Bis Imidazoline Ligands Research Articles

Chiral Self-Sorting Process With C2 Symmetric Bisimidazoline Ligands.

We have studied the coordination chemistry of chiral imidazoline-based C2-symmetric ligands with zinc (II) and copper (II). Two types of bisimidazoline ligands were studied, one with the free amine (BIM-H) and the other with the amine protected by a toluene sulfonyl group in position 6 (BIM-Ts). The complexes formed were isolated, purified, and characterized, in particular by X-ray diffraction studies and CD in the case of the enantiopure complexes. By playing with the choice of ligand system (enantiopure or racemate), we were able to show that the selective formation of homoleptic and heteroleptic metal complexes can be controlled by means of the chiral molecular instruction of bisimidazoline ligands.

Palladium/N,N'-Disulfonyl Bisimidazoline-Catalyzed Enantioselective Addition of Arylboronic Acids to Cyclic N-Sulfonyl Ketimines.

The combination of Pd(TFA)2 and an N,N'-disulfonyl bisimidazoline ligand shows high catalytic activity and excellent asymmetric induction in the addition of arylboronic acids to cyclic N-sulfonyl ketimines including benzo[d]isothiazole-1,1-dioxides, benzo[e][1,2,3]oxathiazine-2,2-dioxides, and 1,2,5-thiadiazole-1,1-dioxides, by which three types of chiral quaternary carbon-containing sultams with substantial substitution diversity were synthesized with high yields and excellent enantioselectivities (up to >99% ee). The current catalysis demonstrated a remarkable tolerance to oxygen and thus provided an operationally simple approach for constructing enantioenriched cyclic quaternary stereocenters.

Enantio‐ and Regioselective NiH‐Catalyzed Reductive Hydroarylation of Vinylarenes with Aryl Iodides

AbstractA highly enantio‐ and regioselective hydroarylation process of vinylarenes with aryl halides has been developed using a NiH catalyst and a new chiral bis imidazoline ligand. A broad range of structurally diverse, enantioenriched 1,1‐diarylalkanes, a structure found in a number of biologically active molecules, have been obtained with excellent yields and enantioselectivities under extremely mild conditions.

Enantio- and Regioselective NiH-Catalyzed Reductive Hydroarylation of Vinylarenes with Aryl Iodides.

A highly enantio- and regioselective hydroarylation process of vinylarenes with aryl halides has been developed using a NiH catalyst and a new chiral bis imidazoline ligand. A broad range of structurally diverse, enantioenriched 1,1-diarylalkanes, a structure found in a number of biologically active molecules, have been obtained with excellent yields and enantioselectivities under extremely mild conditions.

N-Sulfonyl Bisimidazoline Ligands and Their Applications in Pd(II)-Catalyzed Asymmetric Addition toward α-Tertiary Amines.

A new class of chiral N-sulfonyl bisimidazoline (Bim) ligands have been designed, prepared, and applied in Pd(II)-catalyzed asymmetric addition of arylboronic acids to isatin-derived N-Boc ketimines. The combination of Pd(OCOCF3)2 and N-tosyl Bim ligand shows high catalytic activity and excellent asymmetric induction, enabling asymmetric addition to offer α-tertiary amines with generally good to high yields and excellent enantioselectivity (up to 96% yield, 96% ee). This asymmetric Pd(II) catalysis can tolerate air conditions, providing a practical and operationally simple protocol toward the construction of an enantioenriched α-tertiary stereocenter.

Iron-catalyzed cross etherification of alcohols to form unsymmetrical benzyl ethers

A Fe(II)-catalyzed direct synthesis of unsymmetrical benzyl ethers from two different alcohols has been developed. In the presence of a catalyst in situ generated by combining Fe(OTf)2 (OTf=trifluomethanesulfonate) with a pyridine bis-imidazoline ligand, benzyl alcohols underwent cross dehydrative etherification with a wide range of aliphatic alcohols in good to excellent yields under mild, operationally simple conditions with low catalyst loading. The catalyst tolerates a number of functional groups in both coupling partners, and is highly chemoselective, affording no symmetrical ether by-products. Ligand is shown to play a crucial role to the success of this dehydrative transformation, and preliminary mechanistic studies indicate that a benzylic cation is involved in the cross etherification.

Green and Efficient: Iron-Catalyzed Selective Oxidation of Olefins to Carbonyls with O2.

A mild and operationally simple iron-catalyzed protocol for the selective aerobic oxidation of aromatic olefins to carbonyl compounds is described. Catalyzed by a Fe(III) species bearing a pyridine bisimidazoline ligand at 1 atm of O2, α- and β-substituted styrenes were cleaved to afford benzaldehydes and aromatic ketones generally in high yields with excellent chemoselectivity and very good functional group tolerance, including those containing radical-sensitive groups. With α-halo-substituted styrenes, the oxidation took place with concomitant halide migration to afford α-halo acetophenones. Various observations have been made, pointing to a mechanism in which both molecular oxygen and the olefinic substrate coordinate to the iron center, leading to the formation of a dioxetane intermediate, which collapses to give the carbonyl product.

Modular ligand variation in calcium bisimidazoline complexes: effects on ligand redistribution and hydroamination catalysis

A series of calcium complexes supported by chiral bisimidazoline ligands have been studied in the catalytic intramolecular hydroamination/cyclisation of amino-olefins. The complexes [Ca(R-BIM){N(SiMe(3))(2)}(THF)] (R = 4-C(6)H(4)Me, 5a, 4-C(6)H(4)F, 5b and (t)Bu, 5c) have given competitive enantioselectivities (up to 12%) when compared to current literature studies involving calcium. Bisimidazolines offer a significant advance over similar bisoxazoline ligands, by allowing a greater structural variance through a modular synthetic pathway.

Copper(II)-Catalyzedsyn-Selective Henry Reaction

The authors report a highly diastereo- and enantioselective Henry reaction of nitroethane with aromatic and aliphatic aldehydes. The bisimidazoline ligand outperforms conventional bisoxazoline ligands in both yield and selectivity.

Chiral Bisimidazoline Ligands for Highly Enantioselective Henry Reaction

In this paper, the authors developed a new synthesis of Beller’s bisimidazoline ligand (Org. Lett. 2005, 7, 3393-3396) that allows modified versions to be readily prepared. They tested several of these ligands in a copper-catalyzed enantioselective nitroaldol reaction and found an N-phenyl bisimidazoline that was particularly effective.