HETEROCYCLIC NONIONIC X-RAY CONTRAST AGENTS .4. THE SYNTHESIS OF DIHYDRO-2(3H)-FURANYLIDENAMINO, 5-OXO-1-PYRROLIDINYL, AND 5-OXO-4-MORPHOLINYL DERIVATIVES BY AN INTRAMOLECULAR IODOCYCLIZATION APPROACH

Intramolecular iodocyclization of omega-alkenylanilides 6 and [omega-(alkenyloxy)alkyl]anilides 7 resulted in the formation of dihydro-2(3H)-furanylidenamines 8 and 1,4-dioxan-2-ylideneamines 9, respectively, by an amide-oxygen participative nucleophilic attack on the expected iodonium intermediate. The latter heterocyclic ring system is new. If a strong base is present, the mode of ring closure was mainly diverted to an amide-nitrogen participative nucleophilic attack, leading to (iodomethyl)-pyrrolidinones 10 and (iodomethyl)morpholinones 11, from 6 and 7, respectively. Unique interconvertible syn-anti isomerism in the imino-ether 8a was demonstrated by variable temperature NMR studies. The major component in this mixture was the 8a anti-isomer. Acetolysis of the iodocyclized products, followed by deacetylation, provided the heterocyclically substituted polyhydroxytriiodoisophthalamides 16-18. Hydrolytic studies on the imidate 16d revealed an interesting pH dependence. As expected the amine 3d and the amide 22 resulted in pH values of 2 and 6. At pH 12, however, the Chapman rearrangement product 17d was the major product. The compounds obtained in this investigation are of interest as X-ray contrast agents.