Synthesis of 2-aryl-1,2-dihydrophthalazines via reaction of 2-(bromomethyl)benzaldehydes with arylhydrazines

Article abstract of DOI:10.1021/jo302491x

The reaction of 2-(bromomethyl)benzaldehydes with arylhydrazines employing K₂CO₃ as a base and FeCl₃ as a catalyst in CH₃CN at 100 C delivers 2-aryl-1,2-dihydrophthalazines with yields ranging from 60 to 91%. The transformation is considered to proceed as an intermolecular condensation/intramolecular nucleophilic substitution.

Full text of DOI:10.1021/jo302491x

Article
pubs.acs.org/joc
Synthesis of 2‑Aryl-1,2-dihydrophthalazines via Reaction of
2‑(Bromomethyl)benzaldehydes with Arylhydrazines
Nayyef Aljaar, Jurgen Conrad, and Uwe Beifuss*
̈
Bioorganische Chemie, Institut fur Chemie, Universitat Hohenheim, Garbenstrasse 30, D-70599 Stuttgart, Germany
̈
̈
S
* Supporting Information
ABSTRACT: The reaction of 2-(bromomethyl)benz-
aldehydes with arylhydrazines employing K2CO3 as a base
and FeCl3 as a catalyst in CH3CN at 100 °C delivers 2-aryl-
1,2-dihydrophthalazines with yields ranging from 60 to 91%.
The transformation is considered to proceed as an
intermolecular condensation/intramolecular nucleophilic sub-
stitution.
Rh-catalyzed oxidative annulation of sulphonylhydrazones with
alkenes using Cu(OAc)2 as the oxidant.11 Altogether, the
number of direct approaches to 1,2-dihydrophthalazines is
rather limited. Therefore, the development of new methods for
the synthesis of 1,2-dihydrophthalazines is highly desirable.
Recently, we have reported on new approaches to hetero-
cycles that rely on reactions between o-disubstituted aromatics
or heteroaromatics with disubstituted reagents.12 As part of this
work, we became interested in the reaction between 2-
(halomethyl)benzaldehydes and arylhydrazines. In this con-
tribution, we report on a practical synthesis of 2-substituted 1,2-
dihydrophthalazines that is based on the reaction between 2-
(bromomethyl)benzaldehydes and arylhydrazines under basic
conditions and with FeCl3 as the catalyst.
INTRODUCTION
■
Phthalazines and phthalazinones are N-heterocycles with a wide
range of biological and pharmacological properties, such as
anticonvulsant, antimicrobial, anti-inflammatory, antimycobac-
terial, antitumor, antihypertensive, antidiabetic, antifungal, and
vasorelaxant activity, among others.1 They also play an
important role as intermediates in organic synthesis. This is
why numerous methods have been developed for their
preparation.2 Besides fully aromatic phthalazines, partially
unsaturated derivatives, such as the 1,2-dihydrophthalazines,
are also of considerable interest in medicinal chemistry, as a
number of them exhibit significant pharmacological properties.
Among the most remarkable compounds are some 1,2-
dihydrophthalazines that inhibit dihydrofolate reductase, an
essential enzyme in most pathogenic bacteria. The 1,2-
dihydrophthalazines have been demonstrated to have potent
antibacterial activities against infections that are caused by
multiresistant gram-positive pathogens, including staphylococ-
ci.3 Of particular interest is the 1,2-dihydrophthalazine RAB1,
which has been identified as a promising inhibitor of antibiotic-
resistant Staphylococcus aureus and trimethoprim-resistant
Bacillus anthracis.4 In addition, it has been found that 1,2-
dihydrophthalazines are potent, selective, and noncompetitive
inhibitors of the AMPA subtype of glutamate receptors.5
In contrast to the synthesis of phthalazines and phthalazi-
nones, the number of methods available for the preparation of
1,2-dihydrophthalazines is only modest. Most of them are
based on the reduction of phthalazinium salts, phthalazines, or
phthalazinones using reducing reagents, such as [Fe3(CO)12]6
and NaBH4,7 or on the addition of organometallic reagents,
such as organolithium,5,8 or Grignard reagents4b to phthala-
zines. Another method is based on the cyclization of
phthaldehyde monoarylhydrazones that can be obtained from
the condensation of phthalaldehyde with arylhydrazines.9 In
addition, a few 1,2-dihydrophthalazines have been synthesized
by reaction between 1,2-bis(halomethyl)benzenes and hydra-
zines under microwave conditions.10 Recently, Xu et al.
reported on the preparation of 1,2-dihydrophthalazines by the
RESULTS AND DISCUSSION
■
It was envisaged that 1,2-dihydrophthalazines can be
synthesized by a domino condensation/intramolecular sub-
stitution using a 2-(halomethyl)benzaldehyde 1 and a hydrazine
2 as the substrates. Therefore, in an initial experiment, 2-
(bromomethyl)benzaldehyde (1a) and phenylhydrazine (2a)
were reacted with 2 equiv of K3PO4 in DMF for 24 h at 110 °C
in a sealed vial. After workup and purification, the desired 1,2-
dihydrophthalazine 3a could be isolated in 40% yield (Scheme
1). It is assumed that the reaction starts with the condensation
between aldehyde 1a and hydrazine 2a to give the hydrazone
4a as an intermediate. In the second step, 4a undergoes an
intramolecular nucleophilic substitution to yield the 2-
substituted 1,2-dihydrophthalazine 3a.
To facilitate the condensation between the aldehyde function
of 1a and the NH2 group of the hydrazine 2a, we decided to
run the transformation in the presence of a Lewis acid. When
the reaction between 1a and 2a with 2 equiv of K3PO4 was
conducted in the presence of 10 mol % CuI in DMF, the yield
of 3a could be increased to 58% (Table 1, entry 1). The
Received: November 13, 2012
© XXXX American Chemical Society
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Scheme 1. Initial Experiment for the Synthesis of 2-
Substituted 1,2-Dihydrophthalazines
Table 2. Influence of Lewis Acids on the Outcome of the
Model Reaction
a
entry
Lewis acid
mol %
yield of 3a (%)
1
2
3
4
5
6
7
8
9
ZnCl2
Cu2O
InBr3
CuI
10
10
10
10
10
5
77
73
82
88
89
70
87
73
49
FeCl3
CuI
Table 1. Influence of Bases and Solvents on the Outcome of
the Model Reaction
a
FeCl3
FeCl3
5
2.5
a
All reactions were performed using 0.5 mmol of 1a and 0.5 mmol of
2a in a sealed vial. The temperatures given refer to oil bath
temperatures.
entry
base (equiv)
solvent
T (°C)
yield of 3a (%)
1
2
K3PO4 (2)
Cs2CO3 (2)
K2CO3 (2)
DABCO (2)
K2CO3 (3)
K2CO3 (1)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
DMF
110
110
110
110
110
110
110
100
110
110
100
100
100
100
110
58
67
86
19
87
72
61
60
84
80
37
88
66
38
43
DMF
demonstrated that the reaction can be conducted with 10 mol
% of a number of Lewis acids, including ZnCl2, Cu2O, InBr3,
CuI, and FeCl3 (Table 2, entries 1−5). The best results were
obtained with CuI and FeCl3 (Table 2, entries 4 and 5). With
10 mol % CuI, 88% of 3a was isolated (Table 2, entry 4). When
the amount of CuI was decreased to 5 mol %, the yield of 3a
amounted to 70% (Table 2, entry 6). With 10 mol % FeCl3 as
the catalyst, the 1,2-dihydrophthalazine 3a was obtained in 89%
(Table 2, entry 5). Furthermore, it was found that the process
tolerates a reduction of the amount of FeCl3 from 10 to 5 mol
% without a significant loss of yield (Table 2, entry 7). A further
decrease of the FeCl3 load to 2.5 mol % was also possible, but
the yield dropped to 73% (Table 2, entry 8). A control
experiment underlines the importance of the Lewis acid on the
outcome of the reaction. In the absence of any Lewis acid, only
49% of the 1,2-dihydrophthalazine 3a could be isolated (Table
2, entry 9).
