Manipulating [2u202f+u202f2] photodimerization of 1,4-dihydropyridines within γ-cyclodextrin

Article abstract of DOI:10.1016/j.jphotochem.2018.03.046

Irradiation of 1,4-dihydropyridines (DHPs) in the presence of γ-cyclodextrin (γ-CD) performs an efficient formation of the cage-dimer under a medium-pressure mercury lamp. The cage-dimer yields for DHPs complexed within γ-CD may achieve approximately 80%, far higher than those in the non-complexed state. It is postulated that the available cavity volume in γ-CD is responsible for the observed selectivity. The formation of 1:2 host-guest inclusion complex plays an important role in this reaction, and manipulates DHPs to perform [2 + 2] photodimerization as expected. In order to investigate the inclusion process, the spectral characteristics were investigated and the theoretical study was performed using density functional theory (DFT).

Full text of DOI:10.1016/j.jphotochem.2018.03.046

Journal of Photochemistry and Photobiology A: Chemistry 359 (2018) 33–39
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Manipulating [2 + 2] photodimerization of 1,4-dihydropyridines within
g
-cyclodextrin
*
Wuji Sun, Qiangwen Fan, Hong Yan
College of Life Science and Bioengineering, Beijing University of Technology, Beijing, 100124, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Irradiation of 1,4-dihydropyridines (DHPs) in the presence of g-cyclodextrin (g-CD) performs an efficient
Received 7 February 2018
Received in revised form 28 March 2018
Accepted 29 March 2018
formation of the cage-dimer under a medium-pressure mercury lamp. The cage-dimer yields for DHPs
complexed within -CD may achieve approximately 80%, far higher than those in the non-complexed
state. It is postulated that the available cavity volume in -CD is responsible for the observed selectivity.
g
Available online 30 March 2018
g
The formation of 1:2 host-guest inclusion complex plays an important role in this reaction, and
manipulates DHPs to perform [2 + 2] photodimerization as expected. In order to investigate the inclusion
process, the spectral characteristics were investigated and the theoretical study was performed using
density functional theory (DFT).
Keywords:
DHPs
gCD
[2 + 2] Photodimerization
Spectral characteristics
DFT
© 2018 Elsevier B.V. All rights reserved.
1. Introduction
To achieve the goal of controlling photoproducts distribution,
manipulation of the reactants by various templates has been the
Photochemical reactions have attracted considerable interest of
chemists because they often lead to rigid and highly symmetric
products that are virtually inaccessible by thermal reactions, such
as cubane [1–3] and pagodane [4]. In particular, our group has
extensively studied the [2 + 2] photodimerization of 1,4-dihydro-
pyridines (DHPs) and reported the head-tail cage dimers [5–7], 3,9-
diazatetraasteranes, which hold promise as novel HIV protease
inhibitors for their C2 symmetry [8]. However, it is usually difficult
to predict and control the outcome of photochemical reactions and
various mixtures of photoproducts are obtained.
best solution to this problem. Previously micelles [9,10] and
inorganic hosts [11] have been used to template [2 + 2] and [4 + 4]
photodimerizations successfully. Recently, calixarenes [12], cucur-
biturils [13,14] and cyclodextrins (CDs)15–17 have already been
employed in template controlled photochemical reactions. Among
these templates,
g-CD, macrocycles composed of 8 glucose units
linked by 1,4 glycosidic bond, offers the advantages of structural
flexibility and available free space [15] (Fig. 1). Herein, we present
the experimental results of manipulating [2 + 2] photodimeriza-
tion of DHPs within
g-CD. DFT method was performed to
Previous studies done by our group have shown an under-
standing of photochemical reactivity of DHPs [6]. As shown in
Scheme 1, irradiation of DHPs 1 with a 250 W medium-pressure
mercury lamp leads to three different adducts, viz., anti-dimer 2,
syn-dimer 3 and cage-dimer 4. The initially formed syn-dimer 3 is
submitted to formation of cage-dimer 4 resulted from a [2 + 2]
cycloaddition reaction of the intramolecular double bonds. We
have used diethyl 1,4-dihydropyridine-3,5-dicarboxylate 1a whose
photochemical reaction has been investigated in solution as model
compound. Photodimerization of a THF solution of 1a resulted in
anti-dimer 2a (37%) and cage-dimer 4a (41%). Due to the
competing reaction, the yield of cage-dimer 4a is comparatively
poor in most cases requiring long irradiation times.
investigate the inclusion complex of
2. Results and discussion
2.1. Chemistry
g-CD with DHPs.
