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Oxidation of 5-Aminotetraazoles a New Route to Isocyanides.

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or glyoxylates and subsequent
']-is, however,
unsuitable for the preparation of simpler alkylidenemalondialdehydes (with R', R 2 = H or alkyl).-Introduction
of two
geminal formyl groups by Vilsmeier formylation meets with
success only in special casesc4!
We have now found that the alkylidenemalondialdehyde
tetramethyl bisacetals (4a)-(4 d ) can be prepared by Wittig
olefination of the mesoxaldialdehyde tetramethyl bisacetal
(3)[5 with the intermediary alkylidenetriphenylphosphoranes
[ I ] Syntheses with Substituted Malondialdehydes, Part 22. This work was
supported by the Fonds der Chemischen Industrie and the Deutsche
21 : C. Reichardr and K . Halbrirter,
Angew. Chem. 87, 124 (1975); Angew. Chem. Int. Ed. Engl. 14, 86 (1975).
[2] R. B. Woodward, Angew. Chem. 78, 557 (1966); R. B. Woodward. K .
Heusfer,J. Gosreli, P. Naegeii, W. Oppoizer, R . Ramage, S. Ranganarhan,
and H . Vorbriiggen, J . Am. Chern. SOC.88, 852 (1966).
[3] R. E . Woodward, French Pat. 1495047 (1967); Chem. Abstr. 69. 51640r
[4] G. A. Reynolds and J . A. VanAllen, J. Org. Chem. 34, 2736 (1969):
C: Dressler and K . Borlendorf, Arch. Pharm. (Weinheim) 303, 481 (1970);
J. Piernik, Collect. Czech. Chem. Commun. 37, 2273 (1972).
[5] A. Maschkeand H. Pnsedach, DBP 1905603 (1969). BASF; Chem. Abstr.
73, 87436a (1970); cf. also C. Reichardr and E.-U. Wiirrhwein, Synthesis,
1976, in press.
[6] H . J . Besrmann and E . Kranz, Chem. Ber. 105, 2098 (1972).
[7] W Pressler, Dissertation, Universitat Marburg 1975; E.-b'. Wurrhwein,
Dissertation, Universitit Marburg 1975.
[8] A . Maercker, Org. React. 14, 270 (1965), especially pp. 388 and 402ff.
Oxidation of 5-Aminotetraazoles, a New Route to Isocyanides[**]
By Gerhard Hojle and Bernd Lunge[*]
For the synthesis of the cyclopropylidene compound (4d)
the cyclopropylidenetriphenylphosphorane(2 d ) , obtained by
reaction of an excess of the corresponding phosphonium salt[61
with potassium tert-butoxide in benzene, was heated under
reflux for three days with (3). Subsequent distillation afforded
( 4 d ) as a colorless liquid [b.p. 105--106"C/12 torr, yield
89 % based on (3); 'H-NMR (CDCIJ: F = 1.20 (s, 4 cyclopropyl H), 3.32 (s, 120CH3),and 4.90ppm (s, 2CH)].
The acetals ( 4 a ) - ( 4 c ) were obtained in 50, 38, and 26 %
yield, respectively, on stirring a mixture of (3) 20 h at room
temperature with the ylides (2a)-(2c),
prepared with
phenyllithium in ether (see Experimental procedure). Subsequent distillation followed by preparative gas-chromatography
of the crude products so obtained afforded analytically pure,
colorless, readily volatile liquids whose elemental analyses,
mass, IR, and 'H-NMR spectra were consistent with the
given constitutions. The compounds (4a)-(4 d) are valuable
starting substances for the synthesis of substituted malondialdehydes and heterocycles['!
Isopropylidenemalondialdehyde tetramethyl bisacetal ( 4 a)
An ethereal solution of phenyllithium, prepared by reaction
of bromobenzene(l3.0g, 83 mmo1)with lithium shavings (1.9g,
274 mmol) in dry diethyl ether (150ml), is added rapidly under
N to a suspension of isopropyltriphenylphosphonium bromideC8](23.1g, 60mmol) in diethyl ether (200ml). After one
hours' stirring (3) (10.0 g, ca. 90 % pure, ca. 50 mmol) is added
dropwise within 2Omin. The viscous suspension is stirred for
20 h at room temperature; the solvent is then removed by
distillation (maximum bath temperature 60°C). The remaining
yellow-brown hygroscopic solid is heated to 225°C at ca.
