Synthesis of a chiral fluorescence active probe and its application as an efficient catalyst in the asymmetric Friedel-Crafts alkylation of indole derivatives with nitroalkenes

Article abstract of DOI:10.1039/c4cy01456a

Novel chiral Zn(ii) complexes were synthesized and these complexes showed fluorescence behaviour. These chiral Zn(ii) complexes were tested in the asymmetric Friedel-Crafts alkylation reaction of indole derivatives with nitroalkenes. In all the cases, the

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Synthesis of chiral fluorescence active probe and its application as an
efficient catalyst in asymmetric Friedel-Crafts alkylation of indole
derivatives with nitroalkenes
Ganesh Vasant More,a and Bhalchandra Mahadeo Bhanage*a
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
The novel chiral Zn(II) Complexes were synthesized and these complexes showed the fluorescence
behaviour. The chiral Zn(II) complex was tested in asymmetric FriedelꢀCrafts alkylation reaction of
indole derivatives with nitroalkenes. In all cases, the desired product was obtained with high yield (up to
10 93%) and good enantioselectivity (up to 78% ee) under the optimized reaction conditions. The effect of
solvent, metallic salt and piperidine ratio on the fluorescence intensity of catalyst and on
enantioselectivity of desired products was discussed.
Introduction
The FriedelꢀCrafts alkylation is a key reaction in organic
15 synthesis for the formation of new carbonꢀcarbon bonds.1 This
reaction requires aromatic substrate and electron deficient alkenes
such as α,βꢀunsaturated ketones,2 ketone enolates,3 arylidene
malonates,4 αꢀhydroxy enones,5 3ꢀnitroꢀ2Hꢀchromenes,6 αꢀ
Substituted βꢀNitroacrylates7, nitrodienes and 2ꢀPropargyloxyꢀβꢀ
20 nitrostyrenes.8 The asymmetric version of FriedelꢀCrafts
alkylation reaction of indoles with electronꢀdeficient alkenes is of
vital importance,9 as enantiomerically pure indole skeleton is
widely used for the synthesis of natural products, active
pharmaceutical intermediates (APIs), agrochemicals and
25 functional materials.10 The potential examples of indole skeleton
alkaloids are Uleine, Hapalindole G, Deethylibophyllidine,
Brevicolline and physostigmine which exhibit important
biological activities (Figure 1).11 Furthermore, nitroalkenes are
very efficient Michael acceptors where the nitro group can easily
30 converted into expensive amino functional group and variety of
different functionalities;12 because of this speciality nitroalkenes
are widely observed in many organic transformations.
The increasing demand of the indole containing compounds in
pharmaceutical sciences has lead to the development of new
35 strategies for the synthesis of enantiomerically pure indole
derivatives with high selectivity. Several reports have appeared in
the literature using chiral Lewis acids derived from chiral ligands
and metal salts for the asymmetric FriedelꢀCrafts alkylation
reaction of indole derivatives with trans βꢀNitrostyrene.13 In
40 addition, some organocatalysts are also applied for asymmetric
FriedelꢀCrafts alkylation reaction.14 The above protocol gave
good yield and enantiomeric excess of products; however few
protocols have some drawbacks such as low enantioselectivity, a
long reaction time, use of additives, low selectivity and multistep
45 designed ligands. This limits the practical applications of reported
protocols.
Fig. 1 Enantiopure indole skeleton in bioactive compounds
In the past, several methods have been developed for the
50 synthesis of moleculeꢀbased highly selective and sensitive
enantioselective fluorescence sensor for chiral recognition of
bioactive enantiomers.15 Chiral recognition of enantiomers also
helps us to know more about interactions of bioloactive
molecules, separation process, designing asymmetric catalysis
55 systems and screening of highꢀthroughput chiral catalysts.16 In
2002, Lin et al. reported the chiral molecular squares bipyridyl
bridging ligands and facꢀRe(CO)3Cl corners for enantioselective
Sensing,17 subsequently they prepared chiral organometallic
triangles Ptꢀacetylide linkage and utilized as a chiral catalyst for
60 enantioselective additions of diethyl zinc to aromatic aldehydes.18
In the last two decades in combination of various chiral ligands
and achiral or meso ligands have been successfully applied as a
combinatorial complex in many reactions19 which showed good
results as compared to original chiral ligands. In the present study
65 we are applying this fluorescence sensor and combinatorial ligand
concept to prepare the enantiomerically pure fluorescence sensor
of novel Schiff base zinc(II) complex with piperidine as an
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achiral combinatorial ligand. The prepared fluorescence active
Schiff base zinc(II) complex is successfully applied for
asymmetric FriedelꢀCrafts alkylation reaction of indole with trans
(DCM), methyl tertbutyl ether (MTBE), chloroform (CHCl3) ,
trifluorotoluene (PhCF3). The most intense fluorescence was
observed in toluene for ligand L1. The Ligand L1 shows
βꢀnitrostyrene. This reaction is carried out at ꢀ15 °C for 40 h and 40 maximum fluorescence intensity at λex = 471 nm (figure 5) in
5
afforded enantiomerically pure 3ꢀsubstituted indole derivatives in
high yields (up to 90%) with excellent enantiomeric excess (up to
78% ee) (figure 2).
