Pseudopericyclic processes

An episulphoxide intermediate has been proposed in the thiophilic reactions of sulphines (see Chap. 3, Pt II, p. 162). The necessity of a pseudopericyclic process in the isomerization of tetrakis(trifluoromethyl)- Dewar thiophen 5-oxide has been questioned. Calculations of the electronic transitions of thiiran and methylthiiran oxides have been related to their u.v. and c.d. spectra. ... 

The participation of the lone-pair orbital in the cyclization process allows its classification as a so-called pseudopericyclic reaction (76JA4325 97JA4509), which is a subset of a general type of pericyclic reactions... 

It has also been previously shown73 that the fluctuation pattern of electron density in the ELF basins provides a consistent description of pseudopericyclic and pericyclic bonding in concerted processes such as thermal chelotropic decarbonilation reactions.74 Experimental support for planar pseudopericyclic transition states in chelotropic decar-bonilations has been recently reported.75 ELF picture of bonding reveals that for the eight transition states analysed (see Scheme 3), the departing CO can be visualized in terms of a carbon monoxide structure with a Tone pair region on the carbon atom. 

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