Wittig Reaction polymer supported reagents

A similar purification method for the alkene product employs a polymer-supported reagent. Westman has developed a one-pot Wittig reaction of alkyl halides with aldehydes mediated by a polymer-supported phosphine and potassium carbonate under microwave irradiation (Scheme 32) [147]. Recently,... 

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. 

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... 

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). 

Other examples concerned the use of macroscopic systems such as Syn-phase lanterns. Lippens et compared the results they obtained using Wittig-Homer condensation on a macroscopic support with earlier results of the same reaction on a standard resin. As in all of the examples shown above, gel-phase HR-MAS NMR spectroscopy proved to characterize better the supported intermediates and final products and provide better understanding of the interactions between the polymer and the reagents. This is an important development in supported organic chemistry. 

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