Competition between inter- and intramolecular photocycloaddition reactions of 9-substituted anthracenes

Article abstract of DOI:10.1055/s-2007-983734

A number of 9-[(arylmethoxy)methyl]anthracenes were prepared and their photoreactivity was studied. The intramolecular [4π+4π]cycloaddition competes with the intermolecular head-to-tail [4π+4π] cyclodimerization. The aryl substituents control the selectiv

Full text of DOI:10.1055/s-2007-983734

PAPER
1995
Competition between Inter- and Intramolecular Photocycloaddition Reactions
of 9-Substituted Anthracenes
I
ntra
-
a
ndIntermo
e
lecular Pho
r
tocycloa
o
ddition of 9-S
n
ubstitutedA
g
nthracenes Cao,a,b Chunmei Gao,a Silvia Dobis,c Herbert Meier*b,c
a
LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, P. R. of China
South China University of Technology, Guangzhou 510640, P. R. of China
Institut für Organische Chemie, Johannes Gutenberg-Universität, Duesbergweg 10–14, 55099 Mainz, Germany
Fax +49(6131)3925396; E-mail: hmeier@mail.uni-mainz.de
b
c
Received 21 March 2007; revised 27 April 2007
In the first approximation, the compounds 3a–n contain
two separate chromophores. Therefore, selective irradia-
tion (l ≥300 nm) into the anthracene chromophore is pos-
sible. This precondition is necessary in order to prevent
Abstract: A number of 9-[(arylmethoxy)methyl]anthracenes were
prepared and their photoreactivity was studied. The intramolecular
[4p+4p]cycloaddition competes with the intermolecular head-to-
tail [4p+4p] cyclodimerization. The aryl substituents control the se-
lectivity; concentration only plays a role in selectivity in certain cas- the light-induced reverse reactions 4,5,5¢ → 3. Table 2
es. The complete reversibility of the cycloaddition makes this
process suitable as a molecular switch, provided that traces of acids
shows the product ratios 4/5 that were obtained in the ir-
radiation experiments of 3a–h. The halogen-containing
are avoided; when acid is present the cyclomers pursue an irrevers-
compounds 3i–k are highly light sensitive. However, their
ible enol ether cleavage route.
irradiation yields product mixtures in which dimers, but
Key words: cycloaddition, cyclodimerization, ether cleavage,
regioselectivity, retrocycloaddition
1
no cyclomers, can be detected by H NMR and FD-MS
measurements; 3k reacts even in daylight. Compound 3l
was studied in another context.7 For the compounds 3a
and 3m, no cyclomers 4a and 4m were reported, but mix-
tures of dimers 5a/5¢a and 5m/5¢m, respectively, were
found;4 on irradiation compound 3n shows a quantitative
intramolecular cycloaddition to give 4n.8
Reversible photochemical reactions between compounds
that have different absorption (and/or emission) are of
great interest for optical switching and optical data storage
processes.1 Recently, we developed such a system, which
is based on the intramolecular [4p+4p] cycloaddition of
benzene and anthracene moieties.2 A prerequisite condi-
tion for this reaction is that the two chromophores are
linked by a three-atom chain, like CH2–O–CH2. Useful
switching systems should have clean, uniform reactions in
both directions. The [4p+4p] cyclodimerization is an al-
ternative photoreaction of anthracenes and is an old and
well-known process.1e,3 Therefore, we have now studied
the competition between the desired intramolecular
[4p+4p] cycloaddition and possible intermolecular
[4p+4p] cyclodimerizations. For this purpose, 9-[(aryl-
methoxy)methyl]anthracenes 3 were generated. Their
preparation was based on the nucleophilic substitution of
1 and 2 (Williamson synthesis), whereby the role of nu-
cleophile and electrophile can be exchanged (Table 1,
Methods A and B). The best results were obtained by us-
ing phase-transfer conditions (KOH, TBAB).
When a monomolecular reaction such as 3 → 4 competes
with a bimolecular process, such as 3 + 3 → 5, it would be
expected that the concentration of the starting compound
would determine the product ratio.
R4
10
H
R3
7
hν
6
H
9
8
5
R2
λ > 300 nm
15
21
3
1
22
23
R1
3
O
α
β
R3
16
R4
R2
R1
4
CH2
H
O
CH2
H
H
The possible photoproducts of 3a–n are shown in
Scheme 1.4–8 Apart from the cyclomers 4, head-to-tail
dimers 5 and head-to-head dimers 5¢ can be expected.9,10
Compared to 5, the dimers 5¢ are highly thermolabile. In
the past such compounds were usually detected in solution
by NMR measurements of the crude product mixture.
Nevertheless, many head-to-head dimers 5¢ have been re-
ported.4,11,12
+
+
H
CH
α
2
CH2 CH2
O
O
O
CH2
CH2
CH2
β
R1
R1
R2
R1
R2
R2
R4
R4
R4
R3
R3
R3
5′
5
SYNTHESIS 2007, No. 13, pp 1995–2001
x
x.
x
x
.
