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cis-1 2-Di(9-anthryl)ethylene Photochemical Isomerization by Intramolecular Diels-Alder Reaction.

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No thermally-induced reaction is observed at - 50 "C,
even after several hours, whereas 1 reacts photochemically
(Philips HPK 125; Pyrex filter) with 3a within a few minutes. (s-cis-Butadiene)zirconocene 2 also proves to be no
cis-1,2-Di(9-anthryl)ethylene:
Photochemical Isomerization by
Intramolecular Diels-Alder Reaction
By Hans-Dieter Beckere, Kjell Sandros, and
Kjell Andersson
Dedicated to Professor Giinther 0. Schenck on the
occasion of his 70th birthday
As part of a study of the relationship between molecular
geometry and excited state reactivity, we recently prepared
cis- 1,2-di(9-anthryl)ethylene 1 in order to compare its photochemical and photophysical properties with those of its
trans-isomer 2[1-31. Attempts to induce photochemical
trans+cis isomerization were not successful, but irradiation of 1 in cyclohexane (1> 300 nm) produced the transisomer 2 in nearly quantitative yield, together with small
amounts of the [4n. 4.111cycloaddition product 3IZ1.At low
conversion of 1, however, equal quantum yields (0.0007)
were estimated for both the geometrical isomerization to 2
and the cycloaddition to 3.
+
[A]:
Fig. 1. Structure of 4a in the crystal. Selected bond lengths
Zr-0
1.946(4), Zr-CI 2.311(7), Cl-C2 1.468(9), C2-C3 1.351(9), C3-C4 1.498(8);
bond angles ["I: Zr-0-C5 150.5(4), 0-Zr-CI 91.9(2).
longer inert towards 3a: on reaction with the mixture of
the isomers 1 and 2, 2 is consumed at a similar rate as 1,
with formation of 4a.
I
3
Ihv
4
1
t
A
2
These observations suggest that-analogous to the reaction of 1+ 2 with 0lefins[~~-4is formed from the intermediary product (q2-butadiene)zirconocene719]oia the intermediates 8 and 9 . Therefore, it appears that the selectivity
control of the zirconocene-induced coupling of conjugated
dienes with aldehydes and ketones may in some cases depend decisively on the formation and properties of intermediary (q2-diene)metallocene complexes"01.
Received: February 2, 1983 [Z 265 IE]
German version: Angew. Chem. 95 (1983) 506
The complete version of this communication appears in:
Angew. Chem. Suppi. 1983, 675-690
(21 G. Erker, J. Wicber, K. Engel, F. Rosenfeldt, W. Dietrich, C. Kriiger, J.
A m . Chem. Soc. 102 (1980) 6344; G. Erker, J. Wicher, K. Engel, C.
Kxiiger, A.-P. Chiang, Chem. Ber. 115 (1982) 3300, 3311.
131 H. Yasuda, Y. Kajihara, K. Mashima, K. Nagasuna, A. Nakamura,
Chem. Leti. 1981, 671.
I41 G. Erker, K. Engel, U. Dorf, J. L. Atwood, W. E. Hunter, Angew. Chem.
94 (1982) 915,916; Angew. Chem. Inf. Ed. Engl. 21 (1982) 913,913; Angew. Chem. Suppl. 1982, 1974, 1984.
(91 U. Dorf, K. Engel, G. Erker, O r g u n o m e f u l h 2 (1983) 462.
1101 A. Stockis, R. Hoffmann, J. A m . Chem. SOC.102 (1980) 2952; V. Skibbe,
G. Erker, J. Orgunomei. Chem. 241 (1983) 15.
Angew. Chem. Int. Ed. Engi. 22 (1983) No. 6
We have now investigated the wavelength dependence
of the photochemical isomerization of 1 and found a novel
intramolecular cycloaddition in which the 1,2-bond of an
anthracene n-system participates as a dienophile in a
Diels-Alder reaction.
Irradiation of 1 (20 mg) in cyclohexane (900 mL) at
50 "C for 6 h under argon (A> 392 nm) results in complete
isomerization. After separation of the trans-isomer 2 (37%
yield) 3 remains and, surprisingly, the novel dissymmetric
photo-isomer 4 (500/0 yield, colorless crystals, m.p. ca.
180 "C, decomp.).
The high-resolution mass spectrum, the 270 MHz 'HNMR spectrum, and the electronic absorption spectrum
are consistent with the structure 4 (Fig. 3a). Evidence for
this structure was also obtained by dehydrogenation with
2,3-dichloro-5,6-dicyanobenzoquinone
(DDQ), which afforded the triptycene derivative 5 (yellow crystals, m.p.
293°C). The structure of 5 is supported by its 'H-NMR
spectrum and by its electronic absorption spectrum, which
[*] Dr. H.-D. Becker, Dr. K. Sandros, K. Andersson
Departments of Organic and Physical Chemistry
Chalmers University of Technology and University of Gothenburg
S-41296 Gothenburg (Sweden)
0 Veriug Chemie GmbH, 6940 Weinheim, 1983
0570-0833/83/0606-0495 $02.50/0
495
is typical of the planar 9-vinylanthracene chromophore
391 (4.9), 371 (I.!+, 314
sh (3.2), 271 (66)].
