Trans-P -bromostyrene

Tin Derivatives. Indole, A-protected by the (trimethylsilyl)ethoxymethyl group, is alkenylated as a 2-stannane 27 with vinyl bromides (Scheme 14). The coupling also proceeds readily with complex heterocycles as exemplified with the structures 28 and 29. 3,4-Bis(tri-n-butyl)stannylfuran or the 3-monostannyl derivative is available by a Diels-Alder reaction between bis(tri- -butylstannyl)acetylene and 4-phenyloxazole. Either substrate, 30 or 31, undergoes alkenylation when reacted with tran -p-bromostyrene (Scheme 15).Pil... 

More recently, alternative cyanation sources have been used to effect this transformation. In their paper on the palladium-catalysed, microwave-assisted cyanation of aryl halides, Alterman and Hallberg (Entry 5) employed zinc cyanide, and included a single example of a vinylic substrate, namely trans-P-bromostyrene [26]. 

The reaction has also been applied to the conversion of vinyl bromides into acrylic acids, e.g. 1-bromo- and 1-chlorocyclooctene are converted into cyclooctene-1-carboxylic acid (ca. 98%) [3], 2-chloro-3,3-dimethylbut-l-ene yields 4,4-dimethylpent-2-enoic acid (95%), and tams-cinnamic acid is obtained (85%) from fran.v-p-bromostyrene. cis-p-Bromostyrene produces a mixture of cis- and trans-cinnamic acids in 38 and 42% yields, respectively [3]. In these reactions, benzyltri-ethylammonium chloride cannot be used as the phase-transfer catalyst, as it leads to the production of phenylacetic acid [3]. 

Vinylic tellnrides (generalprocedure) A solution of the ditelluride (2.0 mmol) and trans-)S-bromostyrene (0.73 g, 4.0 mmol) in THF/HMPA (10 mL) is added dropwise at room temperature and under N2 to AlLiH4 (0.17 g, 4.5 mmol) in THF (2 mL). The dark red colour of the ditelluride disappears at once. The resulting pale green solution is refluxed (R=n-Bu, 15 min R=p-MeOCgH4, 3 h). After cooling to room temperature the reaction mixture is... 

Though reduction of aromatic halides with NaBH4 does not proceed at all, photolytic treatment of the same aromatic halides and NaBH4 with a mercury lamp provides the reduction products via SET pathway. Eq. 9.3 shows the reduction of fra/is-P-bromostyrene (6) with LiAlD4 via SET pathway. The vinyl radical rapidly inverses on the sp2 carbon-centered atom, so a mixture of cis- and trans-styrenes (7a) and (7b) with dx/d0 = 63/37 is formed. <70-Styrene is again formed through the abstraction of a hydrogen atom from the solvent by the vinyl radical. Since the... 

---