Sulfones synthesis, Knoevenagel reaction

J,V-Unsaturated carboxylic acids and their derivatives are valuable synthetic intermediates for various natural products. Two typical multi-step processes for the synthesis of p.y-unsaturated acids, Knoevenagel reaction/isomerization with base and allylic cyanide/hydrolysis,3 are those most commonly used. Other new methods have been developed 4-7 however, there is a problem with E/Z stereoselectivity. One straightforward way to obtain p,y-unsaturated acids is by the carboxylation of an allyl metal Intermediate. In the substituted allylic series, the reaction usually occurs at the more sterically hindered terminus. A stereospecific route for the synthesis of homogeranlo acid and homoneric acid by carboxylation of the lithiated allylic sulfone... 

In 2006, Lam and Gao reported a regioselective procedure for the synthesis of 1,2,3-triazoles via a [3 -b 2] cycloaddition of resin-bound vinyl sulfone and sodium azide in the presence of an alkyl halide. The resin-bound vinyl sulfone 71 was effectively generated by the Knoevenagel condensation of resin 44 (Scheme 12.18). Resin 71 then acted as the vinyl sulfone dipolarophile and the electronegative sulfone that was eliminated in the reaction directed the regiochemistry of the cycloaddition. 

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