Reversible intramolecular photocycloaddition of a bis(9-anthrylbutadienyl) paracyclophane - An inverse photochromic system. (Photoactive cyclophanes 5)

Article abstract of DOI:10.3762/bjoc.5.20

The title compound, 4,13-bis[(1E,3E)-4-(9-anthracenyl)buta-1,3-dienyl][2.2] paracyclophane (2), prepared in 35% overall yield from [2.2]paracyclophane, absorbs light at λ_max = 400 nm with a tail down to 480 nm. By irradiation into this band, 2

Full text of DOI:10.3762/bjoc.5.20

Reversible intramolecular photocycloaddition of a
bis(9-anthrylbutadienyl)paracyclophane – an inverse
photochromic system. (Photoactive cyclophanes 5)
Henning Hopf*,1, Christian Beck1, Jean-Pierre Desvergne2,
Henri Bouas-Laurent*,2, Peter G. Jones3 and Ludger Ernst4
Full Research Paper
Open Access
Address:
Institut für Organische Chemie, Technische Universität
Braunschweig, Postfach 3329, D-38023 Braunschweig, Germany,
ISM, CNRS UMR 5255, Université Bordeaux 1, F-33405 Talence
Beilstein Journal of Organic Chemistry 2009, 5, No. 20.
1
doi:10.3762/bjoc.5.20
2
Received: 25 February 2009
Accepted: 24 April 2009
Published: 07 May 2009
Cedex, France, 3Institut für Anorganische Chemie, Technische
Universität Braunschweig, Postfach 3329, D-38023 Braunschweig,
Germany and 4NMR-Laboratorium der Chemischen Institute der
Technischen Universität Braunschweig, Hagenring 30, D-38106
Braunschweig, Germany
Editor-in-Chief: J. Clayden
©
2009 Hopf et al; licensee Beilstein-Institut.
Email:
License and terms: see end of document.
Henning Hopf* - h.hopf@tu-bs.de; Jean-Pierre Desvergne -
jp.desvergne@ism.u-bordeaux1.fr; Henri Bouas-Laurent* -
h.bouaslaurent@cegetel.net; Peter G. Jones - p.jones@tu-bs.de;
Ludger Ernst - l.ernst@tu-bs.de
*
Corresponding author
Keywords:
anthracenes; cyclophanes; inverse photochromism;
photocycloaddition
Abstract
The title compound, 4,13-bis[(1E,3E)-4-(9-anthracenyl)buta-1,3-dienyl][2.2]paracyclophane (2), prepared in 35% overall yield
from [2.2]paracyclophane, absorbs light at λmax = 400 nm with a tail down to 480 nm. By irradiation into this band, 2 generates a
single photoproduct, 4, whose absorption maximum is situated at 306 nm. The starting material is recovered by irradiation at 306
nm or by heating. This ‘inverse’ photochromic system has a potential for optical information storage, compound 4 being stable in
visible light, at ambient temperature.
Introduction
Photochromism [1], see Figure 1, is currently an active field of materials. Diverse systems are under study for information
research as reflected in the literature [2-6] and finds commer- storage and optical switches [7-9]. The majority of established
cial applications in the domain of reversible optical density systems show a ‘positive’ photochromism in which the elec-
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Beilstein Journal of Organic Chemistry 2009, 5, No. 20.
tronic absorption spectrum of the product P is red-shifted [1].
When the electronic absorption spectrum of P is blue-shifted,
the photochromism is said to be ‘negative’ or ‘inverse’ [1].
Figure 1: Schematic representation of a photochromic system. The
reverse reaction can be a photochemical or thermal process. A and P
have different absorption spectra.
Figure 3: Molecular structure of 4,13-bis[(1E,3E)-4-(9-anthracenyl)-
buta-1,3-dienyl][2.2]paracyclophane (2).
Inverse photochromism is encountered in photoaddition of
conjugated systems [10-17] and may be interesting for informa- The synthesis, molecular structure and photochromic properties
tion storage materials because the photoproducts can be oper- of 2 are reported in this paper.
ated in visible light. Inverse photochromism was recently
Results and Discussion
observed for some vinylogs of cinnamophanes [18,19], such as
compound 1 (Figure 2). Several cycles were recorded but the 1 Synthesis
photoproduct could not so far be isolated.
