Protected amino acids as a nonbonding source of chirality in induction of single-handed screw-sense to helical macromolecular catalysts |
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Authors: | Shoma Ikeda Ryohei Takeda Takaya Fujie Naoto Ariki Yuuya Nagata Michinori Suginome |
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Affiliation: | Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 Japan, |
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Abstract: | Chiral nonbonding interaction with N-protected amino acid methyl esters used as chiral additives in achiral solvents allows dynamic induction of single-handed helical conformation in poly(quinoxaline-2,3-diyl)s (PQX) bearing only achiral substituents. Ac-l-Pro-OMe, for instance, allows induction of energy preference of 0.16 kJ mol−1 per monomer unit for the M-helical structure over the P-helix in t-butyl methyl ether (MTBE). With this new mode of screw-sense induction, homochiral screw-sense has been induced in virtually achiral poly(quinoxaline-2,3-diyl)s 1000-mer containing phosphine pendants (PQXphos). Use of PQXphos as a helically dynamic ligand along with Ac-Pro-OMe (l or d) as a chiral additive in MTBE allowed a highly enantioselective Suzuki–Miyaura coupling reaction with up to 95% enantiomeric excess.Achiral poly(quinoxaline-2,3-diyl) containing Ar2P groups undergo dynamic induction of M-helical conformation through nonbonding interaction with protected AA such as Ac-l-Pro-OMe, serving as a chiral ligand in asymmetric cross-coupling with up to 95% ee. |
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