3
DMF
4
DMF
5
DMF
6
DMF
7
toluene
C2H4Cl2
DMSO
DMA
NMP
8
9
10
11
12
13
14
15
CH3CN
EtOH
H2O
a
All reactions were performed using 0.5 mmol of 1a and 0.5 mmol of
2a in a sealed vial. The temperatures given refer to oil bath
temperatures.
Furthermore, it was demonstrated that the model reaction
can also be conducted under reflux conditions and under
microwave conditions in a sealed vial (Table 3). However, the
yields were markedly lower than under our standard conditions.
In summary, the best results were obtained when 1 equiv of 2-
(bromomethyl)benzaldehyde (1a) and 1 equiv of arylhydrazine
reaction could be performed not only with K3PO4 as the base
but also with Cs2CO3, K2CO3, and DABCO (Table 1, entries
2−4). With 2 equiv of K2CO3 in DMF, the yield of 3a
amounted to 86% (Table 1, entry 3). It is also remarkable that,
with DABCO as the base, only 19% of the product could be
isolated (Table 1, entry 4). An increase of the amount of
K2CO3 to 3 equiv had a negligible impact on the yield (Table 1,
entry 5). However, when the amount K2CO3 was reduced to 1
equiv, the yield of 3a dropped to 72% (Table 1, entry 6).
Next, the influence of different solvents on the outcome of
the model reaction was studied. It was established that it can be
run in a number of solvents, including toluene, 1,2-dichloro-
ethane, DMSO, DMA, NMP, CH3CN, EtOH, and H2O (Table
1, entries 7−14). The highest yield of 3a was obtained in
CH3CN (Table 1, entry 12). It should be noted that, with
DMSO or DMA as the solvents, the yield of 3a was in the same
range (Table 1, entries 9 and 10). In the absence of any solvent,
the yield of 3a dropped to 43% (Table 1, entry 15).
Table 3. Reaction of 2a with 3a under Reflux and Microwave
a
Conditions
entry
1
conditions
yield of 3a (%)
reflux
72
64
b
2
microwave
a
On the basis of the reaction conditions presented in Table 1,
entry 12, the influence of different Lewis acids and different
amounts of the catalysts was investigated (Table 2). It could be
The reactions were performed using 0.5 mmol of 1a and 0.5 mmol of
b
2a under argon for 24 h. The reaction was carried using a microwave
apparatus (300 W, 20 bar, 100 °C) for 1 h.
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a
Table 4. Synthesis of 2-Aryl-1,2-dihydrophthalazines 3b−3j
a
All reactions were performed using 0.5 mmol of 1a and 0.5 mmol of 2 in a sealed vial.
2a were reacted in the presence of 2 equiv of K2CO3 and 5 mol
% FeCl3 in CH3CN in a sealed vial at 100 °C.
After optimizing the model reaction, we focused on the
substrate scope of the new 1,2-dihydrophthalazine synthesis.
For this purpose, arylhydrazines 2b−2j carrying different
substituents on the phenyl ring were studied. It was found
that a number of substituents, such as methyl, isopropyl,
methoxy, halo, and cyano substituents, were tolerated (Table 4,
entries 1−9). The yields of the corresponding 2-substituted 1,2-
dihydrophthalazines 3b−3j were in the range between 63 and
C
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a
Table 5. Synthesis of 2-Phenyl-1,2-dihydrophthalazines 3k−3m
a
All reactions were performed using 0.5 mmol of 1 and 0.5 mmol of 2a in a sealed vial.
Scheme 2. Proposed Reaction Mechanism for the Formation of 2-Phenyl-1,2-dihydrophthalazines
91%. It should be noted that the yields with arylhydrazines
carrying electron-donating substituents were higher than the
yields observed with arylhydrazines with electron-withdrawing
substituents.
was reacted at 100 °C for 24 h, the dihydrophthalazine 3a was
formed in 78% yield.
The structures of the 2-substituted 1,2-dihydrophthalazines
3a−3m were unambiguously elucidated by NMR spectroscopy
1
and mass spectrometry. Full assignment of the H and 13C
In addition, it was studied whether substituted 2-
(bromomethyl)benzaldehydes can be employed as substrates
for the 1,2-dihydrophthalazine synthesis (Table 5). To this end,
the 2-(bromomethyl)benzaldehydes 1b−1d were synthesized
by reduction of the corresponding benzonitriles (see the
Experimental Section) with DIBAL-H and reacted with
phenylhydrazine (2a). It was found that the 1,2-dihydroph-
thalazines 3k−3m could be obtained without any problem. The
yields were in the range between 60 and 74% (Table 5, entries
1−3)
With respect to the reaction mechanism of the dihydroph-
thalazine formation, it is assumed that the first step is a
condensation between the aldehyde group of 1 and the NH2
group of hydrazine 2 to give the corresponding hydrazone 4
(Scheme 2). This was corroborated by the fact that, upon
reaction between 1a and 2a in the presence of 5 mol % FeCl3
for 2h, the CHO signal of 1a at δ = 10.26 ppm had disappeared
and was replaced by a signal at δ = 8.13 ppm, which
corresponds to the signal of a CHN group. The hydrazone
4a could not be isolated, but when 2 equiv of K2CO3 were
added to the above reaction mixture and the resulting mixture
chemical shifts and structure elucidation of all compounds was
achieved by evaluating their gCOSY, gHSQC, and gHMBC
spectra. As an example, in the HMBC spectrum for compound
3c, the quaternary carbon C-4a showed strong 3J-HMBC
correlations to protons 1-H, 6-H, and 8-H (Figure 1). The
3
quaternary carbon C-8a displayed JCH-correlations to the
protons 4-H, 5-H, and 7-H as well as strong 2JCH-correlations to
the proton 1-H. Carbon C-1′ exhibited strong 3JCH-correlations
to the proton 3′-H. The quaternary carbon C-4′ correlated with
the protons 2′-H and 1″-H.
3
Figure 1. Important HMBC correlations of 3c (red arrows, J; blue
2
arrows, J).
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Evaporation of the solvents delivered 1a as a brown liquid in 93% yield
CONCLUSIONS
■
1
(2.37 g, 11.91 mmol): Rf = 0.50 (PE/EtOAc = 3:1); H NMR (300
In conclusion, we have developed a simple to perform and
efficient method for the synthesis of 2-substituted 1,2-
dihydrophthalazines 3 employing simple starting materials.
