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GermanЧDanish Symposium on Organic Chemistry.

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After removal of the solvent at -20°C the deep red reaction mixture is dissolved in methylene chloride (20 ml) and
treated at - 20°C with [(C,H,), O ]BF, (5.70 g, 30 mmol) in
methylene chloride (20ml). The solvent is removed in a
vacuum, the residue extracted with n-hexane, and the
extract filtered and concentrated to a volume of 20ml.
Elution with n-hexane on a chromatographic column
(2 x 55 cm; Merck silica gel) prepared with hexane and
maintained at -10°C gives unreacted Fe(CO), and
Fe,(CO),,, as well as a yellow unstable oil that has not
yet been investigated. The next, deep red zone containing
the novel complex is eluted with hexane/benzene (3 :1). Recrystallization from pentane gives 250 mg of Fe,C, ,H,,O,,
(yield 1.6%).
Received: November 18,1971 [Z 561 IE]
German version: Angew. Chem. 84,214 (1972)
[I]
Transition metal carbene complexes, Part 41.-Part 40: E. 0. Fischer and M . Leupold, Chem. Ber. 105, 599 (1972).
[2] 1956 independent non-zero diffractometer data; R factor 0.06.
[3] 0. S . Mifis and A. D. Redhouse, J. Chem. SOC.A 1968,642.
C O N F E R E N C E REPORTS
German-Danish Symposium on Organic Chemistry
The Universities of Aarhus, Hamburg, Kiel, Copenhagen,
and Odense organised a German-Danish Symposium on
Organic Chemistry at Odense (Denmark) on September 4
and 5,1971.
From the lectures:
Structural Studies on Constituents of Umbelliferae[**I
By Bent Eichstedt Nielsed']
Coumarins, polyacetylenes, monoterpenoids, and sesquiterpenoids are examples of secondary plant constituents
that frequently occur in Umbelliferae.
The coumarins found in Umbelliferae include numerous
optically active compounds. The centers of chirality are
usually situated in the isoprenoid side chains, which are
linked either directly or via ether bonds to the aromatic
skeleton. Isoprenoid C, side chains may also be incorporated into a condensed heterocyclic ring system, as e . g. in the
dihydrofurocoumarins and dihydropyranocoumarins. Side
chains and ring systems of this type are also found in other
naturally occurring compounds, e. g. chromones, isoflavones, and quinoline alkaloids. Accordingly, investigations of the stereochemistry of these systems are of general
interest. Furthermore, knowledge of the stereochemistry
of the optically active coumarins is of interest for the study
of their biosynthesis.
Chemical correlations have been used for the stereochemical investigations on coumarins. Either optically active
degradation products were isolated and their configuration
determined by synthesis and comparison with compounds
of known configuration, or stereospecific syntheses were
carried out.
A number of dihydrofurocoumarins and dihydropyranocoumarins contain two centers of chirality in the basic
skeleton. One of these centers is at a benzylic carbon atom
[*I
Lektor Dr. B. Eichstedt Nielsen
Kemisk Laboratorium B
Danmarks farmaceutiske Hajskole
Universitetsparken 2
DK-2100 Kmbenhavn (D (Denmark)
p'] The experimental work was carried out by E. Lernmich, J. Lemmich, P . K . Larsen, B. E. Nielsen, and P. A . Pedersen.
Angew. Chem. infernat. Edit. 1 Vof. I 1 (1972) N o . 3
carrying either a hydroxyl or an acyloxy group which can
be removed upon hydrogenolysis. The product of hydrogenolysis can be compared with corresponding compounds
containing only one center of asymmetry whose configuration has been determined by degradation reactions. For
the compounds with two centers of chirality, it is then only
necessary to determine the relative configurations. This is
achieved e. g. by spectroscopic studies on synthetic epimers
or by observation of the thermal stability and of the reactivity toward mineral acids.
