2,3-Diarylquinoxaline directed mono ortho-aroylation via cross-dehydrogenative coupling using aromatic aldehydes or alkylbenzenes as aroyl surrogate

Article abstract of DOI:10.1016/j.tet.2014.02.034

2,3-Diarylquinoxaline directed mono ortho-aroylation protocol has been developed using aromatic aldehydes or alkybenzenes as aroyl surrogates. Out of the four available ortho sp² C-H bonds in the two aryl rings of 2,3-diarylquinoxaline one of the C-H bond is selectively ortho-aroylated. The reaction proceeds via the aroyl radical path in the case of aromatic aldehydes while the alkylbenzenes follow either an aroyl radical or a benzyl radical path. Varieties of functional groups present as substituents in 2,3- diarylquinoxalines, aromatic aldehydes and alkylbenzenes are tolerated under the present reaction conditions.

Full text of DOI:10.1016/j.tet.2014.02.034

Tetrahedron 70 (2014) 2422e2430
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2,3-Diarylquinoxaline directed mono ortho-aroylation via
cross-dehydrogenative coupling using aromatic aldehydes or
alkylbenzenes as aroyl surrogate
*
Sourav Kumar Santra, Arghya Banerjee, Bhisma K. Patel
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, India
a r t i c l e i n f o
a b s t r a c t
Article history:
2,3-Diarylquinoxaline directed mono ortho-aroylation protocol has been developed using aromatic
aldehydes or alkybenzenes as aroyl surrogates. Out of the four available ortho sp2 CeH bonds in the two
aryl rings of 2,3-diarylquinoxaline one of the CeH bond is selectively ortho-aroylated. The reaction
proceeds via the aroyl radical path in the case of aromatic aldehydes while the alkylbenzenes follow
either an aroyl radical or a benzyl radical path. Varieties of functional groups present as substituents in
2,3-diarylquinoxalines, aromatic aldehydes and alkylbenzenes are tolerated under the present reaction
conditions.
Received 6 November 2013
Received in revised form 29 January 2014
Accepted 13 February 2014
Available online 20 February 2014
Keywords:
CeH activation
Cross-dehydrogenative coupling
2,3-Diarylquinoxaline
Pd-catalysis
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
aldehydes or alcohols as aroyl surrogates. Recently, ligand directed
decarboxylation of alpha-keto acids strategies have been used for
Recently a number of CeH bond functionalization methods are
available to synthetic organic community. Functionalizations of
such ubiquitous CeH bonds build complex molecular architecture
through the construction of CeC and CeX (X¼heteroatoms) bonds.1
The two most commonly adopted approaches are the directing
group assisted CeH functionalization1g,l,2 and the cross-
dehydrogenative coupling (CDC).3 In the later approach both the
coupling partners are attached through their CeH bonds, whereas
in the former only ortho CeH bonds are functionalized via the
chelation of metals through heteroatoms, such as nitrogen and
oxygen. These two techniques make the synthetic tools highly ap-
preciable due to the requirement of minimal steps and atom
economy point of view. In this perspective Pd-catalyzed ortho CeH
functionalizations have been successfully employed for the syn-
thesis of aryl ketones.4 Due to the use of stoichiometric amount of
reagents the classical FriedeleCraft acylation5 has been lately
replaced by transition metal catalyzed cross-coupling processes.6
To avoid the substrate pre-functionalization in the cross-coupling
reactions CeH functionalizations have come into salvage. Sub-
strates having different directing groups, such as 2-arylpyridine,4a,7
2-arylbenzazoles,8 anilides,4b,9 o-methyl oxime,10 and benza-
mides11 have been successfully ortho aroylated using aromatic
the ortho-aroylations.4cee,12 Following our approach of directing
group assisted ortho-aroylation using alkylbenzenes as aroyl
surrogates4f several other similar reports have emerged in the
literature.4g,h,13
Quinoxaline is an important pharmacophoric unit possessing
diverse biologically activities and are potentially useful in materials
science.14 Thus, any derivatization of 2,3-diarylquinoxaline is ex-
pected to generate further interests. There are three instances of
ortho-functionalization of 2,3-diarylquinoxaline moiety viz. ace-
toxylation,15 fluorination16 and nitration.17 Till to date there is no
precedence of ortho-aroylation of this important scaffold using any
of the aroyl surrogates via the CDC approach.
2. Results and discussion
In light of the above-mentioned ortho-aroylation processes, an
initial trial was attempted with the model substrate 2,3-
diphenylquinoxaline (1) through a chelation-assisted CDC ap-
proach. 2,3-Diphenylquinoxaline (1) (1 equiv) was treated with
benzaldehyde (1.2 equiv) in the presence of Pd(OAc)2 (2 mol %) and
tert-butyl hydroperoxide (TBHP in decane) (1 equiv) in 1,2-
dichloroethane (DCE) (2 mL) at 110 ꢀC, which yielded the product
(1a) in an isolated yield of 35% (Table 1, entry 1). The formation of
mono ortho-aroylation of 2,3-diphenylquinoxaline was confirmed
by spectroscopic data analysis (see Supplementary data). To
* Corresponding author. E-mail address: patel@iitg.ernet.in (B.K. Patel).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.02.034

S.K. Santra et al. / Tetrahedron 70 (2014) 2422e2430
2423
Table 1
aldehydes coupled efficiently with 2,3-diphenylquinoxaline (1)
giving the desired ortho-aroylated products in good to moderate
yields. Aldehydes containing moderately electron-donating groups,
such as p-Me (b), p-tBu (c) and p-Ph (d) afforded aroylated products
(1b), (1c) and (1d), respectively in good yields (Scheme 1). The
transformation was equally successful for aromatic aldehydes
possessing electron-donating substituents, such as p-OMe (e), p-
OBu (f) and 3,4-di-OMe (g) giving the products (1e), (1f) and (1g),
respectively in moderate yields. The structure of mono-ortho-
aroylated product (1e) was further confirmed by X-ray crystallo-
graphic analysis as shown in Fig. 1.
Screening of reaction conditions
Entry
Catalyst (mol %)
Solvent
Oxidant
Yield (%)a
1
2
3
4
5
6
7
8
Pd(OAc)2 (2.0)
Pd(OAc)2 (2.0)
Pd(OAc)2 (2.0)
Pd(OAc)2 (2.0)
Pd(OAc)2 (2.0)
Pd(OAc)2 (2.0)
Pd(OAc)2 (2.0)
Pd(OAc)2 (2.0)
Pd(OAc)2 (5.0)
Pd(OAc)2 (10.0)
PdBr2 (5.0)
DCE
DMF
DMSO
Cyclohexane
o-Xylene
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
(PhCO2)2
K2S2O8
TBHP
TBHP
35
00
00
32
41
Dioxane
Toluene
42
50
Toluene:DCE
Toluene:DCE
Toluene:DCE
Toluene:DCE
Toluene:DCE
Toluene:DCE
Toluene:DCE
Toluene:DCE
Toluene:DCE
Toluene:DCE
58b
67b
72b
10b
7b
9
10
11
12
13
14
15
16
17
PdCl2 (5.0)
Pd(TFA)2 (5.0)
Pd(OAc)2 (5.0)
Pd(OAc)2 (5.0)
Pd(OAc)2 (5.0)
Pd(OAc)2 (5.0)
46b
00b
00b
70c
76d
a
Isolated yield after 8 h, TBHP was added in four equal lots at 1.5 h interval.
1:1 ratio of toluene and DCE.
1.2 equiv of TBHP.
b
c
d
1.5 equiv of TBHP.
improve the yield of the product, other reaction parameters, such as
solvent, catalyst, oxidants and their quantities were varied. The use
of polar aprotic solvents, such as DMF or DMSO failed to give any
traces of product (Table 1, entries 2 and 3). Solvent toluene was
found to be better compared to cyclohexane, o-xylene and dioxane
tested (Table 1, entries 4e7).
A careful scrutiny of the literature revealed that toluene to be
the most appropriate solvent towards Pd-catalyzed ortho-aroyla-
tion4b,8a,9a,b,10 while for ortho-CeH functionalization of 2,3-
diphenylquinoxaline DCE to be the most effective solvent.15e17
Therefore we contemplate that the use of mixed solvents might
improve the product yield. Interestingly, the use of mixture of
toluene:DCE (in 1:1 ratio) gave an improved yield of 58% (Table 1,
entry 8). The yield improved up to 67% when the catalyst loading
was increased to 5 mol % (Table 1, entry 9). However, no significant
improvement in the yield (72%) was observed even when the cat-
alyst loading was increased to 10 mol % (Table 1, entry 10). Other
palladium catalysts, such as PdCl2 and PdBr2 in lieu of Pd(OAc)2
were found to give inferior yields (Table 1, entries 11 and 12). The
catalyst Pd(TFA)2 was good but slightly less effective compared to
Pd(OAc)2 (Table 1 entry 13). Changing the oxidant from TBHP to
benzoyl peroxide and K2S2O8 gave no desired ortho-aroylated
product (Table 1, entries 14 and 15) suggesting the superiority of
TBHP as the oxidant. Interestingly, increasing the oxidant (TBHP)
quantity from 1 to 1.2 equiv and further to 1.5 equiv improved the
yield to 70% and 76%, respectively (Table 1, entries 16 and 17). Thus,
after a series of experimentations catalyst Pd(OAc)2 (5 mol %),
oxidant TBHP (1.5 equiv) and aroyl source aldehyde (1.2 equiv) in an
equivolume mixture of toluene and 1,2-dichloroethane (2 mL) was
found to be the best condition and was subsequently implemented
for further reactions.
