Polymer-bound alkenylstannane

Stannaries have become prominent in multifunctional anchoring groups. A polymer-bound tin hydride 41 has been used to hydrostannylate alkynes under the action of palladium-catalysis to give polymer-bound alkenylstannanes 42. These alkenyl stannanes have been employed in intermolecular [45] and intramolecular Stille reactions [46]. Alkenylstannanes can also undergo protonation to give alkenes 44 in a traceless fashion. This linker is therefore multifunctional (Scheme 6.1.12). 

Aryl-alkenyl and aryl-aryl cydizations via Stille coupling are far less developed. In the case of alkenyl-aryl couplings, the olefmic moiety can be extracyclic or intracyclic with Z or E stereochemistry. An example is the cyclization of polymer-bound alkenylstannane with aryl iodide moiety in the total synthesis of (S)-zeara-lenone [127] (Scheme 6.16). 

Tin hydride reagents are versatile tools for the functionalization of alkenes and alkynes. Based on this concept, Nicolaou and coworkers developed a polymer-bound tin hydride (118) that reacts via Pd-catalyzed hydrostannylation (or nucleophilic attack on the tin chloride with a vinyl lithium) with alkynes to give alkenylstannanes [116]. After further transformation to derivatives 119, the resin-bound substrates undergo proteolytic traceless cleavage to yield unsubstituted alkenes 120. Alternatively, the stannane can be employed for intramolecular Shlle coupling to produce macrolactones 121 in the cleavage step (Scheme 16.28). 

C.ii.b. Stille Couplings. A polymer-bound tin hydride has been used to hydrostannylate alkynes under palladium catalysis hydrostaimylation to give polymer-bound alkenyl-stannanes.t Alternatively, the latter could be prepared from a polymer-bound tin chloride and an alkenyllithium or -magnesium halide reagent. These alkenylstannanes were employed in intermolecular as well intramolecular Stille reactions. The inter-molecular reactions provided the coupling products in good yields. In addition, the... 

---