Superelectrophiles And Their Chemistry PDF Download

This thesis details the research conducted on the synthesis and reactivity of superelectrophilic di- and polycation salts based on 2-DMAP I. The reaction of 2-DMAP I and 1,3-diiodopropane II proceeded unexpectedly to give products III-V, thought to occur via a dicationic intermediate. Investigation of the reaction conditions allowed for the successful synthesis of 2-DMAP disalt VII from 2- DMAP I and ditriflate VI. This represents the first time such a dication species has been synthesised and isolated. Based on the 2-DMAP unit, a variety of superelectrophile disalts have been synthesised (VIII-X) and characterised. 2-DMAP disalt VII showed enhanced reactivity over its monocationic counterparts XI and XII in the methylation of triphenylphosphine. In the 1:1 competition reaction with dimethyl sulfate in the methylation of triethylamine, 2-DMAP disalt VII and 2- dimethylaminopyrimidine disalt VIII showed greater reactivity than dimethyl sulfate, with disalt VIII being over 2.5 times more reactive. The reactivity of 2-DMAP disalt VII towards hydrogenation was also examined. It was found that in the presence of palladium on activated carbon (1 mol%), disalt VII underwent regiospecific hydrogenation (or deuteration) in the 2-position to give pyridinium disalt XIII (or XIV in the case of deuteration). In this case, 2-DMAP disalt VII showed similar reactivity to the substrate CH≡H4MPT+ in the [Fe]-hydrogenase enzyme. This significantly enhanced reactivity over monocationic salts provides support for the proposal that superelectrophilic activation of CH≡H4MPT+ in the enzyme active-site may contribute to the observed reaction of CH≡H4MPT+ with hydrogen gas. Superelectrophile trisalt XV was also synthesised. This trisalt showed slightly decreased reactivity compared to dimethyl sulfate in the methylation of triethylamine. The high reactivity of the tricationic species was tempered by the dimethylamino group in the 4-position, which served to decrease the reactivity by delocalising the positive charge on the pyridinium ring nitrogen. Amidine disalts XVI and XVII based on amides have also been synthesised. Isolation of these superelectrophiles provides some evidence that such species may exist as intermediates in a variety of synthetic reactions cited in this work. Disalt XVI was shown to be an effective reagent for the formylation of anisole under mild conditions. The synthesis and isolation of these superelectrophile disalts based on the 2-DMAP unit shows that highly reactive superelectrophiles can be obtained using standard laboratory conditions, which considerably widens the scope for synthesis and investigation of such species.