Tellurium, reactions with alkynes

The coupling reaction with alkynes was extended to other tellurium-containing unsaturated systems. In this case also, the reaction conditions were similar to the ones described in Scheme 121, using different amounts of PdCl2 (Scheme 124).298 300... 

The reaction of alkynes with tellurium tetrachloride 16 was recently reinvestigated.68 Aryl alkynes (e.g., 24) react with 16 to give the (Z)-vinylic tellurium trichlorides (e.g., 25) (Equation (5)),47,68,69 whereas alkynes bearing a hydroxyl group at C3 26 give olefins of (ft)-stereochemistry 28 or 29 that reflect the steric demand at C3 (Scheme 7).68,72... 

Reaction of 116 with monosubstituted aryl alkynes 120 gives the (Z)-vinylic aryltellurium dichlorides 121, which are reduced to the (Z)-vinyl aryl tellurides 122 by reaction with sodium boro hydride.185 Alkynes bearing an OH at C3 react with aryltellurium trichlorides 116 to give cyclic products 124 or 125 depending on the steric demand on C3, in a similar way that was observed in the reaction with tellurium tetrachloride (Section 9.13.4.2.3). 

The vast majority of radical cascades initiated by addition of higher main group (VI)-centered radicals to alkynes focus predominantly on S-centered radicals, mainly thiyl radicals, whereas considerably fewer intermolecular addition reactions involving radicals with the unpaired electron located on selenium or even tellurium are known. 

---