Bismuth chloride mediated allylation of carbonyl compounds in aqueous media: A mechanistic investigation

Article abstract of DOI:10.1016/j.tetlet.2014.07.031

The bismuth chloride mediated, aluminum promoted aqueous Barbier type coupling of allyl unit with carbonyl compounds which gives the corresponding homoallyl alcohol is studied. The transient in situ generated allylbismuth(III) bromide intermediate was stu

Full text of DOI:10.1016/j.tetlet.2014.07.031

Accepted Manuscript
Bismuth chloride mediated allylation of carbonyl compounds in aqueous media:
A mechanistic investigation
B.D. Jadhav, S.K. Pardeshi
PII:
S0040-4039(14)01184-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.07.031
TETL 44874
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
29 May 2014
7 July 2014
8 July 2014
Please cite this article as: Jadhav, B.D., Pardeshi, S.K., Bismuth chloride mediated allylation of carbonyl compounds
in aqueous media: A mechanistic investigation, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.
2
014.07.031
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Bismuth chloride mediated allylation of carbonyl compounds in
aqueous media: A mechanistic investigation
B. D. Jadhav and S.K. Pardeshi*
Department of Chemistry, University of Pune, Ganeshkhind,
Pune-411007(INDIA)
*
Corresponding author. Tel.:+91 020 25601225 Extn. 514; Fax: +91 020 25691728.
E-mail: skpar@chem.unipune.ac.in(S.K.Pardeshi)
Abstract
The bismuth chloride mediated, aluminum promoted aqueous Barbier type coupling of allyl
unit with carbonyl compounds which gives the corresponding homoallyl alcohol is studied.
The transient in situ generated allylbismuth (III) bromide intermediate was studied by
1
HNMR and GCMS for mechanistic study of allylation. The role of solvent, temperature and
additives in their formation is also studied. The results show that the most reactive
2 2 2
intermediate species is CH =CHCH BiBr which mediates allylation of aldehydes and
ketones with different substituents with good yields.
Keywords: Allylation, Allyl bromide, Bismuth chloride, organobismuth intermediate,
homoallyl alcohol
1

In recent times , organic synthesis in aqueuos media has attracted considerable
attention because of their environmental benefits and favorable effects of water on organic
1
transformations. It was noticed in the early 1980s that allylic halides in particular can be
used to react with aldehydes in presence of metal powder to afford homoallylic alcohols in
aqueous media. This type of allylic carbonyl addition has been called the Barbier-type
allylation. Among the reactions in aqueous media, allylation of carbonyl compounds with
allylic organometallic reagents or allyl halides are of great interest because they are
2
convenient methods to form C-C bond. They provide an approach to synthesize secondary
and tertiary homoallylic alcohols, as valuable synthetic building blocks in natural product
3
synthesis. A number of metals are known to participate in the coupling reaction in aqueous
4
media including zinc, indium, tin, manganese, antimony and magnesium. The most widely
used metals in allylation are zinc and indium.
Among VB group elements, bismuth metal and its salts are cheaper and least toxic
than arsenic and antimony. Bismuth (III) compounds namelyBiCl
3
, BiBr
3
, Bi (NO
3
)
3
and
5
have been used as catalyst in organic synthesis due to its metallic character. Most
Bi (OTf)
3
of these synthetic reactions are performed in organic solvents. The use of water as the
reaction medium is usually avoided since a large number of reactants decompose when
brought in contact with water. Furthermore, many organic reactants are sparingly soluble in
water. Even though these are the disadvantages, water is becoming increasingly popular as a
medium for organic reactions. Being the most abundant solvent on earth, it is very cheap,
easily available, non-hazardous to the environment and non-toxic. Moreover, aqueous
solvents can have beneficial effects on rates and selectivity of important organic
6
transformations. The Barbier reaction is one of synthetic method which became one step
alternative to the Grignard reaction due to the simplicity and applicability in organic
7
synthesis. Therefore we focus our attention on potential use of active bismuth metal
3
generated in situ by the action of BiCl and metallic aluminum for allylation reaction in
aqueous medium.
Wada et al reported that bismuth powder (100 mesh) could promote the addition of
allyl unit to aldehydes using N, N-dimethylformamide (DMF) as solvent but it requires long
8
period of reaction time. In the absence of Al powder and aqueous tetrahydrofuran (THF) as
solvent, trace amount of product was isolated.
2

