Reactions of quinones with aromatic ethers. Part IV. Dibenzofurans from the cyclisation of arylbenzoquinones

摘要

1974 2263Reactions of Quinones with Aromatic Ethers. Part 1V.l Dibenzofuransfrom the Cyclisation of ArylbenzoquinonesBy Oliver C. Musgrave * and Colin J. Webster, Chemistry Department, The University, Old Aberdeen AB9 2UE2.5- and 2.6-Dichlorobenzoquinone react with diazotised 3-methoxy-4-methyl- and 4-methoxy-3-methyl-anilineto form the expected monoaryl- and diaryl-dichlorobenzoquinones which undergo cyclisation on treatment withaluminium chloride to give the corresponding dichlorodibenzofurans.CERTAIN dichloro-3-(3,4-dimethoxyphenyl)benzoquin- H) prepared from the hydroxydimethoxy-compound (2 ;ones, e.g. (1 ; R1 = R2 = MeO, R3 = H), cyclise in R1 = R2 = MeO, R3 = H, R4 = OH)? Both the mono-the presence of 70 v/v aqueous sulphuric acid to give aryl- and the diaryl-benzoquinones behaved in a similarthe corresponding hydroxydibenzofurans, e.g.(2; R1 = manner on being heated with aluminium chloride. TheR2 = MeO, R3 = H, R4 = OH).l To learn more aboutthe scope of this reaction we have examined the cyclis-ation of a number of related monoaryl- and diaryl-benzoquinones each containing one methoxy and onemethyl group at C-3 and C-4 on the aromatic nucleus.Treatment of 2,5- and 2,6-dichlorobenzoquinone with R2 Rl:; ' RZbuffered solutions of diazotised 3-methoxy-4-methyl- and ( 1 )4-methoxy-3-methyl-aniline gave the monoarylbenzo-quinones (1 ; R1 = MeO, R2 = Me, R3 = H), (1 ; R1 ==Me, R2 = MeO, R3 = H), and (3; R1 = Me, R2 = MeO,R3 = H) together with the diary1 compounds (1; R1 ==MeO, R2 = Me, R3 = 3-MeO-4-MeC6H,), (1 ; R1 = Me,R2 = MeO, R3 = 4-MeO-3-MeC6H,), (3; R1 = MeO,R2 = Me, R3 = 3-MeO-4-MeC6H,), and (3; R1 = Me,R2 = MeO, R3 = 4-MeO-3-MeC6H,). 70 v/v Aqueoussulphuric acid proved to be unsuitable for the cyclisationof most of these quinones.A t room temperature it hadno effect while above 60" it usually caused decom-position. Only one quinone (3; R1 = Me, R2 = OMe,R3 = H), was converted into the corresponding dibenzo-furan under the latter, more vigorous, conditions. Wehad previously observed that anhydrous aluminiumchloride also effected the cyclisation of the (dimethoxy-pheny1)quinone (1 ; R1= R2 = MeO, R3 = H) inboiling benzene but caused partial demethylation of theresulting dibenzof uran. After met h ylation, however,the product was identical with a specimen of the tri-methoxydibenzofuran (2; R1 = R2 = R4 = MeO, R3 =Part 111, 0.C . Musgrave and C . J. Webster, preceding paper.0ClQ3' (5) 5' Jproducts isolated (see Table 1) were either the fullymethylated dibenzofurans or, in two cases, the 2-hydroxy-compounds. Their structures follow from theresemblance of their U.V. absorption data to those ofthe hydroxydimethoxydibenzofurans (2 and 4; R1 =R2 = MeO, R3 = H, R4 = OH) (see Table 2) and, mor2264 J.C.S. Perkin TTABLE 1Dichlorodibenzofurans1,4-Dichlorodibenzofurans(2; R1 = R2 = R4 = MeO, R3 = H)(2; R1 = MeO, R2 = Me, R3 = H, R4 = OH)(2; R' = R4 = MeO, R2 = Me, R3 = 3-MeO-4-MeC,H3)(2; R1 = Me, R2 = R4 = MeO, R3 = 4-MeO-3-MeC,H3)(4; R1 = R4 = MeO, R2 = Me, R3 = 3-MeO-4-MeC,H3)(4; R1 = Me, R2 = MeO, R3 = H, R4 = OH)(4; K1 = Me, R2 = R4 = Me0, R3 = 4-MeO-3-MeC,H3)1,3-Dichlorodibenzofurans201*5-203*5 ' Ci,H12CI204178-179 Cl4Hl0C1,O3 d206-207 C,3H20C120,218-219 C23H20C12042 13-2 15 C23H2oCl,O4208-212 b C14Hl,Cl,03(decomp.)205-208 