Transannular Te-S interaction in a new tellurium heterocycle, 5H,7H-dibenzo[b,g][1,5]tellurathiocin

A new heterocycle containing tellurium and sulfur atoms, 5H,7H-dibenzo[b,g][1,5]-tellurathiocin (1), has been synthesized. The chair and the boat forms of 1 can be characterized by ¹H, ¹³C, and ¹²⁵Te NMR spectroscopy. A transannular bond between the tellurium and sulfur atoms was found in the reaction product of 1 with concentrated H₂SO₄ by ¹H, ¹³C, and ¹²⁵Te NMR spectroscopy. Two-electron oxidation of 1 with 2 equiv of NOPF₆ gave the tellurathia dication salt (3) (Te⁺-S⁺, 2PF₆^-), which acts as an oxidizing agent. The reaction of 12-oxo-5H,7H-dibenzo[b, g][1,5]tellurathiocin (8) with acetic anhydride afforded a 12,12-diacetoxy-substituted tellurane (16). Heating of a benzene solution of 16 gave a remote α-acetoxylated sulfide 18 and the parent 5H,7H-dibenzo[b, g][1,5]tellurathiocin (1). Reaction of tellurathiocin 1 with t-BuOCl gave exclusively its telluroxide 8. Tellurathiocin 1 was reacted with Br₂ to give a 12,12-dibromo-substituted tellurane (25). Reaction of the tellurane 25 with aqueous NaOH gave the telluroxide 8 selectively, and variable-temperature ¹H NMR studies revealed that the telluroxide 8 was fixed in boat form. The ¹²⁵Te and ⁷⁷Se NMR spectra of 12-oxo-5H,7H-dibenzo[b,g][1,5]telluraselenocin (28) show a strong transannular interaction between the tellurium and selenium atoms.