BiCl3-catalyzed diastereoselective intramolecular [4+2] cycloaddition reactions leading to pyrazole annulated new sulfur heterocycles

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]thiopyrano[4,3-b]quinolines in excellent yields. The reactions are highly diastereoselective and the only cis products are isolated exclusively.