Sulfenamides radical cations

Aromatic sulfenamides give cation radicals that dimerize to biphenyl derivatives. The latter compound can suffer further oxidation, during which the N-S bond is cleaved, leading to a quinoid structure that can be oxidized to the corresponding cation radical [231] ... 

In sulfenamides (R S—NR R ), the cation-radicals keep an nnpaired electron occupying a n orbital. This orbital is localized between the sulfur and nitrogen atoms. As a matter of fact, a slight S=N double bond character exists in the neutral sulfenamides. A consequence of this double bond character is an increase in the energy barrier, which restricts rotation around the S—N bond. Restricted rotation about the S—N bond is known in neutral sulfenamides (Kost and Raban 1990). Notably, the energy barrier to this rotation is greater for the derived cation-radicals when compared to the parent compounds (Bassindale and Iley 1990). 

The generation of active radicals as a result of bond breakage makes cation radicals useful as synthones. For example, arylsulfenamide cation radicals may be used as sources of sulfenyl radicals. The reaction of 4 -nitrobenzenesulfenanihde with Lewis acids, such as BF3 and A1C13, results in the formation of the sulfenamide cation radical. The latter appears to be an active sulfenyl transfer species. In the presence of anisol, ethenes, or ethynes, it gives phenylthiyl derivatives (Benati et al. 1990 Grossi Montevecchi 1993). 

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