A New Chiral Carbene Catalyst

Significance

A new N-heterocyclic carbene (NHC) precursor 1, an imidazolium salt similar to the known triazolium salt 2, and its concise synthesis from the chiral amino alcohol 3 is reported. The reactivity difference of NHCs derived from 1 and 2 is demonstrated by applying them in several NHC-catalyzed transformations of α,β-unsaturated aldehydes. Whereas the NHC derived from 1 was found to catalyze reactions via homoenolate intermediates 4 (e.g. eq. 1), the corresponding catalyst derived from 2 prefers acyl anion (5) mediated transformations (e.g., eq. 2).