Lista 3

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Mecanismos de Reações Orgânicas 
Lista de Exercícios 
Grossman, cap 3: Polar reactions under acidic conditions 
Problem 3.1. In the rearrangement reaction shown next, a 1,2-shift occurs concerted with loss 
of a leaving group. Draw a mechanism forthis reaction. FeCI3 is a Lewis acid. What by-products 
might be obtained if the migration were not concerted with loss of the leaving group? 
glycinoeclepin precursor 
Problem 3.2. Draw a mechanism for the following rearrangement reaction. SnCI4 is a 
Lewis acid. Treat the Me3Si group as if it were a big proton. 
Me.SiCL 
Er' 
H 
O OMe 
SnCL 
O 
X 
Er" 
H 
Problem 3.3. Draw mechanisms for each of the following substitution reactions. Remember 
that in each case, loss of the leaving group is preceded by coordination of the leaving group to 
a Lewis acid such as H+. 
(a) 
(b ) 
OH 
HC1 
ZnCh 
CH 
HiC-
3 
-Cl 
CH3 
Ar . o Ar 
Problem 3.7. Dihydropyran (DHP) reacts with alcohols under acid catalysis to give 
tetrahydropyranyl (THP) ethers. The alcohols can be released again by treating the THP ether 
with MeOH and catalytic acid. Thus, the THP group acts as a protecting group for alcohols. 
Draw mechanisms for the formation and cleavage of the THP ether. 
.O . ,0 , ,R ,0 . ,OMe 
H O ' R 
cat. H + 
MeOH 
cat. H + 
HO R 
Problem 3.8. Draw a mechanism for the following reaction. Will a halonium ion be an 
intermediate? 
Problem 3.9. Draw mechanisms that account for the formation of each product. The first step 
is the same in every mechanism. Be sure to think about stereochemistry! 
O Br 
Ar 
O 
-< K3 
Problem 3.10. Draw mechanisms for the following electrophilic aromatic substitution 
reactions.