Visible light-sensitive properties of 1,2-dimethyl-2-(2-nitrophenyl)-2,3- dihydro-1H-perimidine

Article abstract of DOI:10.1016/j.tet.2013.01.079

Four o- and p-nitro substituted 2-methyl-2-phenyl-2,3-dihydro-1H-perimidine derivatives were synthesized via a condensation-cyclization of naphthalene-1,8-diamine with nitro substituted acetophenones to study their photochemical properties. Only the o-nit

Full text of DOI:10.1016/j.tet.2013.01.079

Tetrahedron 69 (2013) 2775e2781
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Visible light-sensitive properties of 1,2-dimethyl-2-(2-nitrophenyl)-
2,3-dihydro-1H-perimidine
*
Wei-Zhe Chen, Hao-Yi Wei, Ding-Yah Yang
Department of Chemistry, Tunghai University, No. 181, Section 3, Taichung Port Road, Taichung City 40704, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 May 2012
Received in revised form 16 January 2013
Accepted 28 January 2013
Available online 6 February 2013
Four o- and p-nitro substituted 2-methyl-2-phenyl-2,3-dihydro-1H-perimidine derivatives were syn-
thesized via a condensationecyclization of naphthalene-1,8-diamine with nitro substituted acetophe-
nones to study their photochemical properties. Only the o-nitrophenyl substituted perimidine 1 was
found to be sensitive to light. When exposed to visible light under either aerobic conditions or argon
atmosphere, it undergoes pyrimidine ring-opening/deoxygenation and pyrimidine oxidation to give the
2H-indazole 10 and perimidinone 11, respectively. A new visible light-sensitive o-nitrobenzylamino
scaffold is introduced.
Keywords:
Photochemistry
Perimidine
Perimidinone
Indazole
Ó 2013 Elsevier Ltd. All rights reserved.
EPR
1. Introduction
reported an efficient one-pot three component synthesis of
Hantzsch 1,4-dihydropyridine in aqueous ethanol under visible
The use of visible light as an energy source to carry out organic
synthesis is attractive because it is non-toxic, generates no waste,
can be obtained from renewable sources, and can reduce side re-
actions often associated with photochemical reactions conducted
with high energy UV light. However, despite the practical advan-
tages of visible light as an infinitely available source for chemical
reactions, the simple inability of most organic molecules to absorb
light in the visible range of the spectrum has greatly limited the
potential applications of photochemical reactions. In this regard,
visible light-sensitive catalysts, such as ruthenium or iridium
complexes1 and organic dyes2 offer a means to overcome these
obstacles. Upon irradiation, the photocatalysts are converted into
the more reactive photoexcited states, which can be either oxida-
tively or reductively quenched by the organic substrates. Alter-
nately, the visible light photochemistry of organic molecules in the
absence of any photocatalysts may also become feasible by properly
introducing an electron donor and an electron acceptor into the
reaction mixture. Upon visible light irradiation, the resulting com-
pound presumably may undergo photo-induced electron transfer
from the donor to the acceptor to generate transient radical species,
which can further proceed to products via chemical trans-
formations. For instance, Ghosh3 and co-workers have recently
light irradiation conditions using ammonia as an electron donor and
the carbonyl group of ethyl acetoacetate as an electron acceptor, as
shown in Scheme 1.
In an effort to develop novel visible light-sensitive molecular
scaffolds for chemical transformations, here we describe the syn-
thesis and characterization of four o- and p-nitro substituted
2-methyl-2-phenyl-2,3-dihydro-1H-perimidine derivatives and
subsequent investigation of their photochemical properties. In this
particular design, the electron donor perimidine and the electron
acceptor o-nitrobenzyl group are integrated into a molecular
structure to facilitate intramolecular electron transfer process. The
preliminary photochemical mechanism of the donoreacceptor in-
tegrated heterocycle is also proposed on the basis of the experi-
mental results.
