Aluminium chloride-potassium iodide-acetonitrile system: A mild reagent system for aromatic claisen rearrangement at ambient temperature

Article abstract of DOI:10.1016/j.jics.2021.100024

Claisen rearrangement is used as the standard methods for the generation of complex organic substance. It is one of the well-known methods for the introduction of carbon-carbon bond. We have developed a protocol using allyl aryl ether as a substrate and AlCl₃-KI as a mild reagent system and acetonitrile (CH₃CN) is taken as solvent at ambient temperature. The reagent system presented in this current work is found to be appropriate for Claisen rearrangement of several aromatic alcohols with excellent yields.

Full text of DOI:10.1016/j.jics.2021.100024

Journal of the Indian Chemical Society 98 (2021) 100024
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Aluminium chloride-potassium iodide-acetonitrile system: A mild reagent
system for aromatic claisen rearrangement at ambient temperature
Nayan Kamal Bhattacharyya a,*, Deepjyoti Dutta , Joydeep Biswas a
b
a
Department of Chemistry, Sikkim Manipal Institute of Technology, Majitar, 7371 36, Sikkim, India
North East Institute of Science and Technology - CSIR, Jorhat, 785006, Assam, India
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Claisen rearrangement
Claisen rearrangement is used as the standard methods for the generation of complex organic substance. It is one
of the well-known methods for the introduction of carbon-carbon bond. We have developed a protocol using allyl
aryl ether as a substrate and AlCl -KI as a mild reagent system and acetonitrile (CH CN) is taken as solvent at
3 3
ambient temperature. The reagent system presented in this current work is found to be appropriate for Claisen
rearrangement of several aromatic alcohols with excellent yields.
AlCl
KI
3
Acetonitrile
1. Introduction
3 2
in the presence of BF –OEt lewis acid at very low temperature. Dauben
et al. [42] used montmorillonite clays as a catalyst for the Claisen rear-
rangement of substituted allyl aryl ethers to corresponding ortho-allyl
phenols under mild conditions. Sharma et al. [43] reported the Ytter-
bium catalyzed Claisen rearrangement of allyl phenyl ethers to corre-
sponding ortho allyl phenols under reflux condition at a reaction time
48–72 h. Gignare [44] carried out aromatic Claisen rearrangement by
microwave irradiation under very high thermal condition. Zi Hui [24b]
studied the microwave-accelerated Claisen rearrangement of allyl aryl
ethers using phosphomolybdic acid (PMA) as a catalyst. Ollevier et al.
[45] used Bismuth triflate as a catalyst in catalytic amount for the Claisen
rearrangement of allyl naphthyl ethers to corresponding ortho naphthol.
Deodhar et al. [46] reported selective Claisen rearrangement of allyl aryl
ethers using zeolite mediated catalyst under microwave irradiation.
Claisen rearrangement of allyl aryl ethers catalyzed by zinc to corre-
sponding ortho-allylated adducts was reported by Gupta et al. [47]at
Claisen rearrangement is one of the essential and beneficial synthetic
procedure for organic chemists [1a]. The innovation of the Claisen
rearrangement presented a potentially useful synthetic tool to organic
chemists. Claisen rearrangement attracts most synthetic chemists due to
its versatile application in synthesizing natural products and medicinal
chemistry [1b]. The Claisen rearrangement is a chemical reaction where
strong carbon–carbon bond formation occurs [2]. Investigation and
research established the chemo-, regio-, diastereo-, and enantiose-
lectivity of this reaction and the reaction can be carried out under gentle
conditions and potentially useful for polyfunctionalized molecules [3a].
Ethers are applied as protecting groups for hydroxyl functions in
organic synthesis and moreover a large number of ethers known as good
protecting groups. Several examples illustrating the application of the
Claisen rearrangement in preparing a wide range of synthetically striking
building blocks and natural or biologically active compounds are
considered. A numerous way can be applied to convert aromatic ethers to
corresponding phenols.