A series of DHPs was prepared by a cyclocondensation reaction
of ethyl propiolate, aldehydes and amines in acetic acid [7,18]. The
inclusion complex of
g-CD with DHPs was carried out under
ultrasound irradiation, and the photodimerization of the complex
was conducted by irradiation of medium-pressure mercury lamp
(Scheme 2). In a typical experiment, 1a (1 equivalents) was
dissolved in THF. To this solution was added the aqueous solution
* Corresponding author.
E-mail address: hongyan@bjut.edu.cn (H. Yan).
https://doi.org/10.1016/j.jphotochem.2018.03.046
1010-6030/© 2018 Elsevier B.V. All rights reserved.

34
W. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 359 (2018) 33–39
Scheme 1. [2 + 2] Photodimerization of DHPs in solution.
(37%) in the non-complexed state. The results indicated that it was
well established that -CD formed a 1:2 host-guest complex with
1a. This is based on the reasoning that -CD with a large cavity
volume 427 Å3 will most likely form a 1:2 host-guest complex with
DHPs [19]. -CD as the template not only improves the yields of
photodimerizations but also gives rise to high stereoselectivities.
To examine the general applicability of -CD as a template,
[2 + 2] photodimerizations of DHPs were attempted under the
above conditions. Meanwhile the influence of -CD in the [2 + 2]
g
g
g
g
g
photodimerization was also investigated, and the results were
summarized in Table 1. Irradiation of a solution of 1a-1j for 8 h
generated cage-dimer 4a-4j in 35%–63% total yields. By compari-
son, irradiation of 1a-1j within
g-CD led to a significant rise in
cage-dimer yields, and the yields varied predictably with the
identity of the substituents. When R1 is H, the cage-dimer yields for
1a-1d complexed within
g-CD are increased by 35%–47% higher
than in solution. This trait is especially obvious in other
compounds. When R2 is H, the cage-dimer yields for 1e-1g are
increased by 34%-46% higher than in the non-complexed state.
Futhermore, when both R1 and R2 are aryl, the 1h-1j complexed
Fig. 1. Structure of
g-CD.
of
g-CD (0.5 equivalents) and the mixture was sonicated to obtain a
clear homogeneous solution. Irradiation of a solution of the 1a@g-
CD host-guest complex with a 250 W medium-pressure mercury
lamp produced cage-dimer 4a as major product (77%), and the
anti-dimer 2a was formed as minor product in a detectable amount
compared to the yields of cage-dimer 4a (41%) and anti-dimer 2a
within
dimer 4h-4j with yields of approximately 80%. These results
indicated that -CD had an important influence on the improve-
g-CD undergo a [2 + 2] photodimerization to the cage-
g
ment of the photodimerization, and could manipulate [2 + 2]
photodimerization of DHPs to generate the corresponding cage-
dimer. The structures of cage-dimer 4a-4j were characterized by
Scheme 2. [2 + 2] Photodimerization of DHPs within
g-CD.

W. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 359 (2018) 33–39
35
Table 1
Yields of cage-dimer 4 upon irradiation of DHPs in solution and within
g
-CD.
Entry
Reactant R1
R2
Yields of cage-dimer 4 (%)
in solutiona
within g
-CDb
1
2
3
4
5
6
7
8
9
10
1a
1b
1c
1d
1e
1f
1g
1h
1i
H
H
H
H
H
Ph
41c
38
77
85
83
89
80
73
81
82
88
78
4-MePh 48
4-CF3Ph 50
H
H
H
Ph
Ph
Ph
Ph
40c
39
3,4-diClPh
3,4,5-triOMePh
Ph
4-OMePh
4-FPh
35c
62c
63c
62c
1j
a
Each THF solution of 1a-1j was irradiated with a 250 W medium-pressure
mercury lamp for 8 h.
b
Photochemical reactions of 1a-1j within
conditions similar to those of 1a-1j in solution.
g-CD were carried out under
c
The yields were reported in reference [6,7].
Fig. 3. The absorption spectra of 1d (1 ꢀ10ꢁ5 M) in the presence of
g-CD.