2. Results and discussion
Scheme 2 shows the synthesis of the designed model compounds
1 and 2. It started with a Yb(OTf)3-catalyzed condensationecycliza-
tion4 of naphthalene-1,8-diamine (5) with o-nitroacetophenone (6)
to give 2-methyl-2-phenyl-2,3-dihydro-1H-perimidine 7. The sub-
sequent N-methylation of 7 was realized by treating it with iodo-
methane using either triethylamine or potassium carbonate as a base
in methylene chloride or acetonitrile under reflux conditions to af-
ford the corresponding mono and di N-methylated target perimidine
derivatives 1 and 2. The exact same procedure was used to prepare
* Corresponding author. Tel.: þ886 4 2359 7613; fax: þ886 4 2359 0426; e-mail
address: yang@thu.edu.tw (D.-Y. Yang).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.01.079

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W.-Z. Chen et al. / Tetrahedron 69 (2013) 2775e2781
Ar
EtO2C
Me
CO2Et
Me
CO2Et
COMe
visible light
aq. ethanol (1:1)
5~10 min
Ar-CHO
NH3
N
H
Scheme 1. Visible-light-mediated synthesis of Hantzsch 1,4-dihydropyridine.
NO2
H
N
N
2
MeI, Et3N
CH2Cl2, reflux
13 h, 52%
O2N
1
NH2 NH2
NO2 O
HN
NH
cat. Yb(OTf)3
+
CH3CN, reflux
3 d, 60%
MeI, K2CO3
CH3CN, reflux
24 h, 43%
2
N
6
5
7
N
O2N
2
Scheme 2. Preparation of compounds 1 and 2.
compounds 3 and 4 (Scheme 3), except that o-nitroacetophenone
was replaced with p-nitroacetophenone (8). The molecular struc-
tures of 1e4 were confirmed by single-crystal X-ray diffraction
analysis as presented in Fig. 1,5 which all reveal a 2,3-dihydro-1H-
perimidine moiety along with a nitrophenyl group substituted at C-2
position. For compounds 2e4, the nitrophenyl groups were found
to occupy exclusively the equatorial position on C-2 of the half chair
conformation-like 2,3-dihydro-1H-perimidine plane. Only the
o-nitrophenyl group of 1 is situated at the axial position on C-2 of the
2,3-dihydro-1H-perimidine plane with the o-nitro group perpen-
dicular to the benzene ring and pointing toward the N-methyl amine
moiety. Note that although the structural difference between 1 and 2
is merely that the former is N-methyl-substituted and the latter is
N,N-dimethyl-substituted, the presence of the extra methyl group on
2 renders the o-nitrophenyl group to adopt the equatorial position
on C-2 position. These observations suggest that the conformation of
these perimidine derivatives is greatly influenced by the ortho
substituent on the benzene moiety as well as the substituents on the
two amine groups.
With the compounds 1e4 in hand, their photochemical prop-
erties were then investigated. None of the prepared compounds
were found to be light-sensitive except 1. After compound 1 was
exposed to visible light under argon atmosphere in dry CH3CN for
24 h, the photogenerated products were isolated and characterized
to be the 2H-indazole 10 and perimidinone 11 (Scheme 4). Fig. 2
shows the X-ray crystal structures of 10 and 11,5 which display
a naphthalene-substituted 2H-indazole moiety and a 1H-peri-
midin-6(2H)-one moiety, respectively. Since the only structural
difference between the light-sensitive 1 and light-insensitive 3 is
the position of the nitro substituent, cyclic voltammetry measure-
ments of 1 and 3 were performed in acetonitrile to explore the
substituent effects on their redox potentials (see Fig. S1 in the
Supplementary data). Both compounds exhibited a similar oxida-
tion wave around 0.66 eV (vs ferrocene/ferrocenium) at a scan rate
H
N
2
MeI, Et3N
NO2
N
CH2Cl2, reflux
4 h, 83%
3
NO2
NH2 NH2
O
HN
NH
cat. Yb(OTf)3
+
EtOH, rt
24 h, 91%
NO2
MeI, K2CO3
CH3CN, reflux
9 h, 88%
N
N
2
5
8
9
NO2
4
Scheme 3. Preparation of compounds 3 and 4.

W.-Z. Chen et al. / Tetrahedron 69 (2013) 2775e2781
2777
Fig. 1. ORTEP crystal structures of 1e4.
