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New Aspects of the Fries Rearrangement.

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of the bromo compounds with magnesium in either diethyl
ether or tetrahydrofuran gave no trace of the Grignard
compound, but exclusively disproportionation products,
and these-unlike the anion cas+from the clearly more
stable open-chain radical. The complete absence of cyclopropane derivatives from the products of radical reaction,
even if cyclopropylmethyl bromide is used as starting
material, is a further indication of the carbanionic nature
of these Grignard rearrangements[' '1.
Received: July 2, 1973 [Z 884 IE]
German version: Angew. Chem. X i . 823 (1973)
6, -
R &R,6H5
Table 1. Fries rearrangement of phenyl benzoates ( I ) with catalytic
amounts of trifluoromethanesulfonic acid.
Products ["A] [a]
( 2 1 [b]
( 3 ) decomp.
[ I ] M . S. Silver, P . R . Shafrr, J . E . Nordlander, C. Riichardt, and J .
D. Roberts, J. Amer. Chem. SOC.82, 2646 (1960).
[2] D. J . Parel, C. L. Hamilron, and J . D. Roberts, J. Amer. Chem.
SOC.87, 5144 (1965).
131 R . M . Beesky, C. K . lngold, and J . F . Thorpe, J. Chem. SOC. 107,
1080 (1915); C. K . lngold, ibid. 119, 305, 951 (1921); G. A. R. Kon, A.
Stecenson, and J . F. Thorpe, ibid. 121, 650 (1922).
[4] Cf. N . L. Allinger and V. Zalkow, J. Org. Chern. 25, 701 (1960).
[S] 1 . - M . Andrl, M.-C. AndrP, and G . Leroy, Bull. SOC. Chim. Belges
[a] Average yields from several parallel runs, determined by glc (Varian
[b] p-Hydroxyaryl ketones are formed in less than 2 % yield, if at all.
80. 265 (1971).
[6] W D. Good, J. Chem. Thermodyn. 3, 539 (1971).
[7] A. Maercker and R. Geuss, Chem. Ber. 106. 773 (1973).
[8] A. Maerckrr and J . D. Robrrfs, J . Arner. Chem. SOC.88, 1742 (1966).
[9] A. Maercker, Angew. Chem. 79, 576 (1967); Angew. Chem. internat.
Edit. 6. 557 (1967).
[lo] H . G. Richey. J r . and W C. Kossa, J r . . Tetrahedron Lett. 1969,
2313: cf. also M. Santelli and M . Berrrund, C. R. Acad. Sci. C271,
757 ( I 970).
[I I] Cf A. M a e n krr and W Streit, Angew. Chem. X4,531 (1972); Angew.
Chem internat. Edit. 1 1 , 542 (1972)
New Aspects of the Fries Rearrangement[']
By Franz Effenberger, Herbert Klenk, and Peter Ludwig
Dedicated to Professor Karl Winnacker on the occasion
yields identical within the error limit with those in Table
1. Phenolic esters of aliphatic carboxylic acids also undergo
Fries rearrangement with TFMS.
Electron donors in position 3 of the phenolic ester favor
the TFMS-catalyzed rearrangement as the results in Table
1 indicate: starting from ( I d ) , ( 2 d ) was obtained in 78 %
yield while ( 1 b ) remained unchanged under the reaction
conditions. Surprisingly, ( I e ) did not rearrange even
though the two methyl groups at C-3 and C-5 should
enhance acylation of the arene nucleus. This finding can
be rationalized in terms of reversibility of the Fries rearrangement.
In order to test this hypothesis, we have heated several
o-hydroxyaryl ketones with TFMS under the conditions
given above. These experiments (Table 2) clearly show
the Fries rearrangement to be indeed reversible.
of his 70th birthday
Even in the most recent literature, the Fries rearrangement
of phenolic esters (I ) not substituted in the arene nucleus
(R = R' = H) is held to be an irreversible process yielding
0- and/or p-hydroxyaryl ketones (acylphenolsy'l. Rosenmund and SchnurrI3]as well as Miguei et ~Z.1~1
have reported
a reversal of the Fries rearrangement for 4-acyl-3-alkylphenols whereas Cullinane and Edwards''1 maintain that
the Fries rearrangement is irreversible in this case too.