Using the above optimized condition this methodology was
further applied to 2,3-diphenylquinoxaline (1) with a variety of
aromatic aldehydes. Both activated and deactivated aromatic
Scheme 1. Scope of aldehydes in Pd-catalyzed ortho-aroylation of 2,3-
diphenylquinoxaline. Confirmed by IR, 1H NMR and 13C NMR spectroscopy. Yields af-
ter silica gel column chromatography.

2424
S.K. Santra et al. / Tetrahedron 70 (2014) 2422e2430
Fig. 1. ORTEP view of compound 1e.
Aromatic aldehydes possessing weekly electron-withdrawing
groups, such as p-Cl (h), m-Cl (i) and m-F (j) also underwent
efficient conversion giving corresponding ortho-aroylated prod-
ucts (1h), (1i) and (1j), respectively in good yields. Aldehydes
possessing strongly electron-withdrawing groups, such as p-NO2
(k), m-NO2 (l) and p-CO2Me (m) served as good aroyl sources and
provided the desired ortho-aroylated products (1k), (1l) and
(1m), respectively in good yields. Aromatic aldehydes possessing
two electron-withdrawing groups as in 4-Cle3-NO2 benzalde-
hyde (n) gave slightly lower yield of product (1n) when
employed as an aroyl surrogate. Heteroaromatic aldehyde (o) and
fused aromatic aldehyde (p) also afforded good yields of their
respective ortho-aroylated products (1o) and (1p) when reacted
with 2,3-diphenylquinoxaline (1) under the optimized condition
(Scheme 1).
This selective ortho-aroylation strategy was further extended to
other substituted 2,3-diphenylquinoxalines keeping benzaldehydes
as fixed aroylating partner (Scheme 2). 2,3-Diphenyl substituted-
quinoxaline containing electron-donating group (eMe) in its aryl
rings gave excellent yield of the desire aroylated product (2a) when
reacted with benzaldehyde under the reaction conditions. Chloro
substituents present in the quinoxaline ring as in (3) on reaction
with benzaldehyde (a) afforded decent yield (67%) of the mono-or-
tho-aroylated product (3a). However 2,3-aryl ring bearing methyl
groups and the quinoxaline possessing chloro groups as in (4)
afforded better yield of mono-ortho-aroylated product (4a). Methyl
substituted unsymmetrical 2,3-diphenylquinoxaline (5) upon re-
action with benzaldehyde gave an inseparable regioisomeric mono
ortho-aroylated products 5a/5a0 in the ratio of 5:4 as can be judged
from its 1H and 13C NMR spectra. However it was not possible
to assign the exact regioisomers (5a or 5a0) from its 1H and 13C
NMR spectra. The chloro substituted unsymmetrical 2,3-
diphenylquinoxaline (6) also gave identical results and the two
regioisomers 6a/6a0 were obtained in the ratio of 5:3. Further ortho-
aroylation reactions were performed using unsymmetrically
substituted 2,3-diarylquinoxalines with benzaldehyde as the aroy-
lating source. In case of substrate (7) containing two electron-
donating substituents (eMe and eOMe) in one of the phenyl ring
provided regioisomeric mono ortho-aroylated products (7a and 7a0)
in the ratio of 6.7:1 suggesting the preferential oxidative palladation
at the more electron rich aryl ring. For substrate (8) containing
weaklyelectron-withdrawing substituent (eBr) in one of the phenyl
ring of 2,3-diarylquinoxaline ortho-aroylation takes place at the
other electron neutral phenyl ring giving product (8a) exclusively
reconfirming the preferential ortho-aroylation at comparatively
electron rich phenyl ring.
Scheme 2. Scope of 2,3-diphenylquinoxaline in Pd-catalyzed ortho-aroylation with
benzaldehyde. Confirmed by IR, 1H NMR and 13C NMR spectroscopy. Yields after silica
gel column chromatography.
as the solvent in presence of aromatic aldehyde but no ortho-
aroylated product derived from toluene was observed in any of the
reactions. This is possibly due to the presence of sub-
stoichiometric amount of aromatic aldehydes (1.2 equiv) with
respect to the substrate quinoxalines in the reaction. These ob-
servations suggest that perhaps the aromatic aldehyde is a facile
aroyl source compared to alkylbenzene. To confirm this 2,3-
diphenylquinoxaline (1) was treated with an equimolar mixture
of p-methoxy benzaldehyde (1 equiv) and p-xylene (1 equiv) un-
der the experimental conditions. The progress of the reaction was
monitored by TLC and GC over a period of 10 h. During the first 1 h
product derived from p-methoxy benzaldehyde (1e) was formed
with no traces of (1b) (Scheme 3). After 2 h aroylated products
derived from p-xylene (1b) was observed in about 10% yield. At
the end of the reaction (10 h) products (1e) and (1b) were isolated
in the ratio of 7:3 in overall 68% yield, there by suggesting the
higher ortho-aroylating ability of aromatic aldehyde over
alkylbenzene.
Taking cues from this and from our previous work4f under the
forcing conditions alkylbenzenes may serve as aroyl surrogate to-
wards ortho-aroylation of 2,3-diphenylquinoxalines. Thus, in the
absence of aldehyde using toluene as the aroyl source as well as
Recently the inert alkylbenzenes have been exploited as ex-
cellent aroyl surrogates by us4f and several others.4g,h,13a,b Al-
though in present reaction alkylbenzene (toluene) has been used

S.K. Santra et al. / Tetrahedron 70 (2014) 2422e2430
2425
Scheme 3. Competitive reaction of aromatic aldehyde and alkylbenzene.
a solvent under the present optimized condition the product (1a)
was obtained in 22% yield. Interestingly when the oxidant (TBHP)
quantity was increased to 3.5 equiv from 1.5 equiv and toluene was
used as the sole solvent in place of toluene/DCE mixture the yield of
the product improved to 71% whereas using 2 or 3 equiv of oxidant
(TBHP) the yields obtained were 41% and 63%, respectively. How-
ever increasing the oxidant quantity to 4 equiv and even to 5 equiv
no significant improvement in the yield was observed. Thus in lieu
of aromatic aldehydes various alkylbenzenes were reacted with
2,3-diphenylquinoxaline (1) and the results are summarized in
Scheme 4. Alkylbenzenes, such as p-xylene, o-xylene served as
good aroyl sources giving ortho-aroylated products (1b) and (1q),
respectively. Alkylbenzene possessing electron-donating group as
in p-methoxy toluene gave low yield (46%) of ortho-aroylated
product (1e). This methodology was also equally successful for
alkylbenzene possessing weakly electron-withdrawing groups.
Thus p-chlorotoluene and m-fluorotoluene both gave good yields of
their ortho-aroylated products (1h) and (1j), respectively (Scheme
4). Alkylbenzene possessing strongly electron-withdrawing
groups, such as p-nitrotoluene provided ortho-aroylated product
(1k) in a meager yield of 28%. This is in part due to the inheter-
ogenity of the reaction mixture because of the insolubility of p-
nitrotoluene in the reaction medium. When 1,2 dicholoroethane
was used as the solvent for the above reaction no doubt the reaction
mixture was homogeneous but the transformation was not at all
effective. It may be mentioned here that the yields obtained using
alkylbenzenes were slightly lower as compared to the use of
analogous aromatic aldehydes.
Scheme 4. Scope of alkylbenzenes in Pd-catalyzed ortho-aroylation with quinoxalines.
Confirmed by IR, 1HNMR and 13CNMR spectroscopy. Isolated yield.
followed by the oxidative addition of the in situ generated aroyl
radical obtained from aryl aldehyde and to form a dimeric Pd(III)18
intermediate (II). In the final stage reductive elimination gave or-
tho-aroylated product regenerating the active PdII species for fur-
ther catalytic cycle (Scheme 5, path-A). Using toluene as the aroyl
equivalent it is expected that the reaction may proceed via the
sequential oxidation of toluene to benzyl alcohol and to aldehyde,
which then enters in to the catalytic path-A (Scheme 5) giving or-
tho-aroylated product. Alternatively, the mechanism is expected to
proceed similar to the one recently proposed by us during analo-
gous substrate directed ortho-aroylation where a benzyl radical
insertion followed by the benzylic oxidation has been proposed.4f
In the later case the o-palladated intermediate (I) undergoes oxi-
dative addition with the benzylic radical19 generated in situ by the
action of toluene and TBHP to give intermediate (III). Further oxi-
dation at the benzylic carbon of intermediate (III) with TBHP pro-
vides intermediate (II) (path-B, Scheme 5). Reductive elimination of
the Pd-catalyst from the intermediate (II) provides ortho-aroylated
product. No di-ortho-aroylation was observed in the second ortho
position of the aryl ring or in the two available ortho positions of the
second aryl ring even with an excess of aroylating source, which
may be due to the loss of planarity of the pendant aryl rings with
respect to the quinoxaline moiety. The out of the plane orientation
of the two aryl rings can be clearly seen from one of the mono-
ortho-aroylated product (1e) as shown in Fig. 1.
