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Isomerization of Quinone Methides to Alkenylphenols.

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(2), which decomposes into (3), ( 4 ) , and CO,; a similar
mechanism has been formulated for the oxidation of alkylidenepho~phoranes~~].
The ions (3) and ( 4 ) do not
combine. We assume rather that ( 4 ) attacks a second molecule of the starting material ( I ) , while the R; ion (3)
reacts with H,O to yield R,H and HO-. The HO-. then
clearly adds to the cation (Sb), forming (6). In a final step,
(6) stabilizes itself to the ester (7). The stable by-products
CO, and 1H-perfluoroalkane (R,H) were unambiguously
identified in all cases.
Received: May 7,1971 [Z 441 It]
German version: Angew. Chem. 83,587 (1971)
[i] E . Lindner,H.-D. Ebert, and P. Junkes, Chem. Ber. 103,1364 (1970).
[2] E. Lindner, Angew. Chem. 82,143 (1970); Angew. Chem. internat.
Edit. 9, 114 (1970).
[3] E. Lindner,H.-D. Ebert, and A . Haag, Chem. Ber. 103,1872 (1970).
[4] We thank Prof. H . J . Bestmann for numerous discussions.
[S] H . J . Bestmann, H . Haberlein, and 0. Kratzer, Angew. Chem. 76,
226 (1964); Angew. Chem. internat. Edit. 3, 226 (1964); H . J . Bestmann
and 0. Kratzer, Chem. Ber. 96, 1899 (1963).
Experimental
2,6-Di-tert-butylbenzoquinone
4-dimethylmethider21(1 g,
0.00406 mol), anhydrous neutral aluminum oxide (1to 2 g),
and light petroleum (15 ml ; b. p. 50-70°C) are heated
and stirred magnetically under nitrogen (gas stream) in a
round-bottomed flask, fitted with a reflux condenser, in an
oil-bath (70-80°C). The deep yellow color disappears at
once. The reaction is complete in 5-1 5 min. After cooling,
the mixture is placed together with the aluminum oxide
on a silica gel column and eluted with anhydrous light
petroleum (50 ml). Removal of the solvent affords 2,6-ditert-butyl-4-isopropenylphenol(0.95-1.0 g, 95-100%),
m. p. 77-78°C.
Received: May 13, 1971 [Z 442 IE]
German version: Angew. Chem. 83,617 (1971)
[I] D.Braun, R . J . Faust, and B. Meier,Angew. Chem. 80,407 (1968);
Angew. Chem. internat. Edit. 7, 393 (1968).
[ 2 ] C . D.Cook and B. E. Norcross, J. Amer. Chem. SOC.78,3797 (1956).
Nucleophilic Aromatic Substitution:
A New Synthetic Route to Biphenyls'']
By Franz Effenberger, Klaus Nagel, and Wolfgang Agster"'
Isomerization of Quinone Methides to
Alkenylphenols[**I
By Dietrich Braun and Bertold Meierr4'
During our studies of oxygen polyradicals['] we have
found a new synthesis of sterically hindered polymerizable
phenol derivatives by isomerization of the stable 2,6-ditert-butylbenzoquinone methides ( I ) to the corresponding
alkenylphenols (2).
The most important methods for preparation of biphenyls
are the Ullmann[21 and Gomberg reaction^'^], which
involve radical or organometallic intermediates ; furthermore, biaryls are formed by benzidine rearrangementL4]
and oxidative dirnerizationfs1,as well as in the course of
reactions involving aryne intermediates16].
OH
0
70-759:
Petroleum e t h e r
RNC'CH3
(1)
+
Y=CH2
R
(2)
= tert-Butyl; R = H , CH3, Phenyl
The isomerization occurs extremely rapidly and quantitatively on use of neutral aluminum oxide. Use of acid
aluminum oxide is possible but leads to yields of only
50-60% because part of the isomeric compounds are
bound to the catalyst as carbonium ions or react further
by oligomerization. Basic aluminum oxide is not suitable
because sterically hindered phenols are oxidized in a basic
medium by atmospheric oxygen, yielding oily products
when the reaction mixture is worked up. It is also impossible
to isolate the alkenylphenols if the aluminum oxide is
replaced by traces of protic or Lewis acids. This method
of isomerization is superior to the classical processes
(dehydration of carbinols or decarboxylation of substituted
cinnamic acids)['] because the alkenylphenols are immediately provided in a very pure state.
R'
R2
R3
Pyr
Pyr
Pyr
Pyr
Pyr
Pyr
Pyr
CH,
H
H
H
H
H
NO2
NO2
CN
COOCH,
COOH
H
H
H
H
H
R4
H
H
NO2
COOCH,
[*I
Prof. Dr. D. Braun and Dip1.-Ing. B. Meier
Deutsches KunststoR-Institut
61 Darmstadt, Schlossgartenstrasse 6 R (Germany)
[**IThis work was supported by the Deutsche Forschungsgemeinschaft.
566
[*I
Prof. Dr. F. Effenberger, Dip].-Chem. K. Nagel, and W. Agster
Institut f i r Organische Chemie der Universitat
7 Stuttgart, Azenbergstr. 14-18 (Germany)
Angew. Chem. internat. Edit. Vol. 10 (1971) 1 NO.8
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