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Condensation Reactions of 1 3-Dimethyl-6H-cyclohepta[c] thiophen-6-one.

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ation of ( / ) is slow and does not interfere with the electrode
reaction. Logarithmic analysis of the broad reduction wave,
by computer
demonstrated two one-electron transitions
with similar half-wave potentials a n d equal limiting currents. The difference between the half-wave potentials
and EFi2 is 70 mV; this is a measure of the electrostatic
repulsion energy of the two electrons in the highestoccupied
M O of ( l ) [ l O l . For the hydrocarbon (41,the potential
diKerence is 200 mV [81. It becomes intelligible why these
potential differences should not be identical if one assumes
that ( I ) has a triplet ground state; i.e., the electron correlation for the triplet state leads t o a repulsion energy that
is lower than that for the singlet.
ESR spectroscopic measurements were carried out with the
object of detecting the triplet ground state of ( I ) . To avoid
complete association of ( I ) , we dehalogenated a toluene
solution of ( I ) for a short time with Ag powder, then
filtered the solution, warmed it t o 80"C, a n d thereafter immediately cooled it t o -180 "C. T h e ESR spectrum of the
resulting glassy toluene solution showed, as well a s an
intense monoradical transition at 3250 G, several lines with
Am
1 which are characteristic of a triplet molecule
(Fig. 1). We assign the triplet spectrum t o the monomeric
hydrocarbon ( I ) . The zero-field splitting parameters determined from t h e lines with Am - 1 [ 1 1 1 have the following
values. ID/ = 0.0079 cm-1, I€] < 0.0005 cm-1. The resonance field strength of the extremely weak transition with
d m = 2 could not be measured.
3250 G
LI"
Fig. I . ESR-Spectrum of rn-phenylenebis(diphenyliiiethy1) (I) In
glassy t o l u e n e at ca. -180°C. R e s o n a n c e field s t r e n g t h of t h e free electron Hi,
3251 G.
We have determined the relation between the amplitudes of
the transitions with Am = I and temperature in the region
lo&-150 "K. If the effect of temperature T o n signal amplitude I is interpreted as a result of a singlet-triplet equilibrium, the following relation applies [31:
T o verify our results theoretically we have carried o u t
SCF-CI calculations for ( I ) by the Pariser-Parr-Pople
procedure [12-131. The parameters used were gauged from
t h e electron spectra of carbonium ions of the triphenylmethane series"41. 41 singly excited conhgurations were
introduced into the configuration interaction. The calculations were effected for a planar and for a twisted conformation of ( l ) , whose structure is related t o that of the
triphenylmethane carhonium ions. I n each case the calculations gave a triplet ground st;t:e T1 which is more stable
than the singlet state SO by, respectively, 1.07 and 1.19 eV.
The calculations thus ccnfirm that ( I ) has a triplet ground
state.
Received: S e p t e m b e r 7. 1970
[Z 286 IE]
G e r m a n version: Angew. Chcni. 82, 9 3 5 (1970)
.
[*I Dip1.-Chem. G . Kothe, K.-H. Denkel, and
Dip1.-Chem. W. Siimmermann
Institut ftir physikalische Chemie der Universitit
78 Freiburg, Albertstrasse 21 (Germany)
[ l ] P . Baumgartner, E . Weltin, G. WagniPre, and E . Heiihronner. Helv. Chim. Acta 48, 751 (1965).
[2] R. E. Jesse, P. Biloen, R. Prim, J . D . W . v m Voomt, and
G. J . Huijrink, Mol. Physics 6, 663 (1963).
[ 3 ] R. Breslow, R . Hill, and E. Wassernian, J . Amer. Chem.
SOC.86,5349 (1964).
[4] H . van Willigen, J . A . M . van Broeklroven, and E. de Boer,
Mol. Physics 12, 533 (1967).
IS] H . C. Longuet-Higgins, J. Chem. Phys. 18, 265 (1950).
161 W . Schfenlc and M . Brauns, Ber. Dtsch. Chem. Ges. 48. 661
(191 5 ) .
[7] R. C. Reitz and S . I . Weissman, J. Chem. Phys. 33, 700
(1960).
[8] W . Siimmermann, G . Kothe, H. Baunigurtel, and H . Zinimermann, Tetrahedron Lett. 1969, 3807.
[9] H. Werner, unpublished.
[lo] H . S . Hi& and 1. Blackledge, J. Chem. Phys. 23, 514
(1955).
