Photolysis of dibenzo[a,d]cycloheptene dimer

Article abstract of DOI:10.1002/jccs.201200570

Photolysis reaction of dibenzo[a,d]cycloheptene dimer 3 provides three dibenzo[a,d]cycloheptyl dimmers 4, 5 and 6 under different irradiation conditions via the intramolecular degradative cyclodimerization. A tetracyclic benzo[4,5]cyclohepta[1,2,3-de]naphthalene core is also synthesized.

Full text of DOI:10.1002/jccs.201200570

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Photolysis of Dibenzo[a,d]cycloheptene Dimer
Meng-Yang Chang* and Yu-Ping Huang
Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan, R.O.C.
(Received: Oct. 31, 2012; Accepted: Jan. 28, 2013; Published Online: ??; DOI: 10.1002/jccs.201200570)
Photolysis reaction of dibenzo[a,d]cycloheptene dimer 3 provides three dibenzo[a,d]cycloheptyl dimers
4, 5 and 6 under different irradiation conditions via the intramolecular degradative cyclodimerization. A
tetracyclic benzo[4,5]cyclohepta[1,2,3-de]naphthalene core is also synthesized.
Keywords: Photolysis; Dibenzo[a,d]cycloheptene; Dimer.
INTRODUCTION
In the context of the photochemical reaction of cis- or
Synthesis of dimer 3 and its photolytic reac-
tion
Scheme I
trans-stilbene libraries, many synthetic methodologies for
the construction of strained molecules have been investi-
gated.1-2 Many organic researchers have reported that the
photochemistry of aromatic o-stilbene compounds (b-
heteroaryl 1,2-divinylbenzenes) provided some strained
photo-adducts via a series of intramolecular cycloaddition
reactions.3-4 As an extension of the studies on the skeleton
of dibenzosuberenone (1) for the synthesis of dizocilpine
(MK-801),5 we became interested in determining the pho-
tolytic cyclodimerization reaction of dibenzo[a,d]cyclo-
heptene and in the identification of the isolated products af-
ter observation under different experimental conditions
(Figure 1).
sponding allyl compound 2a with the Grubbs second gen-
eration catalyst. First, compound 2a produced with a 95%
yield following a treatment of compound 1 with allylmag-
nesium bromide (1.0 M in tetrahydrofuran) for 2 h at rt.
Cross metathesis of compound 2a was treated with Grubbs
second generation catalyst to provide a sole (E)-isomer 3 in
a 70% yield. The structure of compound 3 was constructed
using single-crystal X-ray analysis (Figure 2).7 Further-
more, intramolecular photolytic degradative cyclodimeri-
Because dibenzosuberenone (1) and its analogues are
known as the building partners in the synthesis of useful
compounds with potential applications, a number of strate-
gies have been employed for preparing the structures with
different functionalized substitutents.6 The starting mate-
rial 2a with a C-5 allyl and C-5 hydroxyl functional group
represents a cyclic cis-stilbene bearing two fused benzene
rings and is easily synthesized through Grignard allylation
of commercial grade compound 1.
As shown in Scheme I, the synthetic two-step route of
compound 3 involved: (1) Grignard allylation with allyl-
magnesium bromide and (2) cross metathesis of the corre-
Fig. 1. Structures of trans-Stilbene, trans-o-Vinylstil-
bene and 1.
Fig. 2. X-ray Structure of Compound 3.
* Corresponding author. E-mail: mychang@kmu.edu.tw
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Chang and Huang
Table 1. Photolytic reaction of compound 3a-d
zation was investigated next.
Products, Yields (%)b-c
In order to contract the strained dimeric molecules,
photochemical reaction of compound 3 was examined at rt
for 2 h via different polar or nonpolar solvent (ethyl acetate
or benzene) and different wavelengths (l = 3600, 3060,
2540 Å). Under the irradation conditions, compounds 1, 4,
5, and 6 could be generated in different ratios. As shown in
Table 1, compounds 1 and 4 were isolated as major prod-
ucts and the lower yields of compounds 5~6 and the re-
corvery compound 3 in different ratios were observed.
