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Catalytic Allylic Oxidation of Alkenes Using an Asymmetric Kharasch–Sosnovsky Reaction
Author(s) -
Eames Jason,
Watkinson Michael
Publication year - 2001
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/1521-3773(20011001)40:19<3567::aid-anie3567>3.0.co;2-c
Subject(s) - allylic rearrangement , chemistry , enantioselective synthesis , stereocenter , oxazoline , ligand (biochemistry) , trifluoromethanesulfonate , chirality (physics) , medicinal chemistry , catalysis , amination , organic chemistry , stereochemistry , combinatorial chemistry , biochemistry , chiral symmetry breaking , receptor , physics , quantum mechanics , quark , nambu–jona lasinio model
Kharasch and Sosnovsky reported the allylic oxidation of alkenes to give racemic allylic benzoates. This could be achieved efficiently using a tert ‐butyl perester as the oxidant, in the presence of a copper or cobalt salt. The use of C 2 ‐symmetric bis(oxazoline) ligands in the presence of copper( I ) triflate with cyclic olefinic substrates gave the first synthetically useful asymmetric variant. The enantioselective control was good (up to 84 % ee ) although yields were variable. In all cases the facial preference of the newly formed C−O bond was the same giving an S configuration at the allylic stereocenter. Lower stereocontrol was observed for large‐ring alkenes and substantially reduced enantioselectivities were found with open‐chain alkenes. This reaction has been further screened using a variety bis(oxazoline) and proline‐derived ligands, which give a direct correlation between the chirality of the ligand and the enantioselectivity obtained. Individual substrates were found to be extremely sensitive to both the ligand structure and copper salt used as well as the presence of additives such as zinc, hydrazine, and molecular sieves.