[ll] E. Wasserrnrmn, L. C. Snyder, and W. A . Yager, J. Chem.
Phys. 41, 1763 (1964).
[12] R . Pariser and R . G. Parr, J. Chem. Phys. 21, 466, 767
(1953).
[13] J . A . Pople, Trans. Fdraday SOC.49, 137 (1953).
I141 G. Kuthe, N . Fliegen, E . Sciiulre Steinberg, J . Heinze, and
H . Zitnmerrrrann, Ber. Bunsenges. Phys. Chem. 74, 977 (1970).
Condensation Reactions of 1,3-Dimethyl6H-cyclohepta [clthiophend-one [1,21
By Glinther S e i t i a n d Heinrich Monnighoff[*l
where A E
= Etriplet - - Eslnglet
and C is a constant.
When AE = 0, the relation simplifies t o the Curie law,
which is approximately followed for o u r measurements.
We were unable t o determine A E exactly from the divergences from the Curie law. Since the divergence from the
equation of the simple Curie law must be appreciably
smaller when A E < 0 than when A E > 0, o u r experimental
findings indicate a triplet ground state for (/).
Angew. Chem. internot. Edit. ,' Vol. 9 (1970)
/ No. I1
By using the anhydride rnethod[31 we have effected the first
condensation reactions of compounds containing reactive
methylene groups with 1,3-dimethyl-6H-cyclohepta[c]thiophen-6-one ( 1 ) [41.
Heating ( I ) with l,Z,3,4-tetrachlorocyclopentadiene(2) in
acetic anhydride gives the potentially dipolar 6x-107
system ( 3 a ) , m.p. > 340 O C , in 35 % yield as brownishred crystals, and a similar reaction with pentamethyl
1,2,3,4,5 - cyclopentadienepentacarboxyIate [51 gives (31,
907
m.p. > 340 "C, in 48 % yield as permanganate-colored
needles with a metallic sheen.
By the same method 4,5-dichlorocyclopentene-1,3-dione
( 4 ) [61 afforded the ocher-colored heterosesquifulvalenequinone (51, m.p. > 305 "C (dec.) (43 % yield), which we
characterized by conversion by butylamine into the more
soluble derivative (61, m.p. 232 "C (dec.) (yield 76 %).
however, shifted bathochromically by 20 nm. The positive
solvatochromism established for all the compounds from
the electron spectra indicates high occupancy of the apolar
limiting formula in the ground state. This is confirmed by
the position of the nitrile band in the I R spectrum of (7) at
2217 cm-1, which is at 12 cm-1 shorter wavelength t h a n i t is
for 8,s-dicyanoheptafulvene 191.
Received: February 9, 1970;
revised: September 8, 1970
[ Z 287 IE]
German version: Angew. Chem. 82. 938 (1970)
Separation of Compounds with Failure Sequences
in the Solid-Phase Synthesis of Peptides by Means
of the Anhydride of 3-Sulfopropionic Acid
By Hons Wissinann and Rolf Geiper[*l
'CH3
Treating ( I ) with malonodinitrile led t o the orange-yellow
condensation product ( 7 ) , m.p. > 33OoC (dec.), in 24%
yield.
The new compounds were characterized by elemental analysis and spectroscopic properties. However, their low
solubility prevented us from obtaining usable N M R spectra
for ( 3 a ) and ( 5 ) even by the Cat procedureI71. The N M R
spectra of ( 3 a ) and ( 7 ) are characterized by a n AB quartet
( J = 12.5 Hz) for the four seven-membered ring protons,
whose resonance positions were largely influenced by the
anisotropic effects of the substituents, so that they yield no
information on the polarity of the ground state. In (6) H-5
and H-7 are magnetically non-equivalent; they were recorded as a multiplet centered at 8.12 and 8.45 ppm, whereas
the multiplet for H-4 and H-8 appeared a t 7.03 ppm.
The 1R spectra are characterized by a n intense band in the
region around 1610cm-* which is ascribed to a vc=c
vibration.
The electron spectrum of (Ja) is of the same shape as that
of the iso-x-electronic 7-(tetrachlorocyc1opentadienylidene)7H-benzocycloheptene 181, whose longest-wave maximum is,
[*I Priv.-Doz. Dr. G. Seitz and H. Monnighoff
Institut fur Pharmazeutische Chemie der Universitat
355 Marburg, Marbacher Weg 6 (Germany)
[l] This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
[2] Part 7 of Cyclopentadienylidenes. - Part 6: G . Seitz and
H . Miinnighof, Liebigs Ann. Chem. 732, 131 (1970).
