Rearrangement onium salt

The onium carbanion formed under phase-transfer conditions is unstable depending on the anion source, and in the absence of an electrophilic reaction partner, degradation of the accumulated onium carbanion in the organic phase may be observed. This is known to proceed via Hoffman elimination, nucleophilic substitution and/or Stevens rearrangement (Scheme 1.4) [4f,6,7]. The direct decomposition of onium salt, as influenced by the strong inorganic base at the interface, may be also operative. 

Rearrangement reactions of both iodonium and sulfonium cations proceed out of the lowest excited singlet states of the respective onium salts... 

In view of the low rate of exchange of a-hydrogens in onium salts in aqueous media (which were considered akin in solvation properties to the liquid ammonia often used for these rearrangements), it has been... 

The sulfur and nitrogen series ressemble each other in so far as both amines and sulfides or the corresponding onium salts can be induced to isomerize. Benefitting from a greater driving force, S -ylides rearrange under very mild conditions. 

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