Thallium trinitrate

Thallium trinitrate oxidi2es naphthols and hydroquinone monoethers, respectively, to quinones and 4,4-diaIkoxycyclohexa-2,5-dienones, eg, 4,4-dimethoxy-2-methyl-2,5-cyclohexadienone [57197-11 -2] (108) (111,112). The yield of (108) is 89%. Because the monoacetal is easily converted to the quinone, the yield of 5-hydroxy-l,4-naphthoquinone [481-39-0] is 64%. 

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). 

An attempt to oxidise vanillin (3-methoxy-4-hydroxybenzaldehyde) was made using thallium trinitrate and when formic acid at SO C as a solvent was present. The extremely violent redox reaction that followed was put down to the effect of salt on acid. 

The thallium trinitrate-mediated ring contraction of frani-decal-2-ones has opened up a new route to the hydrindane system, and fluorinative ring contraction of cyclic alkenes to afford difluorocycloalkanes has been induced by iodotoluene difluoride and EtsN-HF. A possible mechanism is shown in Scheme 78. The double bond of the cyclohexene ring is attacked by iodotoluene difluoride activated by HF from the axial direction, followed by the addition of a fluoride ion from the trans direction. Reductive elimination of iodotoluene from the resulting adduct, ring contraction and the addition of the fluoride ion to the carbocation stabilized by fluorine then take place to give the ring-contracted difluorinated product. 

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

Stereochemical aspects of the thallium trinitrate-mediated ring contraction of 3- and 4-alkylcyclohexanones to alkylcyclopentanecarboxylic acids have been investigated.418 TMSOTf-promoted cyclization of several methylenecyclohexanesiloxy acetals of the... 

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). ... 

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