0.2 torr, whereupon (4a) distils over at 55-57"C/0.2 torr
as crude product (8.0g, ca. 65% pure); overall yield [based
on pure (3) and (4a)l ca. 50%. Further purification of the
product is accomplished by preparative gas chromatography
(Perkin-Elmer F 21, 2 m x 23 mm column with 5 % SE-30
on Chromosorb G N A W at 135"C and a column feed-pressure
of 1.6kp/cm2 N2). 'H-NMR (CDC13): 6= 1.88 (s, 6CH3), 3.36
(s, 12 OCH3), 4.85 ppm (s, 2CH).
Received: December 2, 1975 [Z 359 IE]
German version : Angew. Chem. 88.88 (1976)
CAS Registry numbers:
f 2 a ) . 16666-80-1 ; / 2 b ) , 1754-88-7; i 2 c i . 3487-44-3; (2d). 14633-95-5:
( 3 ) . 19256-30-5: (4a1, 57842-93-0: (4h), 57842-94-1 ; ( 4 ~ ) 57842-95-2:
( l d j , 57842-96-3
Angew. Chem. I n r .
Ed. Engl.
Vol. 15 (1976) N o . 2
Attempis to prepare the unknown compounds
gave US cause to search for reagent-free
isocyanide syntheses. The thermal or photochemical fragmentation of imino-substituted cyclic compounds according to the
following scheme1'] appeared promising :
As concerted processes these reactions are not symmetry
forbidden since the isocyanide fragment can be extruded in
a linear or nonlinear manner13'; they ought to proceed particularly easily provided particles X of low energy are formed.
We report here on a model reaction in which one molecule
of isocyanide (3) and two molecules of nitrogen are formed
from 5-iminotetrazoles (2) in a [2+2 + 23 cycloreversion.
Starting materials for the synthesisof (2) were the 5-alkyl(ary1)aminotetrazoles (/), which are readily accessible from commercially available S-amin~tetrazole'~~
or monosubstituted
Oxidation of ( I a)-(I c) [R: seeTable 11leads to liberation
of two moles of nitrogen and formation of the isocyanides
(3a)-(3 c) or the corresponding N-substituted formamides.
The pentaazafulvenes (2) presumed to be formed as intermediates could neither be detected, even at - 20"C, nor trapped
with N-phenylmaleimide or acetylenedicarboxylates. Oxidation. with sodium hypobromite in aqueous medium and with
lead tetraacetate/triethylamine in dichloromethane proved to
be preparatively useful, while bromine/triethylamine and anodic oxidation['] are less promising.
As an alternative to the oxidative degradation of ( 1 ) we
attempted the elimination of sodium toluenesulfinate from
the salt (4a), which is formed by tosylation of ( I a) in sodium
hydroxide. ( 4 a ) was found to be unexpectedly stable; it starts
[*] Priv.-Doz. Dr. G. Hone and DipLChem. B. Lange
lnstitut fur Organische Chemie der Technischen Universitit
1 Berlin 12, StraBe des 17. Juni 135 (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschafl.
[4] R . A. Henq and W G. Finnegan, J. Am. Chem. Soc. 76, 926 (1954).
[5] R . Stolle, J. Prakt. Chem. 134, 288 (1932); W L. Gorbrecht and R.
M . Herbst, J. Org. Chem. 18, 1278 (1953).
[6] Conditions: Carbon rod as anode, cylindrical copper cathode (length
3.5cm). electrode gap 2cm, 2 N sodium hydroxide without diaphragm.
Table I. Prepared isocyanides ( 3 ) . All compounds are spectroscopically
pure and were isolated by distillation.
Yield [%] [a] o n using
Pb(OAc)J Br,/NEt3
NEts CCl
oxidation [h]
as oxidizing agent
Simple Synthesis and Resolution of a Diaza[7]helicene[**l
[a] Yields can he improved.
[h] In 2 N sodium hydroxide solution.
[c] In dichloromethane.
By Hermann Rau and Otto Schuster[*]
Diazahelicened'l containing a -N=N-grouping
the structural elements of aromatic azo compounds. Since
azo compounds behave spectroscopically and photochemically
differently from the analogous carbon compounds on account
of the longwave n+n* transition[z], such diazahelicenes can
be expected to display interesting properties.
to dccomposeat 280 "C,whereby, in addition to other unidentified products only small amounts of isocyanide are formed. Irradiation in aqueous solution led to the same result.
