Remote chiral transfer into [2+2] and [2+4] cycloadditions within self-assembled molecular flasks

Abstract

AbstractA self-assembled chiral coordination cage was prepared from triangular triazine-panel ligands and Pd(II) complexes with chiral diamine auxiliaries. The chiral environment of the cage is induced by the structural deformation of the triazine panels ascribed to the steric bulk of the substituents on the chiral auxiliaries. The chiral cage can accommodate a pair of two hydrophobic molecules to form a specific diastereomeric ternary complex. We succeeded in conducting unusual [2+2] and [2+4] asymmetric cycloadditions from the identical ternary complex including a maleimide derivative and aromatic compounds with 6–50% enantiomeric excess (ee). It is remarkable that the remote chirality on the auxiliaries is efficiently transmitted to the chiral orientation of achiral ligands, which define a chiral cavity, to induce up to 50% ee. The present strategy is widely applicable to cavity-directed asymmetric reactions and maintaining inherent properties of the cage.Keywords: self-assemblyhost–guest systemspericyclic reactionenantioselectivitychiral transfer AcknowledgementsThis research was supported in part by the Global COE Program (Chemistry Innovation through Cooperation of Science and Engineering), MEXT, Japan.Notes1. The remaining 50% is a dimer formation of maleimide 3 within the cage, 1 · (3)2.2. The conversion is almost 100% as starting compounds and any by-products were not extracted from the cage after the reaction. The moderate yield (60%) is due to escape of the substrates from the cage under the reaction conditions.