Reductive detelluration of tellurolactones

The reductive removal of the tellurium moiety from aryldichlorotellurolactones is achieved by treatment with tributyltin hydride (TBTH) in refluxing toluene. High yields are conditional on a previous careful deoxygenation of the reaction mixture. 

If the dichlorotellurolactones are reduced previously to the parent tellurolactones by treatment with NaBH4, the successive detelluration saves 2 equiv of TBTH, and the 

Reductive detelluration of aryldichlorotellurolactones (general procedure) f To a solution of the dichloroteUurolactone (1 mmol) in deoxygenated toluene, (10 mL), under reflux and N2, is added dropwise BujSuH (4 mmol). The reaction is monitored by TLC. After 4 h the solvent is evaporated and the residue chromatographed on Si02 (eluted first with petroleum ether to remove Te and Sn by-products, and then with petroleum ether/EtOAc, 1 5), giving the tellurium-free lactone. 

By treatment of the dichloroteUurolactone with excess NaBH4, the fission of the Te-C bond takes place with recovery of the starting y 5-unsaturated carboxylic acid.  

The overall process (lactonization/NaBH4 reduction) therefore constitutes a formal protective method for y 5-unsaturated acids. 

---