Synthesis of a novel class of chiral N,N,N-tridentate pyridinebisimidazoline ligands and their application in Ru-catalyzed asymmetric epoxidations

A new class of easily tunable N,N,N-pyridinebisimidazoline (pybim) ligands have been synthesized. The synthesis and tunability of these chiral tridentate ligands are much easier and flexible compared to the popular pyboxes, making the former a suitable ligand tool box for various asymmetric transformations. Ruthenium complexes of the new ligands were synthesized and applied in the asymmetric epoxidation of olefins using hydrogen peroxide as the oxidant. Excellent yields and moderate to good enantioselectivities were achieved in the epoxidation of aromatic olefins.

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2,6-Bis-([4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC35H29N5[α]D20=+112.4 (c 0.52, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-([3aR,7aR]-3a,4,5,6,7,7a-hexahydro-1H-benzoimidazol-2-yl)-pyridineC19H25N5[α]D20=+242.4 (c 0.52, CHCl3)Source of chirality: asymmetric synthesis

(3aR,6Z,8aS)-4,5,8,8a-Tetrahydro-6-(6-((Z,3aR,8aS)-4,5,8,8a-tetrahydro-2,2-dimethyl-3aH-[1,3]dioxolo[4,5-e][1,3]diazepin-6-yl)pyridin-2-yl)-2,2-dimethyl-3aH-[1,3]dioxolo[4,5-e][1,3]diazepineC21H29N5O4[α]D20=+32.7 (c 0.21, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-Benzoyl-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC49H38N5O2[α]D20=-68.1 (c 0.50, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(2-methyl-benzoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC51H41N5O2[α]D20=-115.7 (c 0.67, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(4-methoxy-benzoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC51H42N5O4[α]D20=-86.4 (c 0.41, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(4-trifluoromethyl-benzoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC51H35N5F6O2[α]D20=-41.9 (c 0.50, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(2,6-dimethoxy-benzoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC53H46N5O6[α]D20=-86.1 (c 0.37, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(2,4,6-trimethoxy-benzoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC55H50N5O2[α]D20=-49.2 (c 0.43, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(3,5-di-tert-butylbenzoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC65H69N5O2[α]D20=-93.3 (c 0.45, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-phenylacetyl-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC51H41N5O2[α]D20=+27.4 (c 0.23, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(diphenylacetyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC63H49N5O2[α]D20=-29.6 (c 0.13, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-naphthoyl-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC57H42N5O2[α]D20=-104.3 (c 0.20, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-[(2S)-2-(6-methoxy- naphthalen-2-yl)-propionyl]-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC63H53N5O4[α]D20=-46.6 (c 0.25, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(2-(1R,2S,5R)-2-isopropyl-5-methylcyclohexyloxy-acetyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC59H69N5O4[α]D20=-21.8 (c 0.16, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-adamantoyl-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC57H58N5O2[α]D20=-22.0 (c 0.50, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-acetyl-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC39H33N5O2[α]D20=+24.5 (c 0.35, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-pentanoyl-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC45H45N5O2[α]D20=-9.6 (c 0.24, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(2-methyl propanoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC43H41N5O2[α]D20=-34.8 (c 0.22, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(3-methyl butanoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC45H45N5O2[α]D20=-21.7 (c 0.21, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(3,3-dimethyl butanoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC47H49N5O2[α]D20=-35.4 (c 0.21, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(phenoxycarbonyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC49H37N5O4[α]D20=+8.4 (c 0.38, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(1-naphthyloxycarbonyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC57H41N5O4[α]D20=-7.2 (c 0.34, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(9-fluorenylmethyloxycarbonyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC65H49N5O4[α]D20=+21.7 (c 0.12, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-((1R,2S,5R)-2-isopropyl-5-methylcyclohexyloxy carbonyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC57H65N5O4[α]D20=-48.7 (c 0.25, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-(1,1-dimethylethyloxy carbonyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC45H45N5O4[α]D20=-17.1 (c 0.19, CHCl3)Source of chirality: asymmetric synthesis

2,6- Bis-(1-benzyl-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC49H41N5[α]D20=+33.7 (c 0.14, CHCl3)Source of chirality:asymmetric synthesis

2,6-Bis-(1-[toluene-4-sulfonyl]-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC49H41N5O4S2[α]D20=-29.6 (c 0.50, CHCl3)Source of chirality:asymmetric synthesis

2,6-Bis-(1-benzyl-[3aR,7aR]-3a,4,5,6,7,7a-hexahydro-1H-benzoimidazol-2-yl)-pyridineC33H37N5[α]D20=+191.2 (c 0.37, CHCl3)Source of chirality:asymmetric synthesis

2,6-Bis-(1-[toluene-4-sulfonyl]-[3aR,7aR]-3a,4,5,6,7,7a-hexahydro-1H-benzoimidazol-2-yl)-pyridineC33H37N5O4S2[α]D20=+60.4 (c 0.50, CHCl3)Source of chirality:asymmetric synthesis

1-((4R,5R)-4,5-Dihydro-2-(6-((4R,5R)-4,5-dihydro-4,5-diphenyl-1H-imidazol-2-yl)pyridin-2-yl)-4,5-diphenylimidazol-1-yl)(mesityl)methanoneC45H38N5O[α]D20=+47.8 (c 0.16, CHCl3)Source of chirality:asymmetric synthesis

1-(3,5-Di-tert-butylphenyl)((4R,5R)-4,5-dihydro-2-(6-((4R,5R)-4,5-dihydro-4,5-diphenyl-1H-imidazol-2-yl)pyridin-2-yl)-4,5-diphenylimidazol-1-yl)methanoneC50H49N5O[α]D20=-2.9 (c 0.19, CHCl3)Source of chirality:asymmetric synthesis

1-((1R,2R,5S)-2-Isopropyl-5-methylcyclohexyloxy carbonyl)((4R,5R)-4,5-dihydro-2-(6-((4R,5R)-4,5-dihydro-4,5-diphenyl-1H-imidazol-2-yl)pyridin-2-yl)-4,5-diphenylimidazole-1- carboxylateC46H47N5O2[α]D20=+60.6 (c 0.23, CHCl3)Source of chirality: asymmetric synthesis

1-((4R,5R)-4,5-Dihydro-2-(6-((4R,5R)-4,5-dihydro-4,5-diphenyl-1H-imidazol-2-yl)pyridin-2-yl)-4,5-diphenylimidazol-1-yl)(diphenyl)phosphine oxideC47H38N5P1O1[α]D20=+53.1 (c 0.72, CHCl3)Source of chirality: asymmetric synthesis

2-(1-(2,4,6-Trimethyl-benzoyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-6-(1-((1R,2R,5S)-2-isopropyl-5-methylcyclohexyl-3-oxy carbonyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)pyridineC56H57N5O3[α]D20=-23.9 (c 0.13, CHCl3)Source of chirality: asymmetric synthesis

2-(1-((4R,5R)-(1R,2R,5S)-2-Isopropyl-5-methylcyclohexyl-3-oxycarbonyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-6-(1-(acetyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)pyridineC48H49N5O3[α]D20=-11.1 (c 0.23, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(2-naphthoyl-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC57H41N5O2[α]D20=+39.1 (c 0.39, CHCl3)Source of chirality: asymmetric synthesis

2,6-Bis-(1-((1S,2R,5S)-2-isopropyl-5-methylcyclohexyloxy carbonyl)-[4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridineC57H65N5O4[α]D20=-1.1 (c 0.50, CHCl3)Source of chirality: asymmetric synthesis