Active bismuth mediated allylation of carbonyls/N-tosyl aldimines and propargylation of aldehydes in water

Article abstract of DOI:10.1007/s12039-019-1625-6

Abstract: Active bismuth is synthesized by the chemical reduction of bismuth trichloride using freshly prepared sodium stannite solution as the reducing agent at room temperature. The as-synthesized active bismuth is applied as a reagent for the synthesis of homoallyl alcohol/homopropargyl alcohol from allyl bromide/propargyl bromide and carbonyl compounds in water at 50°C. The homoallyl amines are also synthesized from N-tosyl aldimines and allyl bromide using active bismuth reagent in good yields. No assistance of organic co-solvent, co-reagent, phase transfer catalyst or inert atmosphere is required for this reaction. The waste bismuth material obtained after the completion of the organic reaction can be reduced to active bismuth by sodium stannite solution and successfully reused for mediating the allylation of aldehydes. Graphical Abstract:: Synopsis Active bismuth mediated allylation/crotylation of aldehydes is developed in water to get homoallyl alcohols. The method is also applied for the allylation of N-tosyl aldimines and propargylation of aldehydes in water to achieve the homoallyl amines and homopropargyl alcohols, respectively. The reactions do not require the assistance of organic co-solvent, co-reagent, phase transfer catalyst or inert atmosphere.[Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-019-1625-6

J. Chem. Sci.
(2019) 131:51
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-019-1625-6
REGULAR ARTICLE
Active bismuth mediated allylation of carbonyls/N-tosyl aldimines
and propargylation of aldehydes in water
MICKY LANSTER SAWKMIEa, DIPANKAR PAULa, SNEHADRINARAYAN KHATUAb and
PARESH NATH CHATTERJEEa,∗
aDepartment of Chemistry, National Institute of Technology Meghalaya, Bijni Complex, Laitumkhrah, Shillong,
Meghalaya 793 003, India
bCentre for Advanced Studies, Department of Chemistry, North Eastern Hill University, Shillong, Meghalaya
793 022, India
E-mail: paresh.chatterjee@nitm.ac.in
MS received 18 July 2018; revised 20 March 2019; accepted 25 March 2019
Abstract. Activebismuthissynthesizedbythechemicalreductionofbismuthtrichlorideusingfreshlyprepared
sodium stannite solution as the reducing agent at room temperature. The as-synthesized active bismuth is applied
as a reagent for the synthesis of homoallyl alcohol/homopropargyl alcohol from allyl bromide/propargyl bromide
and carbonyl compounds in water at 50 ◦C. The homoallyl amines are also synthesized from N-tosyl aldimines
and allyl bromide using active bismuth reagent in good yields. No assistance of organic co-solvent, co-reagent,
phase transfer catalyst or inert atmosphere is required for this reaction. The waste bismuth material obtained
after the completion of the organic reaction can be reduced to active bismuth by sodium stannite solution and
successfully reused for mediating the allylation of aldehydes.
Keywords. Active bismuth; allylation; crotylation; propargylation; carbonyl; N-tosyl aldimine; homoallyl
alcohol; homoallyl amine; homopropargyl alcohol.
1. Introduction
powder has been reported for the reductive allylation
of aldehydes under varying reaction conditions.5 Wada
et al., reported several bimetallic reducing systems
consisting of a metal and BiCl3 for the allylation of
carbonyls. They include Al-BiCl3, Mg-BiCl3, Fe-BiCl3
and Zn-BiCl3 systems.5b, 6 Bismuth nanoparticles7 as
well as ball milling technique8 have also been used to
carry out the bismuth mediated allylation of carbonyls.
Shi-Hui et al., demonstrated Barbier allylation of alde-
hydes promoted by in situ generated active Bi(0) from
BiCl3 and sodium borohydride.9 Herein, we report a
versatile method for Barbier-type reaction of various
carbonyls and N-tosyl aldimines in water mediated by
freshly prepared active Bi(0) (Scheme 1). The active
Bi(0) is synthesized via a simple reduction of BiCl3
by freshly prepared sodium stannite (Na2SnO2) solu-
tion at room temperature.10 Moreover, for the first time,
we demonstrate active Bi(0) mediated allylation of N-
tosyl aldimines as well as propargylation of aldehydes
in water to achieve the corresponding homoallyl amines
Metal-mediated Barbier allylation reaction of carbonyls
is a very important C-C bond forming reaction in
organic synthesis,1 driven in part by the versatility
of the homoallyl alcohols as synthetic intermediates.2
Numerous metals, such as antimony, cerium, magne-
sium, manganese, indium, tin and zinc are known to
participate in this fundamental C-C bond forming reac-
tion.3 In view of elemental resources, it is desired to
explore various elements for catalyzing or mediating
organictransformations. Amonggroup15elements, bis-
muth is inexpensive, safe and environmentally-benign
compared to arsenic and antimony with enhanced metal-
lic character. It is also used in cosmetics and anti-viral
creams and as a component of oral gastrointestinal
formulations.4 The commercially available bismuth
*
For correspondence
MICKY LANSTER SAWKMIE and DIPANKAR PAUL
have contributed equally to this work.
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-019-1625-6) contains
supplementary material, which is available to authorized users.
0123456789().: V,-vol