The 1,2-dihydrophthalazines 3 can be prepared in a single
preparative step between 2-(bromomethyl)benzaldehydes 1
with arylhydrazines 2 via Lewis acid catalyzed domino
condensation/intramolecular substitution. Best results were
achieved when 1 equiv of 2-(bromomethyl)benzaldehyde 1 and
1 equiv of arylhydrazine 2 were reacted in the presence of 2
equiv of K2CO3 and 5 mol % FeCl3 in CH3CN. Using this
protocol, the 2-substituted 1,2-dihydrophthalazines 3a−3m
were obtained selectively with yields ranging from 60 to 91%.
The new method is one of the few examples for the synthesis of
1,2-dihydrophthalazines that does not start from a phthalazine
or a phthalazine derivative.
4
3
MHz, CDCl3) δ 4.95 (s, 2H, CH2Br), 7.49 (dd, J = 1.8 Hz, J = 7.2
Hz, 1H), 7.51 (td, 4J = 1.8 Hz, 3J = 7.2 Hz, 1H), 7.58 (td, 4J = 1.8 Hz,
3J = 7.2 Hz, 1H), 7.84 (dd, 4J = 1.8 Hz, 3J = 7.2 Hz, 1H), 10.25 (s, 1H,
CHO); 13C NMR (75 MHz, CDCl3) δ 29.5, 129.1, 131.7, 133.1,
133.8, 133.9, 139.2, 192.0.
2-(Bromomethyl)-6-chlorobenzaldehyde (1b).15 A solution of
2-(bromomethyl)-6-chlorobenzonitrile (500 mg, 2.17 mmol) in dry
dichloromethane (15 mL) was purged with argon for 20 min. The
solution was cooled using an ice−water bath, and a 0.1 M solution of
diisobutyl aluminum hydride (DIBAL-H) in hexane (2.5 mL, 2.5
mmol) was added dropwise during 25 min with stirring under argon.
The reaction mixture was allowed to warm slowly to room
temperature (4 h) by removing the ice−water bath. The reaction
mixture was cooled again using an ice−water bath and poured into a
500 mL beaker filled with ice (35 g) and precooled aqueous 6 N HBr
(15 mL). The mixture was vigorously stirred for 1.5 h and then
extracted with dichloromethane (3 × 20 mL). The combined organic
layers were washed with 1N NaHCO3 (2 × 20 mL) and H2O (2 × 20
mL) and dried over MgSO4. Evaporation of the solvents delivered 1b
as a brown liquid in 60% yield (300 mg, 1.29 mmol): Rf = 0.46
(cyclohexane/EtOAc = 5:1); IR (ATR) ν 1691, 1583, 1425, 1246,
1148, 875, 833, 674 cm−1; UV (MeCN) λmax (log ε) 299 (3.18), 249
EXPERIMENTAL SECTION
■
General Remarks. All commercially available reagents were used
without further purification. Glassware was dried for 4 h at 140 °C.
Solvents used in reactions were distilled over appropriate drying agents
prior to use. Solvents used for extraction and purification were distilled
prior to use. Reaction temperatures are reported as bath temperatures.
Microwave-assisted reactions were performed using a Discover single-
mode cavity microwave synthesizer (CEM Corp.) producing
continuous microwave irradiation at 2450 MHz. The reaction
temperatures were measured using an external IR probe. Thin-layer
chromatography (TLC) was performed using TLC silica gel 60 F254.
Compounds were visualized with UV light (λ = 254 nm) and/or by
immersion in an ethanolic vanillin solution or by immersion in
KMnO4 solution, followed by heating. Products were purified by flash
chromatography on silica gel, 0.04−0.063 mm. Melting points were
obtained on a melting point apparatus with open capillary tubes and
are uncorrected. IR spectra were measured on an FT-IR spectrometer.
1
(3.72) nm; H NMR (300 MHz, CDCl3) δ 4.90 (s, 2H, CH2Br),
7.39−7.47 (m, 3H), 10.64 (s, 1H, CHO); 13C NMR (75 MHz,
CDCl3) δ 29.7, 129.9, 130.7, 131.0, 134.1, 139.5, 141.0, 191.7; MS (EI,
70 eV) m/z 233 (20) [M]+, 153 (100); HRMS (EI, M+) calcd for
C8H6BrClO (231.9291), found 231.9268.
2-(Bromomethyl)-3-chlorobenzaldehyde (1c).15 A solution of
2-(bromomethyl)-3-chlorobenzonitrile (2.472 g, 10.75 mmol) in dry
UV spectra were recorded with a spectrophotometer. H (13C) NMR
1
spectra were recorded at 300 (75) and 500 (125) MHz using CDCl3
1
or DMSO-d6 as the solvent. The H and 13C chemical shifts were
referenced to residual solvent signals at δ H/C 7.26/77.0 (CDCl3) and
2.5/39.5 (DMSO-d6) relative to TMS as internal standard. HSQC,
HMBC, NOESY, ROESY, HSQMBC, and COSY spectra were
recorded on an NMR spectrometer at 500 and 300 MHz. Coupling
constants J [Hz] were directly taken from the spectra and are not
averaged. Splitting patterns are designated as s (singlet), d (doublet), t
(triplet), q (quartet), m (multiplet), and br (broad). 1D and 2D
homonuclear NMR spectra were measured with standard pulse
sequences. Low-resolution electron impact mass spectra (MS) and
exact mass electron impact mass spectra (HRMS) were obtained at 70
eV using a double focusing sector field mass spectrometer. Intensities
are reported as percentages relative to the base peak (I = 100%).
2-(Bromomethyl)benzaldehyde (1a).13 A solution of 2-
(bromomethyl)benzonitrile (2.5 g, 12.75 mmol) in dry dichloro-
dichloromethane (30 mL) was purged with argon for 20 min. The
solution was cooled using an ice−water bath, and a 0.1 M solution of
diisobutyl aluminum hydride (DIBAL-H) in hexane (11.0 mL, 11.0
mmol) was added dropwise during 25 min with stirring under argon.
The reaction mixture was allowed to warm slowly to room
temperature (4 h) by removing the ice−water bath. The reaction
mixture was cooled again using an ice−water bath and poured into a
500 mL beaker filled with ice (40 g) and precooled aqueous 6 N HBr
(40 mL). The mixture was vigorously stirred for 1.5 h and then
extracted with dichloromethane (3 × 40 mL). The combined organic
layers were washed with 1N NaHCO3 (2 × 50 mL) and H2O (2 × 50
mL) and dried over MgSO4. Evaporation of the solvents delivered 1c
as a brown liquid in 78% yield (1.95 g, 8.35 mmol): Rf = 0.50
(cyclohexane/EtOAc = 5:1); IR (ATR) ν 1693, 1563, 1442, 1202,
1180, 878, 674 cm−1; UV (MeCN) λmax (log ε) 297 (3.54), 249 (4.06)
nm; 1H NMR (300 MHz, CDCl3) δ 5.12 (s, 2H, CH2Br), 7.47 (t, 3J =
7.7 Hz, 1H), 7.65 (dd, 4J = 1.3 Hz, 3J = 7.7 Hz, 1H), 7.77 (td, 4J = 1.4
methane (38 mL) was purged with argon for 20 min. The solution was
cooled using an ice−water bath, and a 0.1 M solution of diisobutyl
aluminum hydride (DIBAL-H) in hexane (13.0 mL, 13.0 mmol) was
added dropwise during 25 min with stirring under argon. The reaction
mixture was allowed to warm slowly to room temperature (4 h) by
removing the ice−water bath. The reaction mixture was cooled again
using an ice−water bath and poured into a 500 mL beaker filled with
ice (50 g) and precooled aqueous 6 N HBr (50 mL). The mixture was
vigorously stirred for 1.5 h and then extracted with dichloromethane
(3 × 40 mL). The combined organic layers were washed with 1N
NaHCO3 (2 × 50 mL) and H2O (2 × 50 mL) and dried over MgSO4.
