A Chiral [2+3] Covalent Organic Cage Based on 1,1’‐Bi‐2‐naphthol (BINOL) Units

Abstract

AbstractA [2+3] chiral covalent organic cage is produced through a dynamic covalent chemistry approach by mixing two readily available building units, viz. an enantiopure 3,3’‐diformyl 2,2’‐BINOL compound (A) with a triamino spacer (B). The two enantiomeric (R,R,R) and (S,S,S) forms of the cage C are formed nearly quantitatively thanks to the reversibility of the imine linkage. The X‐ray diffraction analysis of cage (S,S,S)‐C highlights that the six OH functions of the BINOL fragments are positioned inside the cage cavity. Upon reduction of the imine bonds of cage C, the amine cage D is obtained. The ability of the cage D to host the 1‐phenylethylammonium cation (EH+) as a guest is evaluated through UV, CD and DOSY NMR studies. A higher binding constant for (R)‐EH+ cation (Ka=1.7 106±10 % M−1) related to (S)‐EH+ (Ka=0.9 106±10 % M−1) is determined in the presence of the (R,R,R)‐D cage. This enantiopreference is in close agreement with molecular dynamics simulation.