From our work on acetylenes and terpenoids, mention
may be made of the determination of the configuration of
the naturally occurring alkyne falcarinol and the isolation
and structural elucidation of some monoterpene esters
having a cyclohexadiene skeleton.
Catalysis by Phthalocyanine Complexes
By Heinz Kropf ['I
The phthalocyanine (Pc) complexes of Cu, Zn, Pd, Pt, Ag,
Hg, Ni, Fe, Co, and Mn catalyze the initial step in the autoxidation of benzene hydrocarbons, i . e. chain initiation in
the absence of hydroperoxide, by reaction of a metalPc-0, complex with the hydrocarbon. As soon as hydroperoxide is formed, other catalysis mechanisms are observed :
1. In the autoxidation of phenylalkanes and phenylcycloalkanes in the presence of the Pc complexes of Cu, Zn, Pd,
Pt, Ag, and Hg, the metal-Pc-0,
complex reacts with
dimeric hydroperoxide to form alkylperoxy radicals ; at
higher temperatures, the Pc complex itself reacts with dimeric hydroperoxide. In the autoxidation of diphenylcycloalkanes, the bimolecular collision of the dimeric hydroperoxide on the catalyst surface can be detected. The relative
reactivities of the phenylcycloalkanes and diphenylcycloalkanes can be explained by an extended I-strain theory.
2. The Pc complexes of Fe, Co, and Mn are deactivated by
monomeric hydroperoxide as a result of the formation of a
[*] Prof. Dr. H. Kropf
Institut fur Organische Chemie und Biochemie der Universitat
D-2 Hamburg 13, Papendamm 6 (Germany)
239
Pc-hydroperoxide addition product. The known secondary
catalysis occurs at the same time.
3. Ni-Pc is poisoned by chemisorption of products formed by a special chain termination reaction.
VO-Pc, on the other hand, catalyzes autoxidation entirely
by decomposition of the dimeric hydroperoxide on the
catalyst surface. In the presence of alkali metal-Pc, a basecatalyzed autoxidation occurs after a metal-hydrogen
exchange with hydroperoxide.
In the decomposition of cumyl hydroperoxide in the presence of Pc complexes, three groups of Pc complexes can be
distinguished :
Rearrangementsof Spirolactarnswith Synthetic
cis- and trans-Erythrinanes as Example
By Albert Mondon"'
Wolff-Kishner reduction of the bromo keto lactam ( I )
gives not only compounds having the erythrinane skeleton['] but also products with rearranged ring systems, such
as (2) and ( 5 ) . The structure of (2) is shown by the UV
spectrum with h, = 348 nm (log&= 4.281, which is similar
to that of 6-phenyl-a-pyridone and agrees with that of the
synthetic structural isomer (3)['I; an independent synthesis of (2) has recently been achievedc3],so that the structure
of the rearrangement product has now been fully verified.
1. Fe, Co, and Mn complexes: the Pc complexes are
attacked during the fast reaction.
2. Ni, Cu, Zn, Mg, and AI(0H) complexes: reaction
proceeds much more slowly, and the Pc complexes remain
unchanged.
%%
R
3. VO-Pc : decomposition proceeds autocatalytically
R
Finally, Pc complexes (Ni > Fe >Co >Cu) have been found
to be hydrogenation, dehydrogenation, and hydrogenolysis catalysts in the system ally1 alcohol/n-propanol/propionaldehyde/acroIein; the products formed on hydrogenolysis are propane, propene, and allene or propyne, depending on the Pc complex used. In the case of Cu-Pc, sudden
changes in activity occur at 280-290°C; these may be
explained by phase transformations.
R
R
R
R
/%
R
R
(4)
Photochemistry of Aromatic Amine Oxides
q
By Christian Lohse[*]
The photoisomerization of isoquinoline N-oxides such as
( I ) [ ' ] to isocarbostyrils ( 2 ) in polar solvents and benz[f][1,3]oxazepines ( 3 ) in non-polar solvents could be shown
to proceed via singlet excited states.