toluene. The fluorescence intensity for L1 was found to decrease
in different solvents with following order as Toluene > DCM >
MTBE > CHCl3 > PhCF3.
L1 (10 mol%)
Zn(OTf)2 (10 mol%)
NO2
NO2
+
N
H
Piperidine (50 mol%)
Toluene, -15 oC
N
H
Indole
Nitroalkene
Fig. 2 Asymmetric FriedelꢀCrafts alkylation reaction of indole with trans
10 βꢀnitrostyrene.
Result and Discussion
Initially we prepared the (1S,2R)ꢀ1ꢀ[(2ꢀHydroxyꢀ3,5ꢀdiꢀtertꢀbutylꢀ
benzylidene)ꢀamino]ꢀindanꢀ2ꢀol according to
a
reported
procedure.20 3,5ꢀDiꢀtertꢀbutylsalicylaldehyde (10 mmol) was
15 dissolved in 60 mL ethanol. (1S,2R)ꢀ1ꢀAminoꢀ2ꢀindanol (10.5 45 Fig. 5 Effect of solvent on fluorescence intensity chiral Zn(II) complex
mmol) was added in one portion. The solution instantly turned
Then the effects of metal salts such as Zn(OTf)2, Sc(OTf)3,
bright yellow in colour. The mixture was stirred for 2 h at room
In(OTf)3, Yb(OTf)3, Cu(OTf)2 on the fluorescence intensity of
temperature; ethanol was removed on the rotary evaporator. The
ligand L1 in toluene were studied; where we observed that ligand
resulting solid was dried under vacuum to give L1 (Figure 3).
L1 showed maximum fluorescence intensity in combination with
50 Zn(OTf)2. The Ligand L1 showed fluorescence intensity at λex
tBu
tBu
=471 nm with Zn(OTf)2 (figure 6). While the fluorescence
NH2
tBu
intensity of ligand L1 with Sc(OTf)3 showed lower intensity as
compared to Zn(OTf)2 even in double concentration with
decreasing wavelength (456 nm). The fluorescence intensity of
55 the complex formed between In(OTf)3, Yb(OTf)3, Cu(OTf)2 with
ligand L1 was negligible at same wavelength (471nm).
Ethanol, RT
3 hr
+
N
OH
H
OH
tBu
O
OH
OH
L 1
3,5-di-tert-butyl-2-hydroxy
(1S,2R)-1-Amino-2-indanol
benzaldehyde
20
Fig. 3 Synthesis of chiral ligand L1
The chiral Zn(II) complex was prepared at room temperature by
addition of L1(0.04 mmol) and Zn(OTf)2 (0.04 mmol) in 3 mL
25 toluene and stirred it for 10 min. Then, we added piperidine (0.2
mmol) and the resulting reaction mixture were stirred for 30
minutes at room temperature (30 °C) (see figure.4). The prepared
chiral Zn(II) complex was studied by fluorescence spectroscopy.
In this study, we investigated the effect of various parameters
30 such as solvatochromic effect with different metal salts and effect
of piperidine concentration on fluorescence intensity of chiral
Zn(II) complex.