To ascertain the nature of the mechanism(s) involved in each of
these reactions a series of experiments were performed. Rate re-
tardation with <10% conversion was observed when the reaction
was performed in the presence of a radical scavenger 2,2,6,6-
tetramethylpiperidine-1-oxyl (TEMPO, 1 equiv). This suggests the
radical nature of the reactions for both aroyl surrogates viz. aro-
matic aldehyde and alkylbenzene. A mechanism similar to ortho-
aroylation of 2-arylbenzazole (and other directing groups) using
aryl aldehyde as aroyl surrogate can be proposed for this reactions
as shown in Scheme 5, path-A.8a,9a,10 Cyclopalladation of 2,3-
diphenylquinoxaline leads to the formation of intermediate (I)

2426
S.K. Santra et al. / Tetrahedron 70 (2014) 2422e2430
Scheme 5. Plausible mechanistic cycle.
3. Conclusions
(0.75 mmol) was added in four equal lots at an intervals of 1.5 h. The
progress of the reaction was monitored by TLC after each addition.
After completion of the reaction (8 h) the reaction mixture was
cooled to room temperature and was admixed with water (5 mL).
The product was extracted with ethyl acetate (3ꢁ10 mL) and the
combined organic layer was washed with saturated sodium bi-
carbonate solution (5 mL), dried over anhydrous sodium sulfate
(Na2SO4) and evaporated under reduced pressure. The crude
product so obtained was purified by silica gel column chromatog-
raphy (hexane/ethyl acetate, 10:0.8) to give pure phenyl(2-(3-
phenylquinoxalin-2-yl)phenyl)methanone (1a) (0.147 g, yield
76%). The identity and purity of the product was confirmed by
spectroscopic analysis.
In conclusion, we have developed a selective mono ortho-
aroylation protocol for 2,3-diphenylquinoxaline employing Pd-
catalyst in the presence of oxidant TBHP in an air atmosphere us-
ing aryl aldehyde or alkylbenzene as aroyl precursors. This is the
first such aroylation protocol for 2,3-diphenylquinoxaline. Using
aldehyde as aroyl surrogate the reaction goes via aroyl radical path
while the use of alkylbenzene as aroyl surrogate it can proceed
either via an aroyl radical or by a benzyl radical path.
4. Experimental section
4.1. General remarks
4.3. Synthesis of phenyl(2-(3-phenylquinoxalin-2-yl)phenyl)
methanone (1a) from 2,3-diphenylquinoxaline (1) and
toluene
All the reagents were commercial grade and purified according
to the established procedures. Organic extracts were dried over
anhydrous sodium sulfate. Solvents were removed in a rotary
evaporator under reduced pressure. Silica gel (60e120 mesh size)
was used for the column chromatography. Reactions were moni-
tored by TLC on silica gel 60 F254 (0.25 mm). NMR spectra were
recorded in CDCl3 with tetramethylsilane as the internal standard
for 1H NMR (400 and 600 MHz) CDCl3 solvent as the internal
standard for 13C NMR (100 and 150 MHz). MS spectra were recor-
ded using ESI mode. IR spectra were recorded in KBr or neat.
In an oven-dried 25 mL round bottom flask containing 2 mL of
toluene, 2,3-diphenylquinoxaline (1) (0.141 g, 0.5 mmol) and
Pd(OAc)2 (0.006 g, 0.025 mmol) was added in sequence. The re-
action mixture was the kept in an oil bath preheated to 110 ꢀC. TBHP
(1.75 mmol) was added in four equal lots at an intervals of 2 h. The
progress of the reaction was monitored by TLC after each addition.
After completion of the reaction (10 h) the reaction mixture was
cooled to room temperature and was admixed with water (5 mL).
The product was extracted with ethyl acetate (3ꢁ10 mL). The
combined organic layer was washed with saturated sodium bi-
carbonate solution (5 mL), dried over anhydrous sodium sulfate
(Na2SO4) and evaporated under reduced pressure. The crude
product so obtained was purified by silica gel column chromatog-
raphy (hexane/ethyl acetate, 10:0.8) to give pure phenyl(2-(3-
phenylquinoxalin-2-yl)phenyl)methanone (1a) (0.137 g, yield
71%). The identity and purity of the product was confirmed by
spectroscopic analysis.
4.2. Synthesis of phenyl(2-(3-phenylquinoxalin-2-yl)phenyl)
methanone (1a) from 2,3-diphenylquinoxaline (1) and
benzaldehyde
In an oven-dried 25 mL round bottom flask containing 1 mL
each of toluene and dichloroethane (DCE), 2,3-diphenylquinoxaline
(1) (0.141 g, 0.5 mmol), benzaldehyde (0.064 g, 0.6 mmol) and
Pd(OAc)2 (0.006 g, 0.025 mmol) was added sequentially. Then re-
action mixture was kept in an oil bath preheated to 110 ꢀC. TBHP

S.K. Santra et al. / Tetrahedron 70 (2014) 2422e2430
2427
4.3.1. Phenyl(2-(3-phenylquinoxalin-2-yl)phenyl)methanone
(1a). The general procedure was followed. The product was purified
by column chromatography (8% EtOAc/hexane) to give the title
compound 1a (147 mg, 76%) as Gummy; Rf (10% EtOAc/hexane) 0.45;
purified by column chromatography (8% EtOAc/hexane) to give the
title compound 1e (141 mg, 68%) as Solid mp 112.8 ꢀC; Rf (10%
EtOAc/hexane) 0.33; 1H NMR (CDCl3, 400 MHz):
d 8.13 (d, 1H,
J¼7.6 Hz, Ar. CeH), 8.06 (d, 1H, J¼8.8 Hz, Ar. CeH), 8.00 (d, 1H,
J¼7.6 Hz, Ar. CeH), 7.75e7.68 (m, 2H, Ar. CeH), 7.62 (d, 1H, J¼7.6 Hz,
Ar. CeH), 7.58e7.54 (m,1H, Ar. CeH), 7.44 (d, 4H, J¼6.8 Hz, Ar. CeH),
7.22 (d, 1H, J¼7.6 Hz, Ar. CeH), 7.16 (t, 2H, J¼7.2 Hz, Ar. CeH), 6.95
(d, 1H, J¼8.8 Hz, Ar. CeH), 6.78 (d, 2H, J¼8.8 Hz, Ar. CeH), 3.83 (s,
1H NMR (CDCl3, 400 MHz):
d
8.13 (d, 1H, J¼9.2 Hz, Ar. CeH), 8.01 (d,
1H, J¼8.0 Hz, Ar. CeH), 7.75e7.69 (m, 2H, Ar. CeH), 7.66 (d, 1H,
J¼7.6 Hz, Ar. CeH), 7.61e7.57 (m, 1H, Ar. CeH), 7.45e7.39 (m, 7H, Ar.
CeH), 7.28 (t, 2H, J¼9.0 Hz, Ar. CeH), 7.23 (d, 1H, J¼7.2 Hz, Ar. CeH),
7.16 (t, 2H, J¼7.4 Hz, Ar. CeH); 13C NMR (CDCl3, 100 MHz):
d
196.5,
3H, AreOCH3); 13C NMR (CDCl3, 100 MHz):
d 195.3, 163.3, 153.9,
153.8, 153.4, 141.4, 141.0, 140.9, 138.8, 138.5, 137.1, 132.6, 131.6, 131.3,
130.3, 130.2, 130.1, 129.9, 129.8, 129.3, 129.1, 128.8, 128.3, 127.9; nmax
(KBr): 3052, 2922, 2851, 1789, 1736, 1658, 1597, 1572, 1475, 1446,
1393, 1342, 1315, 1291, 1269, 1218, 1059, 1025, 977, 937, 919, 761;
HRMS (ESI) calcd for C27H18N2O (MþHþ) 387.1492, found 387.1485.
153.5,141.4, 141.1, 140.7,139.3,138.5,132.5,132.4,131.6, 130.3,129.9,
129.8, 129.3, 129.2, 128.8, 128.2, 127.9, 113.8, 113.3, 55.6; nmax (KBr):
2923, 2835, 2362, 1637, 1595, 1572, 1418, 1341, 1286, 1257, 1176,
1152, 1059, 1026, 924, 845, 775; HRMS (ESI) calcd for C28H20N2O2
(MþHþ) 417.1598, found 417.1603.
