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Chapter 22 749
Copyright © 2017 Pearson Education, Inc.
In one mechanism, the negatively charged aldehyde oxygen (which is a much better nucleophile than
water) is the nucleophile that adds to the ester. The tetrahedral intermediate collapses to form a lactone.
Iminium ion formation followed by imine hydrolysis forms the final product.
O
O
OCH
3
N
O
−
O
N
O
O
+
CH
3
OH
H
C
O
O
O
HN O
H
2
O
imine
hydrolysis
C
C
N O
+
C
C O
O
OCH
3
HN O
C
O
H
H
O
−
−
In the other mechanism, the reaction of morpholine with the aldehyde forms an iminium ion. The posi-
tively charged iminium ion makes it easier for water to add to the ester by stabilizing the negative charge
that develops on the oxygen. Collapse of the tetrahedral intermediate followed by imine hydrolysis forms
the final product.
HN O
imine
formation
+
CH
3
OH
HN O
H
C
C
N O
O
OCH
3
H
2
O
H
C
C
N O
OCH
3
HO
H
C
C
N O
O
OH
CH
C
O
O
−
O
+
−
+ +
+
C
C O
H
O
OCH
3
O
H
2
O
imine
hydrolysis