SYNTHESIS OF BIOLOGICALLY ACTIVE NITROGEN AND OXYGENshodhganga.inflibnet.ac.in/bitstream/10603/4039/10/10_chapter 3.pdf · analogous reaction to the Ehrlich test, where indole reacts

Chapter III

Environmentally Benign Synthesis of

Bis (indolyl) methanes in Water

Catalyzed by Polystyrenesulphonic

acid

This work is communicated to Catalysis Letters

CHAPTER 3 Environmentally Benign Synthesis of Bis(indolylmethanes) in Water Catalyzed by Polystyrensulphonic

acid.

88

CHAPTER - 3

Environmentally Benign Synthesis of Bis(indolyl)methanes in Water Catalyzed by Polystyrenesulphonic acid.

3.1 INTRODUCTION AND LITERATURE SURVEY

Bis (indolyl) alkanes and their derivatives constitute an important group

of biologically active metabolites of terrestrial and marine origin. In the recent

years bis (indolyl) methanes and bis (indolyl) ethanes has been found in marine

sources. Bisindole metabolites bearing imidazole or a piperazine nucleus has

been isolated from various genera of sponges.

Bis (indolyl)methanes and their derivatives exhibit diverse biological

activities which affect central nervous system[1] and used as tranquilizers.[2] The

important indole derivative, 9H-pyrralo[1,2-a]indole called fluorazine[3] [1] is

an important compound because of its anticholinergic activity [4] and for the

inhibition of GABA transport and Na+/ K+-ATPase.[5] Several synthetic routes

to 9H-pyrralo[1,2-a]indoles have been inscripted in literature[6] however, most

of them have been directed towards the synthesis of mitomycin antibiotics .

Another important family of bis (indolyl)methanes are

cytonortopsentins[7] [2], which exhibit in-vitro cytotoxicity. Moreover, some

other bis(indolyl) alkaloids in which imidazole moiety of nortopsentins was

replaced by thiazole [3], pyrimidine [4], pyrazine [5] and pyrazinone [6] rings

have been reported[8] 2, 4 -Bis(indolyl) thiazole analogue [7] exhibited

cytotoxic activities against a wide range of human tumor cell lines at

micromolar concentrations.[9] Similar antitumor properties reported by

N

Me

R

R'

OMe

MeO

[1]


acid.

89

dragmacidin D.[10] Recently Lee and co-workers found that 1,1,3-tri(3-

indolyl)cyclohexane inhibits cancer cell of xenograft model[11] [8].

NH

R'

N

NHO

NH

R

[6]

NH

S

NH

R'R'

[7]

NH

N

N

NH2

Br

[8]

3.2 METHODS OF SYNTHESIS The lead indole derivatives reported in the literature are bis (indolyl) and

tris (indolyl)alkanes. Their method of synthesis involves both one step as well

as multistep synthesis. Fischer in 1886 prepared 3,3-bis(indolyl)methanes [9]

NH

N

NH

NHR R'

[2] Nortopsentin A R = R1 = Br

Nortopsentin B R = Br, R1 = H

Nortopsentin C R= H, R1 = Br

NR

N

S

NR

RR

2 2

1

[3]

NR

N

N

NR

R3

2 2

[4]

N R

N

N

NR

R3

2

2

[5]


acid.

90

for the first time which was a mere acid catalyzed Friedel-Crafts reaction

between indole and carbonyl compounds, generally aldehydes and ketones

(Scheme 3.1).The acid catalyzed reaction of an electron rich heterocyclic

compounds such as indole and pyroles with p-dimethylaminobenzaldehyde is

known as the Ehrlich test[13] Generally 3,3`-BIM`s are synthesized by an

analogous reaction to the Ehrlich test, where indole reacts with aliphatic or

aromatic aldehydes or ketones in the presence of an acid catalyst to produce

azafulvene[14] [10]. The enamine can undergo further addition reaction with a

second indole molecule to produce BIM`s (Scheme 3.2). The synthetic utility

of this synthetic route to obtain wide structurally diversed BIM`s has been

rooted in recent years.

NH R R'

O

NH

NH

R R'

Acid catalyst2 +

R = alkyl or aryl.

Rl = H or alkyl

[9] Scheme 3.1

NH

R

O

H

H+

R

OH

NH

H

-H+NH

R

OH H+

-H2O

R

NH

NH

NH

R

NH

H

- H+

NH

R

NH

+ ++

+

+

10

Scheme 3.2


acid.