Fig.6 Effect of various metal salts on fluorescence intensity of ligand L1
in toluene
tBu
60 Furthermore, we studied the effect of ligand to piperidine ratio on
fluorescence intensity of chiral Zn(II) complex. Different molar
ratio was also screened ranging from 01:01, 01:02, 01:03 and
01:04. Herein, we synthesized the chiral Zn(II) complex with
above mentioned ligand to piperidine ratio. The chiral Zn(II)
tBu
N
OH
N
H
Zn (OTf)2
Chiral Zn(II) Complex
Flurosence active
OH
Toluene,
stirr 10 min
Stirr for 30
min
L1
65 complex
with molar ratio 01:01gave slight fluorescence
intensity, when we increase the molar ratio from 01:01 to 01:02
the fluorescence intensity increases dramatically, further
increasing the molar ratio from 01:02 to 01:03, 01:04 the
fluorescence intensity increases slightly. The molar ratio 01:04
Fig. 4 Synthesis of chiral Zn(II) Complex
35 The fluorescence spectra of chiral Zn(II) complex were
investigated in different solvents like toluene, dichloromethane
2
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shows maximum fluorescence intensity λex = 471 nm (figure 7).
35 enantiomeric excess; therefore ligand L1 was used for further
experiments. In the L1 is there are two sterically hindered tertꢀ
butyl groups on the phenol ring which act as donor group in the
complex formation, because of this sterically hindered group
ligand L1 showed good enantiomeric excess as compared to
40 ligand L2. Then, we screened various metallic salts such as
Cu(OTf)2, Sc(OTf)3, Yb(OTf)3, In(OTf)3 (Table 1, entries 3ꢀ6).
The Cu(OTf)2, Sc (OTf)3 provided good yields but failed to give
high enantiomeric excess of desired product. In combination of
ligand L1 with Yb(OTf)3, In(OTf)3 provided desired product 5a
45 in racemic form with moderate yield (Table 1, entries 5ꢀ6). Thus
in present study L1 as a chiral ligand and Zn(OTf)2 as the
metallic salt was selected as the best catalyst for further
optimization study (Table1, entry 1).
Fig.7 Effect of piperidine concentration on fluorescence intensity chiral
Zn (II) complex in toluene
NO2
Conditions
NO2
5
Based on these results, we focused on the experiments to check
the role of every components of chiral Zn(II) complex on
fluorescence behaviour. Initially, we omitted the metal from
chiral complex and observed that the fluorescence intensity was
decreases dramatically. Moreover the fluorescence intensity was
+
N
H
Toluene, RT
48 h
N
H
4a
3a
5a
50 Table 1 Effect of ligands, metal salts and catalyst loading on the
asymmetric Friedelꢀ Crafts alkylation of indole.a
10 not observed in absence of metal and piperidine. Later on, we
performed the control experiments only with the piperidine and in
combination of piperidineꢀmetal which did not show fluorescence
intensity. All these experiments proved that all components are
necessary to from the active chiral Zn(II) complex. The complex
15 showed maximum fluorescence intensity at λex = 471 nm which
confirms that there is strong interaction in the ligand L1,
Zn(OTf)2, and piperidine which is shown in figure 8.
Entry
Ligand
Ligand Screening
Metal salt
% Yieldb
%eec
1
2
L1
L2
Zn(OTf)2
Zn(OTf)2
92
88
60
19
Metal screening
3
4
5
6
L1
Cu(OTf)2
Sc(OTf)3
Yb(OTf)3
In(OTf)3
47
91
54
47
16
4
L1
L1
L1
Racemic
Racemic
a
Reaction conditions: nitrostyreneꢀ0.5 mmol, indoleꢀ0.6 mmol, tolueneꢀ
3mL, ligandꢀ0.05 mmol, metalꢀ0.05 mmol, piperidineꢀ0.15 mmol,
b
c
temperatureꢀ RT, timeꢀ48 h, Isolated yield, Determined by chiral
55 HPLC analysis on a Chiralcel ODꢀH column..
The effect of catalyst loading ranging from 5ꢀ20 mol% of
substrate for model reaction of indole 3a with transꢀβꢀnitrostyrene
4a was studied (Table 2, entries1ꢀ4), and it was observed that
60 increasing the catalyst loading from 5 mol% to 10 mol% led to
remarkable increases in the yield and enantiomeric excess of
desired product 5a. Further increase in the catalyst loading did
not show any profound effect on yield and enantiomeric excess of
desired product.
Fig. 8 Comparison of fluorescence intensity of piperidine (P) with
20 Zn(OTf)2 metal (M), L1 ligand (L), ligand with metal and combination of
ligand, metal , piperidine (chiral Zn(II) complex) in toluene.
