Page 68 - Org 3 theoritical book 2024-25
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Clinical Pharmacy PharmD - 2024/2025 Level 2 Pharmaceutical Organic Chemistry-3 (PC 305)
II- Six-Membered Rings With Two Nitrogen Atoms
The six-membered ring systems containing two nitrogen atoms can exist in the
following three isomeric structures:
N N
N
N N N
Pyridazine Pyrimidine pyrazine
(1,2-diazine) (1,3-diazine) (1,4-diazine)
a) Pyridazines
Pyridazines can be prepared by the action of hydrazine on unsaturated 1,4-
diketones
R
C R
O H N
+ 2 N
O H N N 3,6-dialkylpyridazine
C 2
R R
Pyridazine itself may be prepared from maleic dialdehyde and hydrazine hydrate.
The 3,6-dihydroxypyridazine is the tautomeric form of maleic acid hydrazide.
They form the dichloro derivative on treatment with POCl 3, which gives
pyridazine on hydrogenation.
O O H Cl
N H N POCl 3 N H / Pd N
2
N H N N N
O OH Cl
maleic acid 3,6-dihydroxypyridazine
hydrazide
b) Pyrimidines
Pyrimidines occur in many compounds vital to living systems. Hydrolysis of
nucleic acid gives the following pyrimidine bases:
