Chalcogenopyranones from disodium chalcogenide additions to 1,4-pentadiyn-3-ones. The role of enol ethers as intermediates

Enol ethers 9 are formed as a mixture of E- and Z-isomers from the addition of ethanol to 1,4-pentadiyn-3-ones 2 in sodium ethoxide/ethanol. The enol ethers react with disodium chalcogenides to give the corresponding 2,6-disu bstituted chalcogenopyranones 1 bearing alkyl, aryl, or heteroaryl substitu ents in high yield as the only heterocyclic product of reaction. Diynones 2 react with disodium chalcogenides to give mixtures of products in which th e chalcogenopyranones 1 are minor components and the dihydrochalcogenophene s 3 are the major products. The addition of hydrogen sulfide to diynone 2b in ethanol gives a product mixture nearly identical to that observed for th e addition of disodium sulfide in sodium ethoxide in ethanol to 2b. Interme diates for the addition of hydrogen chalcogenides and disodium chalcogenide s to both 2 and 9 are described, which lead to the heterocyclic products.