91

Shrihari et al[15] have demonstrated that phosphomolybdic acid (PMA)

together with silica (SiO2) works efficiently for the one pot three component

reaction of aldehyde, excess N-methylaniline and indole to yield 3-substituted

indole derivatives [11] (scheme 3.3).

.

HN

R

O

H NH

PMA/SiO2N

NH

R+ +

[11]

Scheme 3.3

BIM`s derivatives of ferrocene [13] has been reported by the reaction

between ferrocene aldehyde or ketone [12] in the presence of ZnCl2[16] as a

catalyst .The resultant derivatives formed with low yields (Scheme 3.4).

O

R

FeNH

ZnCl2Solid state

NH

NH

R

Fe+

[12] [13]

Scheme 3.4

Nucleophilic attack of indole on carbonyl carbon of aldehyde is more

facile than carbonyl carbon of ketone it may be due to steric hindrance.

Formation of BIM`s derived from ketones required more energy. Use of

microwave irradiation was reported for indole and diethylketomalonate in the

presence of montmorillonite K-10 clay[17] to give the corresponding indol-3`-


acid.

92

ylcarbinols [14] and respective BIM`s [15] with 20-45% and 5-35% yields

(Scheme 3.5).

NH

COOEt

COOEtO K clay

MWNH

OH COOEt

COOEt

NH

NH

COOEtEtOOC

2 + 10

+

[14] [15]

Scheme 3.5

Furanose and allose 3, 3`-BIM`s derivatives[18] [16, 17] were produced

from the reaction of indole and the corresponding aldehyde in the presence of

HClO4 in good yields (Scheme 3.6).

NH

NH

O

OO

OMe

NH

NH

O

O

O

BTSO

[16] [17]

Scheme 3.6

In case of conjugated aldehydes like crotonaldehyde reaction never stops

at BIM stage but further Michael addition of third indole molecule takes place

on carbon-carbon double bond to offer compound [18] in good yields. In this

reaction three molecules of the indole get consumed. Both Lewis as well as

protic acid catalyst gives better yield of the products (Scheme 3.7). Amongst

them cerric ammonium nitrate[19] offered good yields of the product.


acid.

93

NH

NH

NH

NH

OCAN mol%

CH3CN rt+ 10

,

[18]

Scheme 3.7

C-Glucosylation of indole was attempted by Sato et al.[20] In this method

10 mol % Sc (OTf)3 was used as a reusable catalyst. Best yield of the products

[19] were obtained for 0.1 equivalent amount of catalyst and 80 0C reaction

temperature .It took 11 hrs. for completion (Scheme 3.8).

NH

H OHHOHOHHOHH

CH2OH

CHO

HOH

H OHOH HOH H

CH2OH

NH

NH

EtOH :H2O

Sc(OTf)3

+ 1 :1

[19]

Scheme 3.8

Strategy of BIM synthesis served as a profitable subject for the synthesis

of polycyclic compound. This method covers the synthesis of aza-crown ether

through the condensation of indole [20] with anisaldehyde in the presence of

H4[Si (W3O10)3] as a catalyst.[21] The reaction proceeds at room temperature in

acetonitrile as a solvent, affording crown ether bearing indole [21] in moderate

yields (Scheme 3.9).


acid.

94

N N

OO

O

ArCHO H4(SiW3O10)3 mol%

CH3CNNN

Ar

OO

O

+ 20

, rt, 45min

[20] [21]

Scheme 3.9

Bergmann and his associates[22] have successfully synthesized

pentacyclic compound [22] from Friedel-Crafts reaction between 1,2 bis(1H-

indol-2-yl) ethane [23] and either aldehyde and ketone under acidic condition

(TFA or p-TsOH) in good yields (Scheme 3.10).

NHN

H

O

RR

TFA or PTSA

EtOH refluxNHN

H

R R

+ 12

1 2

[22] [23]

Scheme 3.10

Bis (indolyl) nitroethanes[23] are important synthetic intermediate for

synthesis of some naturally occurring analogues. In this synthesis, Michael

addition of indole takes place on activated 3-(2-nitrovinyl)indole [24] on silica

gel under microwave irradiation to give high yields Michael adduct [25].

(Scheme 3.11) Reaction could takes place at room temperature but takes longer

time to complete .

NH

NO2

NH

Silica gel

MW, minor, rt, N

H

NO2

NH

+7-108-14 hr

[24] [25]

Scheme 3.11


acid.

95

Some miscellaneous methods demonstrated for the synthesis of BIM`s

where quite diversion found in utility of indole and an aldehyde as a reactant.

Synder and Eliel[24] applied Fischer indole synthesis for the synthesis of N-

substituted BIMs [26] in acidic condition which offered the compound in

moderate yields (Scheme 3.12).