1H NMR, 13C NMR and HRMS. The single crystal X-ray diffraction of
4d (CCDC number 1537604) was carried out which further proved
that the photoproduct was the head-tail cage dimer (Fig. 2).
suggesting that the new intense red shifted emission is due to
the formation of 1:2 host-guest complex. Furthermore, the rate
constant (k0) and lifetime (t0) of the excited state were estimated
according to the Strickler-Berg equation [20].
R
2.2. Spectral characteristics
k0 = 1/t0 = 2.880 ꢀ 10ꢁ9 n2 nf2
e
dln
n
(1)
The absorbance spectra of 1d in THF/H2O and in the presence of
g
-CD are presented in Fig. 3. The absorption maximum of 1d locate
in the range of 340–430 nm shifted from 381 nm to 370 nm in the
presence of -CD (0.5 equivalents), which is probably due to the
ground state interactions between the manipulated two molecules
of DHPs within -CD. The emission spectra of 1d in THF/H2O and in
the presence of -CD are presented in Fig. 4. Fluorescence studies
In the Eq. (1), n was the refractive index of the solvent. nf was the
emission frequency in wavenumbers, and approximated by the
maximum emission wavelength in wavenumbers (lems, cmꢁ1).
g
R
The integral
e
dlnv represented the area of the absorption band
) against wave-
g
g
from a plot of molar extinction coefficient (
e
numbers (
n
, cmꢁ1). As shown in Table 2 and Fig. 3, the absorption
using 1d indicated that there was a significant red shifting of the
spectrum with the increase in intensity in the presence of 0.5
equivalents of g-CD. In this case, emission due to 1d (444–456 nm)
was replaced by an intense emission around 449–471 nm. The
fluorescence excitation spectrum recorded by monitoring emission
at 461 nm was similar to that of the absorption spectrum
maxima located in the range of 340–430 nm with the rate constant
for about 108 sꢁ1 and the molar extinction coefficient for about
104 Mꢁ1 cmꢁ1, indicating the lowest excitation states of 1d are
dominated by
were affected much by the complexation of
increased from 1.41 ns to 6.21 ns in the presence of
p-p
* transition [21]. The lifetimes of
-CD, and the lifetimes
-CD
p–p* states
g
g
Fig. 2. X-ray crystal structure of cage-dimer 4d.

36
W. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 359 (2018) 33–39
(0.5 equivalents). It was clear that the formation of 1:2 host-guest
complex led to longer lifetimes of the excited state.
2.3. Theoretical study
In order to gain a better understanding of the cage-dimer
formation, the theoretical study of 1d@g-CD host-guest complex
as a model was investigated by means of DFT method [22]. The
inclusion complex obtained by exploring the conformational
space, was exposed to a full geometry optimization using the
B3LYP-D3 function associated with the 6–31G (d, p) basis set [23].
To quantify the interaction between
g
-CD and 1d in the optimized
Eb2) were calculated at
geometries, the binding energy ( Eb1 and
D
D
the same theoretical level according to the following relation (1)
and (2):
D
Eb1 = Ecom1–(Ehost + Eguest
)
(1)
Fig. 4. The emission spectra of 1d (1 ꢀ10ꢁ5 M) in the presence of
g-CD.
D
Eb2 = Ecom2–(Ecom1 + Eguest
)
(2)
Table 2
Strickler-Berg estimates of the rate constant k0 and lifetime t0 of the excited state.
where Ecom1, Ecom2, Ehost and Eguest were the Hartree-Fock (HF)
energies of 1:1 host-guest complex, 1:2 host-guest complex, -CD
k0 (108 sꢁ1
)
t0 (ns)
g
species
1d
labs (nm)
lems (nm)
and 1d from optimization, respectively. The formation of 1:2 host-
guest complex can be explained by a stepwise mechanism,
involving the initial formation of 1:1 host-guest complex as
represented by relation (1), followed by complexation of a second
guest to give 1:2 host-guest complex described in relation (2).
