Visible-Light-Mediated Cyclization of Enynes toward Medium-Sized Carbocycles with Copper Catalyst.

The development of efficient methods for the construction of medium-sized carbocycles is extremely important in organic synthesis since many pharmaceutical agents contain these frameworks. Herein, we report an efficient strategy for the synthesis of seven- and eight-membered carbocycles via the intramolecular radical cyclization of 1,8- and 1,9-enynes. The reaction is proposed to proceed through a short-lived excited species derived from a copper acetylide complex, which engages the tethered π-system to generate a reactive intermediate capable of cyclization. The synthetic utility of this method is demonstrated through derivatizations leading to structurally diverse polycyclic compounds. This transformation offers a pratical approach to access strained medium-ring system under mild, visible-light-mediated conditions.