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Scheme 1. Active bismuth mediated Barbier-type reaction of carbonyls and N-tosyl aldimines.
and homopropargyl alcohols, respectively. The impor- data using PW1710 diffractometer (Philips, Holland) and
1
analyzed with JCPDS software. H and 13C NMR spectra
tance of homoallyl amines and homopropargyl alcohols
were measured on a Bruker NMR spectrometer. Chemical
as versatile building blocks for the synthesis of valuable
organic moieties is well established.11 We find success
shifts are reported in ppm from tetramethylsilane (TMS),
with the solvent resonance as the internal standard (chloro-
in active Bi(0) mediated crotylation of aldehydes with
form δ 7.26 ppm). Data are reported as follows: chemical
100% γ -regioselectivity. The synthetic protocol does
shifts, multiplicity (s=singlet, d=doublet, t=triplet, q=quartet,
not require an organic co-solvent, co-reagent, phase
br=broad, dd=double doublet, m=multiplet), coupling con-
transfer catalyst or inert atmosphere. It is noteworthy
stant (in Hz), integration.13C NMR spectra were recorded
to point out that the resulting white bismuth material
with proton decoupling. Chemical shifts are reported in ppm
after the completion of the reaction can be reduced to
Bi(0) by Na2SnO2 solution and can be used to mediate
the allylation of aldehydes, thereby making the method
from tetramethylsilane with the solvent resonance as the inter-
nal standard (chloroform δ 77.0 ppm). Elemental analyses
were carried out using a CHNS/O Analyzer Perkin Elmer
economical. Versatility, practicality and the economic 2400 Series II instrument.
use of this method of Barbier reaction provides excel-
lent value for laboratory applications.
2.2 Preparation of sodium stannite (Na2SnO2)
solution12
In a 100 mL beaker, SnCl2.2H2O (677 mg, 3 mmol) and
distilled water (8 mL) were taken and mixed well using a
magnetic bar. Then 8 mL of 5 (M) NaOH solution was added
slowly with continuous stirring until the milky white suspen-
sion turned into a colorless Na2SnO2 solution.
2. Experimental
2.1 General remarks
All reagents and solvents are of AR grade and purchased
from Sigma-Aldrich, Alfa Aeser, Spectrochem and Sisco
Research Laboratories Pvt. Ltd., and used without further
purification unless otherwise stated. Propargyl bromide (80%
2.3 Preparation of active Bi(0)10
solution in toluene) from Alfa Aeser was used as a reagent In a 50 mL round bottom flask, BiCl3(630 mg, 2.0 mmol)
for propargylation. All the Barbier reactions were done in was taken and 2 mL of distilled water was added to it which
double-distilled water under air atmosphere. Reactions were forms a milky white suspension of BiOCl. Then 16 mL of
monitored by thin-layer chromatography (TLC) on silica gel the freshly prepared Na2SnO2solution was added drop-wise
60 F254. Purification of organic products was performed by to the milky white suspension of BiOCl with constant stir-
column chromatography using 100–200 mesh silic◦a gel as ring at room temperature. Instantaneously, a black precipitate
the stationary phase and petroleum ether 60–80 C/ethyl of Bi(0) metal was formed and the stirring was continued
acetate as the eluent. The phase purity of synthesized Bi(0) for 5 min. The resultant mixture was allowed to stand and
material was characterized by recording X-ray diffraction the supernatant is decanted followed by washing of the black

