5-membered rings containing heteroatom11
One hetero atom11 Figure 1.3: Structure showing the heterocyclic compound having one hetero atom
Two hetero atoms Figure 1.4: Structure showing the heterocyclic compound having two hetero atoms
6-membered ring containing heteroatom11 Figure 1.5: Structure showing the six membered heterocyclic compounds
Unsaturated and saturated heterocyclic compound12 Figure 1.6: Structure of saturated and unsaturated heterocyclic compounds
1.7 AZOLES
Azoles are the class which contain five member ring, having nitrogen heterocyclic ring compound containing at least one other heteroatom (or non-carbon atom) of nitrogen, sulfur or oxygen and are considered to be derived from pyrrole, furan and thiophene by substitution of methane groups (―CH=) by pyridine type nitrogen (―N=) atoms from the different positions. Azole mainly consists of:
(i) Oxygen is referred as oxazole
(ii) Sulphur is referred as thiazole and
(iii) Nitrogen is referred as pyrazole, imidazoles or imidazolines12.
1, 3-Azoles synthesis12
Scheme 1.1: Synthesis of 1, 3-Azoles by Cyclodehydration of α-acylaminocarbonyl compound12
1.8 OXAZOLE
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During the world war when penicillin was considered to contain the oxazole ring system at that time the chemistry of oxazole was come in concern, but the invention of oxazoles as dienes in Diels-Alder reaction and in 1, 3-dipolar cycloaddition reaction of mesoionic heterocycles give idea for progress of oxazole chemistry. Oxazole contain an oxygen atom and a pyridine type nitrogen atom at the 1 and 3 positions of the ring and like pyridine, oxazole are weekly basic substances. Oxazole be considered as derived from furan by the replacement of –CH= (methane group) from the position-3 by the azomethine nitrogen (-N=) group13. Oxazole ring is numbered as