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Chapter-5
Synthesis of highly substituted pyrroles
Figure 12
2-Acylaziridines undergo ring expansion reactions to provide pyrroles
involving ring-opened dipolar intermediates (Figure-13). 22
Figure-13
Vinylazirines also undergo ring expansion reactions, but two isomeric pyrroles
are obtained depending on the reaction conditions. Thermal reactions involve a
nitrene intermediate, while photochemical reaction proceeds via a nitrile ylide
intermediate (Figure-14). 23
Figure-14
The complex ring systems, formed by (3+2) cycloaddition of activated alkynes
substituted with electron-withdrawing substituents, with mesoionic heterocycles,
undergo extrusion reactions with the cleavage of larger ring leaving the pyrrole ring
system intact (Figure-15). 24-26
Figure-15
Department of Chemistry, Saurashtra University, Rajkot-360005 162