NO2
N
N
N
NO2
NH
visible light, Ar
N
NH
N
+
CH3CN, 24 h
79% conversion
O
11
1
10
60%
26%
Scheme 4. Photogenerated products 10 and 11 under anaerobic conditions.
of 100 mV sꢀ1, which presumably attributes to the abstraction of an
electron from the amine nitrogen atom. This result suggests that the
position of the nitro group (either at ortho or para) on the benzene
moiety has little effect on its oxidation potential. Fig. 3 shows the
UVevis spectra of 1 (lmax¼346 nm, log ε¼3.94), 10 (lmax¼257, 308,
347 nm, log ε¼4.40, 3.96, 3.94), and 11 (lmax¼278, 516 nm,
log ε¼4.33, 3.25). While the compounds 1 and 10 are colorless,
the compound 11 is purple. The fact that neither perimidine nor
o-nitrophenyl chromophore of 1 exhibits absorption at visible re-
gions implies that the light-sensitive properties of 1 are likely due to
a charge-transfer interaction between the two chromophores upon
visible light irradiation. To gain more insights into the proposed
radical mechanism for this visible light-mediated photoxidation,
the perimidine 1 was subjected to EPR spectral measurements. Fig. 4
shows the EPR spectra of 1 recorded in degassed CH2Cl2 solution at
room temperature under visible light (408 nm) irradiation. In the
absence of light, no apparent EPR signal was observed. Upon visible
light irradiation, the EPR signals were clearly detected, presumably
resulting from the coupling between two radical species. The
intensity of the signals, centered around 3521 G (g¼2.0036), in-
creases when the exposure time increases. This observation sug-
gests that the photochemical reaction of 1 involves, at least in part,
a biradical as a transient species or intermediate. It is worth to
mention that compounds 2, 3, and 4 are all EPR-silent, indicating
that o-nitrophenyl group and the adjacent secondary amine of 1
play a key role on its light-sensitive properties.
On the basis of above information, a plausible mechanism for the
formation of the 2H-indazole 10 from 1 is proposed in Scheme 5. We
speculate that the photoreaction involves a light-mediated single-
electron transfer (SET) from the amine to the nearby nitrophenyl
group of 1 to generate the biradical species 12,6 which we believe is
responsible for the observed EPR signals. Compound 12 then un-
dergoes pyrimidine ring-opening to give the charge separated
transient species 13. The subsequent intramolecular hydrogen
transfer from iminium hydrogen to nitrogen radical regenerates the
biradical species 14. Final light-induced deoxygenation of the
nitro radical anion follows by cyclization via NeN bond formation
affords 15, which is a contributing structure of the 2H-indazole 10.

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W.-Z. Chen et al. / Tetrahedron 69 (2013) 2775e2781
Fig. 2. ORTEP crystal structures of 2H-indazole 10 and perimidinone 11.
Fig. 3. UVevis spectra of 1 (7.12ꢁ10ꢀ5 M), 10 (4.35ꢁ10ꢀ5 M), and 11 (4.50ꢁ10ꢀ5 M) in
CHCl3.
Scheme 5. Proposed mechanism for the formation of 2H-indazole 10 from 1.
Essentially, the key step of this mechanism is the formation of the
radical cation/anion species 12, which can only occur when the
amine and nitro groups are in close proximity and suitable confor-
mation to affect the intramolecular electron transfer process upon
irradiation. This proposed mechanism also explains why only 1
is sensitive to visible light and others are not, since compounds
2e4 lack the well-positioned o-nitrobenzylamino scaffold for SET
to occur.
Fig. 4. EPR spectra of 1 recorded in degassed CH2Cl2 solution at room temperature
after irradiation with a 408 nm laser source, 0e14 min, with increments of 2 min.

W.-Z. Chen et al. / Tetrahedron 69 (2013) 2775e2781
2779
Scheme 6 shows the proposed mechanism for the formation of
the minor product 11 from 1. Presumably, the molecular oxygen
generated in situ from the negatively charged nitro group on 14
(Scheme 5) was trapped by the para radical of the contributing
structure 16 to form the peroxide radical 17. The subsequent loss of
one molecule of water from 17 affords the perimidinone radical
cation 18. Final charge neutralization via back electron transfer
(BET) from the nitro radical anion to the iminium radical cation
furnishes the product 11. Interestingly, when compound 1 was
exposed to visible light under an air atmosphere (w21% oxygen) or
100% oxygen in a balloon, the isolated yields of the products 10 and
11 were similar to that of the reaction carried out under anaerobic
conditions. This result demonstrates that the presence of excess
molecular oxygen does not facilitate the formation of the oxidized
product 11, which suggests that the formation of the peroxide
radical 17 (Scheme 6) should not be the rate-determining step. This
evidence prompted us to speculate that the rate-determining step
for the visible light-mediated photoreaction of 1 is likely to be the
generation of the biradical species 12. Once the biradical species 12
is formed via visible-light-mediated single-electron transfer,
it can undergo either pyrimidine ring-opening and subsequent
deoxygenation to give the 2H-indazole 10 or can be trapped by
molecular oxygen to afford the perimidinone 11.