2
0
0
7
Advanced online publication: 18.06.2007
DOI: 10.1055/s-2007-983734; Art ID: T05807SS
Scheme 1 Possible photoproducts of 9-substituted anthracenes 3
© Georg Thieme Verlag Stuttgart · New York

1996
D. Cao et al.
PAPER
Table 1 Preparation of 9-[(Arylmethoxy)methyl]anthracenes 3a–n
R3
H2C
O
α
β
R2
R1
R4
A / B
base
+
CH2
CH2X
R1
R2
CH2Y
A: X = Cl, Y = OH; B: X = OH, Y = Cl
R4
R3
1
2a–n
3a–n
Product
R1
H
R2
H
R3
H
R4
H
A/B
Yield (%)
73
Ref.
3a
A
B
A
A
A
A
A
A
A
A
A
A
B
A
A
this work
<50
80
4
3b
3c
3d
3e
3f
H
OMe
H
H
H
5
H
OMe
H
79
this work
H
OMe
H
H
OMe
OMe
H
82
6
OMe
OMe
H
H
71
this work
OMe
OMe
Me
F
H
77
5
3g
3h
3i
OMe
OMe
Me
F
63
6
H
H
79
this work
H
H
43
this work
3j
H
Cl
H
Cl
39
this work
3k
3l
H
Br
H
H
28
this work
H
H
NMe2
(CH=CH)2
H
H
–
7
4
8
3m
3n
H
H
<50
74
(CH=CH)2
H
However, Table 2 demonstrates that the majority of reac-
tions are highly selective in one direction. The concentra-
tion has a notable effect in the cases 3b → 4b,5b and
3e → 4e,5e. At a concentration of 1.8 mM the ratio 4b/5b
is 44:56, at ca. 3.0 mM only small amounts of 4b are
formed and 5b is obtained in 82% isolated yield.5 The pre-
ferred reaction route can even be altered in the case of 3e.
The ratio 91:9 of 4/5 shown in Table 2 can be changed to
22:78 when the concentration of 3e is raised from 1.8 mM
to 113.0 mM. Dilution does not favor the generation of
cyclomers in cases where dimers (and oligomers) are the
sole products, as apparent in the 1H NMR reaction spectra
of 5a,c,f,h–j. Due to the aggregation of the anthracenes,
dimerization works also in these cases in 0.1 mM solu-
tions.
Table 2 Product Ratios on Irradiation of 3a–j
Starting compound
Product ratioa 4/5
3a
3b
3c
3d
3e
3f
0:100
44:56
0:100
100:0
91:9
0:100
100:0
0:100
0:100
0:100
3g
3h
3i
The structure determination of the dimers 5a–c,e,f,h–j
was much more complicated. We recently described the
crystal structure of compound 3f and its structure in solu-
tion, which is characterized by different rotamers.5 Tem-
3j
a 1.8 × 10–3 M soln of 3a–h in benzene; irradiation (l ≥300 nm).
Synthesis 2007, No. 13, 1995–2001 © Thieme Stuttgart · New York

PAPER
Intra- and Intermolecular Photocycloaddition of 9-Substituted Anthracenes
1997
1
perature-dependent H and 13C NMR spectra reveal the ferentiation between A and C is much more difficult. The
same phenomenon for all head-to-tail dimers studied here. benzene rings of the side chains in C can lie above the
The number of resonance signals at room temperature is bridgehead protons, so that the high-field singlet at
much higher than that would be expected for a single d = 3.54 can be assigned to the bridgehead protons of C;
structure 5.
proof for this assignment was found by NOE measure-
ments. The antiperiplanar arrangement of the OR groups
in A leads to the neighborhood of the bridgehead proton
and the two a-CH2 protons, whereas in rotamer C only
one a-CH2 proton is close to the bridgehead. Thus the dif-
ferent signal enhancement in the NOE difference spectra
indicates the assignments given for 5c in Figure 1. The
NMR data of the dimers 5a,b,e,f,h are very similar, so that
analogous rotamers can be assumed as for 5c. To our best
knowledge, there is only one rotamer discussion in the lit-
erature of anthracene dimers, namely for 1-hydroxy-1-
methylethyl side chains.13 However, antiperiplanar ar-
rangements of the OH groups, comparable to the arrange-
ment of the OR groups on one side of B and both sides of
A, were not found.
Figure 1 shows the 2D NMR spectrum HMQC of 5c in the
high field region. The signals (CDCl3, 5 °C) reveal the
presence of three rotamers. Figure 2 shows the staggered
conformers A, B, and C. The OR group can have an anti-
periplanar orientation related to the C–C bond that was
generated in the dimerization. Steric hindrance of OR and
the hydrogen atoms at the condensed benzene rings results
then in a ‘frozen’ rotation at this temperature. Thus rota-
mer A has a relatively rigid C2h structure. When both OR
groups have skew orientations to the newly formed C–C
bonds, as realized in C, partial rotation provokes a fast
equilibration between the drawn structure C(C2), its enan-
tiomer, and the structure C(Ci), which is obtained from
C(C2) by a 120° rotation on one side. Thus, C2h symmetry
is valid for this conformer also. Finally in rotamer B, an When the NMR measurement of 5c in 1,1,2,2-tetrachloro-
antiperiplanar OR orientation is given on one side and a ethane-d2 is performed at 90 °C, the signals collapse as
flexible skew orientation on the other; the result is de facto demonstrated in Figure 1. At this temperature the rotation
1
Cs symmetry. Accordingly B has twice as many H and of both side chains is fast in terms of the NMR timescale,
1
13C NMR signals as A and C. Therefore, the assignment so that in H and 13C NMR spectroscopy one signal ap-
of the NMR signals of B in Figure 1 is apparent. The dif- pears for the bridgehead CH, a-CH2, b-CH2, and OCH3
Figure 1 High-field region of the 2D NMR (HMQC) spectrum of 5c (400 MHz, CDCl3, 5 °C); The 1H and 13C NMR signals correspond to
the three rotamers A, B, and C shown in Figure 2. Heating (CDCl2CDCl2, 90 °C) leads to the collapse of the singlets demonstrated for OCH3,
a-CH2, b-CH2, CH and Cq (The signals for Cq and OCH3 could not be definitely assigned to the rotamers A, B, and C.).