Three strutural frameworks of the isolated products 4, 5
and 6 are constructed using single-crystal X-ray crystallog-
raphy. Single-crystal X-ray diffraction analysis was ob-
tained to prove the constitution and relative configuration
of the isolated product. These ORTEP plots clearly show
the dimeric configuration of dibenzo[a,d]cycloheptyl skel-
eton (Figures 3~5).8
Wavelength
(Å)
Entry Solvent
1
4
5
6
3
1
2
EtOAc
EtOAc
3600
3060
2540
2540
3600
3060
50
39
20
15
42
30
12 trace --
15
10
22
38
45
10
20
8
6
8
3
EtOAc
EtOAc
Benzene
Benzene
14
11
--
trace
4d
5
10 trace
--
12
20
10
6
15
a For the reaction condition: compound 3 (50 mg), solvent (10
mL), rt, 2 h. b The recovery yield of compound 3. c The shown
yields of compounds 1 and 3~6 were determined by the isolated
products. d Methylene blue (1 mM, 0.1 mL) was added.
2540 Å), we found that the ratios of products 1 and 3 were
stepwise decreased and the increasing yields of compounds
4~6 were observed. Under the photolytic conditions (en-
tries 1~3), we found that the yields of compound 4 were in-
creased (12% ® 22% ® 38%) and the yields of compound
1 were decreased (50% ® 39% ® 20%), respectively. For
the formation of compounds 5 and 6, only trace amounts
were generated (for 5: trace ® 8% ® 14%; for 6: no de-
tected ® 6% ® 8%). By the addition of catalytic amounts
of methylene blue (a photosensitizer), compound 4 is ob-
tained in better yield (entry 4). The product distributions
are similar between entry 3 and entry 4. Therefore, the iso-
lated photoadducts 4~7 should be predicted from the triplet
excited state during the photolytic procedure.9 Changing
the solvent from ethyl acetate to benzene (entries 5~6), we
found that the yields of compound 4 (10% ® 20%) were in-
creased and the yields of compound 1 (42% ® 30%) were
decreased, respectively. The yield distribution of products
4~6 were increased along with the increased energy. By the
increasing energy (3600 Å ® 3060 Å), the above results re-
vealed that compound 3 could be converted completely
into these rigid products 4~6.
When ethyl acetate was chosen as the reaction solvent
by the different irradiation wavelengths (3600 Å, 3060 Å or
Fig. 3. X-ray Structure of Compound 4.
Fig. 5. X-ray Structure of Compound 6.
Fig. 4. X-ray Structure of Compound 5.
2
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Photolysis of Dibenzo[a,d]cycloheptene Dimer
Table 2. Crystal data for compounds 4, 5 and 6
CCDC number
839171 (4)
Monoclinic
P 1 21/c 1
10.3270(9)
10.6469(7)
18.8079(13)
90
839174 (5)
Monoclinic
P 1 21/n 1
10.2910(2)
8.3098(17)
12.3890(3)
90
841658 (6)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Orthorhombic
P n m a
8.4960(5)
19.7509(12)
12.0282(7)
90
a (°)
b (°)
g (°)
99.232(5)
90
2041.2(3)/4
100(2)
108.914(6)
90
1002.3(4)/2
100(2)
1.267
0.072
90
90
Volume (Å3)/Z
Temperature (K)
Dc (Mg/m3)
2018.4(2)/8
296(2)
1.259
1.342
Absorption coefficient (mm-1) 0.083
0.071
Crystal size (mm)
0.20 ´ 0.15 ´ 0.10
2.00 to 26.45
15990
4188 (R = 0.0526)
0.0733, 0.1593
0.0454, 0.1208
1.135
0.30 ´ 0.28 ´ 0.15
2.24 to 26.36
8234
2050 (R = 0.0851)
0.0859, 0.1742
0.0630, 0.1409
1.156
0.35 ´ 0.25 ´ 0.22
1.98 to 26.36
12379
2127 (R = 0.0320)
0.0817, 0.1874
0.0634, 0.1727
1.051
q range for data collection (°)
Reflections collected
Independent reflections
