Wittig reaction synthetic utility

The main interest in unsaturated sugars prepared by the Wittig reaction (and described in this Section) has concerned their synthetic utilization. The pathways of the latter depend on the structure of the unsaturated precursor. In the case of C-glycosylated alkenes, addition to the double bond (mainly hydration and hydrogenation) leads to a branched-chain or long-chain sugar, although correct choice of the reactant to be added may provide a variety of derivatives. 

With the objective of synthetic utilization of a,/3-unsaturated dialdoses, the Wittig reaction with certain compounds of this series... 

It is also worthwhile to add that the versatility of the Wittig reaction suggested entirely new opportunities for the synthetic utilization of carbonyl compounds. Thus, the employment of methoxymethylenephosphorane 83 (easily prepared from chloromethyl ether) as the ylide component represents a standard protocol for the transformation of aldehydes or ketones into homologous aldehydes 84, via the intermediate formation of enol ether 84a. 

Several synthetic methods (some general, others quite specific) have been reported for the synthesis of stilbenes and bibenzyls. Most syntheses utilize the Wittig reaction between a properly substituted benzaldehyde and a benzyl triphenyl phosphonium halide, as represented in the Scheme 1 [1, 8 ]. Several variations of this approach have been reported and concern the protecting group chosen for hydroxyls, the type of organolithium used, the solvent (organic or aqueous). 

Wittig reactions play an important role in expanding the synthetic utility of lactaldehydes. Aldehyde 689 can be converted to the useful intermediate a,j5-unsaturated ester 775a by reaction with Ph3P=CHCOOCH3 (51% yield) [220]. A 7.3 1 mixture of E and Z isomers is formed under these conditions, which can be separated by chromatography. 

Another class of activated alcohols employed in the tandem Mn02 reaction are a-hydroxyketones. The synthetic utility of the intermediate a-ketoaldehydes had previously been limited by the hyperreactivity of the aldehyde group. However, by employing the TOP Mn02 protocol, good to excellent yields of the resulting Wittig products may be obtained (eqs 78 and 19) ... 

The synthetic utility of the Wittig reaction in the preparation of c/s-olefins is further illustrated in the reactions between ( )-ethyl 4-oxobutenoate and alkyl phosphorylides (generated from the parent phosphonium salt using sodamide)... 

The synthetic utility of the Wittig reaction can be expanded beyond its ability to form double bonds by the use of certain functionalized ylides. Thus, methoxy-... 

Meyers and co-workers have continued their studies to exploit the synthetic potential of a-lithio-formamidines and have now described an efficient synthesis of 2-aryl- or 2-heteroaryl-pyrrolidines and -piperidines (266 ). " Alkylation of formamidines (264) gives intermediates (265) which cyclize in situ after cleavage of the amidine unit. The aza-Wittig reaction has been utilized in a general synthesis of heterocyclic vinylogous ure-thanes and amides (268). Staudinger reaction of azides (267)... 

Georg Wittig, a German chemist, was awarded the 1979 Nobel Prize in Chemistry for his work with phosphorous compounds and his discovery of a reaction with enormous synthetic utility. Below is an example of this reaction, called the Wittig reaction (pronounced Vittig) ... 

Another useful synthetic method for the synthesis of complex heterocyclic compounds is the aza-Wittig reaction, involving carbodiimides as intermediates . Carbodiimides have also found utility as agricultural chemicals and pharmaceutical intermediates. For example, Ai-arenesulfonyl-Ai -alkylcarbodiimides are precursors of the antidiabetic sulfonyl ureas Sulfonylureas are also very potent herbicides. 

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