Compound 2 was prepared from dialdehyde 3 using the Wittig
reaction, as outlined in Scheme 1, in 48% yield. Dialdehyde 3
It occurred to us that the performance of these systems could be wasobtained in five steps from [2.2]paracylophane, a commer-
improved by incorporating the anthracene substrate, well known cial product, in 72% overall yield as described previously [19].
for its ability to generate definite photodimers [10-15], in the Therefore, the overall yield of 2 from the parent cyclophane
pseudo-gem positions of the cyclophane acting as a convenient was found tobe 35% on the gram scale.
scaffold, as demonstrated previously [18,19]. To avoid steric
crowding and excessive distance between the chromophores, it The Wittig reaction provides a mixture of cis and trans isomers,
seemed reasonable to select the rigid all-trans butadienyl tether but the pure all-trans isomer was isolated by crystallization as
as represented in compound 2 (see Figure 3).
orange crystals (see Experimental). 9-(anthrylmethyl)triphen-
Figure 2: Photochromic reaction of pseudo-gem disubstituted tetraene [2.2]cyclophane 1 in acetonitrile, conc. 5 × 10−4 M.
Scheme 1: Preparation of 2 (last step), using the Wittig reaction. The preparation of 3 has been described in ref [19].
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Beilstein Journal of Organic Chemistry 2009, 5, No. 20.
ylphosphonium bromide was easily obtained from triphen-
ylphosphine and 9-bromomethylanthracene.
2
X-ray structure analysis
Single crystals suitable for X-ray structure determination were
grown by slow evaporation of a solution of 2 (150 mg) in
dichloromethane (10 mL) by diffusion of pentane vapour. The
molecular structure of 2 is presented in Figure 4.
Figure 5: Projection of the molecular structure of 2 exhibiting the
closest internuclear distances (distances in Å).
that the lowest energy band (λmax = 400 nm with a tail down to
4
80 nm) is clearly red-shifted as compared to those of all the
cinnamophane vinylogs studied so far [18,19], including
compound 1 (λmax = 370 nm). The presence of the twisted
butadienyl system introduces several torsional vibrations about
the pseudo single bonds and attenuates the fine structure usually
observed for anthracene derivatives (see Figure 6). The differ-
ence between the two solutions is thought to reflect some
charge transfer in the more polar solvent, affecting the intensity
Figure 4: Molecular structure of 2 in the crystal. Radii are arbitrary;
only selected H atoms are shown.
The double bonds are clearly all-trans and their average planes balance but not the wavelength maxima.
form twist angles with the two anthracene nuclei of 47° and
4
4°,respectively; the two ethylenic systems are also not parallel
to each other but subtend twist angles of 42–43° (see Table 1).
Finally, the interplanar angle between the two anthracene
substrates is ca 4.5° (Table 1). Consequently, the inter-ring
distance varies between 3.40 and 3.80 Å. Two lateral anthra-
cene nuclei are thus in close proximity (see Figure 5), in which
two carbons are separated by the van der Waals distance, C31-
C48 (ca. 3.40 Å); two other carbons are also very close to each
other: C32-C51 (ca. 3.65 Å). These remarkable features suggest
preferred sites of reactivity inasmuch as this rigid geometry is
not disfavoured in solution.
Figure 6: Electronic absorption spectra of 2 (conc. ca 10−4 M) in MCH
full line) and CH3CN (dotted line) at 20 °C.
(
3
Electronic absorption spectra and photo-
chemistry
3.2 Irradiation
3.1 Electronic absorption spectra
Compound 2 was irradiated in acetonitrile in a quartz cell, at
The electronic absorption spectra of 2 in methylcyclohexane 400 nm (selected with a monochromator) using a Xenon lamp.