RF, Rw(F2) (all data)a
RF, Rw(F2) (I > 2s(I))a
GOF
a RF = S|Fo-Fc|/S|Fo|; RW (F2) = [SW|Fo -Fc2|2/SW Fo ]
2
4 1/2
The possible mechanism for reaction of
compound 1f
Scheme II
The possible mechanism is explained in Scheme II by
pathways a~g.3 Under the photochemical irradiation condi-
tions, the possible 1,2-diradicals intermediate I are pre-
ferred insofar as initiating the photolytic procedure (path-
way a).3a After the photolytic degradation of intermediate
I, two equivalents of intermediate II and butadiene should
be afforded (pathway b). Dehydrogenation of intermediate
II is further converted to compound 1 via the intermolecu-
lar [2 + 2] cycloaddition (pathways c~d).3d For minor route,
intermediate II is dimerized to form intermediate III (path-
way e). By the double dehydroxylation of intermediate III,
compound 5 is generated (pathway f).10 Then, compound 6
is obatined via the intramolecular [2 + 2] cycloaddition
(pathway g).3e Changing the solvent from ethyl acetate to
benzene, the similar phenomenon is also observed. Under
the irradiation conditions with 3600 Å and 3060 Å, the iso-
lated yields of compounds 5 and 6 were incresed to nearly
twofold in comparison with ethyl acetate. Furthermore, the
relationship between absorption wavelength and product
distribution is examined. From the UV-vis spectra, the
maximum absorption wavelength (lmax) of compound 3 is
distributed with 295 nm. According to the phenomenon, we
think that UV-vis light within a range of 254~360 nm
should excite the (E)-double bond firstly. Then, the diben-
zo[a,d]cycloheptene core is likely to be the chromophore
that absorbs the UV-vis light. Therefore, the interesting ir-
radiation wavelength dependent product distribution is ob-
served.
With the above results in hand, our attention turned to
irradiate compound 2a. As shown in Table 3, major com-
pound 7 with cage skeleton was isolated in high yields
(68% for 3600 Å; 81% for 3060 Å; 70% for 2540 Å) via
intramolecular [2 + 2] cycloaddition of compound 2a using
three kinds of wavelengths (entries 1~3). Under the irradia-
tion conditions, dimer 4 or starting material 2a were iso-
lated in minor or trace amounts. By the increasing energy,
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Table 3. Photolytic reaction of compound 2aa-c
2b was recovered and no photo-adducts were found under
this irradiative dehydration condition.
H
b
H
c
H
a
Photolysis
To further explore the application of polycyclic com-
pounds,11 the tetracyclic benzo[4,5]cyclohepta[1,2,3-de]-
naphthalene core 11 was chosen as a model substrate
(Scheme IV). Boron trifluoride etherate-mediated dehy-
droxylation of compound 2a with triethylsilane afforded
compound 9 with a 72% yield. After the regioselective
hydroboration of terminal olefin on the compound 9 and
Jones oxidation of the resulting alcohol, compound 10 was
synthesized in a 67% yield of two-step.12 The structural
framework of compound 10 was constructed using sin-
gle-crystal X-ray crystallography.8 Hydrogenation of com-
pound 10 with acetic acid in the presence of palladium on
carbon in acetic acid produced tetracyclic compound 11 in
a 64% yield. In particular, the skeleton of 1-tetralone was
also achieved by the palladium catalyzed intramolecular
Friedel-Crafts annulation.