Earlier reports have explained the solvent effect on the
product distribution in these rearrangements in terms of a
possible oxaziridine intermediate. This compound could
not be observed,in fact laser experimentsshowed the formation of isocarbostyril from isoquinoline N-oxide within the
time of a laser puke (20 ns)"].
R
R
A triplet excited state of isoquinoline N-oxides was observed, and it could be shown that this state is responsible for
the deoxygenation of the N-oxides to the parent amines.
This process can be used for oxidation of organic compounds in their excited state to yield products different
from those obtained by ground state oxidations.
OH
11
f2)
p] Dr. C. Lohse
Odense Universitet,
DK-5000 Odense (Denmark)
[I]G. G. Spence, E . C. Taylor, and 0.Buckardt, Chem. Rev. 70, 231
(1970).
[2] C . Lohse, J. Chem. SOC., in press
240
Closely related to the structural elucidation of ( 5 ) are
comprehensive studies on a phenomenon that was first
observed for the dihydroxy lactam ( 4 ) and its diacetate
(6) 14]. Though the acetylation and hydrolysis are trivial
reaction steps, they each involve a rearrangement of the
skeleton, which can be detected only through the NMR
spectra. Whereas ( 4 ) , as a typical trans-erythrinane, gives
two widely separated singlets for the two aromatic protonsts1, (6) gives only one singlet for two protons at a
relatively high field strength.
['I
Prof. Dr. A. Mondon
Institut fur Organische Chemie der Universitat
D-23 Kiel, Olshausenstrasse 40/60 (Germany)
Angew. Chem. internat. Edit. 1 Vol. I 1 (1972) No. 3
Since the NMR spectra of ( 5 ) and its acetate agree with
that of (6) in the region of the aromatic protons, ( 5 ) and
(6) should have the same basic skeleton. The interconversion of these compounds has not yet been achieved, but
the new ring system has been confirmed for (6) by degradation reactions and for ( 5 ) by independent synthesis of the
compound containing no hydroxyl groups.
After reaction with HF for 24 hours, tetrabenzoylarabinopyranose ( I ) gives the benzoxonium ion ( 2 ) , which is
converted into (3) on reaction for a further 3 to 4 days.
The inversion on C-2 is thus followed by a ring contraction.
When tetrabenzoylxylopyranose ( 4 ) is dissolved in HF,
the very stable dibenzoxonium ion ( 5 ) is formed in the
course of 24 hours, with inversion on C-2 and C-3.
Degradation of the mesylate acetate (7) corresponding to
the diacetate (6) to give the carboxylic acid ( 9 ) was recently
reportedr4].Thermal decarboxylation leads to the saturated
lactam ( l o ) and to the unsaturated lactam ( I I ) , which is
formed by cleavage of the C-N bond and a hydrogen
shift. An interesting reaction is the extensive rearrangement
of ( 9 ) by dilute sulfuric acid, which leads on gentle heating
to the excellently crystallizing yellow chelate (12). The
amide obtained from homoveratrylamine and 2,2-ethylenedioxy-I-cyclohexanecarboxylic acid also gives (12) on
Bischler-Napieralski ring closure, and so confirms its
structure.
Many other carbohydrate esters also react with inversion
and/or ring contraction on treatment with anhydrous
hydrofluoric acid. Thus some glucofuranose, mannofuranose, and glucopyranose derivatives give the same
stable dioxolanylium ion (6) on treatment with H F for
24 to 48 hours.
The ring system of ( 5 ) can also be synthesized directly
from 3-0x0-I-cycloheptanecarboxylic acid and homoveratrylamine via the hydroxy lactam (13) by ring closure
with hydrofluoric acidt6]; the excellently crystallizing
cyclization product (8) is found to be identical with the
compound containing no hydroxyl group that is obtained
from ( 5 ) on reduction of the tosylater3].
