Synthesis of hybrid polycycles containing fused hydroxy benzofuran and 1H-indazoles via a domino cyclization reaction

Article abstract of DOI:10.1039/c9nj01991j

A stoichiometry controlled domino cyclization reaction of hydrazone and p-benzoquinone to an angularly fused 3H-benzofuro[3,2-e]indazole core with an embedded oxygenated dibenzofuran framework under mild reaction conditions is disclosed. The reaction involves palladium catalyzed 5-hydroxy-1H-indazole formation followed by TFA mediated [3+2] annulation between the in situ formed 5-hydroxy-1H-indazole and p-benzoquinone. The developed method is attractive because of the concomitant formation of two heterocyclic rings with consecutive multiple bond forming events that include two C-C, one C-N and one C-O bonds. Spectroscopic and theoretical studies of the blue emissive benzofuroindazole derivatives have also been described.

Full text of DOI:10.1039/c9nj01991j

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Janardhanan, K. James, A. Puthuvakkal, R. P. Bhaskaran, C. H. Suresh, V. K. Praveen, N. Manoj and B. P
Babu, New J. Chem., 2019, DOI: 10.1039/C9NJ01991J.
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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Synthesis of hybrid polycycles containing fused hydroxy
benzofuran and 1H-indazoles via domino cyclization reaction
Received 00th January 20xx,
Accepted 00th January 20xx
Jith C. Janardhanan,a Kiran James,a Anisha Puthuvakkal,b Rasmi P. Bhaskaran,c Cherumuttathu H.
Suresh,b Vakayil K. Praveen,*b Narayanapillai Manoj*a and Beneesh P. Babu*c
DOI: 10.1039/x0xx00000x
Stoichiometry controlled domino cyclization reaction of hydrazone and p-benzoquinone to angularly fused 3H-
benzofuro[3,2-e]indazole core with an embedded oxygenated dibenzofuran framework under mild reaction condition is
disclosed. The reaction involves palladium catalyzed 5-hydroxy-1H-indazole formation followed by TFA mediated [3+2]
annulation between the in situ formed 5-hydroxy-1H-indazole and p-benzoquinone. Developed method is attractive
because of concomitant formation of two heterocyclic rings with consecutive multiple bond forming events that include
two C-C, one C-N and one C-O bonds. The spectroscopic and theoretical studies of the blue emissive benzofuroindazole
derivatives has also been described.
molecules and natural products.4 Their abundance in the
pharmaceuticals necessitate the need in the development of
step-economic, one-pot strategy for the synthesis of fused
Introduction
Development of efficient synthetic routes to construct
complex hybrid molecular scaffolds is a prevalent area of
research in synthetic organic chemistry due to their diverse
biological activities.1 In fact, hybrid molecules contribute
significantly towards the development of polypharmacology.
The hybrid molecular scaffolds, usually a combination of two
or more biologically relevant molecules, exhibit enhanced
performance in their application compared to their individual
counterparts.1b,f Thus the synthesis of polycyclic hybrid
molecules with two or more heterocycles gained much
attention in recent years.2 However, synthesis of hybrid
molecules is always challenging as it demands highly atom and
step-economical protocols with multiple bond formation in
one-pot.3 The strategy will be more appealing if multiple ring
formations occur in a sequential manner during the course of
the reaction rather than the direct coupling of individual
hybrid heterocycles containing oxygen and nitrogen.5
Gamendazole
Methoxsalen
Lonindamine
Bendazac
Psoralen
Benzbromarone
Fig. 1 Representative examples of indazole and benzofuran
components. Nitrogen and oxygen containing heterocycles are containing drug molecules.
the key architectural scaffolds in many potent drug molecules
because of their omnipresent nature in biologically active
Indazole and benzofuran are important class of
heterocyclic compounds having a wide range of biomedical
and pharmaceutical applications (Fig. 1).6,7 In this context, a
hybrid molecule with these two heterocycles - indazole8 and
benzofuran9 - as key components could be of potential
interest. To the best of our knowledge the direct synthesis of
such a hybrid molecule, based on readily available substrates,
is not yet reported. Domino cyclization reactions, with multiple
C-C and C-hetero atom bond formations in one-pot, have
attracted the widespread attention in organic synthesis. The
a.Department of Applied Chemistry, Cochin University of Science and Technology
(CUSAT), Cochin 682022, India. E-mail: manoj.n@cusat.ac.in
b.Chemical Science and Technology Division, CSIR-National Institute for
Interdisciplinary Science and Technology (CSIR-NIIST), Thiruvananthapuram
695019, India. E-mail: vkpraveen@niist.res.in
c. Department of Chemistry, National Institute of Technology Karnataka (NITK),
Surathkal 575025, India. E-mail: pbbeneesh@nitk.edu
†
Electronic Supplementary Information (ESI) available: Additional figures and
tables, copies of NMR spectra and CIF for 3a (CCDC 1850077). See
DOI: 10.1039/x0xx00000x.
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strategy enables to stitch heterocycles of different biological two fractions, the major one being the 5-hydroxy-1H-indazole
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functions in a sequential manner, which left a mark in drug 4a, while the other fraction was identifieDdOaI:s110.,130-3d9i/pCh9eNnJy0l1-939H1J-
developments. The approach is well used for the construction benzofuro[3,2-e]indazol-9-ol 3a (Table 1, entry 2). This
of complex fused heteroaromatic polycycles.10 During the last preliminary result encouraged us to pursue the reaction
decade domino cyclization reaction strategies were screening in detail and the observations are summarized in
successfully employed for the practical synthesis of many Table 1. The compound 3a formed exclusively in 40% yield
molecules of biological relevance.11 Furthermore, one-pot when the hydrazone to p-BQ stoichiometry enhanced to 1:3
bicyclization reactions ensure the bond forming efficiency and (Table 1, entry 4) and further increase in p-BQ did not improve
realize the formation of new rings in a step-economic the conversion (Table 1, entry 5). Interestingly, the
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manner.10
stoichiometry of TFA was also found to be very crucial (Table 1,
Very recently, we have reported an efficient method entry 6 and 7) and maximum product formation observed
towards the synthesis of N-protected 5-hydroxy-1H-indazoles when the TFA stoichiometry is 28 equiv. (7 mmol) (Table 1,
via modified aza-Nenitzsescu reaction (Table 1).12 In this entry 7). However, loading of more Pd(OAc)2 (10 mol%) did not
approach, palladium(II) catalyzed condensation between p- improve the yield (Table 1, entry 8).
benzoquinone (p-BQ) and hydrazone in presence of
trifluoroacetic acid (TFA) afforded 5-hydroxy-1H-indazoles in Table 1 Optimization of the stoichiometry controlled reaction
good to moderate yield. The method is quite versatile as it between hydrazone and p-benzoquinonea
affords biologically relevant 3-substituted 5-hydroxy-1H-
indazoles in one-pot from common reagents such as
hydrazones and p-BQs. Cyclization of phenols across activated
olefins is one of the prominent methods for benzofuran
synthesis and both inter and intramolecular strategies have
well been studied.13 Encouraged by our previous work, we
assumed the possibility for in situ domino annulation of 5-
hydroxy-1H-indazole across p-BQ if excess p-BQ and TFA are Entry Hydrazone,
present in the reaction medium (Table 1). This domino
cyclization will lead to a polycyclic hybrid molecule in one-pot
Yieldb
p-BQ,
2a
(equiv.)
TFA
(equiv.)
1a (equiv.)
Benzofuro-
indazole, 3a
Indazole,
4a
with a fused 1H-indazole and hydroxy benzofuran moieties
1c
2
1
1
1.2
2
14
14
0
69
30
with an embedded dibenzofuran framework. Herein, we
report an efficient method leading towards the synthesis of a
novel polycyclic hybrid molecule containing angularly fused
hydroxy benzofuran and 1H-indazole with an embedded
dibenzofuran framework. Concomitant formation of two
potent heterocycles from common precursors such as
hydrazones and p-BQs is highly noteworthy as the reported
methods for the synthesis of hybrid molecules depend on late
stage coupling of pre-functionalized substrates.14 Furthermore,
in the present case, the reaction involves the formation of two
new C-C, one C-N and one C-O bonds in one-pot under
relatively mild conditions leaving behind a free hydroxyl group
for further fabrication of the 3H-benzofuro[3,2-e]indazole
core. We also report the photophysical properties of some of