4.3.2. (2-(3-Phenylquinoxalin-2-yl)phenyl)(p-tolyl)methanone
(1b). The general procedure was followed. The product was puri-
fied by column chromatography (6% EtOAc/hexane) to give the title
compound 1b (144 mg, 72%) as Gummy; Rf (10% EtOAc/hexane)
4.3.6. (4-Butoxyphenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
anone (1f). The general procedure was followed. The product was
purified by column chromatography (6% EtOAc/hexane) to give the
title compound 1f (150 mg, 66%) as Gummy; Rf (10% EtOAc/hexane)
0.56; 1H NMR (CDCl3, 400 MHz):
d
8.10 (d, 1H, J¼7.2 Hz, Ar. CeH),
0.52; 1H NMR (CDCl3, 400 MHz):
d
8.10 (d, 1H, J¼7.6 Hz, Ar. CeH),
7.98 (d, 1H, J¼7.2 Hz, Ar. CeH), 7.72e7.66 (m, 2H, Ar. CeH), 7.59 (d,
1H, J¼7.6 Hz, Ar. CeH), 7.56e7.52 (m, 1H, Ar. CeH), 7.43e7.41 (m,
4H, Ar. CeH), 7.31 (d, 2H, J¼8.4 Hz, Ar. CeH), 7.22 (d, 1H, J¼5.6 Hz,
Ar. CeH), 7.17e7.11 (m, 2H, Ar. CeH), 7.07 (d, 2H, J¼8.0 Hz, Ar. CeH),
7.98 (d, 1H, J¼7.6 Hz, Ar. CeH), 7.72e7.65 (m, 2H, Ar. CeH), 7.59 (d,
1H, J¼7.6 Hz, Ar. CeH), 7.54e7.51 (m, 1H, Ar. CeH), 7.43e7.39 (m,
6H, Ar. CeH), 7.20 (d, 1H, J¼7.2 Hz, Ar. CeH), 7.14 (t, 2H, J¼7.0 Hz, Ar.
CeH), 6.64 (d, 2H, J¼9.2 Hz, Ar. CeH), 3.96 (t, 2H, J¼6.4 Hz,
AreOCH2e), 1.79e1.72 (m, 2H, aliphatic-CH2e), 1.51e1.43 (m, 2H,
aliphatic-CH2e), 0.97 (t, 3H, J¼7.4 Hz, aliphatic-CH3); 13C NMR
2.34 (s, 3H, AreCH3); 13C NMR (CDCl3, 100 MHz):
d 196.4, 153.9,
153.5, 143.4, 141.4, 141.1, 140.9, 139.2, 138.6, 134.7, 131.6, 131.1, 130.4,
130.3, 130.0, 129.8, 129.4, 129.2, 128.9, 128.8, 128.3, 127.9, 21.8; nmax
(KBr): 3054, 2912, 2846, 1659, 1602, 1443, 1399, 1338, 1262, 1050,
1024, 927, 801, 771; Anal. Calcd for C28H20N2O: C 83.98, H 5.03, N
6.99; found: C 84.17, H 5.11, N 7.06.
(CDCl3, 100 MHz):
d 195.3, 162.9, 154.0, 153.5, 141.4, 141.1, 140.8,
139.5, 138.6, 132.6, 131.6, 130.9, 130.4, 130.0, 129.8, 129.4, 129.3,
128.9, 128.3, 127.9, 113.8, 68.1, 31.3, 19.4, 13.9; nmax (KBr): 3063,
2948, 2867, 1661, 1598, 1573, 1506, 1469, 1418, 1395, 1345, 1280,
1247, 1178, 1151, 1109, 1068, 1025, 977, 929, 841, 766; Anal. Calcd for
4.3.3. (4-(tert-Butyl)phenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)
methanone (1c). The general procedure was followed. The product
was purified by column chromatography (5% EtOAc/hexane) to give
the title compound 1c (155 mg, 70%) as Gummy; Rf (10% EtOAc/
C31H26N2O2: C 81.20, H 5.72, N 6.11; found: C 81.37, H 5.85, N 6.21.
4.3.7. (3,4-Dimethoxyphenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)
methanone (1g). The general procedure was followed. The product
was purified by column chromatography (10% EtOAc/hexane) to
give the title compound 1g (140 mg, 63%) as Gummy; Rf (10% EtOAc/
hexane) 0.67; 1H NMR (CDCl3, 400 MHz):
d
8.11 (d, 1H, J¼6.8 Hz, Ar.
CeH), 8.02 (d, 1H, J¼6.8 Hz, Ar. CeH), 7.74e7.68 (m, 2H, Ar. CeH),
7.66 (d, 1H, J¼7.6 Hz, Ar. CeH), 7.59 (t, 1H, J¼7.2 Hz, Ar. CeH),
7.49e7.45 (m, 2H, Ar. CeH), 7.41 (d, 2H, J¼7.6 Hz, Ar. CeH), 7.36 (d,
2H, J¼6.4 Hz, Ar. CeH), 7.27 (d, 2H, J¼7.2 Hz, Ar. CeH), 7.21 (d, 1H,
J¼6.4 Hz, Ar. CeH), 7.14 (t, 2H, J¼7.2 Hz, Ar. CeH), 1.28 (s, 9H, 3ꢁ
hexane) 0.09; 1H NMR (CDCl3, 400 MHz):
d
8.05 (d, 1H, J¼8.0 Hz, Ar.
CeH), 7.93 (d, 1H, J¼7.2 Hz, Ar. CeH), 7.67e7.61 (m, 2H, Ar. CeH),
7.54e7.46 (m, 2H, Ar. CeH), 7.42e7.35 (m, 4H, Ar. CeH), 7.19e7.09
(m, 4H, Ar. CeH), 6.93 (d, 1H, J¼8.4 Hz, Ar. CeH), 6.63 (d, 1H,
J¼8.4 Hz, Ar. CeH), 3.83 (s, 3H, AreOCH3), 3.76 (s, 3H, AreOCH3);
aliphatic-CH3); 13C NMR (CDCl3, 100 MHz):
d 196.2, 156.3, 154.0,
153.6,141.5, 141.1, 140.9, 139.2, 138.5, 134.4, 131.6, 131.3, 130.4, 130.2,
130.0, 129.8, 129.4, 129.3, 128.9, 128.3, 128.1, 124.9, 35.2, 31.2; nmax
(KBr): 3057, 2961, 2862, 1728, 1657, 1603, 1476, 1462, 1396, 1343,
1311, 1289, 1268, 1103, 1056, 1025, 977, 931, 845, 789, 763; HRMS
(ESI) calcd for C31H26N2O (MþHþ) 443.2118, found 443.2110.
13C NMR (CDCl3, 100 MHz):
d 195.3, 153.9, 153.5, 153.1, 148.7, 141.4,
141.1, 140.9, 139.3, 138.6, 131.6, 130.9, 130.4, 130.0, 129.9, 129.4,
129.2, 128.9, 128.2, 127.9, 125.8, 111.8, 109.7, 56.2, 56.0; nmax (KBr):
3054, 2950, 2929, 2829, 1638, 1578, 1511, 1459, 1452, 1417, 1343,
1292, 1267, 1233, 1180, 1134, 1059, 1027, 978, 799, 763; HRMS (ESI)
calcd for C29H22N2O3 (MþHþ) 447.1703, found 447.1694.
4.3.4. [1,10-Biphenyl]-4-yl(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
anone (1d). The general procedure was followed. The product was
purified by column chromatography (6% EtOAc/hexane) to give the
title compound 1d (168 mg, 73%) as Gummy; Rf (10% EtOAc/hexane)
4.3.8. (4-Chlorophenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
anone (1h). The general procedure was followed. The product was
purified by column chromatography (5% EtOAc/hexane) to give the
title compound 1h (172 mg, 82%) as Gummy; Rf (10% EtOAc/hexane)
0.50; 1H NMR (CDCl3, 400 MHz):
d
8.13 (d, 1H, J¼6.8 Hz, Ar. CeH),
8.03 (d, 1H, J¼8.8 Hz, Ar. CeH), 7.75e7.70 (m, 2H, Ar. CeH), 7.67 (d,
1H, J¼7.6 Hz, Ar. CeH), 7.62 (d, 1H, J¼7.2 Hz, Ar. CeH), 7.58 (d, 3H,
J¼7.2 Hz, Ar. CeH), 7.53e7.45 (m,10H, Ar. CeH), 7.39 (t,1H, J¼7.4 Hz,
Ar. CeH), 7.25 (t, 1H, J¼7.2 Hz, Ar. CeH), 7.17 (t, 1H, J¼7.4 Hz, Ar.
0.58; 1H NMR (CDCl3, 400 MHz):
d
8.14 (d, 1H, J¼8.6 Hz, Ar. CeH),
8.01 (d, 1H, J¼8.6 Hz, Ar. CeH), 7.77e7.70 (m, 2H, Ar. CeH), 7.67 (d,
1H, J¼6.8 Hz, Ar. CeH), 7.61 (t, 1H, J¼7.6 Hz, Ar. CeH), 7.47e7.39 (m,
4H, Ar. CeH), 7.34 (d, 2H, J¼8.4 Hz, Ar. CeH), 7.27 (d, 3H, J¼7.2 Hz,
Ar. CeH), 7.17 (t, 2H, J¼7.6 Hz, Ar. CeH); 13C NMR (CDCl3, 100 MHz):
CeH); 13C NMR (CDCl3, 100 MHz):
d 196.1, 153.8, 153.5, 145.3, 141.4,
141.1, 140.9, 140.1, 138.9, 138.5, 135.8, 131.7, 131.3, 130.7, 130.4, 130.2,
130.1, 129.9, 129.4, 129.2, 129.1, 128.9, 128.3, 128.1, 127.4, 126.7; nmax
(KBr): 3054, 2956, 2920, 2851, 1651, 1603, 1478, 1397, 1344, 1311,
1275, 1215, 1155, 1056, 1026, 976, 934, 853, 798, 760; Anal. Calcd for
d 195.4, 153.6, 153.4, 141.4, 141.1, 140.9, 139.9, 138.5, 135.5, 131.8,
131.6, 131.5, 130.4, 130.2, 130.0, 129.9, 129.4, 129.2, 128.9, 128.6,
128.4, 128.1; nmax (KBr): 3058, 2918, 2845, 1661, 1585, 1479, 1443,
1398, 1343, 1270, 1218, 1174, 1090, 1054, 977, 929, 849, 771; HRMS
(ESI) calcd for C27H17ClN2O (MþHþ) 421.1102, found 421.1094.
