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Carbo-Claisen Rearrangement of 8-endo-Phenylbicyclo[5.1

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of the diazo compounds ( 4 a)-(4e)l31 in cycloheptatriene,
isomerize to the tricyclic compounds ( 9 ) at as low a temperature as ca. 130°C. Their structures are established by the
'H-NMR spectra and X-ray structure
of ( 9 b ) .
The structures of the hitherto undescribed compounds (all
compounds in Table 1) follow unequivocally from the spectra
(MS, 'H-NMR, IR) and elemental analysis.
Procedure:
Diphenylvinylarsane (1.28g, 5 mmol) dissolved in THF
(75 ml) is added dropwise to n-butyllithium ( 5 mmol) in T H F
(75 ml) at room temperature. After 30min, the reaction mixture
is hydrolyzed with HzO, the aqueous phase extracted with
chloroform (3 x 75 ml), and the dried organic phases evaporated. Distillation of the oily residue affords n-hexyldiphenylarsane [I .48 g (95 %), b. p. 102"C/0.6 torr].
Received: July 6, 1977 [Z 805b IE]
German version: Angew. Chem. 89, 760 ( 1 977)
Publication delayed at authors' request
R.
JJ
Nz=C,
R
(41
r
CAS Registry numbers:
( I ) , Alk=C2H5, 811-49-4; ( I ) , Alk=nC4H9, 109-72-8; ( I ) , Alk=sC4H9,
.
598-30-1; ( l ) , Alk=tC4H9, 594-19-4; (31, 61193-58-6; ( 4 ~ ) Alk=CzHS,
38563-45-0; ( 4 a ) , Alk =nC4H9, 63866-85-3; ( 4 a ) , Alk=sC4H9. 63866-86-4;
( 4 a ) , Alk=fC4H9, 63866-87-5; ( 4 6 ) , Alk=nCqH9, 63866-88-6; ( 4 6 ) , Alk=
sC4H9, 63866-89-7; ( 4 6 ) , Alk =rC4H9, 63866-90-0; phenyl vinyl selenide,
351 67-28-3; A S ( C ~ H ~ ) ~3095-87-2;
/B~,
As(C6H&/CI, 712-48-1
(71
( a ) : R = PO(OCH3),, X = H
[l]
[2]
[3]
[4]
[5]
Compounds Alk-CH2-CHLi-As(C6Hs)2
command little interest as
reagents owing to their modest nucleophilicity.
Cf. Th. Kauffmann, H. Fischer, A . Wolrrrmann, Angew. Chem. 89, 52
(1977): Angew. Chem. Int. Ed. Engl. 16, 53 (1977).
Cf., e.g., E. J . Wakefield: The Chemistry of Organolithium Compounds.
Pergamon, Oxford 1974. The action of lithium leads to coupling in
the case of alkyl iodides.
Exchange for a CI atom has not yet been accomplished.
M . S e w i n , W Dumonr, L . Heuesi, A . Krief, Tetrahedron Lett. 1976,
2647, achieved ca. 20 %, C6H5Se/Brexchange with primary alkyl phenyl
selenides.
Carbo-Claisen Rearrangement of
&endo-Phenylbicyclo[5.l.O]octa-2,4-dienes~**~
By Gerhard Maas and Manfred Regitzpl
In contrast to the Claisen rearrangement of ally1 phenyl
ethers, the Cope rearrangement of a 1,s-hexadiene whose double bond belongs to an aromatic system as in ( I ) , known
as the "carbo-Claisen rearrangement'"'], normally defies
attempts at direct observation. This is because the only way
in which the primary product (2) of the sigmatropic [3,3]
shift can undergo rearomatization, apart from the reverse
reaction to ( I ) , is by a thermally forbidden 1,3 hydrogen
shift to form (3). The isomerization ( 1 ) -+ (3) is therefore
only observed in the presence of a strong base, which presumably catalyzes the step ( 2 ) + (3)['].
We have found that the 8-endo-phenyl substituted bicyclo[5.1.0]octa-2,4-dienes ( 5 ) , formed together with minor
amounts of the exo isomer (6) on photolytic decomposition
[*] Prof. Dr. M . Regitz, Dr. G. Maas
Fachbereich Chemie der Universitat
Pfaffenbergstrasse 95, D-6750 Kaiserslautern (Germany)
[*'I Carbenes, Part 16.-Part 15: G. Maas, M. Regirz, W lllger, Chem.
Ber. 111 (1978).
Angew. Chem. Int. Ed. Engl. 16 (1977) No. 10
( b ) : R = PO(OCH3)z, X = OCH,
(C):
R = C02CH3, X
( d ) : R = PO(CsHs)z, X = H
l e i : R = CsH9 X = H
H
The transformation ( 5 ) + ( 9 ) can be interpreted as a carboClaisen rearrangement of ( 5 ) to (8), which is subsequently
stabilized in a thermally allowed 1,s-homodienyl hydrogen
shift with regeneration of the aromatic system to give ( 9 ) .
