AbstractHerein is described a diastereoselective Michael addition of Grignard reagents to α, β- unsaturated diethyl malonates incorporated with a 2-oxazolidone chiral auxiliary. The catalyst-free Michael addition proceeds with good chemical efficiency and excellent stereoselectivity; and it provides new thoughts to the asymmetric synthesis of β-substituted β3 amino acid derivatives.
This paper describes an efficient method for constructing cyclic β-amino acids bearing quaternary stereocenters. NaHMDS-promoted asymmetric α-alkylation was employed to obtain the key intermediates with quaternary stereogenic centers, which were subsequently reduced by NaBH4 in 10% methanol in THF, with high yields and high diastereoselectivities. By removing the allyl ester group and the chiral auxiliary, the corresponding cyclic β-amino acid hydrochlorides were finally obtained.
Enantiomerically Pure [2.2]Paracyclophane-4-thiol: A Planar Chiral Sulfur-Based Building Block Readily Available by Resolution with an Amino Acid Chiral Auxiliary