65 Table 2 Effect of catalyst loading on the asymmetric FriedelꢀCrafts
alkylation of indole.a
Fig. 8 Comparison of fluorescence intensity of piperidine (P) with
Zn(OTf)2 metal (M), L1 ligand (L), ligand with metal and combination of
ligand, metal , piperidine (chiral Zn(II) complex) in toluene
Entry
Ligand
(mol %)
Metal
(mol %)
Piperidine
(mol %)
%
Yieldb
87
92
92
94
16
25
88
%
eec
1
2
3
4
5
6
7
8
5
5
15
30
45
60
30
30
ꢀꢀ
ꢀꢀ
54
60
60
58
50
Racemic
10
15
20
10
ꢀꢀ
10
15
20
ꢀꢀ
10
10
ꢀꢀ
25 Initially we performed the FriedelꢀCrafts alkylation of indole 3a
with transꢀβꢀnitrostyrene 4a in toluene at room temperature using
L1ꢀZn(OTf)2ꢀPiperdene complex as a catalyst. The desired
product 5a was obtained in 92 % yield with 60% ee (Table 1,
entry 1). To compare the efficiency of ligand L1, we prepared
30 another ligand L2 by reaction of (1S,2R)ꢀ1ꢀAminoꢀ2ꢀindanol and
4ꢀ(diethylamino)benzaldehyde using above mentioned procedure
and applied on substrate indole 3a with transꢀβꢀnitrostyrene 4a at
room temperature; where we observed that the desired product 5a
was obtained with good yield but failed to provide high
10
10
5
8
<10
a
Reaction conditions: ligand ꢀL1, Metalꢀ Zn(OTf)2, nitrostyreneꢀ0.5
mmol, indoleꢀ0.6 mmol, tolueneꢀ3mL, b Isolated yield, Determined by
c
chiral HPLC analysis on a Chiralcel ODꢀH column.
70
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Table 3 Effect of reaction parameters on the asymmetric Friedelꢀ Crafts alkylation of indole.a
Entry
Solvent
Amines
L1 : Piperidine
Temp.
( °C)
Time
(h)
%
%
ratio
Yield b
ee c
Effect of solvent
1
2
3
4
5
6
7
ACN
MTBE
THF
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
1:3
1:3
1:3
1:3
1:3
1:3
1:3
RT
RT
RT
RT
RT
RT
RT
48
48
48
48
48
48
48
85
72
78
82
90
70
92
53
44
44
53
51
46
60
DCM
CHCl3
nꢀhexane
Toluene
Effect of amines
8
9
Toluene
1:3
1:3
RT
RT
48
48
38
91
45
31
Toluene
Toluene
Toluene
10
11
1:3
1:3
RT
RT
48
48
86
79
39
47
12
Toluene
1:3
RT
48
84
50
Effect of piperidine ratio
13
14
15
16
17
18
19
20
21d
22e
23f
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
1:1
1:2
1:3
1:4
1:5
1:6
1:7
1:8
1:5
1:5
1:5
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
48
48
48
48
48
48
48
48
48
48
48
94
94
92
91
92
92
90
89
92
92
90
11
53
60
63
64
64
64
63
64
64
64
Effect of temperature
24
25
26
Toluene
Toluene
Toluene
Piperidine
Piperidine
Piperidine
1:5
1:5
1:5
0
ꢀ15
ꢀ20
48
48
48
91
91
90
70
75
73
Effect of time
27
28
29
30
31
32
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
1:5
1:5
1:5
1:5
1:5
1:5
ꢀ15
ꢀ15
ꢀ15
ꢀ15
ꢀ15
ꢀ15
14
20
24
28
40
48
34
46
76
89
92
92
58
60
67
68
75
75
5
a Reaction conditions: a nitrostyreneꢀ0.5 mmol, indoleꢀ0.6 mmol, tolueneꢀ3mL, L1ꢀ0.05 mmol, Zn(OTf)2ꢀ0.05 mmol, b Isolated yield, c Determined by
chiral HPLC analysis on a Chiralcel ODꢀH column, d 150mg 3Å MS, e 150mg 4 Å MS, f 150mg 5 Å MS
Based on these results, we performed the test experiments to 10 experiments showed that ligand L1, Zn(OTf)2 and piperidine
check the roles of every component in the catalytic system. These
were necessary for the efficient catalytic system (Table 2, entries
4
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5ꢀ8). To get the optimal reaction conditions, we studied the effect
of the various reactions parameters such as effect of solvents,
amines, piperidine ratio, molecular sieves, temperature and time
on the yield and enantiomeric excess of desired product (Table
3). The influence of solvent on the asymmetric FriedelꢀCrafts
reaction was investigated (Table 3, Entries 1ꢀ7). Solvents such as
ACN (Acetonitrile), MTBE (methyl tertiary butyl ether), THF
10 (tetrahydrofuran), DCM (dichloromethane), CHCl3 (chloroform),
toluene and nꢀhexane were screened. Our catalyst showed high
activity in toluene with 92% yield and 60% ee of desired product
5a (Table 3, entry 7). Other solvents gave low enantioselectivity
enantioselectivity of the desired product 5a was obtained. Thus
the optimized reaction conditions are indole (3a, 0.5 mmol),
transꢀβꢀnitrostyrene (4a, 0.6mmol), Ligand (L1, 0.05mmol),
Zn(OTf)2 (0.05mmol), piperidine (0.15mmol) at ꢀ15°C for 40 h.