NCH3

NH2O OR ORO

O OAcOH

HCI NHO2CCO2H

NCH3CH3

+

[26]

Scheme 3.12

One pot synthesis of BIM`s through annulation/Friedel Crafts alkylation

from alkynes [27] and aldehydes. The mechanism towards the formation of

BIMs [28] is supposed to be formation of bisindole prior to the Friedel-Crafts

step. This transformation is well catalyzed by FeCl3–PtCl2 and AuCl[25]

(Scheme 3.13)

Ph

NH2

R

CHO

FeCI3-PtCI2CH2CI2

NH

NH Ph Ph

+

2

, 80 C0

8h

[27] [28]

Scheme 3.13

Conversion of ketones into alkanes [29] by the use of lithium aluminum

hydride and reverse oxidation reaction to regain ketone were demonstrated by

Bergman et al [26] (Scheme 3.14).


acid.

96

NH

N

H

O

NH

N

H

LAH

DDQ

[29]

Scheme 3.14

Use of Gallium (III) halide as a catalyst for the effective transformation of

indole and phenyl acetylene into bis(indolyl)phenylethanes [30] was

demonstrated by J. S. Yadav et al.[27] The reaction went to completion in 6 hr

and the product was obtained in 86% yields (Scheme 3.15).

N

H NH

N

H

CH3% GaCl3, BaBr3

R'Ph

C6H5CH3, rt+

10

[30]

Scheme 3.15

Besides to the conventional and microwave methods researchers prefer

ultrasonic irradiation for single step synthesis. Xiao-Fei Zeng and co-

workers[28] have developed a simple, novel and efficient synthetic protocol for

synthesis of unsymmetrical BIMs [31] using catalytic amount of CAN under

ultrasonic irradiation at room temperature (Scheme 3.16).The superiority of

this method behinds the use of cheap and non toxic CAN as a catalyst.

N

H

ROH

NH

N

H

R

NH

CAN

U S EtOHR' R'+

[31]

Scheme 3.16


acid.

97

Among the several methods reported in the literature for the synthesis of

BIMs, the reaction between an Indole and an aldehyde is most popular with

good synthetic utility. This transformation is catalyzed effectively by Lewis

acid as well as protic acid catalyst. Use of ionic liquid as good alternative for

toxic solvents, offers bis (indolyl) alkanes in good yields. The factors that

prompted to search newer methods with low cost of catalyst, higher yield of the

product, reaction rates, simplicity of the workup process and green chemistry.

Cerric compounds like Cerric ammonium nitrate (CAN),[29]

CeCl3.7H2O/glycerine,[30] nanoceria (CeO2) supported on vinyl pyridine

polymer[31] are effective Lewis acids which promote the bis (indolyl) alkane

formation. The use of natural clay like montmorilonite clay K-10[32] and

bentonite clay[33] have been made by Bhattacharya and Banerji. Habib

Firouzabadi et al have reported ZrOCl2·8H2O/silica gel[34] and Aluminum

dodecatungstophosphate (AlPW12O40)[35] as water tolerant Lewis acid as a

catalyst for bis (indolyl) alkanes. Silica supported acid catalysts like NaHSO4-

SIO2,[36] HBF4-SiO2,

[37] HClO4-SiO2,[18] catalyzed reaction for BIMs offering

good yields. Recently, a new type of water-usable catalyst, namely, “Lewis

acid-surfactant-combined catalyst (LASC)” has shown high efficiencies in

various organic transformations.[38] It was reported that metal codicil sulfates,

can be efficiently employed in the synthesis of 3,3′-BIMs.[39-42]

Dodecylbenzenesulfonic acid (DBSA)[43] and dodecylsulfonic acid (DSA)[44-45]

also promote BIM formation from aldehydes and indoles in water.

In addition to microwave (MW),46 sonochemistry,[47] and ionic liquids

raised as green solvent a most wanted alternative to toxic, volatile solvents. J.

S. Yadav et al explored the utility of 1-bytyl-3-methylimidazolium

tetrafluoroborate ([bmim]BF4) and 1-bytyl-3-methylimidazolium

hexafluorophosphate ([bmim]PF6).[48]

Many of the above mentioned methodologies are associated with the

drawbacks like longer reaction time, high expenditure on catalyst, which causes


acid.

98

environmental pollution. These factors alarmed to search out chief,

environmentally benign protocol for BIMs.