2a
1
4
+
+
EtOAc, rt, 2h
HO
7
Products, Yields (%)b-c
Wavelength
(Å)
Entry Solvent
1
4
7
2a
1
2
3
EtOAc
EtOAc
EtOAc
3600
3060
2540
25
8
trace
trace
6
12
68
81
70
trace
trace
--
a For the reaction condition: compound 2a (200 mg), EtOAc (40
mL), rt, 2 h. b The recovery yield of compound 2a. c The shown
yields of compounds 1, 2a, 4 and 7 were determined by the
isolated products.
the yield of compound 1 was decreased due to the higher
energy triggered the conversion from compound 1 to 4. In
comparison with the photolysis of compound 3 and 2a, the
only difference was the generation of cage compound 7.
For constructing compound 7, the results demonstrated that
the teminal olefinic motif was a key factor in the intra-
molecular [2 + 2] cycloaddition of compound 2a. The 1H-
NMR spectrum of compound 7 exhibited one triplet at d
4.07 for Ha proton. Both of protons of Hb and Hc appeared
as multiplets in the range of d 2.89-2.82 and d 3.73-3.68.
One CH2 protons between Hb and hydroxyl group appeared
as one doublet of doublet of doublet (d 2.13) and one dou-
blet (d 2.43). The other CH2 protons between Hb and Hc ap-
peared as one doublet (d 1.47) and one multiplet (d 2.81-
2.74). The proton of hydroxyl group showed as one singlet
at d 2.32.
Scheme IV Synthesis of tetracyclic compound 11
In conclusion, we have successfully presented a
photolytic reaction of dimer 3 and compounds 2a~2b for
preparing dibenzosuberenone (1), three dimers 4, 5 and 6,
and cage molecules 7, and one compound 8 in ethyl acetate
or benzene at rt under three irradiation conditions (l =
3600, 3060, 2540 Å). The possible photochemical mecha-
nism was also proposed. Synthesis of tetracyclic com-
pound 11 was also achieved via a simple transformation of
compound 2a. Several structures of the products were con-
firmed by X-ray crystal analysis. Further studies on the de-
rivatives of dibenzosuberenone are actively underway in
laboratories.
When the C5-allyl group of compound 2a was re-
placed to C5-benzyl group, only product 8 was produced
with a 60% yield via photolytic dehydration of compound
2b with 3060 Å wavelength (Scheme III). Compound 2b
was yielded from Grignard benzylation of compound 1
with benzylmagnesium bromide (1.0 M in THF) with a
87% yield. Among the formed products, 12% of compound
Scheme III Photolytic reaction of compound 2b
EXPERIMENTAL
General. All other reagents and solvents were obtained
from commercial sources and used without further purification.
Reactions were routinely carried out under an atmosphere of dry
nitrogen with magnetic stirring. Products in organic solvents were
4
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Photolysis of Dibenzo[a,d]cycloheptene Dimer
dried with anhydrous magnesium sulfate before concentration in
vacuo. Melting points were determined with a SMP3 melting ap-
296 nm (1 mg/50 mL); HRMS (ESI, M++1) calcd for C30H21O2
413.1542, found 413.1543; 1H NMR (200 MHz): d 7.74 (dd, J =
2.0, 7.2 Hz, 4H), 7.41-7.34 (m, 8H), 7.03 (dd, J = 2.0, 6.8 Hz, 4H),
4.11 (s, 4H). Single-crystal X-ray diagram: crystal of compound 4
was grown by slow diffusion of ethyl acetate into a solution of
compound 4 in dichloromethane to yield colorless prism. The
compound crystallizes in the monoclinic crystal system, space
group P 1 21/c 1, a = 10.3270(9) Å, b = 10.6469(7) Å, c =
18.8079(13) Å, V = 2041.2(3) Å3, Z = 4, Dcalcd = 1.342 g/cm3,
F(000) = 864, 2q range 2.00~26.45o, R indices (all data) R1 =
0.0733, wR2 = 0.1593. Compound 5:8b-8d Yield = 8% (33 mg);
Colorless solid; M.p. > 230 oC (recrystallized from hexanes and
ethyl acetate); UV (dichloromethane) lmax (log e): 295 nm (1
mg/50 mL); HRMS (ESI, M++1) calcd for C30H23 383.1800,
found 383.1802; 1H NMR (200 MHz): d 7.22 (dd, J = 1.6, 7.6 Hz,
4H), 7.06 (s, 4H), 7.00-6.85 (m, 8H), 6.60 (dd, J = 1.6, 7.6 Hz,
4H), 4.71 (s, 2H). Single-crystal X-ray diagram: crystal of com-
pound 5 was grown by slow diffusion of ethyl acetate into a solu-
tion of compound 5 in dichloromethane to yield colorless prism.
