Effect of Microwave Irradiation on the Catalytic Activity of Palladium Supported Catalysts in the One-Step Isomerisation of Cinchona Alkaloids to Δ3,10-Isobases

Efficiency of palladium solid supported (Pd/SS) catalysts for one-step isomerisation of the side chain of four natural Cinchona alkaloids have been explored under controlled microwave heating in the green media (50% aqueous ethanol or ethylene glycol with HCl). Conversion progress and products purity was monitored by TLC and by 1H NMR spectrometry. Final conversion is dependent on the support (Al2O3, C or BaSO4), reaction time and temperature. Very good results: high yields and purity of (Z/E) Δ3,10-isomers were obtained from quinine and quinidine with 10% Pd/BaSO4 as the catalyst, which is less effective for isomerisation of cinchonine and cinchonidine. Enhancing energy efficiency can be possible when the responsive support selective absorbs of microwave energy, which is translated to the palladium giving acceleration of the formation and disintegration of the transition state leading to Δ3,10-isomers.