Franr-Stilbene

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). ... 

Periodic acid is a versatile oxidant since, depending on pH, the redox potential for the periodate-iodate couple varies from 0.7 V in aqueous basic media to 1.6 V in aqueous acidic media.Based on this observation, Villemin and Ricard devised an oxidative cleavage of glycols, in which me50-l,2-diphenyl-1,2-ethanediol was oxidized by periodic acid on alumina to benzaldehyde in 82% yield in aqueous ethanol (90% ethanol) at room temperature in 26 h. The same supported oxidant converted aromatics into quinones. In the presence of transition metal complexes (Mn"), a-arylalkenes suffer oxidative cleavage to aldehydes. For example, franr-stilbene gives benzaldehyde at room temperature. 

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