Generally acidic environment is necessary to promote reactivity of metal and also to
increase the solubility of carbonyl compounds in water. However a number of carbonyl
compounds bearing different substituent groups are unstable in acidic environment. Moreover
the side reactions such as reduction and pinacol type of coupling can take place readily in
acidic environment. Yang et al reported that phase transfer catalyst promoted allylation of
carbonyl compounds in water mediated by tin without NH
4
Cl to produce homoallyl alcohols
9
in good yields, however its reaction mechanism is unclear.
Herein we report our studies on the allylation of carbonyl compounds with allyl
bromide effected with active bismuth (Bi*) in aqueous medium which is more convenient
and environmental friendly. Effect of organic co solvent, amount of catalyst, role of metal
salt additives on the yields of homoallyl alcohols along with mechanistic aspect are also
discussed.
In aqueous medium, a black suspension of active bismuth (Bi*) was obtained by
3
stirring BiCl (5 mmol) with aluminum powder (5 mmol) in ice bath for fifteen minutes. The
resulting black suspension was reacted with a solution of allylbromide and carbonyl
compounds at room temperature for specified time (Scheme1)
O
OH
Br
+
Bi*
1
R
1
2
R
R
2
R
H O, RT
2
1
2
3
a-m
Scheme 1 General allylation reaction
To explore the generality and scope of this reaction further,BiCl
3
mediated and Al (0)
promoted reaction in aqueous THF at room temperature was examined using other
functionality and sterically diverse carbonyls as shown in Table1.
3

Table 1 BiCl
3
mediated aluminum promoted allylation of carbonyl compounds with
a,b
allylbromide
1
R Substrates
2
R
Entry
Product
Yield (%)/time (h)
c
1
2
3
4
5
6
7
8
9
Ph
H
H
H
H
H
H
H
H
H
H
H
3a
3b
3c
3d
3e
3f
88/16(85/10)
4-CH
3
OC
6
H
4
89/12
82/16
70/16
4-ClC
6
H
4
2-C
4-CH
2-OHC
2-OH-5-CH OC
3-NO
Ph-CH=CH
n-C
5 4 2
H O
d
3
C
6
H
4
85/16
c
6
H
4
96/12(94/10)
3
6
H
3
3g
3h
3i
94/16
73/16
2
6 4
C H
d
85/16
c
1
1
1
1
0
1
2
3
5
H
10
3j
78/10(81/6)
d
CH
3
-CH=CH
3k
3l
75/16
c
Ph
Me
Ph
65/12(83/5)
c
Ph
3m
53/15(50/6)
a
All reactions were performed with aldehyde (5 mmol), allyl bromide (7.5mmol),
(5 mmol)and aluminum powder (5 mmol) in THF: H O at room temperature.
Isolated yields. All physical data including IR &NMR spectra were consistent with
BiCl
b
3
2
the literature data
c
Combined yields.
The yield was estimated by GCMS.
d
From Table 1 it is clearly seen that all aromatic, heteroaromatic and aliphatic
aldehydes reacted smoothly to provide the corresponding homoallyl alcohols in excellent
1
2
yields of 53-96%.As per Scheme 1, the nature of R and R group and either electron
donating or electron withdrawing sustitutents are not significant. 4-methoxybenzaldehyde
and4-chlorobenzaldehyde (Entries 2 and 3) showed the tendency of decrease in yield. It is
thought that the benzaldehyde with electron-donating groups is more difficult to be attacked
by allyl metal reagents. It is interesting to note that unsaturated aldehyde such as
cinnamaldehyde affords 1, 2 addition product selectively than 1, 4 addition product (Entry9).
4