131 G . Seitz, Angew. Chem. 81, 518 (1969); Angew. Chem.
internat. Edit. 8, 478 (1969).
[4] A . A . Ginesina, L . N . Kivokurtseva, and A . V . El'tsov, Zh.
Org. Khim. 5, 570 (1969); H . Monnigho$; Dissertation, Universitat Marburg, probably 1971.
(51 E. Le Goffand R . B. La Count, J. org. Chem. 29, 423 (1964).
[6] A . Roedig and L . Hornig, Chem. Ber. 88, 2003 (1955).
[7] We thank Drs. H . Feltkamp and D . Wendisch, Farbenfabriken Bayer, for the nuclear resonance measurements by the
Cat method.
181 Y . Kitahara, I . Murata, and S . Karagiri, Angew. Chem. 77,
345 (1965); Angew. Chem. internat. Edit. 4 , 353 (1965); Tetrahedron 23, 3613 (1967).
[9] T . Noroe, T. Mukai, K . Osaka, and AT. Shishido, Bull. Chem.
SOC.Japan 34, 1384 (1961).
908
The synthetic steps i n the Merrifield solid-phase synthesis
of peptides d o not always afford homogeneous peptides in
desirably high yields "-31. This leads to impurities and compounds with failure sequences that are often so similar to
the desired end products that they cannot be separated from
them by the available methods of purification. One way of
overcoming this difficulty is t o use a n acylating agent t o
block the amino groups that escape reaction, a method that
also facilitates removal of by-products. For this purpose
Wieland and his co-workers [41 used 3-nitrophthalic anhydride. We use the cyclic anhydride of 3-suIfopropionic
acid (I) [51, which reacts with the by-products to give N a (3-sulfopropionyl) derivatives that, owing to their high
acidity, can be separated by simple filtration through a
weakly basic ion-exchanger (acetate form). This treatment
with a n ion-exchanger has usually to be undertaken in any
case so as to afford the acetates from the peptides liberated
from the carrier by HBr/trifluoroacetic acid; thus o u r purification does not require any additional experimental step.
If peptide bonds are also attacked under the conditions o f
acylation with (Z), the diacylamides can be cleaved by
cautious aminolysis before the peptide is separated from
the polymer. This would either regenerate the original
peptide bond or, in the case of cleavage of the peptide chain,
afford fragments that can be washed out or separated by
means of the incorporated sulfo groups.
Experimental:
H-Cys(Bz1)-Tyr(Etoc)-Phe-Gln- Asn- Cys(Bz1)- Pro-Arg(N02)-Gly-NHz 161: Boc-Gly polymer ester (10 g), prepared
as described in ref.
with 0.36 mmole of Gly per g of resin,
is deacylated and acylated with Boc-Arg(N02)-OH. The
resin is then extracted with dimethylformamide (50-ml portions) by shaking four times, each for 3 min. During this
period, ( 1 ) (4g) is dissolved, with cooling, in anhydrous
tetrahydrofuran (20 ml), and the cooled solution is added
to the Boc-Arg(NO2)-Gly polymer. N-Ethylmorpholine
(7.5 ml) in dimethylformamide (1 5 ml) is then a t once added
and the whole is shaken for 1 hour a t room temperature.
Thesolvent is then filtered off and the solid is washed four
times with ethanol (50-ml portions) and four times with
glacial acetic acid (40-ml portions), after which the Boc
group is removed by 1 N HCI in glacial acetic acid. The
further amino acids are added by analogous procedures,
the following derivatives being used: Boc-Pro-OH 171,
Boc-Cys(Bz,l)-OH "1,
Nps-Asn(Mbh)-OH (81,
Nps-Gln(Mbh)-OH[sl, Boc-Phe-OH [71, Boc-Tyr(Etoc)-OH [91.
Yield: 14.9 g of peptide-polymer compound.
This compound (3.0 g) was treated with HBritrifluoroacetic
acid as described in ref. [I]. The crude peptide mixture was
reprecipitated from ethanol by ether and then heated in t r i fluoroacetic acidianisole ( 9 : l ) for 5 min for complete
removal of the Mbh groups, and was finally precipitated by
Angew. Chem. infernnt. Edit.
/ Vol. 9
(1970) 1 No. 11
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