Enantioselective Synthesis of Axially Chiral Styrene‐Carboxylic Esters by Rhodium‐Catalyzed Chelation‐Controlled [2+2+2] Cycloaddition
Daisuke Yokose, Yuki Nagashima, Suzuka Kinoshita, Juntaro Nogami, Ken Tanaka
Abstract
Abstract Axially chiral styrene‐carboxylic esters were synthesized in high yields with excellent enantioselectivity by the cationic rhodium(I)/H 8 ‐BINAP complex‐catalyzed chelation‐controlled [2+2+2] cycloaddition reactions of 1,6‐ and 1,7‐diynes with 1,3‐enyne‐carboxylic esters. The diastereo‐ and enantioselective synthesis of C 2 symmetric axially chiral cis and trans ‐stilbene‐dicarboxylic esters was also achieved by the double [2+2+2] cycloaddition reactions of two molecules of the 1,6‐diyne with 2,3‐dialkynylmaleate and 2,3‐dialkynylfumarate, respectively. In these reactions, the 1,3‐enyne‐carboxylic esters coordinating to rhodium with a five‐membered chelate were more reactive than those coordinating to rhodium with a six‐membered chelate, although both chelation modes realized excellent enantioselectivity. The enantioselection mechanism of the cationic rhodium(I)‐catalyzed chelation‐controlled [2+2+2] cycloaddition was elucidated by DFT calculations.