Alkylation, enolate ions dehydration reactions

The most reliable method for making the enone is to alkylate the Mannich base with Mel and then treat the ammonium salt with base. Enolate ion formation leads to an ElcB reaction rather like the dehydration of aldols, but with a better leaving group. 

Stork and Ponaras have developed a method, involving the intermediacy of P-hydroxyhydrazones, for the introduction of alkyl and aryl groups on the a-carbon of an aP-unsaturated ketone, based on principles discussed previously. The method is particularly useful in situations where the thermodynamic enolate ion (y-carbon) cannot, or must not for the sake of other sensitive groups, be formed. Acid-catalysed dehydration of substituted cyclohex-3-ene-l,2-diols, readily formed from dienone precursors, yielded mixtures of cyclohex-2-enones and substituted benzenes. The product ratio was strongly dependent on reaction conditions and on the substituent group at C-1, but independent of the initial diol configuration, thus indicating a common cationic intermediate. Conditions were found which allow the synthetic use of the transformation sequence shown (Scheme 2) in up to 90 % yield. 

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