Design And Synthesis Of New Chiral Expanded Ring Carbene Ligands Aind Their Application In Catalytic Reaction

N-heterocyclic carbenes(NHCs)play an important roles in modern organic synthesis.NHCs with larger heterocycle than the 5-membered imidazolium,which was also called "expanded ring" N-heterocyclic carbenes(RE-NHCs),attracted increasing attention recently.Comparing to their five-membered analogue,the RE-NHCs have corresponding larger N-CNHC-N angel,result in stronger electron-donating and nucleophilic ability,which made them excellent ligand in organometallicchemistry.Herein,we designed and synthesized twenty two new chiral 6-membered NHC precursors,including seven chiral pyrimidone salts and eighteen C2 symmetric 6-membered NHC precursors.There are mainly two aspects for the application of the new ligands in catalysis:1.The catalytic enantioselective addition of diethylzinc to aldehydes:chiral pyrimidone salts were used in the catalytic enantioselective addition of diethylzinc to aldehydes.Among the precursors screened,the salt 3d showed the best enantioselectivity.A number of chiralaryl secondary alcohols were obtained with high yields(up to 99%yield)and moderate enantioselectivities(up to 58%ee).In addition,C2-symmetric six-membered NHC precursors were used in the same transformation.The salt 6c showed the best enantioselectivity.A number of chiralaryl secondary alcohols were obtained with high yields(up to 96%yield)and moderate enantioselectivities(up to 66%ee).2.Palladium-catalyzed deprotonative-cross-coupling processes(DCCP)in diarylmethanes:After deprotonation of the NHC with base and formation of the palladium complexes in situ,eight C2-symmetric ligands were tested in palladium-catalyzed C(sp3)-H arylation of 4-oenzylpyridine with aryl bromides.The salt 4a showed the best activity.The corresponding triarylmethane derivatives were obtained with high yields(up to 96%yield).