370
374
381
376
450
453
461
455
7.08
4.88
1.61
5.95
1.41
2.05
6.21
1.68
1d:
1d:
1d:
g
g
g
-CD = 1:1
-CD = 1:0.5
-CD = 1:0.25
According to the relation (1) and (2), the binding energy
DEb1 and
D
Eb2 was calculated. The binding energy was usually an important
parameter of the driving force towards inclusion, and the more
negative value meant more favorable inclusion. It could be seen
Table 3
Energies of 1d calculated at the B3LYP-D3/6-31G (d, p) theoretical level.
from Table 3 that the binding energy
DEb2 was much larger than
Energies (kJ molꢁ1
)
host:guest = 1:1
host:guest = 1:2
the binding energy Eb1, which indicated that the formation of 1:2
D
Eguest
Ehost
Ecom1
Ecom2
ꢁ3478561.7467
ꢁ3478561.7467
host-guest complex was energetically favored. As displayed in
Fig. 5, the optimal conformation showed two molecules of 1d were
ꢁ12572033.1286
/
ꢁ16050627.8791
ꢁ16050627.8791
ꢁ19529235.4544
/
ꢁ45.8286
accommodated within the cavity of
arrangement and the carbon atoms of C
reactive distance, which favored [2 + 2] photodimerization and the
g
-CD in a parallel and head-tail
/
D
D
Eb1
Eb2
ꢁ33.0038
¼C bond were held within
/
Fig. 5. The schematic drawing of 1d@g-CD complex.

W. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 359 (2018) 33–39
37
Fig. 6. The schematic drawing of cage-dimer 4d within g-CD.
formation of cage-dimer. However, anti-dimer and syn-dimer
could barely be obtained in the complexed state. It was attributed
performed in a GEX750-5C ultrasonic instrument. Irradiation for
the photodimerization was conducted using an Osram HBO 250W
medium-pressure mercury lamp. The melting points were deter-
mined on a XT-5A digital melting point apparatus and were
uncorrected. 1H NMR and 13C NMR spectra were recorded on a
Bruker Avance 400 spectrometer at 400 MHz and 100 MHz
respectively. HRMS were recorded using an Agilent G3250AA
LC/MSD TOF mass spectrometer with an ESI source. The X-ray
single-crystal diffraction was performed on CCD area detector. The
UV–vis absorption spectra were measured on a SHIMADZU UV-
2600 spectrophotometer in THF/H2O solution. The fluorescence
that the cavity volume of
g-CD could not hold anti-dimer on the
one hand, on the other hand, it drew two molecules of 1d closer,
thus forming cage-dimer directly from the cycloaddition reactions
without formation of syn-dimer. Based on the optimal conforma-
tion and the cavity volume of
g-CD, it was clear that the cage-
dimer appeared to better fit into the
g-CD cavity than other
photoproducts, as depicted in Fig. 6.
3. Conclusions
emission spectra were measured on
a SHIMADZU RF-6000
spectrofluorometer in THF/H2O solution.
In summary, a series of DHPs was prepared by a cyclo-
condensation reaction of ethyl propiolate, aldehydes and amines in
4.2. General procedure for synthesis of DHPs (1a-1g)
acetic acid, and irradiation of DHPs complexed within
investigated under a mercury lamp. The results indicated that the
[2 + 2] photodimerization of DHPs within -CD was manipulated
as expected. The cage-dimer yields for DHPs complexed within
-CD exhibited a significant improvement with the yields of about
g-CD was
A mixture of ethyl propiolate (0.10 mol), aldehydes (0.05 mol),
amines (0.05 mol), and 5.0 mL of acetic acid was heated in a steam
bath for 25 min. The product was crystallized from methanol/
water (V:V = 4:1), then recrystallized from acetone/hexane
(V:V = 1:1).
g
g
80%, compared to that in the absence of
g-CD. The structures of
cage-dimer 4a-4j were determined by 1H NMR, 13C NMR, HRMS
and single crystal X-ray diffraction analyses. The formation of 1:2
host-guest inclusion complex was supposed to play an important
role in this reaction. The spectral characteristics of DHPs in the
Diethyl 1,4-dihydropyridine-3,5-dicarboxylate (1a). Yield 66.4%,
m.p.108.2–109.6 ꢂC; 1H NMR (400 MHz, CDCl3):
d
(ppm) 1.27 (t, 6H,
CH3), 3.24 (s, 2H, CH2), 4.17 (q, 4H, J = 7.2 Hz, CH2), 6.59 (brs,1H, NH),
7.09 (d, 2H, J = 4.8 Hz, CH).
Diethyl 1-phenyl-1,4-dihydropyridine-3,5-dicarboxylate (1b).
