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On the Intermediate Occurrence of 1 2-Cyclohexadiene.

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On the Intermediate Occurrence of
1,2-Cyclohexadiene
By Prof. G. Wittig and Dr. P. Fritze
Institut fur Organische Chemie,
Universitat Heidelberg (Germany)
1,3-Diphenylbenzo[c]furan ( I ) has proved of particular
value for the detection of lower-membered cycloalkynes [I].
In order to ascertain that it is cyclohexyne which is trapped,
in accordance with equation (a), and not perhaps 1,2-cyclohexadiene, we have generated the cyclic allene by an independent route and allowed it to react with ( I ) .
Sublimed potassium t-butoxide was treated with l-bromocyclohexene in dimethyl sulfoxide in the presence of ( I ) for
several hours at 40OC. Chromatography on A1203 then
gave, among other products, two compounds, ( 3 4 (m.p.
137-138 "C) and (3b) (m.p. 195-196 "C), in a total yield of
37 %; these are isomers of compound (2) (m.p. 170-171 "C)
and are clearly differentiated from it by mixed melting
point determinations and by I R and N M R spectroscopy.
Whereas only aliphatic and aromatic protons can be recognized in the spectrum of (
2), the spectra of (3u) and
(3b) both show a multiplet at o = 4.3, due to an olefinic
proton. This indicates that the exo- and endo-isomers of
1,2-~yclohexadieneadducts have been formed. Control experiments confirmed that the uNene was trapped: compound
(2) does not isomerize to (3u) or (3b) under the conditions
used.
Synthesis of 2,4,6-Tricyanopyndine 1-Oxide from
Nitroacetonitrile
Bv Prof. K.-D. Gundermann and Dr. H.-U. Alles
Organisch-Chemisches Institut, Bergakademie-Technische
Hochschule, Clausthal-Zellerfeld (Germany)
In order to obtain a further protected 2-nitroacrylic acid
derivative[ll, we treated potassium mi-nitroacetonitrile,
m.p. 150-155 "C (decomp.), obtained from nitroacetonitrile
in anhydrous ether and an equivalent amount of a solution
of potassium methoxide in anhydrous methanol, in 4 0 %
aqueous solution with about the two-fold molar amount of
formaldehyde solution at room temperature; on vacuum
evaporation of thz mixture we isolated potassium 3-hydroxy2-nci-nitropropionitrile ( I ) , yield 75 %, m.p. 188-120 "C
(decomp.) (from methanol/ether). When kept for 24 hr in the
seven-fold volume of 2 N sulfxic acid, this salt evolves
nitrogen oxides and gives 2,4,6-tricyanopyridine 1-oxide (2),
yield ca. 50 '4, m.p. 222°C (from acetone/water). The
structure of the oxide (2) was ascertained by elemental
analysis, molecular-weight determination, N M R spectrum
(only a sharp singlet at T -= 8.82 ppm), mass spectrum (peak
at M-16; characteristic for N-oxides [2, *I), and IR spectrum.
Reduction of the oxide (2) for 3 hr with iron powder and
glacial acetic acid/acetone at 95 "C, extraction of the basic
components with sodium hydroxide/ether/acetone, evaporation of the ethereal solution, heating of the residue with
HCl in anhydrous methanol, and treatment of the concentrated methanol solution with potassium carbonate gave
the known trimethyl 2,4,6-pyridinetricarboxylatein ca. 60 %
yield.
Duden and Ponndorf[31 obtained a compound C5H2N407 of
then unknown structure from potassium 2,2-dinitroethanol
(3) and dilute sulfuric acid; from its mode of formation and
I R and N M R spectra this is also a substituted pyridine
1-oxide, namely, (4). The compounds (2) and ( 4 ) are strong
electron acceptors and with, e.g., dimethylaniline give deep
red or violet n-complexes.
Studies of the general applicability and mechanism of this
new synthesis of substituted pyridine 1-oxides are in progress;
reaction presumably occurs by way of Dewar-pyridine
derivatives.
/
[Z 3001El
Received: July 25th. 1966
German version: Angew. Chem. 78, 906 (1966)
Treatment of 1-bromocyclohexene with potassium t-butoxide
on dimethyl sulfoxide in the absence of ( I ) affords in 7 %
yield a hydrocarbon (m.p. 53-54 "C) whose structure (4) was
proved by its mass spectrum, elemental analysis, NMR, infra= 237 mp, log E = 4.1761,
red, and ultraviolet spectra ,,A(
and a diene reaction with tetracyanoethylene to give (5) [21.
In contrast, reaction of 1,2-dibromocyclohexene with lithium
amalgam or magnesium gives a trimer, (C&8)3, and a
tetramer, (C6H8)4, whose structures and probable modes of
formation have been determined [31.
Analogous experiments have been carried out on compounds
with 7- and 8-membered rings [41.
[Z 298 I€]
Received: July 28th, 1966
German version: Angew. Chem. 78, 905 (1966)
[I] G . Witgig acd A . Krebs, Chem. Ber. 94,3260 (1961); G . Witfig
and R. Pohlke, ibid. 94, 3276 (1961).
[2] Cf. W. J. Bull and S. R. Lundor, J. chem. SOC.(London)
1962, 2298.
[3] G . Wittig and U.Muyer, Chem. Ber. 96, 342 (1963); G. Wittig
and J. Weinlirh, ibid. 98, 471 (1965).
141 P. Fritzt, J. Schiiller, and H . L. Dorsch, Dissertations,
Universitat Heidelberg, 1966.
846
[*] Prof. W. Liittks and Prof. G . Spiteller, Gottingen, to whom
we are indebted for measurement of the NMR and mass spectra,
first suggested, on the basis of the spectroscopic results, that
compound (2) was a symmetrical tricyanopyridine 1-oxide and
not, as we had then assumed, 3,5,7-tricyanooxazepine.
[ l ] K.-D. Gundermnnn and H . - U . Alles, Angew. Chem. 77, 812
(1965); Angew. Chern. Internat. Edit. 4, 788 (1965).
[2] T . A. Bryce and J. R. :Maxwell, Chem. Commun. 1965, 206.
[3] P. Duu'en and G . Punndurf, Ber. dtsch. chem. Ges. 38, 2031
(1 905).
2,4,6-Triphenylphosphabenzene
By Dr. G . Mark1
Institut filr Organische Chemie,
Universitat Wiirzburg (Germany)
The reaction of phenylphosphine with 2,4,6-triphenylpyrylium tetrafluoroborate ( I ) [11 is to be interpreted as involving the intermediate formation of a cation (2) that is unstable
under the reaction conditions.
Angew. Chem. internat. Edit. 1 Vol. 5 (1966)
1 NO.9
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