heterocyclic rings thiophene. importance pyrantal 49, is a broad spectrum anthelmintic agent (...
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Heterocyclic Rings
Thiophene
Importance• Pyrantal 49, is a broad spectrum anthelmintic agent ( للديدان طاردeffective against pinworm and hookworm (المعوية
• Bioten50 (Vitamin H),, occurs in yeast and egg• Thiophene also occurs in organic conducting polymers
Ring SynthesisThe Pall Synthesis
• Lawesson's reagent can be used also in this synthesis.
Applications of Lawesson’s reagent
N N
NN
O
CH3Ph
N N
NN
S
CH3PhLR
The Hinzberg Synthesis
The Gewald Synthesis
Reactions of Thiophene• Electrophilic Substitution Substitution takes place at the 2- position • Reactivity pyrrole >> furan > thiophene > benzene• Thiophene tends to undergo substitution rather than addition
reactions and it is not so readily cleaved by acids as is furan.
Substitution of 2-substituted thiophene
S Me
S CHO
S MeO2N
S CHO
O2N
S CHOO2N
nitration
+
3 :1 ratio
electron releasing
electron withdrawing
Nucleophilic Substitution
Cycloaddition Reaction Thiophene is a poor diene
S O
O
O
O
O
O
O+
Diels-Alder Cycloaddition
Cycloadditions of thiophene