Yield70.7%, m.p.131.5–132.9 ꢂC;1HNMR(400 MHz, CDCl3):
(ppm)
1.31 (t, 6H, CH3), 3.35 (s, 2H, CH2), 4.23 (q, 4H, J = 7.2 Hz, CH2), 7.19–
7.26 (m, 3H, Ar-H), 7.40 (d, 2H, J = 8.0 Hz, Ar-H), 7.44 (s, 2H, CH).
¼
presence of
inclusion complex was performed to investigate the inclusion
process by DFT method. The -CD could manipulate two molecules
g-CD were investigated. The theoretical study of the
d
g
of DHPs in a parallel and head-tail arrangement, and the optimal
conformation promoted the formation of cage-dimer which not
only improved the yields of photodimerizations but also gave rise
to high stereoselectivities.
¼
Diethyl 1-(4-methylphenyl)-1,4-dihydropyridine-3,5-dicarbox-
ylate (1c). Yield 75.1%, m.p. 129.1–130.7 ꢂC; 1H NMR (400 MHz,
CDCl3):
4.26 (q, 4H, J = 7.2 Hz, CH2), 7.07 (d, 2H, J = 8.4 Hz, Ar-H), 7.19 (d, 2H,
J = 8.4 Hz, Ar-H), 7.39 (s, 2H, CH).
d (ppm) 1.29 (t, 6H, CH3), 2.35 (s, 3H, CH3), 3.33 (s, 2H, CH2),
4. Experimental
¼
Diethyl 1-(4-trifluoromethylphenyl)-1,4-dihydropyridine-3,5-
dicarboxylate (1d). Yield 67.0%, m.p. 144.6–145.9 ꢂC; 1H NMR
4.1. General procedures
(400 MHz, CDCl3):d(ppm)1.32 (t, 6H, CH3), 3.35(s, 2H, CH2), 4.26(q,
All of the chemicals were purchased from commercial sources
and used without further purification. Ultrasound irradiation was
4H, J = 7.2 Hz, CH2), 7.31 (d, 2H, J = 8.4 Hz, Ar-H), 7.49 (s, 2H,
7.68 (d, 2H, J = 8.4 Hz, Ar-H).
¼CH),

38
W. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 359 (2018) 33–39
Diethyl 4-phenyl-1,4-dihydropyridine-3,5-dicarboxylate (1e).
Yield 51.8%, m.p.121.6–123.8 ꢂC; 1H NMR (400 MHz, CDCl3):
(ppm)
1.21 (t, 6H, CH3), 4.02–4.16(m, 4H, CH2), 4.91(s,1H, Ar-CH), 6.91(brs,
1H, NH), 7.17–7.37 (m, 5H, Ar-H), 7.27 (d, 2H, J = 4.8 Hz, CH).
(t, 6H, CH3), 2.29 (s, 3H, CH3), 2.34 (s, 2H, CH2), 4.25 (q, 4H, J = 7.2 Hz,
CH2), 4.79 (s, 2H, CH), 7.03–7.09 (m, 4H, Ar-H); 13C NMR (100 MHz,
d
CDCl3):
d (ppm) 14.2, 20.5, 25.1, 46.9, 57.3, 61.3, 117.7, 129.8, 129.9,
¼
147.9,174.2; HRMS (ESI) m/z calcd 631.3014 for C36H43N2O8 [M+H]+,
found 631.3019.
Diethyl 4-(3,4-dichlorophenyl)-1,4-dihydropyridine-3,5-dicar-
boxylate (1f). Yield 47.0%, m.p. 168.1–169.8 ꢂC; 1H NMR (400 MHz,
Tetraethyl 3,9-bis(4-trifluoromethylphenyl)-3,9-diazahexa-
cyclo[6.4.0.02,7.04,11.05,10]dodecane-1,5,7,11-tetracarboxylate
(4d). Yield 89.2%, m.p. 255.0–256.3 ꢂC; 1H NMR (400 MHz, CDCl3):
CDCl3):
Ar-CH), 7.09 (brs, 1H, NH), 7.19–7.41 (m, 3H, Ar-CH), 7.33 (d, 2H,
J = 5.2 Hz, CH).