C
33H22N2O: C 85.69, H 4.79, N 6.06; found: C 85.91, H 4.88, N 6.17.
4.3.5. (4-Methoxyphenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
4.3.9. (3-Chlorophenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
anone (1e). The general procedure was followed. The product was
anone (1i). The general procedure was followed. The product was

2428
S.K. Santra et al. / Tetrahedron 70 (2014) 2422e2430
purified by column chromatography (6% EtOAc/hexane) to give the
title compound 1i (168 mg, 80%) as Gummy; Rf (10% EtOAc/hexane)
hexane) 0.35; 1H NMR (CDCl3, 400 MHz):
d
8.06 (d, 1H, J¼7.6 Hz, Ar.
CeH), 7.93 (d, 1H, J¼7.2 Hz, Ar. CeH), 7.88 (d, 2H, J¼6.8 Hz, Ar. CeH),
7.69e7.64 (m, 2H, Ar. CeH), 7.61 (d, 1H, J¼7.6 Hz, Ar. CeH), 7.55 (t,
1H, J¼7.4 Hz, Ar. CeH), 7.41e7.31 (m, 6H, Ar. CeH), 7.19 (t, 1H,
J¼7.0 Hz, Ar. CeH), 7.09 (t, 2H, J¼7.0 Hz, Ar. CeH), 3.87 (s, 3H,
0.56; 1H NMR (CDCl3, 400 MHz):
d
8.14 (d, 1H, J¼6.8 Hz, Ar. CeH),
8.06 (d, 1H, J¼7.6 Hz, Ar. CeH), 7.77e7.71 (m, 3H, Ar. CeH), 7.65 (t,
1H, J¼7.4 Hz, Ar. CeH), 7.47 (t, 1H, J¼7.6 Hz, Ar. CeH), 7.43 (s, 1H, Ar.
CeH), 7.41e7.37 (m, 3H, Ar. CeH), 7.31 (t, 2H, J¼8.4 Hz, Ar. CeH),
7.26 (t, 2H, J¼2.8 Hz, Ar. CeH), 7.22e7.16 (m, 2H, Ar. CeH); 13C NMR
AreCO2CH3); 13C NMR (CDCl3, 100 MHz):
d 195.9, 166.4, 155.2,
153.5, 153.4, 141.5, 141.1, 141.0, 140.7, 138.6, 133.4, 131.9, 130.4, 130.2,
130.0, 129.9, 129.4, 129.3, 129.2, 128.9, 128.4, 128.2, 52.6; nmax (KBr):
3058, 2949, 2840, 1723, 1661, 1476, 1435, 1404, 1344, 1274, 1104,
1056, 1018, 977, 931, 868, 798, 768; Anal. Calcd for C29H20N2O3: C
78.36, H 4.54, N 6.30; found: C 78.51, H 4.63, N 6.42.
(CDCl3, 100 MHz):
d 195.0, 153.5, 153.3, 141.4, 141.1, 141.0, 138.6,
138.4, 138.1, 134.1, 132.6, 131.9, 130.4, 130.2, 129.9, 129.4, 129.2,
129.0, 128.3, 128.2, 127.9; nmax (KBr): 3053, 2918, 2845, 1660, 1591,
1568,1477,1440,1418,1390,1344,1289,1257,1219,1154,1071,1054,
1025, 977, 939, 769; HRMS (ESI) calcd for C27H17ClN2O (MþHþ)
421.1102, found 421.1106.
4.3.14. (4-Chloro-3-nitrophenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)
methanone (1n). The general procedure was followed. The product
was purified by column chromatography (8% EtOAc/hexane) to give
the title compound 1n (153 mg, 66%) as Gummy; Rf (10% EtOAc/
4.3.10. (3-Fluorophenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
anone (1j). The general procedure was followed. The product was
purified by column chromatography (6% EtOAc/hexane) to give the
title compound 1j (157 mg, 78%) as Gummy; Rf (10% EtOAc/hexane)
hexane) 0.37; 1H NMR (CDCl3, 400 MHz):
d
8.13 (d, 1H, J¼6.8 Hz, Ar.
CeH), 8.04 (d, 1H, J¼7.6 Hz, Ar. CeH), 7.78 (t, 1H, J¼7.0 Hz, Ar. CeH),
7.76e7.73 (m, 2H, Ar. CeH), 7.69 (t, 1H, J¼7.6 Hz, Ar. CeH), 7.61e7.57
(m, 2H, Ar. CeH), 7.49 (t, 2H, J¼6.8 Hz, Ar. CeH), 7.34e7.32 (m, 3H,
Ar. CeH), 7.19 (t, 1H, J¼7.2 Hz, Ar. CeH), 7.12 (t, 2H, J¼7.4 Hz, Ar.
0.52; 1H NMR (CDCl3, 400 MHz):
d
8.12 (d, 1H, J¼8.0 Hz, Ar. CeH),
8.03 (d, 1H, J¼8.0 Hz, Ar. CeH), 7.76e7.72 (m, 2H, Ar. CeH), 7.69 (s,
1H, Ar. CeH), 7.63 (t, 1H, J¼6.7 Hz, Ar. CeH), 7.46 (t, 1H, J¼7.6 Hz, Ar.
CeH), 7.40 (t, 3H, J¼7.6 Hz, Ar. CeH), 7.26e7.23 (m, 2H, Ar. CeH),
7.19 (d, 2H, J¼9.2 Hz, Ar. CeH), 7.15 (d, 2H, J¼7.2 Hz, Ar. CeH), 7.02
CeH); 13C NMR (CDCl3, 100 MHz):
d 192.9, 153.1, 147.4, 141.5, 141.1,
138.4, 137.0, 136.4, 133.6, 132.6, 132.3, 131.9, 131.3, 130.6, 130.5,
130.3, 129.5, 129.2, 129.1, 128.6, 128.5, 126.8; nmax (KBr): 3060, 2926,
2851, 1728, 1664, 1596, 1535, 1390, 1344, 1294, 1273, 1246, 1047,
1023, 977, 949, 908, 770; HRMS (ESI) calcd for C27H16ClN3O3
(MþHþ) 466.0953, found 466.0949.
(d,1H, J¼9.2 Hz, Ar. CeH); 13C NMR (CDCl3,100 MHz):
d 195.2,163.5,
161.0, 153.6, 153.4, 141.5, 141.1, 141.0, 139.2, 138.5, 138.3, 131.9, 131.7,
130.4, 130.2, 130.0, 129.8, 129.7, 129.4, 129.2, 128.9, 128.4, 128.2,
125.8, 119.8, 119.6, 116.8, 116.6; nmax (KBr): 3060, 2923, 1840, 1731,
1660, 1585, 1478, 1441, 1394, 1344, 1292, 1270, 1205, 1128, 1056,
1025, 977, 861, 840, 800, 769; HRMS (ESI) calcd for C27H17FN2O
(MþHþ) 405.1402, found 405.1390.
