Organocatalysis with azahelicenes: the first use of helically chiral pyridine-based catalysts in the asymmetric acyl transfer reaction

Abstract

The successful utilisation of a helicene-based organocatalyst in acylative kinetic resolution of racemic secondary alcohol was described. Employing rac-1-phenylethanol, optically pure (–)-(M)-2-aza[6]helicene (5–20 mole %), isobutyric anhydride and N-ethyldiisopropylamine in chloroform at 22–40 °C, an asymmetric acyl transfer reaction took place overwhelming the uncatalysed background process. Moderate reactivity as well as selectivity factor (s = 9, 10) were observed. An effective control of the enantiodiscriminating step in acylative kinetic resolution by the helically chiral organocatalyst was proven for the first time.