Aromatic Compounds
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RETROSYNTHETIC RETROSYNTHETIC APPROCHAPPROCH
TOTOORGANIC SYNTHESISORGANIC SYNTHESIS
Dr. Shaikh S. NizamiDr. Shaikh S. NizamiDepartment of ChemistryDepartment of ChemistryUniversity of KarachiUniversity of Karachi
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RETROSYNTHESIS RETROSYNTHESIS
OFOF
AROMATIC AROMATIC
COMPOUNDSCOMPOUNDS
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CONTENTSCONTENTS
1.Aromatic Eletrophilic Substitution Reactions
2.Aromatic Nucleophilic Substitution Reactions
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Retrosynthesis of Aromatic Retrosynthesis of Aromatic Electrophilic Substitution Electrophilic Substitution
ReactionsReactions
TM
C X
SYNTHON REAGENT
R
_
+X
+
R
H
?R
X
Addition of cationic synthons to the aromatic ring
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Reagents forReagents for Aromatic Aromatic Electrophilic SubstitutionElectrophilic Substitution
REAGENT REACTION
R+
RBr + AlCl3 Friedel-Crafts Alkylation
+ROH H+
+ H+Alkene
RCO+
+RCOCl AlCl3 Friedel-Crafts Acylation
SYNTHON
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Reagents forReagents for Aromatic Aromatic Electrophilic SubstitutionElectrophilic Substitution
REAGENT REACTIONNO2
+
Cl2 FeCl3+
HNO3 H2SO4+ NitrationCl
+Chlorination
Br+ Br2 Fe+ Bromination
H2SO4 Sulphonation+SO2Cl
+SO2OH
ClSO2OH Chloro-Sulphonation
ArN2+
ArN2+Cl
-Diazocoupling
SYNTHON
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Friedel-CraftsFriedel-Crafts AlkylationAlkylation
TM'BHT' butyled hydroxytoluenean antioxidant used in foodF.C. alkylation useful reactionfor tertiary halides
OH
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Retrosynthesis of BHT & Retrosynthesis of BHT & SynthesisSynthesis
TM
C C
FriedelCrafts
_
OH
HH
+ +
Synthesis OH
+ H+
ort BuCl/AlCl3
TM
OH
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Friedel-Crafts AcylationFriedel-Crafts Acylation
TM
C C
FriedelCrafts
_ + Cl
Rearrangement is possible in primary alkylhalide
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Friedel-Crafts AcylationFriedel-Crafts Acylation
Cl
AlCl3
+
COCl
AlCl3
O
Zn,Hg
HCl(conc.)TM
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One-carbon electrophile One-carbon electrophile for aromatic synthesisfor aromatic synthesis
TM
R
H
+ X+
REAGENT REACTION+CH2Cl CH2O/HCl/ZnCl2 Chloromethylation
+CHO CHCl3/
-OH Reimer-Tieman
Me2NCHO/POCl3VilsmeierHaak
-
R
X
SYNTHON
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Retrosynthesis of Piperonol Retrosynthesis of Piperonol (perfumery compound) & (perfumery compound) &
SynthesisSynthesis
FGI
OO
CH2Cl
C-C
chloro-methylation
OO
H
Synthesis
OO
CH2O/ZnCl2HCl
OO
CH2Cl
Oxidation
hexamine
TM
TM
CHO
OO
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AROMATIC SIDE CHAINS BY AROMATIC SIDE CHAINS BY Function Group Function Group InterconversionInterconversion
Y
R R
X
Y X Reagent
Reduction
-NO2
-NH2
H2, Pd, CSn,
conc.HCl-COR -CH(OH)R NaBH4
-COR -CH2R
Zn/Hg/conc.HCl
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AROMATIC SIDE CHAINS BY AROMATIC SIDE CHAINS BY Functional Group Functional Group InterconversionInterconversion
Y
R R
X
OxidationY X Reagent
-CH2Cl -CHO hexamine-CH2R -CO2H KMnO4
-CH3
-COR-OCOR R’CO3H
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Aromatic Side Chains by Aromatic Side Chains by Functional Group Functional Group InterconversionInterconversion
Y
R R
X
SubstitutionY X Reagent
-CH3
-CCl3 Cl2,PCl
5-CCl3
-CF3 SbF5-CN -COOH HO-, H2O
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Nucleophilic Aromatic Nucleophilic Aromatic Substitution ReactionsSubstitution Reactions
Addition of an oxygen atomto an aromatic ring
Add anionic reagents RO- to an Aromatic compound with a leaving Group.
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Nucleophilic Aromatic Nucleophilic Aromatic SubstitutionSubstitution
•Nucleophilic aromatic substitution works best when the leaving groups is N2 (diazonium salts)
•The synthetic sequence is nitration, reduction,diazotisationand substitution
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Nucleophilic Aromatic Nucleophilic Aromatic SubstitutionSubstitution
RHNO3
H2SO4R
NO2 H2
Pd,C
R
NH2NaNO2
HCl, 5oCR
N2+
H2O
R
OH
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Retrosynthesis of PhenolRetrosynthesis of Phenol
OH
BrMe
TM
subst.
via N2+
NH2
BrMe
C Br
bromination
NH2
Me
FGINO2
Me
C N
NitrationMe
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SynthesisSynthesis
Me
HNO3
H2SO4
NO2
Me
Sn/H+
NH2
Me
HOAcNHAc
Me
Br2
NaOH
NH2
BrMe
NaNO2/HCl
H2OTM
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Aromatic compounds made by Aromatic compounds made by nucleophilic displacement of nucleophilic displacement of
daizonium saltsdaizonium saltsArNH2
NaNO2
HClArN2
+ Z-
ArZ
Reagent_____ HO H2ORO ROHCN Cu(I)CNBr/Cl Cu(I)Br/Cu(I)ClI KIH H3PO2 or EtOH/H+
____Z_____
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Retrosynthetic analysis & Retrosynthetic analysis & synthesissynthesis
Me
CNSubst.
Me
NH2
FGI
Me
NO2
Me
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SYNTHESISSYNTHESIS
MeHNO3
H2SO4
Me
NO2
H2
Pd,c
Me
NH2
NaNO2,HClCu(I)CN
TM
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NUCLEOPHILIC NUCLEOPHILIC SUBSTITUTION OF SUBSTITUTION OF
HALIDESHALIDESDirect displacement of halide from anaromatic ring is possible only if :
There are ortho and para nitro groupsOR
Similar electron-withdrawing groups
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NUCLEOPHILIC NUCLEOPHILIC SUBSTITUTION OF SUBSTITUTION OF
HALIDESHALIDESCl
HNO3H2SO
4
Cl
NO2
NO2Nu-
Nu
NO2
NO2
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Retrosynthetic analysisRetrosynthetic analysisTrifluralin B- a herbicideTrifluralin B- a herbicide
NC3H7
CF3
NO2O2N
Cl
CF3
NO2O2N
Cl
CF3
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SYNTHESISSYNTHESIS
Cl
CF3
HNO3
H2SO
4
Cl
CF3
NO2O2N base
N-Pr2NH
TM