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472 CHAPTER 13 
 
retrosynthetic analysis represents one such method. An 
explanation of each of the steps (a-f) follows. 
 
 
 
a. The cyclic product can be made by treating a 
dianion with a dihalide (via two successive SN2 
reactions). 
b. The dianion can be made by treating the 
corresponding diol with two equivalents of a strong 
base (such as NaH). 
c. The diol can be made from an epoxide, via a ring-
opening reaction (either under acidic conditions or 
under basic conditions). 
d. The epoxide can be made by treating the 
corresponding alkene with a peroxy acid. 
e. The dibromide can be made via bromination of the 
corresponding alkene. 
f. The alkene can be made via hydrogenation of the 
corresponding alkyne, in the presence of Lindlar’s 
catalyst. 
 
Now let’s draw the forward scheme. Acetylene 
undergoes hydrogenation in the presence of Lindlar’s 
catalyst to afford ethylene, which can be converted to an 
epoxide upon treatment with a peroxy acid. Acid-
catalyzed ring-opening of the epoxide gives a diol (base-
catalyzed conditions can also be used). Treatment of the 
diol with two equivalents of a strong base, such as NaH, 
gives a dianion. The dianion will react with 1,2-
dibromoethane (formed from bromination of ethylene) to 
give the desired cyclic product via two successive SN2 
reactions. 
 
 
 
13.49. There are certainly many acceptable methods for 
achieving the desired transformation. The following 
retrosynthetic analysis represents one such method. An 
explanation of each of the steps (a-d) follows. 
 
 
 
a. The product has two ether groups, each of which 
can be formed via a Williamson ether synthesis, 
from the dianion shown. 
b. The dianion can be made by treating the 
corresponding diol with two equivalents of a strong 
base (such as NaH). 
c. The diol can be made from an alkene, via a 
dihydroxylation process. 
d. The alkene can be made via hydrogenation of the 
corresponding alkyne, in the presence of Lindlar’s 
catalyst. 
 
Now let’s draw the forward scheme. Acetylene 
undergoes hydrogenation in the presence of Lindlar’s 
catalyst to afford ethylene, which can be converted to a 
diol via a dihydroxylation process. Treatment of the diol 
with two equivalents of a strong base, such as NaH, 
gives a dianion. The dianion will react with two 
equivalents of methyl iodide giving the product (via a 
Williamson ether synthesis, twice). 
 
 
 
13.50. There are certainly many acceptable methods for 
achieving the desired transformation. The following 
retrosynthetic analysis represents one such method. An 
explanation of each of the steps (a-f) follows. 
 
O
OH
O
H
O
OHO
OH
a
b
c
d
e
f
 
 
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