Lect.1hetero.pdf_50235

Pharmaceutical Organic Chemistry III
POC2031
A: Heterocyclic Compounds
Lect. 1
Nomenclature of monoheterocyclic comp.

Heterocyclic compounds are rings containing in addition to carbon one or
more heteroatoms ( usually O, N, S or Se).
*** Importance of heterocyclic chemistry;
Heterocycles occur in nature (carbohydrate, nucleic acids & haeme), vitamins
(Vit B6, Vit B1), several synthetic drugs and antibiotic.
N
Pyidine
N
H
Pyrrole
Nomenclature of heterocyclic compounds:
I- Nomenclature of Monocyclic heterocycles:
1-IUPAC name:

1-The IUPAC name consist of:
Prefix + Stem + Suffix
Indicates the heteroatom
Table 1
Indicate the ring size & unsaturation
Table 2
*** and the name is preceded by the substitutents.
Table1: Prefixes in order of decreasing priority.
Element valence prefix
O II Oxa
S II Thia
Se II Selena
N III Aza
P III Phospha or phosphor
before in or ine
Si IV Sila
B III Bora
***The final a in the prefix (e.g. oxa) is omitted if followed by a vowel.

Table2: (stem+suffix) indicating ring size and unsaturation
(Hantzsch-Widman system stems).
Ring Size Unsaturated Saturated Ring
Size
Unsaturated Saturated
3 irene/irine irane/iridine 7 epine epane
4 ete etane/etidine 8 ocine ocane
5 ole olane/olidine 9 onine onane
6 ine ane/inane 10 ecine ecane
A (O, S, Se) B (B, N)
2-Begin numbering from the heteroatom with highest priority in table1 &
continue in the direction that gives the next heteroatom the lowest possible
number.
If there is a choice, give the lowest possible number to the saturated positions.

Examples:
thiepine
oxocane
1,5-diazocine
1
O
7
2
S
1,3-dioxolane
6 S
3
5
4
1,3-thiazole
1,2-oxathiolane
1,2,6-oxadithiepane
1,2,5-oxazaphosphole
7
1
O
NH
2
6
O
3
5
4
1,6,2-dioxazepane

N.B. Selecting the stem+suffix names for:
a) 3-, 4-, or 5-membered rings
(i) The stem ‘irine’ is used in place of ‘irene’ for rings containing only nitrogen
otherwise the stem ‘irene’ is used.
Examples:
H
N
O
1H-azirine oxirene oxazirene
N
O
(ii) The stems ‘iridine’, ‘etidine’ and ‘olidine’ are used when nitrogen atoms are
present in the ring; otherwise the ‘ane’ stems are used.
Examples:
NH
O
1
O
S
2
1
O
2
PH
azetidine oxetane 1,2,3-oxathiazolidine 1,2-oxaphospholane
NH
3

) six-membered rings:
Depends on the least senior heteroatom in the ring, i.e., the heteroatom whose
name directly precedes the ending.
(O, S, Se) → take the stem ane for saturated rings,
(B, N) → take the stem inane for saturated rings (Table 2).
The stem is selected in accordance with the group to which the least senior
heteroatom belongs.
O
N
P
O
1,4-dioxine
N N
1,3,5-triazine
O
P
P
NH
1,3,5-triphosphinine
1,3-oxazinane

2-Common name:
a-Unsaturated five memebered:
N
H
S
O
Pyrrole Thiophene furan
(1H- azole) (thiole) (oxole)
N
N
N
N
H
S
O
Imidazole Thiazole Oxazole
1H-1,3-diazole 1,3-thiazole 1,3-oxazole

-Unsaturated six memebered:
N
N
N
N
N
N
N
Pyridine pyridazine pyimidine pyrazine
d-Saturated six memebered:
H
N
O
N
H
N
H
N
H
piperidine piperazine morpholine

II-Nomenclature of Fused Ring Heterocycles:
A-Many fused heterocyces have common names which were accepted in the IUPAC.
The most important heterocycles having accepted (common) names are the following:
6
7
8
5
4
5 4
3
6
3
2
N:
Ṇ .
1
7
8
1
2
quinoline
isoquinoline
6
7
5 4
N
8 1
quinazoline
N 3
2
5
6
4
7
Indole
3
N 1
H
2
*Denotes exception to systematic numbering