Recent advances for the catalytic asymmetric construction of medium-sized rings

The synthesis of enantioenriched medium-sized rings has been recognized as a long-standing challenge. Typical strategies referring to "head-to-tail" cyclization approaches rely on using stoichiometric chiral substrates in most cases, and these limit quick access to these target scaffolds. Asymmetric catalysis provides a new insight for the assembly of enantiopure medium-sized ring scaffolds. In this manner, optically pure compounds are generated from achiral substrate by using a small quantity of chiral catalyst. Over the past few decades, catalytic asymmetric synthesis of medium-sized rings has seen remarkable progress. A series of protocols, such as transition-metal catalysis and organocatalysis, have proven to be practical for assembling medium-sized ring systems. In this review, we provide a concise overview of the most recent breakthroughs in catalytic asymmetric synthesis of medium-sized rings. By summarizing these elegant strategies, we aim to inspire chemists to develop more efficient approaches for the asymmetric synthesis of medium-sized rings.