Wittig reaction General considerations

Wittig reaction (see also Methylenation) General considerations, 14 Reactions to form Z olefins (3-Dimethylaminopropyl)triphenyl-phosphorane, 119 Sodium amide, 278 Other reactions... 

The basicity of the medium is considerably less when resonance-stabilized phosphoranes are employed, resulting generally in a normal course for the Wittig reaction. A direct correlation between the basicity of certain phosphoranes and their reactivity towards 2,4 3,5-di-0-benzylidene-aZde/n/do-D-ribose and 2,3,4,5,6-penta-O-acetyl-aldehydo-D-g ucose was not found,21 thus indicating a steric influence prevalent in the sugar components, in comparison with electronic factors in phosphoranes. 

Generally the Wittig reaction yields a mixture of cis and trans geometrical isomers of an alkene. The stereochemical considerations are discussed elsewhere. 

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