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No abstract

The esters (I) react with the allene (II) in the presence of a base to afford the title quinolones (III).

198 ChemInform Abstract Reaction of the enamino ketones (I) with the allene dicarboxylate (II) gives rise to the thiopyran derivatives (III). The analogues (V) can be likewise prepared by this method (yield 65/62%); however, their preparation from the aldehydes (IV) and the allene (II) is preferred (no yield given).

The title reagent is easily prepared on a large scale from pyrazine and CrO3 in 6 M HCl.