Oxidation with Fremy’s salt

Reduction of ketone (81) with zinc and acetic acid produced the 4-hydroxypyrazoles (87), whereas reaction with dithionite gave the corresponding 1,4-dihydroxypyrazoles (88). These compounds could be oxidized with Fremy s salt (potassium nitrosodisulfonate) to the 3,4-diazacyclopentadienone 3-oxides. 

Or/fto-Quinone Enhanced Pulp. The pulp was oxidized with Fremy s salt as described by Lebo (2). 

The peroxide-bleached groundwood pulp was also severely oxidized with Fremy s salt Although the pulp was almost stabilized against any further brightness decrease during irradiation, die photochromic effect remained (Table HI). 

Sec. 17.10) from phenols by oxidation with Fremy s salt [(KSC NO]... 

The use of radical cyclizations (see Section 3.02.2.7) in the synthesis of intermediates to biologically active indole-quinones was illustrated by the conversion of compound 956 (n = 2, R = BnO, = MeO) into the indolequinone 1206 by hydrogenolytic removal of the benzyl group followed by oxidation with Fremy s salt (Equation 273) <1997J(P1)2639>. 

There are also few compounds corresponding to 4. 2,3-Diphenyl-6-hydroxyindole afforded the corresponding 6,7-dione upon oxidation with Fremy s salt (61JCS3516). Similarly, the 1,2-dione was obtained from 2-hydroxycarbazole (54CB1251). By a nonoxidative procedure, the quinone... 

A complex reaction mixture was obtained when the amino compound 39 was oxidized with Fremy s salt. In addition to the anticipated quinone 40 (6.9% yield), the dimeric quinones 41 (2.9% yield) and 42 (4.9% yield) were also obtained. On the other hand, the aromatic analog 43 gave only 40 in 43% yield and the compound rearranged under the influence of acid into the p-quinone 44 (72CPB1785). 

There are only few representatives of 79. When 2,3-diphenyl-7-hydroxy-benzofuran was oxidized with Fremy s salt, a mixture of the 6,7- and 4,7-dione was obtained (70MI2). Similarly, nitric acid oxidation of the dihydroxy precursor afforded the quinone 82 or the related 5,6-dione, corresponding to the system 81 (12LA384). 

There are also a few compounds belonging to the 7,8-dione system 238. 8-unsubstituted 7-hydroxyquinolines are oxidized with Fremy s salt to 238. Because the formation of these quinones is slow, other reactions can take place. In acid solution, dimeric compounds are formed and, in neutral solution, ethers similar to those in the 5,6-dione series (237) are formed (67CB2077). 

D. Oxidation with Fremy s Salt, Ammonium Nitrate-Acetic Anhydride, Dioxygen-terr-butoxide, Sodium Periodate, Chlorous Acid... 

As examples of functionalised compounds aurogalaucin (ref.35) and flavoglaucin provide a link with synthetic monoprenyl dihydric phenols of the type discussed in 12.4. Although these two compounds (Table 12.1) do not appear to have been synthesised a study of their biosynthesis (ref. 36) illustrates a potential laboratory route through oxidation of 7-heptylsalicylic acid, synthesised by standard methods (ref. 83), by procedures such as Teuber oxidation with Fremy s salt followed by reduction, conversion of the methoxycarbonyl to the formyl group by hydride reduction and oxidation of the benzylic alcohol and finally prenylation, which would probably be non-specific. 

On the other hand, the synthesis of the makaluvamine family by route b shown in Schemes 2 and 4 has rarely been reported. Kraus et al. reported the total S3mthesis of makaluvamine C (Scheme 7). In their synthesis, the 6,6-bicyclic compound 14 was formed first. The reduction of 14 then gave the indole 15, which was converted to makaluvamine C by demethylation and in situ oxidation with Fremy s salt [49]. 

As was mentioned above, the pyrrolinediones IQ, can be transformed into oxoaporphines (H) by oxidation with Fremy s salt. In view of this, we proceeded to prepare the former by cycloaddition of an aryne to the pyrrolinedione 29a. Surprisingly, this reaction produced not only the desired compound 23 (in 11% yield its oxidation with Fremy s salt led, as expected, to lysicamine (22) (Ref. 16), but also a 61% yield of the protoberberine 21. possibly via the mechanism indicated in Scheme 10. 

As an alternative -nitrosamines can be prepared, in aqueous sodium carbonate solution, from secondary amines by oxidation with Fremy s salt and hydroxylamine, the addition of which greatly improves the... 

---