the selected benzofuroindazole derivatives.
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Trace
0
0
0
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3
8d
3
aUnless and otherwise stated all reactions were carried out with 1a (0.25
mmol), 2a (1.2-4 equiv.), Pd(OAc)2 (5 mol%) in DCE (0.125 M, 2 mL), TFA (14-
28 equiv.) under N2 at 75 °C for 6 h. bIsolated yields after column
chromatography, cRef. 12. d10 mol% of Pd(OAc)2.
Results and Discussion
Encouraged by our recent report on the synthesis of 5-hydroxy
1H-indazoles12 and in order to expand the synthetic utility of
the reaction, we speculated the possibility to annulate the 1H-
indazoles across olefin so that potent polycyclic hybrid
molecules can be readily accessed. For this, our hypothesis
was to annulate the hydroxyl group of 1H-indazole in situ
across the p-BQ maintaining its concentration excess in the
reaction medium. Keeping this in mind, we commenced our
investigation by performing the reaction under the optimized
condition12 with a change in stoichiometry of the reactants,
hydrazone:p-BQ, as 1:2. Justifying our hypothesis we isolated
We then performed a series of control experiments to
understand the reaction in detail (Scheme 1). Treating the
preformed 5-hydroxy-1H-indazole 4a (1 equiv.) and p-BQ 2a (2
equiv.), in the absence of both Pd(OAc)2 (5 mol%) and TFA (14
equiv.), afforded no product at all. Similar result was observed
when we repeated the reaction with Pd(OAc)2 in the absence
of TFA. However, the expected product, 3a was isolated in 66%
yield when we carried out the reaction in presence of TFA (14
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equiv.) alone without Pd(OAc)2. These experiments proved
that Pd(OAc)2 has a role of catalyzing the first cyclization to investigated the substrate scope and functional group tolerance of
indazole ring and benzofuran ring was formed by TFA this promising annulation reaction with various substrates (Table 2).
mediated [3+2] annulation reaction of 5-hydroxy-1H-indazole, Hydrazones of varying electronic nature smoothly afforded the
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Having established the optimal reaction conditions, we further
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DOI: 10.1039/C9NJ01991J
4a and p-BQ.
benzofuroindazoles in moderate to good yield. It is interesting to
note that a number of acid sensitive functional groups such as –
OMe (3g), –CN (3f), –COOMe (3d) and –CHO (3b) showed good
tolerance to the reaction conditions to afford the hybrid molecule
derivatives with these potent functional groups, which will be quite
useful for a late stage derivatization. In addition to Cl (3j) and Br
(3k), F (3i) as well as CF3 (3c) substituted hydrazones also
successfully afforded the product in moderate yield. Employing p-
nitro derivative of hydrazone in this annulation reaction managed
to yield the polycyclic hybrid molecule (3e) in 48% yield, while β-
naphthaldehyde hydrazone resulted in the similar derivative (3l) in
36%. Similarly, N-bromophenyl hydrazones also smoothly
underwent the reaction to yield respective tetracycles (3m-p) in 47-
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Scheme 1 Control experiment between 5-hydroxy-1H-indazole, 4a and
p-BQ, 2a.
Table 2 Substrate scope of the reactiona
3a (63%)
3a
3b (56%)
3c (51%)
3d (54%)
3h (42%)
3e (48%)
3f (46%)
3g(45%)
3i (53%)
3k (48%)
3m (49%)
3l (36%)
3j (44%)
3n (52%)
3o (47%)
3p (50%)
a Standard reaction condition: 1a-p (0.25 mmol), 2a (0.75 mmol), Pd(OAc)2 (5 mol%), DCE (0.125 M, 2 mL) TFA (28 equiv., 7 mmol), under N2 at 75 °C
for 6 h.
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52% yield. Even though the isolated yields of the reaction were bromo p-benzoquinone and 2,6-dichloro p-benzoquinone have
moderate to good, it is quite noteworthy that the strategy readily been tested in this two-step annulation reaction. With 2-chloro
gives access to a complex polycyclic hybrid molecule via multiple benzoquinone the reaction proceeded up to the indazole level
bond formation in one-pot and most importantly starting from (36%) and the reaction with 2-bromo p-benzoquinone yielded the
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DOI: 10.1039/C9NJ01991J
readily available precursors, the hydrazones and p-BQs.
corresponding indazole in trace (confirmed by HRMS†). However,
attempts to isolate the pure product was not successful due to the
complex reaction mixture. But 2,6-dichloro p-benzoquinone did not
afford any product (Table 3). We attributed the poor reactivity of
substituted quinones to steric and electronic effects.
After exploring the versatility of the method towards a number
of hydrazones with different electronic and steric nature, we next
investigated the scope of different p-BQ derivatives. With 2-methyl
p-benzoquinone, the expected benzofuroindazole derivatives were
isolated in good yields. 2,6-dimethyl p-benzoquinone could afford
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Interestingly, when a preformed indazole 4a was treated with 2-
only the indazole (4d) derivative, which failed to annulate further in chloro p-benzoquinone 2c in presence of TFA, the annulation
presence of TFA. In contrast, 2,5-dimethyl and 2,6-dimethoxy proceeded smoothly to afford the expected polycycle in 29% yield
derivatives completely failed in the reaction, neither the indazole as a white solid (Scheme 2). In order to ascertain the synthetic
nor the fused polycycle were formed. Subsequently, we turned our utility of the new method, we carried out the reaction with 1 g of 1a
attention towards haloquinones. 2-chloro p-benzoquinone, 2- (5.15 mmol) under the optimized conditions and the corresponding
Table 3 Substrate scope of the reaction with substituted p-benzoquinonesa
Hydrazone
p-benzoquinone
Benzofuroindazole
Indazole
R = H (3q: 69%)
R = CF3 (3r: 56%)
R = Cl (3s: 48%)
R = H (1a)
R = CF3 (1c)
R = Cl (1j)
(2b)
R = Cl (4b: 36%)
R = Br (4c: Trace)
1a
R = Cl (2c),
Br (2d)
bNF
(4d: 62%)
1a
1a
NF
(2e)
(2f)
cNR
NR
NR
1a
1a
(2g)
(2h)
a Standard reaction condition: 1 (0.25 mmol), 2b - h (0.75 mmol), Pd(OAc)2 (5 mol%), DCE (0.125 M, 2 mL) TFA (28 equiv., 7 mmol), under N2 at 75 °C for 6
h. bNot formed, cNo reaction.
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benzofuroindazole 3a was isolated in 46% yield after column 342 nm) and fluorescence emission with maxima VriaewngAirtnicglefOrnolimne
DOI: 10.1039/C9NJ01991J
chromatography.
392-445 nm (Figure 2). The longer wavelength absorption
bands except in 3b can be assigned to the π-π* transitions
centered on benzofuroindazole moiety. In the case of 3b, the
lower energy absorption band can be attributed to the
intramolecular charge transfer (CT) transitions from
benzofuroindazole moiety to formyl group attached C3-phenyl
ring. From the emission spectra, it is clear that substituents at
C3-phenyl ring did not have a significant effect on the spectral
characteristics of benzofuroindazole derivatives except when it
is having a formyl group. In the latter case it resulted in a red
shift of 53 nm in the emission maximum (λem = 445 nm)
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4a
2c
3t (29%)
Scheme 2 Reaction between 4a and 2c.
compared
to
the
unsubstituted
1,3-diphenyl-3H-
benzofuro[3,2-e]indazo-9-ol 3a
(
λem = 392 nm), which can be
correlated to a D-A characteristics in the molecule owing to
the presence of formyl group. The fluorescence quantum yield
of 3a-n were measured by comparative method16 using
quinine sulfate in 0.1 M H2SO4 as the quantum yield standard
On the basis of control experiments a plausible mechanism for
the formation of 3H-benzofuro[3,2-e]indazole is proposed (Scheme
3). The first step involves the aza-Nenitzescu reaction and we
recently reported a modified, Pd(II) catalyzed protocol for this
reaction in which 5-hydroxy-1H-indazole is obtained from
hydrazone and p-BQ in presence of TFA.12 The proposed mechanism
for the formation of hydroxy indazole IV, first involves the addition
of hydrazone to p-BQ to generate a hydroquinone adduct I. This
adduct subsequently oxidized by Pd(II) to quinone intermediate II
followed by an intramolecular cyclization to afford a carbinolamine
intermediate III. Reduction of the carbinolamine intermediate III to
hydroxy indazole helps to regenerate Pd(II) in the catalytic cycle.15
This in situ generated hydroxy indazole IV from step 1, subsequently
participate in a [3+2] annulation reaction13a with excess p-BQ in
presence of TFA to afford the final product. The benzofuran
annulation reaction initiates with the formation of oxacarbenium
ion by the activation of p-BQ by TFA. Nucleophilic addition of 5-
hydroxy-1H-indazole to this oxacarbenium intermediate proceed
