A new synthetic procedure to methylethers has been developed by the reaction of alcohols with dimethylcarbonate, a non-toxic and environmentally friendly reagent. The methylation of alcohols is catalysed by alumina or hydrotalcite. The methylcarbonate formed in the first step undergoes decarboxylation in the second step, to give the corresponding methylether. The reactivity follows the order: primary > secondary ≫ tertiary alcohols. The reaction can be efficiently performed under both batch and continuous flow conditions
A convenient method for the preparation of aldehydes from the corresponding carboxylic acids is presented. By reaction of the carboxylic acids with o‐mercaptophenol and perchloric acid in phosphorus oxychloride, the corresponding 2‐substituted 1,3‐benzoxathiolium perehlorates were obtained. Reduction of the salts with lithium aluminium hydride in dry ether gave 2‐substituted 1,3‐benzoxathioles, which, when hydrolyzed by mercuric chloride, gave the corresponding aldehydes. Twenty five aldehydes of different structure were obtained in good yields, by a fast and simple procedure.
The reactions of 2‐phenyl‐1,3‐benzoxathiolium perchlorate with common nucleophilic reagents (water, sodium hydroxide, ethanol, thiophenol, morpholine, phenylmagnesium bromide), with reducing agents (zinc, lithium aluminium hydride) and with manganese dioxide, were studied. In every case the reactions proceed by attack of the reagents at the C‐2 position of the cationic system, giving rise either to 1,3‐benzoxathiole derivatives or to ring‐opening products. The 1,3‐benzoxathiolium salts were shown to be suitable intermediates for converting the carboxylic acids into aldehydes and ketones.
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