(
MCH) and acetonitrile are represented in Figure 6. One notes Nitrogen was bubbled through the solution to prevent photoox-
Table 1: Angles between various partial planes in molecule 2 in the crystal.
torsion angles
interplanar angles
C19–C20–C21–C22
7.1°
C17–C20/C21–C34
1.6°
butadienes C17–C20//C35–C38
C37–C38–C39–C40
4
43.9°
C35–C38/C39–C52
4
43.3°
anthracenes C21–C34//C39–C52
4.5°
deviation from parallelism
9°
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Beilstein Journal of Organic Chemistry 2009, 5, No. 20.
idation, and the spectra were recorded at various time intervals
Figure 7). Three isosbestic points at 220, 289, and 329 nm
(
were observed as well as new absorptions at 306 nm and in the
far UV. Similar features were noted for the MCH solutions. At
that concentration, no intermolecular reaction could compete
with an intramolecular process [12].
Figure 8: Irradiation at 306 nm of the photoproduct 4 obtained at 400
nm in the same setup; the spectra were recorded at various time inter-
vals, within 10 min, at ambient temperature.
Figure 7: Irradiation of 2 (2.6 × 10−5 M) in CH3CN at 400 nm at 20 °C.
The spectra were recorded at various time intervals within 60 min. The
arrows point to the maxima.
Disappearance quantum yields at 394 nm were found to be low
in methylcyclohexane (1.5 × 10−4) and in acetonitrile
Figure 9: Reversibility of the formation of the photoproduct 4 at 400
nm (40 min) and photodissociation of 4 at 306 nm in MCH.
(
4.2 × 10−2). The weakness of the cyclophotoaddition probably
reflects a preference for internal conversion among the diverse
deactivation channels of the S1 state. The clear difference
between the two media may result from an electron transfer The photolysis at 306 nm must involve one or several photore-
between the two anthracene nuclei in the more polar solvent, as actions leading to products transparent at 392 nm. Thermal
demonstrated in previous work [20]. The ion pair can accel- dissociation (a retro Diels-Alder reaction, see below) was
erate a closure reaction involving a donor and an acceptor expected to exhibit a quantitative yield as shown hereafter. The
partner, such as a Diels-Alder reaction (see below).
photoproduct 4, prepared and isolated as described below, was
heated at 55 °C in CDCl3. The dissociation was evaluated with
time by following the intensity change of the characteristic δ =
3.3 Photodissociation
Under the same experimental conditions, the photoproduct 4 4.73 ppm signal (see spectrum below) until complete extinction
was irradiated at 306 nm for 10 min until the starting material (see Supporting Information p S2). The dissociation kinetics
spectrum was recovered (Figure 8). Disappearance quantum were found to be first order with a half-life of ca 3.8 h. This
yield of 4 at 306 nm was found to be 1.6 × 10−1 for both suggests a much longer lifetime at ambient temperature, as
solvents.
observed experimentally.
3.4 Photochromic cycles
4 Structure of the photoproduct
Using the preceding dilute solution in a quartz cell and the same Preparative irradiation of a solution of 2 in CH2Cl2 through
setup, the medium was alternatively irradiated at 400 nm and at which nitrogen was bubbled with a medium pressure mercury
3
06 nm in both solvents, and the absorbance measured at 392 lamp in a Pyrex photoreactor (UV light filtered by NaNO2
nm at each cycle. The results are represented for MCH solution aqueous solution) gave 4 as a white powder after a week at −20
in Figure 9. One observes a drop of 50% absorbance after 8 °C. That a single photoproduct was produced is borne out by
cycles for MCH and 5 cycles for CH3CN (not shown).
HPLC, showing the increase of a single peak at the expense of
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Beilstein Journal of Organic Chemistry 2009, 5, No. 20.
the starting material (see Supporting Information p S3). No C (132 to 142 ppm), 28 to CH (121.3 to 140.4), 4 to other CH
melting point could be determined because the powder decom- likely corresponding to bridgehead carbons (54.9 to 66.0 ppm)
poses back to 2 on heating. The mass spectrum was found to be and finally 4 to CH2 (31.6 to 36.5 ppm), attributable to the
that of 2 (see Experimental). Single crystals suitable for X-ray ethanocyclophane bridges.
structure analysis could not be obtained. Evidence for the struc-
ture rests on the electronic absorption spectrum and the NMR In previously studied cyclophanes, the cyclobutane rings exhib-
spectral data. The UV spectrum clearly shows the disappear- ited 13C signals between 42 and 51 ppm [18,19]. No such
ance of the 350–450 nm absorption band, indicating that the signals are apparent in the present case; therefore it is proposed
anthryl groups have reacted. The new band with a maximum at that no reaction has occurred between the ethylenic bonds. This
3
06 nm suggests the formation of substituted naphthalenes [21], statement is borne out by the observation of the 1H NMR spec-
but because the disubstituted cyclophane also absorbs in that trum.
region [22], it is difficult to get more precise information.