[l] A . Mondon, Chem. Ber. 104,270 (1971).
[2] R . Schickfluss, Diplomarbeit, Universitat Kiel 1965.
[3] A . Mondon and E. Oelrich, unpublished.
[4] S. Mohr, A. Mondon, G. Vilhuber, and Chr. Fischer, Angew. C:hem
81,933 (1969); Angew. Chem. internat. Edit. 8, 914 (1969).
[S] A. Mondon and P.-R. Seidel, Chem. Ber. 104,2937 (1971).
[6] G. Aunianri, Diplomarbeit, Universitat Kiel 1970.
Rearrangementof CarbohydrateEsters with
Anhydrous Hydrofluoric Acid
By Christian Pedersed']
Carbohydrate esters form glycosyl fluorides after reaction
for a short time (approximately 15 min) with anhydrous
hydrofluoric acid ; longer exposure leads to further reactions. These reactions have been followed with the aid of
the NMR spectra in hydrofluoric acid as the solvent.
CBH5
RCOO
To gain a better understanding of these reactions, the
behavior of some model compounds toward H F was investigated. Esters of cis-1,2-cyclohexanediol react with H F
to form dioxolanylium ions. If the mixed esters (7) are
used as the starting materials, the isomeric ions (8) and ( 9 )
may be formed. Our investigations have shown that this
reaction is kinetically controlled, and that the less stable
ion is often formed. Thus the acetate nitrobenzoate (7),
R=CH,, R' =p-N02C6H4, yields only the nitrobenzoxonium ion (Y), R' =p-N0,C6H4, whereas the acetate
methoxybenzoate (7), R = CH,, R' =p-CH30C6H4,yields
only the acetoxonium ion (8), R=CH,. cis-1,2-Cyclopentanediols behave similarly.
To determine the thermodynamic stability of the dioxolanylium ions, the reaction between esters of 1,5-anhydroarabinitol (10) and H F was investigated. (10) reacts with
H F to give mainly the ion (If), which exists in equilibrium
with the isomeric ion (12). The position of this equilibrium
is an expression of the relative stabilities of these two ions.
When ( l o ) ,R=CH,, R'=C6H5, is dissolved in HF, only
the benzoxonium ion (12) is obtained (NMR spectrum).
Only the acetoxonium ion (111, on the other hand, is formed from ( l o ) , R=CH,, R1=p-N02C6H4.From these and
other experiments it can be concluded that the stabilities of
the dioxolanylium ions vary as follows with the substituent
on C-2: p-N0,C6H4<CH,<C6H, <p-CH,0C6H4
= p-CH,C,H.+.
Free-Radical Alkylation with Sulfoxides
and Fenton's Reagent
By Kurt Torssell[']
Methyl radicals ( 1 ) are formed in the Fe3+-induced decomposition of hydrogen peroxide in DMSO"]. They have
p] Prof. Dr. C. Pedersen
Organisk-kemisk Laboratorium
Danmarks tekniske Hojskole
DK-2800 Lyngby (Denmark)
Angew. Chem. internat. Edit. 1 Vol. I1 (1972) 1 No. 3
[*] Prof. Dr. K. Torssell
Chemical Institute, University of Aarhus
DK-8000 Aarhus C (Denmark)
241
also been detectedL3]by the nitroxide method[21, in a
quantity so large that we found it interesting to check the
reaction on a preparative scale.
CHj
+
R’NO
-
0‘
I
R ’ - N- C H3
(1)
The nitroxide method has been largely used in our laboratory for the detection and structural elucidation of radicals,
and it is also suitable for use as a kind of “synthetic spectroscopy” for the interpretation of free-radical reactions. It
was found that reactive substrates such as quinones, nitroaromatic compounds, thiophenes, furans, pyridines, and
quinolines could actually undergo free-radical substitutionC4].Benzene, benzoic acid, indole, and simple alkenes
are alkylated only in traces, if at all. Diethyl, dibutyl, and
tetramethylene sulfoxides have been used with varying
success as alkylating agents/solvents. Iron(@ sulfate was
OH
found to be most suitable as the catalyst. On photolysis of
hydrogen peroxide in DMSO, the alkylated product was
formed in a lower yield.
