2.6- dimethoxy-1,4-benzoquinone

Coenzyme Qo (2,3-Dimethoxy-5-methyl-l,4-benzoquinone, 3,4-dimethoxy-2,5-tolu-quinone, fumigatin methyl ether), colchicine and colchicoside see entries in Chapter 6. 

Dimethoxy-l,4-benzoquinone [530-55-2] M 168.1, m 256 . Crystd from acetic acid. Sublimes in a vacuum. 

Coenzyme Q4 (Ubiquinone-4, 2,3-dimethoxy-5-methyl-6-[3,7,ll,15-tetrametbyl-hexadeca-2/,6/,10/,14-tetraenyl]-[l,4]benzoquinone [4370-62-l]M 454.7, m 30 , 33-45 , A (275nm) 185. A red oil purified by TLC chromatography on Si02 and eluted with Et20-hexane. Purity can be checked by HPLC (silica column using 7% Et20-hexane). It has A- ax 270 nm (e 14,800) in pet ether. [NMR and MS Naruta J Org Chem 45 4097 1980 cf Morton Biochemical Spectroscopy (Adam Hilger, London, 1975) p 491]. It has also been dissolved in MeOH/EtOH (1 1 v/v) and kept at 5 until crystals appear [Lester and Crane Biochim Biophys Acta 32 497 1958]. 

Salcomine is a useful catalyst for the selective oxygenation of 2,6-disubstituted phenols to the corresponding p-benzoquinones when dimethylformamide is used as the solvent laborious procedures are avoided and high yields of pure p-benzoquinones are obtained. Following the procedure described above, the authors have prepared 2,6-diphenyl-p-benzoquinone (m.p. 134—135°, yield 86%) and 2,6-dimethoxy-p-benzoquinone (m.p. 252°, yield 91%) from the appropriate phenols. 

Until now examples for catalytic reactions involving ferrates with iron in the oxidation state of -l-3 are very rare. One example is the hexacyanoferrate 8-catalyzed oxidation of trimethoxybenzenes 7 to dimethoxy-p-benzoquinones 9/10 by means of hydrogen peroxide which was published by Matsumoto and Kobayashi in 1985 [2]. Using hexacyanoferrate 8 product 9 was favored while other catalysts like Fe(acac)3 or Fe2(S04)3 favored product 10 (Scheme 2). The oxidation is supposed to proceed via the corresponding phenols which are formed by the attack of OH radicals generated in the Fe/H202 system. 

In a search for allelopathic agents from common weeds, Amaranthus palmerl S. Wats (Palmer amaranth) and Ambrosia artemisiifolia L. (Louisiana annual ragweed) have been analysed for their organic natural products. From A. palmerl phytol, chondrlllasterol, vanillin, 3-methoxy-4-hydroxynitrobenzene and 2,6-dimethoxy- benzoquinone were isolated. From the roots of Ambrosia artemisiifolia four polyacetylenes, a mixture of sesquiterpene hydrocarbons, methyl caffeate, and a mixture of 8-sitosterol and stlgmasterol were obtained. 

Trituration of fraction 26 with CHClj provided 45mg of yellow needles which were spectroscopically shown to be 2,6-dimethoxy-benzoquinone (8), mp 250-2° [lit. (3) 254°]. 200 MHz XH NMR, 6... 

Commercial 2,3-dimethoxy-5-methyl-1,4-benzoquinone (Aldrich Chemical Company, Inc.) was used without further purification. 

Ubiquinone-1 p-Benzoquinone, 2,3-dimethoxy-5-methyl-6-(3-methyl-2-butenyl)- (8) 2,5-Cyclohexadiene-1,4-dione, 2,3-dimethoxy-5-methyl-6-(3-methyl-2-butenyl)- (9) (727-81-1)... 

In the case of benzoquinone monoacetals 61, the two substituents at the 4-position are equal, and side-selective addition Re versus Si face) creates a single stereocenter (Scheme 7.17(a)). In the (S, R, R)-18/Cu(OTf)2-catalyzed 1,4-addition, depending on the nature of the R2Zn reagent and the size of the acetal moiety, enantioselectivities ranging from 85-99% were found (Table 7.4). The highest ees are provided by a combination of a small acetal moiety and Me2Zn 99% ee was obtained with 4,4-dimethoxy-5-methyl-2-cyclohexenone, for example. 

To date, several naturally occurring compounds which are capable of inducing the development of the haustorium have been characterized. The first haustorial inducers identified were the xenognosins, and their connection with the host s constitutive antibiotics suggested that they were specific recognition cues (8). 2,6-Dimethoxy-p-benzoquinone, the only active principle... 

An alternative regioselective synthesis of 2-anilino-5-methyl-l,4-benzoquinone (842) was developed using 2-bromo-6-methyl-l,4-benzoquinone (846) (route A) and 4,4-dimethoxy-2-methylcyclohexa-2,5-dienone (849) (route B) as synthetic equivalents for methyl-1,4-benzoquinone (841) (623) (Scheme 5.102). 

One of the carbazole-l,4-quinones, 3-methoxy-2-methylcarbazole-l,4-quinone (941), required for the total synthesis of carbazomycin G (269), was already used as a key intermediate for the total synthesis of carbazoquinocin C, and was obtained by the addition of aniline (839) to 2-methoxy-3-methyl-l,4-benzoquinone (939), followed by oxidative cyclization with catalytic amounts of palladium(II) acetate (545,645) (see Schemes 5.124 and 5.125). Similarly, in a two-pot operation, 4-meth-oxyaniline (984) was transformed to 3,6-dimethoxy-2-methylcarbazole-l,4-quinone... 

Cyclohexadienes are available by the methodology of Birch, and the reactions of l-methoxy-, 1,3-dimethoxy-, l,3-bis(trimethyl-silyloxy)-, and l-methoxy-4-methyl-l,3-cyclohexadiene with a number of 1,4-benzoquinones have been investigated. Acid treatment of the adducts and subsequent dehydrogenation provides a synthesis of 2-dibenzofuranols. Thus the adduct 159 (Scheme 41) from 1,4-benzoquinone and 1,3-dimethoxy-1,3-cyclohexadiene, on treatment with a trace of concentrated hydrochloric acid in ethanol at room temperature, affords the tetrahydrodibenzofuranone 161. When the adduct 159 is heated under reflux in aqueous methanol, the reaction can be arrested at the dihydrodibenzofuran 160. The tetrahydrodibenzofuranone 161 on dehydrogenation with palladized charcoal affords 2,7-dibenzofurandiol. ... 

The synthesis of acrylic acid or its ester (228) from ethylene has been investigated in AcOH from the standpoint of its practical production 12]. The carbonylation of styrene is a promising commercial process for cinnamate (229) production[207,213,214]. Asymmetric carbonylation of styrene with Pd(acac)2 and benzoquinone in the presence of TsOH using 2,2 -dimethoxy-6, 6 -bis(diphenylphosphino)biphenyl (231) as a chiral ligand gave dimethyl phenylsuccinate 230 in 93% ee, although the yield was not satisfactory, showing that phosphine coordination influences the stereochemical course of the oxidative carbonylation with Pd(II) salt[215]. 

Dihydroxy-l-tetralone Diisoprene 2,3-Dimethoxy-5,6-dimethyl-l,4-benzoquinone Isosclerone ( )-Limonene Aurantiogliocladin... 

Dimethoxy-5-methyl-l,4-benzoquinone see Coenzyme Qo entry in Chapter 5. 

---