C23H20C120z~a From chloroform-ethanol.b From methanol. C From nitromethane. Found : OMe,Found (yo) Required ()C H C H55.1 3.8 55.05 3.756.6 3.6 56.6 3.464.3 4.6 64.05 4.6563.9 4.5 64.05 4.6564.0 4.8 64.05 4.6556.8 3.3 56-6 3.464-2 4.8 64.05 4.6510.9. Required: OMe, 10.45y0.TABLE 2U.V. absorption * of dichlorodibenzofursnsA,,,./nm (log E) in CHCI,IA 7 Compound _____( 3 ; R' = R2 = McO, R3 = H, R4 = OH) t*'(2; R1 = R2 = R4 = MeO, R3 = H)(2; R1 = MeO, R2 = Me, R3 = H, R4 = OH)(2; R1 = R4 = RfeO, R2 = Me, R3 = 3-MeO-4-MeC,H3)( 2 ; R1 = Me, R2 = R4 = MeO, R3 = 4-MeO-3-MeC,H3)(4; R' = R2 = MeO, R3 = H, R4 = OH) 7"(4; R1 = R4 = MeO, R2 = Me, R3 = 3-MeO-4-MeC,H3)(4; R1 = Me, R2 = MeO, K3 = H, R4 = OH) t(4; R1 = Me, R2 = R4 = MeO, R3 = 4-MeO-3-MeC,H3)233 (4.36) 2453 (4.17), 256i (3.99),260i (4-08), 268 (4-03)264 (4.04)266 (4.06)265i (4.17)257 (4-26), 2671 (4.15)223 (4.45),243i (4.22)234 (4.35)265 (4-01), 278 (3.74)263 (4.38)257 (4.00), 266 (4.14)259i (4-33), 266 (4.33),282 (4.19)29 (4.24), 308 (4.35),298i (4.10), 307 (4.29),308 (4-35), 317i (4.28),313i (4*45), 319 (4.47),315 (4-37), 322i (4-30),311 (4.29), 3321: (3.98)305 (4*37), 310 (4.38),312i (4.36), 320 (4.41)318i (4.21), 3273.(4.03)321i (3-92), 336 (3.77)3331 (4.00)351 (3.66)311 (4*38), 332 (4.09)345i (3.43)317 (4.44), 3243: (4.15)* The symbol i denotes an inflection. t I n ethanol.TABLE 3N.m.r. signals of dichlorodibenzofuransChemical shift ( 6 ) in CDC1, **t3- or9-H 6-H 4-H 2'-H1,4-L>ichlorodibenzofurans(2; R1 = R2 = MeO, R3 = H, R1 = HO) 7.66 7-09 7.15(2; R1 = R2 = R4 = MeO, R3 = H) 7.69 7.08 6.93(2; R1 = MeO, R2 = Me, R3 = H, R4 = HO) 7.58 7-36 7-11(2; R1 = R4 = MeO, R2 = Me, R3 = 3-MeO-4-MeC,H3) 7-72 7.41 6.88(2; R1 = Me, R2 = R4 = MeO, R3 = 4-MeO-3-MeC,H3) 8.06 7-11 7.18(4; R1 = R2 = MeO, R3 = H, R4 = HO) 7.67 7.04 7-42(4; R1 = Me, R2 = MeO, R3 = H, R4 = HO) 7.99 6.99 7.44(4; R1 = R4 = MeO, R2 = Me, R3 = 3-MeO-4-MeC,H3) 7-71 7.26 6.98(4; R1 = Me, R2 = R4 = MeO, R3 = 4-MeO-3-MeC,H3) 8.05 6.97 7.30essentially as AB quartets between 6 7-4 and 6.8.1,3-Dichlorodibenzofurans* Positions numbered as in formula (5).t All the signals are singlets except those of the7-, 8-, 3'-,and 4'-Me04.00, 3.983.98, 3.963-933.97, 3.843.94, 3-913.98, 3-963-914-00, 3-963-99, 3.92C-5' and C-6'2-Me0(or2-h0)(5.48)3.933.533-50(5.53)(5.75)(5.75)3.863.86protons7-, 8-, 3'-,and 4'-Me2.372.39, 2.312.37, 2-292.342.34, 2-322-36, 2-32which appearspecifically, from their n.m.r. spectra. The assignmentsof the proton resonances given in Table 3 are based oncomparison of the spectra and on data for relateddibenzofurans.2 They indicate that in each case cyclis-ation involves the position in the aromatic ring para tothe methoxy or methyl substituent.EXPERIMENTALDetails of the general methods and of the instrumentsU.V.absorption spectra were used were given in Part I.3measured in chloroform solution unless stated otherwise.Arylation of 2,5-Dichlovobenzoquinone.-(a) Using di-azotised 3-wethoxy-4-methylaniline. The solution of thediazonium salt prepared from 3-methoxy-4-methylaniline(276 mg) in 2~-hydrochloric acid ( 5 ml) and sodium nitrite(170 mg) in water (2 ml) at 5" was added together with asolution of sodium acetate (500 mg) in water ( 5 ml) to aS. ForsCn and N. E. Stjernstrom, Arkiv Kemi, 1964, 21, 65;C. Brown, A.R. Forrester, and R. H. Thoxnson, Tetrahedroiz,1973, 29, 3059.3 0. C. Musgrave and C. J. Webster. J. Chem. SOC. (C). 