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Catalytic Asymmetric Fluorination of Copper Carbene Complexes: Preparative Advances and a Mechanistic Rationale
Author(s) -
Buchsteiner Michael,
MartinezRodriguez Luis,
Jerabek Paul,
Pozo Iago,
Patzer Michael,
Nöthling Nils,
Lehmann Christian W.,
Fürstner Alois
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202000081
Subject(s) - carbene , chemistry , indane , catalysis , oxazoline , fluoride , crystallography , medicinal chemistry , organic chemistry , inorganic chemistry
The Cu‐catalyzed reaction of substituted α‐diazoesters with fluoride gives α‐fluoroesters with ee values of up to 95 %, provided that chiral indane‐derived bis(oxazoline) ligands are used that carry bulky benzyl substituents at the bridge and moderately bulky isopropyl groups on their core. The apparently homogeneous solution of CsF in C 6 F 6 /hexafluoroisopropanol (HFIP) is the best reaction medium, but CsF in the biphasic mixture CH 2 Cl 2 /HFIP also provides good results. DFT studies suggest that fluoride initially attacks the Cu‐ rather than the C‐atom of the transient donor/acceptor carbene intermediate. This unusual step is followed by 1,2‐fluoride shift; for this migratory insertion to occur, the carbene must rotate about the Cu−C bond to ensure orbital overlap. The directionality of this rotatory movement within the C 2 ‐symmetric binding site determines the sense of induction. This model is in excellent accord with the absolute configuration of the resulting product as determined by X‐ray diffraction using single crystals of this a priori wax‐like material grown by capillary crystallization.