1
H NMR data: The spectrum exhibits three regions at the
The 1H NMR (Figure 10 and Supporting Information p S2) and following chemical shifts: 7.62–5.97 ppm (28 H) corres-
the 13C NMR spectra (52 distinct signals are observed, see ponding to aromatic and ethylenic protons; 3.8–2.5 ppm, corres-
Experimental) point to the absence of symmetry in the ponding to aliphatic protons (10 H) and a prominent signal at
molecule. This rules out symmetrical cycloadditions such as the 4.73 ppm (2 H, broad singlet) attributable also to aliphatic
9
,9′ : 10,10′ [4+4]reaction of anthracenes [11], whether protons. Compared to 2, there are four new signals corres-
combined or not with two cyclobutane-forming [2+2]additions. ponding to aliphatic protons, in keeping with the cycloadduct
Dissymmetrical closures [11,12] such as 1,4 : 9′,10′ [4+4] or 1,4 pictured in Figure 11.
:
2′,3′[4+2]cycloadditions (as well as rearranged products) are
thus to be considered. A deeper analysis of the experimental This is a Diels-Alder adduct resulting from the reaction of the
data follows.
1,4 positions (C41 and C44) of one nucleus and the 2′,3′ posi-
tions of the other nucleus (C24 and C25).The structure of 4 is
1
3C NMR data: The molecular formula includes 52 carbon further supported by the 1H-1H COSY spectrum (see
atoms; among the 52 signals observed, 16 are due to quaternary Supporting Information p S4).
Figure 10: 1H NMR spectra (400 MHz, CDCl3). A: Compound 2, B: Compound 4.
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Beilstein Journal of Organic Chemistry 2009, 5, No. 20.
Experimental
General Techniques
Melting Points (up to 200 °C) were taken with a Büchi 510
Melting Point Appararus. Those above 200 °C were measured
with a Kofler Heiztischmikroskop Thermopan (Reichert); all
m.p. are uncorrected. HPLC was performed using a Nucleosil
1
00 −7 octadecyl phase (Macherey Nagel, Düren, No 715802)
column, with a pump L-6200 and a photodiode array detector
L-3000 (Hitachi). Column chromatography: Merck Kieselgel 60
Figure 11: Proposed structure of 4 (1,4 : 2′,3′-cycloadduct).
(
70–230 mesh). Thin layer chromatography: Kieselgel (Merck)
or Alox (Macherey-Nagel). Elemental Analyses were obtained
It indicates that the signal at δ = 3.8 (pseudotriplet) is coupled by the Institute of Inorganic and Analytical Chemistry and of
with that at δ = 3.2 and that at δ = 6.05, whereas the signal at Pharmaceutical Chemistry of the Technical University of
3
.2 is coupled with those at δ = 3.8 and 6.38 ppm, respectively. Braunschweig.
The signals at 3.2 and 3.8 ppm can be attributed to allylic
bridgehead H24 and H25, coupled with the vicinal ethylenic Spectrometry
hydrogen atoms (23 and 26) at 6.05 and 6.38 ppm. Bridgehead NMR spectra were recorded with an AC-200 (1H: 200 MHz,
protons H41 and H44 then display the peak at δ = 4.73 ppm, 13C: 50 MHz) or an AM-400 (1H: 400 MHz, 13C: 100 MHz)
reflecting a very small coupling with their neighbours Bruker apparatus. The chemical shifts were measured with
(
H–C–C–H dihedral angles close to 90°) [23,24].
tetramethylsilane as internal reference. The 1H-1H COSY spec-
trum was used to interpret the spectrum of 4, and the DEPT
The majority of anthracene derivatives are known to undergo a technique to assign the class of carbon atoms in the 13C spectra.