and is prone to undergo intramolecular electron transfer upon
visible light irradiation. Further utilization of the light-sensitive
properties of this o-nitrobenzylamino scaffold in the synthesis of
novel indazole derivatives is currently underway.
4. Experimental section
4.1. General
Melting points were determined on a Mel-Temp melting point
apparatus in open capillaries and are uncorrected. MS were per-
formed on JEOL JMS-SX/SX 102A spectrometer. IR spectra were
obtained using a 1725XFTIR spectrophotometer. Absorption spectra
were acquired using an HP8453 spectrophotometer and emission
spectra were obtained on a Hitachi F-4500 fluorospectrometer.
Single-crystal structures were determined by a Bruker AXS SMART-
1000 X-ray single-crystal diffractometer. The EPR spectra were
recorded on a Bruker EMX 10/12 spectrometer. 1H and 13C NMR
spectra were recorded at 300 and 75 MHz on a Varian VXR300
spectrometer. Chemical shifts were reported in parts per million on
the
d scale relative to an internal standard (tetramethylsilane, or
appropriate solvent peaks) with coupling constants given in hertz.
1H NMR multiplicity data are denoted by s (singlet), d (doublet), t
(triplet), q (quartet), and m (multiplet). Analytical thin-layer chro-
matography (TLC) was carried out on Merck silica gel 60G-254
plates (25 mm) and developed with the solvents mentioned. Flash
chromatography was performed in columns of various diameters
with Merck silica gel (230e400 mesh ASTM 9385 Kieselgel 60H) by
elution with the solvent systems. The visible light irradiation re-
action was performed with a 23 W household fluorescence lamp.
NO2
NH
N
NO2
NH
visible light
SET
N
1
4.2. Cyclic voltammetry measurements
12
16
Electrochemical cyclic voltammetry experiments were per-
formed in a three-electrode single-compartment cell using a plati-
num disk working electrode, a platinum wire counter electrode and
a Ag/AgCl (in a saturated KCl solution) reference electrode. The cell
was driven using a PAR Model 273A. The electrochemical reaction
vessel was charged with 5 mL of an acetonitrile solution of 1 or 3
(1ꢁ10ꢀ3 M) and tetra-n-butylammonium hexafluorophosphate
(0.1 M) as the electrolyte. The solutions were deoxygenated by
bubbling nitrogen through them for approximately 5 min. Poten-
tials are reported versus Ag/AgCl and reference to the ferrocene/
ferrocenium (Fc/Fcþ) couple (acetonitrile, þ0.57 V).
+O2
NO2
NH
N
NO2
N
N
BET
-H2O
11
H
O
O
18
O
17
4.2.1. 2-Methyl-2-(2-nitrophenyl)-2,3-dihydro-1H-perimidine (7). To
a solution of 1,8-diaminonaphthalene (100.0 mg, 0.63 mmol) in
acetonitrile (25 mL) was added 1-(2-nitrophenyl)ethanone
(104.0 mg, 0.63 mmol) and a catalytic amount of Yb(OTf)3 at room
temperature. The resulting mixture was refluxed for 3 days (moni-
tored by TLC). After cooled down to room temperature, the reaction
was quenched by water (50 mL) and the product was extracted
twice with methylene chloride. The combined organic extracts were
dried over MgSO4, filtered, and concentrated. The resulting crude
product was purified by column chromatography (1:9 EtOAc/hex-
anes) to give a light brown solid; yield 60%; Rf¼0.2 (15% EtOAc/
SET: single-electron transfer; BET: back electron transfer
Scheme 6. Proposed mechanism for the formation of perimidinone 11 from 1.
