Page 165 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

5A.8 IMINES AND RELATED FUNCTIONAL GROUPS 145
The anion so produced is then protonated on carbon, as shown below:

R 1 N H
− − R 1 N H
C N − OH
C N (5A.45)
R 2
H R 2
H
O H
A second deprotonation then leads to loss of N ; protonation of the resulting carbanion then
2
produces the final product where the original carbonyl group has been replaced by a CH
2
group.
−
OH
R 1 N H R 1
− HOH
C N − C + N N
R 2 R 2
H H (5A.46)

R 1 − R 1
− OH
− C H O C H
R 2 R 2
H H H
The Shapiro reaction, on the other hand, allows the transformation of a tosylhydrazone
to an alkene, as shown below:
H
Ts
N
R 1 Li + R 1 E
R 1 N
2 n-BuLi E
C C C C (5A.47)
C C
H R 2 H R 2
H 2
H R
E = electrophile
+
3
(e.g., H , R CHO, etc.)
Note that the reaction requires (at least) 2 equiv. of a strong base such as n-butyllithium.
The first equivalent deprotonates the NH proton, and the second equivalent plucks off a
proton with respect to (i.e., adjacent to) the C=N double bond, as shown below:
Li
Ts
H
Ts − N
N 1
+ R N
− Li
R 1 N
C C
− n-BuH
C C H 2
H R
H 2
H R