selectively through C4 carbon of indazole to form the adduct V.
Intramolecular cyclization of compound V followed by dehydration
readily afford 1,3-diphenyl-3H-benzofuro[3,2-e]indazol-9-ol 3a.
(
ΦF = 0.54). Most of the compounds showed quantum yield
values in the range of 0.11 to 0.29 except 3b ΦF = 0.02), 3m
ΦF = 0.07) and 3n ΦF = 0.07) having high non-radiative decay
rate constants (Table S1 ). Time resolved fluorescence decay
(
(
(
†
of compounds 3a-n were measured by time-correlated single
photon counting method using an excitation wavelength of
340 nm (Fig. S1
†) and the obtained lifetime values are
summarized in Table S1
†
.
Fig. 2 The absorption (a) and photoluminescence (b) spectra of 3a-n
CHCl3. All the studies were carried out at a concentration of 1 x 10-5
M.
In order to get insight into ground state geometry, energy and
nature of frontier molecular orbital (FMO) of benzofuroindazole
based fluorophores, density functional theory (DFT) of
representative derivatives (3a, 3b and 3g) was carried out using
Gaussian 09 program.17 The ground state geometries were
optimized in gas phase at B3LYP level theory in conjunction with 6-
311+g(d,p) basis set. In the case of model derivative 3a the MO
coefficient of density in highest occupied molecular orbital (HOMO)
was distributed over 3H-benzofuro[3,2-e]indazole with a lesser
extent of distribution over C3-phenyl ring compared to the N-phenyl
ring. In compound 3g, due to the presence of an electron donating
methoxy group, C3-phenyl ring also exhibited a small but sufficient
distribution of MO coefficient density in HOMO. In the case of
compounds 3a and 3g, the MO coefficient of density of LUMO was
distributed over benzofuran and indazole framework. Since MO
coefficient density of HOMO and LUMO was distributed throughout
the entire molecule, these molecules lack ICT characteristics. On the
other hand, in the presence of formyl group at C3-phenyl ring, the
Scheme 3 Plausible mechanism for the formation of 3H-benzofuro[3,2-
e]indazole.
The synthesized benzofuroindazole derivatives are found
to be fluorescent in the solution state. In chloroform, all
compounds showed absorption maxima around 340 nm (339-
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situation is changed. The coefficient density of LUMO of D-A type
molecule 3b was shifted from benzofuran fused indazole
frameworks and mainly localized over formyl group substituted C3-
phenyl ring (Figure 3). To calculate the electronic transitions and
the respective absorption spectra, time-dependent DFT (TD-DFT)
calculations were carried out with electronically optimized ground
state structures in solution state employing polarizable continuum
(PCM) model applying self-consistent reaction field (SCRF) in CHCl3.
The PBE1PBE functional gave a comparable correlation with the
experimentally observed UV/Vis absorption spectral bands. From
economical method towards a new class of polycyclic hybrid
molecule that contains an angularly fused hydroxy benzofuran
and indazole can open up further promising chemistry.
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Experimental
General Remarks
Unless and otherwise stated all reactions were carried out in
Schlenk tube under nitrogen atmosphere. All the reagents
including catalysts were brought from commercial suppliers
and used as such without additional purification. All the
solvents were dried by standard methods and distilled prior to
use. The crude reaction mixture was purified with silica gel (60-
120 mesh) column chromatography using hexane-ethyl
acetate solvent mixture as eluent. Isolated compounds were
characterized by 1H and 13C NMR spectroscopy, infrared
spectroscopy and high-resolution mass spectrometry (HRMS).
Melting points were determined using calibrated digital
melting point apparatus (Stuart melting point apparatus
SMP30). Infrared spectra were recorded on JASCO FTIR-4100
using KBr pellet and only intense peaks were reported. 1H NMR
(400 and 500 MHz) and 13C NMR (100 and 125 MHz) spectra
were recorded in CDCl3, DMSO-d6 and Acetone-d6 on Bruker
Avance III 400 MHz, Bruker AMX 500 spectrophotometer with
tetramethylsilane (TMS; H = 0 ppm) as internal standard and
chemical shifts were reported in ppm relative to TMS. HRMS
were recorded on Thermo Scientific Exactive mass
spectrometer using ESI method with orbitrap mass analyzer.
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TD-DFT results (Table S2 and Fig. S2†) it is undoubtedly confirmed
that transitions from ground state (S0) to first excited state (S1)
having a substantial contribution from H → L transition and is
responsible for the appearance lowest energy band in the
absorption spectrum of these molecules. In the case of 3b, a
transition corresponding H → L + 1 is also found to contribute in the
absorption spectrum (Table S2 and Fig. S2†).
General procedure for the synthesis of hydrazones:
Hydrazones were synthesized according to
a reported
procedure.18 To a stirred solution of phenyl hydrazine (1
equiv.) in methanol at room temperature, the corresponding
aldehyde (1 equiv.) was added (liquid aldehydes were added
dropwise while solid aldehydes in small portions) and the
stirring was continued (2-16 h depending on the electronic
nature of the aldehyde). After the completion of reaction, the
hydrazone was precipitated with ice-cold water and filtered.
The precipitate obtained was dissolved in dichloromethane,
dried over anhydrous Na2SO4 and evaporated under reduced
pressure. The product thus obtained was dried in the vacuum
oven and used without any further purification.
Fig. 3 Calculated molecular orbitals (HOMO and LUMO) and energy
levels of benzofuroindazole derivatives 3a, 3b and 3g.
Conclusions
General procedure for the synthesis of 1,3-diphenyl-3H-
In conclusion, a versatile approach towards the synthesis of a
new skeletally diverse angular polycyclic hybrid heterocycle
with embedded oxygenated dibenzofuran framework having
fused hydroxy benzofuran and indazole unit has been
demonstrated. The developed method is operationally simple,
works under relatively mild conditions and proceeds via
sequential one-pot strategy. Furthermore, the method is
highly step-economical constructing four new bonds in one-
pot and the starting materials are easily available and cheap.
The reaction showed excellent functional group tolerance so
that number of derivatives with free potent functional groups
has been synthesized and it offers possibility for further
benzofuro[3,2-e]indazol-9-ol: To
a
stirred solution of
hydrazone (0.25 mmol; 1 equiv.), p-BQ (0.75 mmol; 3 equiv.)
and Pd(OAc)2 (0.0125 mmol; 0.05 equiv.) in dry DCE (0.125 M,
2
mL) in an oven dried Schlenk tube under nitrogen
atmosphere, TFA (7 mmol, 28 equiv.) was added and the
mixture was heated at 75 °C under nitrogen atmosphere for 6
h. Then the reaction mixture was cooled to room temperature,
diluted with ethyl acetate and filtered through a Celite pad.
The filtrate is neutralized with saturated NaHCO3 solution. The
organic layer was then extracted with ethyl acetate. The
combined organic layer was finally washed with brine solution,
dried over anhydrous Na2SO4 and evaporated under reduced
pressure. The residue was then subjected to silica gel column
chromatography using hexane and ethyl acetate as eluent.
chemistry. The -extended hybrid heterocycles are found to be
fluorescent and their spectral characteristics were evaluated
with the help of theoretical support. This highly atom and step
6 | New. J. Chem., 2019, 00, 1-3
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Characterization of 1,3-diphenyl-3H-benzofuro[3,2-e]indazol-
9-ol derivatives.
167.3, 154.2, 154.1, 151.4, 146.1, 140.8, 140.1, 138.6, 131.4,
View Article Online
131.2 (2C), 130.5 (2C), 130.3 (2C), 128.D3O, I1: 1204.1.0439(2/CC9)N, J1011979.18J,
116.5, 116.3, 115.8, 113.9, 112.6, 111.1, 110.3, 52.6 ppm; FT-
1,3-diphenyl-3H-benzofuro[3,2-e]indazol-9-ol (3a): Following
the general procedure, reaction of 1-benzylidene-2-
phenylhydrazine 1a (0.25 mmol, 49 mg) with p-BQ 2a (0.75
mmol, 81 mg) afforded the desired product 3a (59.5 mg) as an
IR (KBr): 
max = 3408, 1701, 1595, 1496, 1286, 1192, 1124 cm-1;
HRMS (ESI) calcd. for C27H19N2O4 [M+H]+ 435.1339 found
435.1351.
1
off-white solid in 63% yield; m.p. 203-205 °C; H NMR (400
1-(4-nitrophenyl)-3-phenyl-3H-benzofuro[3,2-e]indazol-9-ol
(3e): Following the general procedure, reaction of 1-(4-
nitrobenzylidene)-2-phenylhydrazine 1e (0.25 mmol, 60.3 mg)
with p-BQ 2a (0.75 mmol, 81mg) yielded the desired product
3e (50.6 mg) in 48% yield as a yellow solid; m.p. 270-272 °C; 1H
MHz, CDCl3, TMS): = 7.83-7.77 (m, 5H), 7.68 (d, J = 9.2 Hz

