), 188.2 (–
CHO). MS m/z: 196 [M+]. Anal. calcd. for C9H8O5
(196.157) %: C 55.11, H 4.11; found: C 54.99, H 4.0.
Compound 5b
From 0.046 g of 10b, pale-yellow oil (0.037 g, 82%) was
obtained. The physical and spectral properties were identical
to that of 5b reported earlier.
Acknowledgement
We gratefully acknowledge the financial support for this
work by the Research Council of Malek-ashtar University of
Technology.
3,5-Diphenyl-6-hydroxymethyl-4-oxo-4H-pyran-2-
carboxaldehyde (10a)
A mixture of 9a (0.435 g, 1.25 mmol), tetrahydrofuran
(6 mL), water (3 mL), and concentrated hydrochloric acid
(0.1 mL) was refluxed for 15 h. The mixture was concen-
trated under reduced pressure, and then water (5 mL) was
added to the residue. The mixture was extracted with di-
chloromethane (3 × 10 mL), and the combined organic layer
was washed with water (3 × 10 mL), dried over magnesium
sulfate, and the solvent was distilled under reduced pressure.
Pale-brown crystals (0.34 g, 89%) were obtained; mp 215.1–
216.5 °C. IR υ (cm–1): 1648, 1700, 3439 (br). 1H NMR
(CDCl3): 2.60 (1H, br, –CH2OH), 4.46 (2H, s, –CH2OH),
7.25–7.50 (10H, m, phenyl H), 9.58(1H, s, –CHO). MS m/z:
306 [M+]. Anal. calcd. for C19H14O4 (306.316) %: C 74.50,
H 4.61; found: C 73.91, H 4.71.
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© 2007 NRC Canada