Aims and Objectives: When compared to five-membered N-heterocyclic carbene, recent reports
have demonstrated that ring expanded NHCs showed rather different properties such as increased basicity (nucleophilicity)
and greater steric demand. These unique features provide an opportunity to design new chiral
ligands. This study was undertaken to design and synthesize a series of novel enantiopure pyrimidone salts, the
precursors of N-heterocyclic carbenes, and their activity in asymmetric diethylzinc addition of arylaldehydes
was demonstrated as well.
Material and Method: Commercially available dimethylmalonic acid was treated with thionyl chloride to form
dimethylmalony dichloride, followed by subsequent reaction with different chiral primary amine produced corresponding
diamide. Next, conversion of diamide to monoamide was achieved by partial reduction with lithium
aluminum hydride. Finally, cyclization of monoamide with triethyl orthoformate in the presence of ammonium
salts provided pyrimidone salts in good yields.
Results: Seven enantiopure pyrimidone salts, the precursors of N-heterocyclic carbenes, have been synthesized
starting from dimethylmalonic acid. Their applicability in asymmetric diethylzinc addition of arylaldehydes has
been demonstrated and the corresponding secondary alcohol was obtained with good yields and moderate
Conclusion: Herein we developed an efficient route to prepare a series of novel N-heterocyclic carbene precursors,
which were demonstrated as effective catalysts for asymmetric diethylzinc addition of arylaldehydes, and
the corresponding secondary alcohol was obtained with good yields and moderate enantioselectivities.