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1H), 7.58-7.54 (m, 5H), 7.43 (t, J = 8 Hz, 2H), 6.90 (dd, J = 8.8,
2.4 Hz, 1H), 6.19 (d, J = 2.8 Hz, 1H), 4.74 (s, 1H) ppm; 13C NMR
(100 MHz, CDCl3):
 = 153.2, 151.3, 151.0, 146.5, 139.9, 137.4,
134.6, 130.6 (2C), 129.5 (2C), 128.8, 128.4 (2C), 127.2, 124.2,
123.7 (2C), 117.7, 115.2, 114.8, 112.8, 111.8, 109.9, 109.6
ppm; FT-IR (KBr): max = 3419, 1592, 1496, 1350, 1198, 1134
cm-1; HRMS (ESI) calcd. for C25H17N2O2 [M+H]+ 377.1285 found
377.1295.
NMR (400 MHz, Acetone-d6, TMS):
 = 8.40 (d, J = 8.4 Hz, 2H),
8.37 (s, 1H), 7.98 (d, J= 8.8 Hz, 2H), 7.89-7.86 (m, 1H), 7.79-
7.72 (m, 3H), 7.55 (t, J = 7.5 Hz, 2H), 7.43-7.38 (m, 2H), 6.89
(dd, J = 8.8, 2.4 Hz, 1H), 6.40 (d, J = 2.4 Hz, 1H) ppm; 13C NMR
4-(9-hydroxy-3-phenyl-3H-benzofuro[3,2-e]indazol-1-
yl)benzaldehyde (3b): Following the general procedure,
reaction of 4-((2-phenylhydrazono)methyl)benzaldehyde 1b
(0.25 mmol, 56 mg) with p-BQ 2a (0.75 mmol, 81 mg) afforded
the desired product 3b (56.6 mg) as a white solid in 56% yield;
(100 MHz, Acetone-d6):
 = 154.3, 154.1, 151.5, 149.1, 145.0,
142.0, 140.6, 138.7, 132.0 (2C), 130.6 (2C), 128.5, 124.7, 124.6
(2C), 124.5 (2C), 117.7, 116.5, 115.6, 114.2, 112.8, 111.2, 110.0
ppm; FT-IR (KBr): max = 3418, 1627, 1509, 1454, 1342, 1175
cm-1; HRMS (ESI) calcd. for C25H16N3O4 [M+H]+ 422.1135 found
422.1145.
m.p. 240-242 °C; 1H NMR (500 MHz, Acetone-d6, TMS):
 =
10.23 (s, 1H), 8.19 (d, J = 8.5 Hz, 2H), 8.11 (s, 1H), 8.05 (d, J = 8
Hz, 2H), 7.98 (d, J = 9 Hz, 1H), 7.90 (d, J = 7.5 Hz, 2H), 7.83 (d, J
= 9.5 Hz, 1H), 7.67 (t, J = 8 Hz, 2H), 7.54-7.49 (m, 2H), 7.01 (dd,
J = 8.7, 2.2 Hz, 1H), 6.57 (d, J = 2.5 Hz, 1H) ppm; 13C NMR (125
4-(9-hydroxy-3-phenyl-3H-benzofuro[3,2-e]indazol-1-
yl)benzonitrile (3f): Following the general procedure, reaction
of 4-((2-phenylhydrazono)methyl)benzonitrile 1f (0.25 mmol,
55.3 mg) with p-BQ 2a (0.75 mmol, 81 mg) afforded the
desired product 3f (46.2 mg) in 46% yield as an white solid;
MHz, Acetone-d6):  = 191.9, 153.3, 152.9, 150.6, 145.0, 140.3,
139.9, 137.7, 136.9, 130.8 (2C), 129.6, 129.5, 127.4, 123.9,
123.5 (2C), 116.9, 115.4, 115.3, 114.8, 113.0, 111.8, 110.2,
109.4, 109.3 ppm; FT-IR (KBr): max = 3407, 2859, 1689, 1595,
1499, 1345, 1169 1139 cm-1; HRMS (ESI) calcd. for C26H17N2O3
[M+H]+ 405.1234 found 405.1237.
3-phenyl-1-(4-(trifluoromethyl)phenyl)-3H-benzofuro[3,2-
e]indazol-9-ol (3c): Following the general procedure, reaction
of 1-phenyl-2-(4-(trifluoromethyl)benzylidene)hydrazine 1c
(0.25 mmol, 66 mg) with p-BQ 2a (0.75 mmol, 81 mg) afforded
the desired product 3c (56.7 mg) in 51% yield as weightless
white compound; m.p. 261-263 °C; 1H NMR (500 MHz,
m.p. 306-308 °C; 1H NMR (500 MHz, Acetone-d6, TMS):
 = 8.52
(s, 1H), 7.96-7.90 (m, 4H), 7.87 (d, J = 8 Hz, 1H), 7.79-7.76 (m,
2H), 7.73 (d, J = 8 Hz, 1H), 7.56 (t, J = 8 Hz, 2H), 7.41 (d, J = 8
Hz, 2H), 6.90 (dd, J = 8, 4 Hz, 1H), 6.39 (d, J = 2.4, 1H) ppm; 13C
NMR (125 MHz, Acetone-d6):
 = 154.2, 154.1, 151.4, 145.4,
140.6, 140.1, 138.6, 133.2 (2C), 131.8 (2C), 130.6 (2C), 128.5,
124.7 (2C), 124.5, 119.5, 117.7, 116.4, 115.6, 114.1, 113.3,
112.7, 111.2, 110.1 ppm; FT-IR (KBr): max = 3396, 2234, 1591,
1501, 1348, 1188, 1132 cm-1; HRMS (ESI) calcd. for C26H16N3O2
[M+H]+ 402.1237 found 402.1252.
1-(4-methoxyphenyl)-3-phenyl-3H-benzofuro[3,2-e]indazol-9-
ol (3g): Following the general procedure, reaction of 1-(4-
methoxybenzylidene)-2-phenylhydrazine 1g (0.25 mmol, 56.5
mg) with p-BQ 2a (0.75 mmol, 81 mg) afforded the desired
Acetone-d6, TMS):
 = 8.24 (s, 1H), 8.07 (d, J = 8Hz, 2H), 8.00
(d, J = 9 Hz, 3H), 7.91 (dd, J = 8.7, 1.2 Hz, 2H), 7.84 (d, J = 9.5
Hz, 1H), 7.70 (t, J = 8Hz, 2H), 7.54-7.50 (m, 2H), 7.03 (dd, J =
8.5, 2.5 Hz, 1H), 6.51 (d, J = 2.5 Hz, 1H) ppm; 13C NMR (125
product 3g (47.5 mg) as a white solid in 45% yield; m.p. 218-
MHz, Acetone-d6):  = 153.3, 153.1, 150.6, 144.7, 139.8, 138.6,
1
220 °C; H NMR (400 MHz, Acetone-d6, TMS):
 = 8.46 (s, 1H),
137.7, 130.8 (2C), 130.3, 129.6 (2C), 127.4, 125.3 (q)(-CF3),
123.9 123.5, 116.9 (2C), 115.4, 115.3, 114.8, 113.0, 111.7,
110.2, 109.5, 109.4 ppm; FT-IR (KBr): max = 3414, 1616, 1499,
1406, 1329, 1171, 1110 cm-1; HRMS (ESI) calcd. for
C26H16F3N2O2 [M+H]+ 445.1158 found 445.1165.
7.79 (d, J = 9.2 Hz, 1H), 7.73 (dd, J = 8.2, 1 Hz, 2H), 7.63 (d, J =
9.2 Hz, 1H), 7.56 (dd, J = 6.8, 2 Hz, 2H), 7.50 (t, J = 8 Hz, 2H),
7.33-7.30 (m, 2H), 7.04 (dd, J =6.6, 1.8 Hz, 2H), 6.87 (dd, J =
8.8, 2.4 Hz, 1H), 6.41 (d, J = 2.8 Hz, 1H), 3.80 (s, 3H) ppm; 13C
NMR (100 MHz, Acetone-d6):
 = 161.3, 154.0, 153.9, 151.4,
Methyl-4-(9-hydroxy-3-phenyl-3H-benzofuro[3,2-e]indazol-1-
yl)benzoate (3d): Following the general procedure, reaction of
methyl 4-((2-phenylhydrazono)methyl)benzoate 1d (0.25
mmol, 63.5 mg) with p-BQ 2a (0.75 mmol, 81 mg) afforded the
desired product 3d (58.6 mg) as an off-white solid in 54% yield;
147.1, 141.0, 138.2, 132.3 (2C), 130.4 (2C), 127.9, 127.6, 125.0
(2C), 124.1, 118.4, 116.2 (2C), 116.1, 114.7, 113.6, 112.3,
110.8, 110.6, 55.8 ppm; FT-IR (KBr): max = 3419, 1615, 1500,
1350, 1233,1183, 1132 cm-1; HRMS (ESI) calcd. for C26H19N2O3
[M+H]+ 407.1390 found 407.1399.
m.p. 230-232 °C; 1H NMR (400 MHz, Acetone-d6, TMS):
 =
3-phenyl-1-(p-tolyl)-3H-benzofuro[3,2-e]indazol-9-ol
(3h):
8.38 (s, 1H), 8.15 (d, J = 8 Hz, 2H), 7.87-7.83 (m, 3H), 7.77 (d, J
= 7.6 Hz, 2H), 7.71 (d, J = 9.2 Hz, 1H), 7.54 (t, J = 8 Hz, 2H), 7.38
(d, J = 8.4 Hz, 2H), 6.88 (dd, J = 9, 2.6 Hz, 1H), 6.42 (d, J = 2.8
Following the general procedure, reaction of 1-(4-
methylbenzylidene)-2-phenylhydrazine 1h (0.25 mmol, 52.6
mg) with p-BQ 2a (0.75 mmol, 81 mg) afforded the desired
product 3h (41mg) in 42% yield as an off-white solid; m.p. 204-
Hz, 1H), 3.85 (s, 3H) ppm; 13C NMR (100 MHz, Acetone-d6):
 =
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206 °C; H NMR (500 MHz, Acetone-d6, TMS):

