Synthesis of Benzopyran-4-One and Phloroglucinol Monomethyl Ether Derivatives from the Naturally Occurring Compound (Visnagin)
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Synthesis of Benzopyran-4-one and Phloroglucinol Monomethyl Ether Derivatives from the Naturally Occurring Compound (Visnagin) A. H. ABDEL-RAHMAN, A. M. KHALIL, S. I. EL-DESOKY, and E. M. KESHK Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, Egypt Received 4 May 1998 The reaction of 6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-4-one with dimethyl acetyl- enedicarboxylate and benzil gave the respective 4Я,6Я-ругапо[3,2-р]сЬготепе and imidazolylben- zopyran derivatives. Treatment of the imidazolylbenzopyran with hydrazine hydrate or hydroxyl- ammonium chloride yielded imidazolylpyrazolyl- or imidazolylisoxazolylbenzenes, while the alka line hydrolysis of imidazolylbenzopyran afforded imidazolylacetophenone that reacted with some aromatic aldehydes to give the corresponding chalcones. Oxidation of the chalcone with hy drogen peroxide led to the formation of 6-hydroxy-4-methoxy-5-[4,5-diphenylimidazol-2-yl]-2-(4- methoxybenzylidene)coumaran-3-one, while the reaction with hydrazine hydrate gave the corre sponding imidazolylpyrazolinylbenzene. Also, the imidazolylacetophenone was reacted with phenyl- hydrazine and hydroxylammonium chloride to give the respective hydrazone and oxime products. Fischer indolization of the above hydrazone yielded the corresponding indole derivative. Numerous imidazole derivatives have been pre NMR spectrum showed the presence of 10 aromatic pared and investigated for therapeutic and prophy protons at 6 = 7.5—8.0 of imidazole moiety, and the lactic application [1—3]. IR spectrum revealed the presence of NH group at v Also benzopyran derivatives possess coronary va = 3250 cm"1. sodilating [4], spasmolytic [5], and antiatherogenic and Treatment of IV with hydrazine hydrate or hy antiatherosclerotic activity [6]. In the light of this re droxylammonium chloride led to the formation of the port, compounds having a combination of benzopy only regioisomers: l,3-dihydroxy-5-methoxy-6-[4,5-di- ran and imidazole moieties can be expected to ex phenylimidazol-2-yl]-4-[5-methyl-3-pyrazolyl or isox- hibit marked biological activity. Thus this investiga azolyl]benzene (V) and (VI), respectively, via the tion deals with the synthesis of such type of com opening of the chromone ring followed by reaction pounds. with the above reagents. The naturally occurring furobenzopyran "visna The mass spectrum of V revealed molecular ion gin" (/) yields 6-formyl-7-hydroxy-5-methoxy-2-me- peak [M+] at m/z = 439 as* the base peak, which was thylbenzopyran-4-one (II) upon oxidation with potas in agreement with its molecular mass, also two daugh sium dichromate and sulfuric acid by rupture of furan ter peaks at m/z = 220 and 140 from the rupture of ring [7]. The reaction of Я with dimethyl acetylenedi- the diphenylimidazole and methylpyrazole rings, re carboxylate (DMAD) in the presence of anhydrous spectively. potassium carbonate gave 7,8-bis(methoxycarbonyl)- Bromination of IV using an excess of bromine led 6-hydroxy-5-methoxy-2-methyl-4#,6#-pyrano[3,2-#]- to the formation of 8-bromo-5,7-dihydroxy-2-methyl- chromen-4-one (III). The 1H NMR spectrum of com 6-[4,5-diphenylimidazol-2-yl]benzopyran-4-one (VII). pound III showed the presence of two singlets for two Demethylation of 5-methoxy group was accomplished methyl ester groups at S = 3.90 and 3.99, the IR spec from the effect of the hydrogen bromide formed dur trum showed the absence of aldehyde absorption (v — ing the reaction as reported in the case of khellin and 1710 cm-1), also the mass spectrum revealed a molec visnagin with several reagents such as dilute hydrogen ular ion [M+] at m/z — 376, which was in agreement halides [8, 9]. with its molecular mass. On the other hand, nitration of compound /Vgave When the aldehyde II was refluxed with benzil in 8-nitrobenzopyranone derivative VIII. IR spectrum -1 the presence of ammonium acetate in glacial acetic revealed the vibrations z>as(N02) = 1350 cm and -1 acid, it gave 7-hydroxy-5-methoxy-2-methyl-6-[4,5- i/s(N02) = 1530 cm . The mass spectrum of VIII diphenylimidazol-2-yl]benzopyran-4-one (IV). The XH revealed molecular ion [M+] at m/z = 470 which cor- Chem. Papers 53 (5) 323—327 (1999) 323 A. H. ABDEL-RAHMAN, A. M. KHALIL, S. I. EL-DESOKY, E. M. KESHK ОСНз СНз СбН4С1-4 ЬсНСбН4ОСНз-4 XVII XVIII Scheme 1 responded with its molecular mass. Alkaline hydrolysis of IV gave a quantitative yield The Vilsmeier—Haack formylation of IV failed to of