The compound crystallizes in the monoclinic crystal system,
space group P 1 21/n 1, a = 10.291(2) Å, b = 8.3098(17) Å, c =
12.389(3) Å, V = 1002.3(4) Å3, Z = 2, Dcalcd = 1.267 g/cm3, F(000)
= 404, 2q range 2.24~26.36o, R indices (all data) R1 = 0.0859,
wR2 = 0.1742. Compound 6:8d Yield = 6% (24 mg); Colorless
solid; M.p. > 230 oC (recrystallized from hexanes and ethyl ace-
tate); UV (dichloromethane) lmax (log e): 295 nm (1 mg/50 mL);
HRMS (ESI, M++1) calcd for C30H23 383.1800, found 383.1804;
1H NMR (200 MHz): d 7.06 (t, J = 4.8 Hz, 4H), 6.93-6.85 (m, 8H),
6.77 (t, J = 4.8 Hz, 4H), 4.77 (s, 2H), 4.53 (s, 4H). Single-crystal
X-ray diagram: crystal of compound 6 was grown by slow diffu-
sion of ethyl acetate into a solution of compound 6 in dichloro-
methane to yield colorless prism. The compound crystallizes in
orthorhombic crystal system, space group P n m a, a = 8.4960(5)
Å, b = 19.7509(12) Å, c = 12.0282(7) Å, V = 2018.4(2) Å3, Z = 8,
Dcalcd = 1.259 g/cm3, F(000) = 808, 2q range 1.98~26.36o, R indi-
ces (all data) R1 = 0.0817, wR2 = 0.1874.
1
paratus. H and 13C NMR spectra were recorded on a Varian
INOVA-400 spectrometer operating at 400/200 and at 100/50
MHz, respectively. Chemical shifts (d) are reported in parts per
million (ppm) and the coupling constants (J) are given in Hertz.
High resolution mass spectra (HRMS) were measured with a mass
spectrometer Finnigan/Thermo Quest MAT 95XL. X-ray crystal
structures were obtained with an Enraf-Nonius FR-590 diffracto-
meter (CAD4, Kappa CCD). Elemental analyses were carried out
with Heraeus Vario III-NCSH, Heraeus CHN-OS-Rapid Ana-
lyzer or Elementar Vario EL III. UV-Visible spectra were mea-
sured with a UV/VIS/NIR spectrophotometer JASCO V-570.
Compound 3. Grubbs second catalyst (24 mg, 2.8% mmol)
was added to a stirred solution of compound 2a (75 mg, 0.3 mmol)
in 1,2-dichloroethane (8 mL) at rt. The reaction mixture was
stirred at reflux for 10 h. The reaction mixture was cooled to rt,
concentrated, and extracted with ethyl acetate (3 ´30 mL). The
combined organic layers were washed with brine, dried, filtered
and evaporated to afford crude products under reduced pressure.
