close

Вход

Забыли?

вход по аккаунту

?

Demonstration of Diastereomeric Electron-Donor-Acceptor Complexes by 1H-NMR Spectroscopy.

код для вставкиСкачать
GLC analysis of the crude reaction products revealed yields
of over 90 % of the corresponding esters. The yields of isolated
esters were lower (62-85 %), this being partly due to difficulties in the separation of the esters ( 5 ) from the excess alcohol
employed (Table 1).
[3] K . Griesbaum and H. Keul, Angew. Chem. 87,748 (1975); Angew. Chem.
Int. Ed. Engl. 14, 716(1975).
[4] P. Deslongchamps and C. Moreau, Can. J. Chem. 49, 2465 (1971).
R'OH
RCHO
f
RCH(OR')2
Demonstration of Diastereomeric Electron-DonorAcceptor Complexes by H-NMR Spectroscopy[**]
(3)
(2)
RCH=CHR
(1)
OR'
I
RCHOOH
H+
- H20
(4)
RCOOR'
(5)
Table 1. Yields ofesters on ozonolysis of olefins in the presence of HCI/R'OH
[a].
Olefin (1)
Ester (5)
Yield
["/.I
4-Octene
Stilbene
Cyclopentene
Cyclohexene
Cyclooctene
Cyclodecene
[bl
r.1
1,5-Cyclooctadiene
Norbornene
CH3CH2CH2COOCH3
C6H5COOCH3
CH3OOC(CH2)sCOOCHn
CH3OOC(CH2)4COOCH3
CH,OOC(CH2)6COOCH3
CH300C(CH2)8COOCH3
C2HsOOC(CH2)sCOOC2Hs
C3HiOOC(CH2)sCOOC,H7
CH,OOC(CH2)2COOCH3
Dimethyl 1,3-cyclopentaiie
dicarboxylate
(cis:trans=9: 1)
65
72
78
85
80
62
69
80
64
83
[a] Unless otherwise stated R = C H 3 . [b] R = C 2 H 5 . [c] R =n-CaHl.
Model reactions using selected olefins have shown that
the reaction apparently proceeds via the following steps: Initially, the Criegee-fragments ( 2 ) and ( 4 ) are formed[']. Acidcatalyzed dehydration of the alkoxy hydroperoxide ( 4 ) affords
in an exothermic reaction the ester (5)13], and at the same
time aldehyde ( 2 ) is converted into the acetal ( 3 ) . On further
treatment with ozone, (3) is finally converted into ester (5)k41.
Further work is underway concerning the course of the
reaction, possible side-reactions, and the scope of this method
with respect to variation of olefin and alcohol.
Typical Procedure
A mixture of 8.2g (0.1 mol) of cyclohexene and 87 ml of
a ca. 1 M solution of anhydrous hydrochloric acid in methanol
was ozonized at -78°C until ozone left the reaction vessel
(KI-trap). The mixture was then flushed with nitrogen and
subsequently allowed to warm. At approx. 0°C an exothermic
reaction set in (the mixture was cooled in an ice-bath so
that the temperature did not exceed 35°C). When the mixture
was free of peroxide, ozone treatment was continued for 24 h
at 0°C. Then the mixture was flushed with nitrogen, refluxed
for 3 h, and cooled to room temperature. Solid sodium bicarbonate was added, the mixture filtered, and the filtrate concentrated by evaporation at 35"C/15 torr. The liquid residue
was dissolved in 50ml of ether, washed with 3 x 20ml of
water, dried over sodium sulfate, and the ether distilled off.
Distillation of the residue (15.9 g) afforded dimethyl adipate,
b.p. of 88-9OoC/0.3 torr (purity 98.4 %); yield 14.8g (85.1 %).
Received: September 11, 1978 [Z 96 IE]
German version: Angew. Chem. 90. 999 (1978)
[ l ] Cf. P . S. Bailey: Ozonation in Organic Chemistry, Vol. I, Olefinic Compounds. Academic Press, New York 1978.
