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4‐Hydroxycoumarin reacts with substituted salicylaldehydes, 2,6‐dichloro‐ or ‐chloro‐nitro‐benzaldehydes to yield unstable 3,3′‐benzylidene‐bis‐(4‐hydroxycoumarins), intermediates which undergo ring closure with the hydroxyl group of one of the 4‐hydroxycoumarin moieties, producing derivatives of 7‐[4′‐hydroxycoumarinyl‐(3′)]‐benzopyrano [ 3,2‐c] coumarins. 2,6‐Dimethylbenzaldehyde, pyridine‐2‐aldehyde and 6‐methylpyridine‐2‐aldehyde undergo a similar reaction.

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