= 8.06 (s, 1H), 61.5 mg) with p-BQ 2a (0.75 mmol, 81 mg) afforded the
View Article Online
DOI: 10.1039/C9NJ01991J
7.95 (d, J = 9.5 Hz, 1H), 7.88 (d, J = 7.5 Hz, 2H), 7.77 (d, J = 9 Hz, desired product 3l (38.4 mg) as light pink colored solid in 36%
1H), 7.68 (d, J = 8 Hz, 2H), 7.64 (t, J = 7.7 Hz, 2H), 7.49-7.46 (m, yield; m.p. 201-203 °C; 1H NMR (500 MHz, Acetone-d6, TMS):
2H), 7.44 (d, J = 7.5 Hz, 2H), 6.99 (dd, J = 8.7, 2.2, 1H), 6.54 (d, J = 8.37 (s, 1H), 8.15 (d, J = 8.5 Hz, 1H), 8.07 (d, J = 8 Hz, 1H),
= 2.5 Hz, 1H), 2.51 (s, 3H) ppm; 13C NMR (125 MHz, Acetone- 8.04-7.96 (m, 4H), 7.93 (d, J = 8 Hz, 2H), 7.84 (d, J = 9 Hz, 1H),

d6):
131.9, 131.3 (2C), 130.7 (2C), 128.8 (2C), 125.0, 119.3, 117.0 6.97 (d, J = 8.5 Hz, 1H), 6.67 (s, 1H) ppm; 13C NMR (125 MHz,
(2C), 116.9, 114.4, 113.2, 111.8, 111.7, 111.6, 22.4 ppm; FT-IR Acetone-d6): = 155.1, 154.7, 152.4, 148.0, 141.9, 139.5,
 = 154.8, 154.7, 154.6, 152.4, 148.2, 141.9, 140.4, 139.2, 7.67 (t, J = 7.7 Hz, 2H), 7.64-7.60 (m, 2H), 7.52-7.48 (m, 2H),