3. Conclusions
In summary, four o- and p-nitro substituted 2-methyl-2-phenyl-
2,3-dihydro-1H-perimidines 1e4 were synthesized and character-
ized to investigate the structure and photochemical property re-
lationship. The X-ray crystal structures suggest the conformation of
these perimidine derivatives is greatly influenced by the ortho
substituent on the benzene moiety as well as the substituents on
the two amine groups. Moreover, only 1 with the o-nitrophenyl
group adopting the axial position on C-2 was found to be light-
sensitive and its photogenerated products were characterized to
be the 2H-indazole 10 and perimidinone 11. Our studies have
demonstrated that the perimidine 1, having an o-nitrophenyl sit-
uated at the axial position of 2,3-dihydro-1H-perimidine ring along
with a nearby secondary amine group, is highly sensitive to light
hexanes); mp 232e233 ꢂC; 1H NMR (CDCl3, 300 MHz)
d 7.72 (dd,
J¼8.1, 1.5 Hz, 1H), 7.37e7.30 (m, 2H), 7.24e7.10 (m, 5H), 6.57 (d,
J¼7.2 Hz, 2H), 5.06 (br s, 2H), 2.01 (s, 3H); 13C NMR (acetone-d6,
75 MHz)
d 151.2, 141.3, 140.2, 134.7, 130.8, 129.6, 128.5, 126.8, 124.0,
116.8,114.4,106.3, 67.8, 29.4; IR n (KBr) 3402, 3385, 3352, 3062, 2971,
1604, 1523, 1419, 1375, 1163, 1143, 1040, 794, 764 cmꢀ1; HRMS (EI)
m/z calcd for C18H15O2N3 [Mþ] 305.1164, found 305.1168.
4.2.2. 1,2-Dimethyl-2-(2-nitrophenyl)-2,3-dihydro-1H-perimidine
(1). To a solution of perimidine 7 (100.0 mg, 0.33 mmol) in methylene

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W.-Z. Chen et al. / Tetrahedron 69 (2013) 2775e2781
chloride (25 mL) was added iodomethane (46.5 mg, 0.33 mmol) and
triethylamine (33.2 mg, 0.33 mmol) at room temperature. The
resulting solution was refluxed for 13 h (monitored by TLC). After
cooled down to room temperature, the reaction was quenched by
water (50 mL) and the product was extracted twice with methylene
chloride. The combined organic extracts were dried over MgSO4, fil-
tered, and concentrated. The resulting crude product was purified by
column chromatography (1:9 EtOAc/hexanes) to give a yellow solid;
yield 52%; Rf¼0.2 (10% EtOAc/hexanes); mp 164e165 ꢂC; 1H NMR
(t, J¼8.4 Hz, 1H), 7.23e7.18 (m, 2H), 6.57 (d, J¼7.2 Hz, 1H), 6.48 (dd,
J¼6.9, 1.5 Hz, 1H), 4.44 (br s, 1H), 2.74 (s, 3H), 1.82 (s, 3H); 13C NMR
(CDCl3, 75 MHz)
d 152.1, 147.5, 142.5, 138.9, 134.2, 128.4, 127.3,
126.8, 123.6, 117.7, 117.4, 113.3, 105.8, 104.7, 72.6, 34.0, 21.6; IR
n
(KBr) 3382, 3050, 2969, 1590, 1521, 1406, 1344, 1242, 1072, 1003,
853, 812, 761 cmꢀ1; HRMS (EI) m/z calcd for C19H17O2N3 [Mþ]
319.1321, found 319.1327.
4.2.6. 1,2,3-Trimethyl-2-(4-nitrophenyl)-2,3-dihydro-1H-perimidine
(4). To a solution of perimidine 9 (100.0 mg, 0.33 mmol) in aceto-
nitrile (25 mL) was added iodomethane (93.7 mg, 0.66 mmol) and
potassium carbonate (68.4 mg, 0.50 mmol) at room temperature.
