вход по аккаунту


Aromatic Sigmatropic Rearrangements.

код для вставкиСкачать
The relevant publications from the Hahn-Meitner-lnstitut,
numbering fourty up to the present, were reviewed.
[VB 121 IE]
Lecture at Darmstadt (Germany) on May 28, 1968
German version: Angew. Chem. 80, 706 (1968)
[*] Prof. Dr. K. E. Zimen
Hahn-Meitner-Institut fur Kernforschung
1 Berlin 39, Glienicker Str. 100 (Germany)
Study of the Mechanism of Dehydrogenase
Reactions by Measurement of the Isotope Effects
By D . Palm [*I
Classical kinetic methods for the study of enzyme reactions
have recently been extended by methods for selective determination of fast or slow steps in complex reaction sequences.
Slow and irreversible steps can be detected also in enzyme
kinetics by differences in the reaction rate of isotopically
labeled substrates. This is particularly so for the isotope
effects (IE’s) of the hydrogen isotopes, for which primary and
secondary IE’s can be detected 111. Thus hydrogen transfer in
NAD-dependent dehydrogenases is particularly suited for
investigation of the empirical and theoretical relation of IE
to enzyme-kinetic values.
The primary IE (4.1 to 6.8 at 25OC) for the substrates
[I-TI-ethanol, -1-propanol, and -1-butanol confirm the required rate-determining hydrogen transfer for alcohol dehydrogenase (ADH) from yeast, but an increase in IE with
rising temperature also shows a change in the rate-determining step. For the ADH of liver the small secondary IE
(1.4 to 1.6 at 25 “C) for the homologous alcohols is in agreement with a rate-determining dissociation of the enzyme
NADH complex, which is independent of the substrate.
The reverse reaction, studied with the stereospecifically
labeled [A-4-T]NADH again shows primary IE’s of 2 to 5
(depending on the corresponding homologous aldehydes) for
yeast enzyme, whereas only a small difference from unity was
found for the liver enzyme. The sterically hindered substrate
2-methylcyclohexanone for Iiver ADH stands out with an
IE of 3.6; since 2-[methyZ-T]methylcyclohexanone reacts
4.5 % faster, the site of steric hindrance can be more accurately localized [ZJ.
In the case of lactate dehydrogenase of rabbit muscle the IE
of 2.5 for ~-[ZT]lactatecorresponds to a product of two
secondary IE‘s, which are due to isomerization and dissociation of the enzyme-NADH complex. This interpretation
excludes a kinetic influence of ternary complexes. The reverse
reaction with [A-4-T]NADH also shows an IE of up to 2.0
that indicates isomerizations, but under the influence of
pyruvate inhibition at concentrations > 1 x l o - 3 ~the IE
Finally, a mechanism similar to that for yeast ADH can be
ascribed to glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.
[VB 161 IE]
Lecture at Konstanz (Germany), on May 30. 1968
German version: Angew. Chem. 80, 706 (1968)
[*I Doz. Dr. D. Palm
Chemisches Institut Weihenstephan und
Organisch-Chemisches Institut der Technischen Hochschule
8 Munchen, Arcisstr. 21 (Germany)
[l] H. Simon and D . Palm, Angew. Chem. 78,993 (1966); Angew.
Chem. internat. Edit. 5, 920 (1966).
121 D. Palm, Z. Naturforsch. 216, 540, 547 (1966); D. Palm,
T. Fiedler, and D . Ruhrseitz, ibid. 236, 623 (1968).
Oxidation of Pyrrolic Impurities in Polyamides
By P. Schlack[*l
When prepared under not quite perfect conditions, polyamides may contain pyrrole groups formed in side reactions
and detectable by Ehrlich’s reagent. In nylon 6 (polycapro-
lactam) pyrroles are observed particularly if 1,Il-diaminoundecanone is formed by loss of water and COz from two
moles of 6-aminohexanoic acid or if the corresponding anhydro base is formed from c-caprolactam by loss of water.
This ketimine is very sensitive to oxygen and after autoxidation gives an intense pyrrole reaction.
Polycaprolactam fibers (“Perlon”) that contain units of this
imine show a strong tendency to yellow on fairly long exposure to light in the presence of oxygen or on thermal oxidation. Rochas and Martin have found that polyamide fibers
(nylon 66) may also give a positive pyrrole reaction after
photoxidation 111. They assumed that the pyrroles were formed by reaction of amino end groups in the fiber with a,cr’-dioxoadipic acid formed by oxidation of adipyl groups. Mar&
and Larch came to the conclusion that it was almost wholly
the diamine groups that were involved in pyrrole formation;
they held that primary attack by the oxygen was always o n
the methylene groups next to the amide nitrogen 121.
