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19.12
Reactions of Esters with Grignard Reagents:
Synthesis of Tertiary Alcohols
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Grignard reagents react with esters
– R
R'
••
+ OCH
3
••
C
MgX O ••
••
R'
diethyl
ether
R
C
••
OCH3
••
• O • + MgX
• •• •–
but species formed is
unstable and dissociates
under the reaction
conditions to form a ketone
Grignard reagents react with esters
– R
R'
••
+ OCH
3
••
C
R'
diethyl
ether
R
OCH3
••
• O • + MgX
• •• •–
MgX O ••
••
This ketone then goes
on to react with a
R
second mole of the
Grignard reagent to
give a tertiary alcohol.
C
••
–CH3OMgX
R'
C
O ••
••
Example
O
2 CH3MgBr + (CH3)2CHCOCH3
1. diethyl ether
2. H3O+
OH
(CH3)2CHCCH3
CH3
(73%)
Two of the groups
attached to the
tertiary carbon
come from the
Grignard reagent.
19.13
Reaction of Esters with Lithium Aluminum
Hydride
Reduction of Esters
Gives Primary Alcohols
Lithium aluminum hydride preferred for
laboratory reductions.
Sodium borohydride reduction is too slow
to be useful.
Catalytic hydrogenolysis used in industry
but conditions difficult or dangerous to duplicate
in the laboratory (special catalyst, high
temperature, high pressure).
Example: Reduction of an Ester
O
COCH2CH3
1. LiAlH4
diethyl ether
2. H2O
CH2OH +
(90%)
CH3CH2OH