10.1002/anie.201804315
Angewandte Chemie International Edition
COMMUNICATION
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On the basis of the above mechanistic investigations and
previous studies,[4,5] a working mechanism for the current catalytic
system is tentatively proposed in Scheme 6c: The in situ formed
bis-chelating CuI complex A through ligand exchange could act
as an active catalyst to undergo the initial single electron transfer
with 2a to generate CuII complex B and the CF3 radical. The latter
rapidly added to the alkene to yield radical intermediate C, which
could be trapped by CuII complex B to form a CuII species D
through ligand exchange. Subsequent intramolecular redox
reaction generated a CuIII species E, followed by reductive
elimination to give the final product.[17] However, an alternative
scenario where the anionic sulfonamide monodentately
coordinates to copper and the quinuclidine tertiary amine works
cooperatively as a base to activate the hydroxy group cannot be
ruled out at the present stage (Scheme S2 in SI). Further studies
are required to fully elucidate the mechanistic details of the
reaction.
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In summary, we have successfully developed a class of
cinchona alkaloid-based sulfonamides performing as effective
hybrid ligand in combination with copper metal, which enables the
catalytic asymmetric radical oxytrifluoromethylation of alkenyl
oximes for straightforward access to CF3-containing isoxazolines
bearing an α-tertiary stereocenter with excellent yield and
enantioselectivity. The obtained products can be readily
transformed into useful chiral CF3-containing 1,3-aminoalcohols.
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stereocontrol and the development of other radical-initiated
asymmetric chemistry with such a catalytic system are ongoing in
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Acknowledgements
Financial support from NSFC (nos. 21722203 and 21572096),
Shenzhen special funds for the development of biomedicine
(JCYJ20170412152435366 and JCYJ20170307105638498), and
Shenzhen Nobel Prize Scientists Laboratory Project (C17213101)
is greatly appreciated.
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Keywords: alkene oxytrifluoromethylation • alkenyl oxime •
asymmetric radical reactions • copper catalysis • CF3-containing
isoxazolines
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