P1251328600GJFBD - PowerPoint PPT Presentation

Title: P1251328600GJFBD


1
REACTIONS WITH EPOXIDES
PRIMARY ALCOHOLS
2
Reaction with Oxirane
H3O
ether

R
Notice that

• the carbon chain has added two carbons

• the product is a terminal alcohol

3
Crude outline of a mechanism
alkoxide ion

Li
usually dilute HCl
Workup step
4
REACTION IS AT THE LEAST-SUBSTITUTED
CARBON
O
N
u


R
Why?
5
REACTIONS WITH EPOXIDES
Notice which carbon was
attacked by the nucleophile.
Grignard reagents could have been used instead of
alkyllithiums.
6
REACTION WITH OXETANES
7
Oxetanes add a three Carbon Piece
8
ORGANOMETALLICS FROM ALKYNES
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Acetylenic Grignard Reagents
Acetylenic Grignard Reagents cannot be made
directly. They must be made by exchange.
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Alkynylorganometallic Compounds
React another organometallic compound with an
alkyne ( exchange).
basic
cannot be prepared directly - you must use
exchange
acidic H
preparation of methyllithium
CH3-Br 2 Li
CH3-Li LiBr
ether

exchange

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LITHIUM DIALKYL CUPRATES
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LITHIUM DIALKYLCUPRATES
R2CuLi
Made by treating an alkyllithium compound with
copper (I) iodide.
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STRUCTURE OF THE LITHIUM DIALKYLCOPPER COMPLEX
This structure is an oversimplification. The
actual complex is known to be a dimer. Although
there is a great deal of debate, Li2Cu2(CH4)4 is
thought to have a cluster structure similar to
the one shown below.
R
CuLi
R
The mechanism by which it works is
complicated. It probably involves single electron
transfers to the substrate making radicals which
combine.
We will show the reactions and not attempt to
draw any mechanism.
NOTE This is a structure of a crystal and may
not be the structure of the reagent in solution.
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ALKYLATION WITH R2CuLi
0o C
R-X R2CuLi
R-R R-Cu LiX
ether
X Cl, Br, I
EXAMPLES
(CH3)2CuLi CH3(CH2)4-I
CH3-(CH2)4-CH3

Corey-House Reaction
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COMPARE R2CuLi TO THE WURTZ REACTION
The Wurtz reaction gives only symmetric coupling
R-R
C5 - C5
Must be aliphatic.
Lithium Dialkylcuprates can give asymmetric
coupling R-R
C5 - C2
Can also be an alkene or an aromatic compound.
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MORE LITHIUM DIALKYLCUPRATE COUPLING

KOH
CHBr3
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R2CuLi (CUPRATES) WITH ACID CHLORIDES
Cuprates can also couple with acid chlorides.

KETONE
ACID CHLORIDE