Synthesis 2007, No. 13, 1995–2001 © Thieme Stuttgart · New York

1998
D. Cao et al.
PAPER
OR
OR
H
Summarizing the applicability of the systems discussed
herein, we can make the statement that the intramolecular
cycloadditions/cycloreversions 3d ' 4d and 3g ' 4g are
best suited as molecular switches. These monomolecular
processes are so effective that the bimolecular an-
thracene–anthracene dimerization has no chance, not even
in concentrated solutions. The common feature of 3d and
3g is high electron density at the 4-position of the benzene
ring. Although [4p+4p] cycloaddition may be allowed as
a concerted photoreaction, a stepwise process, in which
the first excited singlet state S1 located in the anthracene
moiety undergoes an electron transfer from the electron-
rich benzene ring, seems to be plausible. Absorption and
fluorescence, which are typical for the anthracene chro-
mophore, disappear in the quantitative step 3d,g → 4d,g
and are recovered completely in the reverse process
4d,g → 3d,g. The optical switching is based on the sepa-
ration of the chromophores; 3d,g show the anthracene ab-
α
α
α
H
H
OR
H
H
H
H
α
H
α
H
α
H
OR
OR
OR
H
H
B
A
C
β
R:
CH2
OMe
Figure 2 Rotamers of 5a that exist in solution (CH2Cl2, CHCl3,
CHCl2CHCl2, benzene)
groups each; a- and b-CH2 groups are then coincidentally sorption with its typical vibrational structure between 325
isochronous.
and 410 nm and the absorption of the benzenoid pp* tran-
sitions below 300 nm. The cyclomers 4d,g have only su-
perimposed benzene and homodiene absorptions below
290 nm. Between 290/300 and 325 nm is an absorption
gap.
The other dimers 5a,b,e,f,h exhibit analogous restriction
of the rotation of the side chains. Head-to-head dimers
were not found. The photodimerization of 3i and 3j is too
non-uniform to permit a final statement.
In contrast to the reversibility 4 → 3, the cleavage of the
dimers 5 → 3 is sufficiently clean. Therefore, we focused
our studies on the switching process 3 → 4. A complete
thermal or photochemical back reaction 4 → 3 is feasible
in the absence of acids; even traces of acids, present, for
example, chloroform that has not been recently purified,
disturb and transform the cyclomers to ketones. Scheme 2
shows the generation of the monoketones 6b and 6e from
4b and 4e, respectively. The other cyclomers 4d and 4g
have comparable sensitivity toward acids, but additionally
the enol ether cleavage can be accompanied by a scaffold
rearrangement.6 All resulting ketones are incapable of
photochemical or thermal cleavage to 9-[(aryl-
methoxy)methyl]anthracenes in which the aryl group
would be a phenol unit.
Melting points were measured with a Büchi melting point apparatus
and are uncorrected. FT-IR spectra were obtained with a Perkin-
Elmer GX/200 and UV/Vis spectra with a Zeiss MCS 320/340 spec-
1
trophotometer. H and 13C NMR spectra were recorded with the
Bruker spectrometer AMX 400. CDCl3 served as solvent, unless
otherwise noted, and TMS was used as the internal standard. The
symbol ‘s’ is used, when a 2J or 3J coupling is not visible in a routine
1H NMR spectrum. Field desorption (FD) MS were obtained with a
Finnigan MAT 95 and ESI (electrospray ionization) MS with a
Micromass QTOF Ultima-3 spectrometer. Elemental analyses were
performed in the microanalytical laboratory of the Institute of
Organic Chemistry of the University of Mainz.
9-[(Benzyloxy)methyl]anthracenes 3a–k; General Procedure
To 9-(chloromethyl)anthracene14 (1, X = Cl, 1.13 g, 5.0 mmol),
benzyl alcohol 2a–k14 (5.5 mmol), and TBAB (0.34 g, 1.05 mmol)
in chlorobenzene (20 mL), a soln of KOH (0.8 g, 14.3 mmol) in
H2O (1 mL) was added. The mixture was stirred at 60 °C under ar-
gon for 3 d. H2O (70 mL) was added and the soln extracted with
CH2Cl2 (70 mL) and then the aqueous layer was extracted with
CHCl3 (100 mL). The combined organic phases were dried
(Na2SO4) and evaporated. The crude product was purified by col-
umn chromatography (3 × 40 cm, silica gel, cyclohexane–CH2Cl2–
EtOAc, 1:1:0.03).
