Heterocycles of Hypervalent Sulfur and Selenium: New Syntheses and Structures

This article describes synthetic and structural studies of heterocycles based on hypervalent sulfur and selenium, in particular 1,6,6aλ4-triheterapentalenes, their monocyclic precursors and related compounds. What may be termed classical 1,6,6aλ4-triheterapentalenes conform to structure (1), in which Y = S, Se or Te and X and Z are O, S, Se or NR [1]. Many aza analogues of (1) are known in which one or more ring carbon atoms at positions 2, 3, 4 and 5 are replaced by nitrogen atoms. In the majority of known 1,6,6aλ4-triheterapentalenes, Y = S. Relatively few analogues are known in which Y = Se, and still fewer are known in which Y = Te. Analogues in which X and/or Ze is Te or PR have not hitherto been prepared.