4+4]cycloaddition from the S1 state [11,12], but some [4+2]- The IR spectra were recorded with a Nicolet 320 FT spectro-
[
cycloadditions were observed to occur under geometrical meter. Mass spectra were performed with a Finnigan MAT
constraints [11,12,24] through a triplet state process [25]. [4+2]- 8430 spectrometer using the classical Electron Ionization at 70
Cycloadditions can take place in a hot ground state [26]. This eV or the FAB technique, respectively. Electronic absorption
result is reminiscent of the [4+2]-photocycloaddition between spectra were recorded with a HP 8542 A-Diode Array or a
two naphthalene substrates for the anti-[2.2](1,4)-naphthaleno- Hitachi UV 3300 spectrometer. The samples were weighed with
phane leading to dibenzoequinine, a stable polycyclic molecule a Mettler UM3 balance (sensitivity 10−7 g).
[
27]. In that case, the first Diels-Alder addition is immediately
followed by a second, because of the superimposition of the Quantum yields
newly formed diene and the ene centres (cascade reaction). This Reaction quantum yields were determined as described else-
is not possible in the present situation, considering Figure 11. where [29], using the Parker iron trioxalate actinometer. The
The non-reactivity of the ethylenic bonds is understandable as monochromatic beams were obtained from a cooled 1000 W
the reaction affects first the anthracene substrates leading to 4 in Xenon lamp, using a Bausch and Lomb monochromator. The
which the double bonds are no longer at mutual distances samples were previously purged of oxygen with an argon or
conducive to further reactions. Such a 1,4 : 2′,3′-cyclophotoad- nitrogen stream.
dition between two anthracene nuclei is unprecedented.
Preparations
Summary and Conclusion
1. 4,13-bis[(1E,3E)-4-(9-anthracenyl)-buta-1,3-dienyl]-
The target molecule (dianthryl-butadienyl[2.2]paracyclophane [2.2]paracyclophane (2):
) was synthesized and shown to possess the anticipated photo-
2
chromic properties. The two interconverting forms exhibit good In a 250 mL, dried round-bottom flask, equipped with a reflux
thermal stability. The cycloreversion can be induced by irradi- condenser, a Claisen adapter, a stirring system, and degassed
ation or by heating. Because of its slow response and the fatigue with nitrogen, 1.3 g dialdehyde (4.1 mmol) was dissolved in
observed in the photodissociation, this system does not seem 50 mL absolute THF. In another vessel, 6.56 g (12.3 mmol) of
suitable as a switch, but might be considered for applications 9-anthryltriphenylphosphoniumbromide, in suspension in 50
such as optical storage [28], owing to the large spectral shift mL THF under nitrogen, was mixed with a solution of 8.2 mL
(
Δ
max ca 7500 cm−1) of the electronic absorption spectra BuLi (1.5 M, hexane). The resulting deep red solution was
between 2 (λmax 400 nm) and 4 (λmax 306 nm) and the stability introduced dropwise with a needle into the dialdehyde solution
of the photoproduct in interior daylight.
and the reaction medium was stirred overnight at ambient
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Beilstein Journal of Organic Chemistry 2009, 5, No. 20.