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51
precipitate with distilled water until the washing was pH neu- neutral. After that, 5 mL of distilled water was added fol-
tral. The as-synthesized Bi(0) was used to mediate the Barbier lowed by the addition of 378 µL (4.0 mmol of 80% solution)
reaction.
of propargyl bromide 2e. The reaction mixture was stirred
for 10 min at room temperature and 4-chlorobenzaldehyde
1a (140 mg, 1 mmol) was added to it. The reaction mixture
was placed in a pre-heated oil bath at 50 ◦C. The progress of
the reaction was monitored by TLC. After the reaction was
completed, the reaction mixture was filtered through a celite
bed followed by washing of the residue by ethyl acetate (2
× 10 mL). Finally, the filtrate was further extracted by ethyl
acetate (2 × 10 mL) and washed with water (2 × 10 mL), brine
(2 × 10 mL) and dried over anhydrous Na2SO4. The com-
bined organic solvent was removed under reduced pressure,
and the crude product was purified by column chromatogra-
phy over silica gel (100–200 mesh, eluent: petroleum ether
2.4 Typical procedure for the active Bi(0) mediated
synthesis of homoallyl alcohol
In a 50 mL round bottom flask, 418 mg (2.0 mmol) of active
Bi(0) was synthesized according to the above-mentioned pro-
cedure and washed several times to make it pH neutral. After
that, 5 mL of distilled water was added, followed by the addi-
tion of 340 µL (4.0 mmol) of allyl bromide 2a. The reaction
mixture was stirred for 10 min at room temperature and 4-
chlorobenzaldehyde 1a (140 mg, 1 mmol) was added to it.
The reaction mixture was placed in a pre-heated oil bath at
50 ◦C. The progress of the reaction was monitored by TLC.
After the reaction was completed, the reaction mixture was fil-
tered through a celite bed, followed by washing of the residue
by ethyl acetate (2 × 10 mL). Finally, the filtrate was fur-
ther extracted by ethyl acetate (2 × 10 mL) and washed with
water (2 × 10 mL), brine (2 × 10 mL) and dried over anhy-
drous Na2SO4. The combined organic solvent was removed
under reduced pressure and the crude product purified by col-
umn chromatography over silica gel (100–200 mesh, eluent:
petroleum ether 60–80 ◦C/ethyl acetate) to afford the corre-
sponding homoallyl alcohol 3a in 81% yield.
◦
60–80 C/ethyl acetate) to afford the corresponding homo-
propargyl alcohol 4a in 80% yield.
All products gave satisfactory spectral data and were com-
pared with authentic samples wherever possible.
Compounds3a,12 3b,13 3c,14 3d-e,12 3f,15 3g,12 3h,15 3i,14
3j,16 3k,15 3l,13 3m,17 3n,5 f 3o,17 3p,5 f 3q,16 3r,15 3s,12
3t,18 3u,18 3w-y,19 4a-b,20 4c,21 are reported in literature.
The characterization data for the new compound 3v is given
below.
2.7 Analytical data of the new compound
2.5 Typical procedure for the active Bi(0) mediated
synthesis of homoallyl amine
4-Methyl-N-(1-(naphthalen-1-yl)but-3-enyl)benzenesulfona
mide (3v): H NMR (400 MHz, CDCl3): δ (ppm) = 7.91–
1
7.89 (m, 1H), 7.81–7.79 (m, 1H), 7.76 (d, J = 7.6 Hz, 1H),
7.48–7.44 (m, 4H), 7.31–7.25 (m, 2H), 6.98 (d, J = 8.0 Hz,
2H), 5.60–5.50 (m, 1H), 5.23–5.20 (m, 1H), 5.12–5.07 (m,
3H), 2.65–2.63 (m, 2H), 2.28 (s, 3H). 13C NMR (100 MHz,
CDCl3): δ (ppm) = 142.9, 137.1, 135.8, 133.7, 133.1, 129.8,
129.1, 128.9, 127.9, 127.1, 126.2, 125.5, 125.0, 124.2, 122.4,
119.4, 53.2, 41.2, 22.7. Anal. Cacld (%) for C21H21NO2S: C
71.77; H 6.02; Found: C 71.81; H 5.98.
In a 50 mL round bottom flask, 418 mg (2.0 mmol) of active
Bi(0), synthesized according to the above-mentioned proce-
dure, was taken and washed several times to make it pH
neutral. After that, 5 mL of distilled water was added, fol-
lowed by the addition of 340 µL (4.0 mmol) of allyl bromide
2a. The reaction mixture was stirred for 10 min at room tem-
perature and N-benzylidene-4-methylbenzenesulfonamide1t
(259 mg, 1 mmol) was added to it. The reaction mixture was
placed in a pre-heated oil bath at 50 ◦C. The progress of the
reaction was monitored by TLC. After the reaction was com-
pleted, the reaction mixture was filtered through a celite bed,
followed by washing of the residue by ethyl acetate (2 × 10
mL). Finally, the filtrate was further extracted by ethyl acetate
(2 × 10 mL) and washed with water (2 × 10 mL), brine (2
× 10 mL) and dried over anhydrous Na2SO4. The combined
organic solvent was removed under reduced pressure and the
crude product purified by column chromatography over silica
3. Results and Discussion
First, we have synthesized active Bi(0) (here after rep-
resented as Bi*) via a redox-driven path (Scheme 2).10
Freshly prepared Na2SnO2 solution can easily reduce
BiCl3 in water at room temperature (Standard reduction
potential of Bi3+/Bi(0) = 0.308 V and standard reduction
◦
gel (100–200 mesh, eluent: petroleum ether 60–80 C/ethyl
acetate) to afford the corresponding homoallyl amine 3t in potential of SnO23−/SnO22− = −0.93 V). The reduction
66% yield.
takes place spontaneously to give a black precipitate of
Bi* (Figure 1d), which is confirmed by the powder XRD
analysis. The XRD pattern of the as-synthesized Bi*
was found to be in excellent agreement with the diffrac-
tion pattern of crystalline Bi(0) (Figure 2). The observed
diffraction peaks at 2θ = 22.73◦, 27.31◦, 38.19◦, 39.80◦,
44.80◦, 46.13◦, 48.96◦, 56.21◦, 59.43◦, 61.36◦, 62.34◦,
2.6 Typical procedure for the active Bi(0) mediated
synthesis of homopropargyl alcohol
In a 50 mL round bottom flask, 418 mg (2.0 mmol) of active
Bi(0), synthesized according to the above-mentioned proce-
dure, was taken and washed several times to make it pH 64.79◦, 67.69◦ corresponds to the (033), (012), (104),

