Premium
Enantioselective Benzylic Hydroxylation of Arylalkanes with H 2 O 2 in Fluorinated Alcohols in the Presence of Chiral Mn Aminopyridine Complexes
Author(s) -
Ottenbacher Roman V.,
Talsi Evgenii P.,
Rybalova Tatyana V.,
Bryliakov Konstantin P.
Publication year - 2018
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201801476
Subject(s) - chemistry , enantioselective synthesis , catalysis , medicinal chemistry , ligand (biochemistry) , solvent , chirality (physics) , hydroxylation , selectivity , stereochemistry , organic chemistry , biochemistry , chiral symmetry breaking , receptor , physics , quantum mechanics , nambu–jona lasinio model , enzyme , quark
A series of chiral bioinspired Mn‐aminopyridine complexes of the type [L*Mn II (OTf) 2 ] (where L* is 2,2′‐bipyrrolidine derived ligand, bearing trifluoroalkoxy and alkyl substituents) have been tested as catalysts in benzylic C−H hydroxylation of arylalkanes with H 2 O 2 in fluorinated ethanols media. In 2,2,2‐trifuoroethanol, the yield of the target ethylbenzene oxidation product, chiral 1‐phenylethanol, reaches 45 %, which is much better than in the common solvent CH 3 CN (5‐6 %). The selectivity for 1‐phenylethanol formation increases in the following order: CH 3 CN<2‐fluoroethanol<2,2‐difluoroethanol<2,2,2‐trifuoroethanol, while 2,2‐difluoroethanol ensures the highest asymmetric induction in this series, affording chiral benzylic alcohols with up to 89 % ee . In trifluoroethanol, the observed primary k H / k D value of 2.3 has been measured for the oxidation of 1‐phenylethanol/ α ‐D‐1‐phenylethanol, which is similar to that in CH 3 CN (2.2). At the same time, depending on the solvent, CH 3 CN or 2,2,2‐trifuoroethanol, the oxidations of 1‐phenylethanol demonstrates drastically different linear free‐energy relationships; possible effect of the hydrogen‐bond donor (HBD) nature of CF 3 CH 2 OH is discussed in this context. Noticeably, it has been shown that by switching the absolute chirality (( S , S )− or ( R , R )−) of the catalyst, the oxidation of complex substrate of natural origin, estrone acetate, can be diverted to predominant formation of either the tertiary C9‐alcohol or of the C6‐ketone, respectively.