Sulfones 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... 

A similar Knoevenagel-type condensation takes place between methyl methyl-thiomethyl sulfone and aromatic aldehydes. In this reaction, use of K2C03 (2 mol equiv) as base and refluxing in isopropanol gave the best result178. 

Further projects dealt with the fabrication of heterogeneous, basic or acidic solid-state catalysts or adsorbents carrying, for instance, amino or sulfonic acid groups. Amino-functionalized silicas were prepared and analyzed for the catalytic activity in Knoevenagel condensation reactions of aldehydes or ketones with ethyl cyanoace-tate ions by Macquarrie et al.154 155 Recently, Zhang et al.156,157 reported on the successful preparation of amino-functionalized silica thin films by means of the EISA approach. 

A range of pentacyclic thiopyran indole-annulated benzo-6-sultone deriratives are obtained through a domino Knoevenagel-hDA reaction of 2-formylphenyl (B)-2-phenylethenyl sulfonates with indohne-2-thiones in water (Scheme 99) (13TL2685). 

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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