Bronsted Acid-Promoted Hydroamination Of Unsaturated Hydrazones: Access To Biologically Important 5-Arylpyrazolines

A novel and efficient Bronsted acid-promoted hydroamination of hydrazone-tethered olefins has been developed. A variety of pyrazolines have been easily obtained in good to excellent yields with high chemo- and regioselectivity under simple and mild conditions. This method represents a straightforward, facile, and practical approach toward biologically important 5-arylpyrazolines, which are difficult to access by previously reported radical hydroamination of beta,gamma-unsaturated hydrazones.