An efficient synthesis of carboxaldehydederivatives 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 substitutedderivatives 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 bythe 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 dela 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 dérivésdi-, 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 étéobtenus 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 and its derivatives have been the subjectof intensive research because of their importance in variousapplications 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 varietyof synthetic methods (7–9). These compounds are useful asfungicides, 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 theoxidation of hydroxymethyl group in derivatives of kojicacid (12–14) and by the formylation of pyrones in thepresence of trifluoroacetic acid (15). Recently, Ghandi andco-workers prepared some mono- and di-carboxaldehyde de-rivatives of 4H-pyran-4-one, substituted at positions 2 and 6by the condensation of mono- and dimethyl derivatives of

4H-pyran-4-one with benzaldehyde, followed by the oxida-tion of the corresponding mono- and di-styryl derivatives inthe presence of osmium tetroxide and potassium periodate(Scheme 1) (16).

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 awide range of reactions that would make them suitable forthe synthesis of a number of 4H-pyran-4-one derivatives. Forexample, host macrocycles, such as azacrown ethers, couldbe obtained from their dicarboxaldehyde derivatives.

We report a novel method for the synthesis of mono- anddi-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-bromoderivatives 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 thebromination of 2,6-dimethyl-4H-pyran-4-one (1b) with2.1 equiv. of N-bromosuccinimide in 10%, 3.1%, 3.4%, and0.3% yields, respectively, (17). As a result, we tried to syn-thesize 2-dibromomethyl-3,5-diphenyl-6-methyl-4H-pyran-

Can. J. Chem. 85: 352–357 (2007) doi:10.1139/V07-034 © 2007 NRC Canada

352

Received 28 November 2006. Accepted 14 March 2007.Published on the NRC Research Press Web site atcanjchem.nrc.ca on 12 May 2007.

R. Teimuri-mofrad1 and F. Abrishami. Department ofChemistry, Faculty of Materials, Malek-ashtar University ofTechnology, Tehran, P.O. Box 16765–3454, Iran.

1Corresponding author (e-mail: teimuri@mut.ac.ir).

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–Zieglerbromination (18, 19). Bromination of 1a with 5 equiv. of N-bromosuccinimide in the presence of dibenzoyl peroxide intetrachloromethane produced a mixture of 6a, 7a, and 8a, asmajor products, and other minor products. The crude prod-uct was chromatographed on silica gel and eluted with ethylacetate – petroleum ether (1:9) to yield 8a, 7a, and 6a as thefirst, second, and third fractions in 43%, 32%, and 17%yields, respectively. The mixture of other minor productswas obtained as the fourth fraction (Scheme 2).

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 presenceof excess N-bromosuccinimide. Since Lowe and co-workerswere looking to obtain 2,6-bis(bromomethyl)-4H-pyran-4-one, they merely used 2.1 equiv. of N-bromosuccinimide, butthey further got 6b, 7b, and 8b as well. Therefore, to in-crease the yields of compounds 6b, 7b, and 8b, we tried touse excess amount of N-bromosuccinimide, longer reactiontime, and sun lamps during the reaction. Bromination of 1b(20) with 8 equiv. of N-bromosuccinimide in presence ofdibenzoyl peroxide in tetrachloromethane under radiation ofIR lamps produced a mixture of 6b, 7b, and 8b, as majorproducts, and other minor products. The crude product waschromatographed 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 thenuclear 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 wasafforded as the fifth fraction (Scheme 2).

Treatment of 6a, 7a, and 8a with silver acetate inrefluxing glacial acetic acid, followed by the reaction withaq. 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-

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) in89% and 81% yields, respectively.

In addition, we decided to oxidize the monohydroxy-methyl derivatives of 4H-pyran-4-one, 10a and 10b, to thecorresponding dicarboxaldehyde derivatives, 5a and 5b, withbarium manganate in dichloromethane and tetrahydrofuranat room temperature. Compounds 5a and 5b were obtainedin 91% and 82% yields, respectively, (Scheme 2).

The data obtained from Mass spectrometry, IR, 1H and13C NMR spectra, and elemental analyses are fully consis-tent with the proposed structures.