O
10
H
H
+ H3O+
H
H
22
23
H
6
9
1
15
21
4b
H
– H+
– MeOH
16
O
Compounds 3b,5 3d,6 3f,5 and 3g6 have been previously described.
6b
9-[(Benzyloxy)methyl]anthracene (3a)
Yellowish solid; yield: 1.085 g (73%); mp 60 °C.
O
10
H
H
H
H
22
23
1H NMR (CDCl3): d = 4.27 (s, 2 H, b-CH2), 5.49 (s, 2 H, a-CH2),
7.31–7.54 (m, 9 H, Harom), 8.00–8.02 (m, 2 H, Harom), 8.30–8.32 (m,
2 H, Harom), 8.46 (s, 1 H, H10).
13C NMR (CDCl3): d = 64.1 (a-CH2), 72.4 (b-CH2), 124.4, 124.9,
126.1, 128.0, 128.0, 128.4, 129.0, 129.0 (CHarom), 128.0, 131.1,
131.4, 138.4 (Cq arom).
+ H3O+
6
9
15
21
4e
H
1
– H+
– MeOH
OMe
16
O
6e
MS (FD): m/z (%) = 298 (100) [M+].
Scheme 2 Enol ether cleavage of 4b,e to the monoketones 6b,e
Synthesis 2007, No. 13, 1995–2001 © Thieme Stuttgart · New York

PAPER
Intra- and Intermolecular Photocycloaddition of 9-Substituted Anthracenes
1999
Anal. Calcd for C22H18O (298.4): C, 88.56; H, 6.08. Found: C,
88.65; H, 6.11.
7.45–7.57 (m, 4 H, Hanthracene), 8.00–8.03 (m, 2 H, Hanthracene), 8.30–
8.33 (m, 2 H, Hanthracene), 8.47 (s, 1 H, H10).
13C NMR (CDCl3): d = 64.5 (a-CH2), 70.6 (b-CH2), 124.1, 125.0,
126.0, 126.4, 127.7, 128.7, 129.1 (CHarom), 127.9, 131.1, 131.4,
134.9, 142.0 (Cq arom).
MS (EI): m/z (%) = 366 (29, Cl2 isotope pattern) [M+].
HRMS: m/z [M(35Cl2)]+ calcd for C22H1635Cl2: 366.0576; found:
366.0580.
9-[(4-Methoxybenzyloxy)methyl]anthracene (3c)
Yellowish solid; yield: 1.290 g (79%); mp 78 °C.
1H NMR (CDCl3): d = 3.83 (s, 3 H, OCH3), 4.68 (s, 2 H, b-CH2),
5.46 (s, 2 H, a-CH2), 6.95, 7.37 (AA¢BB¢, 4 H, Hphenyl), 7.41–7.58
(m, 4 H, Hanthracene), 8.00–8.03 (m, 2 H, Hanthracene), 8.29–8.32 (m, 2
H, Hanthracene), 8.46 (s, 1 H, H10).
13C NMR (CDCl3): d = 55.2 (OCH3), 63.7 (a-CH2), 72.0 (b-CH2),
113.7, 124.3, 124.8, 126.0, 128.3, 128.9, 129.6 (CHarom), 128.7,
130.4, 131.0, 131.4 (Cq arom).
MS (FD): m/z (%) = 328 (100) [M+].
HRMS (ESI): m/z [M + Na]+ calcd for C23H20NaO2: 351.1361;
9-[(3-Bromobenzyloxy)methyl]anthracene (3k)
Yellowish solid; yield: 530 mg (28%); mp 102 °C.
1H NMR (CDCl3): d = 4.64 (s, 2 H, b-CH2), 5.49 (s, 2 H, a-CH2),
7.18–7.30 (m, 2 H, Hphenyl), 7.41–7.56 (m, 6 H, Hanthracene, Hphenyl),
8.00–8.02 (m, 2 H, Hanthracene), 8.28–8.31 (m, 2 H, Hanthracene), 8.46 (s,
1 H, H10).
found: 351.1381.
13C NMR (CDCl3): d = 64.2 (a-CH2), 71.3 (b-CH2), 124.2, 124.9,
126.2, 126.3, 128.5, 129.0, 129.9, 130.7, 130.8 (CHarom), 122.5,
128.2, 131.0, 131.4, 140.8 (Cq arom).
9-[(2,5-Dimethoxybenzyloxy)methyl]anthracene (3e)
Yellowish solid; yield: 1.270 g (71%); mp 124 °C.
1H NMR (CDCl3): d = 3.69 (s, 3 H, OCH3), 3.75 (s, 3 H, OCH3),
4.76 (s, 2 H, b-CH2), 5.52 (s, 2 H, a-CH2), 6.80 (‘s’, 2 H, Hphenyl),
7.00 (‘s’, 1 H, Hphenyl), 7.41–7.52 (m, 4 H, Hanthracene), 7.98–8.00 (m,
2 H, Hanthracene), 8.34–8.36 (m, 2 H, Hanthracene), 8.44 (s, 1 H, H10).
13C NMR (CDCl3): d = 55.7, 56.0 (OCH3), 64.5 (a-CH2), 67.2 (b-
CH2), 111.5, 113.7, 114.9, 124.5, 124.9, 126.1, 128.3, 128.9
(CHarom), 127.8, 131.1, 131.5, 131.5 (Cq arom), 151.5, 153.7 (OCq
arom).