Formerly we had found that aromatic compounds can
be acylated by acyl chlorides or carboxylic anhydrides
under the influence of catalytic amounts of trifluoromethanesulfonic acid (TFMS)[61.Since C-acylation of phenols is
of great practical importance, we have investigated whether
the Fries rearrangement which is usually carried out with
molar amounts of A1Cl3 could also be achieved with
If solutions of phenyl benzoates ( I ) in anhydrous tetrachloroethane are heated with ca. 2mol-% TFMS for 24h
at 170°C in sealed tubes, the reaction mixture contains
o-hydroxyaryl ketones (2), phenols ( 3 ) , and decomposition products besides starting material (Table I).
Reactions run on a preparative scale (e.g. 0.1 mol ( I aJ,
0.02 ml TFMS in 100 ml anhydrous tetrachloroethane) give
p] Prof. Dr. F.
Effenberger, Dip1:Chem. H. Klenk, and DipLChem.
P. L. Reiter
Institut fur Organische Chemie der Universitat Stuttgart
7 Stuttgart 80, Pfaffenwaldring 55 (Germany)
Angew Chem. mfernaf.Edit. J Vol. 12 (1973) 1 N o . 9
0-c 0c gH5
- RJ&
Table 2. Retro Fries rearrangement of o-hydroxyaryl ketones ( 2 ) with
catalytic amounts of TFMS.
(2a), 9
[a] See note [a] in Table 1.
There is qualitative agreement between the isomer distribution for the Fries and the retro Fries rearrangement (Table
1 us. Table 2); this is not sufficient, however, to establish
a truly reversible equilibrium (which should be attained
from either direction) so that further investigations are
The mechanisms proposed so far for the Fries rearrangement must now be critically reviewed since they d o not
take account of the reversibility of the reaction which
has been established beyond doubt by the results reported
here, especially since we have found the retro rearrangement also with typical Friedel-Crafts catalysts such as
Our inference from the experimental data given is that
for the acid-catalyzed Fries rearrangement product formation is subject to thermodynamic control in many cases.
Since phenolic esters and hydroxyaryl ketones seem to
have about the same energy they are present side by side
in solution. Steric hindrance due to buttressing of two
o-substituents as in ( 2 e ) shifts the isomer distribution
in favor of the sterically unhindered ester (Table 2). We
observe almost exclusive o-rearrangement which is another
argument in favor of the thermodynamic control
mechanism since the o-hydroxyaryl ketones are stabilized
by intramolecular hydrogen bonding which is impossible
in the p-isomers.
thus yielding 5,8,14,17-tetramethoxy-2,1
l-dithial3.31paracyclophane (2 a/2 b ) in 20-23 YOyield. Chromatographic
separation from chloroform on silica gel yielded the two
stereoisomers of m. p. 21 1-213°C and 243-246V6] in
the ratio ca. 2 : 1 ; assignment of the two compounds to
the chiral ( 2 a ) and the achiral ( 2 6 ) forms has not yet
been unambiguously effected.
