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Ethylene Ketal of Cyclopentadienone.

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Ethylene Ketal of Cyclopentadienone
By Prof. Dr. E.Vogel and chem. E.-G. Wyes
Institut fur Organische Chemie
der Universitat K6ln (Germany)
Cyclopentadienone [ I ] dimerises in the nascent state at 5 "C.
The reaction is not reversible and gives the product (I) (endoconfiguration [2]).In the presence of excess ethylene glycol
in benzene, the dimer (I) yields the monoketal (II), m.p.
94-95 "C, crude yield 94 %. The position of the keto group
follows from the ultraviolet and infrared spectra. If (11) is
subjected to pyrolysis at 400°C in vucuo, it is converted
almost quantitatively into the ethylene ketal (IV) of the
unknown 8,9-dihydroindenone. Carbon monoxide is evolved.
The product (Iv) exhibits the typical ultraviolet spectrum of
8,9-dihydroindene [3]; on catalytic hydrogenation it takes up
3 moles of hydrogen.
Ethylene Ketal of Cyclopentadienone
By Prof. C. H. DePuy, Dr. B. W. Ponder and J. D. Fitzpatrick
Department of Chemistry, Iowa State University,
Ames, Iowa (USA)
It has not been possible to isolate cyclopentadienone [ I ] in
the form of its monomer. However, it seemed reasonable to
suppose that the ethylene ketal of cyciopentadienone would
be more likely to remain monomeric.
With this view in mind, the cyclic ethylene ketal of cyclopentenone (I) [2] was allowed to react with N-bromosuccinimide in carbon tetrachloride solution. Depending on the
reaction conditions, different products are obtained. In the
presence of an initiator (azobisisobutyronitrile), the expected
4-bromocyclopentenone ketal (IIa) was formed. This allylic
halide reacts with dimethylamine to give compound (11 b);
'1
n
We assume that, in analogy with the reversible Cope rearrangement of a-1-hydroxydicyclopentadiene into syn-8hydroxydicyclopentadiene [4], the pyrolysis of (11) leads
primarily to (111). In agreement with the thermal behaviour of
compound (I), compound (111) should, under the conditions
of pyrolysis decompose into carbon monoxide and (IV).
Compound (IV) reacts with maleic anhydride, even at room
temperature (m.p. of the adduct: 151 "C). It also combines
readily with the dimethyl ester of acetylene dicarboxylic acid
to give (V), m. p. 72-73 'C, yield 90 %. The cyclopentadienone
ethylene ketal formed in an Alder-Rickert thermal cleavage
of (V) at 160 "C proved to be considerably more reactive than
supposed and, similarly to cyclopentadienone, could only be
isolated in the form of its dimer (VI), m.p. 92 "C, yield 7 2 %
[5]. Hydrolysis of the dimer to (I) shows that it has the
endu-configuration.
overall yield from the eneketal: 64 %. In the presencfi of an
inhibitor (di-t.-butyl-p-cresol) and HBr, the 5-bromocyclopentenone ketal (IV, 62 % yield) was formed, probably by an
elimination-addition mechanism [3]. Compound (IV) does
not react with dimethylamine, and hydrolyzes easily to give
5-bromocyclopentenone (V).
Hofmann elimination from (IIc) gives, under a wide variety
of conditions, only the dimer (111) of the ketal. This dimer is
extremely stable, and could not be cracked to monomeric
cyclopentadienone ketal. Apparently, the inductive effect of
the oxygen atoms is sufficient to induce an electron deficiency
into the cyclopentadiene ring [4].
The 4-substituted amino ketal (I1 b) readily hydrolyzes to 4dimethylaminocyclopentenone (VJ). The extension of these
reactions to the synthesis of a variety of cyclopentenones is
under investigation.
Received, M a y 21 st. 1962
By pyrolysis of (V) in the presence of maleic anhydride (50 %
excess) it was possible to capture the ethylene ketal of cyclopentadienone as the adduct (VII), m.p. 148-9 'C, yield 73 %.
[Z 2871111 IE]
[l] C. H. DePuy and C. E. Lyons, J. Amer. chem. SOC.82, 631
(1960); K. Hafner and K. Goliasch, Chem. Ber. 94, 2909 (1961);
C. H . DePuy, M. Isaks, and K . L. Eilers, Chem. and Ind. 429,
1961.
[2] H. W. Wanrlick et al., Chem. Ber. 88, 69 (1955).
[3] A. Marquet et al., C. R. hebd. Seances Acad. Sci. 248, 984
(1959).
[4] C. H . DePuy and E. F. Zaweski, I. Amer. chem. SOC.
81,4920
(1959).
Received. Mav 21st. 1962 (2286/115 IF1
[I] C. H. DePuy and C. E. Lyons, J. Amer. chem. SOC.82, 631
(1960); K. Hafner and K. Goliasch, Chem. Ber. 94, 2909 (1961).
[2] The configurational proof of (I) was carried out by catalytic
hydrogenation to 1,s-diketotetrahydrodicyclopentadienewhich
was then reduced (Wolff-Kishner) to endu-tetrahydrodicyclopentadiene.
[3] K. Alder and F. H. Flock, Chem. Ber. 87,1916 (1954); E. Vogel
Angew. Chem. 73, 548 (1961).
[4] R. B. Woodward and T. J. Katz, Tetrahedron 5 , 70 (1959).
[ 5 ] The dimeric ethylene ketal of cyclopentadienone has also
been prepared in the meantime by C. H. DePuy, B. W. Ponder
and J. D. Fitzpatrick, Angew. Chem. internat. Edit. 1,404(1962).
By agreement with Prof. DePuy, both syntheses are published
simultaneously.
404
Vitamin E-quieone-nickel(0)-cycloocta-1,S-diene
By Dr. G. N. Schrauzer and Dip].-Chem. H. Thyret [I]
Institut fur Anorganische Chemie der Universitat Munchen
(Germany)
In the course of related work [2],we found that vitamin Equinone and nickel carbonyl yield a nickel(0) "sandwich"
complex at 70-80°C in the presence of an excess of cycloocta- 1,Sdiene. Vitamin E-quinone-Ni(0)-cycloocta-l,5-diene was isolated as a deep-red, highly viscous oil, which was
stable up to 150°C. Its structure (I) follows clearly from
Angew. Chem. internat. Edit, I VoI, 1 (1962) NO.7
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