REACTIONS OF DIPHENYL(PHENYLETHYNYL)SELENONIUM SALTS WITH ACTIVE METHYLENE-COMPOUNDS AND AMIDES - FIRST ISOLATION OF OXYSELENURANES [10-SE-4(C3O)] AS A REACTION INTERMEDIATE

The reaction of the diphenyl(phenylethynyl)selenonium triflate 1a with active methylene compounds 5 and t-BuOK in THF gave furan derivatives 6. The [10-Se-4(C3O)] selenuranes 8a and 8b could be isolated from th e reactions with benzoylacetonitrile 5f and with 1,3-indandione 5g, re spectively, as reaction intermediates. The structures of the selenuran es 8 were elucidated by X-ray crystallography and Se-77 high-resolutio n solid-state NMR spectroscopy. The selenuranes 8 underwent ligand cou pling on standing at room temperature or refluxing in chloroform and g ave the furan derivatives 6 and the ring-opened product 9. Similarly, the reaction of 1a with benzamide 13a and pivalamide 13d in the presen ce of NaH in THF afforded oxazole derivatives 14.