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(KBr): max = 3419, 1594, 1500, 1347, 1193, 1142 cm-1; HRMS 135.4, 135.0, 133.8, 131.4 (2C), 131.1, 130.1 (2C), 129.8, 129.6,
(ESI) calcd. for C26H19N2O2 [M+H]+ 391.1441 found 391.1455.
1-(4-fluorophenyl)-3-phenyl-3H-benzofuro[3,2-e]indazol-9-ol
(3i): Following the general procedure, reaction of 1-(4- 1502, 1352, 1172, 1134 cm-1; HRMS (ESI) calcd. for C29H19N2O2
fluorobenzylidene)-2-phenylhydrazine 1i (0.25 mmol, 53.5 mg) [M+H]+ 427.1441 found 427.1461.
with p-BQ 2a (0.75 mmol, 81 mg) afforded the desired product 3-(4-bromophenyl)-1-phenyl-3H-benzofuro[3,2-e]indazol-9-ol
3i (52.3 mg) in 53% as an weightless white solid; m.p. 262-264 (3m): Following the general procedure, reaction of 1-
°C; H NMR (500 MHz, Acetone-d6, TMS):
(d, J = 9 Hz, 1H), 7.89 (dd, J = 8.5, 1 Hz, 2H), 7.86-7.81 (m, 3H), mg) with p-BQ 2a (0.75 mmol, 81 mg) afforded the desired
7.66 (t, J = 8Hz, 2H), 7.52-7.48 (m, 2H), 7.41 (t, J = 9 Hz, 2H), product 3m (55.7 mg) as an off-white solid in 49% yield; m.p.
7.01 (dd, J = 8.7, 2.7 Hz, 1H), 6.50 (d, J = 2.5 Hz, 1H) ppm; 13C 206-208 °C; H NMR (500 MHz, Acetone-d6, TMS):
NMR (125 MHz, Acetone-d6):
153.1, 150.6, 145.3, 140.0, 137.4, 132.2, 132.1, 131.0, 130.9 (m, 5H), 7.63-7.62 (m, 3H), 7.48 (d, J = 9 Hz, 1H), 7.00 (dd, J =
(2C), 129.6, 127.2, 124.0 (2C), 123.3, 117.3, 115.3, 115.2, 8.7, 2.2 Hz, 1H), 6.44 (d, J = 2.5 Hz, 1H) ppm; 13C NMR (125
129.0, 128.4, 128.3, 126.0 (2C), 125.2, 119.0, 117.1, 117.0,
114.6, 113.3, 111.9, 111.5 ppm; FT-IR (KBr): max = 3330, 1594,
1
 = 8.32 (s, 1H), 7.98 benzylidene-2-(4-bromophenyl)hydrazine 1m (0.25 mmol, 68.5
1
 = 8.13 (s,
 = 163.4 (C-F, J = 244 Hz), 153.2, 1H), 7.96 (dd, J = 8.7, 2.2 Hz, 1H), 7.86-7.84 (m, 2H), 7.81-7.77
115.0, 112.8, 111.6, 110.1, 109.3 ppm; FT-IR (KBr): max = 3409, MHz, Acetone-d6):  = 153.1, 150.6, 146.8, 139.3, 137.2, 134.4,
1594, 1501, 1345, 1177, 1142 cm-1; HRMS (ESI) calcd. for 132.6 (2C), 130.2 (2C), 129.0, 128.3 (2C), 124.9 (2C), 124.0,
C25H16FN2O2 [M+H]+ 395. 1190 found 395.1198.
119.7, 117.6, 115.4, 115.3, 112.9, 111.5, 109.9, 109.7, 109.6
ppm; FT-IR (KBr): max = 3384, 1585, 1492, 1344, 1179 cm-1;
1-(4-chlorophenyl)-3-phenyl-3H-benzofuro[3,2-e]indazol-9-ol
(3j): Following the general procedure, the reaction of 1-(4- HRMS (ESI) calcd. for C25H16BrN2O2 [M+H]+ 455.0390 found
chlorobenzylidene)-2-phenylhydrazine 1j (0.25 mmol, 57.5mg) 455.0404.
with p-BQ 2a (0.75 mmol, 81 mg) afforded the desired product 3-(4-bromophenyl)-1-(4-fluorophenyl)-3H-benzofuro[3,2-
3j (45.1 mg) in 44% yield as an ivory white solid; m.p. 237-239 e]indazol-9-ol (3n): Following the general procedure, reaction
1
°C; H NMR (500 MHz, Acetone-d6, TMS):
 = 8.34 (s, 1H), 7.99 of 1-(4-bromophenyl)-2-(4-fluorobenzylidene)hydrazine 1n
(d, J = 9Hz, 1H), 7.90 (dd, J = 8.7, 1.2 Hz, 2H), 7.86-7.82 (m, 3H), (0.25 mmol, 73.3 mg) with p-BQ 2a (0.75 mmol, 81 mg)
7.69-7.65 (m, 4H), 7.53-7.49 (m, 2H), 7.02 (dd, J = 9, 2.5 Hz, afforded the desired product 3n (61.4 mg) as an off-white solid
1H), 6.61 (d, J = 2.5 Hz, 1H) ppm; 13C NMR (125 MHz, Acetone- in 52% yield; m.p. 241-243 °C; H NMR (500 MHz, Acetone-d6,
1
d6):
 = 153.2, 153.1, 150.6, 145.0, 139.9, 137.6, 134.5, 133.4, TMS):  = 8.22 (s, 1H), 7.98 (d, J = 9.5 Hz, 1H), 7.87-7.84 (m,
131.7 (2C), 129.6 (2C), 128.5 (2C), 127.3, 124.0, 123.4 (2C), 3H), 7.82-7.80 (m, 4H), 7.51 (d, J = 9 Hz, 1H), 7.40 (t, J = 8.7 Hz,
117.0, 115.4, 114.9, 112.9, 111.7, 110.1, 109.4 ppm; FT-IR 2H), 7.01 (dd, J = 8.7, 2.2 Hz, 1H), 6.48 (d, J = 2.5 Hz, 1H) ppm;
(KBr): max = 3410, 1592, 1497, 1344, 1186, 1134 cm-1; HRMS 13C NMR (125 MHz, Acetone-d6):
(ESI) calcd. for C25H16ClN2O2 [M+H]+ 411.0895 found 411.0906. 153.2, 153.1, 153.0, 150.6, 145.8, 139.3, 137.3, 132.6, 132.2
1-(4-bromophenyl)-3-phenyl-3H-benzofuro[3,2-e]indazol-9-ol (2C), 132.1, 124.9, 123.9 (2C), 119.8, 117.5, 155.5, 115.4,
(3k): Following the general procedure, reaction of 1-(4- 115.2, 115.1, 113.0, 110.0, 109.3, 109.2 ppm; FT-IR (KBr): max
bromobenzylidene)-2-phenylhydrazine 1k (0.25 mmol, 68.5 = 3416, 1619, 1493, 1341, 1190, 1135 cm-1; HRMS (ESI) calcd.
mg) with p-BQ 2a (0.75 mmol, 81 mg) yielded the desired for C25H15BrFN2O2 [M+H]+ 473.0295 found 473.0308.
product 3k (54.5 mg) as an ivory white solid in 48% yield; m.p. 3-(4-bromophenyl)-1-(4-chlorophenyl)-3H-benzofuro[3,2-
256-258 °C; H NMR (500 MHz, Acetone-d6, TMS):
1H), 7.97 (d, J = 9 Hz, 1H), 7.89 (d, J = 7.5 Hz, 2H), 7.83-7.82 (m, reaction
3H), 7.81-7.77 (m, 2H), 7.66 (t, J = 8 Hz, 2H), 7.53-7.48 (m, 2H), chlorobenzylidene)hydrazine 1o (0.25 mmol, 77.4 mg) with p-
7.02 (dd, J = 9, 2.5 Hz, 1H), 6.62 (d, J = 2.5 Hz, 1H) ppm; 13C BQ 2a (0.75 mmol, 81 mg) afforded the desired product 3o
 = 163.4 (C-F, J = 245 Hz),
1

