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AUTHOR: Ahmed Jibrin Uttu
Compounds classified as heterocyclic probably constitute the largest and most varied family of organic compounds; they are compounds containing cyclic carbon in addition of one, two or many heteroatom in the ring. The heteroatom might be Nitrogen, Sulphur, Oxygen, Silicon, Phosphorus, selenium, etc.
Four Membered Heterocyclic Rings
Four (4) membered heterocyclic ring are heterocyclic compound which contain four atoms in the cyclic ring, one, two or three of the atom might be carbon and three, two or one of the atom might be hetero atom respectively. Heteroatom such as Oxygen ‘O’, Nitrogen ‘N’ and Sulphur ‘S’ are mostly common in the ring of heterocyclic compounds.
STRUCTURE AND NOMENCLATURE OF 4-MEMBERED HETEROCYCLIC RING
i) Monocyclic ring with one heteroatom
ii) Monocyclic ring with one heteroatom and one double bond
iii) Monocyclic ring with two heteroatoms
iv) Monocyclic ring with two heteroatoms and two double bond
v) Monocyclic ring with two different heteroatoms
vi) Monocyclic ring with two heteroatoms and one double bond
vii) Cationic monocyclic rings
viii) Methyl substitute attached to cyclic ring
SYNTHESIS OF 4-MEMBERED HETEROCYCLIC RING
1) Treating a 3-halo alcohol, thiol or amine with base:
2) Paterno-Buchi photocyclizations for oxetane formation:
3) Gem dimethyl substitution:
4) Rigid configuration of substrate:-
Because of strain in the ring, the synthesis of four member ring is irreversible, however some four member ring are made by SN2 displacement. Intermolecular SN2 displacement Cyclisation to give oxetane-2-ones (β-lactones)
a) Formal [2 + 2] cycloaddition:
b) Thermal cyclo addition of cumulene
c) β-Lactams from ketenes and immines (The Standinger reaction) The reaction goes through intermediates rather than by a pericyclic process
d) β-Lactam from Isocyanates and alkenes
REACTIVITY OF 4-MEMBERED HETEROCYCLIC RING
Reactions of four-membered heterocycles also show the influence of ring strain.
1) Acid-catalysis is a common features of ring opening reaction, four member heterocyclic ring also undergo acid-catalysis to open the ring
2) Thietane, sulphur undergoes electrophilic chlorination to form a chlorosulfonium intermediate followed by ring opening
3) Strong nucleophile will also open the straind ether
4) They also undergo intramolecular rearrangement to form an ortho-ester.
5) Azitidine-2-one bearing a potential leaving group in position 4 may also suffer nucleophilic attact at that carbon without ring opening
USES OF 4-MEMBERED HETEROCYCLIC COMPOUND
1) Paclitaxel (Taxol) is an example of a neutral product containing an oxetane ring; it is use in the treatment of cancer. The attached oxetane ring is an important feature that is use for the binding of microtubules in structure activity.
2) Penicillins: one of the first and still one of the most widely use antibiotic agents. It contain 4-membered ring “azetidinone”
3) Cephalosporin: Antibiotics that inhibit the synthesis of structural components of the bacterial cell wall. It contain 4-membered ring “azetidinone”
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