Sonnenberg et al. [39] reported aromatic Claisen rearrangement of
allyl phenyl ethers in the presence of alkyl aluminium halides under mild
conditions. Treatment of allyl phenyl ether in hexane with an excess of
diethyl aluminium chloride in hexane produced ortho allyl phenol.
Borgulya et al. [40] also reported the Claisen rearrangement of allyl aryl
ethers to corresponding phenols using Boron trichloride under thermal
conditions to produce a mixture of ortho and para products. Maruyama
et al. [41] reported the Claisen rearrangement of aryl-penta dienyl ethers
ꢀ
55 C in liquid phase.
In recent years, scientists have given interest in aluminium chemistry
and aluminium iodide, which has attained much importance in synthetic
organic chemistry [3b,38a-38d,49]. However, the chemistry of
aluminium chloride in the presence of potassium iodide is less explored
[3c,3d] although it works as an efficient reagent for various reactions. M.
Boruah et al. [51] used AlCl
media for dehydration of oximes and amides. M. Boruah et al. [52] also
used AlCl ⋅6H O/KI/CH CN/H O system in hydrated media for deoxy-
genation of organic N-oxide. Dilip Konwar et al. [38a] used AlCl –NaI
reagent for dehydration of oximes, amides and Beckmann rearrangement
3 2 2 3
⋅6H O/KI/H O/CH CN system in hydrated
3
2
3
2
3
*
Corresponding author.
E-mail address: nayan.b@smit.smu.edu.in (N.K. Bhattacharyya).
https://doi.org/10.1016/j.jics.2021.100024
Received 24 November 2020; Received in revised form 6 January 2021; Accepted 5 March 2021
019-4522/© 2021 Indian Chemical Society. Published by Elsevier B.V. All rights reserved.
0

N.K. Bhattacharyya et al.
Journal of the Indian Chemical Society 98 (2021) 100024
of ketoximes to anilides at room temperature. Dilip Konwar et al. [49]
also reported the development of aluminium iodide as an efficient re-
agent for dehydration of aldoxime to nitriles and Beckmann rearrange-
3 3
ment of ketoximes to anilides. We report the utility of AlCl -KI in CH CN
as a mild and efficient reagent for the Claisen rearrangement. Aluminium
iodide has multifaceted reactivity. Because of oxophilic character of lewis
acid it can form complexes with esters, ethers, oxiranes, diols, N-oxides,
and sulfoxides that decompose spontaneously to give acids, alcohols and
olefins via ester and ether cleavage, deoxygenation of oxiranes, and
deoxydehydration of diols, respectively [50].
There are various methods developed for modification of this reac-
tion. In general, Claisen rearrangement is carried out in thermal condi-
tion [4]. Nevertheless, in the last few decades, there has been developing
such methods where the reaction is carried out in the low-temperature
condition. In this respect BCl
8], CF COOH [9], pyridine/reflux [10]etc.; some metal triflate such as
Bi(OTf) [11], Yb(OTf) [12], Sn(OTf) , Cu(OTf) , Zn(OTf) [13],
Me SiOTf [14] and other reagents like montmorillonite clays [15],
decline [16] being reported for Claisen rearrangement type reaction.
Some metal complexes such as Rh (OAc) [17], RuCl (PPh [18],
dba) Pd ⋅CHCl [19], PdCl (CH CN) [20], (Cl) (CPy
Ru ¼ CHPh
21], chiral aluminium Bi-Napthol [22], chiral C2-symmetric bisulfona-
3 3 2 2 3
[5], BF –OEt [6], Et AlCl [7], n-Bu SnH
[
3
3
3
2
2
2
3
Scheme 1. Synthesis of o-allylated adducts from corresponding aryl allyl ether
using AlCl -KI-CH CN.
3 3
2
4
2
3 3
)
(
[
3
2
3
2
3
2
2
3 2
)
mide derived Boron reagent [23], etc. have been identified as more se-
lective and efficient reagents for modification of this reaction. Nowadays,
some greener methods such as microwave irradiation [24a,24b], ultra-
violet irradiation [25] etc. are also used in this purpose.
ambient temperature applicable to both phenyl and naphthalene system
to afford the corresponding product in good yield. The noteworthy sig-
nificances of our present system are – (i) comparatively short reaction
time, (ii) ambient temperature condition, (iii) cost-effectiveness and (iv)
simple work-up procedure.
