Copper-mediated aerobic oxidative synthesis of benzimidazo fused quinazolines via a multicomponent approach

Article abstract of DOI:10.1039/c5ra15525h

The first copper mediated aerobic oxidative multi-component synthesis of benzimidazo[1,2-c]quinazolines has been developed from 2-(2-halophenyl)benzoimidazoles, aldehydes and sodium azide as a nitrogen source. This protocol involves the formation of three

Full text of DOI:10.1039/c5ra15525h

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Graphical abstract
Copper-mediated aerobic oxidative synthesis of Benzimidazo
fused quinazolines via multicomponent approach
Byanju Rai, Promod Kumar and Atul Kumar
First copper mediated aerobic oxidative multi-component synthesis of benzimidazo[1,2-
c]quinazolines has been developed from 2-(2-halophenyl)benzoimidazoles, aldehydes and
sodium azide as nitrogen source. This protocol involves formation of three C-N bonds
starting from azidation of haloaryl with sodium azide followed by insitu conversion of azide
into arylamine, which on condensation with benzaldehyde undergoes oxidative cyclization
to afford benzimidazo[1,2-c]quinazoline in good to excellent yield.

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Copper-mediated aerobic oxidative synthesis of
Benzimidazo fused quinazolines via
Cite this: DOI: 10.1039/x0xx00000x
multicomponent approach
Byanju Rai,a Promod Kumara and Atul Kumar*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
ABSTRACT: First copper mediated aerobic oxidative multi- aminophenyl) benzimidazole and their precursors 2ꢀ(2ꢀ
component synthesis of benzimidazo[1,2-c]quinazolines has nitrophenyl)benzimidazole.17
been developed from 2-(2-halophenyl)benzoimidazoles,
Click reaction9
aldehydes and sodium azide as nitrogen source. This protocol
R1
R2
Tetrazole15
Triazole10
involves formation of three C-N bonds starting from
azidation of haloaryl with sodium azide followed by insitu
conversion of azide into arylamine, which on condensation
with benzaldehyde undergoes oxidative cyclization to afford
benzimidazo[1,2-c]quinazoline in good to excellent yield.
N
H
N
N
N
N
N
R2
R1
R
R
N
N
N
R
N
H
NO2
X
CN
Aziridine ring opening11
Fused Tetrazole14
R
N
Ts
NHTs
NaN3
N
N
N
H
N3
N
N
O
O
Schmidt Rerrangement12
Curtius Rearrangement13
Multiꢀcomponent processes have become a productive
concept for the synthesis of complexes and highly diverse
heterocycles in a oneꢀpot fashion.1 In present scenario,
multicomponent reactions considered as effective
chemical tool for the synthesis of polyheterocyles.2
O
R
O
OtꢀBu
CN
OH
N
NH
Br
R
R
O
NH
R
N
N
N
Present work
Tetracyclic bridgehead nitrogen containing motif are
present in many natural products,3 and pharmaceutical
agents.4 Among them benzimidazole and quinazoline
moieties are frequently encountered in several
pharmaceutically active agents.5,6 Benzimidazoles are
present in Vit Bꢀ12, Pantoptazole, Omeprazole, and
Albendazoleas.7 Whereas quinazolines are part of
clinically used cancer drugs such as Gefitinib, Erlotinib,
Alfuzosin, Trimetrexate, and Vandetanib.8 Inspired by
the bioapplicablity of tetracyclic bridgehead nitrogen
containing motifs, we were interested in development of
multicompnent synthesis for benzimidazo fused
Fig. 1 Applications of sodium azide
Recently, Hua Fu et. al. reported the synthesis of
benzimidazo[1,2ꢀc]quinazoline via the copper catalyzed
crossꢀ
coupling
reaction
of
2ꢀ(2ꢀ
halophenyl)benzoimidazoles and amidines.18 Zhang et.
benzimidazole. al. have reported synthesis of
benzimidazo[1,2ꢀc]quinazoline from 2ꢀ(2ꢀbromophenyl
quinazoline
from 2ꢀ(2ꢀhalophenyl)benzoimidazoles,
aldehydes and sodium azide as nitrogen source. Sodium
azide is a versatile reagent and have several applications