123 R . Criegee, Angew. Chem. 87,765 (1975);Angew. Chem. Int. Ed. Engl. 14,
745 (1975).
940
By Albrecht Mannschreck, Peter Roza, Hans Brockmann Jr.,
and Thorsten Kemmer[*]
Electron-donor-acceptor (EDA) complexes can frequently
be detected in the UV/VIS spectrum by a band at long wavelength. This is rendered more difficult if the band is situated
close to the absorption of a component. The change of NMR
shifts can also provide proof of EDA complexes[']; however,
further influences upon the 6 values, e. g. diamagnetic anisotropies, have to be taken into account besides genuine chargetransfer effects. In the case of chiral components, chiroptical
properties['] as well as 'H-NMR signal ~plitting'~]
by diastereomeric complexes represent further possibilities of investigation. The latter phenomenon may in principle be caused by
all types of molecular association, although PirkIe et al.[3a]
were the only ones to discuss such signal splittings in terms
ofan EDA interaction. Pirkle et al. suggested an EDA contribution besides hydrogen bonds for the complexation of dinitrophenyl compounds with 1-( I-naphthy1)ethylamine or 1-(9anthryl)-2,2,2-trifluoroethanol.We have now succeeded in
detecting diastereomeric EDA complexes unequivocally by
NMR spectroscopy.
For this purpose we chose components for association which
are available in optically active and in racemic form and
for which, in addition, a high tendency for complexation was
to be expected[4!
The fluorene derivative (R)-(2)which is used for preparative
and analytical separation of enantiorner~[~l
served as a n-acceptor. The carbazole derivatives[61(RS)-(I ), (RS)-(3),(RS)-(4),
and (RS)-(5) were chosen as n-donors. The charge-transfer
band of such EDA complexes around 500nm overlaps with
the absorption of ( 2 ) at longest wavelength (>.,,,ax = 355 nm,
l g ~ = 4 . 2 ,CHC13)[2a1.The 'H-NMR signals of H-I, H-6, and
H-8 in (R)-(2)as well as of H-4/H-5 in (RS)-(2) are shifted
to higher field by 0.1 to 0.3 ppm when the mixture in [D6]-acetone is cooled from +25"C to -68°C (Fig. 1, Table 1).
At the same time, the H-C-CH3
quartet of ( R S ) - ( I )moves
to lower field by 0.13 ppm, while all other C-H signals (except
the non-analyzed absorptions of further ring protons in (RS)( I )) approximately retain their positions. This behavior is
compatible with equilibria shifted in favor of the association
complexes by lowering the temperature, the shiftsl4I being
mainly due to the diamagnetic anisotropies of the two aromatic
[*] Prof. Dr. A. Mannschreck ['I, Dipl.-lng. P. Roza
Institut f i r Chemie der Universitat
Universitatsstrasse 31, D-8400 Regensburg (Germany)
Prof. Dr. H. Brockmann jr.
Fakultat fur Chemie der Universitat Bielefeld (Germany)
Dr. T. Kemmer
Gesellschaft f i r Biotechnologische Forschung GmbH
Braunschweig-Stockheim (Germany)
['I Author to whom correspondence should be addressed.
[*'I Application of NMR Spectroscopy of Chiral Associates, Part 7. This
work was supported by the Deutsche Forschungsgemeinschaft and by the
Fonds der Chemischen Industrie. Some of the measurements were carried
out by Dr. '
I
Burgemeisterand H.-H. Henschel. Weare grateful to Dr. G . Becher
and Dr. M . Holfk for discussions.-Part 6: M . Holfk, A. Mannschreck, Org.
Magn. Reson., in press.