= 8.35 (s, e]indazol-9-ol (3o): Following the general procedure, the
of 1-(4-bromophenyl)-2-(4-
NMR (125 MHz, Acetone-d6):
139.8, 137.6, 133.8, 132.0 (2C), 131.5 (2C), 129.6 (2C), 127.3, 1H NMR (500 MHz, Acetone-d6, TMS):
124.0, 123.4 (2C), 122.7, 117.0, 115.4, 114.9, 112.9, 111.7, J = 9, 2 Hz, 1H), 7.89-7.87 (m, 2H), 7.85-7.82 (m, 5H), 7.68 (dd, J
110.2, 109.5 ppm; FT-IR (KBr): max = 3416, 1591, 1496, 1343, = 8.5, 2 Hz, 2H), 7.53 (dd, J = 9, 1.5 Hz, 1H), 7.02 (dd, J = 9, 2 Hz,
1187, 1134 cm-1; HRMS (ESI) calcd. for C25H1681BrN2O2 [M+H]+ 1H), 6.60 (t, J = 2, 1H) ppm; 13C NMR (125 MHz, Acetone-d6):

= 153.2, 153.1, 150.6, 145.0, (57.8 mg) in 47% yield as an pale yellow solid; m.p. 254-256 °C;
= 8.23 (s, 1H), 8.01 (dd,


457.0375 found 457.0384.
= 155.0, 152.4, 147.3, 141.0, 139.2, 136.4, 135.0, 134.4 (2C),
1-(naphthalen-1-yl)-3-phenyl-3H-benzofuro[3,2-e]indazol-9-ol 133.5 (2C), 130.3 (2C), 126.8 (2C), 125.7, 121.7, 119.1, 117.2,
(3l): Following the general procedure, the reaction of 1- 116.8, 114.9, 113.5, 111.8, 111.2, 111.1 ppm; FT-IR (KBr): max
(naphthalen-2-ylmethylene)-2-phenylhydrazine 1l (0.25mmol,
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= 3424, 1631, 1490, 1264, 1169,1135cm-1; HRMS (ESI) calcd. Acetone-d6):
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
= 152.0, 151.1, 150.6, 144.8, 140.1, 137.9, 134.3
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for C25H15BrClN2O2 [M+H]+ 489.0000 found 489.0009.
(2C), 133.4 (2C), 131.4 (2C), 129.5, 128.4, 127.0, 125.3 (2C),
DOI: 10.1039/C9NJ01991J
1,3-bis(4-bromophenyl)-3H-benzofuro[3,2-e]indazol-9-ol (3p): 123.5, 123.3, 121.8, 115.1, 114.2, 112.6, 109.1, 108.8, 16.3,
Following the general procedure, reaction of 1-(4- 15.4 ppm; FT-IR (KBr): max = 3398, 1598, 1499, 1488, 1346,
bromobenzylidene)-2-(4-bromophenyl)hydrazine 1p (0.25 1182, 1133 cm-1; HRMS (ESI) calcd. for C27H20ClN2O2 [M+H]+
mmol, 88.5 mg) with p-BQ 2a (0.75 mmol, 81 mg) yielded the 439.1208 found 439.1221.
desired product 3p (68.5 mg) in 50% yield as an off-white solid; 6-chloro-1,3-diphenyl-1H-indazol-5-ol (4b): Following the
9
m.p. 260-262 °C; 1H NMR (500 MHz, Acetone-d6, TMS):

= 8.47 general
procedure,
reaction
of
1-benzylidene-2-
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(s, 1H), 7.90-7.86 (m, 1H), 7.76-7.69 (m, 7H), 7.63 (d, J = 8.4 Hz, phenylhydrazine 1a (0.25 mmol, 49 mg) with 2-
2H), 7.38 (d, J = 8.8 Hz, 1H), 6.90 (dd, J = 8.8, 2.4 Hz, 1H), 6.42 chlorocyclohexa-2,5-diene-1,4-dione 2c (0.75 mmol, 106.9 mg)
(d, J = 2.8 Hz, 1H) ppm; 13C NMR (125 MHz, Acetone-d6):

=
afforded the desired product 4b (29 mg) in 36% yield as a light
154.2, 154.1, 151.5, 146.4, 140.1, 138.3, 134.5, 133.5 (2C), pink colored solid; m.p. 138-140 °C; FT-IR (KBr):

max= 3394,
1
132.9 (2C), 132.4, (2C), 126.0 (2C), 124.7, 123.8, 120.8, 118.1, 2962, 1594, 1498, 1249, 1116 cm-1; H NMR (500 MHz, CDCl3,
116.4, 115.9, 114.1, 112.5, 110.9, 110.3 ppm; FT-IR (KBr): max TMS):  = 7.91-7.90 (m, 2H), 7.73 (s, 1H), 7.67 (dd, J = 8.5, 1 Hz,
= 3418, 1627, 1509, 1454, 1342, 1175 cm-1; HRMS (ESI) calcd. 2H), 7.59 (s, 1H), 7.50-7.43 (m, 4H), 7.37-7.34 (m, 1H), 7.33-
for C25H15Br2N2O2 [M+H]+ 532.9495 found 532.9493.
5,8-dimethyl-1,3-diphenyl-3H-benzofuro[3,2-e]indazol-9-ol
7.29 (m, 1H), 5.45 (s, 1H) ppm; 13C NMR (125 MHz, CDCl3):
146.7, 145.5, 139.9, 135.7, 132.8, 129.7 (2C), 129.0, 128.5 (2C),
 =
(3q): Following the general procedure, reaction of 1- 127.6, 127.0 (2C), 122.9, 122.8 (2C), 122.8, 110.8, 105.8 ppm;
benzylidene-2-phenylhydrazine 1a (0.25 mmol, 49 mg) with 2- HRMS (ESI) calcd. for C19H14ClN2O [M+H]+ 321.0789 found
methylcyclohexa-2,5-diene-1,4-dione 2b (0.75 mmol, 92 mg) 321.0799.
afforded the desired product 3q (69.7 mg) in 69% yield as a 4,6-dimethyl-1,3-diphenyl-1H-indazol-5-ol (4d): Following the
light brown solid; m.p. 207-209 °C; 1H NMR (500 MHz, general
procedure,
reaction
of
1-benzylidene-2-
Acetone-d6, TMS):
 = 7.93 (s, 1H), 7.87 (d, J = 8.5 Hz, 2H), 7.79 phenylhydrazine 1a (0.25 mmol, 49 mg) with 2,6-
(d, J = 6 Hz, 2H), 7.75 (s, 1H), 7.63 (t, J = 7.7 Hz, 2H), 7.59-7.56 dimethylcyclohexa-2,5-diene-1,4-dione 2e (0.75 mmol, 102.2
(m, 3H), 7.46-7.44 (m, 2H), 6.59 (d, J = 2 Hz, 1H), 2.69 (s, 3H), mg) afforded the desired product 4d (48.7 mg) as an off-white
2.34 (s, 3H) ppm; 13C NMR (125 MHz, Acetone-d6):
152.7, 152.4, 148.0, 142.1, 139.5, 136.5, 131.7, 131.2 (2C), Acetone-d6, TMS):