4.3.15. (2-(3-Phenylquinoxalin-2-yl)phenyl)(thiophen-2-yl)meth-
anone (1o). The general procedure was followed. The product was
purified by column chromatography (8% EtOAc/hexane) to give the
title compound 1o (145 mg, 74%) as Gummy; Rf (10% EtOAc/hexane)
4.3.11. (4-Nitrophenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
anone (1k). The general procedure was followed. The product was
purified by column chromatography (8% EtOAc/hexane) to give the
title compound 1k (168 mg, 78%) as Gummy; Rf (10% EtOAc/hexane)
0.37; 1H NMR (CDCl3, 400 MHz):
d
8.13 (d, 1H, J¼8.0 Hz, Ar. CeH),
8.03 (d, 1H, J¼8.4 Hz, Ar. CeH), 7.75e7.70 (m, 2H, Ar. CeH), 7.67 (d,
1H, J¼8.0 Hz, Ar. CeH), 7.62e7.56 (m, 3H, Ar. CeH), 7.46 (t, 1H,
J¼7.4 Hz, Ar. CeH), 7.37 (d, 2H, J¼8.4 Hz, Ar. CeH), 7.13 (t, 1H,
J¼6.6 Hz, Ar. CeH), 7.07 (d, 2H, J¼7.6 Hz, Ar. CeH), 7.03 (t, 1H,
J¼3.6 Hz, Ar. CeH), 6.93 (t, 1H, J¼4.2 Hz, Ar. CeH); 13C NMR (CDCl3,
0.39; 1H NMR (CDCl3, 400 MHz):
d
8.14 (d, 2H, J¼8.8 Hz, Ar. CeH),
8.01 (d, 1H, J¼8.0 Hz, Ar. CeH), 7.79e7.73 (m, 3H, Ar. CeH), 7.67 (t,
1H, J¼7.6 Hz, Ar. CeH), 7.52e7.47 (m, 3H, Ar. CeH), 7.40 (d, 2H,
J¼6.8 Hz, Ar. CeH), 7.37 (t, 2H, J¼7.0 Hz, Ar. CeH), 7.29 (d, 1H,
J¼6.4 Hz, Ar. CeH), 7.18 (t, 2H, J¼7.4 Hz, Ar. CeH); 13C NMR (CDCl3,
100 MHz):
d 188.2, 153.7, 153.5, 143.8, 141.5, 141.2, 140.5, 138.7,
138.3, 135.3, 134.4, 131.9, 131.5, 130.4, 130.1, 129.9, 129.5, 129.4,
129.3, 128.8, 128.2, 128.1, 127.8; nmax (KBr): 3059, 2913, 2851, 1621,
1515, 1474, 1409, 1353, 1342, 1297, 1052, 1023, 976, 845, 760; HRMS
(ESI) calcd for C25H16N2OS (MþHþ) 393.1056, found 393.1051.
100 MHz): d 194.8, 153.1, 149.9, 142.1, 141.4, 141.1, 138.5, 137.7, 132.3,
132.1, 130.8, 130.4, 130.3, 130.2, 129.9, 129.4, 129.1, 128.5, 128.4,
123.2; nmax (KBr): 3060, 2924, 2851, 1731, 1663, 1602, 1523, 1474,
1446, 1393, 1345, 1314, 1265, 1104, 1054, 1025, 977, 932, 864, 851,
771; HRMS (ESI) calcd for C27H17N3O3 (MþHþ) 432.1343, found
432.1333.
4.3.16. Naphthalen-2-yl(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
anone (1p). The general procedure was followed. The product was
purified by column chromatography (6% EtOAc/hexane) to give the
title compound 1p (157 mg, 72%) as Gummy; Rf (10% EtOAc/hexane)
4.3.12. (3-Nitrophenyl)(2-(3-phenylquinoxalin-2-yl)phenyl)meth-
anone (1l). The general procedure was followed. The product was
purified by column chromatography (8% EtOAc/hexane) to give the
title compound 1l (157 mg, 73%) as Gummy; Rf (10% EtOAc/hexane)
0.48; 1H NMR (CDCl3, 400 MHz):
d
8.08 (d, 1H, J¼6.4 Hz, Ar. CeH),
7.99 (d, 1H, J¼7.6 Hz, Ar. CeH), 7.82 (d, 1H, J¼8.0 Hz, Ar. CeH), 7.75
(d, 2H, J¼8.4 Hz, Ar. CeH), 7.74 (s,1H, Ar. CeH), 7.72e7.66 (m, 3H, Ar.
CeH), 7.65e7.59 (m, 2H, Ar. CeH), 7.56 (t, 1H, J¼7.4 Hz, Ar. CeH),
7.52e7.46 (m, 3H, Ar. CeH), 7.42 (d, 2H, J¼6.8 Hz, Ar. CeH),
0.31; 1H NMR (CDCl3, 400 MHz):
d
8.29 (d, 1H, J¼8.4 Hz, Ar. CeH),
8.11 (d, 1H, J¼6.4 Hz, Ar. CeH), 8.03 (d, 1H, J¼6.8 Hz, Ar. CeH), 7.98
(s,1H, Ar. CeH), 7.79 (d, 2H, J¼7.2 Hz, Ar. CeH), 7.75e7.69 (m, 3H, Ar.
CeH), 7.52e7.47 (m, 2H, Ar. CeH), 7.37e7.33 (m, 3H, Ar. CeH),
7.13e7.07 (m, 3H, Ar. CeH); 13C NMR (CDCl3, 100 MHz):
d 196.5,
153.9, 153.5, 141.4, 141.1, 139.1, 138.6, 135.4, 134.4, 132.3, 132.1, 131.7,
131.4, 130.4, 130.0, 129.8, 129.6, 129.4, 129.2, 128.9, 128.4, 128.2,
128.1, 127.8, 126.7, 125.3; nmax (KBr): 3056, 2956, 2922, 2846, 1651,
1625, 1594, 1569, 1476, 1462, 1393, 1344, 1292, 1278, 1232, 1149,
1122, 1100, 1055, 1024, 977, 921, 905, 823, 789, 753; HRMS (ESI)
calcd for C31H20N2O (MþHþ) 437.1648, found 437.1639.
7.15e7.09 (m, 3H, Ar. CeH); 13C NMR (CDCl3, 100 MHz):
d 193.9,
153.2, 147.7, 141.5, 141.1, 138.3, 137.4, 135.3, 132.4, 132.2, 130.5, 130.4,
130.2, 129.7, 129.5, 129.2, 129.0, 128.5, 128.4, 127.0, 124.9; nmax
(KBr): 3060, 2956, 2917, 2846, 1665, 1610, 1528, 1476, 1393, 1344,
1297, 1256, 1215, 1080, 1059, 1023, 971, 910, 768; HRMS (ESI) calcd
for C27H17N3O3 (MþHþ) 432.1343, found 432.1336.
4.3.17. (5-Methyl-2-(3-(p-tolyl)quinoxalin-2-yl)phenyl)(phenyl)
methanone (2a). The general procedure was followed. The product
was purified by column chromatography (5% EtOAc/hexane) to give
the title compound 2a (165 mg, 80%) as Gummy; Rf (10% EtOAc/
4.3.13. Methyl
4-(2-(3-phenylquinoxalin-2-yl)benzoyl)benzoate
(1m). The general procedure was followed. The product was pu-
rified by column chromatography (8% EtOAc/hexane) to give the
title compound 1m (175 mg, 79%) as Gummy; Rf (10% EtOAc/
hexane) 0.59; 1H NMR (CDCl3, 400 MHz):
d
8.07 (d, 1H, J¼8.4 Hz, Ar.

S.K. Santra et al. / Tetrahedron 70 (2014) 2422e2430
2429
CeH), 7.98 (d, 1H, J¼7.2 Hz, Ar. CeH), 7.71e7.64 (m, 2H, Ar. CeH),
7.55 (d, 1H, J¼7.6 Hz, Ar. CeH), 7.44e7.38 (m, 4H, Ar. CeH),
7.29e7.25 (m, 4H, Ar. CeH), 7.22 (s, 1H, Ar. CeH), 6.93 (d, 2H,
J¼8.0 Hz, Ar. CeH), 2.39 (s, 3H, AreCH3), 2.27 (s, 3H, AreCH3); 13C
hexane) to give the title compound 6a and 6a0 (143 mg, 68%) as
Gummy; Rf (10% EtOAc/hexane) 0.74; 1H NMR (CDCl3, 400 MHz):
d
8.05 (s, 1H, Ar. CeH), 7.99 (d, 1H, J¼9.2 Hz, Ar. CeH), 7.92 (s, 1H, Ar.
CeH), 7.87 (d, 1H, J¼8.8 Hz, Ar. CeH), 7.61e7.58 (m, 2H, Ar. CeH),
7.56e7.49 (m, 4H, Ar. CeH), 7.42e7.37 (m, 6H, Ar. CeH), 7.34e7.30
(m, 7H, Ar. CeH), 7.23 (t, 4H, J¼7.6 Hz, Ar. CeH), 7.19e7.16 (m, 3H,
Ar. CeH), 7.10e7.07 (m, 4H, Ar. CeH); 13C NMR (CDCl3, 100 MHz):
NMR (CDCl3, 100 MHz):
d 196.5, 153.7, 153.5, 141.3, 140.9, 138.8,
138.7, 138.2, 137.9, 137.1, 135.7, 132.4, 131.9, 131.5, 130.6, 130.3, 130.0,
129.7, 129.5, 129.2, 129.1, 128.9, 127.8, 21.3; nmax (KBr): 3038, 2912,
1656, 1593, 1443, 1401, 1341, 1286, 1267, 1179, 1050, 996, 828, 779,
696; Anal. Calcd for C29H22N2O: C 84.03, H 5.35, N 6.76; found: C
84.15, H 5.42, N 6.85.
d
196.5, 154.9, 154.3, 154.1, 153.6, 141.6, 141.3, 140.6, 139.9, 139.5,
138.7, 138.1,138.0,136.9,135.6,135.5,132.7,131.5,131.4,130.9,130.8,
130.6, 130.3, 130.1, 129.1, 129.0, 128.3, 128.2, 128.0; IR (KBr, cmꢂ1):
3058, 2919, 1850, 1736, 1656, 1596, 1577, 1466, 1446, 1388, 1341,
1314, 1270, 1192, 1174, 1152, 1067, 1025, 978, 926, 876, 833, 804, 763,
727; HRMS (ESI) calcd for C27H17ClN2O (MþHþ) 421.1102, found
421.1110.