in synthesis of Nꢀhetrocycles, amines, cynadies and
amides (Fig 1 ). Here, we have first time used sodium
azide for developing multicomponent synthesis of
benzimidazo fused quinazoline. Mostly, benzimidazo[1,2ꢀ
c]quinazoline, which exhibit wide therepeautic activities16
were synthesied in multi step protocol starting from 2ꢀ(2ꢀ
Scheme 1. Synthesis of Benzimidazo [1,2-c]quinazoline
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benzoimidazole with benzyl amines(Scheme 1).19
In continuation of our research interest in the
development of novel methodologies for the synthesis of
heterocyclic compounds,20 we wish to report here first
NH
NH
D
N
N
COOH
N
N
H
COOH
H
N
C
N
E
A
B
multiꢀcomponent
synthesis
of
benzimidazo[1,2ꢀ
c]quinazoline derivatives through Cu catalyzed crossꢀ
coupling reactions of 2ꢀ(2ꢀhalophenyl)benzoimidazoles
Ligands Screened
with aldehydes using sodium azide as a nitrogen source. To further optimize the reaction conditions, we screened
Previously, there are several protocols reported where various catalysts, bases, ligands and solvents. The
copper catalysts have been used for oxidative CꢀC bond copper catalysts screened are CuI, CuBr, CuCl, Cu(Oac)2
formation.21 This multicompnent reaction involves and Cu powder. Out of all trials, the best result was
formation of three consecutive CꢀN bond and as aldehyde obtained with Cu powder (Table 1, entry 6). Further
as one of component hence it is easy to generate optimization of solvents, bases and ligands did not
diversity in the molecule.
provide any appreciable results (Table 1).
Optimization of the reaction conditions was carried out
Thus, the best yield of the desired Benzimidazo[1,2ꢀ
using
2ꢀ(2ꢀbromophenyl)ꢀ1Hꢀbenzo[d]imidazole
(1a), c]quinazoline was obtained by carrying out the reaction
sodium azide (2a) and benzaldehyde (3a) as model using Cu powder (10 mol%), proline (20 mol%), and
substrates. Our initial attempt started by using CuI with Cs2CO3 in DMSO at 80 ˚C for 12h. (Table 1, entry 6).
proline and Cs2CO3 as a base in DMSO at 80˚C, provided Recently, DMSO is considered as a recommended
desired fused heterocyclic product 4a in 70% yield (Table solvent for transformations in solvent selection guide
1,entry 1).
developed by Astra Zeneca.22
With the optimized conditions in hand, we explored the
generality of this copper mediated coupling process
(Scheme 2). Gratifyingly the conditions optimized for
benzimidazo[1,2ꢀc]quinazoline provided very good yields
of other benzimidazo[1,2ꢀc]quinazoline derivatives without
any further optimization. The scope of different aldehydes
were examined as shown in (scheme 2), we found that
the reaction depends upon the substitution present on to
the aldehyde ring. Electronꢀdonating groups on phenyl
ring gave better yields in comparison to electronꢀ
withdrawing groups. Aromatic aldehydes with electron
withdrawing groups such as 2,4ꢀ dichloro, 4ꢀ nitro, 4ꢀ
Table 1. Optimization of reaction conditions for the synꢀ
thesis of Benzimidazo [1,2ꢀc]quinazolinea
O
N
N
N
N
H
NaN3
2a
N
Br
3a
1a
4a
Entry
Catalyst
Ligand
Base
Solvent
Yieldb
1
2
3
4
5
6
7
8
9
CuI
CuBr
CuCl
Cu(OAc)2
ꢀ
Cu powder
Cu powder
Cu powder
Cu powder
Cu powder
Cu powder
Cu powder
A
A
A
A
A
A
B
C
D
E
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
70
64
60
40
0
89
55
50
35
58
76
40
cyano
and
4ꢀchloro
gave
the
corresponding
benzimidazo[1,2ꢀc]quinazoline in 75%, 65%, 60% and
79% yields respectively (Scheme 2, entries 4c, 4e, 4l, and
4n).
Benzaldehydes with electrondonating groups such as 4ꢀ
(dimethylamino)benzaldehydes, as well as 2, 5 and 3, 5ꢀ
(dimethoxy)benzaldehydes formed the desired products
in good to excellent yields (Scheme 2, entries 4b, 4f, and
