l-Valinol and l-phenylalaninol-derived 2-phenylamino-2-oxazolines as chiral auxiliaries in asymmetric alkylations

Enantioselective hydrogenation of α,β-unsaturated carboxylic acids over cinchonidine-modified Pd catalysts: effect of substrate structure on the adsorption mode

“…The product mixture resulted from the reactions of compound 7 and its methyl ester contained the (−) enantiomer in excess having R absolute configuration (14) according to literature data [31][32][33]. The low ee value obtained in the hydrogenation of 7 may be explained by the isomerisation of this compound, similarly to other ␣-alkyl-␣,␤-unsaturated acids [34,35] and the decreased steric hindrance of the methyl group relative to the ␣-phenyl group in 8.…”

A New Non‐Cross‐Linked Polystyrene Supported 2‐Phenylimino‐2‐oxazolidine Chiral Auxiliary: Synthesis and Application in Asymmetric Alkylation Reactions

“…In comparison to the related 2-phenylimino-2-oxazolidine chiral auxiliary, the stereoselectivity was similar to those reported for the model alkylation reactions under classical solution conditions. [9,10] These results show that NCPS-supported 2-phenylimino-2-oxazolidine chiral auxiliary 4 is an effective auxiliary for asymmetric alkylation reactions, and it can be recovered by simple filtration.…”

“…[8] This improved auxiliary provides superior performance to many other chiral auxiliaries currently in common usage and has been proved to be particularly efficient in terms of stereoselectivity and yields in asymmetric alkylation reactions. [9,10] However, in most case, the expensive chiral auxiliaries could not be recovered after the reactions; to recycle these expensive materials, chiral auxiliaries have been supported onto polymers. [11][12][13][14][15] Insoluble polymer supports, such as, Merrifield resin and Wang resin, only require simple "filtration" to achieve rapidly the isolation of desired compounds or to recover expensive reagents or catalysts attached onto solid supports for recycling.…”

New Practical Synthesis of Non-Cross-Linked Polystyrene Supported 2-Phenylimino-2-Oxazolidine

“…(S)-4-(4-Hydroxyl-benzyl)-2-phenylimino-2-oxazolidine (7): 20% Pd(OH) 2 /C (0.43 g) and HCOONH 4 (1.15 g, 38.16 mmol) were added to a solution of compound 6 (3.26 g, 9.10 mmol) in EtOAc (20 mL) and CH 3 OH (15 mL). The mixture was stirred at reflux for 3 h. After filtration of the catalyst and evaporation of the solvent, the crude product was further purified by column chromatography (CH 3 ) and then deducting HCl. The number average molecular weight (M n ) and molecular weight distribution (M w /M n ) of polymer 8 were found to be 9000 and 1.4, respectively (gel permeation chromatographic analyses, calibrated by polystyrene standards).…”

“…1 The auxiliary provides a superior performance to many other chiral auxiliaries currently in common use, and has been proved to be particularly efficient in terms of stereoselectivity and yield in asymmetric alkylations. 2,3 However, in most cases, the chiral auxiliaries cannot be effectively recovered after the reaction.…”