1,4-Benzoquinones, reductive methylation

It may not be surprising that a,/ -dihydroxyalkyl radicals are able to achieve one-electron reduction of oxidants such as benzoquinone or methyl viologen, with the rate constants strongly dependent on the nature of the substituents, whereby reducing power of the radical and its rate of dehydration are correlated with each other [66]. This indicates that the push-component might be more important than the pull-component. 

Addition of the arylamines 117 to 2-methoxy-3-methyl-l,4-benzoquinone 118 affords regioselectively the 5-arylamino-2-methoxy-3-methyl-l,4-benzo-quinones 119 (Scheme 37). Palladium(II)-catalyzed oxidative cyclization leads to the carbazole-l,4-quinones 28 [135,136],previously obtained by the iron-mediated approach (cf. Scheme 14). Regioselective addition of methyllithium to the quinones 28 provides carbazomycin G 29a and carbazomycin H 29b [96,135]. Reduction of 29a with lithium aluminum hydride followed by elimination of water on workup generates carbazomycin B 23a [135]. Addition of heptylmag-... 

Bamford-Stevens decomposition of tosylhy-drazones, 351 p-Benzoquinone, 308 Benzyl ether hydrogenolysis, 139 Benzyl thioenol ethers, 87 Birch reduction, 11, 49, 50 Birch reduction of estrone methyl ether diethyl ketal, 51... 

C10H14Oj) C,H. An alternate route leading from 2,3-xylenol to this diether via nitrogen-containing intermediates was explored. The sequence involved the reaction of 2,3-xylenol with nitrous acid (4-nitroso product, mp 184 °C dec.), reduction with sodium dithionite (4-amino product, mp about 175 °C), oxidation with nitric acid (benzoquinone, mp 5 8 °C), reduction with sodium dithionite (hydro-quinone) and final methylation with methyl iodide. The yields were inferior with this process. 

The production of a,m-diesters from fatty esters can be realized via their SM as already explained, but it can also be performed by CM with methyl acrylate. The bulk CM of several unsaturated fatty acid methyl esters containing double bonds in different positions with methyl acrylate was studied by Rybak and Meier (Scheme 6) [43], C4 and C5 displayed very good activities with high conversions and CM selectivities. Among them, C5 showed the best performance for both methyl oleate (97% conversion, 92% selectivity, with 0.2 mol%) and methyl 10-undecenoate (99% conversion, 99% selectivity, with 0.1 mol%). The same conditions were successfully applied to methyl erucate and methyl petroselinate. The reaction conditions were further optimized, also considering the effect of 1,4-benzoquinone as additive for the reduction of double-bond isomerization [39], The CM of methyl 10-undecenoate and methyl acrylate worked with full conversions and high selectivity if five- to tenfold excess of methyl acrylate is used. Furthermore, using a 1 1 ratio between both reactants led, after optimization of the reaction... 

Benzoin, IV, 87 Benzoquinone, oxime, IV, 101 —, phytochemical reduction of, IV, 89 o-Benzoquinone, tetrabromo-, IV, 89 p-Benzoquinone, tetrahydroxy-, III, 48 Benzoxazole, 5-acetamido-2-methyl-, III, 351... 

Reduction (2 F) of 1,2-bis(bromomethyl)benzene leads to a highly reactive o-quino-dimethane, which in the presence of a dienophile may serve as the diene in a Diels-Alder reaction. The dienophiles are typically analogues of maleic anhydride (79), A-phenylma-leimide, and benzoquinone, which are all more easily reduced than the l,2-bis(bromo-methyl)benzene. The radical anion of the dienophile mediates the reductive cleavage of the... 

Thus, the aldol shown, which is susceptible to Sharpless-type epoxidation, has been obtained from phytal and the protected hydroquinone (ref. 120). Formation of the epoxide presumably with a chiral peracid (or perhaps with a conventional peracid relying on the asymmetry of the substrate) and then cleavage reductively in t-butyl methyl ketone containing lithium aluminium hydride led to a diol. The benzylic hydroxyl group of this was hydrogenolysed to afford the hydroquinone dimethyl ether in 85% yield. Ceric ammonium nitrate (CAN) oxidation afforded the intermediate benzoquinone hydrogenation of which was reported to result in 2R,4 R,8 R-a-tocopherol by, presumably, avoidance of a racemisation step. 

FIG. 4 Logarithmic plots of the bimolecular rate constants for ( ) the oxidation ( cat,ox/ M,ox) and (B) the reduction (fccat,red/AM,red) of DI with mediators as a function of the formal potential of the mediators (Fm ) pH 8.5. MV methyl viologen ARS alizarin red S FMN flavin mononucleotide FAD flavin adenine dinucleotide 2,6AQS anthraquinone-2,6-sulfonate VK3, 2-methyl-1,4-naphthoquinone NQ 1,4-naphthoquinone, 2,6DMBQ 2,6-dimethylbenzoquinone BQ 1,4-benzoquinone AP p-aminophenol FMA ferrocenylmethanol. (From Ref. 16.)... 

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