A research team led by Prof. CHEN Qing-an from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has developed a chiral phosphoric acid (CPA) catalyzed multicomponent reaction of anilines, aldehydes, and azetidinones to access tetrahydroquinoline-fused azetidines with three contiguous stereocenters.
Their findings were published in Chem Catalysis on June 20.
Enantiopure fused azetidines are widespread in natural products and medically relevant molecules. Therefore, the exploration of efficient catalytic systems for the rapid assembly of such important frameworks is in great demand. Compared with significant advances achieved in transition-metal catalysis, organocatalytic strategies lag far behind.
In this study, the researchers achieved this goal with chiral phosphoric acid (CPA) catalysis using commercially available anilines, benzaldehydes, and azetidinones as starting materials. This protocol enables one-step construction of three contiguous stereocenters with high diastereo- and enantioselectivities.
DFT calculations implied that a stepwise mechanism consisting of enamine-imine addition and Friedel-Crafts attack is likely involved.
"This work not only provides an efficient alternative to access chiral fused azetidines, but also opens up an avenue to design other asymmetric multicomponent reaction", said Prof. Chen.
The above research was supported by the Dalian Outstanding Young Scientific Talent and the National Natural Science Foundation of China. (Text by HU Yancheng)