1971,1393.4 F. Ullmann and R. Fitzenkam, Ber.., 1905, 38, 37871974solution of 2,5-dichlorobenzoquinone (390 mg) in acetone(30 ml) a t 5". The solution was warmed t o 10-15" andstirred for 1 h, water (20 ml) was added, and the mixturewas cooled to 0" and filtered. Digestion of the red residuewith ethanol (3 x 15 ml) gave an insoluble orange solid (A)(50 mg). Evaporation of the ethanol washings afforded2,5-dichlovo-3- (3-methoxy-4-met hylphenyl) - 1,4-benzoquinonewhich crystallised from ethanol in red crystals (240 mg),n1.p. 162-163" (Found: C, 56.6; H, 3-6; C1, 22-4.C14H1,Cl,0, requires C, 56.6; H, 3.4; C1, 23-85), vmax-1675 cm-l (quinone GO), A,,, (EtOH) 275 (log E 4.13) and435 nm (3-01), hind.254 (log E 3-97), 267 (4-09), and 321 nm(3.05). The solid (A) crystallised from nitromethane t ogive 2,5-dichlo~o-3,6-bis-( 3-methoxy-4-methylphenyl)-1,4-benzoquinone as orange-red crystals (45 mg), m.p. 295-297" (Found: C, 63-2; H, 4.1; C1, 18-1. C,,H1,C:1,04requires C, 63.3; H, 4-35; C1, 17-oy0), v,,,. 1664 cm-l(quinone G O ) , Anlax. 282 (log E 4-16), 312 (3.82), and 377 nm(3*27), Ainfl. 334 (log E 3.62) and 425 nm (3.25).(b) Using diazotised 4-methoxy-3-~nethylaniline. A similarreaction using 4-methoxy-3-methylaniline (for preparation,see below) yielded 2,5-dichloro-3-(4-methoxy-3-methyl~henyl)-l,.l-benzoquinone (120 mg) as deep red crystals, m.p. 148-149" (from ethanol) (Found: C, 56-8; H, 3-2; C1, 23.6.C14H1,Cl,0, requires C, 56.6; H, 3.4; C1, 23.85), v,,,1676 cm-1 (quinone G O ) , A,,, (EtOH) 264 (log E 4.21) and470 nm (3.24), Aid.325 nm (log E 2-90), and 2,5-dichloro-3,6-bis- (4-nzethoxy-3-methylpJzenyl)- 1,4-benzoquinone ( 17 mg)as deep brown needles, m.p. 265-267" (from nitromethane)(Found: C, 63.1; H, 4.2. C,,Hl,C1,O, requires C, 63.3;H, 4.35), v,,,. 1670 cm-l (quinone GO), ha, 272 (log E4.41) and 456 nm (3-64), A i d . 318 nm (log E 3.14).A rylation of 2,6-Dichlorobenxoquinone.-(a) Using di-azotised 3-metho=cy-4-methylanili.ne. A reaction similar t othat described above for 2,5-dichlorobenzoquinone gave2,6-dichloro-3,5-bis- (3-inethoxy-4-methylphenyl) - 1,4-be~zzo-quinone as deep brown needles (115 mg), m.p.183--186O,which crystallised from ethanol and sublimed at 210" and0.2 mmHg (Found: C, 63.4; H, 4.3; C1, 17.8. C2,H,,C120,requires C, 63.3; H, 4.35; C1, 17.0), vmri 1680 and 1660cm-l (quinone G O ) , A,,, 258 (log E 4-11), 284 (4-26), 318(3-55), and 465 nm (3.31), hind. 365 nm (log E 3.29). Noneof the monoarylated product was obtained and an examin-ation of the rest of the reaction mixture by t.1.c. on silicagel using ether-hexane showed the presence of unchanged2,6-dichlorobenzoquinone and the diarylated product only.(b) Using diazotised 4-methoxy-3-methylaniline. A similarreaction was performed with 4-methoxy-3-methylanilineusing ethanol in place of acetone as the solvent for thequinone. The mixture was stirred for 4 h, and the resultingbrown solid (A) was collected.The filtrate was dilutedwith water and extracted with ether. The resulting syrupwas separated by column chromatography on silica gelusing ether-hexane into 2,6-dichlorobenzoquinone (53 mg)and 2,6-dichloro-3- (4-metJzo.