Enantioselective Annulations with NHC-bound Ester Enolate Equivalents

7 Enantioselective Annulations with NHC-bound Ester Enolate Equivalents 

Beyond their role as catalysts for the benzoin reaction, which is formally a 1,2-addition of an acyl anion equivalent to an aldehyde, NHCs were also employed as catalysts for a number of interesting 1,2 addition processes. 

The ability of NHC to activate silylated nucleophiles led to further investigations and useful procedures. Song reported the formation of silyl enol ethers by an NHC-catalyzed silyl exchange reaction that transferred a silyl group from a silyl ketene acetal to a ketone. When aldehydes, rather than ketones, were used as substrates the NHC catalysts promoted a Mukaiyma aldol reaction to give p-hydroxy esters and ketones in good yields.  

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