HeteroCyclic System for Pharmacy students

Five-membered Heterocycles L.3
Pyrrole, Furan and Thiophene

Objectives:

1-To identify types of five membered heterocyclic compounds
2- To know their sources .
3-To know syntheses methods of five membered heterocyclic compounds
4-To understand their chemical reactions .

A. Five-membered Rings with one Heteroatom
1) The main reason for the study of pyrrole came from the work on the structure of heme;the blood respiratory pigment, and the chlorophyll; the green photosynthetic pigment of plants.
2) Thiophene and its derivatives occurs in petroleum.
3) Furan occurs widely in secondary plant metabolites, especially in terpenoids.
Unsubstituted pyrrole, furan, and thiophene are usually obtained from petroleum.
4) Pyrrole, furan and thiophene are colorless liquids of boiling points 126o, 32o, and 84oC respectively.
5) Pyrrole has a relatively high boiling point as compared to furan and thiophene, this is due to the presence of intermolecular hydrogen bonding in pyrrole.

Structure and Aromaticity
? Pyrrole furan and thiophene are aromatic because:
1) they fulfill the criteria for aromaticity, the extent of delocalization of the nonbonding electron pair is decisive for the aromaticity.