Phenyl isocyanide ( 3 a )
A solution of lead tetraacetate (2.7 g, 6.1 mmol) in dichloromethane (50ml) is added dropwise within 15min at 20°C
to a stirred solution of 5-phenylaminotetrazole (1 a)['] (0.89g,
5.5 mmol) and triethylamine (1.3 g, 12.9mmol) in dichloromethane (20ml). The theoretical quantity of nitrogen is liberated. The dark-colored reaction mixture is concentrated in
a vacuum at room temperature and the isocyanide ( 3 a )
extracted with petroleum ether; yield after concentration and
distillation in a bulb-tube: 0.4Og (70 %), b. p. 7O0C/2Otorr.
n-Bury1 isocyanide ( 3b )
To a solution of n-butylaminotetrazole ( I b ) 14] (6.25 g,
44.3mmol) in 2N sodium hydroxide (50ml) is added 50ml dichloromethane and the mixture stirred during dropwise addition of sodium hypobromite solution (4.9mmol) at 0°C (ca.
15 min). The aqueous phase is then extracted several times with
dichloromethane, the combined organic phases dried over
MgSO,, and the solvent removed by distillation through a
40-cm packed column. Distillation of the residue affords (3b)
b.p. 119-12OoC, in 75% yield (2.77g).
Benzyl isocyanide ( 3 c )
To a solution of 5-benzylaminotetrazole ( I c)I4] (1.22g,
7mmol) in 2~ sodium hydroxide (50ml) is added 20ml ether at
0°C. The stirred mixture is electrolyzed for 4 h at 3.8V and
0.55A[']. The aqueous phase is extracted serveral times with
ether, the combined organic phases dried'with MgSO, and
concentrated in uacuo. Distillation of the residue in a bulb-tube
affords ( 3 c ) , b.p. 10O0C/16 torr in 48" yield (0.39g).
Received: November 28, 1975 [Z 350 IE]
German version: Angew. Chem. 88, 89 (1976)
CAS Registry numbers:
( l a j , 14832-59-8;( l b ) , 57885-60-6;( l c ) , 14832-58-7;
( 3 a ) , 931-54-4;( 3 b ) . 2769-64-4;( 3 c ) , 10340-91-7
G. Hofle, Z . Naturforsch., in press.
[2] Known, e.9.. are the cleavage of a-iminolactones: K . Bott, Tetrahedron
Lett. 1968, 3323; H. Kagen and I . Liifien, J. Org. Chem. 31, 3728 (1966);
of iminocyclopropanes: H . Quast and W Rider, Angew. Chem. 85. 411
(1973):Angew. Chem. Int. Ed. Engl. 12,414(1973)and of diaziridinimines:
H . Quast and E. Schmitt, Angew. Chem. 81.428 (1969); Angew. Chem.
Int. Ed. Engl. 8, 448 (1969).
[3] R. B. Woodw,ard and R. Hofmann: The Conservation of Orbital Symmetry.
Verlag Chemie, Weinheim 1970,pp. 152ff.
We report here on a simple and very productive two-step
synthesis of the diazadibenzo[7]helicene (4)[31 and on its
A suspension of 6-aminochrysene ( I ) (0.01 mol) in glacial
acetic acid (20ml) and conc. hydrochloric acid (7ml) was
diazotized to (2) with a solution of sodium nitrite (0.7g)
in water (3ml). The cold solution was buffered with sodium
acetate (3g, anhydrous) in water (1 5 ml) and then treated
dropwise with a saturated solution of sodium sulfite (1.55g)[']
in water, whereupon 6,6'-azochrysene ( 3 ) precipitated out.
After 10 minutes at 7 0 T , (3) was filtered off, washed, and
dried; yield 98 %. A sample of the product, after recrystallization from toluene, was found to transform without melting
at 268 "C into a yellow fluorescent solid which was not identical
with the helicene (4).-Crude
( 3 ) was dissolved in conc.
sulfuric acid and precipitated almost quantitatively as helicene
(4) on careful addition to water. After purification on a silicagel-60 column with benzene, (4) was obtained as a yellow,
strongly fluorescing substance of m. p. 345 "C.
The structure of ( 4 ) was confirmed by mass and C D spectra.
The rapid quantitative transformation of (3) into ( 4 ) is surprising, for this would require that (3) be present only in
the cis form.
The resolution of ( 4 ) was carried out with the n complexing
agent TAPA, synthesized according to Newman's methodL6I.
( 4 ) and a threefold excess of (-)-TAPA were treated at 40°C
with just sufficient chloroform to dissolve them. After one
day at 4°C dark-red crystals of the complex of (-)-TAPA
and an enantiomer of ( 4 ) had precipitated out. The crystals
[*] Prof. Dr. H. Rau and DipLChem. 0. Schuster
Institut fur Chemie, Fachgebiet Physikalische Chemie der Universitat
Garbenstrasse 30,7000 Stuttgart 70 (Germany)
[**] This work was supported by the Deutsche Forschungsgemeinschaft.
Angew. Chem. Int. Ed. Engl.
/ Vol. IS (1976) N o . 2
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oxidation, aminotetraazoles, new, route, isocyanides
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