Alkenes Cleavable by 3-Elimination

PhCHO(lOeq), K2C03, 18-crown-6, PhMe, 65 °C, 3 h R alkyl 

The palladium-catalyzed coupling of aryl iodides with vinylstannanes (Stille coupling) leads to the formation of styrenes. With resin-bound vinylstannanes, this reaction can be conducted in such a way that simultaneous detachment from the support of the newly formed styrenes occurs. This has been realized intramolecularly in the preparation of macrocyclic lactones (Entry 4, Table 3.43). The required resin-bound vinylstannanes were prepared either by hydrostannylation of alkynes with a resin- 

Alkyl sulfoxides undergo thermal (3-elimination to yield alkenes. This strategy for the preparation of alkenes has also been applied to solid-phase synthesis, but only substrates with a high tendency to undergo elimination (e.g., y-oxo sulfoxides) could be thermally released from the support (Entry 5, Table 3.43). Unactivated sulfoxides could not be cleaved, not even under forcing conditions (199°C [767]). 

Loaded resin Cleavage conditions Product, yield (purity) Ref. 

Support-bound sulfonylhydrazones can also be used as linkers for alkenes. Cleavage is effected by heating in the presence of an alcoholate, whereby diazoalkanes are initially formed these then undergo thermal fragmentation into the alkene and nitrogen (Entry 12, Table 3.43 Bamford-Stevens reaction). Polystyrene-bound alkynyl 

---