Synthesis of Six-Membered N -Heterocyclic Carbene Precursors Based on Camphor.

The endo - and exo - N -heterocyclic carbene precursors based on camphor were prepared diastereoselectively in five synthetic steps starting from (1 S )-(+)-ketopinic acid. The obtained N -heterocyclic carbene precursors were investigated in an asymmetric benzoin reaction. All new compounds were fully characterized, and the absolute configurations were determined via X-ray diffraction and NOESY measurements.