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Pharmaceutical Organic Chemistry III<br />
POC2031<br />
A: Heterocyclic Compounds<br />
Lect. 1<br />
Nomenclature of monoheterocyclic comp.
Heterocyclic compounds are rings containing in addition to carbon one or<br />
more heteroatoms ( usually O, N, S or Se).<br />
*** Importance of heterocyclic chemistry;<br />
Heterocycles occur in nature (carbohydrate, nucleic acids & haeme), vitamins<br />
(Vit B6, Vit B1), several synthetic drugs and antibiotic.<br />
N<br />
Pyidine<br />
N<br />
H<br />
Pyrrole<br />
Nomenclature of heterocyclic compounds:<br />
I- Nomenclature of Monocyclic heterocycles:<br />
1-IUPAC name:
1-The IUPAC name consist of:<br />
Prefix + Stem + Suffix<br />
Indicates the heteroatom<br />
Table 1<br />
Indicate the ring size & unsaturation<br />
Table 2<br />
*** and the name is preceded by the substitutents.<br />
Table1: Prefixes in order of decreasing priority.<br />
Element valence prefix<br />
O II Oxa<br />
S II Thia<br />
Se II Selena<br />
N III Aza<br />
P III Phospha or phosphor<br />
before in or ine<br />
Si IV Sila<br />
B III Bora<br />
***The final a in the prefix (e.g. oxa) is omitted if followed by a vowel.
Table2: (stem+suffix) indicating ring size and unsaturation<br />
(Hantzsch-Widman system stems).<br />
Ring Size Unsaturated Saturated Ring<br />
Size<br />
Unsaturated Saturated<br />
3 irene/irine irane/iridine 7 epine epane<br />
4 ete etane/etidine 8 ocine ocane<br />
5 ole olane/olidine 9 onine onane<br />
6 ine ane/inane 10 ecine ecane<br />
A (O, S, Se) B (B, N)<br />
2-Begin numbering from the heteroatom with highest priority in table1 &<br />
continue in the direction that gives the next heteroatom the lowest possible<br />
number.<br />
If there is a choice, give the lowest possible number to the saturated positions.
Examples:<br />
thiepine<br />
oxocane<br />
1,5-diazocine<br />
1<br />
O<br />
7<br />
2<br />
S<br />
1,3-dioxolane<br />
6 S<br />
3<br />
5<br />
4<br />
1,3-thiazole<br />
1,2-oxathiolane<br />
1,2,6-oxadithiepane<br />
1,2,5-oxazaphosphole<br />
7<br />
1<br />
O<br />
NH<br />
2<br />
6<br />
O<br />
3<br />
5<br />
4<br />
1,6,2-dioxazepane
N.B. Selecting the stem+suffix names for:<br />
a) 3-, 4-, or 5-membered rings<br />
(i) The stem ‘irine’ is used in place of ‘irene’ for rings containing only nitrogen<br />
otherwise the stem ‘irene’ is used.<br />
Examples:<br />
H<br />
N<br />
O<br />
1H-azirine oxirene oxazirene<br />
N<br />
O<br />
(ii) The stems ‘iridine’, ‘etidine’ and ‘olidine’ are used when nitrogen atoms are<br />
present in the ring; otherwise the ‘ane’ stems are used.<br />
Examples:<br />
NH<br />
O<br />
1<br />
O<br />
S<br />
2<br />
1<br />
O<br />
2<br />
PH<br />
azetidine oxetane 1,2,3-oxathiazolidine 1,2-oxaphospholane<br />
NH<br />
3
) six-membered rings:<br />
Depends on the least senior heteroatom in the ring, i.e., the heteroatom whose<br />
name directly precedes the ending.<br />
(O, S, Se) → take the stem ane for saturated rings,<br />
(B, N) → take the stem inane for saturated rings (Table 2).<br />
The stem is selected in accordance with the group to which the least senior<br />
heteroatom belongs.<br />
O<br />
N<br />
P<br />
O<br />
1,4-dioxine<br />
N N<br />
1,3,5-triazine<br />
O<br />
P<br />
P<br />
NH<br />
1,3,5-triphosphinine<br />
1,3-oxazinane
2-Common name:<br />
a-Unsaturated five memebered:<br />
N<br />
H<br />
S<br />
O<br />
Pyrrole Thiophene furan<br />
(1H- azole) (thiole) (oxole)<br />
N<br />
N<br />
N<br />
N<br />
H<br />
S<br />
O<br />
Imidazole Thiazole Oxazole<br />
1H-1,3-diazole 1,3-thiazole 1,3-oxazole
-Unsaturated six memebered:<br />
N<br />
N<br />
N<br />
N<br />
N<br />
N<br />
N<br />
Pyridine pyridazine pyimidine pyrazine<br />
d-Saturated six memebered:<br />
H<br />
N<br />
O<br />
N<br />
H<br />
N<br />
H<br />
N<br />
H<br />
piperidine piperazine morpholine
II-Nomenclature of Fused Ring Heterocycles:<br />
A-Many fused heterocyces have common names which were accepted in the IUPAC.<br />
The most important heterocycles having accepted (common) names are the following:<br />
6<br />
7<br />
8<br />
5<br />
4<br />
5 4<br />
3<br />
6<br />
3<br />
2<br />
N:<br />
Ṇ .<br />
1<br />
7<br />
8<br />
1<br />
2<br />
quinoline<br />
isoquinoline<br />
6<br />
7<br />
5 4<br />
N<br />
8 1<br />
quinazoline<br />
N 3<br />
2<br />
5<br />
6<br />
4<br />
7<br />
Indole<br />
3<br />
N 1<br />
H<br />
2<br />
*Denotes exception to systematic numbering