Catalytic Asymmetric Fluorination of Copper Carbene Complexes: Preparative Advances and a Mechanistic Rationale.
Chemistry
; 26(11): 2509-2515, 2020 Feb 21.
Article
em En
| MEDLINE
| ID: mdl-31916634
ABSTRACT
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 C6 F6 /hexafluoroisopropanol (HFIP) is the best reaction medium, but CsF in the biphasic mixture CH2 Cl2 /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 C2 -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.
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Base de dados:
MEDLINE
Idioma:
En
Revista:
Chemistry
Assunto da revista:
QUIMICA
Ano de publicação:
2020
Tipo de documento:
Article
País de afiliação:
Alemanha