Design, synthesis and structure of new chiral squaric acid monoaminoalcohols and diaminoalcohols and their use as catalysts in asymmetric reduction of ketones and diketones

Design and synthesis of heterocyclic enamine derivatives based on skeleton of neonicotinoids

“…3,4-Diethoxycyclobut-3-ene-1,2-dione (2) A mixture of squaric acid (1.25 g, 0.01 mol), ethanol (50 mL), and benzene (20 mL) was heated under reflux for 10 h, and then concentrated to afford crude compound 2 as an oil (Zhou et al, 2001) (yield 1.27 g, 75%); GC-MS: m/z 170 [M] + , 142, 113, 85, 68, 58, 29. N 1-((6-Chloropyridin-3-yl)methyl)ethane-1,2-diamine (5) A solution of ethane-1,2-diamine (6.06 g, 100 mmol) in acetonitrile (30 mL) was dropwise added over a period of 30 min to a solution of 2-chloro-5-(chloromethyl)pyridine ( 3 ) (3.24 g, 20 mmol) in 30 mL of acetonitrile. After 8 h of stirring, the solution was treated with 100 mL of water, and extracted with chloroform (3 × 30 mL).…”

Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments

“…Interesting results have been reported in which squaric acid is used as a backbone to bind chiral aminoalcohol fragments [20][21][22][23]. The squaramides obtained have been used as ligands in borane reduction of activated ketones, providing high enantioselectivity (up to 99% ee).…”

“…Based on these results, it can be concluded that the rigid and flat squaric acid skeleton in combination with chiral aminoalcohol fragments provides a structurally well-defined chiral environment for the asymmetric reaction. For explanation of the extraordinarily high asymmetric induction, a transition state model involving the squaramide ligand in the formation of the catalyst complex has been proposed [21][22][23]. Consequently, it is conceivable that novel structures obtained through the combination of squaric acid core as a backbone and suitable chiral amine and/or aminoalcohol moieties might have a positive influence on the borane reductions.…”

A series of new C2‐symmetric amino alcohols with multicoordination groups: Promising catalysts for synthesis of both enantiomers in the borane‐mediated reduction of prochiral ketones

“…5,6 In fact, since the introduction of the first structurally more rigid (S)-proline-based b-amino alcohol by Itsuno et al in 1981, 7 the study of catalysts derived from prolinol remains an active research area. New derivatives such as sulfonyl prolinol, 8 polymer-supported sulfonamide, 9 imidazolium-tagged sulfonamide, 10 phosphinamides, 11 squaric prolinols, [12][13][14] amides 15 , polymer-supported prolinol 16 , and N-alkyl prolinols 17 have been reported and good enantioselectivities were obtained. Catalysts with C 2 -symmetry have also received much attention and have been successfully applied in the borane-mediated reduction.…”