Carboanions and Organometal Compounds Carboanions and

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Carboanions and Organometal Compounds
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Outline 1. Acidity of hydrocarbons 2.
Carboanions stabilized by functional groups 3.
Carboanions as nucleophiles 4. Organometal
compounds as catalysts
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1. Acidity of hydrocarbons
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Acidity of alkynes
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2. Carboanions stabilized by functional groups
Both polar and resonance effects are involved in
the stabilization.
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Kinetic acidity
Diastereotopic deprotonation
Ylides
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3. Carboanions as nucleophiles
Alkylation of Malonates (ORA 982)
A good leaving group favors C- vs.
O-alkylation. Higher dissociation favors O- vs.
C-alkylation. In general, regioselectivity
depends on the relative importance of the total
negative charge and the negative charge,
associated with the HOMO
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The relatively high acidity of alkynes
significantly affects their chemical properties.
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Formation of acetylenides is specific for
1-alkynes, because a terminal atom of hydrogen
must be present. Using acidity of alkynes and
nucleophilicity of acetylenides, any alkyne can
be synthesized from acetylene
Alkynes are convenient starting materials to
synthesize pheromones natural compounds, used
by animals and insects to exchange information
such as sex attraction, threat, warning etc.
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4. Organometal compounds as catalysts
For transition metals, insertion to s-bonds is
very characteristic
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The Heck Reaction