Trinitrobenzene gave e. g. trinitrotoluene (25“C,1.5 equivalents of H,O,, 0.2 equivalents of FeSO,, 1 hour) in 67%
yield. The products (2) -( 7 ) were formed from benzoquinone. Methyl 5-nitrofuran-2-carboxylate gave the products (8) -( l o ) , the formation of which can be explained
by free-radical attack on C-5, C-4, and C-2 respectively.
The replacement of the nitro group by methyl is remarkable.
The reaction course can be represented by the reaction
sequences (1 and (2).
[I] W T. Dixon, R . 0 . C. Norman, and A. L. Buley, J. Chem. SOC.1964,
3625.
[21 s. Forshuk c. Lagercrantz, and K . Torssell,Acts Chem. S c a d .
23, 522 (1969); K. Torssell, Tetrahedron 26, 2759 (1970).
[3] C. Lagercrantz and S. Forshuk, Acta Chem. Scand. 23, 811 (1969).
[ 4 ] 8 . - M . Bertilsson. B. Gustafson, J . Kuhn, and K. Torssell, Acta
Chem. Scand. 24, 3590 (1970); U . Rudquist and K . Torssell, ibid. 25,
2183 (1971).
I
Fez+ + CH 3-S-C H3
I
1.
OOH
EPR Spectroscopy as a Method of Conformational Analysis
By Jiirgen VOSS~‘]
On the basis of the Heisenberg uncertainty principle
V
At x A H
> 5.7
x IO-*gausss
it is shown that the EPR time scale allows the observation
of states with lifetimes of the order of microseconds. Thus
species that are converted into one another by rotation
[*I
242
Dr. J. Voss
Institut fur Organische Chemie und Biochemie der Universitat
D-2 Hamburg 13, Papendamm 6 (Germany)
Angew. Chem. internat. Edit. / Vol. I 1 (1972) 1 No. 3
about formal single bonds appear as distinct isomers, and
it is difficult to differentiate conceptually between conformers and configurational isomers.
This phenomenon is illustrated by the radical-anion of
terephthalaldehyde. Its EPR spectrum shows the presence
of a cis form and a trans form together, the lifetimes of these
forms being 5 x lo-’ s[‘~.Similarly, the preparation of biacetylsemidione yields a mixture of isomers in which the
trans form predominates in a ratio of 95 :5. The configuration can be assigned on the basis of steric considerations
and particularly of the complex-forming properties (only
the cis form gives a Li chelate)[’!
Conformation analysis in the true sense is possible by EPR
spectroscopy with the aid of the relation
a:H
B p,
cos2
e
HFS coupling constant
B = constant of proportionality
a& =
p, = spin density
For example, from the coupling constants of the alkyl
protons in the radical-anions of oxalic esters (“dialkoxysemidiones”), it is possible to determine the time-averaged
dihedral angle 0 between the C-H bond and the z axis of
the z-electron system[31.For primary alkyl groups, 8 =47”,
while for secondary alkyl groups, 0 = 60” ; these values can
be shown to be plausible by estimation of the space requirements from Newman projections. This also provides
an explanation for the surprisingly small value 8 = 42 for
the neopentyl ester, while the deviation from the normal in
the case of the cyclobutyl derivative (e=49’) is attributed
to ring strain.
An example of the determination of a dynamic quantity is
the calculation of the activation energy E,= 8.6k0.5 kcal/
mole for the rotation of the angled N O group of the nitrosobenzene radical-anion from the temperature dependence
of its EPR ~pectrum‘~].