51 Page 4 of 12
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mixture of the specified solvent with water (Table 1,
entries 6–9) at room temperature. Although the yield
of the homoallyl alcohol 3a improved in the aqueous
mixture of the solvents, the result was still below our
expectation. This prompted us to assess the effect of
temperature in this C-C bond forming reaction in view
of achieving a better yield of 3a. In this regard, we tested
the two most promising water-organic solvent combi-
Scheme 2. Synthesis of active Bi(0).
◦
nations viz. MeCN-H2O and THF-H2O at 50 C and
we were pleased to observe that the reaction performed
significantly better (Table 1, entries 10–11). However,
it is advantageous to avoid the use of organic solvents
such as MeCN and THF in a synthetic organic reac-
tion for economic and environmental benefits. This led
us to carry◦out the reaction in water as the only sol-
vent at 50 C and the reaction proceeded remarkably
well to yield 81% of the corresponding homoallyl alco-
hol 3a (Table 1, entry 12) in 3◦0 min. Further increase
in reaction temperature to 70 C did not improve the
yield of 3a (Table 1, entry 13). We found that the reac-
tion mixture was strongly acidic after the completion
of the reaction which may increase the electrophilicity
of the reacting aldehyde.6c,9Recent literature of Barbier
allylation reaction mediated by in situ generated Bi(0)
shows that the molar ratio of the allyl bromide 2a to
Bi(0) plays a crucial role.6c Prompted by this infor-
mation, we varied the amount of aldehyde 1a, allyl
bromide 2a and our in-house synthesized Bi* in the
allylation reaction as illustrated in Table 1 (entries 14–
15). We noted that the highest yield of 3a is obtained
when the molar ratio of 1a:2a:Bi* is taken as 1:4:2
(Table 1, entry 12). The yield of the homoallyl alco-
hol 3a was found to be only 21% after 2 h of reaction
when commercially available bismuth powder was used
instead of Bi* (Table 1, entry 16). The low reactivity
of the commercially available bismuth powder can be
Figure 1. Photographs of (a) BiCl3 (b) BiOCl (c) freshly
prepared Na2SnO2 solution and (d) active Bi(0).
Figure 2. XRD pattern of the synthesized Bi(0).
(110), (015), (113), (202), (024), (107), (205), (116), attributed to the aerial oxidation of the metallic surface
(112) and (018) planes of Bi(0) (JCPDS 05-0519).
After confirming the identity of the black Bi(0),
over time.22
After optimizing the reaction conditions of Barbier
we applied the metallic bismuth for Barbier allya- allylation mediated by our in-house synthesized Bi*,
tion of carbonyls and N-tosyl aldimines and propar- we interested ourselves in exploring the substrate scope
gylation of aldehydes. In this regard, we chose 4- of this reaction and to study the effect of several sub-
chlorobenzaldehyde 1a as the model electrophile and stituents present at varying positions of the electrophile.
allyl bromide 2a as the model allylating reagent to opti- We noticed that substituents such as -Cl, -Br, -Me,
mize the reaction conditions. To begin our investigation, did not affect the reaction significantly, irrespective of
we tested several aprotic and protic solvents in addition their position in the aromatic ring of the aldehyde 1
to their aqueous mixture (Table 1, entries 1–12). We (Table 2, entries 1–5 and 8). However, the presence
found that DMF, MeCN and THF afforded moderate of -NO2 group as a substituent causes a noticeable
yields of the homoallyl alcohol 3a at room temperature decline in the yield of the corresponding homoallyl
(Table 1, entries 1–3), whereas use of water as the only alcohol 3f (Table 2, entry 6). The presence of electron-
solvent afforded a better result (Table 1, entries 5). On donating groups on the aromatic ring such as –OMe
realizing the positive effect of water on the progress of and -OH was found to decrease the yield of the corre-
the reaction, we carried out the Barbier reaction in 1:1 sponding homoallyl alcohol marginally (Table 2, entries

