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Contrasting Behavior in the Substitution Reactions of 9-(2-Bromomethyl-6-methylphenyl)fluorene Rotamers.

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The concentration of the various species-free fl,J(C),the
1 :1 complex (C .M), and the 2 :1 complex (C .M,) could be sp-(7). X = Br
ap-(l), x = Br
determined by integration of the well resolved 600-MHz sp-(2), X =fiCgHqCH3
ap-(2), X = fiCgHqCH3
'H-NMR spectrum. The excellent resolution is due to the
relatively slow rates of exchange involved in complexation
of Hg(CN)2 with these ethers. In contrast, alkali metals
showed rapid exchange rates and resulted in averaged
ene"] and separated by preparative high pressure liquid
spectra for the various species.
chromatography (SiO,/hexane). Since the activation paThe ratio K2/KI =[C.M,].C/[C.MJ2 of the macrorameters for interconversion of both rotamers are known
scopic association constants K , =[C. M]/[C].[M] and
( E A= 27.1 kcal/mol, logA= 11.4), the time necessary for
conversion of 5% ('H-NMR detection limit) of one isomer,
K2 =[C . M2]/[C. MI. [MI can be determined directly from
into the other by internal rotation can be calculated e.g.
the 'H-NMR-spectrum. It is found that Kz=(2.5+0.2) K,.
27.2 h at 62°C. In order to detect the differences in reactivHowever, these constants must be corrected for statistical
ities of the respective rotamers, the reactions must be careffects. The corrected (intrinsic) association constants are
K; = 10 K; i. e. the system shows positive cooperativity. The
ried out under conditions which will not permit isomerizaHill plot of the datafs1produces a slope of n= 1.5, with
tion to a detectable degree. At the outset we focused our
mid-point at a free metal concentration of ca. 0.03 M. This
attention on SN2-typereactions in dimethyl sulfoxide. Precorresponds to K; = 1 0 -',
~ in good agreement with that
liminary experiments with methanol indicated that, while
observed for the monocyclic polyether (3) ( K = 13 M - I ) .
sp-(I) reacted with measurable rates at 57 "C, up-(1) was almost inert. Since methanolysis produces hydrogen bromThe receptivity of the ether toward a second Hg(CN)2is
ide, the reaction is autocatalyzed and hence, to compare
enhanced 10-fold by the binding of the first Hg(CN)2.The
conformational restrictions imposed on the open site by
the rates of clean sN2 reactions, we used 2-methylpyridine
as a nucleophile[zl.The pseudo-first order rate constants of
binding of the first metal are modest-only one of the
many internal rotations are removed, yet receptivity is inthe reactions in acetone in the presence of 2-methylpyridcreased by a n order of magnitude[61. This suggests that
ine at 3 4 ° C were 1 . 4 lo-'
and 4 . 0 ~
min-' for speven greater cooperativity should be available to systems
(I) and a~-(]), respectively. Thus sp-(1) is ca. 35 times more
composed of less flexible subunits.
reactive than up-(I), under the conditions used. The products were the corresponding 2-methylpyridinium salts: spReceived: November 7, 1980 [Z 763 IE]
(2) (m. p. =226-227 " C (decomp.)) and up-(2) (oil)f31.The
German version: Angew. Chem. 93, 584 (1981)
poorer reactivity of the up-form may be attributed to the
CAS Registry numbers:
blocking of the back-side of the leaving group BrQ by the
( l j , 77846-54-9; (2), 61358-43-8, (3). 77825-22-0; tetraethylene glycol ditosyfluorene moiety.
late, 37860-5 1-8
For an investigation of SN1reactions, we chose trifluoroacetic acid as solvent which has a high dielectric constant
111 D. E. Koshland, Jr. in P. Boyer: The Enzymes. Vol. 1, Academic Press,
New York 1970, p. 341.
but low nucleophilicity. Heating a solution of up-(1) in
121 J. Rebek. Jr., R. V. Wattley. J. Am. Chem. SOC.I02,4853-54(1980); for
CF,C02H/CDC13 (1 : 1) at 61.2"C caused a decrease in inother systems in which allosteric effects can be invoked see J.-M.Lehn,
tensity of the methyl and methylene signals in the 'H-NMR
Acc. Chem. Res. II,49 (1978) and T. G. Traylor, Y. Tufsumo.D . W. Powe//, J. B. Cannon, J. Chem. SOC.Chem. Commun. 1977,732.
spectrum of up-(1) from which a rate constant of ca.
