Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Imines with Propioloylpyrazoles Induced by Chiral π−Cation Catalysts

Masahiro Hori, Akira Sakakura,* Kazuaki Ishihara* 
J. Am. Chem. Soc.2014, 136 (38), 13198–13201.  (Published online: Sept 16, 2014) 
DOI: 10.1021/ja508441t 

We developed 1,3-dipolar cycloadditions of azomethine imines with propioloylpyrazoles catalyzed by a chiral copper(II) complex of 3-(2-naphthyl)-l-alanine amide.  The asymmetric environment created by intramolecular π–cation interaction and the N-alkyl group of the chiral ligand gives the corresponding adducts in high yields with excellent enantioselectivity.  This is the first successful method for the catalytic enantioselective 1,3-dipolar cycloaddition of azomethine imines with internal alkyne derivatives to give fully substituted pyrazolines. 

This paper was highlighted in  Synfacts2014, 10 (12), 1288.   
Synthesis of Chiral Pyrazolines via Chiral π-Cation Catalysis 
DOI: 10.1055/s-0034-1379534