Wittig reaction polymer supported

Polymer-supported Wittig reagents have recently been developed as an extension to the traditional reagents.29 For example, polystyryldiphenylphosphine has been developed in an attempt to replace the use of triphenylphosphine in the preparation of phosphoranes (see Protocol 1). The hope is that these polymer-bound regents will overcome the practical problem of removing the triphenylphosphine oxide by-product formed in Wittig reactions. Polymer supported phosphonates and Wittig substrates have also been prepared for use in solid phase synthesis and combinatorial chemistry.30... 

Scheme 4 Microwave-assisted Wittig reactions using polymer-supported triphenylphosphine in methanol...

The Wittig reaction has been carried out with polymer-supported ylids (see p. 509). It has also been done on silica gel. " ... 

Very recently a novel one-pot three-step Wittig reaction using microwave irradiation and polymer-supported triphenylphosphine has been reported [57]. By use of... 

Scheme 2.2 Polymer-supported triphenylphosphine equivalents for use in Wittig reactions.

Ford, W. T., Wittig Reactions on Polymer Supports, Chap. 8 in Polymeric Reagents and Catalysts, W. T. Ford, ed., Am. Chem. Soc. Symp. Ser., Vol. 308, American Chemical Society, Washington, DC, 1986b. 

Table 2. Comparison of yields in Wittig-reaction on polymer supports...

One of the main drawbacks of the Wittig reaction is the formation of unwanted triphenylphosphine oxide. A new route, which makes use of polymer-supported triphenylphosphine and microwave dielectric heating has been developed (Scheme 13), which yields the required alkene without the triphenylphosphine oxide. An alternative strategy for separation of the product alkene from unwanted phosphine oxide by-product is to carry out the Wittig reaction in a fluorous solvent using a perfluorinated ylide such as (45). One drawback of this... 

The use of the Wittig reaction and its modifications for the synthesis of vinylchalcogenides, ketene chalcogenoacetals and related species has been reviewed. New developments on this topic include the synthesis of a series of polymer-supported alkyltriphenylphosphoranes (46) which have been utilised in the preparation of vinylic selenides. The synthesis of vinylic selenides, such as 1-chloro-l-phenylselenoalkenes, has also been accomplished in a one-pot reaction which proceeds through the formation of selenoylphosphorane (47) intermediates. ... 

Polymer-supported Wittig reagents were first prepared more than 20 years ago [32]. It has been shown that the success of the reaction depends strongly upon (i) the preparation of the reagent by bromination and phosphination of cross-linked polystyrene rather than by co-polymerization using styryldi-phenyl phosphine, and (ii) the generation of the phosphorane with a base/ solvent system that swells the phosphonium sites in the polymer network (Scheme 6) [33]. Thus, bromination of polystyrene 1 yielded phenyl bromide 32, and this was followed by phosphination with n-butyUithium and chlor-odiphenylphosphine or with Hthium diphenylphosphide to give 33, a compound which is commercially available (Scheme 6). 

Numerous compounds have been prepared from polymer-supported phos-phoranimines. These are versatile starting materials for solid-phase methods based on the aza-Wittig reaction. " ... 

Aldehyde is immobilized in a Wittig or Wit-tig-Horner reaction (phosphorane or dicthyl-phosphonoacetamide on the polymer support) giving the unsaturated bond. 

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