d (ppm) 1.22 (t, 6H, CH3), 4.03–4.17 (m, 4H, CH2), 4.88 (s,1H,
¼
d
(ppm) 1.34 (t, 6H, CH3), 2.31 (s, 2H, CH2), 4.28 (q, 4H, J = 7.2 Hz,
CH2), 4.92 (s, 2H, CH), 7.22 (d, 2H, J = 8.4 Hz, Ar-H), 7.53 (d, 2H,
J = 8.4 Hz, Ar-H); 13C NMR (100 MHz, CDCl3):
(ppm) 14.1, 25.2,
Diethyl 4-(3,4,5-trimethoxylphenyl)-1,4-dihydropyridine-3,5-
dicarboxylate (1g). Yield 60.5%, m.p. 181.7–182.9 ꢂC; 1H NMR
d
(400 MHz, CDCl3):
3.81(s, 6H, OCH3), 4.05–4.15 (m, 4H, CH2), 4.86(s,1H, Ar-CH), 6.58(s,
2H, Ar-H), 7.27 (brs, 1H, NH), 7.36 (d, 2H, J = 5.2 Hz, CH).
Diethyl 1,4-diphenyl-1,4-dihydropyridine-3,5-dicarboxylate
(1h). Yield 42.5%, m.p.134.6–136.8 ꢂC; 1H NMR (400 MHz, CDCl3):
(ppm) 1.20 (t, 6H, CH3), 4.04–4.18 (m, 4H, CH2), 4.97 (s, 1H, Ar-CH),
7.15–7.48 (m, 10H, Ar-H), 7.67 (s, 2H, CH).
d
(ppm) 1.21 (t, 6H, CH3), 3.78 (s, 3H, OCH3),
46.9, 56.8, 61.8, 116.8, 120.4, 121.8, 122.1, 122.4, 122.7, 123.1, 125.8,
126.7,126.8,128.5,152.4,173.5; HRMS (ESI), m/z calcd 739.2449 for
¼
C
36H37F6N2O8 [M+H]+, found 739.2451.
Tetraethyl 6,12-diphenyl-3,9-diazahexacyclo[6.4.0.02,7.04,11.05,10
]
d
dodecane-1,5,7,11-tetracarboxylate (4e). Yield 80.1%, m.p.
210.4–212.3 ꢂC; 1H NMR (400 MHz, CDCl3):
d
(ppm) 1.00 (t, 6H,
¼
CH3), 3.02(br s, 1H, NH), 3.92-4.03 (m, 4H, CH2), 3.93 (s, 1H, Ar-CH),
4.34 (s, 2H, CH), 7.14–7.23 (m, 3H, Ar-H), 7.54(d, 2H, Ar-H); HRMS
(ESI) m/z calcd 603.2701 for C34H39N2O8 [M+H]+, found 603.2704.
Tetraethyl 6,12-bis(3,4-dichlorophenyl)-3,9-diazahexacyclo
Diethyl 4-(4-methoxylphenyl)-1-phenyl-1,4-dihydropyridine-
3,5-dicarboxylate (1i). Yield 50.7%, m.p. 120.8–121.6 ꢂC; 1H NMR
(400 MHz, CDCl3): d(ppm) 1.21 (t, 6H, CH3), 3.77(s, 3H, OCH3), 4.06–
4.16 (m, 4H, CH2), 4.91 (s, 1H, Ar-CH), 6.79 (d, J = 8.8 Hz, 2H, Ar-H),
7.29 (d, J = 8.8 Hz, 2H, Ar-H), 7.26–7.48 (m, 5H, Ar-H), 7.65 (s, 2H,
[6.4.0.02,7.04,11.05,10]dodecane-1,5,7,11-tetracarboxylate
(4f).
Yield 72.9%, m.p. 213.5–214.9 ꢂC; 1H NMR (400 MHz, CDCl3):
d
¼
CH).
Diethyl 4-(4-fluorophenyl)-1-phenyl-1,4-dihydropyridine-3,5-
dicarboxylate (1j). Yield 60.4%, m.p. 136.0–136.9 ꢂC; 1H NMR
(400 MHz, CDCl3): (ppm) 1.20 (t, 6H, CH3), 4.04–4.18 (m, 4H,
CH2), 4.95 (s, 1H, Ar-CH), 6.91 (t, J = 8.8 Hz, 2H, Ar-H), 7.44 (d,
(ppm) 1.07 (t, 6H, CH3), 3.08 (br s,1H, NH), 3.84 (s,1H, Ar-CH), 3.96–
4.05 (m, 4H, CH2), 4.30 (s, 2H, CH), 7.29 (d, 1H, Ar-H),7.44 (d, 1H, Ar-
H), 7.77 (s,1H, Ar-H); 13C NMR (100 MHz, CDCl3):
d (ppm) 14.0, 43.3,
d
48.5, 54.6, 61.3, 129.7, 130.7, 131.1, 131.7, 133.2, 137.5, 172.5; HRMS
(ESI) m/z calcd 739.1142 for C34H35Cl4N2O8 [M+H]+, found 739.1143.
