Diels-Alder reactions of 1,1,4,4-tetrafluorobutatriene

Article abstract of DOI:10.1039/b922424f

At low temperature 1,1,4,4-tetrafluorobutatriene undergoes Diels-Alder reaction with various dienes; the structure of one product and its isomerisation derivative has been elucidated by X-ray crystallography. The Royal Society of Chemistry.

Full text of DOI:10.1039/b922424f

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Diels–Alder reactions of 1,1,4,4-tetrafluorobutatrienew
Christian Ehm and Dieter Lentz*
Received (in Cambridge, UK) 27th October 2009, Accepted 9th February 2010
First published as an Advance Article on the web 24th February 2010
DOI: 10.1039/b922424f
At low temperature 1,1,4,4-tetrafluorobutatriene undergoes
Diels–Alder reaction with various dienes; the structure of one
product and its isomerisation derivative has been elucidated by
X-ray crystallography.
methyl methacrylate, acrylonitrile, octafluoro-1,2-dimethylene-
cyclobutane, tetraphenylcyclopentadienone, 2,5-dimethyl-
1,3,4-thiadiazole, trimethylsilylazide, N-methylpyrrole,
1-methoxynaphthalene, tetraphenylfurane and pentaphenyl-
cyclopentadiene, respectively. Most likely this is a result of
either insufficient solubility of the diene, steric hindrance
(e.g. pentaphenylcyclopentadiene for both reasons) or
insufficient reactivity. Interestingly, fluorine NMR indicates
in some cases (e.g. thiophene derivatives) an increased
decomposition rate of the triene.
Honoured in 1950 with the Nobel prize, the Diels–Alder
reaction is still one of the most remarkable organic reactions.1
We studied the scope of tetrafluorobutatriene in this type of
reaction by subjecting it to various dienes and enes. Although
tetrafluorobutatriene (1) was synthesized and characterized by
IR- and 19F-NMR spectroscopy by Martin and Sharkey as
early as 1959, its chemistry remained almost unexplored due
to the compound’s extreme instability: it polymerizes even at
ꢀ85 1C and is said to explode violently on warming to ꢀ5 1C
or on contact with air.2
Tetrafluorobutatriene reacts solely as an ene component in
the Diels–Alder reaction. The perfect linear shape of the three
cumulated double bonds is most likely the reason for that since
for the diene the s-cis configuration is required for sufficient
reactivity.6 Employing the inverse electron demand hexachloro-
cyclopentadiene or octafluoro-1,2-dimethylene-cyclobutane
did not lead to reaction at the terminal double bonds. Since
the reaction with electron rich dienes is restricted to the central
double bond well defined products result. Almost quantitative
reactions were observed with 2a–f and single crystals of the
reaction product 3a with 1,3-diphenylisobenzofurane could
be obtained. However, 3a also isomerized during the
crystallization forming a few crystals of the naphthalene
derivative 4. Similar rearrangement reactions have been
observed previously.7
This limited the known chemistry of 1 to a few derivatives
also reported by Martin and Sharkey using addition of
bromine and chlorine, and oxidation. Later, Raman- and
PE-spectroscopic data were added3 and its structure and
experimental charge density were elucidated by high-
resolution X-ray diffraction.4
Compound 1 decomposes even in anhydrous solvents under
vacuum or inert atmosphere within a few hours forming
numerous unstable decomposition products which could not
be characterized thus far. Nevertheless it was possible
to synthesize two of its transition metal complexes,
[M(Z2-C4F4)(CO)(PPh3)2Cl] (M = Ir, Rh).5
The structures of 3a and 4 were determined by X-ray
crystallography. As depicted in Fig. 1 the asymmetric unit of
3a consists of two molecules which are connected by H–F
contacts. The crystal packing of the molecules is dominated
by numerous H–F interactions8 rather than by fluorine
segregation.9 The two phenyl substituents are twisted against
each other by 70.51 and 82.11 probably due to intra-molecular
H–F contacts shown in red. The conjugated cisoid double
bonds are non-planar (C1–C2–C11–C12 ꢀ27.61/ꢀ31.51) to
minimize the repulsion of the fluorine atoms F2 and F4.
Several short H–F contacts can be found in the rearranged
naphthalene derivative 4 depicted in Fig. 2 but again no
fluorine segregation can be observed.
After the development of
a more efficient synthesis
of 1,1,4,4-tetrafluorobutatriene (1) we were able to further
examine its chemistry.
Once prepared, it can only be transferred by condensation
at reduced pressure and must be stored at ꢀ196 1C. This
method has so far prevented explosions and polymerization.
Herein we report on the Diels–Alder reaction of 1 with
various dienes 2a–k of different reactivity as outlined in
Scheme 1. Due to the instability of the triene all reactions
have to be performed at or below ambient temperature.
