Pd II -catalysed homocoupling of vinyl tellurides

Vinyl tellurides bearing a stiryl moiety give the corresponding 1,3-dienes homocoupling products with moderate to good yields, by treatment with a catalytic amount of Pd(OAc)2 in the presence of AgOAc as reoxidant.  

The characteristic feature of this catalytic reaction is the preferential formation of a (Z,Z)-diene, the Z stereochemistry of the starting telluride being largely retained. 

The formation of the stylbenes, only in low yield, clearly shows that the fission of a vinyl tellurium bond is favourable towards the Ph-Te bond. 

Each of the above tellurides reacts smoothly to give the corresponding dienes where the selectivity to Z,Z and E,E isomers in the product is high from Z and E isomers. 

Cross-over experiments suggest that the homocoupling reaction occurs between an alkenyl telluride and an alkenyl Pd species, which is formed via the migration of an alkenyl moiety from Te to Pd. 

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