In order to assess the usefulness of the reaction with other types of aldehydes,
reactions were conducted with a heterocyclic aldehyde, 2-furaldehyde (Entry 4, Table 1),
which gives the desired homoallyl alcohol with 70% yields. Aliphatic aldehyde for example
valeraldehyde (Entry 10) and crotonaldehyde (entry 11) were reacted under these conditions
giving moderate yields of corresponding allyl alcohols. When aromatic keto carbonyl
compound, such as benzophenone (Entry 13, Table 1) is taken it exhibits reduced
electrophilicity, resulted in 53% yields, reflecting improved reactivity of the carbonyl group.
1
0
This was compared with similar reactions using an allyl gallium reagent in THF hexane.
Another noteworthy observation is that no side products resulting from Wurtz or pinacol
coupling are observed however, some unreacted starting material is detected. General
1
1
procedure for allylation of aldehydes with allyl bromide is given in reference section. In
order to optimize the reaction conditions such as Lewis acid catalyst, effect of solvent and
role of additives, benzaldehyde was chosen as a model substrate.
Considering that Lewis acids were usually employed as auxiliary agents to promote
2 4 3
the allylation, we screened different Lewis acids such as SnCl , SnCl , and InCl to improve
the yield of allyl alcohol and compared with BiCl
3
. The results are summarized in Table 2
a, b
Table 2 Lewis acid-aluminum mediated allylation of benzaldehyde with allylbromide
Entry
Lewis Acid (mmol) Time (h)
Yield (%)
1
2
3
4
5
6
7
8
_
24
12
12
12
12
6
30
39
56
SnCl
4
(2mmol)
(2mmol)
(2mmol)
SnCl
2
c
InCl
3
80 (85)
BiCl
3
(2mmol)
(1mmol)
(0.5mmol)
(1 mmol)
80
c
BiCl
BiCl
BiCl
3
92 (88)
3
12
12
55
93
3
a
Reaction conditions: PhCHO (1 mmol), allylbromide (1.5 mmol), aluminum powder
1.5mmol)
(
b
4
Lewis acid in NH Cl (0.1 mmol) and water (20 ml) at room temperature for a specified
time.
c
Isolated yield
5

With the help of bismuth trichloride, the reaction rate was accelerated and the product
yield improved significantly (Entry 6, Table 2). The amount of bismuth trichloride used had a
large influence on the allylation outcome. With 0.5 mmol of bismuth trichloride, the product
yield improved from 30% to 55% (Entries 1 and 7, Table 2). When the amount of BiCl
increased to 1mmol, the yield improved further with decrease in stirring time. (Entry 6, Table
). When reaction was continued further for 12 hours with the same mole ratio of BiCl , yield
of the allyl alcohol reaches upto 93% (Entry 8, Table 2).However, when the amount of BiCl
3
was
2
3
3
was 2mmol, the product yield decreased gradually (Entry 5, Table 2).Hence 1mmol bismuth
chloride and its different mole ratio were used as Lewis acid catalyst. Under the set of
varying catalytic amounts of the different Lewis acids employed in allylation, the yields of
the allyl alcohols differ significantly with Lewis acid amount. It is shown graphically in
Figure1.
Figure1: Catalyst chemoselectivity study
3
As seen from the above figure the yields of allylation by BiCl in all millimolar ratio
are higher than respective InCl , SnCl and SnCl respectively.
3
2
4
The allylation of benzaldehyde with allyl bromide was studied as a model reaction in
different solvents with catalytically active bismuth metal generated in situ by the action of
3
BiCl /Al (0). Typical solvent effect on the yield of allyl alcohols and stirring time required
for completion of reaction are represented in Table 3.
6

Table 3 The effect of solvent on the BiCl
3
mediated, aluminum promoted allylation of
a, b
benzaldehyde with allylbromide
c
Entry
Solvent
DMF
Amount (equiv)
Time (h)
36
Yield %
1
2
3
4
5
6
7
8
9
6
65
H
2
O
O
O
2
24
24
36
24
24
24
36
48
24
24
70
H
2
6
65
H
2
6
56
DCM
THF/H
DCM/H
DMF/H
CH OH
CH OH / H
THF
6
Trace
95
2
O
6:6
6:6
6:6
6
2
O
68
2
O
80
3
77
1
1
0
1
3
2
O
3:7
6
80
Trace
a
All reactions except THF, DCM were performed with aldehyde (5mmol), Allyl bromide
(
10mmol), aluminum powder (5mmol) and BiCl
3
(5 mmol) at room temperature
b
The reactions were carried out at room temperature for specified time.
c
Combined yield.
Initially, we treated allyl bromide with benzaldehyde and bismuth chloride in 0.1 N
aqueous NH
4
Cl for 3 h at room temperature. TLC analysis of the ethyl acetate extract clearly
1
showed a spot that corresponds to the desired allylation product. Subsequently, HNMR
measurement of the crude reaction mixture showed about 30% of the allylation product. This
promising result encouraged us to examine factors that influence the reaction. We then
examined in greater detail the effect of the solvent system on the allylation reaction by using
various combinations of water and organic co solvents in the reaction.
The results show that the reaction proceeds slow in water and only 56 % yield was
obtained even after 36 hours stirring at room temperature (Entry4, Table 3). When reaction
was conducted in freshly distilled THF dried over sodium/ benzophenone, or in DCM the
reaction between benzaldehyde, allyl bromide, and bismuth chloride generated the expected
allylation product only in trace amount (Entry 5 and 11, Table 3). However, when a
7