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51
Table 1. Optimization of reaction conditions for Barbier allylation of aldehyde 1a.a
Entry
Solvent
Temperature (◦C)
Time (h)
Yield 3a (%)
1
2
3
4
5
6
7
8
DMF
MeCN
THF
EtOH
H2O
RT
RT
RT
RT
RT
RT
RT
RT
RT
50
50
50
70
50
10
10
10
24
6
10
10
10
24
10
10
0.5
0.5
0.5
0.5
2
50
55
57
29
68
61
64
66
45
70
76
81
80
42
69
21
DMF-H2O (1:1)
MeCN-H2O (1:1)
THF-H2O (1:1)
EtOH-H2O (1:1)
MeCN-H2O (1:1)
THF-H2O (1:1)
H2O
9
10
11
12
13
14c
15d
16e
H2O
H2O
H2O
H2O
50
50
a
Reaction conditions: 1a (1 mmol), 2a (4 mmol), Bi* (2 mmol), Solvent (5 mL)
bIsolated yields
cMolar ratio –1a (1 mmol): 2a (1 mmol): Bi* (1 mmol)
dMolar ratio –1a (1 mmol): 2a (2 mmol): Bi* (1 mmol)
eCommercially available bismuth powder was used instead of Bi*.
9–11). The reaction also performs well in the case of could be reduced again to Bi* by freshly prepared
1-naphthaldehyde 1l and terephthalaldehyde 1m, giv- Na2SnO2 solution and the active metal, regenerated in
ing rise to good yields (Table 2, entries 12–13). Next, we this way, could also efficiently mediate the allylation of
have extended the substrate scope by including the ally- aldehydes in very good yield (Table 2, entry 22). We
lation of aliphatic aldehydes 1n-p, which react equally also applied our current method toward the large scale
well to give the desired homoallyl alcohols 3n-p in synthesis of homoallyl alcohol 3a using 10 mmol of 4-
very good yields (Table 2, entries 14–16). Cinnamalde- chlorobenzaldehyde 1a, 40 mmol of allyl bromide 2a
hyde 1q as a representative α,β-unsaturated aldehyde and 20 mmol of Bi* in water at 50 ◦C to obtain 78% iso-
reacts under the optimized reaction conditions to give lated yield (Table 2, entry 23). As the method described
the 1,2-addition product 3q exclusively (Table 2, entry here does not involve any suitable co-reagent capable
17). Our method worked well for heterocyclic aldehyde of inducing enantiomeric purity in the products, hence
e.g., 2-thiophenecarboxaldehyde 1r producing 72% of the homoallyl alcohols are obtained as a racemic mix-
the desired homoallyl alcohol 3r in presence of NH4Cl ture.
as an additive (Table 2, entry 18). Acetophenone 1s, a
Allylation of N-tosyl aldimines in water is consid-
weaker electrophile, is also demonstrated to give the ered a challenging prospect due to their proneness to
desired allylation product 3s although in lower yield hydrolyze in the reaction medium. Although there are
after prolonged reaction time (Table 2, entry 19). When reports of allylation of N-tosyl aldimines in water,23
allyl chloride 2b and allyl alcohol 2c were employed bismuth mediated protocols have not been developed so
as allylating reagents instead of allyl bromide 2a in far. Our Bi* mediated method for the allylation of alde-
our reaction conditions, the expected product 3a did hydes can also be applied fruitfully for the allylation of
not form at all (Table 2, entries 20–21) and the unre- N-tosyl aldimines. In our optimized reaction conditions,
acted aldehyde 2a was recovered almost quantitatively N-tosyl aldimines 1t-v reacted smoothly to produce the
after 24 h. It is noteworthy to mention that the resulting corresponding homoallyl amines 3t-v in good yields in
white precipitate after the completion of the reaction 1 h (Scheme 3).24