3
Hz, J = 7.7 Hz, 1H), 10.22 (s, 1H, CHO); 13C NMR (75 MHz,
CDCl3) δ 24.5, 129.8, 132.3, 134.6, 134.7, 135.0, 136.7, 190.9; MS (EI,
70 eV) m/z 233 (16) [M]+, 153 (8); HRMS (EI, M+) calcd for
C8H6BrClO (231.9291), found 231.9306.
4-Bromo-2-(bromomethyl)benzaldehyde (1d).15 A solution of
4-bromo-2-(bromomethyl)-benzonitrile (2.0 g, 7.3 mmol) in dry
dichloromethane (25 mL) was purged with argon for 20 min. The
solution was cooled using an ice−water bath, and a 0.1 M solution of
diisobutyl aluminum hydride (DIBAL-H) in hexane (7.5 mL, 7.5
mmol) was added dropwise during 25 min with stirring under argon.
E
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(cyclohexane/Et2O = 5:1); IR (ATR) ν 1600 (CN), 1561, 1486,
1451, 1395, 1322, 1143, 804, 752, 688 cm−1; UV (MeCN) λmax (log ε)
1
382 (4.08), 248 (4.21) nm; H NMR (300 MHz, CDCl3) δ 2.39 (s,
3H, CH3), 4.79 (s, 2H, 1-H), 6.82 (d, 3J (4′-H, 5′-H) = 7.2 Hz, 1H, 4′-
H), 7.08 (dd, J (4′-H, 6′-H) = 1.9 Hz, 3J (5′-H, 6′-H) = 7.9 Hz, 1H,
4
The reaction mixture was allowed to warm slowly to room
temperature (4 h) by removing the ice−water bath. The reaction
mixture was cooled again using an ice−water bath and poured into a
500 mL beaker filled with ice (35 g) and precooled aqueous 6 N HBr
(35 mL). The mixture was vigorously stirred for 1.5 h and then
extracted with dichloromethane (3 × 40 mL). The combined organic
layers were washed with 1N NaHCO3 (2 × 50 mL) and H2O (2 × 50
mL) and dried over MgSO4. Evaporation of the solvents delivered 1d
as a brown liquid in 99% yield (2.0 g, 7.2 mmol): Rf = 0.38
(cyclohexane/EtOAc = 5:1); IR (ATR) ν 1692, 1556, 1202, 1077, 896,
821, 761 cm−1; UV (MeCN) λmax (log ε) 265 (4.14), 221 (4.35) nm;
1H NMR (300 MHz, CDCl3) δ 4.88 (s, 2H, CH2Br), 7.64−7.73 (m,
6′-H), 7.13 (d, 3J (7-H, 8-H) = 7.6 Hz, 1H, 8-H), 7.16−7.20 (m, 2H,
3
3
2′-H, 5-H), 7.24 (dd, J (4′-H, 5′-H) = 7.8 Hz, J (5′-H, 6′-H) = 7.8
Hz, 1H, 5′-H), 7.31 (ddd, 4J (6-H, 8-H) = 0.9 Hz, 3J (5-H, 6-H) = 7.1
3
4
Hz, J (6-H, 7-H) = 7.1 Hz 1H, 6-H), 7.34 (ddd, J (5-H, 7-H) = 1.4
Hz, 3J (6-H, 7-H) = 7.3 Hz, 3J (7-H, 8-H) = 7.3 Hz, 1H, 7-H), 7.45 (s,
1H, 4-H); 13C NMR (75 MHz, CDCl3) δ 21.8 (CH3), 46.2 (C-1),
111.7 (C-6′), 115.6 (C-2′), 122.1 (C-4′), 124.5 (C-5), 125.6 (C-4a),
125.7 (C-8), 128.1 (C-6), 128.8 (C-5′), 129.2 (C-8a), 130.2 (C-7),
136.0 (C-4), 138.8 (C-3′), 147.0 (C-1′); MS (EI, 70 eV) m/z 222
(100) [M]+, 207 (38) [M − CH3]+; HRMS (EI, M+) calcd for
C15H14N2 (222.1157), found 222.1140.
2-(4-Methylphenyl)-1,2-dihydrophthalazine (3c). According to the
general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
3H), 10.20 (s, 1H, CHO); 13C NMR (75 MHz, CDCl3) δ 28.2, 129.0,
131.9, 132.3, 134.7, 134.8, 140.8, 190.8; MS (EI, 70 eV) m/z 277 (8)
[M]+, 222 (8), 197 (24); HRMS (EI, M+) calcd for C8H6Br2O
(275.8785), found 275.8768.
General Procedure for the Synthesis of 2-Aryl-1,2-dihy-
drophthalazines 3. An oven-dried vial was charged with K2CO3
(138 mg, 2 mmol), 2-(bromomethyl)benzaldehydes 1, (99.5 mg, 0.5
mmol), arylhydrazine 214 (0.5 mmol), and FeCl3 (4 mg, 5 mol %)
under argon. After sealing the vial, dry CH3CN (2 mL) was added and
the reaction mixture was stirred at 100 °C (oil bath temperature) until
the aldehyde 1a was consumed. After cooling to room temperature,
the vial was opened and the reaction mixture was poured into water
(40 mL) and extracted with EtOAc (3 × 30 mL). The combined
organic layers were dried over anhydrous Na2SO4 and concentrated in
vacuo. The residue was purified by flash chromatography over silica gel
to afford the product.
