N-heterocyclic carbene-catalyzed Michael additions of 1,3-dicarbonyl compounds.

A study of the organocatalytic activity of N-heterocyclic carbenes (NHCs) in the Michael addition of 1,3-dicarbonyl compounds has allowed us to identify 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) as an excellent catalyst for this transformation (up to 99 % yield with a 2.5 mol % catalyst loading), and the reaction was found to be of broad scope. Two early applications of this unprecedented catalytic activity of NHCs are described, that is, the domino carbocyclization reactions of simple cyclic 1,3-dicarbonyl and malonic acid derivatives, which allow stereoselective access to bridged bicyclic compounds, and the stereoselective synthesis of cyclohexanols (or cyclohexene). Early mechanistic investigations are also reported.