The isomerization ( 5 a)-+(9a) was examined by
H-NMR spectroscopy in the temperature range 1 19.21463°C; it is found to be a first-order reaction with
k=(6.4+3.5)x 10'l exp[(29.3+0.4)RT]
and A S * = -7.1
k0.9 cal K-' mol-' (for a mean temperature of 133°C).
These data do not permit any decision whether the formation
of (8) is concerted or proceeds via the diradical (7); however,
evidence favoring participation of ( 7) comes from the known
ease of homolytic ring opening of vinylcycl~propanes~~~
and
from the observation that ( 5 e ) rearranges to the tricyclic
about twice as fast as ( 5 a ) - ( 5 d ) .
Procedure:
A solution of ( 4 a ) (11.32 g,- 50 mmol) in cycloheptatriene
(1 80ml) is irradiated for 22 h (Philips HPK 125W). The excess
of cycloheptatriene is distilled off, and the oily residue dissolved
in ether (30ml). Colorless ( 5 a ) (2.50g) of m.p. 121°C is
obtained at 0°C. Chromatography of the filtrate on silica
gel (360g, Woelm 0.2-0.5mm) with ethyl acetate (3100ml)
and ethyl acetate/methanol9 :1 (800ml) affords colorless compound ( 6 a ) (0.54g, 4%), m.p. 129°C (ether), and a further
crop of ( 5 a ) (1.31 g; total yield 3.81 g, 26 %).
A solution of ( 5 a ) (1.5Og) in xylene (10ml) is heated under
reflux for 9.5 h. The reaction mixture is evaporated down in
vacuo, the residue treated with activated charcoal/chloroform,
and after filtration the solvent is again removed and the residue
recrystallized twice from ether/petroleum ether 30-75 "C
(1 : 1): yield of ( 9 a ) , 1.Og (67 %); m.p. 69°C. IR (KBr): 3030,
3005, 2963, 2925, 2855 (CH/CHz), 1655, 1607 (C=C), 1255
(PO), 1063, 1038, 1028cm-' (POC). 'H-NMR (CDCI3):
6 = 1.70-2.95 (CH2 and CH-cyclopropane), 3.28-3.55 (CHbenzyl), 3.65 and 3.79 (each d, 'JpH= 10.8 Hz, OCH3), 5.39
and 5.98 (each dd, CH-olefin), 6.85-7.30 (m, 3 H-aromatic),
7.80-8.1 Oppm (1 H-aromatic). A correct elemental analysis
is obtained.
711
Received: August 3, 1977 [Z 809 IE]
German version: Angew. Chem. 89,763 (1977)
CAS Registry numbers:
( 4 a ) , 16965-72-3; ( S o ) , 58576-61-7; ( 5 b ) , 63798-06-1; ( S c ) , 63798-07-2;
( S d ) , 63798-08-3; ( S e ) , 63798-09-4; ( 6 a ) , 63864-77-7; ( 9 a ) , 63798-10-7;
( 9 b ) , 63798-1 1-8; ( 9 c ) , 63798-03-8; ( 9 d ) , 63798-04-9: (9e), 63798-05-0;
cycloheptatriene, 544-25-2
"1
Review: G . Maier: Valenzisomerisierungen, 1st Edit. Verlag Chemie,
Weinheim 1972, pp. 52, 180.
PI W ti. E. Doering, R . A . Bragole, Tetrahedron 22, 385 (1966).
~1 ( 4 a ) and ( 4 b ) : H . Scherer, A . Hartmann, M . Regitz, B. D. Tunggal,
H . Giinther, Chem. Ber. 105, 3357 (1972); ( 4 c ) by analogy with the
ethyl ester; M . Regitz, F . Menz, ibid. 101, 2622 (1968); ( 4 d ) : M . Regirz,
W Anschiitz, ibid. 102, 291 6 (1 969); ( 4 e ) : H. Staudinger, E. Anthes,
F . Pfenninger, Ber. Deut. Chem. Ges. 49, 1928 (1916).
~ 4 1(9b)formsorthorhombiccrystals,Pna21, with a = 1223.5(7),b= 1416.8(8),
c=898,3(8)pm, rx=p=y=90", Z = 4 , d , , , , = I . 3 7 g ~ m ~ ~The
. structure
was solved by direct methods and refined to R =0.030 for 754 reflections
with Fo>4cr(Fo).
PI The activation energy for the vinylcyclopropane/cyclopentenerearrangementis49.7kcalmol~',but can bereduced tovaluesaround 30kcal mol-'
by radical-stabilizing substituents, see, e.g.: J . S. Swenton, A . Wexler,
J . Am. Chem. SOC.93,3066 (1 971); J . M . Simpson, H . G . Richey, Tetrahedron Lett. 1973, 2545; G . H . Richey, D . W Shulf, ibid. 1976, 575.
