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Evidence for the Intermediate Occurrence of Acetylenedicarboxyimide.

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We formulate scission of the carbon-mercury bond by iodine
as an SEi process, depicted in (3) [41. Since this should proceed also with other reagents, it should be possible to prepare
further hetero-substituted diazoacetic esters from the compound ( I ) 151.
Photolysis of (2) (450 W Hanovia lamp, Pyrex filter) gave
ethoxycarbonyliodocarbene (4), from which we obtained
ethyl l-iodo-2,2-dimethylcyclopropanecarboxylate( 5 ) (b.p.
45 "CiO.4 mm; yield 40%; NMR signals of the cyclopropane
protons as an AB spectrum at T = 8.7 with JABw 6 Hz) on
irradiation of (2) in isobutene until evolution of nitrogen
ceased. Products formed by insertion in the C-H bond were
not detectedr61. We conclude that the carbene ( 4 ) is more
selective than ethoxycarbonylcarbene.
[Z 372 IEI
Received: November 1 1th, 1966
German version: Angew. Chem. 79,50 (1967)
16 hr at 110°C. The composition and molecular weight correspond to an adduct of 2 moles of cyclopentadiene t o one of
maleimide and 2 g-atoms of sulfur. IR spectrum in KBr: 1765,
1715,1700cm-1 (imide-CO) ; 1600(C=C); 1550(imide-C=C).
UV spectrum in ethanol: 240 mp (log E = 3.38), 267 (3.85),
424 (3.34). These results indicate a dimercaptomaleimide
system. The NMR spectrum at 90 MHz in CDCI3 [T = 4.34
(2 olefinicprotons), 6.97 (N-CHj), 8.42 (1 H), poorly resolved
multiplet at r=6.4 to 7.9 (9 H)] does not permit unambiguous
decision between the structures (3a) and (36).
The formation of (3a) or (36) is preferred to an asymmetrical
decomposition of ( I ) to a compound (4) V-1 and acetylenedicarboxyimide (5), from which (2) is then obtained. The DielsAlder adduct of cyclopentadiene to (5), not hitherto described, would probably not be stable under the reaction
conditions.
0
0
]*I Dip1.-Chem. F. Gerhart, Prof. Dr. U. Schollkopf, and
Dr. H. Schumacher
Organisch-Chemisches Institut der Universitat
Windausweg 2
34 Gottingen (Germany)
[l] Cf. R. Huisgen, Angew. Chem. 67, 439 (1955).
[2] Chloro- and bromo-diazomethane were recently prepared in
situ; they are stable only below -40 "C. Cf. G. L. Closs and J . J .
Coyle, J. Amer. chem. SOC.87, 4270 (1965).
[3] E. Buchner, Ber. dtsch. chem. Ges. 28, 215 (1895).
[4] For the mechanism of C-Hg fission by iodine see S . Winstein
and T. G. Traylor, J. Amer. chem. SOC.78, 2597 (1956).
[ 5 ] Cf. U. Schollkopf and P. Murkusch, Tetrahedron Letters
1966, 6199.
[6] It is possible that they decompose under the conditions of the
photolysis.
Evidence for the Intermediate Occurrence of
Acetylenedicarboxyimide
By W. Draber[*J
When 1,4-dithiintetracarboxydiimides ( I ) are heated in
pyridine at 120 OC, mellittriimides (2) are obtained in yields
of up to 5 0 % together with sulfur and unidentified brown
products. Small quantities of mellittriimide were also
occasionally obtained in the preparation of the dithiins ( I )
from dichloromaleimides and H2S in the presence of a
material such as CaCO3[" to neutralize the acid formed.
Heating the dithiins without pyridine or in indifferent
solvents such as xylene or ethanol does not lead to formation
of triimides (2).
An indication of the course of the reaction was given by
the formation of a yellow compound,m.p. 137.5-138 "C, yield
7 %, that could be isolated chromatographically together
with the mono- and di-adducts of cyclopentadiene to ( I ) and
24% of (2), after the dithiin ( I ) had been heated with an
excess of dicyclopentadiene and pyridine under nitrogen for
Angew. Chem. internat. Edit.
Vol. 6 (1967)
No. 1
Attempts to prepare the Diels-Alder adduct of cyclopentadiene to acetylenedicarboxylic anhydride from the corresponding acid by dehydration with acetic anhydride gave
a substance that polymerized rapidly even at room temperature.
Received: November 15th, 1966
[Z 377 IE]
German version: Angew. Chem. 79, 51 (1967)
[*] Dr. W. Draber
Shell Grundlagenforschung GmbH
SchloD Birlinghoven
52 Siegburg (Germany)
Present address: Farbenfabriken Bayer
Wissenschaftliches Hauptlaboratorium
509 Leverkusen-Bayerwerk (Germany)
111 W. Druber, unpublished work.
[2] Compounds of 1,2-dithietestructure are known to add readily
to reactive double bonds, yielding 1,4-dithiins: H . E. Simmons,
D . C . Blomstrom, and R. D . Vest, J. Amer. chem. SOC.84, 4782
(1962).
Anisotropic Effects in Heterocyclic Nitrosamines
By Y. L. Chow[*]
The restricted rotation about the partial N-N double bond
of a nitrosamino group derived from a symmetrical amine
gives rise to different NMR chemical shifts for the cis- and
trans-cc-methyleneprotons [**I. A conformationally "frozen"
heterocyclic nitrosamine should allow direct observation of
the long-range shielding of the nitrosamino group, provided
that inversion at the amine center is slow.
The 4-substituted N-nitrosopiperidines ( I b ) and ( I c ) give
four well-separated signals, corresponding to the four ccprotons in different environments (see Table 1). The signals
were assigned on the basis of their splitting pattern and
coupling constant 111 and by decoupling experiments at
100 MHz. The equatorial protons He and Hk, being coplane, absorb at
planar, or nearly so, with the C,-N-N-0
approximately the same (lower) field 121, whereas the axial
protons Ha and H', absorb at higher fields. Since Ha is
situated inside the semi-circular shielding zone of the nitrosamino group, its signal appears at a far higher field. This
anisotropy is even better manifested by an unusually large
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acetylenedicarboxyimide, occurrence, evidence, intermediate
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