Page 186 - Academic Press Encyclopedia of Physical Science and Technology 3rd Organic Chemistry

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Encyclopedia of Physical Science and Technology EN007F-314 July 6, 2001 16:59

342 Heterocyclic Chemistry

Many heterocycles possessing rings with more than Like sulfur, selenium and, less commonly, tellurium
seven atoms are known, some of which are natural prod- form heterocyclic rings, such as selenophene and diben-
ucts. A recently discovered antibiotic, LL-Z1220, under- zotellurophene.
goes reversible valence isomerization to a 1,4-dioxocin,
an eight-membered heterocycle.
O O Se Te
selenophene dibenzotellurophene
boil, EtOAc
O O
O Ac 2 O, 60 °C O
Silicon, tin, and germanium, although in the same pe-
O riodic group as carbon, do not form stable double bonds;
O
consequently, their heteroaromatic derivatives are un-
interconversion of 1,4-dioxocin and antibiotic LL-Z1220
known. However, many saturated heterocyclic derivatives
are known, including 1,1-dimethylsilacyclohexane, ger-
F. Rings with Uncommon Heteroatoms macyclohexane, and 6-stannaspiro[5,5]undecane.
Nitrogen, oxygen, and sulfur are common, but by no
means the only known heteroatoms in heterocyclic rings. Sn
For example, iodonium salts can be prepared by treating Si Ge
Me Me H H
aminobiphenyls with nitrous acid, followed by ring clo-
1,1-dimethyl germacyclohexane 6-stannaspiro [5,5]
sure of the diazonium salt. silacyclohexane undecane

Finally, many boron heterocycles have been reported.
The procedure of hydroboration, chiefly for which H. C.
+
NH 2 N 2 I
I I + Brown received the Nobel Prize, is illustrated below; sub-
iodonium salts via diazotization sequent treatment with carbon monoxide affords replace-
ment of boron by carbon.
The corresponding chloronium and bromonium ions are
not very stable.
Phosphorus, arsenic, and antimony form heterocyclic B 2 H 6 1. CO, 150 °C H OH H
compounds fairly readily, especially the first two. B 2. NaOH, H 2 O 2
1-Phenylphospholane was prepared as early as 1916, and
H
withethyliodidegivesaquaternarysalt,justasdonitrogen carbonylation of a boron heterocycle
heterocycles.
A variety of boron heterocycles are known; one such is
EtI
+ _ prepared by reacting a borazine with biuret.
P P I
Ph Ph Et
Me
quaternization of 1-phenylphospholane O O B
HN NH
(MeBNH) 3 + 3 + 3NH 3
Phosphorins, in which phosphorus replaces one carbon H 2 N N H NH 2 O N O
atom in a benzene ring, can be prepared from pyrylium H
preparation of a boron heterocycle
salts.
Ph Ph It can be expected that many new boraheterocycles will
be prepared in the near future.
+ P(SiMe) 3
Ph O Ph Ph P Ph
+ _
I
preparation of 2,4,6-triphenylphosphorin
SEE ALSO THE FOLLOWING ARTICLES
Examples of arsenic and antimony heterocycles are
isoarsindoline and stibabenzene. ALKALOIDS • ANALYTICAL CHEMISTRY • BIOPOLYMERS
• ELEMENTAL ANALYSIS,ORGANIC COMPOUNDS • OR-
GANIC CHEMICAL SYSTEMS,THEORY • ORGANIC CHEM-
AsH
Sb ISTRY,COMPOUND DETECTION • ORGANIC CHEMISTRY,
isoarsindoline stibabenzene SYNTHESIS • ORGANIC MACROCYCLES