Chiral imidazo[1,5-a]tetrahydroquinoline N-heterocyclic carbenes and their copper complexes for asymmetric catalysis

Novel chiral imidazo[1,5-a]tetrahydroquinoline N-heterocyclic carbenes derived from β-pinene have been developed. The preliminary studies with both the in situ generated and preformed copper–carbene complexes have shown these chiral NHCs are efficient and selective ligands in the Cu-catalyzed asymmetric conjugate borylation of α,β-unsaturated esters.

Figure optionsDownload as PowerPoint slide

6,6-Dimethylbicyclo[3.1.1]heptan-2-oneC9H14O[α]D20=+29.8 (c 2.5, CHCl3)Absolute configuration: (1R,5S)Source of chirality: (−)-β-pinene

7,7-Dimethyl-5,6,7,8-tetrahydro-6,8-methanoquinolin-2(1H)-oneC12H15NO[α]D20=+71.5 (c 0.9, CH2Cl2)Absolute configuration: (6R,8R)Source of chirality: (−)-β-pinene

7,7-Dimethyl-5,6,7,8-tetrahydro-6,8-methanoquinolin-2-yl trifluoromethanesulfonateC13H14F3NO3S[α]D20=-8.9 (c 1.0 , CH2Cl2)Absolute configuration: (6R,8R)Source of chirality: (−)-β-pinene

Methyl 7,7-dimethyl-5,6,7,8-tetrahydro-6,8-methanoquinoline-2-carboxylateC14H17NO2[α]D20=-9.8 (c 1.5, CH2Cl2)Absolute configuration: (6R,8R)Source of chirality: (−)-β-pinene

7,7-Dimethyl-5,6,7,8-tetrahydro-6,8-methanoquinoline-2-carbaldehydeC13H15NO[α]D20=-27.8 (c 1.0, CH2Cl2)Absolute configuration: (6R,8R)Source of chirality: (−)-β-pinene

8,8-Dimethyl-2-phenyl-6,7,8,9-tetrahydro-7,9-methanoimidazo[1,5-a]quinolin-2-ium chlorideC20H21ClN2[α]D20=+60.6 (c 1.1, CH3OH)Absolute configuration: (7R,9R)Source of chirality: (−)-β-pinene

2-Mesityl-8,8-dimethyl-6,7,8,9-tetrahydro-7,9-methanoimidazo[1,5-a]quinolin-2-ium chlorideC23H27ClN2[α]D20=+38.4 (c 1.3, CHCl3)Absolute configuration: (7R,9R)Source of chirality: (−)-β-pinene

2-(2,6-Diisopropylphenyl)-8,8-dimethyl-6,7,8,9-tetrahydro-7,9-methanoimidazo[1,5-a]quinolin-2-ium chlorideC26H33ClN2[α]D20=+26.0 (c 1.0, CHCl3)Absolute configuration: (7R,9R)Source of chirality: (−)-β-pinene

2-(4-Methoxyphenyl)-8,8-dimethyl-6,7,8,9-tetrahydro-7,9-methanoimidazo[1,5-a]quinolin-2-ium chlorideC21H23ClN2O[α]D20=+68.8 (c 0.8, CHCl3)Absolute configuration: (7R,9R)Source of chirality: (−)-β-pinene

2-(3,5-Bis(trifluoromethyl)phenyl)-8,8-dimethyl-6,7,8,9-tetrahydro-7,9-methanoimidazo[1,5-a]quinolin-2-ium chlorideC22H19ClF6N2[α]D20=+34.4 (c 1.0, CHCl3)Absolute configuration: (7R,9R)Source of chirality: (−)-β-pinene