%0 Journal Article
%T Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and ¦Á,¦Â-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives
%A Zhi-Cong Geng
%A Jian Chen
%A Ning Li
%A Xiao-Fei Huang
%J Beilstein Journal of Organic Chemistry
%D 2012
%I 
%R 10.3762/bjoc.8.195
%X 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.
%K aza-Michael
%K domino
%K hydrazine
%K organocatalysis
%K pyrazolidine
%U http://dx.doi.org/10.3762/bjoc.8.195