~y-3-rethylphenyl) - 1,4-bemo-quinone which crystallised from ethanol in deep blue crystals(88 mg), m.p. 130-131" (Found: C, 56-8; H, 3.4; C1, 23.8.C14Hl,C1,0, requires C, 56.6; H, 3-4; C1, 23.85), vm9x. 1685and 1665 cm-l (quinone GO), hmax. (EtOH) 223 (log E 3-96),266 (4.27), 332 (3.16), and 475 nni (3.37). The solid (A)crystallised from chloroform-ethanol to give 2,6-dic hloro-3,5-bis-(4-rvtethoxy-3-mefIzylphenyl)- 1 ,4-benzoquinone as deepbrown crystals (38 mg) which sublimed a t 310" and 0.2mmHg, m.p.208-209° (Found: C, 62.6; H, 4.4; C1, 17.7.C,,H1,C1,O4 requires C, 63.3; H, 4.35; C1, 17-0), vmx1677 and 1660 cm-l (quinone G O ) , A,,, 270 (log E 4.37),321 (3.30), and 480 nm (3.56), h i d . 282 nm (log E 4.26).Cyclisation of the Monoaryl- and Diaryl-dichlorobenzo-quinones.-A mixture of the quinone (200 nig), dry benzene(20 ml), and anhydrous aluminium chloride (250 mg) washeatecl under reflux for 1-2 11. The solvent was evapor-ated under reduced pressure and the dark residue wasshaken with chloroform and 5~-hydrochloric acid. Evapor-ation of the dried (MgSO,) chloroform layer gave the crude2-hydroxydibenzofuran which was either crystallised orheated under reflux for 1 h with a mixture of acetone(10 ml), dimethyl sulphate (0.5 ml), and fused potassiumcarbonate (60 mg).The mixture was evaporated underreduced pressure and the residue was warmed with 2M-sodium hydroxide solution. Crystallisation of the resultingsolid gave the 2-methoxydibenzofuran (27-76y0) whichcould be sublimed near its m.p. at 0.2 mmHg. The com-pounds prepared in this way and their U.V. and n.m.r. dataare recorded in Tables 1-3.1,4-Dichloro-2,7,8-trimethoxydibenzofu~an.-Prepared bythe methylation of 1,4-dichloro-2-hydroxy-7,8-dimethoxy-dibenzofuran using dimethyl sulphate and potassiumcarbonate in acetone, this (72; m.p. 201-203") wasidentical with the specimen prepared by the aluminiumchloride-catalysed reaction.Cyclisation of 2,6-Dichlo~o-3-(4-methoxy-3-1.)zethyl~henyl)-1,4-benzopuinone using Sulphuric Acid.-A mixture of thepowdered quinone (35 mg) and 70"/0 v/v aqueous sulphuricacid (3 ml) was kept a t 75" for 12 h and a t room temperaturefor 2 days, diluted with water (5 ml), and filtered. Theresulting solid crystallised from aqueous methanol t o give1,3-dichloro-2-hydroxy-7-niethoxy-8-methyldibenzofuran asneedles (22 mg), m.p.207-210" (decomp.), identical withthe specimen prepared by the aluminium chloride-catalysedreaction.2-Metho,~y-5-nitrotol.uene.-2-Methoxytoluene ( 14 g) wasadded dropwise to a stirred mixture of Concentrated nitricacid (75 ml) and water (75 ml). The mixture was heateda t 50" for 1 h, poured into ice-water, filtered, and theresidue was washed with aqueous 2~-sodium hydroxide.The solid crystallised from methanol to give 2-niethoxy-5-nitrotoluene (8-6 g), m.p. 60-62" (lit.,6 63").4-Afethoxy-3-methylaniline.-A mixture of 2-methoxy-5-nitrotoluene (6 g), tin(I1) chloride (27 g), concentratedhydrochloric acid (30 ml), and ethanol (60 ml) was heateda t 80" for 30 min, concentrated to ca. 65 ml, and cooled to0'. The resulting crystalline solid was washed withconcentrated hydrochloric acid, dissolved in water, and thesolution was made strongly alkaline by the addition ofsolid sodium hydroxide. Extraction with ether afforded anoily solid which crystallised from ether-light petroleum(b.p. 40-60") giving 4-methoxy-3-methylaniline as plates(3.6 g), m.p. 58-59" (lit.,@ 59-59-5") (Found: C, 70.0; H,7-8. Calc. for C,HllNO: C, 70.05; H, 8.1).We thank the S.R.C. for a research studentship.4/890 Received, 6th May, 19741J. Kenncr and M. Parkin, J . Cliem. SOC., 1920, 117, 862.E. Bamberger, Annalen, 1925, 443, 192