Thallium trinitrate oxidant

Table 2 Intramolecular Thallium Trinitrate Oxidative Coupling 17-19 ...

Thallium trinitrate oxidizes naphthols and hydroquinone monoetliers, respectively, to quinones and 4,4-dialkoxycyclohexa-2,5-dienones, e.g., 4,4-dimethoxy-2-methyl-2.5-cyclohexadienone (5). The yield of (5) is 89%. 

Juglone is most readily synthesized by Bemthsen s method. However, this method is too drastic and results in low yields (56). Somewhat better yields are obtained by using Fremy s salt (potassium nitroso disulfonate) as the oxidant (57). By using thallium trinitrate to oxidize 1,5-dihydroxynaphthalene, yields as high as 70% of juglone have been reported (58). 

While this approach to ring expansion yielded the desired product 252 in an overall yield of 47%, photochemical (room lights) and thermal sensitivity (room temperature) of the dibromomethyl intermediates inspired the development of an alternate approach. As shown in Scheme 21, decalenone 249 could be smoothly methylenated with Tebbe reagent to provide diene 255 in excellent yield. Clean and reproducible oxidative ring expansion could then be effected with thallium trinitrate to furnish enone 252 in 62% overall yield (unoptimized). 

The synthesis13 of the pentacyclic intermediate (10) constitutes a second formal synthesis of ( )-tryptoquivaline G, since (10) has already been converted into tryptoquivaline G by Biichi et al.14a The most noteworthy stages in the synthesis of (10) (Scheme 1) involved the oxidation of the indolepropionic acid derivative (11) by means of thallium trinitrate, which gave the oxindole-lactone (12), and the oxidative removal of the unwanted methyl group in (12) by means of selenium dioxide.13... 

Yamamura and coworkers [158] developed an oxidative cyclization method to construct biphenyl ether bonds by thallium trinitrate (TTN) oxidation of the corresponding O,0 -dihalophenols followed by zinc reduction. The antibiotic piperazinomycin 266) was synthesized using this method as a key cyclization step [159]. As shown in Scheme 89, the diketopiperazine 263 was subjected to TTN oxidation in MeOH to afford an inseparable mixture containing plausible intermediate 264, which was directly reduced with zinc powder in AcOH-THF to give rise to the strained 14-membered biphenyl ether 265 in 19% yield together with two other isomers. 

Thallium trinitrate has been shown to be an efficient reagent for the dehydrogenation of chroma-nones and flavanones (Table 10, entry 5). the reaction being carried out in methanol at room temperature. The addition of perchloric acid to chromanone oxidations enhances the yields and reaction rates by promotion of enolization, but qiparently was without effect on flavanones. The ease with which chimanones and similar compound may be dehydrogenated has also permitted unusual procedures such as trimethylsilyl chloride/acetic anhydride and photolysis to be used (Table 10, entries 6 and... 

Methylenecyclopropane undergoes oxidative cleavage and ring expansion with thallium trinitrate in methanol to furnish in quantitative yield a mixture of the ring cleavage product l-methoxybutan-3-one and cyclobutanone in the ratio of 4 1, as in equation (28). ... 

Thallium trinitrate, TI(N03)3 3H20 (mp 102-105 C), oxidizes phenols and dihydroxy aromatic compounds to quinones [409, acetylenes to a-hydroxy ketones, a-diketones, or carboxylic acids 413] and methyl ketones to a-keto acids [414],... 

Dialkylalkynes are oxidized to acyloins or their alkyl ethers by thallium trinitrate in aqueous or aqueous-alcoholic solutions, respectively 4I3. Only symmetrical alkynes give acceptable yields (70-90%) (equation 141). 

Diarylacetylenes are converted in 55-90% yields into a-diketones by refluxing for 2-7 h with thallium trinitrate in glyme solutions containing perchloric acid [413. Other oxidants capable of achieving the same oxidation are ozone [84], selenium dioxide [509], zinc dichromate [660], molybdenum peroxo complex with HMPA [534], potassium permanganate in buffered solutions [848, 856, 864,1117], zinc permanganate [898], osmium tetroxide with potassium chlorate [717], ruthenium tetroxide and sodium hypochlorite or periodate [938], dimethyl sulfoxide and iV-bromosuccin-imide [997], and iodosobenzene in the presence of a ruthenium catalyst [787] (equation 143). 

Whereas internal acetylenes are oxidized to a-diketones, terminal acetylenes give carboxylic acids with one less carbon on treatment with thallium trinitrate [413], potassium permanganate [843], iodosobenzene with tris(triphenylphosphine)ruthenium dichloride as a catalyst [787], or a rather rare oxidant, pentafluoroiodobenzene bis(trifluoroacetate) [797] (equation 144). 

Another way of oxidizing aryl methyl ketones without degradation is by their reaction with thallium trinitrate in methanolic solution and in the... 

Oxidative cleavage of hydrazino substituents in pyridazines and phthalazines proceeds with thallium trinitrate in methanol, under mild conditions (Equation (24)) to give the corresponding methoxy derivatives in moderate yields <95JOCl466>. 

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