Cyclophilic reactions of allene-1,3-dicarboxylic ester. Part 7. Synthesis of bicyclic and tricyclic heterocyclic compounds involving nitrogen, sulphur, and carbon as nucleophiles

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Abstract
Dimethyl allene-1,3-dicarboxylate (1) is an excellent substrate for heterocyclic syntheses giving products with ester side-chains capable of further elaboration. The allene (1) has been converted into the condensed pyridones (8)–(13) by reactions with 2-aminoazoles and azines and also into the pyridones (15) and (17) using benzamidine (14) and guanidine hydrochloride (16). Reactions with thiols lead to thiol-enol ethers (19), (20), (24), (25), and (29)–(32). The thiazopyrone (22) and thiazinone (27) were formed from 2-thiohydantoin (21) and 4-methyl thiosemicarbazide (26), respectively. The thiochromone (33) was obtained by cyclising the enol ethers (29)–(32). Thienopyridones (37) and (40) were formed from 2-aminothiophene-3-carboxylates (35) and (38) with the isolation of their respective enamine intermediates (36) and (39). The X-ray crystal structures of the pyridones (9) and (11) provide evidence for the mode of cyclisation. The 6-aminouracils (41) and (45) each react as an enamine in their mode of addition to (1) to give 7-oxopyrido[2,3-d]pyrimidines (44) and (46).
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