Prep aration of 3-allyloxy-4-pyrone (II), the Claisen rearrangement
of II to 3 .~hydroxy -2-allyl-4 -pyrone (IV) an d synthesis of a
number of related compounds are described

S. Kukolja

V. Hahn

English

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CR 0 AT IC A CHEMIC A ACT A 33 (1961) 2W CCA-236 547.812.5 :547.823.07 Studies on· 4-Pyrones and 4-Pyridones. II.* The Preparation .and Rearrangement of 3-Allyloxy-4-pyrone** S. Kukolja*** and V. Hahn Laboratory of Organic Chemistry, Faculty of Technology, University of Zagreb, Zagreb, Croatia, Yugoslavia Received November 9, 1961 Preparation of 3-allyloxy-4-pyrone (II), the Claisen rearrange-ment of II to 3.~hydroxy-2-allyl-4-pyrone (IV) and synthesis of a number of related compounds are described. In recent years ·several papers describing examples of Claiser. rearrange-ment in the 4-pyrone, series {allyl kojate1-2, a-deoxykujyl allyl ether3) have bE.en pubEshed. As p<Jrt of 'Jur studies en 4-pyrones the rearrangement of 3-allyloxy-4-·pyrone (allyl ether of pyromeconic acid) has been investigated. In the present communication the preparation and properties of the hitherto· undescribed 3-allyoxy-4-pyrone (II) and of several related compounds (IV-IX) is reported. ' Pyromeconic acid (3-hydroxy-4-pyrone, I) , needed as starting material, could be readily prepared by complete decarboxylation of meconic acid (3-hy-droxy-4-pyrone-2,6-dicarboxylic acid) , under reduced pressure. Although yields: of I obtained ,j.n this reaction by different authors4- 13 are rather low, we were· able to ?At.~in a!1 average yield of 650/o. 3-Allyloxy-4-pyrone (II) was prepared by refluxing a mixture of the sodium salt of I with an equivp.lent amount of allyl bromide in methanol. It could be isolated as a colourless'6n having b. p. 107-110'0 at 2.5-3 mm. For identification purposes 3..:methoxyT4:..pyrone (III) was also prepared11. In ultraviolet analysis: the spectra of II and III showed to be very similar. It was observed that during distillation nf II at higher temp€ratures and pressures rearrangement takes plaee and crystalline 3-hydroxy-2-allyl-4-pyrone· (IV) is obtained in good yield. Compound IV could be distilled at 135-1400/ 16 mm. and crystallized from water, having m. p. 88-89°. Evidence for the free hydroxyl group of IV is given by the positive colour test with ferric chioride (violet colour) and by reaction with.diazomethane affording 3-methoxy--2-allyl-4-pyrone (VIII). The colour test' ~f VIII with ferric chloride was-negative. Heating of either II or IV with acetic anhydride yielded 3-acetoxy-2-pro-penyl-4-pyrone (V). Deacetylation of V with hydro.xylamine according to Beelik and Purves14 gave 3-hydroxy-2-propenyl-4-pyrone (VI). The structure of VI is supported by the positive ferric chloride test, the ultraviolet spectrum and . * Paper I, V. Hahn and S. Kuk o 1 j a, Croat. Che.m. Acta 33 (1961) 137. •• Presented in part at the I. Yugoslav Congress for Pure and Applied Chemistry~ Zagreb, June 1960 · *** Part of the Thesis of S. Kukolja, presented to the University of Zagreb, 1958, in partial fulfilment of the requirements for the degree of Boctor of Chemistry (Ph. D.> 230 S . KUKOLJA AND V. HAHN by hydrogenation. Compound VI shows an expressive bathochromic shift (350 A) with respect to IV. Catalytic hydrogenation of both VI and IV led to 3-hydroxy--2-propyl-4-pyrone (VII). 6-""-'' 0 0 II II 0-0CH 1 ~H~CH 2 00COCH 3 CH•CHCH 3 0 0 I II v I CH1N1 / 0 0 0 II II CrOH 0-0CH, CtOH' CH CH=CH CH=CHCH 0 1 2 0 ) Ill IV VI 0 / 0 / 0 II II II UOCHJ UOH ():cOGH 3 O CH 2CH·CH 2 O CH1CH2CH3 cf.1'=CHCH 0 J vm Vil lX Finally, 3-methoxy-2-propenyl-4-pyrone (IX) was prepared by treatmen,t of VI with diazomethane in ethereal solution.. From the ultraviolet spedrum of IX it can be concluded that the side chain double bond is in conjugation with the 4-pyrone ring system. The spectrum of the corresponding allyl derivative (VIII) points at an isolated double bond. The ultraviolet absorption maxima for compounds II-IX are listed in Table I. TABLE I Ultraviolet Absorption Maxima Compound Amax , A log E II 2700 3.95 III 2700 3.93 IV 2800 3.99 v 2800 4.23 VI 3150 4.26 VII 2800 4.07 