Phthalimidesulfenyl Chloride. 9. A Simple Access to α,α'-Dioxothiones, a New Class of Bis-heterodienes. Synthesis of 1,4-Oxathiin Systems

Article abstract of DOI:10.1021/jo00125a030

α,α'-Dioxothiophthalimides 4a and 4b react with pyridine to generate the α,α'-dioxothiones 5a and 5b which undergo chemo- and regiospecific inverse electron demand Diels-Alder reactions with electron-rich alkenes to give 1,4-oxathiin heterocyclic syszems.Enol ethers, silyl enol ethers, vinyl sulfides, vinyl amides, substituted styrenes, and electron rich alkynes and allenes can be fruitfully employed as dienophiles.Among the vinyl ethers tested tri-O-benzylglucal was successfully used as a dienophile.Ab initio molecular orbital calculations performed on thiones 5a and 5b as well as on a selected enol ether are consistent with the experimental results.When thione 5a was generated in the presence of 2,3-dimethyl-2-butene (31) and -(β)-pinene (33) a selective ''thiophlic ene reaction'' was observed leading to the formation of sulfides 32 and 34.Thione 5b reacted similarly with 33 to generate the sulfide 35.Additionally a competition between the dienic versus dienophilic behavior of α,α'-dioxothiones 5a and 5b was observed in reactions with 2,3-dimethoxy-1,3-butadiene (45) and 2-methoxyfuran (50).A preliminary screening of the reactivity of 1,4-oxathiins 7c and 8b, used as model substrates, is also outlined.