[3] Satisfactory elemental analysis and anticipated spectroscopic features
7 x lop4 min-' for the reaction involved was obtained. In
were obtained for (I) and (3).
contrast, sp-(I) did not react with a measurable rate
141 I. Agranaf, M. Rabinovifz, W. Shaw, J. Org. Chem. 44, 1936 (1979).
under the same conditions. The enhanced reactivity of the
[5] For an excellent discussion of this topic see A. Leuifzki:Quantitative Asup-form may be ascribed to the interaction of the n-elecpects of Allosteric Mechanisms, Mol. Biol. Biochem. Biophys. 28, 15
trons of the fluorene ring with the carbenium ion formed;
[6] With the larger homologue (22-membered ring) of ( l j , the sites were
the inertness of the sp-form is due to the lack of such parfound to act independently: J . Rebek, R . V. Wattley, T. Costello, R. Gadticipation.
wood, L. Marshall. J. Am. Chem. SOC.102,7398 (1980).
Contrasting Behavior in the Substitution Reactions
of 9-(2-BromomethyI-6-methyIphenyI)fluorene
By Shigeru Murata. Seiichiro Kanno, Yo Tanabe, Mikio
Nakamura, and Michinori Okif"
We wish to report that the sp- and up-rotamers of 9-(2-
bromomethyl~6-me~hylphenyl)fluorenebehave quite
differently in substitution reactions. sp-(,) and up-(]) were
prepared by bromination of 9-(2,6-dimethylphenyl)fluor[*] Prof. Dr. M. Oki, S . Murata, S. Kanno, Y. Tanabe, Dr. N. Nakamura
Department of Chemistry, Faculty of Science
The University of Tokyo
Bunkyo-Ku, Tokyo 113 (Japan)
Reactivity of Stable Rotamers, Part 5 : This work was supported by the
Toray Science Foundation.-Part 4: H. Kikuch;. T. M;tsuhashj, N.
kamura. M . Oki. Chem. Lett. 1980. 209.
0 Verlug Chemie GrnbH. 6940 Weinheim, 1981
The product of the reaction of up-(1) in CF3C0,H/
CDC13 (1 : 1) was a mixture of polymers which could be formed by an intermolecular Friedel-Crafts reaction. However,
when the reaction was carried out in dilute solution, identifiable products were Obtained i. e. heating 33 mg Of ap-(l)
in 1.5 cm3 of CHC13 and 25 cm3 of CF3C02H afforded
8 mg of 12-methyl-8,12b-dihydrobenz[a]aceanthrene (3)
(m.p.= 180-181 0C)[51 and 3 mg of 12-methylbenz[a]aceanthrene (4) (yellow-orange
The yield of
(4) decreased if the reaction was carried out under N2, indicating that (4) is formed from (3) by dehydrogenation of
(2) by 0 2 . Formation Of (3) is expected if ionization occurs
at the CHZ-Br site and intramolecular Friedel-Crafts cy-
0570-0833/81/0707-0606 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 20 (1981) No. 6 / 7
clization follows. The reason why the concentrated solution of up-(1) only gave polymeric product may be, that for
the cyclization, rotation about the C9-Cl'-bond
has to
take place: since the barrier to rotation is high, polymerization is preferred.
In conclusion, the rotamers sp-(1) and up-(1) exhibit remarkable differences in nucleophilic substitution reactions. In SN2reactions sp-(I) is-predominantly for stereochemical reasons-more reactive, however, in SN1 reactions up-(1) is-predominantly because of electronic interactions-more reactive.
Received: January 25, 1980 [ Z 764a IE]
German version: Angew. Chem. 93, 579 (1981)
CAS Registry numbers:
(I), 52883-19.9; (2) bromide, 77825-19-5;(3). 77825-20-8;(4). 77825-21-9
[ I ] M. Nakamuru, M. Okr, Tetrahedron Lett. 1974, 505.
[2] J. W. Baker. J. Chem. SOC.1936, 1448; J. W. Baker, C. M . Easfy, ibid.
1935, 519.
131 'H-NMR ([DeJDMSO) S P - ( ~ )6=
. 1.12 (s, 3 H), 2.96 (s, 3 H), 5.50 (s, 1 H),
2H), 5.77 (s, I H), 6.6-8.5 (m,I5H).