Purification on silica gel (hexanes/ethyl acetate = 10/1 ~ 6/1) af-
forded compound 3 (99 mg, 70%). Colorless solid; M.p. =
195-197 oC (recrystallized from hexanes and ethyl acetate); UV
(dichloromethane) lmax (log e): 295 nm (1 mg/50 mL); HRMS
1
(ESI, M++1) calcd for C34H29O2 469.2168, found 469.2171; H
NMR (400 MHz): d 7.84 (dd, J = 1.2, 8.4 Hz, 4H), 7.45 (dt, J =
2.4, 6.8 Hz, 4H), 7.35-7.28 (m, 8H), 6.93 (s, 4H), 4.79-4.76 (m,
2H), 2.53-2.51 (m, 4H), 2.30 (br s, 2H); 13C NMR (100 MHz): d
141.9 (4x), 132.3 (4x), 131.6 (4x), 130.3 (2x), 129.5 (4x), 128.7
(4x), 126.6 (4x), 124.3 (4x), 75.3 (2x), 39.0 (2x). Single-crystal
X-ray diagram: crystal of compound 3 was grown by slow diffu-
sion of ethyl acetate into a solution of compound 3 in dichloro-
methane to yield colorless prism. The compound crystallizes in
the orthorhombic crystal system, space group P c a 21, a =
21.6617(18) Å, b = 9.2296(8) Å, c = 24.861(2) Å, V = 4970.5(7)
Å3, Z = 8, Dcalcd = 1.252 g/cm3, F(000) = 1984, 2q range 1.64~
26.43o, R indices (all data) R1 = 0.1602, wR2 = 0.1696.
Arepresentative photolysis procedure of compound 2a is as
follows (for Table 3, entry 2). Compound 2a (200 mg, 0.81 mmol)
was dissolved in ethyl acetate (40 mL) free of oxygen was irradi-
ated under a nitrogen atmosphere with a lamp (l = 3060 Å), using
a pyrex glass filter at rt for 2 h. The reaction vessel was collected
and the solvent was evaporated to afford crude product. Purifica-
tion on silica gel (hexanes/ethyl acetate = 10/1~8/1~6/1~4/1) af-
forded compounds 1, 4 and 7. Compound 7: Yield = 81% (162
mg); Colorless oil; HRMS (ESI, M++1) calcd for C18H17O
249.1280, found 249.1283; 1H NMR (400 MHz): d 7.87 (dd, J =
1.2, 7.6 Hz, 1H), 7.64 (dd, J = 1.2, 7.6 Hz, 1H), 7.26-7.08 (m, 5H),
A representative photolysis procedure of compound 3 is as
follows (for Table 1, entry 2). Compound 3 (50 mg, 0.1 mmol)
was dissolved in ethyl acetate (10 mL) free of oxygen was irradi-
ated under a nitrogen atmosphere with a lamp (l = 3060 Å), using
a pyrex glass filter at rt for 2 h. Ten reaction vessels were col-
lected and the solvent was evaporated to afford crude product. Pu-
rification on silica gel (hexanes/ethyl acetate = 10/1~8/1~6/1~
4/1) afforded compounds 1, 4, 5 and 6. Compound 4:8a Yield =
22% (97 mg); Colorless solid; M.p. > 230 oC (recrystallized from
hexanes and ethyl acetate); UV (dichloromethane) lmax (log e):
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Chang and Huang
6.89 (dd, J = 1.6, 7.6 Hz, 1H), 4.07 (t, J = 7.2 Hz, 1H), 3.73-3.68
(m, 1H), 2.89-2.82 (m, 1H), 2.81-2.74 (m, 1H), 2.43 (d, J = 12.8
Hz, 1H), 2.32 (br s, 1H), 2.13 (ddd, J = 1.2, 8.8, 12.8 Hz, 1H), 1.47
(d, J = 10.8 Hz, 1H); 13C NMR (100 MHz): d 146.1, 144.0, 139.8,
134.8, 129.4, 127.3, 127.1, 127.0, 126.7, 126.1, 123.0, 120.0,
75.5, 47.0, 44.3, 41.5, 37.5, 32.2; Anal. Calcd for C18H16O: C,
87.06; H, 6.49. Found: C, 87.54; H, 6.65.
mixture and the solvent was concentrated under reduced pressure.