The resulting solution was refluxed for 9 h (monitored by TLC). After
cooled down to room temperature, the reaction was quenched by
water (50 mL) and the product was extracted twice with methylene
chloride. The combined organic extracts were dried over MgSO4,
filtered, and concentrated. The resulting crude product was purified
by column chromatography (1:9 EtOAc/hexanes) to give a yellow
solid; yield 88%; Rf¼0.8 (20% EtOAc/hexanes); mp 204e205 ꢂC; 1H
(CDCl3, 300 MHz)
(d, J¼6.9 Hz, 1H), 6.54 (dd, J¼6.9, 0.9 Hz, 1H), 5.01 (br s, 1H), 2.95 (s,
3H), 1.95 (s, 3H); 13C NMR (CDCl3, 75 MHz)
150.9, 143.0, 138.7, 138.6,
134.1, 130.7, 128.7, 128.5, 127.0, 126.6, 124.4, 118.8, 117.9, 115.5, 109.1,
d
7.50 (dd, J¼7.5, 1.2 Hz, 1H), 7.34e7.11 (m, 7H), 6.70
d
106.5, 72.4, 36.5, 25.9; IR
n (KBr) 3405, 3381, 3047, 2983, 2869, 1595,
1523, 1407, 1368, 1214, 1196, 1006, 819, 767 cmꢀ1; HRMS (EI) m/z calcd
for C19H17O2N3 [Mþ] 319.1321, found 319.1312.
4.2.3. 1,2,3-Trimethyl-2-(2-nitrophenyl)-2,3-dihydro-1H-perimidine
(2). To a solution of perimidine 7 (100.0 mg, 0.33 mmol) in ace-
tonitrile (25 mL) was added iodomethane (93.7 mg, 0.66 mmol)
and potassium carbonate (68.4 mg, 0.50 mmol) at room temper-
ature. The resulting solution was refluxed for 24 h (monitored by
TLC). After cooled down to room temperature, the reaction was
quenched by water (50 mL) and the product was extracted twice
with methylene chloride. The combined organic extracts were
dried over MgSO4, filtered, and concentrated. The resulting crude
product was purified by column chromatography (1:9 EtOAc/
hexanes) to give a brown solid; yield 43%; Rf¼0.4 (15% EtOAc/
NMR (CDCl3, 300 MHz)
2H), 7.37 (t, J¼7.5 Hz, 2H), 7.26e7.23 (m, 2H), 6.54 (dd, J¼7.2, 0.9 Hz,
2H), 2.52 (s, 6H),1.60 (s, 3H); 13C NMR (CDCl3, 75 MHz)
152.0, 147.8,
141.8,133.9,129.4,127.0,123.8,117.5,113.0,104.1, 78.3, 34.6,12.9; IR
d
8.29 (d, J¼9.0 Hz, 2H), 7.90 (d, J¼9.0 Hz,
d
n
(KBr) 2964, 2812, 1581, 1516, 1417, 1348, 1333, 1194, 1065, 989, 811,
759 cmꢀ1; HRMS (EI) m/z calcd for C20H19O2N3 [Mþ] 333.1477, found
333.1474.
4.2.7. N-Methyl-8-(3-methyl-2H-indazol-2-yl)naphthalen-1-amine
(10) and 1,2-dimethyl-2-(2-nitrophenyl)-1H-perimidin-6(2H)-one
(20). A dried 50 mL round bottom flask was charged with 1
(20.0 mg, 0.07 mmol), and freshly distilled and degassed CH3CN
(25 mL) under argon atmosphere. The mixture was placed at
a distance of approximate 10 cm from a 23 W fluorescent lamp
and was irradiated for 24 h. The solvent was then evaporated and
the photogenerated products were purified by column chroma-
tography (1:9 EtOAc/hexanes) to give 4.20 mg of the starting
material 1 (79% conversion) and 8.53 mg of the white solid 10;
yield 60%; Rf¼0.5 (15% EtOAc/hexanes); mp 215e216 ꢂC; 1H NMR
hexanes); mp 261e262 ꢂC; 1H NMR (CDCl3, 300 MHz)
d 7.65 (dd,
J¼7.5, 1.8 Hz, 1H), 7.52 (td, J¼7.5, 1.8 Hz, 1H), 7.48 (td, J¼7.5, 1.8 Hz,
1H), 7.37 (dd, J¼7.5, 1.8 Hz, 1H), 7.32 (t, J¼7.5 Hz, 2H), 7.18 (dd,
J¼8.4, 0.9 Hz, 2H), 6.52 (dd, J¼7.5 Hz, 2H), 2.72 (s, 6H), 1.69 (s, 3H);
13C NMR (CDCl3, 75 MHz)
d 150.9, 141.2, 136.1, 133.8, 130.2, 129.7,
129.4, 126.9, 124.4, 117.5, 113.7, 104.7, 34.8, 29.7, 16.4; IR
n (KBr)
2975, 2881, 2814, 1583, 1533, 1415, 1330, 1197, 1046, 983, 811,
760 cmꢀ1; HRMS (EI) m/z calcd for C20H19O2N3 [Mþ] 333.1477,
found 333.1468.
