Quinones with ceric ammonium nitrate

The upper echelons who were running the show were serious about this hydroquinone thing. Therefore, this product Z-7.2, that should have been entered into human evaluation, was instead processed further by the substitution of a t-BOC on the amine group, oxidation to the quinone with ceric ammonium nitrate, reduction to the hydroquinone with dithionite, and finally deprotection of the blocking t-BOC group by hydrochloric acid. The final product,... 

The three-step sequence used to convert enone 65 to miltirone (56) is shown in Scheme 5.7 and consists of, first, a Wolff-Kishner reduction to convert the C(5) carbonyl moiety into a methylene, followed by deprotection of the aryl methyl ethers and oxidation to an ortho-quinone using ceric ammonium nitrate. The physical and spectroscopic data of our synthetic miltirone are identical with those reported for the natural material. 

The oxidative cyclization of the alcohol (214) with ceric ammonium nitrate gave a mixture of the two naphthopyrans (215) and (216) in a ratio of 3 1 (81CC534). The reaction is of interest because of the natural occurrence of quinones containing the naphtho[2,3-c]pyran ring system. 

A series of azophenol acerands 4 was prepared by condensation of crowned benzoquinones 10 with 2,4-dinitrophenylhydrazine in ethanol [7b], The quinone was derived from p-methoxyphenol (6) as shown in Scheme 1 [8]. By bis(hy-droxymethylation) (67% yield of 6, followed by methylation (92%) of the phenol group and Williamson-type reaction with ditosylates of oligoethyleneglycol in the presence of sodium hydride, crowned 1,4-dimethoxybenzene 9 was obtained in reasonable yields. Oxidative demethylation of 9 with ceric ammonium nitrate (CAN) in aqueous acetonitrile at 50 °C gave the desired crowned benzoquinones 10 in good yields. 

As mentioned above, quinones can be formed from derivatives of resorcinol or catechol as well as from the parent hydroxyl compounds. When dimethoxy compound 144 was treated with ceric ammonium nitrate (CAN), for example, a 92% yield of quinone 145 was obtained as part of De Kimpe s synthesis of isagarin.222... 

Stille et al. completed the total synthesis of amphimedine (297) in eight steps and overall 21-23% yield (Scheme 33) (136). Their synthesis started with the readily available 4-quinolinone 298 (144), which was reacted with trifluoromethanesulfonic anhydride to give the triflate 299. Coupling of 299 with the organostannane 302 in the presence of Pd(PPhs)4 yielded the 4-arylquinoline 303, oxidation of which with ceric ammonium nitrate (CAN) or silver(II) oxide failed to produce any of the expected quinone. Thus,... 

Chromium-carbene complexes can be prepared from 2- and 3-substituted indolyllithium compounds and chromium hexacarbonyl, followed by methylation. These reactive species combine with alkynes to give cyclization products, which are oxygenated carbazoles. Oxidation to the quinone can be effected with ceric ammonium nitrate (can) where possible, otherwise the product is a cyclohexadiene (Scheme 66) <89JOC3249>. 

Trifluoromethyl-indoles can be prepared in a similar manner as shown in Eq. 64. In this case, anodic oxidation provides p-benzo-quinone imine derivatives 29, which are easily converted into trifluoromethyl-indoles 30 by heating or by treatment with ceric ammonium nitrate. 

Reaction of 61 with ethylmagnesiiun chloride in THF at -78 °C was fully stereoselective yielding a single product that furnished hydroxyketone 58 after hydrolysis. Reduction of 58 with potassiiun borohydride gave a mixtine of diols in the ratio 15 2, from which a major isomer was isolated by column chromatography and oxidized with ceric ammonium nitrate (CAN) to quinone 62 in 40% overall yield (Scheme 13). 

Thus, in the first operation, 31 was treated with ceric ammonium nitrate (CAN) in aqueous MeCN to effect the oxidative conversion of its C-ring into a quinone, an event attended by the concomitant scission of its B-ring to afford a hydroxymethyl function in the product (30). However, since a residual aldehyde from the Diels- Alder reaction was present on the same side of the A-ring as this newly generated alcohol, the isolated product was not 30, but instead was lactol 74. Although this latter ring closure was not critical for the operations ultimately needed to reach 28, it did serve to protect the oxidized substrate (30) from the action of excess CAN. For example, only decomposition resulted when the exo Diels—Alder variant of 31 was subjected to the same conditions, presumably because the hydroxymethyl function that was produced in this case could not form a lactol since its aldehyde partner was on the opposite side of the molecule. 

Harrity and co-workers described the application of 2-substituted 1-alkynylboronic esters in the Dotz cycloaddition of Fisher chromium carbene complexes, affording in a highly regioselective fashion a novel class of hydroxy-naphthyl boron pinacolates (entry 18, Table 1.3) [217]. These reaction products also provided, upon treatment with ceric ammonium nitrate, the corresponding quinone boronic esters. 

Ceric ammonium nitrate converts a 1,4-dimethoxy aromatic compound to the quinone, which is reduced with sodium dithionite to give a depro-tected hydroquinone. ... 

Release and Reactivity of tf-o-QMs Although the r 2-o-QM Os complexes 11 are stable when exposed to air or dissolved in water, the quinone methide moiety can be released upon oxidation (Scheme 3.8).16 For example, reaction of the Os-based o-QM 12 with 1.5 equivalents of CAN (ceric ammonium nitrate) in the presence of an excess of 3,4-dihydropyran led to elimination of free o-QM and its immediate trapping as the Diels-Alder product tetrahydropyranochromene, 14. Notably, in the absence of the oxidizing agent, complex 12 is completely unreactive with both electron-rich (dihydropyran) and electron-deficient (A-methylmaleimide) dienes. 

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