[ V B 128 IE]
German version. Angew. Chem. 84, 219 (1972)
[1]
[2]
[3]
[4]
A . H . Mnki, J. Chem Phys. 35,761 (1961).
G. A . Russell and R. D.Stephens, J. Phys. Chem. 70, 1320 (1966).
J . Voss, Tetrahedron 27, 3753 (1971).
W Karninskr and K . MBbrus, 2. Naturforsch. ZSa, 635 (1970)
Reactions and Compounds with Molecular Nitrogen
By Wilhelm Preetz‘”
It has recently been shown that molecular nitrogen, which
was previously considered to be very inert, can undergo a
number of chemical reactions under mild conditions.
Because of the importance of nitrogen assimilation in
Nature, a great deal of interest has been shown in the
search for models displaying the ability to bind nitrogen.
Since transition metal ions appear to play a key role in the
enzymatic fixation of nitrogen attention has mainly been
directed to the following two possibilities:
1. Complexes with elements of the higher sub-groups, i. e.
of the type [Ru(NHJ5(N 2)]C1,, which were discovered by
Allen and SenojJ[’l;
2. The binding of nitrogen by Ziegler catalysts, e. g. Cp,TiC1,
(Cp = n-cyclopentadienyl), and reduction to ammonia in
the presence of organomagnesium compounds, as was first
reported by Volpin and Shur”].
Comparison of the electronic structure of the N, molecule
with those of the isoelectronic ligands CO, CN-, C,H,,
and N O + reveals only slight differences. Because of its
stable triple bond, low polarizability, and weak donor
properties, the N, molecule is the least conducive to bonding. The best partners prove to be metal ions having a fully
occupied t,, level (d6 system) in which the electrons are
not too firmly bound. The most favorable of such partners
are, therefore, low-valency transition metals of the higher
groups which are able to effect back-bonding on donation
of electrons to the unoccupied z*-state of the N, molecule.
A maximum stability seems to occur with 0s”.
In the complexes previously isolated and characterized by
structural analysis, the nitrogen is bound to the metal ion
in the direction of its molecular axis (M :N-N :; “end
on”). In the case of enzymatic nitrogen fixation, however,
bonding cia the n-system perpendicular to the molecular
+
N
axis (M + 111 ; “edge on”) must be taken into consideration
N
since, e.g., C,H, inhibits uptake of N,. All mononuclear
nitrogen complexes (the known symmetrical binuclear
complexes[31of the type M-N-N-M
are excluded here)
show an intense, sharp IR band in the range 2050-2150
cm- which is indicative of an “end on” bonded N, molecule. Compared with the known stretching vibration at
2331 cm- in the Raman spectrum of free N,, a long-wave
shift of about 200--250cm-’ is observed in the case of
nitrogen complexes, corresponding to the loosening of the
bond between the N atoms; simultaneously the N-N bond
length, which is 1.098 A in the free molecule, increases by
about 0.02A. The degree of loosening of the bond-as
shown by IR spectroscopic investigations-is very much
dependent on the nature of the nearest and near neighbors.
’,
All nitrogen complexes are reactive and therefore suitable
for planned substitution reactions. Much preparative work
remains to be done to establish the most favorable metal
ions for bonding to N, and the most suitable ligand environment, thus opening a wide new field of study in coordination
chemistry.
Lecture at Kiel on October 28. 1971 [VB 332 IE]
German version: Angew. Chem 84, 267 (1972)
Institut fur anorganische Chemie der Universitat
23 Kiel, Olshausenstrasse 40-60 (Germany)
[I]A . D. Allen and C. V. Senofi Chem. Commun. 1965,621.
[2] M . E. Volpin and V: B. Shur, Nature 209, 1236 (1966).
[3] C. M . Elson, J . Gulens, and J . A. Page, Can. J. Chem. 49.207 (1971).
Angew. Chem. internat. Edit. 1 Vol. 11 (1972) 1 N o . 3
243
[*] Prof. Dr. W. Preetz
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