4.2.4. 2-Methyl-2-(4-nitrophenyl)-2,3-dihydro-1H-perimidine (9). To
a solution of 1,8-diaminonaphthalene (100.0 mg, 0.63 mmol) in
ethanol (25 mL) was added 1-(4-nitrophenyl)ethanone (104.0 mg,
0.63 mmol)anda catalytic amountofYb(OTf)3. The resulting solution
was stirred at room temperature for 24 h (monitored by TLC). After
the solvent was evaporated, water (50 mL) was added and the
product was extracted twicewith methylene chloride. The combined
organic extracts were dried over MgSO4, filtered, and concentrated.
The resulting crude productwas purified bycolumn chromatography
(2:8 EtOAc/hexanes) to give a yellow solid; yield 90%; Rf¼0.4 (30%
EtOAc/hexanes); mp 191e192 ꢂC (lit.7 192.13 ꢂC); 1H NMR (CDCl3,
(CDCl3, 300 MHz)
d
7.95 (dd, J¼1.5, 0.6 Hz, 1H), 7.75 (dt, J¼9.0,
0.9 Hz, 1H), 7.67 (dt, J¼8.4, 1.2 Hz, 1H), 7.49 (d, J¼7.2 Hz, 1H), 7.45
(t, J¼7.2 Hz, 1H), 7.41 (d, J¼7.8 Hz, 1H), 7.40 (td, J¼6.6, 1.2 Hz, 1H),
7.32 (dd, J¼8.1, 0.9 Hz, 1H), 7.25 (dd, J¼9.0, 1.2 Hz, 1H), 7.15 (ddd,
J¼7.5, 6.9, 1.2 Hz, 2H), 6.54 (d, J¼7.8 Hz, 1H), 3.49 (br s, 1H), 2.43 (d,
J¼5.1 Hz, 3H), 2.30 (s, 3H); 13C NMR (CDCl3, 75 MHz)
d 148.9, 145.1,
136.7, 136.2, 134.4, 131.1, 127.5, 127.3, 125.8, 124.5, 121.1, 120.9,
120.2, 119.5, 117.3, 117.2, 106.1, 31.5, 10.5; IR
n (KBr) 3364, 3055,
1580, 1372, 1333, 1301, 821, 750 cmꢀ1; HRMS (EI) m/z calcd for
C19H17N3 [Mþ] 287.1422, found 287.1414. The red solid 11
(4.29 mg); yield 26%; Rf¼0.3 (30% EtOAc/hexanes); mp
300 MHz)
d
8.08 (d, J¼9.0 Hz, 2H), 7.71 (d, J¼8.7 Hz, 2H), 7.22 (d,
179e181 ꢂC; 1H NMR (CDCl3, 300 MHz)
d
7.71 (d, J¼7.8 Hz, 1H),
J¼7.2 Hz, 2H), 7.15 (dd, J¼8.1, 0.9 Hz, 2H), 6.61 (dd, J¼7.2, 0.9 Hz, 2H),
7.64e7.58 (m, 1H), 7.50 (d, J¼3.9 Hz, 2H), 7.43 (d, J¼7.8 Hz, 1H),
7.37 (dd, J¼7.8, 1.5 Hz, 1H), 7.08 (d, J¼9.9 Hz, 1H), 6.73 (dd, J¼8.1,
1.2 Hz, 1H), 6.72 (d, J¼10.2 Hz, 1H), 2.60 (s, 3H), 1.97 (s, 3H); 13C
4.84 (br s, 2H), 1.84 (s, 3H), 1.56 (s, 3H).