Angew. Chem. Int. Ed. Engl. 17 (1978) N o . 12
4-p
y-5
Q2Y
tation['] of the components in the complex, which means a
change in the shift differences AS.-As expected, some signals
of the fluorene derivative (RS)-(2) are split (Fig. 2), if the
carbazole (R)-(3)16]is used as the optically active component.
yo2
0.01
0.01
H-1
II
H-8
0.02
N
0.01
0'
'
-0.01
H+COOH
c H3
(+ ( R ) - ( j ) ; -8OOC)
4-H
8.7.96
< 0.01
H-5
0.038
0.022
4-H
H-5
4-H
H-5
1.10
4.20
N
T
N
0.026 I
0.01
H7
' .C
OOH
CH3
(RS)-(3)
N
I
aro.01
I
H'F'C
OOC H3 H%-C OOC H, C H,
CH, 0.023
CH,CH,
0.02 0.01
< 0.01 < 0.01
( R S ) - (5)
(RS)-(4)
v
(+ ( R ) - ( 2 ) ; -7OOC)
Fig. 2. rr-Acceptor ( R S ) - ( 2 ) and rr-donors ( R S ) - ( 3 ) , ( R S ) - ( 4 ) , and ( R S ) - f 5 ) .
The numbers are A6 values in [D,]-acetone, i.e. differences between the
'H-NMR shifts of the ( R ) -and the (S)-enantiomer for the given combinations.
The molar ratio of optically active compound to (RS)-substrate is 1 . 1 : 1.
The above association complexes might be caused not only
by the EDAinteraction, but also by hydrogen bonds ofcarbonyl
groups. This possibility is excluded when two carboxylic esters
are paired. Thus, the ester (RS)-(I) behaves largely analogously in the presence of the carboxylic acid (R)-(2) (Fig.
1 and Table 1) and in the presence of its methyl ester"];
in addition, the AS values for both mixtures are very similar.
These findings, combined with literature statements['01,enable
us to conclude, that the EDA interaction, and not a possible
hydrogen bond, is of decisive importance for the relative orientation of the partners in the above complexes of esters with
acids.
The phenomenon described in this paper can serve to
demonstrate the presence of EDA complexes and, if optimized,
Fig. I . Some 'H-NMR signals (YO MHz, PFT method) of the x-donor ( R S ) - ( l )
in [D6]-acetoneat - 68°C in the presence of 1 .I 5 equivalents of the n-acceptor
( R ) - ( 2 ) (top) and ( R S ) - ( 2 ) (bottom). & Mean shift of corresponding protons
in ( R ) - ( 1 ) and (S)-(1 j . Ah: Difference of shifts of corresponding protons
in ( R ) - ( l ) and ( S ) - ( I ) . See Table 1 for details.
systems. The existence of the diastereomeric complexes[71(R)(2)...(R)-(f )and(R)-(2)...(S)-(I) followsfrom the additional
splittings of several absorptions of ( R S ) - ( I ) at - 68 "C, which
are diminished by raising the temperature. As expectedc3],
these shift differences (AS in Fig. 1, top, and in Table 1)
disappear by averaging, if the racemic compound (RS)-(2)
is used instead of the optically active one (Fig. 1, bottom).
Table 1. 'H-NMR signals of a mixture of ( R S ) - ( I ) and 1.15 equivalents ( R ) - ( 2 ) in [D,]-acetone at -68°C. 6: Chemical shifts; in the case of ( R S ) - ( 1 ) , 6
represents the averaged shift of ( R ) - ( l ) and (S)-(1 1. Ah: Difference of shift of corresponding protons in ( R ) - ( I ) and ( S ) - ( I ).
~
~1~
~~~~~~~~
(R)-(2)
( R S H1)
-
--
~
1.78
7.0
4
:
?
5.85
7.0
0.01
r.1
0.023
H-I, H-2, H-3
H-6, H-7, H-8
H-C-CH,
H-C-CH2
CH,-CH,
7.5-6.8
Assign- H-4, H-5 [b]
ment ,
~~
LF19.36
J13=2.1
0.029 H-1 [c]
~~
~
8.97
J13=2.1
8.79, 8.65
J68=2.1
5.34
7.0
1.85
7.0
-
-
-
-
H-3
H-6, H-8
H-C-CHa
H-C-CHJ
_
[a] This value cannot be determined precisely because the H-C-CH3
absorption of ( R ) - ( 2 ) IS close; A6 IS probably <0.01. [b] Assignment analogous to
cdrbazole and 9-methylcarbazole, the protons of which were assigned via "C-NMR shifts and selective "C{ 'H} decoupling experiments. We are grateful to
Dr. L. Ernsf, Braunschweig-Stockheim, for these measurements. Cf. P. J. Black, M . L. Hefernan, Aust. J. Chem. 18, 353 (1965). [c] Assignment analogous to
H . Paulsen, K . Todt, H. Ripperger, Chem. Ber. 101, 3365 (1968), and references cited therein.
