Acyclic radicals, structural properties

ESR properties of RSSR cations were reviewed by Bassindale and Hey [1]. Typical g values for the acyclic species with smaller alkyl groups are g, = 2.035, g2 = 2.018, and = 2.003, with = 2.018. The fact that the value of g is close to the free spin value indicates that the cation radicals have relaxed from the orthogonal parent structures to planar structures [1]. The seven line spectrum, which is observed for MeSSMe [1,98] indicates coupling to six equivalent protons, which would not be possible if the radical center were localized on one sulfur. Theoretical calculations indicate a spin population of 0.48 on each S [98]. Other evidence for localization of the unpaired electron in a ti orbital involving both S atoms of disulfide cations comes from an analysis of the anisotropic g tensors and the splittings in symmetrical alkyl disulfides [ 1 ]. 

Radical domino strategies have been scarcely described in the construction of polycyclic cyclopropanic structures. Indeed, radicals formed by 3-exo-trig cyclization are being rapidly reopened, and this property is notably used in radical clocks experiments. In order to suppress this unwanted event, Malacria and Fensterbank have devised a (dichloromethyl)dimethylsilyl ether able to play both roles of the initiation and termination sites of the radical process [108]. By designing an appropriate acyclic structure 98, the expected cyclopropanic compounds 99 have been obtained in good yields and diastereoselectivities after addition of MeLi to the silyloxycyclopentene intermediate (Scheme 5.35). 

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