Chemoselective reactions of dimethyl carbonate catalysed by alkali metal exchanged faujasites: the case of indolyl carboxylic acids and indolyl substituted alkyl carboxylic acids

摘要

At 160–180 uC, in the presence of alkali metal exchanged faujasites (MX or MY; M = Li, Na, K),\udthe reaction of dimethyl carbonate with indolyl-3-acetic, -3-propionic, and -3-butyric acids\udproceeds towards the formation of the corresponding methyl esters or carbamate esters which can\udbe isolated in 93–99% yields. The methylation of the indolyl-NH group is never observed. This\udhigh chemoselectivity is driven by the nature of the catalyst and the reaction temperature. In\udparticular, among the six different zeolites used, the more basic MX faujasites show better\udperformances in terms of both activity and selectivity than MY solids. A similar trend also holds\udfor the reaction of dimethyl carbonate with indolyl-carboxylic acids, where MX compounds are\udstill efficient catalysts for the formation of methyl esters. In this case, however, the overall\udreactivity/selectivity also reflects the relative positions of the NH and CO2H groups which may\udaccount for significant decarboxylation reactions observed for indolyl acids substituted at\udpositions 2 and 3. This process is totally absent for indolyl-6-carboxylic acid.