[Figure not available: see fulltext.] Castagnoli–Cushman reaction of imines derived from 2-chloropyridine-3-carboxaldehyde with a cyclic anhydride (4-(methylsulfonyl)-morpholine-2,6-dione) conducted at 110°C in DMF over 1 h, as expected, led to a mixture of trans- and cis-configured carboxylic acids. However, the latter underwent a spontaneous intramolecular reaction of the carboxylic functionality onto the labile nearby 2-chloropyridine moiety to give the respective tricyclic lactones in 17–23% yield, along with 41–68% yield of the uncyclized trans-configured products (isolated as methyl esters).
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- Organic Chemistry