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 4-methyl-
phenylhydrazine (2c) (61 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %)
in dry CH3CN (2 mL) was reacted for 22 h. Flash chromatography
over silica gel (cyclohexane/Et2O = 20:1) gave 3c as a pale yellow
solid in 89% yield (99 mg, 0.45 mmol): mp 102−103 °C; Rf = 0.52
(cyclohexane/Et2O = 5:1); IR (ATR) ν 1600 (CN), 1512, 1450,
1394, 1276, 1259, 1138, 903, 7987, 751, 715 cm−1; UV (MeCN) λmax
1
(log ε) 363 (4.04), 249 (4.18) nm; H NMR (300 MHz, CDCl3) δ
2-Phenyl-1,2-dihydrophthalazine (3a).9 According to the general
procedure, a mixture of K2CO3 (138 mg, 0.5 mmol), 2-
2.33 (s, 3H, CH3), 4.78 (s, 2H, 1-H), 7.14 (d, 3J (7-H, 8-H) = 7.0 Hz,
1H, 8-H), 7.16−7.18 (m, 2H, 3′-H, 5′-H), 7.20−7.23 (m, 3H, 2′-H, 5-
H, 6′-H), 7.31 (ddd, 4J (6-H, 8-H) = 1.5 Hz, 3J (5-H, 6-H) = 7.2 Hz, 3J
4
3
(6-H, 7-H) = 7.2 Hz 1H, 6-H), 7.35 (ddd, J (5-H, 7-H) = 1.4 Hz, J
(6-H, 7-H) = 7.1 Hz, 3J (7-H, 8-H) = 7.1 Hz, 1H, 7-H), 7.45 (s, 1H, 4-
H); 13C NMR (75 MHz, CDCl3) δ 20.6 (CH3), 46.4 (C-1), 114.8 (C-
2′, C-6′), 124.5 (C-5), 125.65 (C-4a), 125.70 (C-8), 128.1 (C-6),
129.2 (C-8a), 129.5 (C-3′, C-5′), 130.1 (C-7), 130.6 (C-4′), 135.8 (C-
4), 144.9 (C-1′); MS (EI, 70 eV) m/z (%) 222 (44) [M]+, 207 (3) [M
− CH3]+ 193 (6), 165 (7); HRMS (EI, M+) calcd for C15H14N2
(222.1157), found 222.1144.
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), phenyl-
hydrazine (2a) (54 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %) in dry
CH3CN (2 mL) was reacted for 24 h. Flash chromatography over
silica gel (cyclohexane/Et2O = 20:1) gave 3a as a pale yellow solid in
87% yield (90 mg, 0.43 mmol): mp 137−138 °C (lit.9 mp 136−137
°C); Rf = 0.56 (cyclohexane/Et2O = 5:1); 1H NMR (300 MHz,
2-(2,4-Dimethylphenyl)-1,2-dihydrophthalazine (3d). According
to the general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
4
3
CDCl3) δ 4.82 (s, 2H, 1-H), 7.02 (ddd, J (2′-H, 4′-H) = 1.6 Hz, J
(3′-H, 4′-H) = 7.2 Hz, 3J (4′-H, 5′-H) = 7.2 Hz, 1H, 4′-H), 7.15 (d, 3J
(7-H, 8-H) = 7.3 Hz, 1H, 8-H), 7.21 (brd, 3J (5-H, 6-H) = 6.9 Hz, 1H,
5-H), 7.31−7.35 (m, 3H, 2′-H, 6′-H, 6-H), 7.36−7.40 (m, 3H, 3′-H,
5′-H, 7-H), 7.48 (s, 1H, 4-H); 13C NMR (75 MHz, CDCl3) δ 46.1 (C-
1), 114.6 (C-2′), 121.2 (C-4′), 124.6 (C-5), 125.5 (C-4a), 125.7 (C-
8), 128.1 (C-6), 129.0 (C-3′), 129.1 (C-8a), 130.2 (C-7), 136.1 (C-4),
147.0 (C-1′); MS (EI, 70 eV) m/z (%) 208 (40) [M]+, 180 (3) [M −
N2]+, 143 (5), 129 (6), 104 (40).
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 2,4-
dimethylphenylhydrazine (2d) (68 mg, 0.5 mmol), and FeCl3 (4
mg, 5 mol %) in dry CH3CN (2 mL) was reacted for 23 h. Flash
chromatography over silica gel (cyclohexane/Et2O = 20:1) to give 3d
as a pale yellow oil in 84% yield (99 mg, 0.42 mmol): Rf = 0.52
(cyclohexane/Et2O = 5:1); IR (ATR) ν 1610 (CN), 1452, 1376,
1224, 1110, 904, 808, 757, 729 cm−1; UV (MeCN) λmax (log ε) = 321
2-(3-Methylphenyl)-1,2-dihydrophthalazine (3b). According to
the general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
1
(4.02), 238 nm (4.21); H NMR (300 MHz, CDCl3) δ 2.34 (s, 6H,
CH3), 4.38 (s, 2H, 1-H), 7.07 (brs, 1H, 3′-H), 7.10 (brd, 3J (5′-H, 6′-
H) = 8.0 Hz, 1H, 5′-H), 7.11−7.12 (m, 1H, 8-H), 7.20−7.22 (m, 1H,
5-H), 7.31 (d,3J (5′-Ha, 6′-H) = 7.7 Hz, 1H, 6′-H), 7.34 (ddd, 4J (6-H,
8-H) = 1.7 Hz, 3J (5-H, 6-H) = 7.7 Hz, 3J (6-H, 7-H) = 7.7 Hz, 1H, 6-
3
3
H), 7.36 (ddd, 4J (5-H, 7-H) = 1.7 Hz, J (6-H, 7-H) = 7.6 Hz, J (7-
H, 8-H) = 7.6 Hz 1H, 7-H), 7.59 ppm (brs, 1H, 4-H); 13C NMR (75
MHz, CDCl3) δ 18.0 (C-2″), 20.8 (C-4″), 50.8 (C-1), 122.7 (C-6′),
124.0 (C-5), 125.1 (C-8), 126.1 (C-4a), 127.3 (C-5′) 128.0 (C-6),
130.0 (C-7), 130.4 (C-8a), 131.8 (C-3′), 132.7 (C-2′ or C-4′), 134.8
(C-2′ or C-4′), 138.2 (C-4), 145.7 (C-1′); MS (EI, 70 eV) m/z (%)
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 3-methyl-
phenylhydrazine (2b) (61 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %)
in dry CH3CN (2 mL) was reacted for 24 h. Flash chromatography
over silica gel (cyclohexane/Et2O = 20:1) gave 3b as a pale yellow
solid in 83% yield (92 mg, 0.41 mmol): mp 61−62 °C; Rf = 0.54
F
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The Journal of Organic Chemistry
Article
236 (100) [M]+, 221 (100) [M − CH3]+, 206 (3) [221 − CH3]+;
HRMS (EI, M+) calcd for C16H16N2 (236.1313), found 236.1340.
