Lead tetraacetate oxidations properties

Methoxyvincamine (vincine, XXXV R = OMe), whose ring A methoxyl is so placed because of its UV-spectrum and a color reaction specific for that position, had properties (Chart III) that paralleled those of vincamine (21). This conclusion was reached independently on the basis of mass spectral comparisons (18). The stereochemistry of both alkaloids is regarded as being the same (21). Tetradehydro compounds (XXXVII) were formed by lead tetraacetate oxidation, and XXXVII... 

The structure of the new product from D-glucosamine has also been confirmed by Muller and Varga,7 who oxidized the compound (obtained by Garda Gonz lez) with lead tetraacetate and isolated ethyl 5-formyl-2-methyl-3-pyrrolecarboxylate (XXII), the melting point and other properties of which agreed with those of the compound described by Fischer and Schubert.24... 

A number of reagents exhibit relatively sharp specificity for the cleavage of bonds between adjacent carbon atoms carrying hydroxyl groups. The most important of these are periodic acid and lead tetraacetate. The requisite properties of an oxidant of this type have been defined 212) as follows ... 

Periodic acid and lead tetraacetate are the most important agents of this type, but sodium perbismuthate (NaBiOs) and hydrated trivalent silver ion (Ag" ) also possess the necessary properties and oxidize glycols in a similar manner (212). 

Transition metals will promote oxidative reactions by hydrogen abstraction and by hydroperoxide decomposition reactions that lead to the formation of free radicals. Prooxidative metal reactivity is inhibited by chelators. Chelators that exhibit antioxidative properties inhibit metal-catalyzed reactions by one or more of the following mechanims prevention of metal redox cycling occupation of all metal coordination sites thus inhibiting transfer of electrons formation of insoluble metal complexes stearic hinderance of interactions between metals and oxidizable substrates (e.g., peroxides). The prooxidative/antioxidative properties of a chelator can often be dependent on both metal and chelator concentrations. For instance, ethylene diamine tetraacetic acid (EDTA) can be prooxidative when EDTAiiron ratios are <1 and antioxidative when EDTAiiron is >1. The prooxidant activity of some metal-chelator complexes is due to the ability of the chelator to increase metal solubility and/or increase the ease by which the metal can redox cycle. 

---