Addition reactions arylsulfonates

The reaction of cotton cellulose with phenyl isocyanate, to give a cellulose phenylurethan, has been investigated further. The extent of the reaction depends on the ability of the solvent to swell the cellulose, methyl sulfoxide being the best medium, followed by i r,f T-dimethylformamide and P3Tidine. The reaction is catalyzed by the addition of di-w-butyltin diacetate, but toluene 2,4-diisocyanate and 1,2,4,5-tetramethylbenzene diisocyanate do not show high reactivity. A survey of the relative behavior of chitin and cellulose toward esterification under comparable conditions, mainly to give arylsulfonate esters, concluded that, of the two, chitin is the less reactive. 

One of the challenges in Suzuki-type cross-coupling is to extend this reaction from electron-rich aryl iodides, bromides, and triflates to less reactive aryl sulfonates and aryl chlorides, which show poor reactivity toward oxidative addition in the catalytic cycle. Aryl mesylates, benzenesulfonates, and tosylates are much less expensive than triflates and are unreactive toward palladinm catalysts. The Ni(0)-catalyzed Suznki-type ctoss-coupling reaction of arylsulfonates including mesylates with arylboronic acids in the presence of K3PO4 was reported. 

Aryl sulfonates are the least reactive SM substrates since the C-O bond is less polarized and thus oxidative addition to palladium(0) or nickel(O) proceeds much slower. Furthermore, the steric demands of all common arylsulfonate groups are considerably higher than in any halide analogue. However, the SM reactions have been... 

One of the challenges is to extend the reaction from triflates to less reactive arylsulfonates. The palladium-catalyzed reaction of aryl mesylates results in low yields because of their slow oxidative addition to a palladium(O) complex, but they readily participate in the nickel-catalyzed cross-coupling reaction at 80°-100 °C. A nickel(O) species incorporating dppf ligand, obtained by in situ reduction of 10 mol% of NiCljCdppf) with zinc dust, is recognized as the most effective catalyst (Eq. 43). However, again the reaction needs to be optimized because a... 

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