2-(3,4-Dimethylphenyl)-1,2-dihydrophthalazine (3e). According
to the general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
132 °C (lit.9 mp 132−133 °C); Rf = 0.31 (cyclohexane/Et2O = 5:1);
IR (ATR) ν 1603 (CN), 1506, 1448, 1277, 1225, 1184, 1134, 1034,
816, 754, 717 cm−1; UV (MeCN) λmax (log ε) 366 (4.12), 248 (4.31)
nm; 1H NMR (300 MHz, CDCl3) δ 3.80 (s, 3H, OCH3), 4.74 (s, 2H,
1-H), 6.90−6.94 (m, 2H, 3′-H, 5′-H), 7.13 (d, 3J (7-H, 8-H) = 7.9 Hz,
4
3
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 3,4-
dimethylphenylhydrazine (2e) (68 mg, 0.5 mmol), and FeCl3 (4
mg, 5 mol %) in dry CH3CN (2 mL) was reacted for 23 h. Flash
chromatography over silica gel (cyclohexane/Et2O = 20:1) gave 3e as
a pale yellow solid in 82% yield (97 mg, 0.41 mmol): mp 84−85 °C ;
Rf = 0.36 (cyclohexane/Et2O = 5:1); IR (ATR) ν 1588 (CN), 1499,
1451, 1395, 1380, 1323, 1226, 1142, 1104, 910, 862, 795, 752, 715
1H, 8-H), 7.18 (dd, J (5-H, 7-H) = 1.5 Hz, J (5-H, 6-H) = 7.4 Hz,
1H, 5-H), 7.23−7.26 (m, 2H, 2′-H, 6′-H), 7.31 (ddd, 4J (6-H, 8-H) =
1.4 Hz, 3J (5-H, 6-H) = 7.4 Hz, 3J (6-H, 7-H) = 7.4 Hz 1H, 6-H), 7.34
(ddd, 4J (5-H, 7-H) = 1.4 Hz, 3J (6-H, 7-H) = 7.4 Hz, 3J (7-H, 8-H) =
7.3 Hz, 1H, 7-H), 7.45 (s, 1H, 4-H); 13C NMR (75 MHz, CDCl3) δ
46.9 (C-1), 55.6 (OCH3), 114.3 (C-3′, C-5′), 116.4 (C-2′, C-6′),
124.3 (C-5), 125.64 (C-8), 125.67 (C-4a), 128.1 (C-6), 129.1 (C-8a),
130.0 (C-7), 135.9 (C-4), 141.4 (C-1′), 154.7 (C-4′); MS (EI, 70 eV)
m/z (%) 238 (96) [M]+, 223 (12) [M − CH3]+, 205 (6), 193 (4), 167
(5); HRMS (EI, M+) calcd for C15H14N2O (238.1106), found
238.1117.
1
cm−1; UV (MeCN) λmax (log ε) = 364 (4.08), 248 (4.23) nm; H
NMR (300 MHz, CDCl3) δ 2.28 (s, 3H, 4″-H), 2.35 (s, 3H, 3″-H),
4.86 (s, 2H, 1-H), 7.05 (dd, 4J (2′-H, 6′-H) = 2.7 Hz, 3J (5′-H, 6′-H) =
3
8.3 Hz, 1H, 6′-H), 7.15 (brd, J (7-H, 8-H) = 8.3 Hz, 1H, 8-H), 7.16
(d, 3J (5′-Ha, 6′-H) = 8.3 Hz, 1H 5′-H), 7.20 (dd, 4J (5-H, 7-H) = 1.3
2-(3-Chlorophenyl)-1,2-dihydrophthalazine (3h). According to
the general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
3
Hz, J (5-Ha, 6-H) = 10.0 Hz, 1H, 5-H), 7.21 (brs, 1H, 2′-H), 7.32
(ddd, 4J (6-H, 8-H) = 1.7 Hz, 3J (5-H, 6-H) = 7.3 Hz, 3J (6-H, 7-H) =
4
7.3 Hz, 1H, 6-H), 7.36 (ddd, J (5-H, 7-H) = 1.8 Hz, 3J (6-H, 7-H) =
7.3 Hz, 3J (7-H, 8-H) = 7.3 Hz, 1H, 7-H), 7.48 (s, 1H, 4-H); 13C NMR
(75 MHz, CDCl3) δ 18.9 (C-4″), 20.2 (C-3″), 46.3 (C-1), 112.0 (C-
6′), 116.4 (C-2′), 124.3 (C-5), 125.60 (C-4a), 125.62 (C-8) 128.0 (C-
6), 129.15 (C-8a), 129.30 (C-4′), 129.92 (C-5′), 129.94 (C-7), 135.5
(C-4), 137.1 (C-3′), 145.2 (C-1′); MS (EI, 70 eV) m/z (%) 236 (92)
[M]+, 221 (5) [M − CH3]+, 206 (3) [221 − CH3]+ 192 (4); HRMS
(EI, M+) calcd for C16H16N2 (236.1313), found 236.1304.
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 3-chlorophe-
nylhydrazine (2h) (71 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %) in
dry CH3CN (2 mL) was reacted for 22 h. Flash chromatography over
silica gel (cyclohexane/Et2O = 15:1) gave 3h as a pale yellow solid in
78% yield (95 mg, 0.39 mmol): mp 106−107 °C; Rf = 0.49
(cyclohexane/Et2O = 5:1); IR (ATR) ν 1600 (CN), 1560, 1452,
1390, 1392, 1323, 1275, 1137, 1003, 906, 850, 716 cm−1; UV (MeCN)
λmax (log ε) 356 (4.07), 250 (4.16) nm; 1H NMR (300 MHz, CDCl3)
δ 4.79 (s, 2H, 1-H), 6.94−6.96 (m, 1H, 4′-H), 7.14−7.18 (m, 2H, 6′-
H, 8-H), 7.21 (brd, 3J (5-H, 6-H) = 7.3 Hz 1H, 5-H,), 7.26 (dd, 3J (4′-
H, 5′-H) = 7.3 Hz, 3J (5′-H, 6′-H) = 7.3 Hz, 1H, 5′-H), 7.30−7.34 (m,
2H, 2′-H, 6-H), 7.37 (ddd, 4J (5-H, 7-H) = 1.4 Hz, 3J (6-H, 7-H) = 7.4
2-(4-Isopropylphenyl)-1,2-dihydrophthalazine (3f). According to
the general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
3
Hz, J (7-H, 8-H) = 7.4 Hz, 1H, 7-H), 7.46 (s, 1H, 4-H); 13C NMR
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 3-isopropyl-
phenylhydrazine (2f) (75 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %)
in dry CH3CN (2 mL) was reacted for 22 h. Flash chromatography
over silica gel (cyclohexane/Et2O = 20:1) gave 3f as a pale yellow solid
in 78% yield (98 mg, 0.39 mmol): mp 108−109 °C; Rf = 0.53
(cyclohexane/Et2O = 3:1); IR (ATR) ν 1606 (CN), 1560, 1510,
1451, 1392, 1135, 1110, 829, 805, 755, 718 cm−1; UV (MeCN) λmax
(log ε) = 351 (4.08), 249 (4.25) nm; 1H NMR (300 MHz, CDCl3) δ
(75 MHz, CDCl3) δ 46.0 (C-1), 112.4 (C-6′), 114.6 (C-2′), 120.8 (C-
4′), 124.9 (C-5), 125.2 (C-4a), 125.8 (C-8), 128.3 (C-6), 129.0 (C-
8a), 129.9 (C-5′), 130.5 (C-7), 134.9 (C-3′), 136.7 (C-4), 148.0 (C-
1′); MS (EI, 70 eV) m/z 242 (46) [M]+, 241 (100) [M − 1]+, 206
(4); HRMS (EI, M+) calcd for C14H11ClN2 (242.0611), found
242.0586.
