Carbene catalysis Michael additions

Keywords Absolute configuration, Amines, Amino acids, Carbenes, Cascade reactions, 2-chloro-2-cyclopropylideneacetates. Combinatorial libraries. Cycloadditions, Cyclobutenes, Cyclopropanes, Diels-Alder reactions. Heterocycles, Michael additions. Nitrones, Nucleophilic substitutions, Peptidomimetics, Palladium catalysis. Polycycles, Solid phase synthesis, Spiro compounds. Thiols... 

As well as the traditional benzoin and Stetter reactions, some new synthetic transformations were disclosed via carbene catalysis. In 2007, the Scheldt group developed an intramolecular Michael-type reaction with unsaturated substrates 56 through catalysis with chiral triazolium salt 55. The intermediates 57 were generated via a domino Michael addition/lactonization sequence, and bicyclic products 58 were afforded in satisfactory yields and with excellent enantioselectivity after... 

Due to the unique bivalent carbene and diversity of the N-heterocyclic motif, NHCs have been demonstrated to be efficient organocatalysts for various enantioselective reactions. In addition to the traditional thioazolium and imidazolium NHCs, triazolium NHCs have become the most successful organocatalysts. Recently, NHC/Lewis acid cocatalysis and bifunctional NHCs have shown a very promising future. Beyond the classic NHC-catalysed umpolung of aldehydes, the extended umpolung of functionalised aldehydes are extremely successful. A series of NHC-catalysed reactions of ketenes have been developed for the synthesis of various enantioriched heterocycles. Esters, anhydrides, carboxylic acids and even Michael acceptors are useful alternative substrates for NHC-catalysed reactions. With increasing interest and rapid development of NHC catalysis, new structures of the catalysts, new reaction modes, and synthetic applications can be expected in the near future. 

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