Chiral Bipyridine Derivatives in Asymmetric Catalysis

Vibrational and electronic circular dichroism studies on the axially chiral pyridine-N-oxide: trans-2,6-di-ortho-tolyl-3,4,5-trimethylpyridine-N-oxide

“…42 Similarly to the previously studied 2,6-di-sec-butyl-4-methylpyridine-N-oxide 9 derivative, 37 the two intramolecular hydrogen bonds formed between the hydrogen of the methyl groups and the nitroxide oxygen govern the relative orientations of the tolyl moieties. The length of the D(HÁ Á ÁO) intramolecular hydrogen bond, the (CAHÁ Á ÁO) angle and the stabilization energy E (2) vary with the applied functionals and basis sets (see Table 1 Concerning the most important stabilization energies within the molecule, they are given by the resonance as in the case of 2,6-di-sec-butyl-4-methylpyridine-N-oxide 9. 37 Therefore the interaction energy calculated at B3PW91/TZVP level (the same level used for calculations of the flexible conformers of 2,6-di-sec-butyl-4-methylpyridine-N-oxide 9) for charge transfer from LP(3) O to the antibonding acceptor p * (N-C 2 0 ) is 52.5 kcal/mol and is higher than in the case of conformers of 9, which is in the range 35-45 kcal/mol.…”

“…[1][2][3][4][5] Typical reactions tested so far for enantioselectivity include allylations of aldehydes with polyhalosilanes, [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] aldol additions of trichlorosilylenol ethers to aldehydes 6,7,22 or ketones, 23,24 and epoxide ring openings [25][26][27] as typical tested enantioselective reactions.…”

Chiral N‐Oxides in Asymmetric Catalysis

“…Similarly, allenyl trichlorosilane (19) gives homopropargyl alcohols 20. [18,19] The reagents 17 and 19 were synthesized by metal-catalyzed reactions between propargyl chloride and Cl 3 SiH: CuCl catalysis gave 17 (Ͼ99:1), whereas the reaction catalyzed by (acac) 2 Ni produced 19 (Ͼ99:1). [18,19] The asymmetric version has been reported by Nakajima, [19a] who employed the axially chiral biquinoline bis-N-oxide 4 as catalyst (10 mol-%) but the enantioselectivities attained were rather modest (40-62 % ee).…”

“…[1] At the same time, amine N-oxides, despite their pronounced nucleophilic character, remained in the shadows and have only made a visible impact in the field of asymmetric catalysis in the last decade. The use of pyridine-derived N-oxides was summarized recently, [2] and this microreview provides an update on the latest developments in the application of chiral N-oxides derived from tertiary amines and pyridines in asymmetric catalysis.…”

Highly Enantioselective Synthesis of α‐Stereogenic Esters through Catalytic Asymmetric Michael Addition of 4‐Oxo‐4‐arylbutenoates

“…[6,7] ScA C H T U N G T R E N N U N G (OTf) 3 , which features such advantages as stability, recovery, and reusability, has shown highly catalytic activity in many transformations. [8] As excellent chiral scaffolds, N,N'-dioxides [9] were able to coordinate with ScA C H T U N G T R E N N U N G (OTf) 3 and exhibited great potential in various reactions such as allylation, [10a] aza-Diels-Alder reactions, [10b] Michael reactions, [10c] FriedelAbstract: Highly enantioselective Michael addition of 1,3-dicarbonyl compounds and nitromethane to 4-oxo-4-arylbutenoates catalyzed by N,N'-dioxide-ScA C H T U N G T R E N N U N G (OTf) 3 complexes has been developed. Using 0.5-2 mol % catalyst loading, various a-stereogenic esters were obtained regioselectively with excellent yields (up to 97 %) and enantioselectivities (up to > 99 % ee).…”