Wittig reaction Unsaturated carboxylic acid synthesis

New applications of the Wittig reaction continue to be reported. Some recent examples are the synthesis of, / -unsaturated carboxylic acids by Wadsworth and Emmons,1019 of <%,/ -unsaturated ketones by Normant and Sturtz,1020 and of acrylonitrile derivatives in the steroid field by Drefahl, Ponsold and Schick.1021 It has, however, transpired that in some cases PO-activated ole-fination is to be preferred to the Wittig reaction.1012... 

Ammonia lyases catalyze the enantioselective addition of ammonia to an activated double bond. A one-pot, three-step protocol was developed for the enantioselective synthesis of L-arylalanines 50 using phenylalanine ammonia lyase (PAL) in the key step (Scheme 2.20). After formation of the unsaturated esters 48 in situ via a Wittig reaction from the corresponding aldehydes, addition of porcine Ever esterase and basification of the reaction mixture resulted in hydrolysis to the carboxylic acids 49. Once this reaction had gone to completion, introduction of PAL and further addition of ammonia generated the amino acids 50 in good yield and excellent optical purity [22]. 

In the area of longer-chain systems, the dideoxy-heptonolactone 4 has been made using a Wittig reaction on unprotected D-arabinose, and a dr-selective Wittig reaction was also used to prepare the unsaturated lactone 5, potentially useful for the synthesis of sialic acids and analogues, from 2,4 5,6-di-0-isopropylidene-a/deAydo-D-glucose.l3 2,4-O-Benzylidene-L-xylose was converted, by Wittig reaction and one-carbon chain extension at C-5, into the carboxylate 6, which was... 

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