The residue was extracted with ethyl acetate (3 ´30 mL). The
combined organic layers were washed with brine, dried, filtered
and evaporated to afford crude product under reduced pressure.
Without further purification, Jones reagent was added to the re-
sulting primary alcohol product in acetone (8 mL) at ice bath. The
reaction mixture was stirred at ice bath for 10 min. Water (2 mL)
was added to the reaction mixture and the solvent was concen-
trated under reduced pressure. The residue was extracted with
ethyl acetate (3 ´ 30 mL). The combined organic layers were
washed with brine, dried, filtered and evaporated to afford crude
product under reduced pressure. Purification on silica gel (hex-
ane/ethyl acetate = 1/1~1/2) afforded compound 10 (91 mg,
Compound 8. Compound 2b (200 mg, 0.67 mmol) was dis-
solved in ethyl acetate (40 mL) free of oxygen was irradiated un-
der a nitrogen atmosphere with a lamp (l = 3060 Å), using a pyrex
glass filter at rt for 2 h. The reaction vessel was collected and the
solvent was evaporated to afford crude product. Purification on
silica gel (hexanes/ethyl acetate = 10/1~8/1) afforded compound
8 (60%, 113 mg). Colorless solid; M.p. = 69-70 oC (recrystallized
from hexanes and ethyl acetate); HRMS (ESI, M++1) calcd for
o
67%). Colorless solid; M.p. = 174-175 C (recrystallized from
hexanes and ethyl acetate); HRMS (ESI, M++1) calcd for
1
1
C22H17 281.1330, found 281.1332; H NMR (400 MHz): d 7.57
C18H17O2 265.1229, found 265.1232; H NMR (400 MHz): d
(d, J = 7.2 Hz, 1H), 7.47-7.42 (m, 2H), 7.36-7.29 (m, 3H), 7.23-
7.11 (m, 6H), 7.02 (d, J = 12.0 Hz, 1H), 6.97 (s, 1H), 6.97-6.95
(m, 2H); 13C NMR (100 MHz): d 142.4, 142.3, 137.4, 136.9,
134.9, 134.3, 132.2, 131.4, 131.2, 129.2 (2x), 129.1, 128.9, 128.8,
128.7, 128.3, 127.8 (2x), 127.2, 127.0, 126.9, 126.7.
7.40-7.24 (m, 8H), 6.91 (s, 2H), 4.01 (t, J = 7.6 Hz, 1H), 3.39 (br s,
1H), 2.11-2.01 (m, 4H); 13C NMR (100 MHz): d 179.7, 140.1
(2x), 134.0 (2x), 130.8 (2x), 129.9 (2x), 129.7 (2x), 128.8 (2x),
126.6 (2x), 54.0, 32.2, 24.8. Single-crystal X-ray diagram: crystal
of compound 10 was grown by slow diffusion of ethyl acetate into
a solution of compound 10 in dichloromethane to yield colorless
prism. The compound crystallizes in the triclinic crystal system,
space group P-1, a = 9.0372(4) Å, b = 11.3033(5) Å, c =
15.0270(6) Å, V = 1446.32(11) Å3, Z = 4, Dcalcd = 1.214 g/cm3,
F(000) = 560, 2q range 1.90~26.78o, R indices (all data) R1 =
0.0793, wR2 = 0.1473.
Compound 9. Trimethylsilane (1 mL) was added to a solu-
tion of compound 2a (200 mg, 0.81 mmol) in dichloromethane (5
mL) at rt. The reaction mixture was stirred at rt for 5 min. Boron
trifluoride etherate (BF3-OEt2, ~0.1 mL) was added to the reac-
tion mixture. The reaction mixture was stirred at rt for 3 h. Satu-
rated sodium bicarbonate solution (2 mL) was added to the reac-
tion mixture and the solvent was concentrated under reduced
pressure. The residue was extracted with ethyl acetate (3 ´ 30
mL). The combined organic layers were washed with brine, dried,
filtered and evaporated to afford crude product under reduced
pressure. Purification on silica gel (hexane/ethyl acetate = 6/1~
3/1) afforded compound 9 (135 mg, 72%). Colorless oil; HRMS
Compound 11. Palladium on activated carbon (10%, 15
mg) was added to a solution of compound 10 (60 mg, 0.23 mmol)
in acetic acid (10 mL) at rt. Then hydrogen was bubbled into the
mixture for 10 min, and stirring occurred at rt for 20 h. The reac-
tion mixture was filtered and evaporated to yield crude product.