MS (FD): m/z (%) = 376/378 (100, Br isotope pattern), [M+].15
Irradiation of the Anthracene Derivatives 3a–h
An argon stream was purged for 30 min through a dilute soln of 3a–
h [0.30 mmol in anhyd benzene (165 mL)]. The soln was irradiated
with a Hanovia-450 W medium-pressure Hg lamp, equipped with a
Duran glass filter (l ≥300 nm). During the irradiation period of 15–
30 min, a slow argon stream was maintained. Evaporation of the
solvent at 20 °C under reduced pressure gave the photoproducts as
a solid residue; they were purified by crystallization (CH2Cl2–
EtOH, 1:2). In the case of 3b and 3e mixtures 4b/5b and 4e/5e re-
spectively were obtained, which could be separated by fractional
crystallization (CH2Cl2–EtOH), because the dimers 5b and 5e have
much lower solubility.
MS (EI): m/z (%) = 358 (50) [M+], 192 (100), 179 (72), 151 (50).
Anal. Calcd for C24H22O3 (358.4): C, 80.42; H, 6.19. Found: C,
80.43; H, 6.23.
9-[(3,5-Dimethylbenzyloxy)methyl]anthracene (3h)
Yellowish solid; yield: 1.290 mg (79%); mp 90 °C.
Compounds 4b,5 5b,5 4d,6 5f,5 and 4g6 have been previously char-
acterized.
1H NMR (CDCl3): d = 2.32 (s, 6 H, CH3), 4.65 (s, 2 H, b-CH2), 5.46
(s, 2 H, a-CH2), 6.95 (‘s’, 1 H, Hphenyl), 7.02 (‘s’, 2 H, Hphenyl), 7.43–
7.53 (m, 4 H, Hanthracene), 7.99–8.02 (m, 2 H, Hanthracene), 8.30–8.32
(m, 2 H, Hanthracene), 8.45 (s, 1 H, H10).
13C NMR (CDCl3): d = 21.2 (CH3), 64.0 (a-CH2), 72.5 (b-CH2),
124.5, 124.9, 125.9, 126.1, 128.4, 129.0, 129.3 (CHarom), 128.5,
131.1, 131.5, 138.2, 138.2 (Cq arom).
5,11-Bis[(benzyloxy]methyl]-5,6,11,12-tetrahydro-
5,12[1¢,2¢]:6,11[1¢¢,2¢¢]dibenzenodibenzo[a,e]cyclooctene (5a)
Colorless crystals; yield: 43 mg (48%); mp 226 °C (dec.).
FT-IR (KBr): 1475, 1453, 1135, 1109, 1028, 777, 746, 733, 693
cm–1.
1H NMR (CDCl3, 25 °C): d = 3.53 (s)/4.70 (s) (2 H, bridgehead H),
4.47 (s)/4.49 (s) (4 H, a-CH2), 4.75 (s)/4.99 (s) (4 H, b-CH2), 6.75–
7.64 (m, 26 H, Harom).
MS (FD): m/z (%) = 327 (100) [M + H+].
Anal. Calcd for C24H22O (326.4): C, 88.31; H, 6.79. Found: C,
88.27; H, 6.80.
MS (FD): m/z (%) = 597 (12) [M+], 298 (100).
9-[(3,5-Difluorobenzyloxy)methyl]anthracene (3i)
Yellowish solid; yield: 720 mg (43%); mp 139 °C.
1H NMR (CDCl3): d = 4.62 (s, 2 H, b-CH2), 5.53 (s, 2 H, a-CH2),
6.67–6.75 (m, 1 H, Hphenyl), 6.86–6.90 (m, 2 H, Hphenyl), 7.45–7.57
(m, 4 H, Hanthracene), 8.00–8.03 (m, 2 H, Hanthracene), 8.30–8.32 (m, 2
H, Hanthracene), 8.47 (s, 1 H, H10).
Anal. Calcd for C44H36O2 (596.8): C, 88.56; H, 6.08. Found: C,
88.09; H, 6.15.
5,11-Bis[(4-methoxybenzyloxy)methyl]-5,6,11,12-tetrahydro-
5,12[1¢,2¢]:6,11[1¢¢,2¢¢]dibenzenodibenzo[a,e]cyclooctene (5c)
Colorless crystals; yield: 25 mg (25%); mp 198 °C (dec.).
13C NMR (CDCl3): d = 64.5 (a-CH2), 70.9 (b-CH2), 102.9 (t,
2J(C,F) = 25 Hz, CHphenyl), 110.1 (CHphenyl), 124.1, 125.0, 126.4,
128.7, 129.1 (Cq anthracene), 142.6 (Ci phenyl), 163.0 (dd,
1J(C,F) = –247 Hz, 3J(C,F) = 16 Hz, CF).
