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.
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Sabitha et al. (2003) studied this question.
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