Sidearm Approach: A Promising Strategy for Construction of Bisoxazoline-Based Ligand Library

摘要

Combinatorial chemistry offers the premise of increasing the efficiency to discover new catalysts for asymmetric transformations. In this context, rapid construction of diverse chiral ligands with different activities and selectivities is one of the most important issues. C_2-symmetrical bisoxazolines have been found to be very valuable for a wide range of metal-catalyzed reactions and thus, much effort has been devoted to the creation of superior bisoxazoline-based ligands by varying amino alcohols bridging linkers or backbones as demonstrated by the wide application of bisoxazoline (BOX) 1 DBPHOX and PYBOX Although significant achievements have been obtained, the development of inexpensive, easily accessible and highly efficient bisoxazoline-based ligands is still of great interest. Very recently, we designed a pseduo-C3-symmetric trisoxaozline (TOX) 2a by a sidearm approach and found this trisoxazoline 2a to be very useful in indole alkylation,10a,c the Kinugasa reaction,10b and the Diels-Alder reaction.