Ring contraction to give 4,7,12,15-tetramethoxy[2.2]paracyclophane ( 3 a ) or ( 3 b ) has beesachieved in three ways:
first, by gas-phase pyrolysis (44O0C/1O- torr, 30-45 Y
yield) of the disulfones obtained ( H 2 0 2 ,chloroform/glacial
acetic acid, %70% yield) from ( 2 a ) and ( 2 b ) or the
( 2 a ) / ( 2 b ) mixture; secondly, by photolysis of the disulfones (suspension in benzene, Hg high-pressure lamp, 75
min, 50 % yield); and thirdly, by direct photolytic desulfuration of ( 2 a ) / ( 2 b ) in triethyl phosphite in a modification
of a procedure due to Bruhin and Jennyc7].Independently
of whether the starting material was ( Z a ) , ( 2 b ) or the
( 2 a ) / ( 2 b ) mixture, by each of these ring contraction reactions only one product was obtained [m.p. 121-122°C;
'H-NMR (CDC13): s=3.91 (s, 4 arom. H), 6.34 (s, 12
methoxy-H), 7 . 6 4 . 6 (AA'BB, 8 methylene-H)][6! The decision between ( 3 a ) and ( 3 b ) was established in favor
of the chiral ( 3 a ) since partial separation of the enantiomers was effected by chromatography on (-)-2-(2,4,5,7tetrani tro-9-fluoreny1ideneaminooxy)propionicacid - )TAPA" ; 10%]/silica gel from cyclohexane/methylene
chloride (3: 1): the maximum
rotations were
(1.03g/100ml; CHC13) and -18.0"
(0.4g/100ml; CHC13); ( - ) - ( 3 a ) formed the more stable
complex with (-)-TAPA. The subsequent products from
( 3 a ) very probably also have the pseudoortho conformation.
Received: July 24, 1973 [Z 882 IE]
German version: Angew. Chem. 85, 819 (1973)
[I] Electrophilic Substitution of Aromatic Compounds, Part 8.-Part
7: F . Effrnberger and H. Klenk, Chem. Ber., in press-We are indebted
to the Fonds der Chemischen Industrie and the Deutsche Forschungsgemeinschaft for support of this work.
[2] M . J . S . Dewar and L. S. Hart, Tetrahedron 26, 973 (1970).
[ 3 ] K . W Rosenmund and 19: Schnurr, Liebigs Ann. Chem. 460,56 (1928).
[4] J . F . Miguel, P. Miller, and Nh. Ph. Buu-Hor, Bull. SOC. Chim.
Fr. 1965, 633.
[ S ] N . M . Cullinan: and B . F . R . Edwards, J. Chem. SOC. 1958, 434.
[6] f.Effenberger and G. Epple, Angew. Chem. 84, 295 (1972); Angew.
Chem. internat. Edit. 11, 300 (1972).
An "Intramolecular Quinhydrone'"
By Walter Rebafka and Heinz A . S t u d y ]
In the context of our investigations of transannular interactions in [2.2]phane~['.~]we became interested in compounds where high electron affinity in one part of the
molecule and low ionization energy in the other favor
intramolecular donor-acceptor interactions. Ideal conditions for this interaction should be provided by"intramo1ecular q ~ i n h y d r o n e s " in
~ ~the
] [2.2]paracyclophane series, for
which pseudoortho- and pseudogeminal stereoisomers (1a)
and (ib) can be foreseen. We report here the synthesis of
( l a ) 141.
1,4-Bis(bromomethyl)-2,5-dimethoxybenzene(0.1 M in tetrahydrofuran) and 1,4-bis(mercaptomethyl)-2,5dimethoxyin dimethylformamide) were 'Yclized by
being dropped simultaneously into a suspension Of anhydrous potassium carbonate (excess)in boiling tetrahydrofuran/dimethylformamide ( l : ') (for apparatus see Ref. [5i)>
[*] DipLChem. W. Rebafka and Prof. Dr. H. A. Staab
Institut fur Organische Chemie der Universitiit
69 Heidelberg, Im Neuenheimer Feld 7 (Germany)
Demethylation of ( 3 a ) could only be achieved by heating
with methylmagnesium iodide (15 min, 170-185"C, under
Without being purified, the resulting rather unstable
tetrahydroxy[2.2]paracyclophane was oxidized by sodium
periodate in tetrahydrofuran (20°C, 40-60 min) to the
bis-quinone ( 4 ) [yield (3a) + ( 4 ) z S O % ] which formed
yellow crystals decomposing above 200°C. 'H-NMR
Angew. Chem. internat. Edit. / Vol. I2 ( 1 9 7 3 ) / No. 9
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