Initially, we carried out the synthesis of allyl aryl ether by adding a
solution of NaOH to the phenol solution using phase transfer catalyst
like cetyltrimethylammonium bromide (CTAB). In this process, the
drop-wise addition of allyl bromide was gradually completed and
dichloromethane was used as a solvent. After this, the reaction mixture's
stirring was continued at ambient temperature and the reaction's
progress was monitored using TLC. We observed that reaction was
being completed at 3 h and corresponding phenyl allyl ether was being
isolated [37].
Besides these other reagents such as MgI
2
-bis(oxazolinyl)aryl ligands
[
26], KDMSO-LiCl ligands [27], Ag-KI/HOAc system [28], etc. and some
of the metals such as Zn dust [29], Zn in THF [30], domino Cu [31],
Al-MCM-41 [32], zeolite catalyst [33] being also reported.
Introduction of various solvents such as tetradecane, carbitol,
2
EtOH–H O, etc., affecting the Claisen rearrangement reaction [34]. Some
polar solvents in mild condition give rearrangement products, but it
cannot be obtained via classical conditions due to thermal decomposition
[
35].
However, the majority of these methods have some limitations like
harsh conditions, monotonous work up procedure, uncomfortable prod-
uct isolation and bi-products formation. Besides a large number of cat-
alysts reported in the literature are expensive. Therefore, looking of new
procedure is still going on to carry out the Claisen type rearrangement
reaction at ambient temperature condition using a cheap, commercially
available reagent.
After the success of this reaction, the process was extended to a va-
riety of phenol derivatives. It can be seen from Table 2 that various
phenols containing functional groups reacted successfully to give corre-
sponding ether in sufficiently high yields. In general, the phenyl system
derivative takes 3–8 h to complete the reaction while the naphthalene
ring containing derivatives reacts at faster reaction rates that take 1.5–2 h
to complete the reaction. Naphthalene is more reactive than benzene,
because the resonance energy of naphthalene (61 kcal/mol) is less
Anhydrous AlCl
varieties of conversions as a low-cost and readily available reagent. Gogoi
et al., 2006 used the AlCl -KI-CH CN system for chemoselective C–O
3
has recently been applied as a lewis acid catalyst for
3
3
(
11 kcal/mol) than that of two benzene rings (2*36).
bond cleavage of esters, acetals, ethers and oxathiolanes [38b]. Node
et al., 1992 explained a method for selective dealkylation aliphatic
The main part is to carry out Claisen rearrangement at ambient
temperature using AlCl
first, AlCl and KI (1:3) were taken in dry acetonitrile and the stirring of
the mixture was continued magnetically at ambient temperature for
0 min. After that phenyl allyl ether was added and stirring was
3 3
-KI- CH CN system [38] as a mild reagent. At
methyl ether under mild conditions using AlCl
Sang et al., 2018 proposed a method for cleavage of aryl methyl ether
under mild conditions using AlCl -KI-CH CN system [38c]. Keeping this
3 3
–NaI–CH CN system [36].
3
3
3
4
in mind, we have used the same reagent system for the Claisen rear-
rangement of aromatic alcohols from its ether moiety (Scheme 1).
continued at ambient temperature. Thin-layer chromatography was used
to monitor the progress of the reaction. It was observed that reaction was
taken place at ambient temperature and correspondingly o-allylated
phenol was being isolated.
2. Results and discussion
After the reaction's success, the process was also extended to various
allyl aryl ether derivatives. It was being seen from Table 3 that allyl aryl
ethers containing functional groups reacted successfully to give corre-
sponding o-allylated alcohol products in suitably high yields. In general,
allyl aryl ether derivatives require 16–20 h for the completion of the
reaction. It was also observed that the naphthalene ring containing ether
derivative took 6–10 h for the completion of the reaction and also the
percentage of yield was moderately high.
