Quinols, isomeric

A different type of tautomeric relationship exists between compounds of types 323 and 324. Both types of structure can be isolated, pyridones (324, Z = N—Me) and pyrones (324, Z = 0) being formed when 323 (Z = N—Me or 0) is heated with palladium on charcoal in ethylene glycol. Similar isomerizations in the quinol-4-one series have been reported."... 

Intramolecular [n2 + 2] photocycloadditions are equally numerous and many have considerable synthetic potential. 4-(But-3-enyloxy)quinol-(l//)2-one (254), for example, is converted into a mixture of isomeric adducts 255 and 256 on irradiation in methanol.208 Intramolecular cycloaddition has also been observed in the pyrimidinedione 257209 and in the dehydrovaline acrylamide 258 which on irradiation in dioxane affords the novel /1-lactam system 259.210... 

This synthesis, by a purely chemical route, confirmed the structure of the thermally stable 2-acetoxy-isomer 3, since the 4-isomer (4), which can be produced from the 4-hydroxyquinol derivative by acetylation with acetanhydride and pyridine, rearranges at 100° in organic solvents to give 3 (see p. 155). On the contrary, the thermodynamic structures of methyl- or ethyl-ethers or the hydroxy quinol derivatives (the last two are only known as the 4-substituted quinol derivatives) are the 4-substituted quinols. Table 15 gives some physical data of the two isomeric 2,4,6-triphenyl-quinol derivatives. 

Hydro-quinol, 1-4-Di-hydroxy Benzene.—The third isomeric dihydroxy benzene, viz., the para compound, i-4-di-hydroxy benzene, is known as hydro-quino or hydro-quinone. The latter name is derived from its relation to quinone (p. 636) from which it is obtained on reduction and which it yields on oxidation. Both hydro-quinol and quinone derive their names from the fact that they are obtained by the oxidation of quinic acid, an acid derived from the alkaloid quinine. The phenol is found in various plants or may be obtained from them by the hydrolysis of glucosides present, e.g., arbutin, which is a glucoside hydrolyzing into glucose and hydro-quinol. 

The migration of oxygen from a quaternary center in a cyclohexadienone may be preferred to a carbon shift, when present as an ether or ester function rather than free hydroxy. Thus the p-quinol acetate (117) yields the orcinol monoacetate (118 79%) on treatment at room temperature with trifluoroacetic anhydride, and the p-quinol ether (119) forms the resorcinol diethyl ether (120 71%) in ethanolic sulfuric acid. In the second case, hemiketalization must intervene also some methyl shift (12%) is observed. With the quinol (121), treatment with acetic anhydride-sulfuric acid leads to the lactone (122) acetylation or lactonization probably precedes oxygen shift. A number of related examples can be found in the steroid area. - Thermal 1,3-shifts of p-quinol acetates can also be induced acetate (117) yields catechol acetate (123 50-60%, 45 °C) by way of isomerization of the first-formed acetate (124). In the o-quinol acetate series, 1,2-acetoxy shift is seen in (125) (126 92%) and in (127) (128 90%), both in... 

Recently, Gozler et al. (123) proposed the stereostructure 1,4-ci s-l,2,3,4-tetrahydro-4,6-dihydroxy-7-methoxy-l-(3,4-dimethoxyben-zyl)-2-methylisoquinoline (446) for (-l-)-roemecarine. However, the stereostructure was revised to 449 based on the synthesis of 446 (124). Namely, two epimeric acetates, ( )-l,4-(ij- and ( )-l,4-/r zi.v-4-acetoxy-l,2,3,4-tetrahydro-6-hydroxy-7-methoxy-1 -(3,4-dimethoxybenzyl)-2-methyliso -quinolines (447 and 448), previously prepared via a thermal isomerization of the corresponding o-quinol acetates (19), were used for synthesis of ( )-roemecarine and its epimer (Scheme 60). Hydrolysis of 447 and 448 with 5% methanolic potassium hydroxide proceeded with retention of the configuration at C-4 to give the authentic ( )-1,4-c/.v- and ( )-i,4-tran.s-diols 446 and 449. As a result, structure 446 was inconsistent with natural roemecarine on the basis of H-NMR spectral comparison, while 449 was identical with the alkaloid with respect to spectroscopic data. 

The three isomeric dihydroxybenzenes, C6H4(OH)2, are catechol (pyro-catechin) discovered by H. Reinsch resorcinol by Hlasiwetz and Barth by fusing guaiacum, galbanum, or ammoniacum resins with caustic potash and quinol (hydroquinone) by Pelletier and Caventou (1820) and Wohler (1844 see p. 326). Hydroquinone had been obtained by A. Kawalier, who called it arctuvin , by hydrolysis of the glycoside arbutin (Ci2Hie07) which he discovered in the leaves of the bear-berry. The orientations of the three di-hydroxybenzenes were established by Th. Petersen. Resorcinol was synthesised from benzene by Korner. ... 

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