Thermal Rearrangement of Silylmethyl Acetates"]
By Manfred T Reetz and Norbert Greifl"]
Two routes are formally open for dyotropic rearrangements['] of compounds of type (I) to form a strong Si-0
bond: a silyl-acyl or an acyloxy-methyl exchangef31 to the
more stable valence isomers (2) and ( 3 ) , respectively. Heating
of ( l a , b ) at 130--195°C in inert solvents gives (3a, b )
in almost quantitative yield.
c
\
4) The trifluoroacetate rearranges faster than the acetate:
564.
5) The fluorene derivative (1 c) is stable under the reaction
conditions; only on raising the temperature (230°C)does slow
decomposition set in.
6) Replacement of the trimethylsilyl group in ( l a ) by a
[D9]-trimethylsilyl group leads to a secondary kinetic isotope
effect of kH/kD=0.81 f0.05.
7) In the acetate ( 4 a ) both the methyl and the phenyl
groups migrate to form ( S a ) and ( 6 a ) in the ratio 60:40
(yield > 90 %), while in the bromide ( 4 b ) only a quantitative
migration of the methyl groups is observed to give (Sb)"].
k(tbi/k(iai=
YfiHS
HSC6,
C--Si-CH3
-+
(C6H5)3C-Si(CH3)2 +
I
&H3
H5c6/i
X
151
(4)
H5C6\7H3 76H5
,C-Si-CH3
H5c6
14)
(a): X = OC(O)CH3
(b): X
=
Br
The entropy of activation for (Ia)+(3a) and the unexpectedly high thermal stability of ( I c ) can be rationalized neither
by a concerted dyotropic process nor by a two-step free-radical
mechanism. An ionic mechanism involving contact ion pairs
(7) and (8) also appears unlikely on account of the lack
of solvent dependence. Without precedent, and yet in accord
with our findings, is a rate-determining intramolecular migration of the nucleofugal group to the silicon to form an inverted
ylide ( 9 ) , which transforms via a fast 1,2 shift into (3). The
differing behavior of ( 4 a ) and ( 4 b ) could be the result of
stereoelectronic factors at pentavalent silicon. The results of
solvent studies could be interpreted by assuming the formal
positive charge at the cationic center of ( 9 ) to be delocalized
as a result of hyperconjugation with pentacoordinate silicon.
The question whether negatively charged hypervalent groups
can stabilize carbenium ions has not previously been posed
in general terms. However, it is known that compounds of
pentacoordinate silicon are stable only if electronegative
ligands effect a d-orbital contraction171. In this connection,
carbenium ions are ideal substituents.
H3
--Si( C H3)2
R /
R' O\, )O
C
2C
,
( a j : R' = R 2 = c 6 H 5 , R~ = C H ~
( b J : R1 = R 2 = C6H,, R3 = C F 3
(C): R1 f R 2 = 2,2'-Biphenyldiyl,R3 = CH3
I
R3
(31
We attempt to interpret the mechanism of this smooth
valence i~omerization[~]
with the aid of the following findings:
1 ) Crossover experiments prove that both the methyl and
also the acetoxy groups undergo intramolecular migration
to an extent exceeding 95%.
2) The rate of rearrangement is practically independent
of solvent polarity: k,,, for ( I a)+ ( 3 a ) : 1.0 (benzene); 0.9
(acetonitrile); 1.3 (propylene carbonate).
3) The activation parameters for ( 1 a ) - ( 3 a ) in benzene
are: AH*=33.1+0.8 kcal mol-', AS*=-5.3&1 cal mol-'
K - I ; in acetonitrile they are: AHf=34.0+0.8 kcal mol-';
A S + = -3.6+lcalmol-'K-'.
p]
712
Doz. Dr. M. T. Reetz, Dr. N. Greif
Fachbereich Chemie der Universitat
Lahnberge, D-3550 Marburg 1 (Germany)
I
R3
(9)
Two-step dyotropic mechanisms forming inverted ylides
are therefore conceivable for related rearrangernent~l~,
']-this
working hypothesis is currently being tested.
Received: August 4, 1977 [Z 811 IE]
German version: Angew. Chem. 89, 765 (1977)
CAS Registry numbers:
(1 a ) , 63832-90-6; (1 b ) , 63832-91-7; (1 c ) , 63832-92-8; (3a), 63832-93-9;
( 3 6 ) , 63848-87-3: ( 4 a ) , 63832-94-0; ( 4 b ) , 62092-84-6; ( 5 a ) , 63832-95-1 ;
( S b ) , 62092-85-7; ( 6 a ) . 63832-96-2
[I]
Dyotropic Rearrangements, Part 14. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Induhe.-Part 13: M . 7: Reetr, N. Greif; Chem. Ber. 110, 2958 (1977).
Angew.
Chem. In?. Ed. Engl. 16 (1977) No. 10
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