With the optimal reaction conditions in hand, we performed
the asymmetric FriedelꢀCrafts alkylation reaction between indole
65 derivatives and nitrostyrene derivatives (Table 4, entries 1ꢀ12).
We first surveyed a variety of indoles 5aꢀ5f bearing different
substituents (Table 4, entries 1ꢀ6) which could react with
nitrostyrene in good yields with high enantioselectivity. The
substitution on the Cꢀ5 position of indole, with halogen (ꢀBr, ꢀCl,
5
as compared to toluene (Table 3, entries 1ꢀ6), therefore, toluene 70 ꢀF) substituent provided good enantioselectivities (78ꢀ76% ee,
15 was used for further studies. The chiral Zn(II) complex with
amines plays an important role on the enantioselectivity of
desired product 5a.Various amines such as 2,2,6,6ꢀ
tetramethylpiperidine (45% ee), cisꢀ3,5ꢀdimethylmorpholine
Table 4, entries 2ꢀ4). Further, electron donating (ꢀOMe, ꢀMe)
substituent at Cꢀ5 of indole provided good enantioselectivities
with 5e:70% ee, 5f:76% ee (Table 4, entries 5ꢀ6). The substituent
effect on the nitrostyrene ring was also studied. The nitrostyrene
(31% ee), 4ꢀ(2ꢀfluorophenyl)piperidine(39% ee), 1,2,3,4ꢀ 75 with halogen (ꢀBr, ꢀCl, ꢀF) substituent at para position gave
20 tetrahydro isoquinoline (47% ee), pyrrolidine (50% ee) were
screened (Table 3, entries 8ꢀ12). Out of these amines piperidine
provided (60% ee) good enantioselectivity; hence it was used for
remaining experiments.
corresponding products with good enantiomeric excess (69ꢀ76 %
ee, Table 4, entries 7ꢀ9).
Table 4 Asymmetric FriedelꢀCrafts alkylation of indole derivatives with
nitroalkenes.a
In the fluorescence study of chiral Zn(II) complex it was
25 observed that when we increase the ratio of L1 to piperidine the
fluorescence intensity of catalyst increases, hence we checked the
effect of molar ratio on enantioselectivity of the desired product.
Therefore we screened the piperidine molar ratio ranging from 1:
1 to 1: 8 (ligand L1: piperidine) and observed that when we
30 increase the molar ratio from 1:1 to 1:5, there was increase in the
enantioselectivity desired product 5a from 11% ee to 64% ee
(Table 3, entries 13ꢀ17). These experiments was clearly indicates
that when increase the fluorescence intensity of the chiral Zn(II)
complex increases the enantioselectivity of desired product 5a.
35 With further increase in the piperidine ratio from 1:6 to 1:8 there
is no effect on the enantioselectivity of desired product.
Furthermore, we screened the role of molecular sieves on the
yield and enantioselectivity of desired product 5a (Table 3,
Entries 21ꢀ23) and it was observed that there is no effect on the
40 yield and enantioselectivity of product 5a. Then we checked the
effect of acid additives on yield and enantioselectivity of desired
product 5a. We screened the various racemic and
enantiomerically pure acids such as paraꢀtrifluoro benzoic acid,
Dꢀ camphor sulphonic acid, Nꢀboc proline, Lꢀ lactic acid, triflic
45 acid, (R)ꢀtetrahydrofuranꢀ2ꢀcarboxylic acid and tartaric acid, but
they failed to increase the enantiomeric excess of desired product
5a(see ESI† Table 1). Thus the next experiments were carried out
without acid additives. The effect of temperature on the yield and
enantioselectivity of the product 5a was studied and the reactions
50 were carried out at various temperatures ranging from room
temperature to ꢀ20 °C (Table 3, entries 25ꢀ27). At room
temperature, the enantioselectivity of 5a was low, whereas
decreasing the temperature to 0 °C leads to increase in
enantioselectivity up to 70% ee. Further decrease in the
55 temperature to ꢀ15 °C increases the enantioselectivity up to 75%
ee. A further decrease in the temperature to ꢀ20 °C decreases the
enantioselectivity to 73% ee. Hence optimized temperature is ꢀ15
°C.