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Table 2. Substrate scope of Bi* mediated Barbier allylation of carbonyls.a
Entry
1.
Substrate 1
Allylating
Product 3
Time Yield (%)b
(h)
agent 2
0.5
1
81
79
78
70
2a
1a
3a
2.
3.
4.
2a
2a
2a
1b
3b
1
1c
3c
1
1d
3d
5.
6.
7.
8.
9.
1
4
1
1
1
80
60
81
78
70
2a
2a
2a
2a
2a
1e
3e
1f
3f
1g
3g
1h
3h
1i
1j
3i
3j
10.
11.
1
1
68
72
2a
2a
1k
3k

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51
Table 2. (contd.)
12.
1
74
2a
1l
3l
13.
14.
4
1
62
78
2a
1m
3m
2a
1n
1o
3n
15.
16.
1
1
79
76
2a
2a
3o
3p
1p
17.
2
62
2a
1q
1r
3q
18.c
19.
1
6
72
50
2a
2a
3r
3s
1s
1a
1a
1a
1a
20.
21.
No product
No product
24
24
1
-
2b
2c
-
22.d
23.e
80
78
2a
2a
3a
3a
2
aReaction conditions: 1 (1 mmol), 2 (4 mmol), Bi* (2 mmol), H2O (5 mL), Temp. 50 ◦C.
bIsolated yields. c5 mL saturated NH4Cl solution was used as a solvent instead of H2O.
dBi* reproduced from the resulting white precipitate of the first time reaction (entry 1).
eReaction conditions: 1 (10 mmol), 2 (40 mmol), Bi* (20 mmol), H2O (50 mL), Temp. 50 ◦C.