temperature. Finally, the reaction mixture was hydrolyzed with for a week. A white precipitate appeared, which was filtered off
crushed ice/water. The crude product was filtered off, dissolved and washed with pentane. After desiccation under high vacuum,
in a small volume of CH2Cl2 and dried over MgSO4. After 4 was isolated (71 mg: 0.11 mmol, 53%). From the mother
adding 3 g of silica gel to the filtered solution, the solvent was liquor, some additional powder was collected and identified as
distilled off under reduced pressure and the residue was eluted the starting material 2. The irradiation was followed by HPLC
on a 100 g silica gel column with 1.5 L of pentane and then a monitoring after 30, 90, and 120 min (see Supporting Informa-
pentane/CH2Cl2: 4/1 mixture. Compound 2 (1.83 g) was tion p S3). Rf (Alox; CH2Cl2): 0.49. mp. dec. by heating;
obtained as a mixture of cis/trans isomers. The solid was 1H-NMR (400 MHz, CDCl3, 25 °C, TMS): δ = 7.62–7.58 (m, 2
dissolved in about 200 mL of CH2Cl2 in an ultrasonic bath, H), 7.38–7.17 (m, 8 H), 7.08–6.95 (m, 2 H), 6.93–6.67 (m, 4
with gentle warming. To this solution was added about 500 mL H), 6.40–6.20 (m, 9 H), 6.13 (dd, 3J(H,H) = 7.6 Hz, 3J(H,H) =
of pentane and the flask was cooled to −20 °C. After two days, 11.8 Hz, 1 H), 6.08 (br-s, 1 H), 5.97 (dd, 3J(H,H) = 8.7 Hz,
a precipitate of fine crystals appeared, which were filtered off 3J(H,H) = 14.8 Hz, 1 H) 4.65 (br-s, 2 H), 3.70 (ps-t, 3J(H,H) =
and carefully washed with pentane. After drying under high 8.3 Hz, 1 H), 3.32–3.08 (m, 5 H), 2.87–2.75 ppm (m, 4 H); –
vacuum, 1.32 g (1.99 mmol, 48% yield) of all-trans 2 was isol- 13C-NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 142.0 (qC),
ated as an orange microcrystalline powder. – Rf (SiO2; pentane/ 141.6 (qC), 140.5 (qC), 140.4 (CH), 139.9 (qC), 139.4 (qC),
CH2Cl2: 2/1): 0.41; mp 217 °C; – 1H-NMR (400 MHz, CDCl3, 139.2 (qC), 138.6 (qC), 137.6 (qC), 137.1 (qC), 137.0 (qC),
2
5 °C, TMS): δ = 8.00 (s, 2 H; 28-H, 46-H), 8.00 (br-d, 3J(H,H) 136.6 (qC), 136.1 (CH), 136.0 (qC), 135.8 (qC), 135.71 (qC),
8.4 Hz, 4 H; 26-H, 30-H, 44-H, 48-H), 7.68 (br-d, 3J(H,H) = 135.67 (qC), 135.6 (CH), 135.0 (CH), 134.3 (CH), 133.3 (CH),
.4 Hz, 4 H; 23-H, 33-H, 41-H, 51-H), 7.32 (d, 3J(H,H) = 15.7 132.0 (qC), 131.5 (CH), 130.8 (CH), 130.5 (CH), 129.9 (CH),
Hz, 2 H; 20-H, 38-H), 7.05 (br-ps-t, 3J(H,H) = 8.4 Hz, 4 H, 129.8 (CH), 128.6 (CH), 128.32 (CH), 128.28 (CH), 128.2
4-H, 32-H, 42-H, 50-H), 6.96 (dd, 3J(H,H) = 15.3 Hz, 3J(H,H) (CH), 126.7 (CH), 126.5 (CH), 125.4 (CH), 125.35 (CH),
10.4 Hz, 2 H; 18-H, 36-H), 6.87–6.81 (m, 8 H; 5-H, 12-H, 125.32 (CH), 125.1 (CH), 125.0 (CH), 124.8 (CH), 124.5 (CH),
7-H, 35-H, 25-H, 31-H, 43-H, 49-H), 6.75 (dd, 3J(H,H) = 15.7 124.0 (CH), 123.9 (CH), 121.5 (CH), 121.3 (CH), 66.0 (CH),
Hz, 3J(H,H) = 10.4 Hz, 2 H; 19-H, 37-H), 6.57 (d, 3J(H,H) = 56.2 (CH), 55.0 (CH), 54.9 (CH), 36.5 (CH2), 36.3 (CH2), 35.4
=
8
2
=
1
7
1
.8 Hz, 2 H; 8-H, 15-H), 6.53 (dd, 3J(H,H) = 7.8 Hz, 4J(H,H) = (CH2), 31.6 ppm (CH2). The mass spectrum was found to be
.7 Hz, 2 H ; 7-H, 16-H), 3.67–3.64 (m, 2 H ; 1a-H, 2a-H), 3.17 identical to that of compound 2.