THF/H
THF: H
was sufficient for this reaction. When the composition of the solvent is changed to water
Entry 3, Table 3) alone, a smooth reaction occurred generating the allyl alcohol with a low
2
O mixture was used as solvent, 95% yields were achieved. Different volume ratios of
2
O were also examined and we found that 10 mL of solvent with 8:2 compositions
(
conversion. This may be attributed to the formation of bismuth oxychloride (BiOCl) as water
insensitive material, which may get accumulate on the metal surface and block further
reactions.
When the reaction was conducted in dimethyl formamide (DMF) it works well but
requires a relatively long period of reaction time (Entry 1).The function of water in the
reaction has been investigated. We thought that catalytic system generates Bi* metal by redox
step and is favorable in aq.THF. We checked this hypothesis by conducting the reaction in
absence of Al metal where starting aldehyde gets recovered back. It is possible that the
allylbismuth reagent cannot be formed in THF solvent without water probably due to lack of
redox step generating Bi (0). On the other hand, it was found that the solution was strongly
acidic. Thus, it is thought that the role of water lies in two ways: the first is to accelerate the
formation of allylbismuth reagent and the second is to make the aldehyde more liable towards
the attack by allylbismuth reagent in acidic media.
4
Additional side reactions using 0.1 N HCl or NH Cl solutions as the reaction solvents
gave a quantitative conversion, generating a mixture of the reduced and pinacol coupling
products as indicated by TLC and GCMS. Other aromatic aldehydes gave similar results,
whereas reactions of aliphatic aldehydes gave more complicated mixtures.
1
2
13
Recent reports indicate that, the performance of bismuth and antimony metals in
aqueous Barbier type reactions was enhanced by the presence of fluoride salt which
successfully activates C-C bond-forming reactions. Therefore, we investigated the effect of a
variety of additives and mole ratios of reactants, beginning with a similar mole ratio as that
1
3
adopted by Li et al in Sb-mediated allylation reactions. We tried various salts like NaF, KBr,
KCl, KF, NH4Cl andBu NBr in aqueous media as additives. Apart from KF, NH Cl and
NBr most of them are either ineffective or give poor yields. However NH Cl, KF or
NBr were found to be quite effective in activating bismuth, which gave a good yield of
4
4
Bu
Bu
4
4
4
the corresponding homoallyl alcohols. Unfortunately, from a green chemistry viewpoint a
reaction using KF is not ideal therefore it was not used in further studies. Aliphatic aldehydes
(
Table 1, Entries10 -11) or aromatic ketone (Table 1, Entry 12), which are usually thought to
be unreactive, in presence of Bu NBr, get accelerated and transformed to corresponding
alcohol in good yield. For rest of the substrates use of NH Cl is quite effective. We therefore
4
4
8