2-(3-Fluorophenyl)-1,2-dihydrophthalazine (3i). According to the
general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
3
1.25 (d, J (1″-H, 2″-H) = 7.0 Hz, 6H, 2″-H), 2.89 (m, 1H, 1″-H),
4.77 (s, 2H, 1-H), 7.12 (d, 3J (7-H, 8-H) = 7.1 Hz, 1H, 8-H), 7.17 (dd,
4J (5-H, 7-H) = 1.4 Hz, 3J (5-H, 6-H) = 7.3 Hz, 1H, 5-H), 7.21−7.25
4
(m, 4H, 2′-H, 3′-H, 5′-H and 6′-H,), 7.29 (ddd, J (6-H, 8-H) = 1.4
3
3
Hz, J (5-H, 6-H) = 7.4 Hz, J (6-H, 7-H) = 7.4 Hz, 1H, 6-H), 7.33
(ddd, 4J (5-H, 7-H) = 1.5 Hz, 3J (6-H, 7-H) = 7.3 Hz, 3J (7-H, 8-H) =
7.3 Hz, 1H, 7-H), 7.44 (s, 1H, 4-H); 13C NMR (75 MHz, CDCl3) δ
24.1 (C-2″), 33.3 (C-1″), 46.3 (C-1), 114.8 (C-2′, C-6′), 124.4 (C-5),
125.6 (C-4a), 125.7 (C-8), 126.9 (C-3′, C-5′), 128.1 (C-6), 129.2 (C-
8a), 130.0 (C-7), 135.7 (C-4), 141.8 (C-4′), 145.1 (C-1′); MS (EI, 70
eV) m/z 250 (88) [M]+, 249 (100) [M − 1]+, 235 (6) [M − CH3]+
205 (6); HRMS (EI, M+) calcd for C17H18N2 (250.1470), found
250.1456.
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 3-fluorophe-
nylhydrazine (2i) (63 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %) in
dry CH3CN (2 mL) was reacted for 24 h. Flash chromatography over
silica gel (cyclohexane/Et2O = 15:1) gave 3i as a pale yellow solid in
69% yield (78 mg, 0.35 mmol): mp 116−117 °C; Rf = 0.46
(cyclohexane/Et2O = 5:1); IR (ATR) ν 1587 (CN), 1563, 1454,
1330, 1224, 1162, 1103, 911, 861, 756, 718 cm−1; UV (MeCN) λmax
2-(4-Methoxyphenyl)-1,2-dihydrophthalazine (3g).9 According to
the general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 4-methox-
yphenylhydrazine (2g) (69 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %)
in dry CH3CN (2 mL) was reacted in a sealed vial at 100 °C for 22 h.
Flash chromatography over silica gel (cyclohexane/Et2O = 15:1) gave
3g as a pale yellow solid in 91% yield (108 mg, 0.45 mmol): mp 131−
1
(log ε) 356 (3.97), 248 (4.11) nm; H NMR (300 MHz, CDCl3) δ
4.79 (s, 2H, 1-H), 6.65−6.70 (m, 1H, 4′-H), 7.01−7.04 (m, 1H, 6′-H),
3
7.05−7.07 (m, 1H, 2′-H), 7.14 (d, J (7-H, 8-H) = 7.4 Hz, 1H, 8-H),
4
3
7.20 (dd, J (5-H, 7-H) = 1.3 Hz, J (5-H, 6-H) = 7.4 Hz 1H, 5-H,),
7.27−7.30 (m, 1H, 5′-H), 7.32 (ddd, 4J (6-H, 8-H) = 1.1 Hz, 3J (5-H,
G
dx.doi.org/10.1021/jo302491x | J. Org. Chem. XXXX, XXX, XXX−XXX

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6-H) = 7.4 Hz, 3J (6-H, 7-H) = 7.4 Hz, 1H, 6-H), 7.37 (ddd, J (5-H,
7-H) = 1.3 Hz, 3J (6-H, 7-H) = 7.4 Hz, 3J (7-H, 8-H) = 7.4 Hz, 1H, 7-
H), 7.46 (s, 1H, 4-H); 13C NMR (75 MHz, CDCl3) δ 46.0 (C-1),
101.9 (d, 2JCF = 26.9 Hz, C-2′), 107.5 (d, 2JCF = 21.9 Hz, C-4′), 109.5
(d, 4JCF = 2.9 Hz, C-6′), 124.9 (C-5), 125.2 (C-4a), 125.8 (C-8), 128.3
(C-6), 129.0 (C-8a), 130.0 (d, 3JCF = 9.8 Hz, C-5′), 130.5 (C-7), 136.5
(C-4), 148.6 (d, 3JCF = 10.8 Hz, C-1′), 163 (d, 1JCF = 163.7 Hz, C-3′);
MS (EI, 70 eV) m/z (%) 226 (26) [M]+, 197 (4), 170 (5), 151 (5);
HRMS (EI, M+) calcd for C14H11FN2 (226.0906), found 226.0891.
2-(4-Cyanophenyl)-1,2-dihydrophthalazine (3j). According to the
general procedure, a mixture of K2CO3 (138 mg, 1 mmol), 2-
(bromomethyl)-3-chlorobenzaldehyde15 (1c) (117 mg, 0.5 mmol),
phenylhydrazine (2a) (54 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %)
in dry CH3CN (2 mL) was reacted for 22 h. Flash chromatography
over silica gel (cyclohexane/Et2O = 5:1) gave 3l as a pale yellow solid
in 70% yield (82 mg, 0.35 mmol): mp 91−92 °C; Rf = 0.26
(cyclohexane/Et2O = 5:1); IR (ATR) ν 1597 (CN), 1545, 1445,
1132, 919, 848, 775, 751 cm−1; UV/vis (MeCN) λmax (log ε) 371
(3.94), 252 (4.13) nm; 1H NMR16 (300 MHz, CDCl3) δ 4.87 (s, 2H,
1-H), 7.02 (d-like, 3J (3′-H, 4′-H) = 7.4 Hz, 1H, 4′-H), 7.03 (d, 3J (5-
H, 6-H) = 8.1 Hz, 1H, 5-H), 7.21 (dd, 3J (5-H, 6-H) = 8.4 Hz, 3J (6-H,
4
3
7-H) = 8.3 Hz 1H, 6-H), 7.32 (d, J (6-H, 7-H) = 8.2 Hz, 1H, 7-H),
7.33 (brd-like, 3J (2′-H, 3′-H) = 8.3 Hz, 2H, 2′-H, 6′-H), 7.34 (s, 1H,
3
4-H), 7.36 (brd-like, J (2′-H, 3′-H) = 8.1 Hz, 2H, 3′-H, 5′-H); 13C
NMR (75 MHz, CDCl3) δ 43.6 (C-1), 114.4 (C-2′, C-6′), 121.4 (C-
4′), 122.8 (C-5), 127.07 (C-8a), 127.14 (C-4a or C-8), 128.97 (C-6),
129.0 (C-3′, C-5′), 130.2 (C-7), 131.6 (C-4a or C-8), 134.1 (C-4),
146.5 (C-1′); MS (EI, 70 eV) m/z (%) 242 (76) [M]+, 179 (8);
HRMS (EI, M+) calcd for C14H11ClN2 (242.0611), found 242.0590.