The comparison of the A6 values of the carbazole derivative
(RS)-(I) (Table 1) with those of (RS)-(3), (RS)-(4), and (RS)( 5 ) (Fig. 2) shows that the spatial positions of H-4 and H-5
in the complexes with (R)-(2) are changed by modifications
of the distant substituent in the 9-position of the carbazole
nucleus. The spatial position of the N-C--H
atom is
apparently changed to a lesser extent. The modification of
a substituent probably brings about a change in relative orienAngew. Chem. I n t . Ed. Engl. 17 (1978) N o . 12
to measure the enantiomeric purity. Independently, we aim
to understand the 6- and AS-values in terms of the orientation
of the components in solution.
Received: August 28, 1978 [Z 94 IE]
German version: Angew. Chem. 90, 995 (1978)
[ l ] 1 . P r i m , J . W Verhoeven, 7: J . d e Boer, Org. Magn. Reson. 9, 543
(1977), and references cited therein.
941
_
[2] a ) G . Brieyleb, H . C . Kuhull. K. Henschel, Z. Phys. Chem. N. F. 46.
229 (1965); b) H . Wjnherg, K . Lammertsmu, J. Am. Chem. Soc. 95,
7913 (1973).
[3] a ) W H . Pirkle, D . L . Sikkenqu. J. Org. Chem. 4 2 . 1370 (1977), and
earlier papers by W H . Pirkle et a!.: b) A . Munnschreck. Nachr. Chem.
Tech. 23, 295 (1975).
[4] Cf. R. Foster. Organic Charge-Transfer Complexes. Academic Press,
London 1969.
[5] F . Mike.?, G . Bosltart, E. GI/-At,, J. Chromatogr. 122, 205 (19761, and
references cited therein.
[6] ( R S ) - ( I ) . m.p. 50-52°C; (RS)-(3), m.p. 148°C; ( R H 3 ) . m.p. 100103°C. [ x ] : i 9 = -65" (<=0.23, CHC13), enantiomeric purity 2 9 2 %,
absolute configuration by chemical correlation with (R)-alanine;
( R S ) - ( 4 ) ,m.p. 92- 94"; (RS)-(SJ, m.p. 66- 67°C.
[7] EDA complexes consisting of more than two components would not
change the conclusions drawn.
[8] Cf. H. A. Srauh, I! Tuglieher. Chem. Ber. 110. 3366 (1977). and earlier
papers.
[9] 7: Burqemeister, P. Rozu, A. Munnschreck. unpublished results.
[lo] N . Muller. P. I. Rose, J. Phys. Chem. 69. 2564 (1965).
1,5-CycIooctadien-%yne-A
CsH8 Hydrocarbon[**]
Novel, Highly Reactive
By Herbert Meier, Toni Echter, and Herrnanr~Petersen"]
To the prominent family of C& hydrocarbons belong
the well-known members styrene, cyclooctatetraene, cubane,
barrelene, semibullvalene, and 1,5-cyclooctadiyne. We have
now succeeded in isolating a new isomer, namely the highly
strained and thus highly reactive eight-membered ring compound 1,5-cyclooctadien-3-yne (7).
I
140°C
CsH,
I
(91, m.p.= 2 2 2 " C
I
~
69%
111). m.p. = 2 6 6 - 2 6 8 ° C
The cyclooctadienyne (7) can be stored in the solid state
in the absence of oxygen. Above the melting point at ca.