141 T. W. Eenlley, C. T. Bowen, W. Parker, C. I . F. Watt. J. Am. Chem. SOC.
TO]. 2486 (1979)and references cited therein.
[5] (3) showed the expected reactions and gave a correct molecular weight in
the mass spectrum ( M0 = 268), as well as a satisfactory elemental analysis. 'H-NMR (CDCI,): 6= 2.48 (s, 3H), 3.99 (d, 1H, J= 16.4 Hz), 4.14
The dehydrogenation of (3) with dichlorodicyano-p-benzoquinone afforded (4).
161 'H-NMR (CDCI,): 6=3.17 (s, 3H) and signals from the aromatic protons; UV, h,,%,(loge): 430 (3.63), 366 (3.40), and 260 nm (4.54).which is
in accord with the spectrum of benzIalaceanthrylene (E. Clar, W. Willicks.
J. Chem. SOC.1958, 942).
gave, stereoselectively, the up-rotamers of (2)-(5)14]. A
study of the kinetics of the up- fsc isomerization was carried out by NMR spectroscopy (by I9F- for (2) and 'HNMR for the others) in 1-chloronaphthalene solutions between 160-280°C (Table 1). The ksc-rotamers were isolated upon chromatographic separation of the equilibrated
Table I . Equilibrium and kinetic parameters for up- f s c isomerization in 1chloronaphthalene.
f sc-rotamer
K = 2 k , / k _ t =[*sc]/[apl
periSubstituent [a]
- 9.3
- 1.9
- 0.1
- 7.0
- 13.9
perisubstituent Effects on the Rotational Barrier
of 9-(l,l-Dimethyl-2-phenylethyl)tripty~ene~**~
[a] In parentheses are the van der Waals radii after Pauling [S] (in
der Waals radius of an oxygen atom.
A). [b] van
By Gaku Yamamoto, Masahiko Suzuki, and
Michinori Oki"'
Substitution at the peri-position of 9-substituted triptycene derivatives generally raises the barrier to rotation
about the 9-substituent-to-bridgehead bond, when the 9substituent is a primary or a secondary alkyl groupt'l. In 9(1-cyano- or 1-methoxycarbonyl-1-methylethyl)triptycene,
introduction of a chloro or a methyl group into the peri-position has been found to decrease the rotational barrierl2].
In order to see if this is a general phenomenon in 9-tert-alkyl substituted triptycene derivatives, and to investigate
the effects of some other perzsubstituents, we studied the
rotational barriers in 9-( 1,l-dimethyl-2-phenylethyl)triptycenes with a variety of peri-substituents and found an interesting dependence of the barrier on the nature of the
Previously we reported the stereoselective synthesis and
high rotational stability of 2,3-dichloro-9-( l,l-dimethyl-2pheny1ethyl)triptycene (1)'31.Reaction of 9-( 1 ,l-dimethyl-2phenylethy1)anthracene with dehydrobenzene derivatives
[*] Prof. Dr. M. Oki, Dr. G. Yamamoto, M. Suzuki
Department of Chemistry, Faculty of Science
The University of Tokio
Bunkyo-Ku, Tokyo 113 (Japan)
Restricted Rotation Involving the Tetrahedral Carbon, Part 32. This
work was supported by the Japanese Ministry of Education.-Part 31:
Angew. Chem. Int. Ed. Engl. 20 (1981) No. 6 / 7
Table 1 reveals that relatively small perz-groups (F or
OCH3) considerably increase the barrier relative to that for
the peri-unsubstituted derivative (1). while bulkier groups
(C1 or CH3) decrease the barrier. Since the barrier is the energy difference between the ground and the transition
states, the effects of peri-substitution on both should be examined.
9-tert-Butyltriptycene was used as a model compound
for these investigations. The crystal structure of its 1,2,3,4tetrachloro derivative (6) reveals the effects of peri-substitution on the ground state geometry16'. The most prominent
feature is the tilting of the tert-butyl and the peri-chloro
groups away from each other, due to steric compression.
This feature may be found to a greater or less extent in any
of the peri-substituted derivatives and can be represented
by the Newman projection (8); the peri-unsubstituted compound is shown in (7). The bulkier the peri-group, the
greater the degree of tilting of the axis bond and the
greater the ground state energy level.
0 Verlag Chemre GmbH. 6940 Weinheim, 1981
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fluorene, behavior, substitution, reaction, contrasting, bromomethyl, rotamer, methylphenyl
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