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Chapter 10 377
Copyright © 2017 Pearson Education, Inc.
58.
Only one
S
N
2
reaction takes place in
a
and
b
, so the product has the inverted configuration compared to the
configuration of the reactant.
a.
C
D
OH
H
CH
3
CH
2
+
O
S
O
Cl
R
C
D
OSO
2
R
H
CH
3
CH
2
C
OH
D
H
CH
3
CH
2
HO
pyridine
pyridine
−
S
N
2
+
O
S
O
Cl
R
CH
2
CH
3
H
D
HO
CH
2
CH
3
H
D
RSO
O
O
HO
−
S
N
2
CH
2
CH
3
H
OH D
(
R
)-1-deuterio-1-propanol
(
S
)-1-deuterio-1-propanol
(
S
)-1-deuterio-1-propanol
(
R
)-1-deuterio-1-propanol
or
b.
C
D
OH
H
+
O
S
O
Cl
R
C
D
OSO
2
R
H
C
OCH
3
D
H
CH
pyridine
pyridine
3
O
−
−
S
N
2
+
O
S
O
Cl
R
CH
2
CH
3
H
D
HO
CH
2
CH
3
H
D
RSO
O
O
CH
3
O
S
N
2
CH
2
CH
3
H
OCH
3
D
(
R
)-1-deuterio-1-propanol
(
S
)-1-deuterio-1-methoxypropane
(
R
)-1-deuterio-1-propanol
or
(
S
)-1-deuterio-1-methoxypropane
CH
3
CH
2
CH
3
CH
2
CH
3
CH
2
c.
Because the desired product has the same configuration as the starting material, it can be synthesized
using reactions that do not break any of the bonds to the asymmetric center.
D
H
OH
NaH
CH
3
I
(
R
)-1-deuterio-1-propanol
(
R
)-1-deuterio-1-methoxypropane
D
H
O
−
D
H
OCH
3
C
C
C
CH
3
CH
2
CH
3
CH
2
CH
3
CH
2
It can also be synthesized using two consecutive
S
N
2
reactions. Because each one involves inversion of
configuration, the final product will have the same configuration as the starting material. For example,
treating the starting material with
PBr
3
forms
1
S
2
-1-bromo-1-deuteriopropane. Treating
1
S
2
-1-bromo-
1-deuteriopropane with methoxide ion forms
1
R
2
-1-deuterio-1-methoxypropane.
PBr
3
/ pyridine
D
C
CH
2
CH
3
Br
H
CH
3
O
−
D
C
OCH
3
H
D
C
OH
H
CH
3
CH
2
CH
3
CH
2
(
R
)-1-deuterio-1-propanol
(
S
)-1-bromo-1-deuteriopropane
(
R
)-1-deuterio-1-methoxypropane
S
N
2
S
N
2