The stereospecific arylation of olefins

Triphenylvinyl bromide (I) and diphenylvinyl iodide (XII) can be made to undergo replacement of the halogen atom by a phenyl group; n-BuLi (2·5 moles) is added to a mixture of the vinyl halide and o-bromofluorobenzene in ether at −78° followed by warming to −35°. The intermediate o-lithium derivative in the reaction of I could be converted to o-methyltetraphenylethylene (VI) by treatment with methyl iodide or to o-bromotetraphenylethylene (V) with ethylene dibromide. The p-chloro derivatives of I (cis- and trans-IX) undergo the same reaction followed by treatment with ethylene dibromide to give 1-(o-bromophenyl)-2,2-diphenylethylene (X), a different stereoisomer predominating in each case. o-Bromotetraphenylethylene (V) was readily converted back to the lithium reagent with n-BuLi in tetrahydrofuran. Carbonation gave the expected carboxylic acid. With dimethyl carbonate, however, there was formed none of the expected carbonyl addition product but instead up to 25% of 9,10-diphenylphenanthrene (VIII). A study was made of the effect of solvent on the relative amounts of lithium-halogen and lithium-hydrogen exchange in the reaction of n-BuLi with 2,2-diphenylvinyl bromide (XI). It has been found that triphenylvinyl bromide with two models of n-BuLi in ether at room temperature for 24 hr followed by treatment with ethylene dibromide gives as the only dibromide detected 2-(o-bromophenyl)-1,2-diphenylvinyl bromide (XVII). Possible significance of this seemingly selective ortho-metalation reaction is discussed.