Enantioselective Catalytic Borane Reductions of Achiral Ketones: Synthesis and Application Of New Catalysts Prepared from(S)-Tert-Leucine and (S)-Azetidinecarboxylic Acid

Efficient asymmetric addition of diethylzinc to aldehydes using 3‐hydroxyazetidine derivatives as chiral ligands

“…The initial experiments provide encouraging results since the addition reactions carried out with all azetidine ligands proceed smoothly to give the desired secondary alcohol, in high yields and excellent enantioselectivities ( Under similar reaction conditions, various aromatic aldehydes have been studied for the ethylation using diethylzinc as reagent catalyzed by 10% mol of L1a in toluene. Similar to the result for benzaldehyde, all the additions to aromatic aldehydes provide the corresponding S-configuration alcohols as the major isomer with excellent enantioselectivities and in high yields (Table 1, entries [11][12][13][14][15][16]. Electron-deficient and electron-rich aromatic aldehydes demonstrate similar enantioselectivity in this process.…”

“…After this mixture had been refluxed for 2 h, then cooled to 0 • C, 20 ml of water was carefully added. The water phase was extracted with dichloromethane and dried over 13…”

Synthesis of new chiral cis‐3‐hydroxyazetidines and their application in diethylzinc addition to aldehydes

“…Chiral azetidines have been extensively used as a chiral auxiliary in recent years, 12 but only few studies have focused on the applications of its derivatives as chiral catalysts. [13][14][15][16][17][18][19][20][21][22][23][24] Chiral azetidines that can effectively catalyze the diethylzinc addition with high levels of enantioselectivity are scarcely reported, [20][21][22][23][24] and to our knowledge, no example of chiral hydroxyazetidine (hydroxyl group seated on the azetidine ring) for enantioselective catalysis has been described. We report herein the synthesis of a new series of chiral cis-3-hydroxyazetidines and their application in asymmetric addition of diethylzinc to aldehydes.…”

New Phenylglycine‐Derived Primary Amine Organocatalysts for the Preparation of Optically Active Warfarin

“…They are easily prepared on a large scale, with no chromatographic purification involved, by treating the appropriate methyl or ethyl ester hydrochloride salt of the amino acid with a five‐ to tenfold excess of PhMgBr in Et 2 O or THF. In this way, naturally occurring L ‐leucine and L ‐phenylalanine gave 13 and 14 ,13 whereas synthetic or semisynthetic L ‐phenylglycine, D ‐cyclohexylglycine and L ‐ tert ‐leucine gave increasingly bulky amino alcohols 15 – 17 , respectively 14–16 . D ‐Cyclohexylglycine is available by simple hydrogenation of D ‐phenylglycine,15 and L ‐ tert ‐leucine is produced on a ton scale by Evonik Degussa GmbH through an enzymatic process 17.…”