BiCl3-Catalyzed Diastereoselective Intramolecular [4+2] Cycloaddition Reactions Leading to Pyrazole Annulated New Sulfur Heterocycles

Abstract

Intramolecular 4+2] cycloaddition reactions of N-aryl imines generated in situ from anilines and the S-allyl derivatives of pyrazole aldehydes have been carried out in the presence of catalytic amounts of BiCl₃ to provide the corresponding hexahydropyrazolo 4′,3′:5,6]thiopyrano4,3-b]quinolines in excellent yields. The reactions are highly diastereoselective and the only cis products are isolated exclusively.