Sulphur and Selenium Stabilised Anions

Sulphur and Selenium-Stabilised Anions - As in previous years, anions stabilised by an adjacent sulphur, and to a lesser extent, a selenium residue have found extensive use in synthetic chemistry. A range of new methods have been developed for the generation of these stabilised anions. 

A useful entry to functionalised ketene-S,S- acetals is based on the reaction of the alkenyl anion (81) with electrophiles (alkyl and silyl halides, aldehydes). This anion was prepared by bromine-lithium 

Further advances within the area of nucleophilic carbohydrates have been reported by the Konstanz research group. Treatment of the 

The lithio derivative (97) can be used as both a formyl and carboxyl acyl anion equivalent, and this species undergoes conjugate addition to a,6-unsaturated carbonyl groups to give 1,4-adducts in good yield. This versatile reagent has also been used to prepare a-hydroxy aldehydes and ketones. 

The question of the extent to which oxygen stabilises a negative charge has been studied within the context of S-stabilised systems. Although 1,3-oxathiane (98) is deprotonated at C-2, a mode of reactivity that has been impressively exploited by Eliel, the corresponding sulphone (99) undergoes lithiation exclusively at C-4  

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