In studies of the yellowing of polyamide textiles in our Institute, F. Sommermann [31 found that pyrroles are also formed
on oxidation of N-free olefinic substances such as 3-heptene,
oleic acid, methyl linoleate, and squalene in the presence of
prjmary amines or amino acids and also on subsequent addition of such amines. Since sweat contains glycerides of polyunsaturated fatty acids, squalene, ammonium salts, and other
nitrogenous bases, pyrroles or their colored oxidation products could be formed on textile substrates even without
chemical participation of the fiber substance.
Only the primary amino end groups of the fiber come into
question as a nitrogen source for pyrrole formation within
the fiber substance. If however, the amino groups are inactivated by acylation, e.g. by acetic anhydride [4J, then pyrrole
can no longer be formed on the fiber unless ammonia or
amino groups are newly formed. Autoxidation in light is then
also greatly hindered. Most of the amino groups can be
blocked under remarkably mild conditions that can be realized in practice, nameIy, by impregnating the textile goods
with solutions of anhydride-forming aromatic polycarboxylic
acids, e.g. trimellitic acid, then drying them, and heating
them for one to two minutes at 170-180°C by passage
through a thermofixing apparatus. The tendency to yellowing
is much reduced by this pretreatment.
From the UV spectra of the dyes formed in the fiber by p (dimethy1amino)benzaldehyde it can be concluded that both
a- and P-methine dyes occur side by side, whereas the dyes
formed from unsaturated fatty acid esters and amino acids
appear to consist mainly of @-derivatives.
[VB 164 IE]
Lecture at Karlsruhe (Germany) on May 30, 1968
German version: Angew. Chem. 80, 761 (1968)
[*I Prof. Dr. P. Schlack
Deutsche Forschungsinstitute fur Textilindustrie
Institut fur Chemiefasern
7 Stuttgart-Wangen, Ulmer Strasse 227 (Germany)
(11 P. Rochas and J . C. Martin, Bull. Inst. Textile France 83, 41
[2] B. Marek and E. Lerch, J. SOC. Dyers Colourists 81, 481
[3] F. Sommermann, unpublished.
[4] F. H . Steiger, Textile Res. J. 27, 459 (1957); see also [I].
Aromatic Sigmatropic Rearrangements
By Hans Schmid [ *I
Aromatic sigmatropic rearrangements are thermal reactions
whose transition states can, to a first approximation, be
considered as interaction complexes between two pseudoradical halves that have arisen by homolysis of the bond that
is attacked. At least one of these halves must be aromatic in
nature, i.e. its x-system is to be described by aromatic molecular orbitals. A well-known example is the thermal Claisen
rearrangement of ally1 aryl ethers that occurs with inversion
Angew. Chem. internat. Edit.
Vol. 7 (1968) 1 No. 9
of the ally1 group. The transition state for the sigmatropic[3,3]-reactions involved (allyl aryl ether z 2-allyl-3,5-cycloare conhexadien-1-one e 4-allyl-2,5-cyclohexadien-l-one)
trolled in accord with the Woodward-Hoffmann rules by
suprafacial-suprafacial interaction of the single occupied $2
of the allyl radical and the singly occupied $4 of the phenoxy
radical (cf. ref. ill).
Aryl propargyl ethers behave like allyl aryl ethers. Their
thermal ring closure to chromenes, observed by Iway and
Ider21 does not occur directly, but by a [3,3]-sigmatropic
rearrangement, followed by enolization to o-allenylphenol
which even a t about 80°C undergoes a n aromatic Il,5]hydrogen shift and thereupon a n electrocyclization to the
chromene t31.
The rearrangement of 3-(1-methyl-2.2,2-trichloroethylidene)1,4-cyclohexadiene to 1-methyl-4-(2,2,2-trichloroethyl)benzene which occurs at 20-70°C and was observed by von
Auwers[4Jmay also be a suprafacial C,C-[1,5] aromatic sigmatropic reaction that is controlled by the $ 3 of the tolyl
radical and the p-orbital of the CCl;. However, this would
lead to a very strained transition state.
On the basis of the MO diagrams the formation of o-(1-vinylally1)phenol (13.31-rearrangement) and of p-(2,4-pentadienyl)phenol ([5,5]-rearrangement) is to be expected in the thermolysis of 2,4-pentadienyl phenyl ether. Experiments with substituted ethers have given the following’series:~[5.5] > [3,3]
:;,([1,5]?) [SJ.