VIII 2650 4.01 IX 2940 4.17 STUDIES ON 4-PYRONES AND 4-PYRIDONES EXPERIMENTAL All melting and boiling points are uncorrected. Pyromeconic acid (I) 231 In a 500 ml. distilling flask 50 g. of copper turnings was placed and a mixture of 50 g. of copper powder and 50 g. of partially anhydrous meconic acid added: A thermometer was immersed into the mixture and the flask heated by means of ci.n electrical heating mantle under reduced pressure (13-20 mm.). The temperature was raised during one hour to 2450 and during the next one to 33ooc. The sublimate was dissolved in chloroform, the suspension filtered and the solvent evaporated. Almost colourless pyromeconic acid having m. p. 117-1180 was obtained. Average yield 65-0/o. 3-Allyloxy-4-pyrone (II) A solution of sodium methoxide prepared from 4.6 g. (0.2 g. atom) of sodium and 120 ml. of dry methanol was a.dded to a suspension of 22.4 g. (0.2 mole) of pyromeconic acid in 240 ml. of dry methanol. The mixture was refluxed during 10 minutes and 24.2 g. (0.2 mole) of allyl bromide added at once. Refluxing was continued for 4 hours. The solvent was evaporated and the separated sodium bromide removed by suction. The resulting 01ily product distilled at 107-1100/2.5-3 mm.; yield 24.5 g. (80-0/o). On standing for several days the oil partially crystallized and a small amount of crystals melting at 81-830 could be separated by filtration. After recrystallization from water the crystalline product melted at 88-890 and was identified as IV. The oily ether (II) was purified by distillation at 108-1090/3 mm. to give a colourless oil, d~~ = 1.2066, n~ = 1.5468. AnaL. CeHs0 3 (1512.14) calc'd.: C 63.15; H 5.300/o found: C 63.38; H 5.42°/t 3-Methoxy-4-pyrone (III) It was prep<!ii:.ed from pyromeconic acid and diazomethane according to Bickell•. For ultraviolet analysis the substance was sublimated at 1350/19 mm. Colourless crystals having m. p. 94.5-950 were obtained. 3-Hydroxy-2-allyl-4-pyrone (IV) 3-Allyloxy-4-pyrone (19.3 g., 0.127 mole) was distilled at 137-1400/ 15 mm. After cooling the oily distillate crystallized in the receiver. Recrystallization from a mixture -of ethanol-water (1 : 5) afforded 10.5 g. of colourless crystals melting at 85-860. The solvent was evaporated and the residue repeatedly distilled at 135---1400/16 mm. There was obtained 4.0 g. of colourless . oFystals having m . p. 85--860 and 3.5 g. of a ·pale yellow oil. The total yield of IV "was 14.$ g. After recrystallization from a mixture of ethanol-water (1 : 5), colourless prisms of pure IV, m. p. 88-890 were -obtained. They were soluble in water, ethanol, chloroform, benzene and d ioxane. An analytical sample was recrystallized from water, m. p. 88-890. Anai. CsHs0 3 (152.14) calc'd.: C 613.15; H 5.30°/o found: C 62.99; H 5.240/o 3-Acetoxy-2-propenyl-4-pyrone (V) A mixture of 3-hydroxy-2-allyl-4-pyrone (.0.76 g., 0.005 mole) and acetic anhy-<lride (5 ml.) was refluxed for 7 hours, the excess of anhydride evaporated in vacuo and the residue distilled at .135-1450/0.15 mm. There was obtained 0.7 g. of a viscous yellow oil which crystallized on standing. Recrystallization from ether gave colourless crystals, m .p. 81-820. The acetate is soluble in water and the common organic solvents, except petroleum ether. Anal. C10H1004 (194.18) calc'd.: C 61.85; H 5.190/o found: C 62.13; H 5.270/o 23~ S. KUKOLJA AND V. H<'\HN The same acetate was obtained in a similar way from II, y ield 87.50/o. Identity of the products obtained from II and IV was established by means of mixed melting point and ultraviolet spectra. · 3-Hydroxy-2-propenyl-4 -pyrone (VI) T6 a solution of 0.7 g. (0.01 mole) hydroxylamine hydrochloride· .in ' 125. ml. of pyridine 0.97 g. (0.005 mole) of V was addded. After keeping the mixture overnight · at room temperature 5 ml. of water was added and the solvent evaporated in va.cuo. 'Crystallization of the residue from ethanol-water (1 : 1) afforded 0·.38 g. (500/o) of almost colourless crystals melting at 118-1200. The compound gave a positive ferric chloride test. After two crystallizations from water-ethanol (1 : 1) the pure product m elted at 122--1230. Anal. CsHs03 (152.14) calc'd: C 63.15; H 5.30-0/o found: C 63.24; H 5.390/o 3-Hydroxy-2-propyl-4-pyrone (VII) Hydrogenation of 0.76 g. (0.