FT-IR (KBr): 1512, 1247, 1171, 1095, 1030, 817, 758, 694 cm–1.
1H NMR (CDCl3, 25 °C): d = 3.52 (s)/4.68 (s,) (2 H, bridgehead H),
3.84 (s)/3.85 (s) (6 H, OCH3), 4.42 (s)/4.44 (s) (4 H, a-CH2), 4.68
(s)/4.92 (s) (4 H, b-CH2), 6.75–7.56 (24 H, Harom).
1H NMR (CDCl3, 0 °C): d = 3.52 (s)/3.54 (s)/4.67 (s)/4.70 (s) (2 H,
bridgehead H), 3.84 (s)/3.85 (s)/3.86 (s) (6 H, OCH3), 4.39 (s)/4.41
(s)/4.42 (s)/4.46 (s) (4 H, a-CH2), 4.67 (s)/4.70 (s)/4.91 (s)/4.93 (s)
(4 H, b-CH2), 6.76–7.56 (m, 24 H, Harom).
1H NMR (CDCl2CDCl2, 90 °C): d = 3.90 (s, 6 H, OCH3), 4.25 (br s,
2 H, bridgehead H), 4.53 (s, 4 H, a-CH2), 4.88 (s, 4 H, b-CH2), 6.78–
6.85 (m, 4 H, Harom), 6.87–6.89 (m, 8 H, Harom), 7.03/7.51 (AA¢BB¢,
8 H, Hphenyl), 7.14 (m, 4 H, Harom).
MS (FD): m/z (%) = 334 (100) [M+].
Anal. Calcd for C22H16F2O (334.4): C, 79.03; H, 4.82. Found: C,
79.03; H, 4.82.
9-[(3,5-Dichlorobenzyloxy)methyl]anthracene (3j)
Yellowish solid; yield: 720 mg (39%); mp 97 °C.
1H NMR (CDCl3): d = 4.58 (s, 2 H, b-CH2), 5.51 (s, 2 H, a-CH2),
7.21 (d, 4J = 1.8 Hz, 2 H, Hphenyl), 7.26 (d, 4J = 1.8 Hz, 1 H, Hphenyl),
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D. Cao et al.
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13C NMR (CDCl3, 0 °C): d = 53.7, 54.3, 55.8 (Cq, bridgehead),
55.1, 55.2, 55.2, 55.3 (OCH3), 56.1, 56.9, 58.9, 59.7 (CH, bridge-
head), 70.0, 70.3, 74.1, 74.2 (a-CH2), 73.0, 73.0, 73.4, 73.4 (b-
CH2), 113.6, 113.8, 123.4, 123.9, 124.7, 125.1, 125.3, 125.4, 127.2,
127.7, 127.8, 129.3, 129.4, 129.5, 129.9 (CHarom, partially superim-
posed), 128.1, 128.7, 142.5, 142.6, 142.7, 142.9, 143.3, 143.7,
144.8, 159.0, 159.1 (Cq arom, partially superimposed).
13C NMR (CDCl2CDCl2, 90 °C): d = 55.2 (Cq, bridgehead), 55.4
(OCH3), 58.3 (CH, bridgehead), 73.4 (a-CH2, b-CH2), 114.2, 129.5
(CHphenyl), 124.4, 125.1, 125.3, 127.7 (CHarom), 130.3, 159.5 (Cq
phenyl), 143.3, 144.2 (Cq arom).
4.44 (s)/4.46 (s)/4.49 (s) (4 H, a-CH2), 4.67 (s)/4.71 (s)/4.93 (s)/
4.95 (s) (4 H, b-CH2), 6.77–7.27 (m, 22 H, Harom).
MS (FD): m/z = 653 (6) [M + H+].
Anal. Calcd for C48H44O2 (652.9): C, 88.31; H, 6.79. Found; C,
88.31; H, 6.81.
Irradiation of the Anthracene Derivatives 3i,j
An argon purged soln of 3i (14.0 mg, 0.042 mmol) or 3j (21.4 mg,
0.058 mmol) in benzene-d6 (1 mL) was irradiated with a Hanovia
450W middle-pressure lamp equipped with a Duran glass filter. Re-
action spectra after 5, 15, and 35 min revealed the generation of the
dimers 5i or 5j and the absence of the cyclomers 4i or 4j. Both pho-
toreactions are non-uniform and the enrichment of the dimers did
not exceed 20%. Therefore we did not isolate and purify 5i or 5j.
(Compound 3k decomposed already in daylight.)
MS (FD): m/z = 657 (5) [M + H+], 328 (100).
HRMS (ESI): m/z [M + Na]+ calcd for C46H40NaO4: 679.2824;
found: 679.2806.
7,23-Dimethoxy-3-oxahexacyclo[7.6.6.25,8.01,5.010,15.016,21]tri-
cosa-6,10,12,14,16,18,20,22-octaene (4e)
Yellowish solid; yield: 91 mg (85%); mp 122 °C (dec.).
