Lanthanum trichloride: A simple and efficient catalyst for allylation of aldehydes with allyltributylstannane

Article abstract of DOI:10.1080/00397910902840843

Aldehydes undergo smooth nucleophilic addition with allyltributyl-stannane in the presence of lanthanum trichloride to afford the corresponding homoallylic alcohols in excellent yields. All the reaction conditions were carried out in acetonitrile solvent at room temperature. In all the cases, the catalyst was used in a catalytic amount (10% mol). Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910902840843

1
Synthetic Communications , 39: 3905–3911, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910902840843
Lanthanum Trichloride: A Simple and Efficient
Catalyst for Allylation of Aldehydes
with Allyltributylstannane
G. S. Satyanarayana Reddy, B. Sammaiah, and L. N. Sharada
Department of Chemistry, College for Women, Koti, Osmania University,
Hyderabad, India
Abstract: Aldehydes undergo smooth nucleophilic addition with allyltributyl-
stannane in the presence of lanthanum trichloride to afford the corresponding
homoallylic alcohols in excellent yields. All the reaction conditions were carried
out in acetonitrile solvent at room temperature. In all the cases, the catalyst
was used in a catalytic amount (10% mol).
Keywords: Aldehydes, allytributylstannane, homoallylic alcohols, lanthanum
trichloride
The allylation of aldehydes with allyltributylstannane is a powerful
method for carbon–carbon bond formation. The homoallylic alcohols
are important building blocks for the construction of various biologically
[1]
active compounds. Hence, the synthesis of homoallylic alcohols is
important. Consequently, several methods have been developed for
allylation of aldehydes with allylmetal complexes to produce homoallylic
[
2,3]
alcohols.
One of the most straightforward synthetic procedures
involves the nucleophilic addition of allyltin reagents to aldehydes in the
presence of catalysts. However, many of these catalysts are expensive,
moisture sensitive, and difficult to handle and involve the use of
strongly acidic conditions, which limit their use in the synthesis of
Received December 3, 2008.
Address correspondence to L. N. Sharada, Department of Chemistry, College
for Women, Koti, Osmania University, Hyderabad 500 095, India. E-mail:
reddy_gssn@yahoo.co.in
3
905

3906
G. S. S. Reddy, B. Sammaiah, and L. N. Sharada
Scheme 1.
complex molecules containing acid-sensitive functionalities. Thus, there is
scope for further improvements to create milder reaction conditions and
better yields. Among Lewis acids, metals and transition-metal complexes
have been extensively utilized to catalyze or promote the allylation in past
[
4–6]
years.
the allylation of aldehydes, but they are rather expensive.
Water-tolerant Lewis acids have been developed as catalysts for
[
7,8]
Therefore,
there is interest in development of new catalysts for efficient allylation
of aldehydes under mild reaction conditions. The catalyst lanthanum
trichloride (LaCl ) is known for various organic transformations in the
3
[
9]
literature as a mild, inexpensive, and moisture-stable Lewis acid.
However, there are no reports on allylation of aldehydes with lanthanum
trichloride. In this article, we describe an efficient and high-yielding
method for allylation of aldehydes with allyltributylstannane in the
presence of lanthanum trichloride.
Accordingly, an equimolar amount of benzaldehyde 1 and allyltribu-
tylstannane 2 were treated in the presence of lanthanum trichloride (10%
mol) to obtain the corresponding product of 1-phenyl-3-buten-1-ol in
9
3% yield (entry a) as shown in Scheme 1. The reaction proceeds
smoothly at room temperature in acetonitrile solvent. Encouraged by
the result obtained with benzaldehyde, we turned our attention to various
aldehydes such as aliphatic, aromatic, a,b-unsaturated, heterocyclic, and
alicyclic aldehydes. The acid-sensitive aldehydes such as furfural (entry c)
and 2-phenylacetaldehyde (entry g) were efficiently converted into the
corresponding homoallylic alcohols. In the case of a,b-unsaturated
aldehyde (entry d), the allylation reaction takes place smoothly without
forming 1,4-addition by-product. In a similar manner, 4-methoxybenzal-
dehyde (entry b) and 3,4,5-trimethoxybenzaldehydes (entry k) were
reacted efficiently to give the corresponding homoallylic alcohols in
excellent yields, and no bis-allylated products were observed. The alipha-
tic system of n-octnal (entry f), n-butanal (entry i), and cyclohexanal
(entry l) were treated with allyltributylstannane in the presence of
lanthanum trichloride to afford the corresponding homoalllylic alcohols
in very good yields. The reactions were very clean, and no side products
were observed. In general, all the reactions were carried out at room

