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Design of Chiral NHC‐Carboxylates as Potential Ligands for Pd‐Catalyzed Enantioselective C−H Activation
Author(s) -
Niggli Nadja E.,
Baudoin Olivier
Publication year - 2021
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.202100015
Subject(s) - chemistry , bifunctional , enantioselective synthesis , enantiopure drug , catalysis , yield (engineering) , combinatorial chemistry , stereochemistry , carboxylate , organic chemistry , materials science , metallurgy
Despite numerous efforts, the synthesis of scalemic carbo‐ and heterocycles through Pd 0 ‐catalyzed C(sp 3 )−H activation employing chiral ancillary ligands or chiral bases is still limited. Inspired by the recently reported outstanding performance of IBiox‐type NHC ligands and bifunctional ligands in similar transformations, a new class of bifunctional NHC‐ligands bearing a pendant carboxylate group was designed. A library of 10 imidazolium‐carboxylic acids was obtained in five to six steps from enantiopure l ‐ tert ‐leucinol. In addition, four well‐defined Pd(DMBPA)‐NHC palladacycles were synthesized in good to excellent yields from the corresponding imidazolium precursors. These complexes were tested in a prototypical C(sp 3 )−H arylation reaction, and the most active one afforded the indoline product in low yield but significant enantioselectivity. These new bifunctional NHCs could find broader applications in catalytic enantioselective transformations occurring under milder conditions.