In conclusion, we developed a new efficient method forthe preparation of mono- and di-carboxaldehyde derivativesof 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 someadvantages over the previous one. For instance, it usescheaper reagent and has higher total yields. Some of thesecompounds can be used as precursors to synthesize the hostmolecules. This work is now under investigation.

Experimental

Melting points were determined with an ElectrothermalInstrument model 9100 and are uncorrected. IR spectra wererun on a Shimadzu FTIR-4300 Spectrophotometer as KBrdisks or as smears between salt plates. The 1H and 13C NMRspectra were recorded on a FT-NMR Bruker 300 MHz spec-trometer. Chemical shifts (δ) were reported in ppm usingTMS as internal standard. Mass spectra were recorded on aShimadzu MS-QP 1100 EX mass spectrometer. Elementalanalyses 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 of1a (5.52 g, 0.02 mol), N-bromosuccinimide (17.8 g, 0.1mol), and dibenzoyl peroxide (0.4 g) in tetrachloromethane(60 mL) was refluxed for 96 h. After cooling, the reactionmixture was filtered. The filtrate was concentrated in vac-uum, and then dichloromethane (150 mL) was added to theresidue. The mixture was washed with several portions ofsatd. sodium hydrogen carbonate and then water (3 ×50 mL). The organic layer was dried over magnesium sulfateand concentrated in vacuum. The resulting solid was purifiedby column chromatography on silica gel with ethyl acetate –petroleum ether (1:9) as eluent. Compounds 6a, 7a, and 8awere obtained as major products in 0.4:0.74:1 molar ratio,respectively. Specific details are given for each compound.

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Teimuri-mofrad and Abrishami 353

Scheme 1. (i) PhCHO, NaOMe, 1,4-Dioxane; (ii) OsO4, KIO4.

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.IR υ (cm–1): 1250, 1395, 1640, 3025. 1H 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: C52.83, H 3.33.

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.IR υ (cm–1): 1253, 1392, 1638, 3031. 1H 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) %: C44.48, H 2.55; found: C 44.81, H 2.63.

2,6-Bis(dibromomethyl)-3,5-diphenyl-4H-pyran-4-one (8a)Light-brown crystals (5.09 g, 43%); mp 228.1–230.0 °C.

IR υ (cm–1): 1250, 1396, 1650, 3028. 1H NMR (CDCl3):6.35 (2H, s, –CHBr2), 7.10–7.60 (10H, m, phenyl H). 13CNMR (CDCl3): 31.1 (–CHBr2), 122.7 (pyran C-3,-5), 129.2

(br, phenyl C), 157.3 (pyran C-2,-6), 175.7 (pyran C-4). MSm/z: 596, 594, 592, 590, 588 [M+]. Anal. calcd. forC19H12Br4O2 (591.918) %: C 38.55, H 2.04; found: C 38.70,H 2.0.

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), anddibenzoyl peroxide (0.5 g) in tetrachloromethane (80 mL)was refluxed under the radiation of IR lamps for 96 h. Aftercooling, the reaction mixture was filtered. The filtrate wasconcentrated in vacuum, and then dichloromethane(180 mL) was added to the residue. The mixture was washedwith several portions of satd. sodium hydrogen carbonateand then water (3 × 50 mL). The organic layer was driedover 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 in0.29:0.74:1:0.026 molar ratio, respectively. Specific detailsare given for each compound.

2-Dibromomethyl-6-methyl-4H-pyran-4-one (6b)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

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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).

(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: C29.94, H 2.21.

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). 13CNMR (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, H1.40; found: C 23.82, H 1.48.

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 (pyranC-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. forC7H2Br6O2 (597.515) %: C 14.07, H 0.34; found: C 14.15,H 0.32.

