title: Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and α,β-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives.
abstract: The catalytic synthesis of nitrogen-containing heterocycles is of great importance to medicinal and synthetic chemists, and also a challenge for modern chemical methodology. In this paper, we report the synthesis of pyrazolidine derivatives through a domino aza-Michael/hemiacetal sequence with chiral or achiral secondary amines as organocatalysts. Thus, a series of achiral pyrazolidine derivatives were obtained with good yields (up to 90%) and high diastereoselectivities (>20:1) with pyrrolidine as an organocatalyst, and enantioenriched pyrazolidines are also achieved with good results (up to 86% yield, >10/1 regioselectivity, >20:1 dr, 99% ee) in the presence of (S)-diphenylprolinol trimethylsilyl ether catalyst.
authors.affiliation: Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P. R. China; ; Tel: +86 (0)512 65880378.
authors.forename: Zhi-Cong
authors.initials: ZC
authors.lastname: Geng
authors.forename: Jian
authors.initials: J
authors.lastname: Chen
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: Xiao-Fei
authors.initials: XF
authors.lastname: Huang
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ya-Wen
authors.initials: YW
authors.lastname: Zhang
authors.forename: Xing-Wang
authors.initials: XW
authors.lastname: Wang