Acylation preformed lithium enolates

Seebach has also studied the utility of esters in organometallic acylation. In this case, preformed ester enolates of 2,6-di(t-butyl)-4-methylphenyl esters (BHT esters) were slowly warmed above -20 C to form the corresponding ketene. If this was done in the presence of an ad tional equivalent of alkyl-lithium the ketene was trapped to give a ketone enolate in high yield. The same reaction failed to give any product when simple esters such as methyl, ethyl or Nbutyl were uscd. Scheme 17 is illustrative of the method. 

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