imidazolylacetophenone derivative XI which was re give the corresponding 8-formyl derivative IX but acted with some aromatic aldehydes, namely benz- demethylation of 5-methoxy group occurred afford aldehyde, p-anisaldehyde, p-chloro- and p-nitrobenz- ing 5,7-dihydroxy-2-methyl-6-[4,5-diphenylimidazol-2- aldehyde to give the corresponding chalcones Xlla— yl]benzopyran-4-one (X). Xlld. The IR spectra of Xlla—XIId showed a charac- 324 Chem. Papers 53(5)323—327 (1999) DERIVATIVES FROM VISNAGIN teristic a,/3-unsaturated ketone band at v — 1630— C, 4.28 % H. IR spectrum: i>(C=0 chromone)/cm_1: 1640 cm-1, also гЯ NMR spectra of ХПа showed a 1658, i>(C=0 esterj/cm"1: 1723, 1750, 9(011)/cm'1: X doublet signal of —CH=CH—Ar at S = 5.67 (J = 10 3450. H NMR spectrum (CDC13), S: 2.3 (s, 3H, CH3), Hz). 3.8 (s, 3H, OCH3), 3.9 (s, 3H, COOCH3), 3.99 (s, 3H, Oxidation of the chalcone Xllb with hydrogen COOCH3), 5.3 (s, IH, H-4), 6.1 (s, IH, H-7), 6.7 (s, peroxide in sodium hydroxide led to the forma IH, OH), 8.1 (s, IH, H-10). EI mass spectrum, m/z tion of 6-hydroxy-4-methoxy-5-[4,5-diphenylimidazol- (Ir/%): 376 (3, [M+]). 2-yl]-2-(4-methoxybenzylidene)coumaran-3-one(XI/7). The assigned structure of XIII was established on the 7-Hydroxy-5-methoxy-2-methyl-6-[4,5-di- basis of the correct analytical and spectral data. Mass phenylimidazol-2-yl]benzopyran-4-one (IV) spectrum showed a molecular ion peak [M+] at m/z = 516 as the base peak which corresponded to its A mixture of aldehyde II (1.0 g; 4 mmol), ben- molecular mass. Also, when the chalcone XIIc was re zil (0.9 g; 4 mmol), and ammonium acetate (3 g; acted with hydrazine hydrate, it gave the correspond 4 mmol) in glacial acetic acid (20 cm3) was re- ing imidazolylpyrazolinylbenzene derivative XIV. The fluxed for 2 h. The precipitate that formed was fil oxime derivative XV which was obtained from con tered off and washed several times with hot ace densation of compound XI with hydroxylammonium tone to give IV, m.p. = 256—257<C; yield = 70 %. chloride failed to give the isoxazole derivative XVII on For C26H2o04N2 (Mr = 424.45) «4(found): 73.80 % treatment with acetic anhydride/pyridine mixture. On C, 5.00 % H, 6.6 % N; Wi(calc): 73.57 % C, 4.75 the other hand, on boiling phenyl hydrazone deriva % H, 6.6 % N. IR spectrum, />(C=N)/cm-1: 1620, tive X VTthat was obtained from condensation of com />(C=0 chromone)/cm-1: 1658, //(NH^cm"1: 3250, pound XI with phenyl hydrazine with polyphosphoric i/ÍOHJ/cm-1: 3500. XH NMR spectrum (DMSO-cfe), acid gave according to Fischer indole synthesis the cor S: 2.4 (s, 3H, CH3), 3.9 (s, 3H, OCH3), 6.1 (s, IH, H-3), responding indole product XVIII 7.1 (s, IH, H-8), 7.5—8.0 (m, 12H, lOAr—H, OH and NH). EI mass spectrum, m/z (IT/%): 424 (74.4, [M+]). EXPERIMENTAL l,3-Dihydroxy-5-methoxy-6-[4,5-diphenylimid- Melting points were uncorrected. Elemental analy azol-2-yl]-4-[5-methylpyrazol-3-yl]benzene (V) sis was carried out in the Microanalytical Unit at the Faculty of Science, Mansoura and Cairo Universities. A mixture of IV (1.0 g; 4 mmol) and hydrazine IR spectra were recorded on Mattson 5000 FTIR spec hydrate (0.4 cm3, 8 mmol) in absolute ethanol (30 trometer using KBr wafer technique. 1H NMR spec cm3) was refluxed for 8 h. The solid so obtained was tra were determined on Varian-Gemini 200 MHz and filtered off, then washed several times with hot acetone Jeol-Ex-270 MHz NMR spectrometers using TMS as to give compound V, m.p. = 299—300X1; yield = 97 an internal standard with S = 0. Electron impact (EI) %. For C26H22O3N4 (Mr = 438.5) ti*(found): 71.50 % mass spectra were determined on a GC-MS QP-100 C, 5.00 % H, 12.5 % N; u*(cala): 71.22 % C, 5.05 % H, EX spectrometer Shimadzu (Japan). The purity of the 12.78 % N. IR spectrum: i/(C=N)/cm-1: 1630, P(NH, -1 synthesized compounds was tested by TLC. OH)/cm : 3200—3450. EI mass spectrum, m/z (Ir Compound //was prepared adopting the published /%): 439 (100, [M+]). [7] procedure with the same m.p. = 189°C. l,3-Dihydroxy-5-methoxy-6-[4,5-diphenylimid- 7,8-Bis(methoxycarbonyl)-6-hydroxy-5- azol-2-yl]-4-[5-methylisoxazol-3-yl]benzene (VI) methoxy-2-methyl-4ii,6#-pyrano[3,2-0]- chromen-4-one (III) A solution of hydroxylammonium chloride (0.8 g) in water (5 cm3) was added to a solution of IV (1.0 A mixture of aldehyde II (1.0 g; 4 mmol), dimethyl g) in pyridine (10 cm3) and refluxed for 4 h, the mix acetylenedicarboxylate (0.6 g; 4 mmol), and anhy ture was cooled, then acidified with diluted acetic acid. drous potassium carbonate (0.5 g; 4 mmol) in dry The precipitate that formed was filtered off and crys benzene (50 cm3) was refluxed for 6 h.