51 Page 8 of 12
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Scheme 3. Allylation of N-tosyl aldimines in water.
Table 3. Active Bi* mediated crotylation of aldehydes in water.
Entry
1.
Substrate 1
Product 3
Yield % (syn:anti) b
84 (78:22)
3w
1a
2.
3.
72 (76:24)
68 (73:27)
3x
1g
1h
3y
a
b
Reaction conditions: 1 (1 mmol), 2d (4 mmol), Bi* (2 mmol), H2O (5 mL), Temp. 50 ◦C, 1 h.
Isolated yields. The ratio of diastereoselectivity was determined by 1H NMR spectra.
Scheme 4. Propargylation of aldehydes in water.
To extend the scope of the developed method, we have previously reported methods5b−c with syn-isomer being
carried out crotylation of aldehydes using the in-house the major product (Table 3).
synthesized active Bi* and crotyl bromide 2d. The reac-
In our attempt to ascertain the versatility of the devel-
tion proceeds smoothly under the optimized reaction opedprotocol, propargylbromide2ehasalsobeentested
conditions to generate very good yields of the corre- in the optimized reaction conditions as a viable reagent
sponding homoallyl alcohols 3w-y in 1 h with 100% for Barbier type reaction. We find that the aldehydes 1a,
regioselectivity. Thediastereoselectivity(determinedby 1g–h generate the desired homopropargyl alcohols 4a,
1H NMR) observed in our method are comparable with 4b and 4c in good yields in 1 h (Scheme 4). As per our

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51

51 Page 10 of 12
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described herein offers a novel alternative forthe synthe-
sis of homopropargyl alcohol-mediated by Bi* in water.
In order to establish the advantages of our present
method in comparison with the similar Bi(0) medi-
ated allylation reactions in the literature, we summarize
our results along with the existing reports in Table 4.
It is clear from the comparison that our protocol not
only develops the desired homoallyl alcohols in a green
solvent without any additive and in mild reaction con-
ditions, but also covers several carbonyl substrates for
allylation/crotylation reaction. In addition, allylation of
N-tosyl aldimines and propargylation of aromatic alde-
hydes can also be achieved by using our protocol. Broad
substrate scope and simple reaction procedure mark it
as an attractive synthetic protocol in organic synthesis.
4. Conclusions
In conclusion, we have presented a versatile, practical
and economical method for Barbier reaction mediated
by active Bi(0) in water. No assistance of organic co-
solvent, co-reagent, phase transfer catalyst, or inert
atmosphere is necessary for this reaction. The method
can be applied for the allylation of aromatic, aliphatic
as well as α,β-unsaturated aldehydes in addition to N-
tosyl aldimines. The method also works efficiently for
the propargylation of aromatic aldehydes producing a
very good yield of the corresponding homopropargyl
alcohols. The resulting white bismuth material after the
completion of the organic reaction can be reduced again
to Bi(0) and can be reused for the subsequent batch of
Barbier allylation of aldehydes. The active Bi(0) medi-
ated versatile C-C bond forming reaction presented in
this paper is a meaningful addition to the existing meth-
ods in the literature.
Supplementary Information (SI)
1H and 13C NMR data of the known compounds and H
1
and 13C NMR spectra of the new compound are included in
the supplementary information. Supplementary information
is available at www.ias.ac.in/chemsci.
Acknowledgements
Scientific and Engineering Research Board (SERB) is grate-
fully acknowledged for financial support to P.N.C (sanction
order no. SB/FT/CS-115/2014; dated 24/08/2015). We thank
NIT Meghalaya (for financial support to D.P.). P.N.C thanks
Dr. S. Pan, IIT Guwahati for useful discussion and help. IIT
Kharagpur, IIT Guwahati and SAIF, NEHU are also acknowl-
edged for analytical facilities.

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