Deracemization of Quinolonecarboxamides by Dynamic Crystalline Salt Formation and Asymmetric Photoreaction by Using the Frozen Chirality
Published:9 September 2014
DOI: 10.1002/ejoc.201403056
Fumitoshi Yagishita, Naoya Takagishi, Hiroki Ishikawa, Yoshio Kasashima, Takashi Mino, Masami Sakamoto
Abstract
An asymmetric photoreaction by using chirality provided by dynamic chiral salt formation was demonstrated. Crystallization of racemic 2-quinolone-3-carboxamide and 2-quinolone-4-carboxamide with enantiopure L-dibenzoyltartaric acid led to deracemization and gave high diastereomeric excess values of the crystalline salts in almost quantitative yield. The axial chirality was retained for a long period of time after the salts were dissolved in cooled solvent. The frozen chirality derived from the chiral salts was effectively transferred to the products by using a typical [2+2] photocycloaddition reaction with alkenes.