Tetraethyl 6,12-bis(3,4,5-trimethoxylphenyl)-3,9-diazahexa-
cyclo[6.4.0.02,7.04,11.05,10]dodecane-1,5,7,11-tetracarboxylate
J = 8.0 Hz, 2H, Ar-H), 7.29-7.48 (m, 5H, Ar-H), 7.65 (s, 2H,
¼CH).
4.3. General procedure for irradiation of DHPs in solution
(4 g). Yield 81.4%, m.p. 213.5–214.9 ꢂC; 1H NMR (400 MHz, CDCl3):
d
(ppm) 1.03 (t, J = 7.2 Hz 6H, CH3), 3.04 (br s, 1H, NH), 3.80 (s, 9H,
OCH3), 3.82 (s, 1H, Ar-CH), 4.00 (q, J = 7.2 Hz, 4H, CH2), 4.31 (s, 2H,
CH), 6.85 (s, 2H, Ar-H); HRMS (ESI) m/z calcd 783.3335 for
DHPs (1 mmol) was dissolved in 200 mL of tetrahydrofuran,
and the solution was poured into a photochemical reactor, which
led to the N2 protective gas. The reactor was irradiated with a
250 W medium-pressure mercury lamp as the light source for 8 h.
Then the solvent was evaporated and the residue was purified by
chromatography (ethyl acetate/petroleum ether = 1:5) on silica
gel.
C
40H51N2O14 [M+H]+, found 783.3338.
Tetraethyl
[6.4.0.02,7.04,11.05,10]dodecane-1,5,7,11-tetracarboxylate
Yield 82.3%, m.p. 255.9–256.7 ꢂC; 1H NMR (400 MHz, CDCl3):
3,6,9,12-tetraphenyl-3,9-diazahexacyclo
(4h).
d
(ppm) 0.97 (t, 6H, CH3), 3.92–4.05 (m, 4H, CH2), 3.96 (s, 1H, Ar-CH),
5.23 (s, 2H, CH), 6.94–7.37 (m, 10H, Ar-H); HRMS (ESI) m/z calcd
755.3327 for C46H47N2O8 [M+H]+, found 755.3332.
4.4. General procedure for irradiation of DHPs within g-CD
Tetraethyl 6,12-bis(4-methoxylphenyl)-3,9-diphenyl-3,9-dia-
zahexacyclo[6.4.0.02,7.04,11.05,10]dodecane-1,5,7,11-tetracarboxy-
late (4i). Yield 87.7%, m.p. 288.0–289.7 ꢂC; 1H NMR (400 MHz,
In a typical experiment, DHPs (1 mmol) was dissolved in 100 mL
of tetrahydrofuran. To this solution was added an aqueous solution
of
g
-CD (0.5 mmol,100 mL), and the mixture was sonicated at 60 ꢂC
CDCl3): d (ppm) 1.01 (t, 6H, CH3), 3.67 (s, 3H, OCH3), 3.92 (s, 1H, Ar-
for 2 h to obtain a clear homogeneous solution. The mixture
solution was irradiated with a 250 W medium-pressure mercury
lamp under nitrogen for 8 h. The solution was concentrated under
reduced pressure, and the precipitate was filtered off and
recrystallized from dichloromethane/methanol (V:V = 4:1) to
afford cage-dimer 4a-4j.
CH),3.94–4.05(m,4H,CH2),5.21(s,2H,CH),6.58(t,J = 8.8 Hz,2H,Ar-
H), 6.95–7.37 (m, 5H, Ar-H), 7.01 (d, J = 8.8 Hz, 2H, Ar-H); HRMS (ESI)
m/z calcd 815.3538 for C48H51N2O10 [M+H]+, found 815.3544.
