Novel C2-symmetric six-membered NHCs for asymmetric copper-catalysed conjugate addition of Grignard reagents to 3-methylhexenone

A series of novel chiral 3,4,5,6-tetrahydropyrimidinium salts, the precursor of N-heterocyclic carbene ligands, were designed and synthesized from (1S, 3S)-1,3-diphenyl-1,3-propanediamine. In situ prepared corresponding carbenes were tested in asymmetric copper-catalysed 1,4 conjugate addition of Grignard reagents to 3-methylcyclohexenone, allowing enantiomeric excesses of up to 87% to be achieved.