Synthesis of Homoallylic Alcohols
3907
temperature in acetonitrile solvent. In all the cases, the catalyst was used
in a catalytic amount (10% mol). The reactions were completed in 3.0 to
6
.0 h, and the obtained yields ranged from 80% to 95%.The aliphatic
aldehydes and electron-withdrawing group containing an aromatic sys-
tem, such as 4-nitrobenzaldehyde (entry e), required a little more time
for completion of the reaction.
The proposed mechanism shows that the catalyst lanthanum trichlor-
ide activates the carbonyl carbon rapidly, followed by the weakening of
the carbon–stannane bond. This action makes the allyltributylstannane
more nucleophilic and at the same time more susceptible to decomposition.
In conclusion, we have described here a simple, convenient, and
efficient method for the preparation of homoallylic alcohols with various
aldehydes and allyltributylstannane in the presence of lanthanum
trichloride (10% mol). All the reactions were carried out at room
temperature in acetonitrile. The salient features of this methodology
are good conversions, mild reaction conditions, and simplicity in
operation to isolate the products.
GENERAL EXPERIMENTAL PROCEDURE
The catalyst lanthanum trichloride (0.2 mmol) was added to a stirred
mixture of aldehyde (2 mmol) and allyltributylstannane (2 mmol) in acet-
onitrile (5 ml) at room temperature. The resulting reaction mixture was
stirred for a specified period (Table 1). After completion of the reaction,
as indicated by thin-layer chromatography (TLC), the solvent from the
reaction mixture was removed under reduced pressure. Ethylacetate
(
10 ml) and water (10 ml) were added to the obtained residue, stirred well
for some time, and extracted with ethylacetate. The organic layer was
washed with water and brine and dried over Na SO . The ethylacetate
2
4
was removed under reduced pressure, and the obtained crude homoallylic
alcohol product was purified by column chromatography.
SPECTRAL DATA FOR SELECTED COMPOUNDS
1
-Phenylbut-3-en-1-ol (3a)
Colorless oil. IR (neat): n 3416, 3081, 2965, 2853, 1647, 1508, 1459, 1263,
ꢀ
1 1
1
104, 971, 759, 732 cm . H NMR (CDCl ): d 2.18 (brs, 1 H), 2.37–2.43
3
(
m, 2 H), 4.63 (t, 1 H, J ¼ 6.0 Hz), 5.05–5.20 (m, 2 H), 5.35–5.70 (m, 1 H),
þ
7.27–7.40 (m, 5 H). EIMS: m=z (%). 148 (m 12), 130 (10), 115 (15), 107
100), 91 (20), 79 (54), 63 (25), 51 (33).
(

3908
G. S. S. Reddy, B. Sammaiah, and L. N. Sharada
Table 1. Lanthanum trichloride–catalyzed allylation of aldehydes with allyltribu-
tylstannane
Reaction
time (h)
Yield
b
(%)
a
No.
a
Aldehyde
Homoallylicalcohol
4.0
3.5
93
93
b
c
3.0
4.0
94
83
d
e
6.0
86
f
5.5
6.0
85
87
g
h
i
4.5
5.0
90
80
j
3.5
3.0
92
95
k
(
Continued )

Synthesis of Homoallylic Alcohols
3909
Table 1. Continued
Reaction
time (h)
Yield
b
(%)
a
No.
l
Aldehyde
Homoallylicalcohol
5.5
4.5
86
90
m
a
All the products were characterized by spectroscopy data.
Yields were isolated and not optimized.
b
1
-(2-Furyl)but-3-en-1-ol (3c)
Colorless oil. IR (neat): n 3391, 3076, 2951, 2843, 1645, 1568, 1504, 1435,
ꢀ1 1
1
347, 1261, 1138, 1055, 948, 867, 739 cm . H NMR (CDCl ): d 2.10
3
(
2
brs, 1 H), 2.50–2.60 (m, 2 H), 4.70 (t, 1 H, J ¼ 6.0 Hz), 5.10–5.20 (m,
H), 5.70–5.80 (m, 1 H), 6.21 (dd, 1 H, J ¼ 0.8 & 3.5 Hz), 6.29 (dd, 1 H,
J ¼ 1.5 & 3.5 Hz), 7.35 (dd, 1 H, J ¼ 2.5 & 0.8 Hz). EIMS: m=z (%): 138
þ
(m , 18), 119 (62), 96 (38), 91 (100), 89 (26), 77 (15), 63 (18), 49 (12), 29 (31).
1
-Phenylhexa-1,5-dien-3-ol (3d)
1
Colorless oil. H NMR (CDCl ): d 1.80 (brs, 1 H), 2.30–2.40 (m, 2 H),
3
4
.30 (t, 1 H, J ¼ 6.5 Hz), 5.10–5.20 (m, 2 H), 5.70–5.80 (m, 1 H), 6.20
(
dd, 1 H, J ¼ 16.0 & 6.0 Hz), 6.55 (d, 1 H, J ¼ 16.0 Hz), 7.15–7.35 (m, 5 H).
Scheme 2. Proposed mechanism.

3910
G. S. S. Reddy, B. Sammaiah, and L. N. Sharada
Phenylhex-1-en-4-ol (3g)
1
Colorless oil. H NMR (CDCl ): d 1.60–1.70 (m, 2 H), 1.80 (brs, 1 H),
3
2
(
.05–2.20 (m, 2 H), 2.65–2.75 (m, 2 H), 3.50–3.60 (m, 1 H), 4.95–5.05
m, 2 H), 5.65–5.75 (m, 1 H), 7.05–7.20 (m, 5 H).
1
-(4-Methylphenyl)but-3-en-1-ol (3j)
1
Colorless oil. H NMR (CDCl ): d 1.96 (brs, 1 H), 2.30 (s, 3 H), 2.43–2.50
3
(
7
m, 2 H), 4.65 (t, 1 H, J ¼ 6.0 Hz), 5.05–5.15 (m, 2 H), 5.70–5.80 (m, 1 H),
.06 (d, 2 H, J ¼ 7.5 Hz), 7.19 (d, 2 H, J ¼ 7.5 Hz).
1
-Cyclohexylbut-3-en-1-ol (3l)
1
Colorless oil. H NMR (CDCl ): d 0.90–1.20 (m, 6 H), 1.60–1.70 (m, 5 H),
3
1
5
.80 (brs, 1 H), 2.10–2.30 (m, 2 H), 3.30–3.40 (m, 1 H), 5.05–5.15 (m, 2 H),
.75–5.85 (m, 1 H).
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