Polycyclic aromatic hydrocarbons chemoselectivity

Although periodates also oxidize polycyclic aromatic hydrocarbons, phenols, hydrazines, active methylene compounds and sulfides, chemoselectivity can usually be achieved and glycol cleavage oxidation takes precedence. For example, the diol moiety in the diethyl dithioacetal derivative of o-glucose can be selectively oxidized in good yield (equation 6). In contrast, LTA is less selective dum periodate and oxidizes a far greater variety of oiganic compounds. Consequently, in order to minimize undesired reactions, it is customary to add LTA slowly to avoid contact of die initially formed products widi an excess of the oxidant (equation 7). ... 

Palladium catalysts have been used for cycloaddition of dimethylacetylene di-carboxylate (DMAD) to polycyclic arynes 3, 77 and 79 (Schemes 34-36). All these reactions exhibit the same reactivity pattern as is observed in the [2+2+2] cycloaddition of benzyne to DMAD (see Sect. 3.1) Pd2(dba)3 leads selectively to the cocycloaddition of one molecule of aryne and two molecules of DMAD, while Pd(PPh3)4 induces the reaction of two molecules of aryne with one molecule of DMAD. Both reactions afford the corresponding polycyclic aromatic hydrocarbons in good yields and with high chemoselectivity, constituting a novel and versatile method for the synthesis of functionalized PAHs under mild reaction conditions [70-72] (Scheme 34). 

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