(
s, 4 H ; 9-H, 10-H), 3.09–3.06 ppm (m, 2 H ; 1b-H, 2b-H);
3C-NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 139.5 (qC), 3. X-Ray structure determination of 2·1/2CH2Cl2
1
1
1
1
3
38.1 (CH), 137.7 (qC), 134.9 (CH), 132.3 (CH), 131.7 (CH),
31.1 (qC), 130.1 (CH), 129.8 (CH), 129.0 (qC), 128.2 (CH), Crystal data: C52.5H41Cl, Mr = 707.30, monoclinic, P21/c, T =
26.0 (CH), 125.3 (CH), 124.8 (CH), 124.5 (CH), 35.1 (CH2), −100 °C, a = 17.716(3), b = 10.236(2), c = 21.811(3) Å, β =
2.8 ppm (CH2); – MS (70 eV): m/z (%) = 664 (78) [M+], 473 110.523(8)°, U = 3704.1 Å3, Z = 4, F(000) = 1492, λ (Mo Kα) =
(
[
15) [M+-191], 332 (23) [C8H7CHCHCHCH-A+], 331 (43) 0.71073 Å, μ = 0.14 mm−1, Dx = 1.268 g cm−3. Data collection:
C26H19+], 315 (24), 215 (25), 203 (34), 191 (100) [A-CH2+]; – A yellow lath ca. 0.9 × 0.2 × 0.1 mm was mounted in inert oil
UV/Vis (CH3CN): λmax (lg ε) = 256 (4.96), 320 (sh) (4.23), 372 on a glass fibre and transferred to the cold gas stream of a
sh) (4.07), 392 nm (4.19); – UV/Vis (methylcyclohexane): Siemens P4 diffractometer. Data were recorded to 2θ 50°.
λmax (lg ε) = 218 (sh) (4.71), 240 (sh) (4.90), 258 (5.07), 316 Structure refinement: The structure was refined using
(
(
(
4.38), 396 nm (4.36); – IR (KBr): = 3019 cm−1 (m), 2923 SHELXL-97 [30]. Hydrogen atoms were included using a
m), 1621 (w), 1441 (w), 1407 (w), 994 (s), 950 (m), 880 (s), riding model. The dichloromethane molecule is disordered
8
39 (m), 779 (m), 730 (vs), 717 (m); – HRMS (FAB): m/z across an inversion centre. Restraints to light atom U values
calcd: 664.313001, found: 664.313 ± 3 ppm; Elemental were applied. The final wR2 (all reflections) was 0.124 for 6369
analysis: calcd C 93.94, H 6.06, found C 91.74, H 6.03. intensities, 491 parameters and 516 restraints, with R1 (I>2σ(I))
0
.052; S 0.77, max. Δρ 0.31 e Å−3. See also Supporting Inform-
2
. Photoproduct 4: A solution of 133 mg (0.2 mmol) of 2 in 200 ation p S5.
mL of CH2Cl2, carefully degassed by bubbling nitrogen through
it, was irradiated at λ > 400 nm for 2 h with a high pressure X-ray crystallographic data (excluding structure factors) were
mercury lamp in a Pyrex photoreactor. The cooling tube of the deposited under the number CCDC-717774 and can be obtained
latter was filled with a NaNO2 solution (75 g/L) maintaining the free of charge from the Cambridge Crystallographic Data
reaction medium at 10–20 °C. After the end of irradiation, the Centre via www.ccdc.cam.ac.uk/data_request/cif.
solution was concentrated at ca 15 °C to 10 mL; then 25 mL
pentane was added and the medium allowed to stand at −20 °C
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Beilstein Journal of Organic Chemistry 2009, 5, No. 20.
1
9.Hopf, H.; Greiving, H.; Beck, C.; Dix, I.; Jones, P. G.; Desvergne, J.-P.;
Bouas-Laurent, H. Eur. J. Org. Chem. 2005, 567–581.
doi:10.1002/ejoc.200400596
Supporting Information
Supporting Information File 1
2
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Thermal dissociation of photoproduct 4, HPLC diagram of
the photochemical preparation of 4, 1H-1H-COSY spectrum
of photoproduct 4, and other crystal data for 2.
;2-4
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