Alkenyltin compounds coupling reactions

In organic synthetic procedures, alkenyltin compounds are often prepared with a view to subsequent transmetalla-tion with lithium, or to the Stille coupling reaction with a palladium catalyst (Equations (70) and (71)). 

In addition to alkenylboron compounds, alkenylalane, alkenylzirconium, alkenyltin, alkenyl copper, and alkenylmagneslura reagents are reported to undergo a related alkenyl-alkenyl coupling reaction to give l,3-a1kad1enes. 

Some trans-a,, along with cw-a,/3-substituted alkenyltin compounds have been prepared and used in intramolecular coupling reactions to synthesize cyclic compounds,as shown in Scheme 69. The reaction could be mediated by stoichiometric CuCl instead of catalytic Pd complexes,while the use of Cu(I) as a cocatalyst in Stille coupling has been demonstrated. 

The reaction of certain palladium-heteroatom complexes to alkenes and alkynes is a versatile tool for the synthesis of alkanes and alkene having heteroatoms attached. In particular, the various B-B, B-Si, and B-Sn compounds can be used for palladium-catalyzed borylation of alkenes and alkynes (Scheme 5-2). Borostannylation takes place at ambient temperature, whereas silylboration " only proceeds at a temperature above 80 °C due to the slow oxidative addition of a B-Si bond to a palladium(O) catalyst. Both reactions selectively provide cz j-products via addition of silicone or tin to the internal carbon and boron. The reactions are compatible with various functional groups for both terminal and internal alkynes. Cross-coupling reaction of boranes with organic halides selectively occurs at the terminal C-B bonds to provide regiodefined and stereodefined alkenylboron, alkenylsilicon, and alkenyltin compounds. 

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