Wittig Syntheses

Dnstabilised ylids usually give more ais product with aldehydes. Muscature (36) is a house-fly pheromone used to bait traps and the obvious Wittig synthesis gives 85% aio and 15% truMy. ... 

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

J.H. van Steenis, A.M.C.H. van den Nieuwendijk, A. van der Gen, ot-fluoroacryloni-triles Homer-Wittig synthesis and conversion into 2-fluoroallylamines and C-(1-fluor-ovinyl)nitrones, J. Fluor. Chem. 125 (2004) 107-117. 

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

In situ Wittig synthesis through an electrogenerated base has been carried out in a divided cell at a mercury pool cathode in an inert atmosphere the potential of the cathode is controlled at the peak value of the corresponding probase as given in Table 2. 

Scheme 9.1 Stereoisomeric oxaphosphetanes as NMR-detectable intermediates in the Wittig synthesis of alkenes.

In many cases, the second side chain of the cyclopentane ring of prostaglandins possesses a double bond with ( )-geometry at C-13. The introduction of this side chain is usually achieved by olefination with phosphonate anions according to the Homer technique. However, because of the vicinal oxygen function at C-15 it is also recommended to introduce the side chain via ( )-stereoselective Wittig synthesis... 

The figure shows a reaction scheme for the continuous Wittig synthesis. The solution of the C1S triphenylphosphonium salt (13) in methanol is continuously mixed, in a mixing reactor, a, with a methanolic solution of P-formylcrotyl acetate (8), and the mixture is cooled to —30 °C in a pre-cooler, b. A proton acceptor is... 

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. 

Solid-phase Wittig synthesis. Two groups3 4 have reported solid-phase Wittig synthesis. The resin is built up from styrene and the phosphine (1) with a small amount of 1,4-divinylbenzene for cross-linking. Alkylation and treatment with base gives a... 

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