3.3 PRESENT WORK

The mechanism of BIMs reveals that, the reaction can be promoted by

protic as well as Lewis acid catalysts. With an increasing environmental

concerns and regulatory constrains chemists are devoted to the area of green

chemistry which has attained the status of a major scientific discipline,[49]

which involves minimize the amount of toxic waste and by-product from

chemical processes, elimination of hazardous reagent and easy separation

methods. In the development of new processes ecological impact must also be

taken into account. Solvents are central feature, as they are generally used in

large quantities, Such a consideration has prompted synthetic organic chemists

to explore the potential of water as a solvent for organic synthesis. Toward this

end, considerable efforts have been devoted to develop and use nontraditional

solvents for chemical synthesis.[50] Such unconventional medium include

among others are solvent-free condition,[51] supercritical carbon dioxide,[52]

ionic liquids, perfluorinated solvents,[53] and last but not least water. There is

widespread current debate over the relative “greenness” of these individual

reaction media, but water can undoubtedly be considered the cleanest solvent

available. The use and release of clean water clearly will have the least impact

to the environment. Recently R. S. Varma et al have reported the

polystyrenesulphonic acid (PSSA) catalyzed greener synthesis of 1,3-dioxanes

and hydrazones in aqueous medium using microwave (MW) irradiation.[54-56]

We wish to report a greener and highly efficient route for the synthesis of bis-

indolyl methane using inexpensive and commercially available

polystyrenesulphonic acid (PSSA) as a catalyst (Scheme 3.17).

NH

NH

NH

Ar

Ar

O

HPSSA

Water, rt2 +

Scheme 3.17


acid.

99

3.4 RESULTS AND DISCUSSION In order to study the catalytic efficiency of polystyrenesulphonic acid,

we carried out a controlled reaction with an aromatic aldehyde (1mmol) and an

indole (2 mmol) without polystyrensulphonic acid (PSSA) and stirred for

several hours. A sticky reaction mixture was obtained with the formation of bis

(indolyl) methane in very low yield. In another experiment, aldehyde and

indole were taken in 5 mL water to which two drops of PSSA were added and

the reaction mixture stirred at room temperature till completion of reaction as

monitored by TLC. The reaction proceeded cleanly and desired pink red

coloured bis-(indolyl) methane was isolated in good yield.

In order to study the generality of this procedure, a series of bis (indolyl)

methanes were synthesized (Table 3.1). Several aryl aldehydes with electron

withdrawing and donating functional groups undergo efficient formation of the

bis (indolyl)methanes in short reaction time. The product, bis (indolyl)

methanes were obtained in good yields and were separated simply by filtration

on vacuum pump. As reaction proceeds in water with good yields of the

product, we were not interested to examine the feasibility of the reaction in

other organic solvents. This encouraged us to employ same methodology with

ketones. In case of cyclohexanone, product obtained with good yield but it

takes longer time for completion whereas reaction with aromatic ketones like

acetophenone reaction, very low yield of the product was obtained. Poor

reactivity of ketones may be due to the steric hindrance of the alkyl group. The

formation of the desirable BIMs was detected by their melting points and by

IR, 1H NMR, 13C NMR spectroscopic methods.


acid.

100

Table 3.1. Reaction time and Yields of bis-(indolyl)methanes

Entry Compound Time

(min).

Yield (a)

( %)

1.

NNH H

65

90

2.

NNH H

Me

60

87

3.

NNH H

OMe

70

85

4.

NNH H

OMe

OMe

70

85

5.

NH

NH

NMeMe

85

82


acid.

101

6.

NN

N

H H

Cl

Me

85

70

7.

NH

NNH H

70

80

8.

NNH H

NO2

55

90

11.

NNH H

Cl

55

92

12.

NN

N

H H

Cl

90

75


acid.

102

13.

NN

N

H H

Cl

OMe

90

77

a -Refers to yield of the pure and isolated compounds.

Spectral Analysis

The IR spectrum of various compounds reveals that the disappearance of

stretching frequency of carbonyl group at 1690 cm-1 which indicated that

condensation of both indole molecules. N-H Stretching frequency is quite

immaterial as far as BIMs formation is concern. In 1H NMR spectrum, the

signal for aldehyde proton at δ 9.8 disappeared while a singlet corresponding to

one proton at δ 5.6 indicated the methine proton. Appearance of this signal in 1H NMR spectrum clearly confirms the formation of BIMs. Rest aromatic

protons and two NH protons of two indole molecule appeared at downfield

shift in between δ 6.0-8.0. A singlet of two NH protons observed at δ 8, while

aromatic protons shows complex multiplet pattern. The structure elucidation of

the compounds has been explained from its 13C NMR spectral data, as there is

only one methine carbon signal observed at δ 35 while remaining aromatic

carbons of indole and benzene ring are observed in the range of δ 110 to 150.