R2
L1 (10 mol%)
Zn(OTf)2 (10 mol%)
R1
R1
NO2
NO2
+
R2
N
Piperidine (50 mol%)
H
N
H
Toluene, -15 o
C
3a-f
5a-l
4g-l
80
%
%
eec
76
78
75
74
70
76
69
76
76
70
72
Entry
R1
R2
Product
Yieldb
92
1
2
3
4
5
6
7
8
9
H
Br
Cl
F
Ph
Ph
Ph
Ph
Ph
Ph
51
5b
5c
5d
5e
5f
85
87
91
90
89
87
91
93
OMe
Me
H
4ꢀBrC6H4
4ꢀClC6H4
4ꢀFC6H4
4ꢀMeC6H4
4ꢀOMeC6H4
5g
5h
5i
5j
5k
H
H
H
H
10
11
88
85
12
H
5l
94
72
a
Reaction conditions: L1ꢀ(10 mol %), Zn(OTf)2ꢀ(10 mol %), piperidine
(50 mol %), tolueneꢀ(3ml), nitrostyreneꢀ(1mmol), indoleꢀ(1.2 mmol),
temperatureꢀ (ꢀ15 °C), Isolated yield, Determined by chiral HPLC
b
c
85 analysis on a Chiralcel ODꢀH column.
Electronꢀrich (ꢀMe, ꢀOMe) aromatic nitrostyrene at para position
furnished desired product with good enantioselectivity as 5j: 70%
ee and 5k: 72% ee was obtained. It is notable that a heterocyclic
nitrostyrene derivative provides good enantioselectivity as 5l:
90 72% ee.
Conclusions
In conclusion, the novel and efficient catalytic asymmetric
protocol for FriedelꢀCrafts alkylation reaction of indoles with
nitroalkene derivatives by chiral Zn(II)ꢀSchiff base complex was
95 developed. The Chiral Zn(II)complex was showed excellent
fluorescence behaviour. The developed novel catalyst provides
Finally, we examined the effect of time on the model reaction
60 (Table 3, entries 28ꢀ32). After 40 h, the maximum yield and
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high yields (up to 93%) with good enantiomeric excess (up to
78%) for wide range of indoles and aromatic nitrostyrene
derivatives under mild reaction conditions. The developed
protocol offers high yields, good enantioselectivities, short
reaction time, mild reaction conditions and inexpensive catalytic
system.
65
70
75
80
85
90
5
Acknowledgements
G.V.M. is thankful to the Council of Scientific and Industrial
Research (CSIR), New Delhi for providing a senior research
10 fellowship. The authors also thanks to Department of Science and
60 Technology (DST)ꢀSERB, India (project file NO.SR/S1/OCꢀ
09ꢀ2012) for financial support.
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a Institute of Chemical Technology, Department of Chemistry ,Matunga,
15 Mumbai-400019. India. Fax: +91 22 3361 1020; Tel: 022 33612601;
E-mail: bm.bhanage@gmail.com
† Electronic Supplementary Information (ESI) available: general
1
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DOI: 10.1039/C4CY01456A
Synthesis of chiral fluorescence active probe and its application as an
efficient catalyst in asymmetric Friedel-Crafts alkylation of indole
derivatives with nitroalkenes
Ganesh Vasant More a and Bhalchandra Mahadeo Bhanage*a
Department of Chemistry, Institute of Chemical Technology
Matunga, Mumbai-400019. India.
Fax: +91 22 3361 1020
E-mail: bm.bhanage@gmail.com, bm.bhanage@ictmumbai.edu.in
Green protocol for the asymmetric Friedel-Crafts alkylation using fluorescence active Zn(II)
chiral catalyst with high conversion and enantiomeric excess has been developed.