Selective oxidation with mercuric acetate

Methylation of avermectins B and B2 leads to the corresponding derivatives of the A series (49). A procedure involving the oxidation of the 5-methoxy group with mercuric acetate and NaBH reduction of the 5-keto-intermediate allows the conversion of the A to the B components (50). The 23-hydroxy group of the "2" components, after selective protection of the other secondary hydroxy groups, is converted to a thionocarbonate, which can be elirninated to give the 22,23-double bond of the "1" components alternatively it can be reduced with tributyltin hydride to the 22,23-dihydro derivatives (= ivermectins) (51). 

The most general method for synthesis of cyclic enamines is the oxidation of tertiary amines with mercuric acetate, which has been investigated primarily by Leonard 111-116) and applied in numerous examples of structural investigation and in syntheses of alkaloids 102,117-121). The requirement of a tram-coplanar arrangement of an a proton and mercury complexed on nitrogen, in the optimum transition state, confers valuable selectivity to the reaction. It may thus be used as a kinetic probe for stereochemistry as well as for the formation of specific enamine isomers. 

Cycloaddition approaches to pyrazole derivatives were employed extensively in 1997. Thus, aldhydrazones combine with mercuric acetate to form nitrileimines which react in situ with olefins to give 1,3,5-trisubstituted 2-pyrazolines <97SC3737>. Oxidation of the latter to pyrazoles with iodobenzene diacetate was reported <97SC2683>. The most common cycloaddition pathway, however, is from the reaction of alkenes or alkynes with diazo compounds. The facial selectivity of the regiospecific reactions of diazomethane (and other... 

Oxidation and Bromination of Other Functional Groups. Selective oxidation of alcohols may be achieved using a 1 1 complex of NBS and tetrabutylammonium iodide, whereas 1,2-diols are converted into 1,2-diketones using iV-bromosuccini-mide. An efficient and mild procedure has been reported for the preparation of benzoic acids via oxidation of aromatic carbonyl compounds by employing NBS and mercuric acetate. Selective and efficient oxidation of sulfides to sulfoxides has been achieved with NBS in the presence of /3-cyclodextrin in water. Epoxides and aziridines are conveniently oxidized to the corresponding a-hydroxy or Q -amino ketones using cerium(IV) ammonium nitrate and NBS. ... 

It is well known that olefins may form complexes with some metals [80, 81]. Mercuric acetate can form complexes with polyolefins selectively, being removed by acid treatment [82]. Such complexes have been used in the separation of unsaturated fatty acids from mixtures [83]. Subbarao [84] has protected olefins aginst reduction using silver complexes, and Cope used reversible platinum complex formation [85, 86] for the resolution of medium ring trans olefins. Landesburg [87] used the iron tricarbonyl complex of the alcohol (13) to protect it during oxidation to the ketone (14) which was regenerated from the complex by photolysis [88a]. 

Fig. 3. Recording of the limiting current at selected time-interval Oxidation of erj/iftro-butane-2,3-diol by periodate. [Decrease of periodic acid concentration with time followed continuously up to 4 min, then during the time intervals indicated. IM Acetate buffer of pH 5-6, 5 x 10 4m-KIO4, 5 X 10 m 6ry ftro-butane-2,3-diol. Current recorded at 25° at — 0-6 V (mercurous sulphate reference electrode). Figures on the abscissae give the time in minutes. The galvanometer zero and the current before the addition of periodate and after addition at t = 0 are marked. Full scale sensitivity 0-8 fiA.J (Redrawn not accurate to scale.)...

Glutathione may be obtained by the rapid extraction of pressed baker s yeast with 0 1 per cent, acetic acid, and subsequent precipitation with neutral lead acetate followed by mercuric sulphate. After removal of the metals by H S, the peptide is selectively precipitated by addition of cuprous oxide (Hopkins, 1929). The tissue content of glutathione may be estimated by titrating with 0 001 N iodine, the solution that is obtained by exhaustive extraction of the material with 10 per cent, trichloracetic acid until the extract no longer gives a violet colour with nitroprusside and ammonia. The method is not specific, any other labile thiol compound reacts in a similar fashion. 

---