Download Organometallics II

Grignard reagents act as nucleophiles
toward the carbonyl group
δ–
Synthesis of Alcohols
R
diethyl
ether
δ+
C
R
+
• •
MgX
•O•
•• –
MgX O ••
••
Grignard or Organolithium Reagents
C
H3O+
Organolithium reagents react with
carbonyls in the same
general way that Grignard reagents do.
two-step sequence
gives an alcohol as
the isolated product
Grignard reagents react with:
R
C
• OH
•
••
Grignard reagents react with:
formaldehyde to give primary alcohols
formaldehyde to give primary alcohols
other aldehydes to give secondary alcohols
ketones to give tertiary alcohols
esters to give tertiary alcohols
Example
Grignard reagents react with formaldehyde
δ–
H
R
δ+ H
C
diethyl
ether
Mg
H
R
C
•• O ••
•• –
MgX O ••
••
Cl
H
+
MgCl
H
MgX
H3O+
product is a
primary alcohol
diethyl
ether
C
H
R
C
• OH
•
••
O
H
H
CH2OH
(64-69%)
H3O+
CH2OMgCl
Grignard reagents react with:
Grignard reagents react with aldehydes
formaldehyde to give primary alcohols
H
δ–
R
aldehydes to give secondary alcohols
δ+ R'
C
diethyl
ether
H
R
C
R'
+
MgX
•• O ••
•• –
MgX O ••
••
H3O+
product is a
secondary alcohol
H
R
C
• OH
•
••
Example
Question
Mg
CH3(CH2)4CH2Br
CH3(CH2)4CH2MgBr
diethyl
ether
H 3C
C
O
H
CH3(CH2)4CH2CHCH3
H3O+
CH3(CH2)4CH2CHCH3
OH
OMgBr
• What is the product of the reaction of
ethylmagnesium bromide (CH3CH2MgBr) with
butanal (CH3CH2CH2CH=O) followed by dilute
acid?
•
A)
2-hexanol
•
B)
1-butanol
•
C)
3-hexanol
•
D)
3-pentanol
(84%)
Example
H 2C
O
CHLi +
CH
1. diethyl ether
2. H3O+
CHCH
OH
(76%)
CH2
Grignard reagents react with:
formaldehyde to give primary alcohols
aldehydes to give secondary alcohols
ketones to give tertiary alcohols
R'
Grignard reagents react with ketones
R"
δ–
R
δ+ R'
C
diethyl
ether
Question
R"
R
C
+
•• O ••
•• –
MgX O ••
••
• What is the product of the reaction shown at
the right?
R'
MgX
H3O+
product is a
tertiary alcohol
R"
R
C
R'
•
A)
B)
•
C)
D)
• OH
•
••
Example
Question
Mg
CH3Cl
HO CH3
diethyl
ether
H3O+
CH3MgCl
• Two alcohols, each having the molecular
formula C11H22O, are formed in the reaction of
methyl lithium with 3-(R)-tertbutylcyclohexanone. These two alcohols are
•
A)
constitutional isomers.
•
B)
enantiomers in equal amounts.
•
C)
enantiomers in unequal amounts.
•
D)
diastereomers.
O
ClMgO
CH3
(62%)
Remember: Sodium Salts of Acetylenes
NaNH 2
HC
CH
Synthesis of Acetylenic Alcohols
HC
NH3
CNa
O
HC
CNa +
HO
C
1. NH3
2. H3O+
(65-75%)
CH
Using Acetylenic Grignard Reagents
Question
CH + CH3CH2MgBr
MgBr
CH3(CH2)3C
• What compound will be obtained from the
reaction shown below?
diethyl ether
CH3(CH2)3C
•
• A)
B)
• C)
D)
+ CH3CH3
CMgBr
MgBr
1. H2C O
2. H3O+
CH3(CH2)3C
CCH2OH
(82%)
Question
• Which one of the compounds below will
be produced when methylmagnesium
bromide is added to propanoic acid
(CH3CH2CO2H)?
•
A) CH3CH2COCH3
•
B) CH3CH2CO2-MgBr
•
C) CH3CH2CH(OH)CH3
•
D) CH3CH2CH2CH3
Preparation of Tertiary Alcohols
From Esters and Grignard Reagents
Grignard reagents react with esters
δ–
R'
R
••
δ+ OCH3
••
C
MgX O ••
••
diethyl
ether
Grignard reagents react with esters
R'
R
C
••
OCH3
••
• O • + MgX
• •
•• –
but species formed is
unstable and dissociates
under the reaction
conditions to form a ketone
δ–
R'
R
••
δ+ OCH3
••
C
R'
diethyl
ether
R
MgX O ••
••
this ketone then
goes on to react with
a second mole of the
Grignard reagent to
give a tertiary alcohol
C
••
OCH3
••
• O • + MgX
• •
•• –
–CH3OMgX
R
C
O ••
••
R'
Example
O
CHCOCH3
2 CH3MgBr + (CH3)2CHCOCH
1. diethyl ether
2. H3O+
OH
(CH3)2CHCCH
CHCCH3
CH3
(73%)
Two of the groups
attached to the
tertiary carbon
come from the
Grignard reagent
Question
• Which one of the compounds below will be
produced when methylmagnesium bromide is
added to methyl propanoate
(CH3CH2CO2CH3) followed by acid?
•
A)
CH3CH2COCH3
•
B)
CH3CH2CO2-MgBr
•
C)
CH3CH2CH(OH)CH3
•
D)
CH3CH2CH2CH3
•
E)
2-methyl-2-butanol