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Chapter-5
Synthesis of highly substituted pyrroles
R
O
R 0.1 eq. CuI
1
+ H 0.2 eq. N,N-dimethylglycine.HCl
2N R 3
R 2
Br
2eq.K 3 PO 4 ,2eq.NH 4 OAc
MeCN or toluene, reflux, 10 -20 R
h
1
Figure-20
Two methods for the regioselective synthesis of tetra- and trisubstituted N-H
pyrroles from starting vinyl azides have been developed: A thermal pyrrole formation
via the 1,2-addition of 1,3-dicarbonyl compounds to 2H-azirine intermediates
generated in situ from vinyl azides and a Cu(II)-catalyzed synthesis with ethyl
acetoacetate through a 1,4-addition (Figure-21). 39
R
R 3
N
R 2
Figure-21
An operationally simple, practical, and economical Paal-Knorr pyrrole
condensation of 2,5-dimethoxytetrahydrofuran with various amines and sulfonamines
in water in the presence of a catalytic amount of iron(III) chloride allows the synthesis
of N-substituted pyrroles (Figure-22) under very mild reaction conditions in good to
excellent yields. 40
Figure-22
A new and efficient three-component reaction between dialkyl
acetylenedicarboxylates, aromatic amines, triphenylphosphine, and arylglyoxals
afforded polysubstituted pyrrole derivatives in high yields (Figure-23). The reactions
were performed in dichloromethane at room temperature and under neutral
conditions. 41
Figure-23
Department of Chemistry, Saurashtra University, Rajkot-360005 165