NNH H

Me

2-[1H-indol-3-yl(4-methylphenyl)methyl]-1H-indole (Table 3.1, entry

2) in its IR spectrum exhibited N-H stretching band at 3411 cm-1.There was

absence of stretching band of conjugated carbonyl near at 1690 cm-1

(Spectrum 3.1). 1H NMR spectrum of the same compound shows singlet at δ


acid.

103

2.3, which indicates the presence of methyl group attached to aromatic ring, a

singlet for methine proton observed at downfield shift at δ 5.8. The aromatic

protons gave complex multiplet for thirteen protons at δ 6.9 to 7.4, while a

singlet for two protons attached to C-2 shows upfield shift at δ 5.8 is due to

vicinity of nitrogen atom from indole, it appears at δ 5.8. The downfield shift

for N-H proton gives a broad singlet at δ 7.8 (Spectrum 3.2). 13C NMR

spectrum of the molecule shows the signal at δ 21.78, 39.78, 110.99, 119.17,

119.92, 121.85, 123.53, 127.12, 128.56, 135.46, 136.71 (Spectrum 3.3).

NNH H

OMe

Bis(indolyl)methanes synthesized from p-anisaldehyde (Table 3.1,

entry 3) gave a pink coloured solids showed IR stretching band for N-H at

3360 cm-1(Spectrum 3.4).; A singlet appeared at δ 3.7 for three protons of

methoxy group whereas methine proton appeared as singlet at δ 5.8. Multiplet

for aromatic protons observed between δ 6.658-7.735 representing twelve

protons and two NH protons of bis (indolyl) methanes encountered at δ 8.0.

(Spectrum 3.5).

NNH H

OMe

OMe

2-[1H-indol-3-yl(2, 3-dimethoxylphenyl)methyl]-1H-indole (Table 3.1,

entry 4) has methyl protons of dishielded methoxy group observed at δ 3.7 and

3.8 while methine proton resonate at δ 5.8. Rest aromatic protons were

observed between δ 6.6-7.4. The two NH protons of each indole nucleus

appeared at δ 7.8 (Spectrum 3.6).


acid.

104

NH

NH

NMeMe

In 1H NMR spectrum of [1H-indole-3-yl(4-N,N

dimethylaminophenyl)methyl]-1H-indole (Table 3.1, entry 5) a singlet at δ

2.909 indicates equivalent protons of two methyl group attached to nitrogen

atom. A methine proton resonate at δ 5.803 whereas aromatic protons displayed

in the form of multiplet between δ 6.670-7.419. Two N-H protons of indole

nucleus showed broad singlet at δ 7.877 (Spectrum 3.7).

3.5 EXPERIMENTAL

Materials and Methods

All aryl aldehydes and indole were purchased from S. D. fine and

spectrochem Co. and were used without further purification.

Instrumental details and their operational conditions

NMR analysis

NMR analysis was performed on Brucker–Avance 300 MHz, NMR

spectrophotometer. For 1H NMR analysis, CDCl3 was used as solvent and

tetramethylsilane as an internal standard, the chemical shifts are reported in

ppm. Multiplicities are indicated by ‘s’ (singlet), ‘d’ (doublet), ‘t’ (triplet), ‘q’

(quartet), ‘m’ (multiplet) and ‘bs’ (broad singlet). The coupling constant (J) are

reported in Hz.

IR Analysis

Infrared spectra were recorded on Perkin Elmer 1310 FT-IR spectrometer with

KBr pellets.


acid.

105

General Experimental procedure

To the mixture of aryl aldehyde (1 mmol), indole (2mmol), 2-3 drops of

polystyrenesulphonic acid in water (5 mL) were added and the mixture stirred

at room temperature for the appropriate reaction time .The product was isolated

by simple filtration and further purified by column chromatography using

solvent system [ethyl acetate / petroleum ether (1:9)] to get desired bis (indolyl)

methanes in high yields.

3.6 CONCLUSION

We have demonstrated a simple, ecofriendly and elegant protocol for the

synthesis of bis(indolyl)methanes using polystyrenesulphonic acid, which

proceeds very efficiently in water without any use of flammable, volatile

organic solvent. As reaction occurs in the water which excludes the

cumbersome separation methods thus it avoids the exposure to the harmful

solvents. Therefore the use of polystyrensulphonic acid as a catalyst renders

this method environmentally benign.


acid.

106


acid.

107


acid.

108


acid.

109


acid.

110


acid.

111


acid.

112

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