Most of the early preparative methods for the aromatic Claisen
rearrangement were in thermal condition as well as catalyzed by tran-
sition metals. Furthermore, most of the methods suffer from the limita-
tions like – (a) use of a stoichiometric amount of catalyst, (b) high-
temperature condition, (c) use of expensive catalyst, (d) a low percent-
age of yield, (e) cumbersome reaction condition as mentioned in Table 1.
Our present investigation, therefore, directed to address the limita-
tion mentioned above in aromatic Claisen rearrangement. Here we
describe an alternate procedure of aromatic Claisen rearrangement at
The yields were found very good in all cases with comparatively lesser
time. The products were analyzed by spectral analysis.
2

N.K. Bhattacharyya et al.
Journal of the Indian Chemical Society 98 (2021) 100024
Table 1
The following table suggests the various procedure used for Claisen rearrangement.
Substrate
Reaction condition
Product
References
ꢀ
R
2
AlCl, 65 C/Hexane
Sonnenberg et al. [39]
(R ¼ Et, i-Bu)
BCl
3
/Heat
Borgulya et al. [40]
Maruyama et al. [41]
R ¼ H, CH
3
BF
3
–OEt
2
/ꢁ25 ꢀ
C
1 2 3
R R R
Me Me H
Me H Me
MeO H H
H t-Bu H
ꢀ
Clay, Benzene/50
C
Dauben et al. [42]
Sharma et al. [43]
R ¼ H, 4-OCH
3
, 4-OC
2
H
5
, 3,5-CH
3
, 4-COCH
3
Yb(OTf)
3
3
, CH CN/reflux
R ¼ H, CH
3
ꢀ
MW/180
C
Gignare et al. [44]
Ollevier et al. [45]
Bi(OTf)
–40 h
3
.xH
2
O (cat.)
1
–
R ¼ H, 4-OCH
3
, 4-Cl, 5-OCH
3
, 7-OCH
3
–
2 2
, 5-OCH -CH CH
ꢀ
Zeolite, MW/80
C
Deodhar et al. [46]
Gupta et al. [47]
R ¼ H, 6-CH
3 3 3 3
, 4- OCH , 5-CH , 6-OCH , 6-CHO, α-Naphthol, β- Naphthol
ꢀ
Zn/THF, Stirring, 55
C
R ¼ H, 4-OCH
3 2 3
, 4-Cl, 4-Br, 4-NO , 4-COCH 4-Me, 4-OEt
2
0 mol%, Bi(OTf)
3
.xH
2
O
Thierry Ollevier et al. [48]
A proposed mechanism for the AlCl
rearrangement is depicted in Fig. 1. Solvation of AlCl
3
-KI-CH
3
CN mediated Claisen
3. Experimental section
–
3
3
in CH –C
–
N led to
the formation of complex CH
give CH
3
CN–AlCl
CN and an oxonium ion RO CH
3
which reacts with allyl ether to
3.1. Materials and methods
(
þ)
(ꢁ)
3
2
CHCH
2
AlCl
3
. The oxonium
ion reacts with potassium iodide to form allyl iodide. The lewis acid
activated the phenoxide ion undergoes electrophilic substitution reac-
Analytical reagent grade chemicals were used for the synthesis, which
are commercially available, and used without any further purification.
The crude product obtained was purified using column chromatography
where silica gel was used as stationery phase and petroleum ether and
tion. This conversion might involve a transition state where AlCl
3
would
activate the phenoxide ion as well as the allyl group from allyl iodide.
3

N.K. Bhattacharyya et al.
Journal of the Indian Chemical Society 98 (2021) 100024
Table 2
Table 3
AlCl
þKI mixture catalyzed Claisen rearrangement of allyl aryl ethers to o-ally-
lated products in acetonitrile.
Preparation of allyl aryl ether using allyl bromide.