= 153.7, solid in 62% yield; m.p. 160-162 °C; 1H NMR (500 MHz,
= 7.83 (d, J = 7.5 Hz, 2H), 7.68 (d, J = 6.5

130.5, 130.0 (2C), 128.6, 127.2, 127.1 (2C), 125.2, 125.1, 123.7, Hz, 2H), 7.60-7.57 (m, 3H), 7.54-7.46 (m, 3H), 7.37 (t, J = 7.5
117.3, 116.2, 114.2, 110.9, 110.8, 18.1, 17.2 ppm; FT-IR (KBr): Hz, 1H), 7.25 (s, 1H), 2.44 (s, 3H), 2.26 (s, 3H) ppm; 13C NMR
max = 3414, 1594, 1492, 1459, 1369, 1185, 1130 cm-1; HRMS (125 MHz, Acetone-d6):

= 148.4, 146.8, 140.6, 135.3, 135.2,
130.2 (2C), 129.3 (2C), 128.5, 127.9, 127.8 (2C), 125.9, 122.4,
122.2 (2C), 114.7, 108.5, 17.4, 12.4 ppm; FT-IR (KBr): max
(ESI) calcd. for C27H21N2O2 [M+H]+ 405.1598 found 405.1613.
5,8-dimethyl-3-phenyl-1-(4-(trifluoromethyl)phenyl)-3H-
=
benzofuro[3,2-e]indazol-9-ol (3r): Following the general 3412, 1589, 1492, 1281, 1179, 1117 cm-1; HRMS (ESI) calcd. for
procedure,
reaction
of
1-phenyl-2-(4- C21H19N2O [M+H]+ 315.1492 found 315.1497.
(trifluoromethyl)benzylidene)hydrazine 1c (0.25 mmol, 66.1 8-chloro-1,3-diphenyl-3H-benzofuro[3,2-e]indazol-9-ol (3t):
mg) with 2-methylcyclohexa-2,5-diene-1,4-dione 2b (0.75 Following the general procedure, reaction of 1,3-diphenyl-1H-
mmol, 92 mg) afforded the desired product 3r (66.1 mg) as an indazol-5-ol 4a (0.25 mmol, 71.3 mg) and 2-chloro p-BQ 2c
1
very light pink colored solid in 56% yield; m.p. 234-236 °C; H (0.50 mmol, 71.3 mg) in the presence of TFA (14 equiv., 3.5
NMR (500 MHz, Acetone-d6, TMS):
7.96-7.93 (m, 3H), 7.87 (d, J = 7.5 Hz, 2H), 7.75 (s, 1H), 7.65 (t, J solid in 29% yield; m.p. 233-235 °C; H NMR (500 MHz, CDCl3

= 8.03 (d, J = 8 Hz, 2H), mmol) afforded the desired product 3t (29.8 mg) as an white
1
= 7.5 Hz, 2H), 7.49 (t, J = 7.5 Hz, 1H), 7.46 (s, 1H), 6.67 (s, 1H), TMS):  = 7.87 (d, J = 9 Hz, 1H), 7.84 (d, J = 7.5 Hz, 2H), 7.80 (d,
2.69 (s, 3H), 2.35 (s, 3H) ppm; 13C NMR (125 MHz, Acetone-d6): J = 6.5 Hz, 2H), 7.70 (d, J = 9 Hz, 1H), 7.67-7.59 (m, 6H), 7.45 (t,
δ = 152.1, 151.1, 150.6, 144.6, 140.0, 138.6, 138.0, 130.4 (2C), J = 7.2 Hz, 1H), 6.45 (s, 1H), 5.31 (s, 1H) ppm; 13C NMR (125
130.1, 129.8, 129.5 (2C), 127.1, 125.7, 125.5, 125.3 (q) (-CF3), MHz, CDCl3):
 = 153.4, 150.5, 146.9, 146.5, 139.9, 137.5,
123.7, 123.4 (2C), 121.7, 115.0, 114.1, 112.6, 109.2, 109.0, 134.2, 130.4 (2C), 129.5 (2C), 129.1, 128.5 (2C), 127.3, 123.7
16.2, 15.4 ppm; FT-IR (KBr): max = 3419, 1596, 1501, 1468, (2C), 123.6, 118.9, 117.7, 114.9, 112.6, 111.4, 110.4, 110.1
1329, 1190, 1156 cm-1; HRMS (ESI) calcd. for C28H20F3N2O2 ppm; FT-IR (KBr): max = 3409, 1593, 1502, 1461, 1328, 1171,
[M+H]+ 473.1471 found 473.1485.
1130 cm-1; HRMS (ESI) calcd. for C25H16ClN2O2 [M+H]+
411.0895 found 411.0928.
1-(4-chlorophenyl)-5,8-dimethyl-3-phenyl-3H-benzofuro[3,2-
e]indazol-9-ol (3s): Following the general procedure, reaction
of 1-(4-chlorobenzylidene)-2-phenylhydrazine 1j (0.25 mmol,
57.65 mg) with 2-methylcyclohexa-2,5-diene-1,4-dione 2b
(0.75 mmol, 92 mg) afforded the desired product 3s (52.7 mg)
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
1
as an white solid in 48% yield; m.p. 240-242 °C; H NMR (500
MHz, Acetone-d6, TMS):
 = 8.08 (s, 1H), 7.88-7.80 (m, 4H),
J.C.J. is grateful to Council of Scientific and Industrial Research
(CSIR), Government of India for a research fellowship. B.P.B.
7.76-7.72 (m, 1H), 7.64-7.61 (m, 4H), 7.49-7.44 (m, 2H), 6.74 (s,
1H), 2.68 (s, 3H), 2.35 (s, 3H) ppm; 13C NMR (125 MHz,
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019
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acknowledges Department of Science and Technology (DST),
Government of India for an INSPIRE Faculty Award (IFA-13 CH-
98). B.P.B. and R.P.B. thank NITK, Surathkal for providing
laboratory facility and research fellowship for R.P.B. V.K.P. is
grateful to the DST-SERB, for a Young Scientist Fellowship
(SB/FT/CS-131/2014) and CSIR fast-track translation project,
cellular sensor (MLP0027), Government of India for financial
support. N.M. acknowledges UGC-SAP and DST-FIST/PURSE
support.
Zadsirjan, H. Hamidi and P. H. T. Amiri, RSC Adv., 2017, 7,
View Article Online
24470.
DOI: 10.1039/C9NJ01991J
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Table of contents
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Trifluoroacetic acid mediated [3+2] annulation reaction between the 5-hydroxy-1H-indazoles -
generated in situ - and p-benzoquinones has been reported.
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