Sigmatropic rearrangements in polar systems occur particularly rapidly when the charge is better distributed in the
transition state than in the starting materials. In the dienolbenzene rearrangement of 2-allyl-2-methyl-3,5-cyclohexadien-1-01 and 4-allyl-4-methyl-2,5-cyclohexadien-l-of
p-toluenesulfonic acid in ether at -40 “ C the products formed,
with loss of water, are those expected from the MO diagram
of the tolyl radical, $2 of the allyl radical), namely: oallyltoluene by [1,2]-, m-allyltoluene by [3,3]-, and p-allyltoluene by [3,4]-rearrangement. It is always the allyl group
that migrates, in the first reaction without and in the others
necessarily with inversion “1.
The rearrangement of 2- and 4-allylcyclohexadienones t o
allylated phenols effected by B U , 167 occurs similarly. Competing reactions for the crotyl and dimethylallyl compounds
are heterolysis to the phenolic compound and crotyl-cation
or dimethylallyl-cation.
Sigmatropic reactions may also play a part in other aromatic
rearrangements (e.g. the “acid-catalyzed‘’ and the thermal
Fischer indole synthesis f79.
Lecture at Heidelberg (Germany) o n May 1, 1968
[VB 163 IEI
German version: Angew. Chem. 80, 760 (1968)
[*] Prof. Dr. Hans Schmid
Organisch-Chemisches Institut der Universitat
CH-8001 Zurich, Ramistrase 76 (Switzerland)
[l] H.-J. Hansen, B. Sutter, and H . Schrnid, Helv. chim. Acta 51,
828 (1968).
[2] I. Zwui and J. Ide, Chem. pharmac. Bull. (Tokyo) 10, 926
(1962); ZI, 1042 (1963).
[3] J. Zsindely and H. Schrnid, Helv. chim. Acta 51 (1968), in
[4] K. v. Auwers and W. Jiilicher, Ber. dtsch. chem. Ges. 55,2167
[ 5 ] G y . Fruter and H. Schrnid, Helv. chim. Acta 51, 190 (1968).
161 H. Schmid, Gazz. chim. ital. 82, 968 (1962); R. Burner, J.
Borgulya, H.-J. Hansen, J . Zsindely, and H. Schntid, unpublished.
[7] H. J. Shine: Aromatic Rearrangements. Elsevier, Amsterdam
1967, p. 124.
The preparation of a,@-unsaturatedketones by oxidative decarboxylation of y-0x0 carboxylic acids with lead dioxide has
been described by D . V. Hertzler, J. M . Berdahl, and E. J .
Eisenbraun. With y-0x0 carboxylic acids having no alkyl or
aryl substituents in the a or positions, the yield does not exceed 40 %; 84 % of ketone was obtained in the most favoracid). / J. org. Chemable case (3-benzoyl-2-phenylpropionic
istry 33, 2008 (1968) / -Kr.
[Rd 878 IE]
methyl peroxide (2), which is converted by hydrolysis into
bistrifluoromethyl bisperoxycarbonate (3) or triff uoromethyl
hydroperoxide ( 4 ) , depending o n the conditions. Prolonged
photolysis of ( 1 ) leads to bistrifluoromethyl peroxide ( 5 ) .
have been prepared
The new fluorocarbon peroxides (2)-(7)
by R . L. Tulbott. The photolysis of an equimolar mixture of
bis(fluoroformy1) peroxide ( I ) and difluorodiazine in a
quartz apparatus yields infer alia fluoroformyl trifluoro-
[Rd 879 IE]
FCO- 0 -0-COFS CFzN2 +
- ---+
+ by-products
CF3-0- 0-COF
+ by-products
FCO-0 0- COF + CF3-O-O-CF3
-t by-products
CF3-0 -0-CF(0F)-O--O-CF3
Atrgsw. Chern. interrrnt. Edit. i Vol. 7 (1968) ,! No. 9
The low-temperature fluorination of (2) and (3) leads to
fluoroxydifluoromethyl trifluoromethyl peroxide ( 6 ) and
fluoroxybis(trifluoromethy1peroxy)fluoromethane (7). The
new peroxides (2)-(7) are colorless gases or liquids with
high vapor pressures, which are stable for some time at room
temperature. / J. org. Chemistry 33, 2095 (1968) / -Kr.
The thermal rearrangement of phenylnitrene into cyclopentadienecarhonitrile has been studied by E. Hedaya, M. E.
Kent, D. W. McNeil, F. P. Lossing, and 7‘.McAllister. The
mass spectra recorded during the decomposition of phenyl
azide could be best explained by the assumption of the following reactions:
C ~ H S - N+
~ C6Hs-N:+
2 GjHs-N: + C ~ H S N = N C ~ H S
+ H (wall) + C~HS-NH
2 C~HS-NH + C ~ H ~ - N H - N H - C ~ H S
C6Hs-NH-C- H (wall) + CsHs-NHz
C6H5-N: +
74 1
Без категории
Размер файла
255 Кб
rearrangements, sigmatropic, aromatic
Пожаловаться на содержимое документа