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Heterocycles from Acetylene Derivatives.

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Heterocycles from Acetylene Derivatives
E. Wirzlerfeldt, Berlin (Germany)
The betaine-like compounds ( I ) and ( 2 ) can be prepared
from methyl propiolate and dimethyl sulfoxide. When high
concentrations of the ester are used, only compound (2) can
be isolated, but at high dilution the 1: 1 adduct ( I ) is obtained at 125OC.
H3C02C
H3C' 'CH3
(1)
H
0
(31
(2)
Both substances are crystalline and quite stable. When
compound ( 2 ) is heated at 150°C in a vacuum the main
product is the 2-pyrone ( 3 ) , and dimethyl 2,4-furandicarboxylate is formed only to a small extent. Thionyl chloridz
converts compound (2) quantitatively into dimethyl 2,4thiophenedicarboxylate ( 6 ) at room temperature, by way of
the stages ( 4 ) and ( 5 ) .
Reaction of dimethyl acetylenedicarboxylate with isocyanides
usually leads to a large number of products, but if a large
excess of isocyanide is used at -IO°C the main products probably formed from a primary product (7)
are the 1 : 2
adducts (8) and ( 9 ) ; their structures are proved by infrared,
ultraviolet, and N M R spectroscopy, by elemental analyses,
and by molecular-weight determinations.
-
Heating dimethyl acetylenedicarboxylate in a sealed tube at
150-180°C in the presence of copper as catalyst and
oxygen leads to a 50 % yield of the furan derivative (lo),
whose structure is supported by ultraviolet, infrared, and
N M R data as well as by its mass spectrum and conversion
into the enol lactone ( I I ) . Alongside (10) carbon monoxide
is evolved, and the reaction occurs only in the presence of
oxygen.
H3COzC.
COzCH3
These results d o not agree with a reaction mechanism recently
proposed "1. Instead, formation of an a-0x0-ester (12) by
cycloaddition and oxidation is discussed. Trapping experiments with tolan and with sulfur support this hypothesis.
The order of the two steps, uptake of oxygen and condensation, remains an open question.
[Lecture at Marburg (Germany), April 22nd, 19661
[VB 999 IE]
German version: Angew. Chem. 78, 757 (1966)
[ I ] C. F. Hurbneu ef a/., Tetrahsdron Letters 1966, 1185.
Recent Advances in the Chemistry of Quinones
R . H . Thomson, Aberdeen (Scotland)
2-Hydroxy-1,4-naphthoquinonescan be prepared by autoxidation of c(- and p-tetralones in t-butyl aIcohol/potassium
t-butoxide. The reaction probably proceeds via a 1,2-diketone
which aromatizes to a 1,2-dihydroxynaphthalenewhose semiquinone anion combines with a further mole of oxygen at
position 4. Under the same conditions 1,2-dihydroxynaphthalenes rapidly absorb 1 mole of oxygen, giving
2-hydroxy-1,4-naphthoquinones.Autoxidation of 5,7,8-trifollowed by
methoxy- and 5,6,7,8-tetramethoxy-l-tetralone,
demethylation, gives 2,5,7,8-tetrahydroxy- and 2,5,6,7,8pentahydroxy-l,4-naphthoquinone.
These products are identical, respectively, with mompain, a metabolite of Helicobasidium mompn Tanaka and spinochrome D, a pigment
found in the spines of several species of sea urchin.
In the Dam-Karrer test for vitamin K and other allylnaphthoquinones (treatment with ethanolisodium ethoxide)
a blue mesomeric anion is formed by removal of a proton
from the methylene group adjacent to the quinone ring. The
colour is transient, changing to red-brown as a consequence
of cleavage of the side chain to form phthiocol(2-hydroxy3-methyl-l,4-naphthoquinone).2-Benzyl-1,4-naphthoquinone
behaves similarly, giving first a blue and then a red solution
with the formation of lawsone (2-hydroxy-I ,4-naphthoquinone) and benzaldehyde. The reaction is considered to be
a special case of ketone autoxidation, the quinone behaving
as a vinylogous benzyl ketone. If a methyl group is also
present in the quinone ring [ ( I ) , R = C H Z C ~ Hcleavage
~]
of
the benzyl group is accompanied by dimerization, and in
general 2-methyl-l,4-naphthoquinones
of type ( I ) , R =C2H5,
~ S O - C ~ H ~ , C H ~ C H CH2C6H5,CH(CsH5)2,
=CM~~,
p-CH3C6H4
CI, Br dimerize at the methyl group (preferential formation
of a primary carbanion) to give the corresponding diquinones
(2) together with the quinhydrone of (1).
Re-examination of lapacho wood (Tabebuia i p i , Bignoniaceae), a well-known source of lapachol (3), R = O H has
shown it to contain inter alia the naphthoquinones (3),
R = H, CH3, OH, OCH3 and anthraquinones ( 4 ) , R = CH3,
CHzOH, CHzOAc, CHO, COzH), several of which also
occur in teak wood (Tectona grandis, Verbenaceae). The
unusual coexistence of these two groups of quinones suggests
a biogenetic relationship which is supported by a simple
Angew. Chem. internut. Edit. / Vol. 5 (1966)
i No. 8
74 1
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