Depending on the reactivity and solubility of 2a–k the yields
of 3a–k range from quantitative to almost zero.z
We tried to enforce the isomerisation of 3a to 4 by heating in
toluene to 160 1C, bubbling air through a hexane solution of
3a, addition of either potassium hydroxide or sodium fluoride
to a THF/water solution of 3a. The Diels–Alder product
remains stable under all these conditions and not even a trace
of 4 could be detected (Scheme 2).
No product could be detected with 9,10-dimethylanthracene,
a-terpinene, fullerene-C60, various thiophene derivatives,
1,1-difluorobut-1-en-3-yne, hexachlorocyclopentadiene, pyrene,
Freie Universitat Berlin, Institut fur Chemie und Biochemie,
¨
¨
All compounds presented exhibit
a
characteristic
Abt. Anorganische Chemie, Fabeckstr. 34-36, D-14195 Berlin,
Germany. E-mail: lentz@chemie.fu-berlin.de; Fax: +49 30 83853310;
Tel: +49 30 83852695
w Electronic supplementary information (ESI) available: NMR data
for compounds 3b–k and crystallographic data of 3a and 4. CCDC
752618 and 752619. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b922424f
AA0BB0-type 19F-NMR spectrum. We were able to perform
the synthesis of 3a–c in such a manner that no purification of
the product was necessary and all NMR-spectroscopic data
could be taken. In all other cases we could not isolate the
product from the excess diene since starting material and
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Scheme 1 Diels–Alder reactions of tetrafluorobutatriene, conversion determined by 19F-NMR-spectroscopy, reaction time 1 minute (furane) up
to 14 days (anthracene), solvent: CH2Cl2 (anthracene and diphenylisobenzofurane), all others in substance.
Fig. 2 Molecular structure (DIAMOND12) of 4.
product co-elute and have a comparable volatility. We
analysed the AA0BB0-type 19F-NMR spectrum for compound
3a with the gNMR program.10 The geminal fluorine–fluorine
coupling and 2 of the 3 5J-couplings exhibit normal values with
38.1 Hz, 16.3 Hz and 8.9 Hz, respectively. In contrast, the
coupling constant of the two fluorine atoms standing face-
to-face together shows a large 5J through space coupling,
Fig. 1 Molecular structure (DIAMOND12) of 3a (top). Inter- and
resulting in a coupling constant of 62.9 Hz.
intra-molecular H–F contacts between the molecules are symbolized
by blue and red dashed lines, respectively (bottom). Fluorine atoms of
neighbouring molecules are drawn as smaller balls.
The enormous reactivity of 1,1,4,4-tetrafluorobutatriene is
best displayed by a comparison to its tetrabromo-derivative.
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(CDCl3, CFCl3 ref.): ꢀ81.4 (2F, m), ꢀ87.4 (2F, m); dH (CDCl3):
7.36 (4H, m), 7.20 (4H, m), 5.08 (2H, m, 5.5), dC (CDCl3): 152.5
(2C, m, CF2), 141.6 (4C), 125.3 (4C), 123.9 (4C), 88.7 (2C, m,
CQCF2), 45.2 (2C, m, bridging Cs).
Crystal structure analysis:
a suitable crystal was selected using a microscope, mounted onto
glass fiber using silicon grease, and transferred into the cold gas stream
of
a diffractometer. BRUKER-AXS, SMART CCD, MoKa,
l = 0.71073 A, T = 133 K.
Crystal data for 3a and 4:
3a: C24H14F4O, M = 394.35, monoclinic, a = 14.810(6) A, b =
8.927(3) A, c = 26.933(10) A, b = 91.120(10)1, V = 3560(2) A3, T =
133(2) K, space group P21/n, Z = 8, 21 334 reflections measured, 5070
independent reflections (Rint = 0.1449) of which 2944 have Fo
>
2s(Fo). Empirical absorption correction (SADABS13), least squares
refinement (SHELXL-9714), anisotropic temperature factors, H atoms
isotropic on calculated positions. The final R1 values were 0.0971
(I > 2s(I)). The final wR(F2) values were 0.2684 (all data). The
goodness of fit on F2 was 0.987. 4: C24H14F4O, M = 394.35,
orthorhombic, a = 14.189(5) A, b = 7.746(3) A, c = 16.523(5) A,
V = 1816.2(10) A3, T = 123(2) K, space group Pna21, Z = 4, 26 842
reflections measured, 2857 independent reflections (Rint = 0.0410,
Friedel opposites merged) of which 2601 have Fo > 2s(Fo). The final
R1 values were 0.0486 (I > 2s(I)). The final wR(F2) values were 0.1315
(all data). The goodness of fit on F2 was 1.062.
1 (a) O. Diels and K. Alder, Justus Liebigs Ann. Chem., 1928, 460, 98,
for recent reviews see: (b) K. C. Nicolaou, S. A. Snyder,
T. Montagnon and G. Vassilikogiannakis, Angew. Chem., Int.
Ed., 2002, 41, 1668; (c) E. J. Corey, Angew. Chem., Int. Ed.,
2002, 41, 1650.