4 4
utilized NH Cl or Bu NBr in the standard reaction conditions to activate in situ generated
bismuth metal in aqueous medium.
The mechanism of the Barbier reaction in aqueous media is not fully understood. For
4
the mechanism of the metal-mediated allylation reaction in aqueous media, Li proposed a
radical- carbanion-allyl metal triangle which suggests that the specific mechanism of the
1
4
reaction is dependent on the metal being used. In case of zinc and tin mediated Barbier
allylation it has been found that in aprotic solvents, reaction proceeds through a direct
nucleophilic addition, while allylmagnesium bromide reacts through a single electron-transfer
1
5
process. A recent computational study has shown that allylzinc, allylindium, allyltin,
allylantimony, and allylbismuth species are more reactive toward the allylation of carbonyl
compounds than towards hydrolysis, while allylmagnesium bromide shows a similar
1
reactivity in the two reactions. NMR studies have shown that indium, tin and antimony react
6
1
7
with allylbromide in water to form allylmetal intermediates. However, for different metals,
there are still a number of unanswered questions with regard to the nature of the allylmetal
species and the involvement of single electron-transfer processes.
1
8
Encouraged by a short note from Nesmeyanov indicating that bismuth (III) chloride
was reduced by metallic zinc, under similar condition bismuth chloride reacts with metallic
aluminum and gave black powder immediately. The assumption of some allylbismuth reagent
is formed through the oxidative addition of an allylic halide to the in situ generated
bismuth(Scheme 2) was proved by NMR investigations.
Br
Br
Br
H O
2
Bi
H O
2
+
BiCl3
Al
+
or NH Cl
4
Br
1
1
4
Al/H O
2
Br
OH
R
Br
O
Bi
Bi
H O
2
H
2
R
2
5
H
2
O
3
3
Al/H O
2
6
Scheme 2: General outline of the allylation of carbonyl compounds by Al/BiCl
3
In order to check the nature and detection of the intermediate formed during the reaction
course, following set of experiments were performed.
9

In order to check the transient intermediate formed during the allylation of carbonyl
compound by in situ formed active bismuth, aliquots were withdrawn from the reaction
1
mixture at specified time intervals which was followed by its HNMR characterization. In
order to check the selectivity of the intermediate towards allylation, they are quenched by
1
adding benzaldehyde as model electrophile. Figure 2 represents the HNMR assignments in
the 2-3 ppm range from the NMR spectra of the allylation intermediates formed during
reaction.
When allyl bromide, bismuth chloride and aluminum powder were stirred in D
room temperature for 30 min to 10 h without addition of NH Cl,no allyl bismuth type
2
O at
4
1
intermediate 4,5,6 (Scheme 2) was detected as indicated by HNMR of the reaction mixture
(
Figure 2A,B).When mixture was warmed without additive to 60 °C, the appearance of small
1
doublet at 2.33ppm in the HNMR suggesting probable insertion of active bismuth in C-Br
bond and formation of some triallyl bismuth (III) intermediate 6 (Scheme 2) . Such upfield
shift of methylene proton of allyl bromide from 3.97 ppm suggests the diamagnetic shielding
effect caused by bismuth on adjacent methylene protons (Figure 2C). In another set with
3
mmol allyl bromide in the temperature range between 60-80°C methylene proton signal was
1
readily seen at 2.53ppm in the form of doublet in H NMR (Figure 2D), which was attributed
to the intermediate 4 or 5. Such down field shift by 0.3 ppm units might be due to electron
withdrawing nature of bromine attached to bismuth in the intermediate. The signal appearing
at 2.33 ppm in the first set at 60 °C is assigned to triallylbismuth (III)intermediate 6(Scheme
1
9
2
) by comparison with an authentic sample prepared independently (Figure 2E).
The effect of catalytic amount of NH Cl on the formation of intermediates formed by
the action of bismuth chloride, aluminum powder and allyl bromide in D O at room
temperature was evaluated by adding NH Cl under optimized time. It is interesting to note
4
2
4
that the rate of formation of the intermediates 4 and 5 (Scheme 2) has been accelerated as
1
observed by HNMR (Figure 2F). At the end of 10 h, we have quenched the intermediates
formed in the reaction mixture by adding benzaldehyde as model electrophile. Further stirring
of reaction mixture for 2-3 h completely consume benzaldehyde to 1-phenylbut-3-en-1-ol
suggesting selectivity of intermediates for chain extending reactions.
1
0

1
2
Figure 2 Partial HNMR spectra of allyl bromide and bismuth stirred in D O solution
(
(
(
(
(
A) 30 min at room temperature without NH
B) 10 h at room temperature without NH Cl. no signal from 1.0 to 3.0 ppm
C) 30 min at room temperature with NH Cl and at 60°C without additive
D) At 60-80°C with NH Cl
E) Allylbismuth (III) bromide prepared from allyl magnesium bromide and
bismuth (III) chloride in ether, and extracted into D O for NMR
F) At 70°C for 10 h with NH Cl
4
Cl
4
4
4
2
(
4
The above experiments strongly support that the aqueous Barbier reaction with in situ
generated bismuth proceeds through allylbismuth
(
III)dibromide(4),diallylbismuth(III)bromide(5)and triallylbismuth (III) (6) as the
organometallic intermediates according to Scheme 2. The formation of 6 is the slow step and
1
1