3
Entry
1
Substrate
Product
Yield
82%
Time (h)
3
Entry
1
Substrate
Product
Yield (%)
84
Time (h)
20
2
3
76%
80%
8
6
2
3
87
80
16
18
4
72%
65%
5
4
76
72
12
6
a5
1.5
a5
ꢃ
0
ꢃ
0
Reaction condition: Substrate 0.01 mol, allyl bromide 0.01 mol, phenol
.02 mol.
aReaction condition: Substrate 0.01 mol, allyl bromide 0.01 mol, phenol
.015 mol.
ꢃ Reaction condition: Substrate 1 mmol, aluminium chloride 1 mmol, KI 3 mmol.
a
ꢃ
Reaction condition: Substrate 1.5 mmol, aluminium chloride 1 mmol, KI
mmol.
ethyl acetate mixture were used as eluent. The percentage of yield was
calculated using the following relation.
3
Actual Yield
Percentage Yield ¼
ꢂ 100%
Theoretical Yield
.2. General procedure for the preparation of aryl allyl ether
The procedure for the preparation of aryl allyl ether was taken from
where silica gel was used as stationary phase and petroleum ether and
ethyl acetate mixture were used as eluent.
3
4
. Supportive information
literature [37,53]. Phenol (0.01 mol) and NaOH (0.02 mol) was taken in
dichloromethane (5 mL) and water (5 mL) mixture and then
cetyl-trimethyl ammonium bromide (CTAB) (0.0001 mol) was mixed in a
IR spectra were recorded on Elmer FT-IR 2000 spectrometer (KBr
discs) in the range from 4000 to 400 cm . NMR of the compounds were
performed in a 500 MHz NMR spectrometer with tetramethylsilane
ꢁ
1
100 mL round-bottomed flask. Allyl bromide is being added dropwise
(TMS) as internal reference and CDCl
3
as solvent. All chemical shifts (δ)
(
0.02 mol) and stirring of the reaction mixture at ambient temperature
are reported in ppm and coupling constant (J) in Hz.
ꢁ1
was continued for 3 h. Organic and aqueous layer were separated from
each other and 10 mL of dichloromethane (twice) was used to extract the
aqueous layer. The organic layers were combined and then dried with
Phenyl allyl ether: IR (KBr, cm ) ν: 3086.2 (Aromatic C–H,
–
–
C), 1174.4, 1112.5 cm
, δ ppm): 7.17 (2H), 6.91 (2H), 6.82 (1H),
ꢁ1
Alkene ¼ C–H), 1592.4, 1509.2 (Aromatic C
1
(Ether C–O). H NMR (CDCl
3
anhydrous Na
2
SO
4
and then extracted in Buchi Rotavapor under reduced
6.06 (m, 1H, H), 5.43 (1H, dd, H), 5.31 (1H, dd, H), 4.67 (2H, H), 4.67
(2H, H).
pressure. The product was separated by column-chromatographic tech-
nique using 5% of ethyl acetate in petroleum ether as eluent.
Ortho allyl phenol: IR (KBr, cmꢁ1)
ν: 3418.1 (O–H), 1643.9 (Alkene
–
ꢁ1
–
–
3
C). H NMR (CDCl , δ ppm):
1
C
9
–
C), 1485.7, 1460.1 cm (Aromatic C
.68 (s, OH), 7.11 (2H), 6.80 (1H), 6.74 (1H), 5.92 (m, 1H, H), 5.12 (1H,
dd, H), 4.87 (1H, dd, H), 3.33 (2H, H), 3.33 (2H, H).
3
.3. General procedure for the synthesis of o-allyl phenol in
AlCl –KI–CH CN system
3
3
ꢁ
1
Para nitro allyl phenyl ether: IR (KBr, cm
) ν: 3076.7, 2980.2
–
(
(
7
Aromatic C–H, Alkene ¼ C–H), 1659.1, 1621.6 (Alkene C
–
C), 1565.6
, δ ppm): 8.03 (2H),
.15 (2H), 6.06 (m, 1H, H), 5.43 (1H, dd, H), 5.31 (1H, dd, H), 4.67 (2H,
H), 4.67 (2H, H).
