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New Aromatic Systems.

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dichloroisobutene with tetracarbonylnickel leads t o 1,4,7trimethylenecyclononane in good yield, and this reaction
with magnesium gives a series of macrocyclic and openchain oligomers as well as methylenecyclopropane and 1,4dimethylenecyclohexane.
Y
The symmetrical structure of a,a’-disubstituted isobutenes
permits a double allylic rearrangement in accord with the
general scheme ( 3 ) + ( 4 ) + ( 5 ) . These reactions have been
Xr
Ar
Ar
If all three aromatic rings carry hydroxyl groups, compounds
(6) are obtained which can be oxidized to triquinonoid
cyclopropanes (7). Compounds (7) are stable, dark purple
solids with a quite new electronic structure.
specially studied in connection with the Claisen rearrangement; examples are rearrangement of isobutenylenedicarboxylic esters by N a H to y-methylenepimelic acids and of aryl
ethers of isobutenediol at 200 “C to bisphenols. Further,
interesting thermal rearrangements can be effected with
cyclic ethers of isobutenediol: At 450 “ C 5-methylene-l,3dioxanes give the isomeric methylallyl ester and, if C-2 carries
a vinyl group, also the isomeric glutaraldehydes. At 200°C
3,4-dihydro-3-methylene-2H-[l.5]benzodioxepin
gives a 2,4cyclohexadienone by a (presumably stepwise) Claisen rearrangement, and at 450°C this is further converted into
isomeric products consisting mainly of a furylcyclopentenone.
Lecture at Miilheim/Ruhr on November 21, 1968
German version: Angew. Chem 81, 191 (1969) [VB 181 TE]
. .~
In the redox processes (6) z? ( 7 ) , anion radicals and monoradicals can be shown by ESR spectroscopy to occur as intermediates and they can be characterized.
Lecture at Giessen (Germany) o n December 17, 1968,
and at Braunschweig (Germany) on November 4, 1968 [VB 183 IEl
German version: Angew. Chem. 81,229 (19691
[*I Dr. F. Weiss
Ugine Kuhlmann, Centre de Recherches de Lyon
F-69 Pierre-Benite (France)
New Aromatic Systems
[*I Prof. R. West
Department of Chemistry, University of Wisconsin,
Madison, Wisc. 53706 ( U S A )
Present address:
Institut fur Organische Chemie der Universitat
87 Wiirzburg, Rontgenring 7 1 (Germany)
By R . Wesf[*1
It has recently been recognized that the cyclic anions C,Otof squaric acid ( I ) . croconic acid (2), and rhodizonic acid
( 3 ) form a homologous series of aromatic compounds.
Studies on the Mechanism of Mixed Function
Oxygenations
By V. Ullrichl*I
Mixed function oxygenations occur according to the equation:
R H + DH2+
Structural studies show that these anions have symmetric,
planar structures with considerable r;-bonding contributions
from the C-C bonds. The properties of the substances are,
in general, in good agreement with predictions of the HiickelLCAO-MO theory.
Reaction of tetrachlorocyclopropene with AIC13 leads to t h e
trichlorocyclopropenylium ion ( 4 ) , which is an aromatic
system where the C-C bonds are even stronger than i n
benzene. One, two, or three of the chlorine atoms can be
replaced by aryl groups when C3C13’ is treated with aromatic
hydrocarbons.
(4)
If one of the aromatic rings carries a para-hydroxy group,
the triarylcyclopropenylium ion i s readily deprotonated to a
quinonoid system ( 5 ) .
Angew. Chem. internat. Edit.
Vol. 8 (1969) 1 No. 3
0 2
+
ROH$ D t
HrO
where R H is an organic substrate and DH2 is a reduced
hydrogen-donor. The very complicated course of these
enzymatic reactions can be considered according to three
points of view:
1. How is the oxygen molecule activated? 2 . How are the
electrons transferred t o the oxygen? 3. How is the electron
transport coupled with the hydroxylation of the substrate?
To obtain an insight into the activation ofthe oxygen molecule
the model systems described previously “1 have been developed further. Reduction of oxygen by the iron(1r)-thiosalicylic
acid complex leads to an electrophilic oxenoid complex [**I
which hydroxylates aliphatic and aromatic compounds and
compounds containing isolated double bonds in the same
way as enzymically activated oxygen does. A decisive role i n
this system is played by sulfur as ligand, which in combination with the Fez+ ion makes two-electron reduction of the
oxygen molecule possible.
In many mixed-function oxygenases cytochrome P 450
participates in the activation of oxygen. A reaction velocity
fl/, of about 300 msec and 1:l stoichiometry have been
established for its reaction with oxygen. The unusual spectral
and chemical properties of cytochrome P 450 can be explained
on the basis of its function as a two-electron donor.
219
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