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Anhydrous zirconium tetrachloride is found to be an efficient catalyst for the Imino Diels–Alder reactions of N‐benzylideneanilines with 3,4‐dihydro‐2H‐pyran and 2,3‐dihydrofuran to afford pyrano and furo [3,2‐c] quinolines in good yields.
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Mahesh et al. (2004) studied this question.
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