4g). Weak steric effects were observed for the 2, 4, 5 and
3, 4, 5ꢀ(trimethoxy) benzaldehydes (Scheme 2, entries 4h
and 4j). With 1ꢀnaphthaldehyde the corresponding
product was found in 94% yield (entry 4d).
10
11
12
A
A
DMSO
13
14
15
Cu powder
Cu powder
Cu Powder
A
A
A
K3PO4
Cs2CO3
Cs2CO3
DMSO
CH3CN
DMSO:
CH2Cl2
(1:3)
50
44
16
16.
Cu powder
A
Cs2CO3
DMSO:
CH2Cl2
(3:1)
64
2ꢀ(2ꢀIodophenyl) benzoimidazoles gave similar yield for
benzimidazo [1,2ꢀc]quinazoline (Scheme 2, entry 4b, X=I)
but required short reaction time for the completion of
reaction. These exciting preliminary result opens the door
to the first multicomponent synthesis of highly diverse
Benzimidazo [1,2ꢀc]quinazolines .
aReactionconditions:2ꢀ(2ꢀbromophenyl)ꢀ1Hꢀbenzo[d] imidazole (1.0
mmol), Benzaldehyde (1.2 mmol), Sodium azide (2.0 mmol), Cu
catalyst (10 mol%), Ligand (20 mol%), and Base (1.0 mmol) in
solvents (4ꢀ5 mL) , at 80 ˚C for 12hr. bIsolated yield.
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A proposed reaction mechanism is shown in Scheme 4.
Initially , an aryl anion radical was generated by a singleꢀ
electron transfer from Cu to an aromatic ring of the
haloarene and subsequently the elimination of a bromide
ion (Br−) takes place to generate the corresponding aryl
radical.23 Simultaneously, copper (I) azide would be
generated together with the sodium salt of Lꢀ proline from
NaN3 and Lꢀproline. The generation of aryl copper (II)
complex (B)24,25 takes place by the oxidative coupling of
the aryl radical with the copper (I) complex (A), followed
by elimination of copper species and finally, 2ꢀ(1Hꢀ
benzo[d]imidazolꢀ2ꢀyl)aniline (C)26 was obtained.
Scheme 2. CopperꢀCatalyzed Cascade Synthesis of Benꢀ
zimidazo [1,2ꢀc]quinazolinederivativesa
Scheme 4.Proposed reaction mechanisms
N
N
N
N
NO2
N
N
N
O
N
N
O
CN
4l, (60%)b
O
The condensation of 2ꢀ(1Hꢀbenzo[d]imidazolꢀ2ꢀyl)aniline
and aldehyde afforded intermediate (D) and the
O
O
O
4j, (81)b
4k, (65%)b
N
NO2
intramolecular
nucleophilic
attack
of
NH
in
N
N
N
N
NO2
N
benzoimidazole group to carbon and affords the cyclized
product (E) which undergo aerobic oxidation and affords
targeted product benzimidazoquinazoline in good to
excellent yield.
N
O
O
N
N
Cl
O
4o, (74%)b
4m, (61%)b
4n, (79%)b
aReaction conditions: 2ꢀ(2ꢀbromophenyl)ꢀ1Hꢀbenzo[d]imidazole (1.0
mmol), substituted benzaldehyde (1.2 mmol), Sodium azide (2.0
mmol), Cu powder (10 mol%), Lꢀproline (20 mol%), and Cs2CO3
(1.0 mmol) in DMSO (4ꢀ5 mL), at 80˚C for 12hr. bIsolated yield
In conclusion, we have demonstrated first copper
catalysed
multicomponent
synthesis
of
diverse
benzimidazo[1,2ꢀc]quinazolines in aerobic conditions from
2ꢀ(2ꢀhalophenyl) benzoimidazoles, aldehyde, and sodium
azide as nitrogen source. The reaction probably proceeds
through in situ conversion of azide into arylamine followed
by condensation with aromatic aldehyde. We believe
operational simplicity and economic of this procedure will
find important applications in synthesis of nitrogen
hetrocycles in the area of medicinal, and material
chemistry.
Scheme 3.Control Experiment
ACKNOWLEDGMENT
B.R and P.K thankful to CSIRꢀUGC, New Delhi, India for
fellowꢀships. Authors also acknowledge to SAIFꢀCDRI for
providing the spectral and analytical data. CSIR Network
Project BSC0102/0108.
To better understanding of the mechanism, control
experiments was carried out (Scheme 3). When 2 equiv
of 2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxyl (TEMPO) was
added to the reaction under the standard conditions, 15%
of desired product (4a) was detected in the reaction
mixture of eqs 1a, 2a and 3a. Which proves radical
process was involved in the above reaction.
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