4.3.18. (2-(6,7-Dichloro-3-phenylquinoxalin-2-yl)phenyl)(phenyl)
methanone (3a). The general procedure was followed. The product
was purified by column chromatography (4% EtOAc/hexane) to give
the title compound 3a (152 mg, 67%) as Gummy; Rf (10% EtOAc/
hexane) 0.81; 1H NMR (CDCl3, 400 MHz):
d
8.24 (s, 1H, Ar. CeH),
4.3.22. (5-Methoxy-4-methyl-2(3-phenylquinoxalin-2-yl)phenyl)(-
phenyl)methanone (7a). The general procedure was followed. The
product was purified by column chromatography (6% EtOAc/hex-
ane) to give the title compound 7a (159 mg, 74%) as Gummy; Rf
8.12 (s, 1H, Ar. CeH), 7.61e7.59 (m, 2H, Ar. CeH), 7.49 (d, 1H,
J¼7.2 Hz, Ar. CeH), 7.47e7.45 (m, 2H, Ar. CeH), 7.41e7.39 (m, 4H, Ar.
CeH), 7.31 (t, 2H, J¼7.6 Hz, Ar. CeH), 7.25 (t, 1H, J¼7.2 Hz, Ar. CeH),
7.16 (t, 2H, J¼6.6 Hz, Ar. CeH); 13C NMR (CDCl3, 100 MHz):
d
196.4,
(10% EtOAc/hexane) 0.27; 1H NMR (CDCl3, 400 MHz):
d 8.09e8.05
155.2, 154.6, 140.4, 140.1, 139.8, 138.7, 137.8, 136.9, 134.4, 134.2,
132.8, 131.5, 130.4, 130.3, 130.1, 129.9, 129.8, 129.3, 128.3, 128.1; nmax
(KBr): 3059, 2956, 2917, 2846, 1655, 1596, 1574, 1441, 1389, 1337,
1315, 1271, 1190, 1152, 1103, 1075, 1056, 1024, 962, 926, 881, 831,
763, 725; HRMS (ESI) calcd for C27H16Cl2N2O (MþHþ) 455.0712,
found 455.0709.
(m, 2H, Ar. CeH), 7.72e7.67 (m, 2H, Ar. CeH), 7.52 (s, 1H, Ar. CeH),
7.38e7.31 (m, 6H, Ar. CeH), 7.21 (d, 2H, J¼7.6 Hz, Ar. CeH),
7.18e7.13 (m, 2H, Ar. CeH), 6.85 (s, 1H, Ar. CeH), 3.76 (s, 3H,
AreOCH3), 2.33 (s, 3H, AreCH3); 13C NMR (CDCl3, 150 MHz):
d
196.1, 157.3, 153.7, 153.6, 141.1, 141.0, 138.6, 137.4, 137.2, 133.7,
132.8, 132.3, 130.8, 130.3, 129.9, 129.7, 129.2, 128.9, 128.7, 128.2,
127.8, 111.8, 55.7, 16.5; IR (KBr, cmꢂ1): 3442, 3058, 2961, 2924,
2841, 1657, 1598, 1564, 1502, 1478, 1562, 1446, 1339, 1271, 1242,
1220, 1171, 1127, 1110, 1055, 1027, 1013, 968, 907, 872, 813, 766,
732; HRMS (ESI) calcd for C29H22N2O2 (MþHþ) 431.1759, found
431.1766.
4.3.19. (2-(6,7-Dichloro-3-(p-tolyl)quinoxalin-2-yl)-5-
methylphenyl)(phenyl)methanone (4a). The general procedure was
followed. The product was purified by column chromatography (4%
EtOAc/hexane) to give the title compound 4a (188 mg, 78%) as
Gummy; Rf (10% EtOAc/hexane) 0.89; 1H NMR (CDCl3, 400 MHz):
d
8.12 (s, 1H, Ar. CeH), 8.02 (s, 1H, Ar. CeH), 7.45 (d, 1H, J¼7.6 Hz, Ar.
4.3.23. (2-(3-(4-Methoxy-3-methylphenyl)quinoxalin-2-yl)phenyl)(-
phenyl)methanone (7a0). The general procedure was followed. The
product was purified by column chromatography (6% EtOAc/hex-
ane) to give the title compound 7a0 (23 mg, 11%) as Gummy; Rf (10%
CeH), 7.39 (t, 1H, J¼7.4 Hz, Ar. CeH), 7.34e7.30 (m, 3H, Ar. CeH),
7.23e7.16 (m, 5H, Ar. CeH), 6.68 (d, 2H, J¼7.6 Hz, Ar. CeH), 2.33 (s,
3H, AreCH3), 2.20 (s, 3H, AreCH3); 13C NMR (CDCl3, 100 MHz):
d
196.5, 155.2, 154.7, 140.1, 139.8, 139.4, 138.8, 138.5, 137.7, 136.9,
EtOAc/hexane) 0.22; 1H NMR (CDCl3, 400 MHz):
d 8.10 (d, 1H,
135.1, 134.2, 133.9, 132.7, 132.2, 131.5, 130.9, 130.3, 130.1, 129.9,
129.8, 129.1, 127.9, 21.4; nmax (KBr): 3054, 3027, 2920, 2846, 1736,
1655, 1596, 1447, 1386, 1336, 1315, 1293, 1270, 1210, 1182, 1105,
1050, 1020, 963, 880, 824, 800, 759, 715; HRMS (ESI) calcd for
J¼8.4 Hz, Ar. CeH), 8.05 (d, 1H, J¼8.4 Hz, Ar. CeH), 7.78 (d, 1H,
J¼7.2 Hz, Ar. CeH), 7.74e7.69 (m, 2H, Ar. CeH), 7.66 (t, 1H, J¼7.2 Hz,
Ar. CeH), 7.47e7.43 (m, 3H, Ar. CeH), 7.36 (d, 2H, J¼7.2 Hz, Ar. CeH),
7.27 (d, 2H, J¼7.6 Hz, Ar. CeH), 7.16 (s, 1H, Ar. CeH), 7.07 (d, 1H,
J¼8.4 Hz, Ar. CeH), 6.52 (d, 1H, J¼8.8 Hz, Ar. CeH), 3.76 (s, 3H,
C
29H20Cl2N2O (MþHþ) 483.1025, found 483.1017.
AreOCH3), 1.91 (s, 3H, AreCH3); 13C NMR (CDCl3, 150 MHz):
d 195.7,
4.3.20. (2-(6-Methyl-3-phenylquinoxalin-2-yl)phenyl)(phenyl)meth-
anone and (2-(7-methyl-3-phenylquinoxalin-2-yl)phenyl)(phenyl)
methanone (5a and 5a0). The general procedure was followed. The
product was purified by column chromatography (6% EtOAc/hex-
ane) to give the title compound 5a and 5a0 (140 mg, 70%) as
Gummy; Rf (10% EtOAc/hexane) 0.55; 1H NMR (CDCl3, 400 MHz):
158.6,153.9,153.5,141.6,141.4,141.0,136.9,132.9,132.6,131.8,130.4,
130.2, 130.1, 129.9, 129.6, 129.5, 129.3, 129.2, 127.9, 127.8, 126.9,
109.5, 55.5, 16.1; IR (KBr, cmꢂ1): 3442, 3054, 2958, 2923, 2843,
1658, 1609, 1558, 1506, 1447, 1384, 1343, 1268, 1253, 1173, 1134,
1030, 927, 807, 765, 764, 737; HRMS (ESI) calcd for C29H22N2O2
(MþHþ) 431.1759, found 431.1764.
d
7.99 (d, 1H, J¼8.8 Hz, Ar. CeH), 7.88e7.86 (m, 2H, Ar. CeH), 7.76 (s,
1H, Ar. CeH), 7.62e7.59 (m, 2H, Ar. CeH), 7.57e7.50 (m, 5H, Ar.
CeH), 7.45e7.38 (m, 12H, Ar. CeH), 7.29e7.24 (m, 5H, Ar. CeH), 7.20
(d, 2H, J¼7.2 Hz, Ar. CeH), 7.15e7.12 (m, 4H, Ar. CeH), 2.56 (s, 3H,
4.3.24. (2-(3-(4-Bromophenyl)quinoxalin-2-yl)phenyl)(phenyl)
methanone (8a). The general procedure was followed. The product
was purified by column chromatography (6% EtOAc/hexane) to give
the title compound 8a (160 mg, 69%) as Gummy; Rf (10% EtOAc/
AreCH3), 2.54 (s, 3H, AreCH3); 13C NMR (CDCl3, 100 MHz):
d 196.5,
153.5, 153.2, 152.7, 152.5, 141.3, 141.0, 140.9, 140.8, 140.4, 140.2,
139.8,139.5, 138.8,138.6, 137.1, 132.5, 132.3, 132.1, 131.6, 131.2, 130.2,
130.1, 129.9, 128.8, 128.7, 128.6, 128.2, 128.1, 127.9, 127.8, 21.9; IR
(KBr, cmꢂ1): 3056, 3021, 2919, 2857, 1734, 1685, 1619, 1596, 1578,
1486,1446,1343,1314,1269,1203,1178,1154,1137,1074,1056,1025,
979, 937, 925, 829, 805, 765, 753, 730; HRMS (ESI) calcd for
hexane) 0.40; 1H NMR (CDCl3, 600 MHz):
d
8.12 (d, 1H, J¼8.4 Hz, Ar.