[amax(&X10-~):440(13), 414(10.4),
(PhC=CLi),(tmhda),,
A Polymeric Organolithium Compound with
Cubic Li4C4 Structural Units**
By Bernd Schubert and Erwin Weiss*
For systematic investigations on the structure of organolithium compounds we prepared some phenylethynyllithium compounds containing additional diamine ligands: [(PhC = CL),tmeda], [(PhC = Li)tmpda], 1 and
[(PhC=CLi)4(tmhda)z] 2 (tmeda = N,N,N’,N’-tetramethylethylenediamine, Me2N(CH2)2NMe2;tmpda = N,N, N‘,N’tetramethylpropanediamine, MezN(CHZ)3NMe2;tmhda=
N, N,N’,N’-tetramethylhexanediamine,
Me2N(CH&NMe2).
The length of the diamine ligand obviously has a large
influence on the composition and structure of these compounds. Thus, 1 is a dimer with two phenylethynyl
bridges”], isostructural to the phenyl compound (PhLi .
tmeda),[”.
X[nm]-
X [nm] +
Fig. 3. Electronic absorption spectra of cycloaddition products 4 (a) and 3
(b) in cyclohexane.
Upon photo-excitation (1< 360 nm) in cyclohexane, 4
undergoes smooth cycloreversion to give 1: the quantum
yield of this reaction is 0.20, exceeding that of the formation of 4 from l by a factor of 300. Hence, 4 can be obtained only when its photo-excitation is prevented by use
of appropriate filters. The quantum yield for the photolytic
cycloreversion of 3- 1 is three times as high as that of the
reaction 4-1, but its UV spectrum (Fig. 3b) precludes
photo-excitation when 1 is irradiated in Pyrex apparatus.
The low concentration of 1 employed in the experiment
described above (20 mg in 900 mL cyclohexane) is of critical importance for the photochemical formation of 4. Numerous attempts to obtain 4 by photochemical isomerization of higher concentrations of 1 in cyclohexane failed
since the trans-isomer 2, whose solubility at room temperature is only 2 mg/L, always precipitated soon after commencement of irradiation, and became the major product.
Surprisingly, the efficiency of cis-trans isomerization surpasses that of the intramolecular cycloaddition 1+4 after
precipitation of 2 has commenced. Absorption spectroscopy indicates that when most of the incident light is absorbed by crystalline 2 the photochemical formation of 4
from 1 virtually ceases, while the rate of conversion of 1
into 2 is enhanced. The use of other solvents in which 2 is
more soluble than in cyclohexane is impaired by the fact
that the quantum yield of cis-trans isomerization is solvent
dependent[”: specifically in cyclohexane solution can the
intramolecular Diels-Alder reaction of 1 to afford 4 compete efficiently with the geometrical isomerization leading
to 2.
Received: February 3, 1983 [ Z 266 IE]
German version: Angew. Chem. 95 (1983) 507
The complete manuscript of this communication appears in:
Angew. Chem. Suppl. 1983. 609-619
[l] H.-D. Becker, Pure Appl. Chem. 54 (1982) 1589.
[2] H.-D. Becker, L. Hansen, K. Anderson, J . Org. Chem. 46 (1981) 5419.
131 H.-D. Becker, K. Sandros, L. Hansen, J . Org. Chem. 46 (1981) 821.
496
0 Verlag Chemie GmbH, 6940 Weinheim, I983
Fig. 1. SCHAKAL diagram of the structure of 2 in the crystal. Monoclinic,
P2,/n, a = 1574.7(9), b= 1563.9(9), c=2140.3(8) pm, p= 102.87(4)’, pr= 1.003
g cm-’, Z=4; MoK,-radiation, solution by direct methods (MULTAN 78),
refinement (SHEL X) to R=0.092 with 1515 reflections (anisotropic temperature factors, H not determined). Most important distances (pm, average values): Li-Li 272(2), Li-C 220(1), Li-N 211(2), C-C 124(2) pm 161.
The longer chain diamine tmhda adds to P h C 4 L i with
formation of the 1 :2 compound 2. Surprisingly, the X-ray
structure analysis (Fig. 1) revealed that 2 contains a distorted cubic Li4C4-unit similarly as in (CH3Li)4 and
(CH3Li)4(tmeda)2 3f41. Structurally analogous are the
[‘I Prof. Dr. E. Weiss, Dr. B. Schubert
Institut fur Anorganische und Angewandte Chemie
der Universitat
Martin-Luther-King-Platz 6, D-2000 Hamburg 13 (Germany)
[**I Metal-Alkyl and -Aql Compounds, Part 31. This work was supported
by the Deutsche Forschungsgemeinschaft.-Part 30: [l].
0570-0833/83/0606-0496 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 22 (1983) No. 6
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anthryl, intramolecular, reaction, ethylene, isomerization, alder, diels, cis, photochemical
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