-005 mole) of 3-hydrcixy-2-propenyl-4-pyrone, melting · <1 t 122-123~, in 50 rhl. of dry ethano•l with 0.25 g. of pre-1;educed 100/o palladium-on-.. - ch arcoal catalyst, resulted in the uptake of 105 ml. (IJ.005 mole) of hydrogen .. The · catalyst was filtered off, · the solvent removed and the residue recrystaliized from a mixture of petroleum ether-ethyl acetate (5 : l}. Colou.rless leaflets, m. p. 84~350, giving a positive ferric chloride test were obtained. Compound VII was prepared in a similar way from 3-hydroxy-2~allyl-4-pyrone (IV). The ide~1tity was established by means of .the mixed melting point and ultraviolet spectra. • Anai. C8H1003 (154.16) calc'd.: C 62.32; H 6.540/o found: C 62.56; H 6.940/o 3-Methoxy-2-allyl-4-pyrone (VIII) To an ethereal solution of diazomethane (about 1.4 g., 0.0•33 mole) was added with stirring at oo an ethereal solution of 3-hydroxy-'2-allyl-4-py,rone (l.52 g., 0.0.1 mole in. 200 ml. of ether). After keeping overnight in the refrigerator. the solvent was eva-porated and the residue distilled at 96- 970/2 mm. , yield 0.9 g. (!140/o~ of a pale yellow oil. The analytical sample was obtained by distillation at 112-11'30/4 min. · Anal. C9H100 3 (1166.17) calc'd.: C 65.05; H 6.070/o found: C 64.79; H 6.090/o 3-1.\llethoxy-2-propenyl-4 -pyrone (IX) Tb an ethereal solution of diazomethane prepared from about-. 27.5 g. of nitroso:.. rhethylurea was adde<.l with stirring at oo an ethereal solution' of 3-hydroxy'-2:.. properiyl-4-pyrone (prepared from 6.1 g., 0.04 mole, and 370· ml. of ether). After keeping overnight in the refrigerator the ether was evaporated and the residue distil-led af f19'--1~50/3 .5 mm. Yield 3.0 g. (450/o), of a pale· yellow oil. The analytical sample was purified py distillation at 126~1270/4 . 5 mm. · Anal. C9H 100 3 (.HY6.l 7) calc'd : C 65.05; H 6.07% found : C 64.8'2; H 6.350/o Acknowledgement. ~ Wr: .ai:e grateful to Mrs. I. Gustak-Masek from our labo-ratory for the microanalyses and to Mrs. Andrij evic-Barbic and Mr. N. Manger from Research Department, »Pliva« Pharmaceutical an.d Chemical v.[or)rn, Zagreb. for the ultraviolet spectra. One of 1;.he . authors (S. K.)' wishes to express •. his gratitude to »Pliva« Pharmaceutical and Chemical Wdrks, ·za'greb, for a fo}Jowship during this research. · · · · .. REFERENCES l. C. D. Hurd and R. J. Sims, J. Am. Chem. Soc. 71 (1949) 2440. 2. W. M. Mc Lamore, E. Ge 1b1 um, and A. Ba v 1 e y, J. Am. Chem. Soc. 78 (19.56) 2816. 3. C. D. Hurd and S. Tr d f.i men k o, J. Org. Chem. 23 (1958) 1276. STUDIES ON 4-PYRONES AND 4-PYRIDONES 4. J. Sten ho u se, Ann. 49 (1844) 18. 5 J . Br own, Ann. 84 (1853) 33. 6. E. I h 1 e e, Ann. 188 (1877) 32.. 7. H . 0 st, J . prakt. Chem. [2] 19 (1879) 177. 8. W. B ors ch e, B er . 49 (1916) 544 and 2544. 9. C. A. G ar k u s ha, Zhur. Obschchei Khim. 16 (1946) 12.n25. 10. A. Y . B e r 1 in, Zhur. Obshchei Khim. 19 (1949) 1177. 11. A . F . Bick e 1, J . Am. Chem. Soc. 69 (1947) 1801. 1;2. E . L . S him min and F . C h a 11 en g e r , J . Chem. Soc. 1949, 1185. 13 . R. Mayer, B er. 90 (1 957) 2369. 14. A. Be e 1 i k and C. B . Pu rves, Can. J. Chem . 23 (19'55) 1361. IZVOD Studije u redu pirona-(4) i piridona-(4). II. Priprava i premjestaj 3-aliloksi-pirona-(4) .S . Kukolja i V. Hahn 233 Opisuje se p riprava 3-aliloksi-pirona-(4) (II) (aliletera piromekonske kiseline) iz natrijeva piromekonata i a lilbromida u metanolu. Opreznom destilacijom kod n izih p ritisaka (do 3 mm) dobiva se II, dok kod viSih p ritisaka (15-20 mm) nastaje, uz Claisenov premjestaj, 3-hidroksi- 2- a lil- piron-(4) (IV). U r a dnji su opisani jos i ovi spojevi: 3- acetoksi-2-propenil-piron-(4) (V), 3-hi-droksi-12-propenil-piron-(4) (VI) , 3-hidroksi-2-propil-piron-(4) (VII) , 3-rnetoksi-2-alil-piron- (4) (VIII) i 3- rnetoksi .... 2-propenil- piron-(4) (IX). ZA VOD ZA ORGANSKU KEMIJU TEHNOLOSKIFAKULTET ZAGREB Prlmljeno 9. studenoga 19Bl 

Studies on · 4-Pyrones and 4-Pyridones. II. The Preparation . and Rearrangement of 3-Allyloxy-4-pyrone

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