CeH), 8.04 (d, 1H, J¼7.2 Hz, Ar. CeH), 7.76e7.69 (m, 2H, Ar. CeH),
7.69 (d, 1H, J¼7.8 Hz, Ar. CeH), 7.65e7.62 (m, 1H, Ar. CeH), 7.51 (t,
1H, J¼7.5 Hz, Ar. CeH), 7.49e7.43(m, 3H, Ar. CeH), 7.41 (d, 2H,
J¼7.8 Hz, Ar. CeH), 7.35 (t, 2H, J¼7.8 Hz, Ar. CeH), 7.28e7.23 (m, 3H,
AreCH3); 13C NMR (CDCl3, 150 MHz):
d 196.4, 153.7, 152.4, 141.4,
C
28H20N2O (MþHþ) 401.1648, found 401.1653.
141.3, 140.8, 137.5, 136.8, 132.9, 132.1, 131.8, 131.7, 131.5, 130.4, 130.3,
130.2, 130.1, 129.4, 129.3, 128.4, 128.2, 128.1, 123.8; IR (KBr, cmꢂ1):
3440, 3059, 2961, 2923, 2846, 1657, 1596, 1579, 1489, 1478, 1448,
1343, 1316, 1290, 1270, 1220, 1071, 1056, 1037, 1025, 1011, 977, 937,
927, 835, 807, 762, 733; HRMS (ESI) calcd for C27H17BrN2O (MþHþ)
465.0602, found 465.0608.
4.3.21. (2-(6-Chloro-3-phenylquinoxalin-2-yl)phenyl)(phenyl)meth-
anone and (2-(7-chloro-3-phenylquinoxalin-2-yl)phenyl)(phenyl)
methanone (6a and 6a0). The general procedure was followed. The
product was purified by column chromatography (5% EtOAc/

2430
S.K. Santra et al. / Tetrahedron 70 (2014) 2422e2430
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(g) Wu, Y.; Choy, P. Y.; Mao, F.; Kwong, F. Y. Chem. Commun. 2013, 689; (h) Yin,
Z.; Sun, P. J. Org. Chem. 2012, 77, 11339; (i) Pan, C.; Jia, X.; Cheng, J. Synthesis
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4.3.25. (2-(3-Phenylquinoxalin-2-yl)phenyl)(o-tolyl)methanone
(1q). The general procedure was followed. The product was puri-
fied by column chromatography (5% EtOAc/hexane) to give the title
compound 1q (122 mg, 61%) as Gummy; Rf (10% EtOAc/hexane)
0.63; 1H NMR (CDCl3, 400 MHz):
d
8.16 (d, 1H, J¼8.8 Hz, Ar. CeH),
8.09 (d, 1H, J¼6.8 Hz, Ar. CeH), 8.00 (d, 1H, J¼6.4 Hz, Ar. CeH),
7.76e7.72 (m, 2H, Ar. CeH), 7.62e7.57 (m, 2H, Ar. CeH), 7.35e7.29
(m, 3H, Ar. CeH), 7.26e7.20 (m, 3H, Ar. CeH), 7.14 (d, 2H, J¼6.8 Hz,
Ar. CeH), 7.00 (t, 2H, J¼7.2 Hz, Ar. CeH), 2.24 (s, 3H, AreCH3); 13C
NMR (CDCl3, 100 MHz):
d 198.3, 154.4, 153.4, 141.3, 141.0, 140.9,
139.2, 138.8, 138.2, 137.5, 131.8, 131.7, 131.5, 131.0, 130.8, 130.3, 129.9,
129.7, 129.3, 129.1, 128.7, 128.3, 128.2, 124.8, 20.2; IR (KBr, cmꢂ1):
3049, 2961, 2921, 2851, 1742, 1659, 1593, 1563, 1454, 1342, 1297,
1260, 1215, 1098, 1025, 977, 927, 802, 763, 731; HRMS (ESI) calcd for
C
28H20N2O (MþHþ) 401.1648, found 401.1642.
4.4. Crystallographic description
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Mootz, D.; Deeg, A. J. Am. Chem. Soc. 1992, 114, 5887; (f) Chatani, N.; Asaumi, T.;
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529.
8. (a) Banerjee, A.; Santra, S. K.; Guin, S.; Rout, S. K.; Patel, B. K. Eur. J. Org. Chem.
2013, 1367; (b) Ding, Q.; Ji, H.; Ye, C.; Wang, J.; Wang, J.; Zhou, L.; Peng, Y.
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Crystal data were collected with Bruker Smart Apex-II CCD dif-
fractometer using graphite monochromated MoK
a radiation
ꢀ
(l
¼0.71073 A) at 298 K. Cell parameters were retrieved using
SMART20 software and refined with SAINT21 on all observed re-
flections. Data reduction was performed with the SAINT software
and corrected for Lorentz and polarization effects. Absorption cor-
rections were applied with the program SADABS. The structure was
solved by direct methods implemented in SHELX-9722 program and
refined by full-matrix least-squares methods on F2. All non-
hydrogen atomic positions were located in difference Fourier
maps and refined anisotropically. The hydrogen atoms were placed
in their geometrically generated positions. Colourless crystals were
isolated in rectangular shape from acetonitrile at room
temperature.
ꢁ
ꢁ
D.; Wang, X. Adv. Synth. Catal. 2011, 353, 3373; (d) Szabo, F.; Daru, J.; Simko, D.;
ꢁ
Nagy, T. Z.; Stirling, A.; Novak, Z. Adv. Synth. Catal. 2013, 355, 685; (e) Sharma, S.;
Khan, I. A.; Saxena, A. K. Adv. Synth. Catal. 2013, 355, 673; (f) Sharma, S.; Park, J.;
Park, E.; Kim, A.; Kim, M.; Kwak, J. H.; Jung, Y. H.; Kim, I. S. Adv. Synth. Catal.
2013, 355, 332; (g) Park, J.; Kim, A.; Sharma, S.; Kim, M.; Park, E.; Jeon, Y.; Lee,
Y.; Kwak, J. H.; Jung, Y. H.; Kim, I. S. Org. Biomol. Chem. 2013, 11, 2766.
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M.; Sharma, S.; Park, E.; Kim, A.; Lee, S. H.; Kwak, J. H.; Jung, Y. H.; Kim, I. S.
Chem. Commun. 2013, 1654; (c) Sharma, S.; Kim, A.; Park, E.; Park, J.; Kim, M.;
Kwak, J. H.; Lee, S. H.; Jung, Y. H.; Kim, I. S. Adv. Synth. Catal. 2013, 355, 667; (d)
Yao, J.; Feng, R.; Wu, Z.; Liu, Z.; Zhang, Y. Adv. Synth. Catal. 2013, 355, 1517; (e)
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CCDC number for compound 1e: CCDC 956425. This data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/datarequest/cif.
Acknowledgements
We are grateful to the DST (SR/S1/OC-79/2009) and CSIR
[02(0096)/12/EMR-II] for funding. S.K.S. and A.B. thanks to CSIR for
the fellowships. Thanks are also due to DST FIST for X-ray crystal-
lography and IIT Guwahati for Mass and NMR spectroscopic data.
13. (a) Wu, Y.; Choy, P. Y.; Mao, F.; Kwong, F. Y. Chem. Commun. 2013, 689; (b) Xu, Z.;
Xiang, B.; Sun, P. RSC Adv. 2013, 3, 1679.
Supplementary data
14. (a) Thomas, K. R. J.; Velusamy, M.; Lin, J. T.; Chuen, C.-H.; Tao, Y.-T. Chem. Mater.
2005, 17, 1860; (b) Katoh, A.; Yoshida, T.; Ohkanda, J. Heterocycles 2000, 52, 911;
(c) Seitz, L. E.; Suling, W. J.; Reynolds, R. C. J. Med. Chem. 2002, 45, 5604; (d)
Louis, S.; Marc, M. G.; Jory, J. W.; Joseph, P. B. J. Org. Chem. 2003, 68, 4179; (e)
Jonathan, L. S.; Hiromitsu, M.; Toshihisa, M.; Vincent, M. L.; Hiroyuki, F. J. Am.
Chem. Soc. 2002, 124, 13474.
X-ray crystallographic data (CIF file) of 1e as well as copies of 1H
and 13C NMR spectra of products are available. Supplementary data
related to this article can be found at http://dx.doi.org/10.1016/
j.tet.2014.02.034.
15. Yadav, J. S.; Ramesh, K.; Reddy, B. V. S. Synlett 2011, 169.
16. Lou, S.-J.; Xu, D.-Q.; Xia, A.-B.; Wang, Y.-F.; Liu, Y.-K.; Du, X.-H.; Xu, Z.-Y. Chem.
Commun. 2013, 6218.
References and notes
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