TY - JOUR

T1 - Asymmetric Autoamplification in the Oxidative Kinetic Resolution of Secondary Benzylic Alcohols Catalyzed by Manganese Complexes

AU - Talsi, Evgenii P.

AU - Samsonenko, Denis G.

AU - Bryliakov, Konstantin P.

N1 - Publisher Copyright: © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

PY - 2017/7/7

Y1 - 2017/7/7

N2 - Herein, chiral Mn–aminopyridine complexes have been shown to catalyze the oxidation of alkylarenes to enantiomerically enriched 1-arylalkanols with hydrogen peroxide. The observed enantiomeric excess values result from the direct enantioselective benzylic C−H hydroxylation, accompanied by stereoconvergent oxidative kinetic resolution of the resulting alcohol. Testing several (S,S)-bipyrrolidine derived Mn complexes has revealed a novel catalyst (6) that exhibits the best kinetic resolution in the series (krel up to 8.8), along with sufficient reactivity and efficiency (>1000 catalytic turnovers). The mechanistic study of the Mn-mediated alcohol oxidation witnesses electrophilic active species (ρ=−1.2), with rate-limiting H abstraction (kH/kD=2.2), followed by oxygen rebound and dehydration of the resulting gem-diol to form the ketone. Intriguingly, while for the resolution of the relatively bulky 1,2-diphenylethanol, krel is virtually constant throughout the reaction, for less bulky alcohols, krel increases with increasing conversion, in line with the rising optical purity of the 1-arylalkanol. The latter participates in the oxidation as an auxiliary ligand, assisting the chiral recognition. This effect is related to the previously described asymmetric autocatalysis and asymmetric autoinduction, but is not identical with either of those, with the differences being discussed. To unambiguously identify this effect, the term asymmetric autoamplification (chiral autoamplification) is proposed.

AB - Herein, chiral Mn–aminopyridine complexes have been shown to catalyze the oxidation of alkylarenes to enantiomerically enriched 1-arylalkanols with hydrogen peroxide. The observed enantiomeric excess values result from the direct enantioselective benzylic C−H hydroxylation, accompanied by stereoconvergent oxidative kinetic resolution of the resulting alcohol. Testing several (S,S)-bipyrrolidine derived Mn complexes has revealed a novel catalyst (6) that exhibits the best kinetic resolution in the series (krel up to 8.8), along with sufficient reactivity and efficiency (>1000 catalytic turnovers). The mechanistic study of the Mn-mediated alcohol oxidation witnesses electrophilic active species (ρ=−1.2), with rate-limiting H abstraction (kH/kD=2.2), followed by oxygen rebound and dehydration of the resulting gem-diol to form the ketone. Intriguingly, while for the resolution of the relatively bulky 1,2-diphenylethanol, krel is virtually constant throughout the reaction, for less bulky alcohols, krel increases with increasing conversion, in line with the rising optical purity of the 1-arylalkanol. The latter participates in the oxidation as an auxiliary ligand, assisting the chiral recognition. This effect is related to the previously described asymmetric autocatalysis and asymmetric autoinduction, but is not identical with either of those, with the differences being discussed. To unambiguously identify this effect, the term asymmetric autoamplification (chiral autoamplification) is proposed.

KW - asymmetric autoamplification

KW - hydrogen peroxide

KW - kinetic resolution

KW - manganese

KW - oxidation

KW - SELECTIVE OXIDATION

KW - HIGHLY EFFICIENT OXIDATION

KW - NATURAL-PRODUCTS

KW - PORPHYRIN

KW - H2O2

KW - C-H BONDS

KW - EPOXIDATION

KW - GALACTOSE-OXIDASE

KW - HYDROGEN-PEROXIDE

KW - MOLECULAR-OXYGEN

UR - http://www.scopus.com/inward/record.url?scp=85020407379&partnerID=8YFLogxK

U2 - 10.1002/cctc.201700438

DO - 10.1002/cctc.201700438

M3 - Article

AN - SCOPUS:85020407379

VL - 9

SP - 2599

EP - 2607

JO - ChemCatChem

JF - ChemCatChem

SN - 1867-3880

IS - 13

ER -