Enol Ether Cleavage
The photoproducts 4 can be subjected to an enol ether cleavage ac-
cording to the literature.6 However, the monoketones 5b and 6e
could also be obtained in a one-pot reaction from 3b and 3e, respec-
tively. After the irradiation as described above, the solvent was re-
moved and the residue was treated with toluene (30 mL) and
HCO2H (0.5 mL, 610 mg, 13.25 mmol) at 0 °C for 1 h. Column
chromatography (30 × 2 cm, silica gel, cyclohexane–EtOAc, 97:3
to 92:8) yielded the crude monoketones 6b,e, which could be re-
crystallized (CH2Cl2–cyclohexane, 1:9).
FT-IR (KBr): 1716, 1634, 1499, 1471, 1231, 1219, 1157, 1135,
1068, 1020, 756 cm–1.
1H NMR (C6D6/TMS): d = 2.69 (s, 3 H, OCH3), 2.73 (s, 3 H, OCH3),
2
3
3.61/4.73 (AB, J = –9.0 Hz, 2 H, H4), 3.14 (ddd, J = 10.7 Hz,
3J = 7.7 Hz, 4J = 2.3 Hz, 1 H, H8), 4.04 (d, 3J = 10.7 Hz, 1 H, H9),
4.06 (d, 4J = 2.3 Hz, 1 H, Holefin), 4.21 (d, 3J = 7.7 Hz, 1 H, Holefin),
4.55 (‘s’, 2 H, H2), 6.75–7.28 (m, 8 H, Harom).
13C NMR (C6D6/TMS): d = 44.1 (C8), 54.2 (C9), 54.9 (OCH3), 54.9
(OCH3), 66.0 (C1), 61.1 (C5), 71.3 (C2), 75.2 (C4), 99.0 (CHolefin),
103.4 (CHolefin), 123.6, 123.6, 125.1, 125.3, 125.8, 125.9, 127.0
127.3 (CHarom), 145.6, 145.9, 145.9, 146.4 (Cq), 165.5 (OCq), 167.1
(OCq).
MS (FD): m/z = 358 (100) [M+].
HRMS: m/z [M + Na]+ calcd for C24H22NaO3: 381.1467; found:
(5R*,8R*)-3-Oxahexacyclo[7.6.6.25,8.01,5.010,15.016,21]tricosa-
10,12,14,16,18,20,22-heptaen-7-one (6b)
From 4b (132 mg); colorless solid; yield: 26 mg (21%); mp 177 °C.
1H NMR (C6D6): d = 1.84/1.99 (AB, 2J = –18.7 Hz, 2 H, H6), 3.56
2
(m, 1 H, H8), 3.64/4.36 (AB, J = –11.4 Hz, 2 H, H4), 4.02 (d,
2
3J = 8.8 Hz, 1 H, H9), 4.66/4.85 (AB, J = –10.3 Hz, 2 H, H2),
5.53–5.56 (m, 1 H, H22), 5.74 (d, 3J = 8.8 Hz, 1 H, H23), 7.13–7.29
381.1462.
(m, 7 H, Harom), 7.49–7.51 (m, 1 H, Harom).
13C NMR (C6D6): d = 44.1 (C6), 50.5 (C9), 54.7 (C5), 56.5 (C8),
60.7 (C1), 72.3 (C2), 80.4 (C4), 123.7, 124.2, 126.5, 126.6, 127.2,
127.3, 127.5, 128.9 (CHarom), 129.9, 142.1 (CHolefin), 141.0, 141.1,
141.9, 144.4 (Cq arom), 211.1 (CO).
5,11-Bis[(2,5-dimethoxybenzyloxy)methyl]-5,6,11,12-tetrahy-
dro-5,12[1¢,2¢]:6,11[1¢¢,2¢¢]dibenzenodibenzo[a,e]cyclooctene
(5e)
Yield: 9 mg (8%); mp 225 °C (dec.). When the concentration of 3e
(72 mg) in benzene was enhanced to 5.4 mM, the yield of 5e in-
creased to 16 mg (22%) and the yield of 4e decreased to 50 mg
(69%). At 113 mM (40.5 mg 3e in 1.0 mL benzene), the ratio 4:5
amounts to 22:78.
MS (FD): m/z = 315 (100) [M + H+].
Anal. Calcd for C22H18O2 (314.4): C, 84.05; H, 5.77. Found: C,
83.94; H, 5.71.
(5R*,8R*)-23-Methoxy-3-oxahexacyclo[7.6.6.25,8.01,5.010,15.016,21]-
tricosa-10,12,14,16,18,20,22-heptaen-7-one (6e)
From 4e (72 mg); colorless solid; yield: 36 mg (52%); mp 107 °C.
FT-IR (KBr): 1501, 1474, 1455, 1279, 1246, 1218, 1160, 1105,
1053, 1034, 694 cm–1.
1H NMR (CDCl3): d = 3.54 (s)/4.74 (s) (2 H, bridgehead), 3.67 (s)/
3.80 (s) (6 H, OCH3), 3.88 (s, 6 H, OCH3), 4.53 (s)/4.56 (s) (4 H, a-
CH2), 4.78 (s)/4.99 (s) (4 H, b-CH2), 6.71–7.31 (m, 22 H, Harom).
MS (FD): m/z = 717 (4) [M + H+], 359 (100).