- 15°C it begins to decompose. When dissolved in CDCI3
its halflife at 27°C is about 2h. The lifetime of (7) is not
only limited by di- and oligomerizations, as expected for
strained cycloalkynes, but also by an intramolecular process
with a low energy barrier: The transformation into cyclooctatetraene can be explained in terms of two thermally allowed,
suprafacial I ,5 H-shifts. A mechanistic alternative is intramolecular rn2+ ,2 + ,2] cycloaddition, a novel type of reaction with oCH
bonds, reminiscent of the diimine reduction
of olefins141.
The extremely high degree of ring strain (7) is also manifested in the spectroscopic properties. The 3C-NMR spectrum
shows four signals: The saturated C-atoms absorb at 6= 32.6,
the olefinic C-atoms at 6= 152.0 and 112.7; for the sp centers
an extremely large downfield shift of 6=116.3 is observed.
From these data an energy of geometrical strainrS1of ca.
18 kcal/mol is estimated (cyclooctyne has a geometrical strain
energy of 12 kcal/mol). From the data it also follows that the
moleculemust havea symmetry axis or a symmetry plane (C2 or
C, conformation). From the 'H-NMR spectrum recorded at
-40°C it can be concluded that no rapid ring inversion
takes place under these conditions (AA'BB'XX'YY' system).
According to a simple force-field calculation, the C, conformation ought to have a higher energy than the C 2 conformation.
Analysis of the 'H-NMR spectrum is fully consistent with
a C2 conformation.
ASe
N
HA%HA'
H,
I
H,,
H ~ f
,
Hy
(7) (CZ)
(6)
(7), 8 - 1 0 %
In the synthesis of (7) the route to ( 4 ) described by Cantrell
and Solomod'l has been shortened by one step and the yield
of ( 4 ) vastly improved. 1,2,3-Selenadiazole (6) is accessible
via the semicarbazone (5)lz1; thermolysis of (6) over copper
powder in an atmosphere of N 2 leads to (7). As soon as
reaction sets in, the initial pressure is reduced from 70 to
1 torr and the volatile fragmentation product (7) is frozen
out in a cold trap with liquid nitrogen. (7) can be trapped
irz situ in much higher yields; besides tetracyclone ( 8 ) , which
has proven suitable for Diels-Alder cycloaddition, rhodium
complexes of type ( I O ) ~are
~ ] particularly efficient trapping
reagents :
--
[*I
Prof. Dr. H. Meier, T. Echter. Dip].-Chem. H. Petersen
lnstitut f i r Organische Chemie der Universitit
Auf der Morgenstelle 18. D-7400 Tiibingen 1 (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
942
We thus have the relatively rare case of a chiral hydrocarbon
without an asymmetric C-atom. At room temperature the
X and Y parts of the spectrum (at 6 = 1.2 and 2.9, respectively)
broaden and lose their fine structure; the AB part remains
practically unchanged [ S = 5.8 (HA),6.6 (HB)].The coalescence
point is reached at 6 0 T , corresponding to a A G + of ca.
16 kcal/mol for the transition state. At room temperature,
1,5-cyclooctadiene and 1,3,5-cyclooctatriene exhibit rapid ring
inversion; the coalescence temperature lies, e. g, for the triene,
at - 136"C16].Replacement of a CC single or double bond
by a triple bond leads to a rigid conformation owing to
increased ring strain. The coalescence temperatures of cyclooctyne and the cyclo~ctenynes[~~,
however, lie below room temperature. Only introduction of the second double bond into
the eight-membered ring alkyne effects freezing-in of ring inversion. If the double bond is replaced by annelated benzene
units, then the effect is enhanced16*'!
Received: September 8. 1978 [Z 98 IE]
German version: Angew. Chem. 90. 997 (1978)
Aiigew.
Chem. I n t . Ed. Engl. 17 (1978) No. 12
Документ
Категория
Без категории
Просмотров
0
Размер файла
320 Кб
Теги
spectroscopy, nmr, acceptor, demonstration, donor, electro, complexes, diastereomeric
1/--страниц
Пожаловаться на содержимое документа