Enantioselective Synthesis Enantioselective Synthesis of Biphenols from 1,4- of Biphenols from 1,4- Diketones by Traceless Diketones by Traceless Central-to-axial Chirality Central-to-axial Chirality Exchange Exchange Research By: F Guo, LC Konokol, and RJ Thomson; Northwestern University Summary by: Sonja Gamby; UMCP
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Enantioselective Synthesis of Biphenols from 1,4-Diketones by Traceless Central-to-axial Chirality Exchange Research By: F Guo, LC Konokol, and RJ Thomson;
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Enantioselective Synthesis of Enantioselective Synthesis of Biphenols from 1,4-Biphenols from 1,4-
Diketones by Traceless Diketones by Traceless Central-to-axial Chirality Central-to-axial Chirality
ExchangeExchange
Research By: F Guo, LC Konokol, and RJ Thomson; Northwestern University
Summary by: Sonja Gamby; UMCP
Some termsSome terms“Axial Chirality”Axial chirality results from a hindered axis of rotation as opposed to a chiral center
“Traceless”Denotes transition from sp3 to sp2 and the exchange between typical “central” chirality and axial chirality
Common molecule exhibiting Common molecule exhibiting axial chirality - BINOLaxial chirality - BINOL
• The original synthesis of BINOL was reported by Pummerer et al. in 1926.
• Original syntheses involved oxidative coupling of the two naphthol units induced by FeCl3.
• There are two methods for the preparation of chiral binaphthol ligands: (a) through coupling reactions of substituted naphthol units and (b) through regioselective modification of the binaphthol scaffold.
OH
HO
OH
HO
(R)-1,1'-Bi-2-Napthol
(S)-1,1'-Bi-2-Napthol
Derivatives of BINOL: Why Derivatives of BINOL: Why
and How?and How?• Subject to racemization in acidic or basic media• Limited control over electronics and sterics of
metal center• Useful in a variety of transformations
OH
HO
R
R
R=H,Br,Cl
Electrophilic aromatic substitutions in conjunction with protection of the hydroxyl moieties are a quick route to a vast library of derivatives
…Some derivatives
OH
HO
Ph
Ph
O
O
Br
Br
O
O
Zr
L
L
Br
Br
Kelly et al.Diels-Alder reactions of naphthoquinone derivatives
Kobayashi et al.Mannich Reaction involving silyl enolates
HO
N
Ar H
OSiMe3
R
R
R
HO
HN
ArR R
O
R
O
O O
BO O
PhPh
HO
Ph
OH
Ph
I.
II.
BINAP for use in asymmetric BINAP for use in asymmetric catalysiscatalysis
… To discover high-performance asymmetric catalysts, developing an excellent chiral ligand is crucial. Attracted by its molecular beauty [Chemica Scripta 1985, 25, 83], we initiated the synthesis of BINAP (2,2’-bis(diphenylphosphino)-1,1’-binaphthyl) [J. Am. Chem. Soc. 1980, 102, 1932] in 1974 at Nagoya with the help of H. Takaya, my respected long-term collaborator. BINAP was a new fully aromatic, axially dissymmetric C2 chiral diphosphine that would exert strong steric and electronic influences on transition metal complexes. Its properties could be fine-tuned by substitutions on the aromatic rings. …