Tosyl, reaction with enolate anions

Alkylations occur in the reaction of carbanions with simple primary or secondary alkyl chlorides, bromides, iodides, or tosylates. For the reaction in Equation 7.5, a weak base was used to generate a small concentration of the resonance delocalized enolate anion [14], In this case, the electrophile, methyl iodide, is present from the initial stage. The least hindered side of the carbanion attacked to give the diastereomer shown. 

Dicarbonyl donors bearing a thioester has been applied in the Mannich reaction to A -tosyl imines. Ricci presented an enantioselective decarboxylative addition of malonic half thioester 37 to imine 38. In the Mannich-type addition, catalyst 36 deprotonates the malonic acid thioester followed by decarboxylation to generate a stabilized thioacetate enolate. This stabilized anion reacts with facial selectivity to the imine due to steric-tuning from 36 [47] (Scheme 8). 

Alkylations. Many bases which are weaker than t-BuOK are capable of essentially quantitative conversion of active methylene compounds into the corresponding enolates or other anions. However, the alkylation of diethyl malonate with a bicyclic secondary tosylate (eq 1) and the alkylation of ethyl n-butylaceto-acetate with -BuI (eq 2f provide examples of cases where the use of f-BuOK in f-BuOH is very effective. In the latter reaction, cleavage of the product via a retro-Claisen reaction is minimized with the sterically hindered base and yields obtained are higher than when Sodium Ethoxide or EtOK in EtOH, Sodium in diox-ane or toluene, or Sodium Hydride in toluene are used for the enolate formation. 

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