requires heating or the use of catalyst (Al).The conversion of 4 and 5 to 6 depends largely on
the relative amount of allyl bromide and in situ generated Bi* in the reaction system.
Intermediate compound react with benzaldehyde in water to give the corresponding
homoallylic alcohol.
From GCMS studies the presence of allylbismuth and allylbismuth bromide species were
detected in the organic extracts of the reactions. Theoretically, one equivalent of allyl
2 2 1
bromide would be required to produce (CH =CH-CH ) BiBr (4) while two equivalents for
(
CH =CH-CH ) BiBr (5) which efficiently leads to the homoallylic alcohols. However, it is
2
2
2
2
observed that in reactions when only 2 equivalents were added it significantly reduces the
reaction yields but 4 equiv. of allyl bromide were necessary to give high yields. The reason is
physical rather than chemical and stems from the volatility of allyl bromide under
prolonged stirring. In GC-MS spectra of the reaction mixture extracted in ethyl acetate
it has been seen that the peak at RT 15 min corresponding to m/e = 410 suggest the
2 2 2
presence of intermediate 4 (CH =CH-CH ) BiBr (Scheme 2) during the reaction course.
Unlike Grignard reagents, many organometallic complexes cannot be prepared in
preformed fashion due to their low thermal stability. Hence easy way to overcome the
stability problem of such organometallic complexes is its genesis in presence of electrophiles.
This is very common for the organometallic complexes to be generated in situ and then react
with electrophile in real time before it undergoes decomposition.
The stability of the allylating agent prepared in situ in aqueous environment was
checked by leaving the reaction of allyl bromide with Al-BiCl
3
in THF-H
°C for a number of hours ( the molar ratio of allyl bromide : Al : BiC1 : benzaldehyde = 1.5
2.25 : 1.5 : 1.0 ). Benzaldehyde was added to the reaction mixture as per the delay time span
2
O ( 4 : 1 ) at 0-
5
:
3
indicated in Table 4.Yields of allyl alcohol are reported after standard workup.
Table 4 Investigation of the stability of the allylating agent in aqueous environment
Entry
Delay Period
Yield
(%)
82
(
h)
1
1
2
3
4
3
77
5
65
7
53
1
2

It is interesting to note that the reactivity of the allylating agent prepared in situ did not
disappear for several hours in aqueous media at low temperature which is mere indication of
its stability. Up to 1-3 h (Entry 1 and 2) the yield of final allyl alcohol is moderate. Hence we
2
quenched the reaction mixture starting from 10 minutes to 3 h, extracted with D O and
1
analyzed it by HNMR.
O
BiBr -n
3
Br
n
R
H
a
2
1
OBiBr -n
3
AlCl3
Al(0)
Bi(0)
BiCl3
R
b
H O
2
(
OH) AlBr -n
n 3
OH
(
OH) BiBr -n
n 3
Al(0)
4
R
3
Scheme 3: Possible mechanism of allylation using active bismuth in aqueous medium
Bismuth (III) chloride in presence of Al(0) metal gets reduced to Bi (0) (Scheme 3)
which undergoes insertion most probably at weak C-Br bond in allylbromide (1)and forms
terminal organobismuth (III) derivative (a). This derivative combines in the next step with
aldehyde (2)and forms tetrahedral intermediate(b)which in the aqueous media hydrolyses to
homoallyl alcohol(3)and bismuth (III) compound (4).
In freshly dried THF, redox reaction between bismuth chloride and aluminum powder
leading to Bi (0) is sluggish and generation of organobismuth via C-Br bond insertion is very
4 2
slow process. However, in presence of NH Cl as additive and THF: H O as solvent system
there is rapid exothermic reaction generating Bi (0) very effectively and hence fast generation
of organobismuth reagent. The organobismuth halide generated during the reaction might act
as a Lewis acid which in a tandem manner, catalyze the organometallic addition to carbonyl
centre and produce linear homoallyl alcohols as per Scheme1.
2
0
This is supported by the recent computational study by Dametal.
1
3