Purification on silica gel (hexanes/ethyl acetate = 7/1 ~ 4/1) af-
forded compound 11 (36 mg, 64%). Colorless oil; HRMS (ESI,
1
(ESI, M++1) calcd for C18H17 233.1330, found 233.1332; H
1
M++1) calcd for C18H17O 249.1280, found 249.1287; H NMR
NMR (200 MHz): d 7.50-7.27 (m, 8H), 7.04 (s, 2H), 5.68-5.46
(m, 1H), 4.98-4.89 (m, 2H), 4.12 (t, J = 7.8 Hz, 1H), 2.64 (dt, J =
1.2, 7.8 Hz, 2H); 13C NMR (50 MHz): d 140.7 (2x), 136.9, 134.0
(2x), 130.9 (2x), 129.8 (2x), 129.6 (2x), 128.6 (2x), 126.3 (2x),
115.6, 55.3, 34.4.
Compound 10.12 Borane solution (2.0 mL, 1.0 M in tetra-
hydrofuran, 2.0 mmol) was added to a solution of compound 9
(120 mg, 0.52 mmol) in tetrahydrofuran (5 mL) at ice bath. The
reaction mixture was stirred at rt for 3 h. Hydrogen peroxide
(H2O2, 33%, 1.0 mL) and sodium hydroxide (NaOH, 6 M in water,
2.0 mL) were added to the reaction mixture. The reaction mixture
was stirred at rt for 3 h. Water (2 mL) was added to the reaction
(400 MHz): d 7.94 (dd, J = 1.2, 8.0 Hz, 1H), 7.46 (dd, J = 2.4, 6.4
Hz, 1H), 7.39 (d, J = 6.4 Hz, 1H), 7.27-7.10 (m, 4H), 4.94 (t, J =
4.0 Hz, 1H), 3.59 (ddd, J = 4.4, 10.8, 15.2 Hz, 1H), 3.50 (dt, J =
5.6, 16.4 Hz, 1H), 3.12-2.91 (m, 3H), 2.87-2.74 (m, 2H), 2.59-
2.50 (m, 1H); 13C NMR (100 MHz): d 198.0, 144.7, 140.4, 138.8,
138.4, 134.1, 131.2, 130.9, 126.8, 126.8, 126.0, 125.3, 125.1,
35.5, 35.2, 33.3, 32.0, 24.9.
ACKNOWLEDGEMENTS
The authors would like to thank the National Science
Council of the Republic of China for its financial support.
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J. Chin. Chem. Soc. 2013, 60, 000-000

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Photolysis of Dibenzo[a,d]cycloheptene Dimer
shall, C. G.; Lu, W.; Altman, M. D.; Dahlberg, W. K.; Davis,
L.; Falcone, D.; Gabarda, A. E.; Hang, G.; Hatch, H.;
Holmes, R.; Kunii, K.; Lumb, K. J.; Lutterbach, B.;
Mathvink, R.; Nazef, N.; Patel, S. B.; Qu, X.; Reilly, J. F.;
Rickert, K. W.; Rosenstein, C.; Soisson, S. M.; Spencer, K.
B.; Szewczak, A. A.; Walker, D.; Wang, W.; Young, J.; Zeng,
Q. J. Med. Chem. 2011, 54, 4902. (e) Wei, Y.; Chen, C.-T. J.
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J. Chin. Chem. Soc. 2013, 60, 000-000
© 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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