HRMS: m/z [M + Na]+ calcd for C48H44NaO6: 739.3036; found:
1H NMR (C6D6): d = 1.78/1.93 (AB, 2J = –18.4 Hz, 2 H, H6), 2.56
2
(s, 3 H, OCH3), 3.01/4.54 (AB, J = –9.2 Hz, 2 H, H4), 3.41 (dd,
3J = 11.4 Hz, 3J = 7.7 Hz, 1 H, H8), 3.81 (d, 3J = 7.7 Hz, 1 H, H22),
3
4.07 (d, J = 11.4 Hz, 1 H, H9), 4.32/4.54 (AB, 2J = –10.3 Hz, 2 H,
H2), 6.75–6.78 (m, 1 H, Harom), 6.90–7.03 (m, 6 H, Harom), 7.46–
7.49 (m, 1 H, Harom).
739.3046.
13C NMR (C6D6): d = 44.6 (C6), 51.1 (C8), 54.1, 54.7 (C9, OCH3),
56.9, 60.9 (C1, C5), 72.3, 74.4 (C2, C4), 94.9 (C22), 124.3, 125.0,
126.0, 126.5, 127.1, 127.3, 129.1 (CHarom, partly superimposed),
140.9, 142.1, 143.2, 144.7 (Cq arom), 164.9 (C23), 207.8 (CO).
5,11-Bis[(3,5-dimethylbenzyloxy)methyl]-5,6,11,12-tetrahydro-
5,12[1¢,2¢]:6,11[1¢¢,2¢¢]dibenzenodibenzo[a,e]cyclooctene (5h)
Colorless solid; yield: 25 mg (26%); mp 208 °C (dec.).
FT-IR (KBr): 1677, 1474, 1455, 1352, 1285, 1136, 1111, 778,
694 cm–1.
1H NMR (CDCl3, 25 °C): d = 2.34 (s)/2.39 (s) (12 H, CH3), 3.54 (s)/
4.77 (s) (2 H, bridgehead), 4.45 (s)/4.49 (s) (4 H, a-CH2), 4.68 (s)/
4.93 (s) (4 H, b-CH2), 6.76–7.26 (m, 22 H, Harom).
1H NMR (CDCl3, –20 °C): d = 2.35 (s)/2.36 (s)/2.40 (s) (12 H,
CH3), 3.56 (s)/3.57 (s)/4.78 (s)/4.80 (s) (2 H, bridgehead), 4.42 (s)/
MS (FD): m/z = 344 (100) [M+].
Anal. Calcd for C23H20O3 (344.4): C, 80.21; H, 5.85. Found: C,
80.21; H, 5.85.
Cleavage of the Cyclomers 4 (Back Reaction)
In the absence of acid, heating of 4 (neat) to 110 °C provoked a fast
and quantitative back reaction to 3. Irradiation with l = 254 nm had
Synthesis 2007, No. 13, 1995–2001 © Thieme Stuttgart · New York

PAPER
Intra- and Intermolecular Photocycloaddition of 9-Substituted Anthracenes
2001
the same result. The number of possible switching cycles is not
known, but it should be high, because extended irradiation (48 h)
did not show any aging effects.
(3) (a) Bouas-Laurent, H.; Castellan, A.; Desvergne, J.-P.;
Lapouyade, R. Chem. Soc. Rev. 2001, 30, 248. (b) Bouas-
Laurent, H.; Castellan, A.; Desvergne, J.-P.; Lapouyade, R.
Chem. Soc. Rev. 2000, 29, 43. (c) Becker, H. D. Chem. Rev.
1993, 93, 145. (d) Becker, H. D. In Advances in
Photochemistry, Vol. 15; Volman, D. H.; Hammond, G. S.;
Gollnik, K., Eds.; Wiley: New York, 1990, 139–227.
(4) Desvergne, J.-P.; Castellan, A.; Bouas-Laurent, H.
Tetrahedron Lett. 1981, 22, 3529.
(5) Dobis, S.; Schollmeyer, D.; Gao, C.; Cao, D.; Meier, H. Eur.
J. Org. Chem. 2007, 2964.
(6) Cao, D.; Dobis, S.; Schollmeyer, D.; Meier, H. Tetrahedron
2003, 59, 5323.
Acknowledgment
We are grateful to the Deutsche Forschungsgemeinschaft, the Fonds
der Chemischen Industrie, the National Natural Science Foundation
of China (20272059, 20572111) and to Specialized Chinese
Research Fund for the Doctoral Program of Higher Education
(20060561024) for financial support. We thank Prof. Henri Bouas-
Laurent (University of Bordeaux) for many valuable discussions on
this topic.
(7) Tsujiya, N.; Kitaura, K.; Kumamoto, Y. J. Phys. Chem. A
1997, 101, 31.
(8) Desvergne, J.-P.; Bitit, N.; Castellan, A.; Bouas-Laurent, H.
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react mutually, were found for 9,10-disubstituted
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(13) We attribute the quantitatively different concentration
effects to different aggregation tendencies.
(14) Commercially available.
(15) The bromo compound 3k is thermolabile and light-sensitive,
correct elemental analysis could not be obtained.
Synthesis 2007, No. 13, 1995–2001 © Thieme Stuttgart · New York