Enantioselectve Catalytic Reactions for Industrial Use - PowerPoint PPT Presentation

Title: Enantioselectve Catalytic Reactions for Industrial Use


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Enantioselectve Catalytic Reactions for
Industrial Use
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The differentiation remains in that rhodium
asymmetric hydrogenation is a remarkably mild and
specific method for dehydroamino acids together
with a limited range of closely related alkenes
(e.g. itaconates) while ruthenium asymmetric
hydrogenation has a wider compass. For rhodium,
there are many successful ligands and the
opportunity for fine tuning in specific cases,
while BINAP and its close relatives have
prevailed in ruthenium asymmetric hydrogenation.
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Desymmetrisation of the alkene and hydrolysis of
PGs give an enantiomerically pure drug used in
treating Parkinson's disease.
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Major isomer in solution
Minor isomer (lt5)
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Chiral "un-recognition" atoms clashing here
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Chiral Recognition no clash here
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Reduction of g-ketoesters
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Asymmetric hydrogenation of simple ketones
When 45 atm of hydrogen is applied, 601 g of
acetophenone can be hydrogenated quantitatively
with only 2.2 mg of the Ru complex. The turnover
number is 2,400,000, while the TOF at 30
conversion is 228,000 per h or 63 per s. The
catalyst system is among the most
reactive (pre)catalyst so far reported
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Transfer hydrogenation
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Mechanism of Transfer Hydrogenation

• Hydrogen delivery from RuH take place by a
  pericyclic mechanism via a six-membered
  transition structure.
• Neither carbonyl oxygen nor alcoholic oxygen
  interacts with Ru throughout the hydrogen
  transfer.
• The carbonyl oxygen atom interacts with NH on Ru
  via hydrogen bonding.

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HAZARD!!
chemoselective
The alkyl group on boron can be varied. Me and
n-Bu are the common choices.
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Large group equatorial
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Sometimes, control of enolate geometry is
unnecessary.
In open chain carbonyl compounds, control is
necessary.
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We need access to both geometries of enolates.
By contrast,
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Asymetric aldol reactions
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Boron chelation controls enolate geometry, but
boron cannot have gt4 ligands, so chelation must
change for the aldol reaction to occur.
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Catalytic Aldol Reaction with cyclic transition
state
S.E. Denmark
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Stereoselective synthesis of Z and E silyl enol
ethers
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Evans' Chiral Auxiliary in a Different
Context Diastereoselective Diels-Alder
Cycloadditions
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Introduction to Organocatalysis
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Cycloaddition
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Synthetic application of organocatalytic
cycloaddition
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Benzoin Condensation and Stetter Reaction
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Acyl Transfer Kinetic Resolution and
Desymmetrisation
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