2 E. L. Martin and W. H. Sharkey, J. Am. Chem. Soc., 1959, 81,
5256.
3 (a) F. A. Miller, W. F. Elbert and W. Pingitore, J. Mol. Struct.,
1977, 40, 25; (b) H. Basch, G. Bieri, E. Heilbronner and
T. B. Jones, Helv. Chim. Acta, 1978, 61, 46.
4 A. Bach, D. Lentz, P. Luger, M. Messerschmidt, C. Olesch and
M. Patzschke, Angew. Chem., 2002, 114, 311 (Angew. Chem., Int.
Ed., 2002, 41, 296).
5 F. A. Akkerman and D. Lentz, Angew. Chem., 2007, 119,
4989–4992 (Angew. Chem., Int. Ed., 2007, 46, 4902–4904).
6 H.-D. Scharf, H. Plum, J. Fleischhauer and W. Schleker, Chem. Ber.,
1979, 112, 862.
7 C. Dufraisse and R. Priou, Bull. Soc. Chim. Fr., Mem., 1938, 5,
502.
8 H–F contacts range from 2.34 A to 2.79 A for 2a and 2.43 A to
2.78 A for 3.
Scheme 2 Rearrangement of the Diels–Alder product 3a.
While the Diels–Alder reaction with furane in the latter case
needs 48 h for completion, in the former case the reaction is
complete after 1 minute at room temperature.11
Financial support for this work by the DFG is gratefully
acknowledged. We thank Prof. H.-U. Reissig, Freie Universitat
¨
Berlin, for helpful discussions.
Notes and references
z Preparation of 3a–k: all manipulations of air and moisture-sensitive
substance were carried out in an atmosphere of dry argon or under
vacuum. All glassware were carefully dried prior to use. Solvents were
dried with the appropriate drying agents and distilled onto molecular
sieves before use. 1 was prepared as described earlier4 and purified by
fractional condensation. The amount of 1 was determined by pVT
techniques. With the exception of the anthracene and 1,3-diphenyl-
isobenzofurane all reactions were carried out in 4 mm-Duran-glass
tubes. Tetrafluorobutatriene (0.1 mmol) was condensed onto the liquid
nitrogen cooled diene (0.2 mL) and the tube was flame sealed and
rapidly warmed to room temperature. The reaction was monitored by
19F-NMR spectroscopy until all of the triene was consumed. In case
of anthracene (0.25 mmol) high dilution conditions (100 ml)
(dichloromethane or pentane) were used while in case of 1,3-diphenyl-
isobenzofurane 10 ml dichloromethane was used as solvent. In both
cases the same amount of tetrafluorobutatriene was added. The
reaction with 1,3-diphenylisobenzofurane is finished in 2 h when the
yellow solution turns colourless. Spectroscopic data for 3a: dF (C6D6,
CFCl3 ref.): ꢀ78.5 (4F, 62.9, 38.1, 16.3, 8.9 Hz); dH (C6D6): 7.80
(4H, m), 7.38 (1H, d, 5.5), 7.37 (1H, d, 5.5), 7.21 (6H, m), 7.03 (1H, d,
5.5), 7.02 (1H, d, 5.5), dC (C6D6): 151.5 (2C, m, CF2), 146.4 (2C), 133.7
(2C), 130.0 (2C), 129.1 (2C), 128.9 (2C), 128.2 (2C), 121.4 (2C),
95.5 (2C, m, CQCF2), 89.7 (2C). Spectroscopic data for 3h: dF
9 (a) O. Jeannin and M. Fourmigue
´
,
C. R. Chim., 2006, 9,
and E. Faulques,
1287–1294; (b) O. J. Dautel, M. Fourmigue
´
CrystEngComm, 2002, 4, 249; (c) J. J. Wolff, F. Gredel, T. Oeser,
H. Irngartiner and H. Pritzkow, Chem.–Eur. J., 1999, 5, 29.
10 gNMR, P. H. M. Budzelaar, r 2002 IvorySoft.
11 P.-H. Liu, L. Li, J. A. Webb, Y. Zang and N. S. Goroff, Org. Lett.,
2004, 6, 2081.
12 DIAMOND for Windows Visual Crystal Structure Information
System, J. Appl. Crystallogr.1999, 32, 1028.
13 (a) SADABS: Area-Detector Absorption Correction, Siemens
Industrial Automation, Inc., Madison, WI, 1996; (b) R. H. Blessing,
Acta Crystallogr., Sect. A: Found. Crystallogr., 1995, 51, 33–38.
14 G. M. Sheldrick, SHELX97—Programs for Crystal Structure
Analysis (Release 97-2), Institut fur Anorganische Chemie der
¨
¨
Universitat, Tammannstrasse 4, D-37077 Gottingen, Germany,
1998.
¨
ꢁc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 2399–2401 | 2401