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 mixturewas filtered, and the precipitate was washed with dichloro-methane (30 mL). Then, cold water (30 mL) was added tothe filtrate, and the mixture was stirred and separated. Theaqueous layer was extracted with dichloromethane (2 ×20 mL). The combined organic layer was washed with coldwater (4 × 20 mL) and then concentrated in vacuum. A solu-tion of acetic acid (20 mL) and water (20 mL) was added tothe 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 withwater (3 × 20 mL). Organic layer was dried over magnesiumsulfate, and the solvent was evaporated in vacuum. Specificdetails are given for each compound.

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):800, 980, 1260, 1640, 1700, 2820, 2920, 3010. 1H 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),

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: C77.93, 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(cm–1): 1650, 1710, 2880, 3030. 1H 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%) wereobtained; 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). 13CNMR (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.

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 washedwith dichloromethane (40 mL). Then, cold water (20 mL)was added to the filtrate, and the mixture was stirred andseparated. The aqueous layer was concentrated under re-duced pressure, and the residue, after complete drying, wasextracted with dichloromethane (3 × 20 mL). The combinedorganic layer was washed with cold aqueous solution ofsatd. 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 hand then concentrated in reduced pressure. The residue, aftercomplete drying, was extracted with acetone (3 × 10 mL).The combined organic solution was concentrated in vacuumafter drying over sodium sulfate. Specific details are givenfor 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, pyranCH-5), 9.65 (1H, s, –CHO). 13C NMR (CDCl3): 20.5(–CH3), 118.0 (pyran C-5), 121.5 (pyran C-3), 157.2 (pyranC-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) %: C60.87, H 4.38; found: C 60.61, H 4.29.

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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. 1HNMR (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, H2.65; found: C 55.19, H 2.73.

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.

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) wasadded to the residue. The mixture was extracted with di-chloromethane (3 × 10 mL), and the combined organic layerwas washed with water (3 × 10 mL), dried over magnesiumsulfate, 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.

6-Hydroxymethyl-4-oxo-4H-pyran-2-carboxaldehyde (10b)A mixture of 9b (0.118 g, 0.6 mmol), tetrahydrofuran

(3 mL), water (1.5 mL), and concentrated hydrochloric acid(0.05 mL) was refluxed for 15 h. The mixture was concen-trated under reduced pressure and the residue, after completedrying, was extracted with acetone (3 × 10 mL). The com-bined organic solution was concentrated in vacuum afterdrying over magnesium sulfate. Colorless oil (0.075 g, 81%)was obtained. IR υ (cm–1): 1642, 1705, 3450 (br). 1H NMR(DMSO-d6): 2.95 (1H, br, –CH2OH), 4.49 (2H, s, –CH2OH),6.35 (1H, s, pyran CH-3), 6.68 (1H, s, pyran CH-5), 9.63(1H, s, –CHO). MS m/z: 154 [M+]. Anal. calcd. for C7H6O4(154.120) %: C 54.55, H 3.92; found: C 53.89, H 3.99.

Oxidation of 10a and 10b with barium manganate —Synthesis of 5a and 5b

The fine powder of barium manganate (0.84 g) was addedimmediately to a stirred solution of 10a or 10b (0.3 mmol)in dichloromethane–tetrahydrofuran (1:1) (6 mL). The mix-ture was stirred at room temperature for 2 h. Inorganic by-products were removed by filtration of the reaction mixturethrough Celite. The Celite was washed with dichloro-methane, and the latter solution was added to the previouslyobtained dichloromethane–tetrahydrofuran filtrate. Evapora-

tion of dichloromethane–tetrahydrofuran in vacuum gave apale-yellow residue. Specific details are given for each com-pound.

Compound 5aFrom 0.092 g of 10a, 0.09 g pale-yellow residue was ob-

tained, which recrystallized from ethylacetate and petroleumether. Pale-yellow crystals (0.083 g, 91%) were obtained; mp195.7–197.1 °C (lit. 196.9 °C) (16). The physical and spec-tral properties were identical to that of 5a reported earlier.

Compound 5bFrom 0.046 g of 10b, pale-yellow oil (0.037 g, 82%) was

obtained. The physical and spectral properties were identicalto that of 5b reported earlier.

Acknowledgement

We gratefully acknowledge the financial support for thiswork by the Research Council of Malek-ashtar University ofTechnology.

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