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Influences of - and -AlkylGroups on the Rearrangement of 3-Butenyl Grignard Reagents A Stable Primary Cyclopropylmethyl Anion.

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[ 3 ] H. Kessler, Angew. Chem. 82, 237 (1970); Angew. Chem. internat.
Edit. 9, 219 (1970).
[4] Prepared by reaction of tropylium tetrafluoroborate with sodium
thiocyanate. The IR spectrum of its ethereal solution shows a strong band
at 2060 cm-' characteristic of R-NCS compounds.
[ S ] The same effect was observed previously with tropylium azide [6].
[6] D. S. Wulfman, L. Durham, and C. E . Wulfman, Chem. Ind. (London)
[ 7 ] R. A . Hoffman and S. Forst%, Progr. NMR Spectrosc. 1, 15 (1966).
[8] Determined from the broadening of the tropylium signal according
to the approximation k = xbn (bn =line broadening by exchange) [9].
[9] I . 0.Sutherland, Annu. Rep. NMR Spectrosc. 4. 71 (1971).
[lo] A high barrier was also observed for dissociation of Meisenheimer
complexes [ I I]. Thesealsocorrespond to the system: aromatic compound
[ I I] P . Cawny and H . Zollinger, Helv. Chim. Acta SO, 861 11967).
[12] Solvent: SOJCDCI, for NY,CD,CN for ONO- and NCO'.
[I31 C. D. Ritchie, Accounts Chem. Res. 5 , 348 (1972).
Influences of a-and fl-AlkylGroups on the Rearrangement of3-Butenyl Grignard Reagents: Astable Primary Cyclopropylmethyl Anion['*]
By Adalbert Maercker, Paul Giithlein, and Hermann WittrnayrC'1
Investigation of the rearrangement ( 3 a ) + ( 4 ) + ( 3 b )
with X=CI in tetrahydrofuran was only partly successful.
Certainly the tertiary Grignard reagent (3 a ) rearranges
quantitatively (half-reaction time ca. 30 h at 70°C) and
the cyclopropylmethyl compound ( 4 ) (ca. 0.07 %) can be
unambiguously detected but the equilibrium lies more than
99.9% on the side of the primary 3-butenyl Grignard
reagent (3 b ) (determined by gas chromatography after
esterification of the carboxylation products by diazomethane). Thence it follows that the two geminal methyl groups
d o in fact powerfully stabilize the three-membered ring,
yet the Thorpe-Ingold effect alone does not suffice to shift
the equilibrium in favor of the cyclopropylmethyl compound ( 4 ) .
Dedicated to Professor Gerhard Hesse on the occasion of
his 65th birthday
By isotopic labeling experiments Roberts et al.['l demonstrated that the a- and 0-carbon atoms of 3-butenyl
Grignard reagents gradually interchange positions:
( I a ) $ ( ] b ) (half-reaction time ca. 30 h at 27 T).A cyclopropylmethyl Grignard reagent (2) is assumed as an intermediate but its presence in the equilibrium mixture could
not be detected. If (2) is prepared at low temperatures
by an independent route, it rearranges quantitatively to
( I ) already at -24°C with a half-reaction time of 2h['].
The reason for this is the large ring strain in the cyclopropane (27 kcal/mol), which also explains why (2) cannot
be detected in the equilibrium ( I a)+(2)+(1 b ) : the
energy difference between ( 1 ) and (2) was estimated to
be 7 kcal/mol[21.
f l HC./ i H 2
+ BrMg-CHp
The energy difference between (2) and ( I ) can in principle
be reduced by stabilizing the three-membered ring of (2)
or by destabilizing the 3-butenyl Grignard reagent ( I ) .
The best chance of success lies in the combination of
these two possibilities.
We hoped to stabilize the cyclopropane ring by introducing
geminal alkyl groups (Thorpe-Ingold effect)I3 '1.
A possible method of destabilizing the open-chain
Grignard reagent (I) appeared to be the introduction
of alkyl groups on the r-carbon atom, i. e. at the carbanionic
center (cf. Ref. [7]).
[*] Priv.-Doz. Dr. A. Maercker, Dr. P. Guthlein, and H. Wittmayr
lnstitut fur Organische Chemie der Univcrsitiit Erlangen-Nurnberg
852 Erlangen, Henkestrasse 42 (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
Complete success, however, followed introduction of four
methyl groups. In the equilibrium mixture ( 5 ) + ( 6 )
(X=CI) there is only one open-chain compound since the
x- and the 0-carbon atoms are equally substituted. This
tertiary Grignard reagent ( 5 ) rearranges already at room
temperature in tetrahydrofuran (concn. O . W . 4 mol/l)
to give more than 99.9% of the cyclic compound (6)
which, unlike ( 4 ) , cannot pass into a primary 3-butenyl
Grignard reagent by ring opening.
In (6), which is also accessible directly from (6) with
C1 in place of CIMg, we have the first completely stable
primary cyclopropylmethyl Grignard reagent [I'H-NMR :
r-methylene doublet at T = 10.9 (.
7 Hz)]. Except for the
2,2,3,3-tetramethylcyclopropylmethyl anion (7), all the
stable cyclopropylmethyl anions previously known were
substituted at the carbanionic center, e. g. the benzhydryl
(S)['], the phosphane oxide (9)19] and the vinyl anion
( 10)' 0'.
i 9)
Kinetic measurements (NMR and gas chromatography)
gave a half-reaction time of ca. 6 h for the equilibration
( 5 ) = ( 6 ) at 23"C, so the rearrangement is appreciably
faster than that of ( 3 a ) . Remarkable also is that preparation of ( 5 ) and (6) is possible only when X =C1. Reaction
Anguw. Chem. Inlrrnaf. Edit. 1 Vol. 12 (1973)
1 No. 9
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
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butenyl, rearrangements, reagents, primary, anion, grignard, cyclopropylmethylen, influence, stable, alkylgroups
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