Tetraethyl 6,12-bis(4-fluorophenyl)-3,9-diphenyl-3,9-diaza-
hexacyclo[6.4.0.02,7.04,11.05,10]dodecane-1,5,7,11-tetracarboxy-
late (4j). Yield 78.3%, m.p. 264.0–265.8 ꢂC; 1H NMR (400 MHz,
Tetraethyl 3,9-diazahexacyclo[6.4.0.02,7.04,11.05,10]dodecane-
1,5,7,11-tetracarboxylate (4a). Yield 77.2%, m.p. 160.0–161.0 ꢂC; 1H
CDCl3): d (ppm) 0.99 (t, 6H, CH3), 3.94–4.07 (m, 4H, CH2), 3.98 (s,
1H, Ar-CH), 5.21 (s, 2H, CH), 6.75 (t, J = 8.8 Hz, 2H, Ar-H), 6.97–7.40
(m, 5H, Ar-H), 7.09 (d, J = 8.8 Hz, 2H, Ar-H); HRMS (ESI) m/z calcd
791.3138 for C46H45F2N2O8 [M+H]+, found 791.3144.
NMR (400 MHz, CDCl3): d (ppm) 1.28 (t, 6H, CH3), 2.36 (s, 2H, CH2),
4.03 (s, 2H, CH), 4.16–4.22 (q, 4H, OCH2); HRMS (ESI) m/z calcd
451.2075 for C22H31N2O8 [M + H]+, found 451.2077.
Tetraethyl 3,9-diphenyl-3,9-diazahexacyclo[6.4.0.02,7.04,11.05,10
]
4.5. Single crystal X-ray diffraction for 4d
dodecane-1,5,7,11-tetracarboxylate (4b). Yield 84.9%, m.p. 234.6–
235.9 ꢂC; 1H NMR (400 MHz, CDCl3):
(ppm) 1.33 (t, 6H, CH3), 2.35
(s, 2H, CH2), 4.26 (q, 4H, J = 7.2 Hz, CH2), 4.85 (s, 2H, CH), 6.90 (t, 1H,
Ar-H), 7.15–7.30 (m, 4H, Ar-H); 13C NMR (100 MHz, CDCl3):
(ppm)
d
Crystals of 4d suitable for X-ray diffraction analysis were
obtained by the slow evaporation of a methanol/dichloromethane
solution of 4d at room temperature. The single crystal X-ray
diffraction measurements were conducted on a Rigaku Saturn CCD
area-detector diffractometer using graphite monochromated
d
14.2, 25.2, 47.0, 57.2, 61.4,117.7,120.5,129.4,150.1,174.1; HRMS (ESI)
m/z calcd 603.2701 for C34H39N2O8 [M + H]+, found 603.2703.
Tetraethyl
[6.4.0.02,7.04,11.05,10]dodecane-1,5,7,11-tetracarboxylate (4c). Yield
82.9%, m.p. 228.9–230.4 ꢂC; 1H NMR (400 MHz, CDCl3):
(ppm) 1.32
3,9-bis(4-methylphenyl)-3,9-diazahexacyclo
MoKa radiation in the v and w scanning mode. An empirical
absorption correction was applied using the ABSCOR program. All
structures were solved by direct methods using the SHELXS
d

W. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 359 (2018) 33–39
39
Table 4
Crystallographic data for 4d.
Acknowledgment
This work was financially supported by the Key Projects in
the Beijing Municipal Natural Science Foundation (No.
KZ201510005007).
Entry
4d
Empirical formula
Formula weight
Temperature
C36H36F6N2O8
738.67
108 K
Wavelength
Crystal system
Unit cell dimensions
0.71070
Triclinic
a = 8.2463 (11)
b = 9.4172 (11)
c = 11.6964 (12)
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a
b
= 77.849 (9)
= 71.326 (11)
g= 83.325 (10)
Volume
Z
Calculated density
Absorption coefficient
F(000)
840.04 (17)
1
1.460 Mg mꢁ3
0.124 mmꢁ1
384.0
Crystal size
0.30 ꢀ 0.25 ꢀ 0.24 mmꢁ3
3311/0/237
1.056
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4.6. Theoretical study
The isolated g-CD, DHPs, 1:1 host-guest complex and 1:2 host-
guest complex were optimized at the B3LYP-D3/6-31G (d, p)
theoretical level [23]. The polarized continuum model (PCM) was
used in Consistent Reaction Field (SCRF) with THF/H2O as solvent.
All of the quantum chemical calculations were performed using
the Gaussian 09 program package [24].