A Wittig synthesis

Figure 4.87 Flow configuration for a Wittig synthesis in a chip micro reactor with three vertical injections [13].

Phenyl-5-vinyl oxadiazole has been prepared from 3 Phenyl-5-chloromethyl-oxadiazole through a Wittig synthesis 18 a). 

Planning a Wittig Synthesis The Wittig reaction is a valuable synthetic tool that converts a carbonyl group to a carbon-carbon double bond. A wide variety of alkenes may be synthesized by the Wittig reaction. To determine the necessary reagents, mentally divide the target molecule at the double bond and decide which of the two components should come from the carbonyl compound and which should come from the ylide. 

Plan a Wittig synthesis so that the less hindered end of the double bond comes from the ylide. Remember that the ylide is made by Sn2 attack of triphenylphosphine on an unhindered alkyl halide, followed by deprotonation. 

An electrolytically generated base, hydrazobenzene from azobenzene, has been used for a Wittig synthesis. This method permits the maintenance of any desired base concentration by controlling the current Certain ketones can be conveniently obtained through a Horner synthesis of thioenolethers... 

Diene synthesis, intramolecular (s.a. Wittig synthesis-diene synthesis, intramolecular)... 

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

Ramage and co-workers have given full details of their Wittig approach to 2-ulosonic acids (see Vol. 22, p.l61) and have extended this route to the synthesis of 3-deoxy-D-eryt/iro-2-hexulosonic acid (KDG, 30), albeit in low yield in this case.33 A French group have developed two routes to KDG (30) (Scheme 5) involving, respectively, a Wittig synthesis of (28) 4 or P elimination from a gluconolactone derivative to yield (29) 35 the second approach could be modified to make 5- and 6-(2-methyl ethers of (30). 

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