7-Bromo-2-phenyl-1,2-dihydrophthalazine (3m). According to
the general procedure, a mixture of K2CO3 (138 mg, 0.5 mmol), 4-
(bromomethyl)benzaldehyde (1a) (99.5 mg, 0.5 mmol), 4-cyanophe-
nylhydrazine (2j) (67 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %) in
dry CH3CN (2 mL) was reacted for 27 h. Flash chromatography over
silica gel (cyclohexane/Et2O = 5:1) gave 3j as a white solid in 63%
yield (73 mg, 0.31 mmol): mp 166−167 °C; Rf = 0.14 (cyclohexane/
Et2O = 3:1); IR (ATR) ν 2220 (CN), 1600 (CN), 1507, 1451,
1390, 1317, 1224, 1179, 1137, 1107, 900, 865, 831, 805, 762 cm−1;
UV/vis (MeCN) λmax (log ε) 363 (4.53), 280 (4.11), 244 (1.39) nm;
1H NMR (300 MHz, CDCl3) δ 4.95 (s, 2H, 1-H), 7.30 (d, 3J (7-H, 8-
H) = 7.8 Hz, 1H, 8-H), 7.30−7.38 (m, 2H, 5-H, 6-H), 7.43 (d, 3J (2′-
H, 3′-H) = 8.6 Hz, 2H, 2′-H, 6′-H), 7.45 (d, 3J (2′-H, 3′-H) = 8.2 Hz,
2H, 3′-H, 5′-H), 7.45−7.48 (m, 1H, 7-H), 7.70 (s, 1H, 4-H); 13C
NMR (75 MHz, CDCl3) δ 44.7 (C-1), 101.3 (C-4′), 114.0 (C-2′, 6′-
C), 119.7 (CN), 124.2 (C-4a), 125.4 (C-5), 126.1 (C-8), 128.3 (C-6),
129.2 (C-8a), 131.1 (C-7), 133.2 (C-3′, 5′-H), 138.6 (C-4), 149.5 (C-
1′); MS (EI, 70 eV) m/z (%) 233 (42) [M]+, 205 (6), 177 (5), 151
(5); HRMS (EI, M+) calcd for C15H11N3 (233.0953), found 233.0936.
5-Chloro 2-phenyl-1,2-dihydrophthalazine (3k). According to the
general procedure, a mixture of K2CO3 (138 mg, 0.5 mmol), 2-
bromo-2-(bromomethyl)benzaldehyde15 (1d) (139 mg, 0.5 mmol),
phenylhydrazine (2a) (54 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %)
in dry CH3CN (2 mL) was reacted for 20 h. Flash chromatography
over silica gel (cyclohexane/Et2O = 5:1) gave 3m as a pale yellow solid
in 60% yield (86 mg, 0.30 mmol): mp 116−117 °C; Rf = 0.32
(cyclohexane/Et2O = 5:1); IR (ATR) ν 1597 (CN), 1562, 1387,
1308, 1136, 904, 868, 818, 747, 688 cm−1; UV/vis (MeCN) λmax (log
ε) 370 (4.02), 250 (4.20) nm; H NMR16 (300 MHz, CDCl3) δ 4.77
1
(s, 2H, 1-H), 7.04 (t-like, 3J (3′-H, 4′-H) = 8.7 Hz, 1H, 4′-H), 7.06 (d,
3J (5-H, 6-H) = 8.4 Hz, 1H, 5-H), 7.28 (brd-like, 3J (2′-H, 3′-H) = 8.5
3
Hz, 2H, 2′-H, 6′-H), 7.30 (brs, 1H, 8-H), 7.36 (t-like, J (2′-H, 3′-H)
= 8.5 Hz, 2H, 3′-H, 5′-H), 7.41 (s, 1H, 4-H), 7.42 (dd, 4J (6-H, 8-H) =
3
1.8 Hz, J (5-H, 6-H) = 8.1 Hz, 1H, 6-H); 13C NMR (75 MHz,
CDCl3) δ 45.6 (C-1), 114.7 (C-2′, C-6′), 121.5 (C-4′), 123.8 (C-7),
124.3 (C-4a), 125.9 (C-5), 128.9 (C-8), 129.0 (C-3′, C-5′), 130.8 (C-
8a), 131.3 (C-6), 135.0 (C-4), 146.7 (C-1′); MS (EI, 70 eV) m/z (%)
287 (12) [M]+, 207 (4), 179 (6); HRMS (EI, M+) calcd for
C14H11BrN2 (286.0106), found 286.0090.
(bromomethyl)-6-chlorobenzaldehyde (1b) (117 mg, 0.5 mmol),
phenylhydrazine (2a) (54 mg, 0.5 mmol), and FeCl3 (4 mg, 5 mol %)
in dry CH3CN (2 mL) was reacted for 22 h. Flash chromatography
over silica gel (cyclohexane/Et2O = 5:1) gave 3k as a pale yellow solid
in 74% yield (90 mg, 0.37 mmol): mp 86−87 °C; Rf = 0.24
(cyclohexane/Et2O = 5:1); IR (ATR) ν 1592 (CN), 1497, 1445,
1397, 1313, 1133, 946, 808, 782, 687 cm−1; UV/vis (MeCN) λmax (log
ASSOCIATED CONTENT
* Supporting Information
Copies of NMR spectra for all compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
ε) 370 (4.01), 252 (4.16) nm; H NMR16 (300 MHz, CDCl3) δ 4.75
1
AUTHOR INFORMATION
Corresponding Author
*E-mail: ubeifuss@uni-hohenheim.de.
(s, 2H, 1-H), 6.98 (d, 3J (7-H, 8-H) = 7.5 Hz, 1H, 8-H), 7.01 (t-like, 3J
(3′-H, 4′-H) = 7.1 Hz, 1H, 4′-H), 7.21 (dd, 3J (6-H, 7-H) = 8.1 Hz, 3J
(7-H, 8-H) = 8.1 Hz 1H, 7-H), 7.28 (d, 3J (6-H, 7-H) = 8.5 Hz, 1H, 6-
H), 7.29 (d-like, 3J (2′-H, 3′-H) = 8.7 Hz, 2H, 2′-H, 6′-H), 7.33 (brt-
■
Notes
3
like, J (2′-H, 3′-H) = 8.3 Hz, 2H, 3′-H, 5′-H), 7.81 (s, 4-H); 13C
The authors declare no competing financial interest.
NMR (75 MHz, CDCl3) δ 45.8 (C-1), 114.9 (C-2′, C-6′), 121.7 (C-
4′), 123.0 (C-4a), 124.3 (C-8), 129.0 (C-3′, C-5′), 129.1 (C-6), 130.4
(C-5 or C-8a), 130.7 (C-7),, 130.8 (C-5 or C-8a), 132.3 (C-4), 146.5
(C-1′); MS (EI, 70 eV) m/z (%) 242 (100) [M]+, 202 (4), 179 (8);
HRMS (EI, M+) calcd for C14H11ClN2 (242.0611), found 242.0594.
8-Chloro-2-phenyl-1,2-dihydrophthalazine (3l). According to the
general procedure, a mixture of K2CO3 (138 mg, 0.5 mmol), 2-
ACKNOWLEDGMENTS
We thank Ms. Sabine Mika for recording of NMR spectra and
Dr. Alevtina Baskakova for recording of mass spectra.
■
REFERENCES
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dx.doi.org/10.1021/jo302491x | J. Org. Chem. XXXX, XXX, XXX−XXX