Novel applications of the methyltrioxorhenium/hydrogen peroxide catalytic system

Abstract

<p>New applications of the MTO/hydrogen peroxide catalytic system have been uncovered;Pyridine exhibits dramatic effect on the outcome of oxidation of silyl enol ethers. While without pyridine present the mentioned starting materials are hydrolyzed, for all practical purposes instantaneously, to the parent ketones, in its presence their hydrolysis is almost entirely suppressed. The rapid procedure described in this thesis also requires the presence of acetic acid to buffer the reaction system and enable the reaction to be performed with an economical catalyst level. The method described in this thesis appear to be the best thus far available in the literature for the oxidation of silyl enol ethers with aqueous hydrogen peroxide;Ketene acetals, owing to the presence of an additional alkoxy functionality require a more careful approach. Aqueous hydrogen peroxide has to be replaced with urea hydrogen peroxide addition compound. In addition the reaction has to be performed at low temperature with gradual introduction of the water labile substrate to the reaction mixture, all in order to minimize its exposure to the detrimental reaction medium and to reduce the extent of catalyst decomposition. The described method is the first successful one for the oxidation of this class of compounds with hydrogen peroxide;The MTO/hydrogen peroxide catalytic system performs well for the oxidative conversion of N, N-dimethyl hydrazones derived from aldehydes to the corresponding nitriles. The short reaction times, comparatively mild conditions, demonstrated broad functional group tolerance and nearly quantitative yields render it competitive with the methods presently available in the literature for achieving the given transformation;N, N-dimethyl hydrazones derived from ketones are oxidatively cleaved to the parent ketones under comparatively mild conditions with the mentioned catalytic system. Even though it has been established that the reaction is electrophilic in nature, presently is very little known about its exact mechanism. In spite of this uncertainty, from the synthetic point of view this method represents a step forward of the given catalytic system into the world of synthetic chemistry.</p>