Neighbouring-group effects in the oxidation of olefins by mercury(II), thallium(III), and lead(IV) acetates

Abstract

The participation of neighbouring groups during oxidation of olefins by mercury(II), thallium(III), and lead(IV) acetates has been investigated. With the examples chosen lead(IV) reacts exclusively at the neighbouring group (aryl or phenolic), there being no evidence for electrophilic attack on the double bond. Similarly, mercury(II) is capable of substituting an aromatic ring rather than reacting at an olefinic site; however, the latter reaction can be made to predominate in a more polar medium. The initial ion formed during thallium(III) oxidation is less selective towards nucleophilic attack than the corresponding mercury(II) species, and this is attributed to greater interaction between the metal atom and the positive centre in a mercurio- than in a thallio-cation. Whereas the organomercury adducts are stable to the reaction conditions, in thallium(III) oxidations suitable substituents can trap carbocation-like species during both the formation and the destruction of the adducts.