Stilbenes nitro addition reactions

Wittig reactions of phosphonium fluorides in dipolar non-HBD solvents can be carried out without an additional base e.g. 4-nitrobenzaldehyde reacts slowly with (4-nitrobenzyl)triphenylphosphonium fluoride in refluxing acetonitrile to give 4,4 -nitro-stilbene in good yield (84 cmol/mol) [642], In this reaction, the fluoride ion attacks its own cation to give the corresponding Wittig ylide as intermediate. 

The reaction is akin to the Ritter reaction, with activation achieved by nitration, rather than proton-ation, and the products accordingly retain the nitro group. Additions to 1-phenylcyclohexene (59%) and to franr-stilbene (72%) are stereospecific (trans) cfr-stilbene gives the expected tfireo product (39%) plus some erythro (6%). Reactions of nitrogen dioxide with alkenes are very complex and rarely use-ful. A recent mechanistic paper gives many key references. " Addition of NjOs is occasionally usefiil, as with dicyclopentadiene (Scheme 49). ... 

---