We have developed a simple and convenient method for allylation of carbonyl
compounds with less expensive allyl bromide by using Al / BiC1 bimetal system in aqueous
media. Homoallyl alcohols were not obtained when Al alone was used in THF-H O which
3
2
signifies that some water-tolerant allylating agent prepared in situ is stable in aqueous media.
It is shown that the allylbismuth compounds persist during the reaction and that the most
2 2 2
reactive species is CH =CHCH BiBr .
Acknowledgments
B.D.J is grateful to the University Grant Commission, New Delhi for awarding
Teacher Fellowship under F.I.P.
References
1
2
3
4
5
6
7
8
9
)
)
)
)
)
)
)
)
)
Li, C. J. Chem. Rev. 1993, 93, 2023.
Chan, T. H.; Li, C. J. J. Chem. Soc., Chem. Commun. 1992,747.
Zhang, W. C.; Li, C. J. J.Org.Chem.1999, 64, 3230.
Li, C. J. Tetrahedron1996, 52, 5643.
Suzuki. H.; Matano. Y. Organobismuth Chemistry, Elsevier Amsterdam 2001
Araki, S.; Ito, H.; Butsugan, Y. J. Org. Chem. 1988, 53, 1831.
Hin-Soon Cheng and Teck-Peng Loh, Pure Appl. Chem., 2005, 77, 1199.
Wada, M.; Okhi W,; Akiba, K., Bull. Chem. Soc. Jpn., 1990 63, 1738.
Yang Guang, Zha Zheng-gen, Wang Zhi-yong Journal of University of Science and
Technology of China, 2003, 33, 375.
1
1
0)
1)
Tsuiji, T.; Usugi, S.; Yorimitsu, H.; Shinokubo, H.; Matsubara, S.; Oshima, K.
Chem. Lett.2002, 2, 3.
General procedure for the allylation of aldehydes with ally1 bromide:
In a 50 mL round bottom flask a mixture of carbonyl compound (5mmol),
allylbromide (10.8mmol) and bismuth trichloride (5 mmol) in 20mLdistilled water
4
was prepared. Then solid NH Cl (4 mmol) was added followed by aluminum powder
(
5mmol) in one portion with stirring. The resultant mixture was vigorously
stirred at room temperature for a specified time as given in Table1.The mixture was
then extracted with ethyl acetate (20mLx2) and the combined organic layer was dried
over anhydrous MgSO
4
. After filtration and evaporation of the solvent, the residue
was purified by column chromatography over silica gel to give the pure product. The
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corresponding product was identified by HNMR, CNMR, FTIR and GCMS.
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1
2)
Smith K., Lock S., El-Hiti G., Wada M. and Miyoshi N.
Org. Biomol. Chem. 2004, 2,935.
1
1
1
3)
4)
5)
Li, L.H. and Chan, T. H., Tetrahedron Lett.2000, 41, 5009.
Yamataka, H.; Nishikawa, K.; Hanafusa,T. Bull. Chem. Soc. Jpn.1994, 67, 242.
Gajewski, J. J.; Bocian, W.; Harris, N. J.; Olson, L. P.; Gajewski, J. P.
J. Am. Chem.Soc.1999, 121, 326.
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1
6)
7)
Chung, L. W.; Chan, T. H.; Wu, Y.D.Organometallics2005, 24, 1598.
(a) Chan, T. H.; Yang, Y. J. Am. Chem. Soc. 1999, 121, 3228;
(
b) Chan, T. H.; Yang, Y.; Li, C. J. J. Org. Chem. 1999, 64, 4452.
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8)
9)
Nesmeyanov, A., Tolstaya T., and Isaeva L., Chem. Abstr.1959, 53, 4178.
Prepared by the reaction of allylmagnesium bromide with bismuth (III) chloride in
ether
2
0)
Dam, J., Fristrup, P., Madsen, R., J. Org. Chem. 2008, 73, 3228.
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Bismuth chloride mediated allylation of carbonyl compounds in
aqueous media: A mechanistic investigation
B. D. Jadhav and S.K. Pardeshi*
Department of Chemistry, University of Pune, Ganeshkhind,
Pune-411007(INDIA)
*
Corresponding author. Tel.:+91 020 25601225 Extn. 514; Fax: +91 020 25691728.
E-mail: skpar@chem.unipune.ac.in (S.K.Pardeshi)
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