Para nitro ortho allyl phenol: IR (KBr, cm 1)
Anhydrous aluminium chloride (1 mmol) and potassium iodide
3 mmol) were added to dry acetonitrile (20 mL) and the mixture was
N–O), 1236.4 cm (Ether C–O). 1H NMR (CDCl
ꢁ1
3
(
stirred magnetically at ambient temperature for half an hour. Then
phenyl allyl ether (1 mmol) was added, stirred for 6–20 h and thin-layer
chromatographic technique was used to monitor the reaction's progress.
The reaction mixture was added into a cold ammonical water solution
and extracted with diethyl ether. The organic layer was washed with
water and solvent was removed in Buchi Rotavapor so that crude product
was obtained and purification is done using column chromatography
ꢁ
ν
: 3438.7 (O–H),
ꢁ1
–
1
3
045.0 (aromatic C–H), 1594.9 (N–O), 1493.2 cm (Aromatic C
–
C). H
NMR (CDCl
3
, δ ppm): 11.88 (s, OH), 8.21 (1H), 8.12 (1H), 7.07 (1H),
5.92 (m, 1H, H), 5.12 (1H, dd, H), 4.87 (1H, dd, H), 3.33 (2H, H), 3.33
(
2H, H).
4

N.K. Bhattacharyya et al.
Journal of the Indian Chemical Society 98 (2021) 100024
Fig. 1. Proposed reaction mechanism.
[7] Sonenberg FM. J. Org. Chem. 1970;35:3166.
5. Conclusion
[
[
8] Enholm EJ. J. Am. Chem. Soc. 1998;120:3801.
9] Widmer U. Helv. Chim. Acta 1973;56:2644.
In summary, an efficient procedure has been developed for the syn-
[10] Ponaras AA. Tetrahedron Lett. 1983;24:3.
thesis of o-allylated adducts from the corresponding aryl allyl ether using
AlCl -KI-CH CN mild reagent system. Our present reagent system's
[11] Ollevier T. Tetrahedron Lett. 2006;47:4051.
[12] Sharma G. J. Am. Chem. Soc. 1999;121:9726.
[13] Lambert TH. J. Am. Chem. Soc. 2002;124:13646.
[14] Lamieux. J. Org. Chem. 1999;64:4030.
3
3
noteworthy significances are comparatively short reaction time, room
temperature condition, cost-effectiveness, and simple work-up proced-
ure. The procedure is easy to perform at ambient temperature and
applicable to different aryl allyl ether (both phenyl and naphthalene
system) to give corresponding o-allylated phenols. The reagent system
presented in this current work is found to be appropriate for Claisen
rearrangement of several aromatic alcohols with excellent yields. More-
over, this procedure is also applicable to the naphthalene ring system to
give corresponding o-allylated adducts in suitably high yields. Utilizing
this kind of efficient reagent system in organic rearrangements would be
more influential and immensely encouraging to academic and industrial
researches.
[15] Dauben WZ. Tetrahedron Lett. 1990;31:3241.
[
[
[
16] Huang KS. Tetrahedron Lett. 2001;42:6155.
17] Saloman RG, Reuter JM. J. Org. Chem. 1977;42:3360.
18] Novikov VA. J. Org. Chem. 2002;68:993.
[19] Trost BM, Schroder. J. Am. Chem. Soc. 1998;120:815.
[
[
[
20] Hiersemann M. Synlett 1999:1823.
21] Barrett AGM. J. Org. Chem. 2000;65:3716.
22] Lemiieux RM. J. Org. Chem. 1999;64:3585.
[23] Corey EJ, Lee. J. Am. Chem. Soc. 1991;113:4026.
[
24] (a) Daskiwicz J. Tetrahedron Lett. 2001;42:7241.(b) Hui Zi, Jiang Songwei,
Qi Xiang, Ye Xiang-Yang, Tian Xie. Tetrahedron Lett. 11 June 2020;61:151995.
25] Rao Sethi. Ind.J.Chem. 1964;2:323.
[
[26] Sharghi H. J. Org. Chem. 2000;65:2813.
[27] Yoon TP. J. Am. Chem. Soc. 2001;78:66.
[
[
[
[
[
[
[
28] Denmark EScott. J. Org. Chem. 2013;78:66.