4.2.5. 1,2-Dimethyl-2-(4-nitrophenyl)-2,3-dihydro-1H-perimidine
(3). To a solution of perimidine 9 (100.0 mg, 0.33 mmol) in
methylene chloride (25 mL) was added iodomethane (46.5 mg,
0.33 mmol) and triethylamine (33.2 mg, 0.33 mmol) at room
temperature. The resulting solution was refluxed for 4 h (moni-
tored by TLC). After cooled down to room temperature, the re-
action was quenched by water (50 mL) and the product was
extracted twice with methylene chloride. The combined organic
extracts were dried over MgSO4, filtered, and concentrated. The
resulting crude product was purified by column chromatography
(1:9 EtOAc/hexanes) to give a yellow solid; yield 83%; Rf¼0.7 (20%
NMR (CDCl3, 75 MHz) d 185.5, 152.4, 151.2, 143.1, 140.4, 137.4,
134.7, 133.8, 131.1, 129.5, 129.1, 127.4, 124.6, 115.1, 114.9, 111.3, 79.9,
33.1, 25.1; IR
n (KBr) 2923, 2852, 1656, 1630, 1585, 1528, 1359,
1308, 780, 764 cmꢀ1; HRMS (EI) m/z calcd for C19H15O3N3 [Mþ]
333.1113, found 333.1121.
4.3. General procedure for visible light irradiation of
compounds 2e4
A dried 50 mL round bottom flask was charged with 2 (20.0 mg,
0.07 mmol), and freshly distilled and degassed CH3CN (25 mL)
under argon or air atmosphere. The mixture was placed at a dis-
tance of approximate 10 cm from a 23 W fluorescent lamp and was
EtOAc/hexanes); mp 169e170 ꢂC; 1H NMR (CDCl3, 300 MHz)
d
8.20
(d, J¼9.0 Hz, 2H), 7.82 (d, J¼9.0 Hz, 2H), 7.36 (t, J¼8.1 Hz, 1H), 7.25

W.-Z. Chen et al. / Tetrahedron 69 (2013) 2775e2781
2781
2010, 2, 527e532; (c) Narayanam, J. M. R.; Stephenson, C. R. J. Chem. Soc. Rev.
2011, 40, 102e113; (d) Tucker, J. W.; Stephenson, C. R. J. J. Org. Chem. 2012, 77,
1617e1622.
irradiated for 24 h. No reaction was observed for all compounds
2e4 judging from TLC analysis.
2. (a) Hasegawa, E.; Takizawa, S.; Seida, T.; Yamaguchi, A.; Yamaguchi, N.; Chiba, N.;
Takahashi, T.; Ikeda, H.; Akiyama, K. Tetrahedron 2006, 62, 6581e6588; (b)
Neumann, M.; Fuldner, S.; Konig, B.; Zeitler, K. Angew. Chem., Int. Ed. 2010, 50,
951e954; (c) Park, J. H.; Ko, K. C.; Kim, E.; Park, N.; Ko, J. H.; Ryu, O. H.; Ahn, T. K.;
Lee, J. Y.; Son, S. U. Org. Lett. 2012, 14, 5502e5505.
3. Ghosh, S.; Saikh, F.; Das, J.; Pramanik, A. K. Tetrahedron Lett. 2013, 54, 58e62.
4. (a) Prakash, G. K. S.; Mathew, T.; Panja, C.; Vaghoo, H.; Venkataraman, K.; Olah,
G. A. Org. Lett. 2007, 9, 179e182; (b) Olah, G. A.; Farooq, O.; Farnia, S. M. F.; Olah,
J. A. J. Am. Chem. Soc. 1988, 110, 2560e2562.
Acknowledgements
The authors thank the National Science Council of the Republic
of China, Taiwan, for financially supporting this research under
Contract No. NSC 100-2113-M-029-005-MY2. We also thank the
reviewers for their suggestions and comments.
5. Crystallographic data (excluding structure factors) for 1, 2, 3, 4, 10, and
11 have been deposited with the Cambridge Crystallographic Data Centre
as supplementary publication number CCDC-803570, -803571, -803574,
-803575, -803573 and -860835, respectively. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223
336033
Supplementary data
Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.tet.2013.01.079.
References and notes
6. Yong, P. K.; Banerjee, A. Org. Lett. 2005, 7, 2485e2487.
7. (a) Zhang, J.; Zhang, S. L.; Zhang, J. M. Chin. Chem. Lett. 2007, 18, 1057e1060; (b)
Maloshitskaya, O.; Sinkkonen, J.; Ovcharenko, V. V.; Zelenin, K. N.; Pihlaja, K.
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1. For recent reviews on visible light photoredox catalysis, see: (a) Zeitler, K. Angew.
Chem., Int. Ed. 2009, 48, 9785e9789; (b) Yoon, T. P.; Ischay, M. A.; Du, J. Nat. Chem.