29] Ishihara. Molecules 2012;17:14249.
30] Gupta M. Open Catal. J. 2010;3:40.
31] Nordmann G. J. Am. Chem. Soc. 2003;125:4979.
32] Mathew Nevin T. J. Catal. 2005;229:105.
33] Deodhar KD. Ind.J.Chem. 2010;491:1552.
34] Brandes EJ. Org. Chem. 1989;54:5849.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[35] Grieco PA. J.Org.Chm. 1989;54:5849.
[
[
[
36] Node Manabu. Bull. Inst. Chem. Res. Kyoto Univ. 1992;70:308.
37] Purwono HB. IJET-IJENS(Open Access) 2012;12. 0145.
Acknowledgement
38] (a) Konwar D, Boruah M, Sarmah GK, Bhattacharyya NK, Borthakur N,
Goswami BN, Boruah KR. J. Chem. Research (S) 2001:490–2.(b) Gogoi P,
Konwar D, Sharma SD. Synthetic Commn 2006;36:1259–64.(c) sang D, Tu X,
Tian J, He Z, Yao M. Chemistry Select 2018:10103–7.(d) Sarma SD, Pahari P,
Hazarika S, Hazarika P, Borah MJ, Konwar D. Reviews and Accounts 2013:243–63.
We would like to thank the Director, Sikkim Manipal Institute of
Technology, Majitar, Sikkim-737136 and the Director, CSIR – North East
Institute of Technology for providing research facilities. We would also
like to thank Dr. Dilip Konwar for his help in carrying out this work.
[39] Sonnenberg FM. J. Org. Chem. 1970;35:3166.
[40] Borgulya. J. Chim. Acta. 1973;56:14.
[41] Maruyama K. J. Org. Chem. 1986;51:5083.
[42] Z W. Tetrahedron Lett. 1990;31:3241.
References
[43] Sharma G. J. Am. Chem. Soc. 1999;121:9726.
44] Daskiwicz J. Tetrahedron Lett. 2001;42:7241.
[
[
1] (a) Castro M. Chem. Rev. 2004;104:3002.(b) Ireland RE. Tetrahedron Lett. 1977:
839. 02.
[45] Ollevier T. Tetrahedron Lett. 2006;47:4051.
[46] Deodar K. Indian J. Chem. 2010;49:1552.
[47] Gupta M. Open Catal. J. 2010;3:40.
[48] Ollevier Thierry, Mwene-Mbeja Topwe M. Tetrahedron Lett. 6 June 2006;47(24):
4051–5.
[49] Konwar Dilip, Boruah Romesh C, Sandhu Jagir S. Tetrahedron Lett. 1990;31(7):
1063–4.
[50] Tian Juan, Sang Dayong. ARKIVOC 2015;vi:446–93.
[51] Boruah M, Konwar D. J. Org. Chem. 2002;67(20):7138–9.
[52] Boruah M, Konwar D. Synlett 2001:795–6. 06.
[53] Sanford EM, Lis CC, McPherson NR. J. Chem. Educ. 2009;86(12):1422.
2
[
[
2] Clayden.org Chem.Oxford univ press.second ed..
3] (a) Claisen L. Justus liebigs. Ann. Chem. 1918;418:69.(b) Dictionary of Inorganic
Compounds, vol. 1. London: Chapman & Hall; 1992. p. 36.(c) Node M, Kajimoto T,
Nishide K, Fujita E, Fuji K. Tetrahedron Lett. 1984;25:219.(d) Node M, Ohta K,
Kajimoto T, Nishide K, Fujita E, Fuji K. Chem. Pharm. Bull, Japan 1983;31:4176.
4] (a) Claisen L. Chem. Ber. 1912;45:3157.(b) Ziegler FE. Acc. Chem. Res. 1977;60:
[
2
22.(c) Jolidon S, Hansen HJ. Helv.Cheim.Acta. 1977;60:978.
[
[
5] Kozlkowski AL. Tetrahedron Lett. 1981;22:3381.
6] Maryama K. J. Org. Chem. 1986;51:5083.
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