Highly efficient allylation of aldehydes and three-component synthesis of homoallylamines using bismuth triflate catalyst

Article abstract of DOI:10.1055/s-2002-34239

Bismuth triflate catalyzed allylation of a variety of aldehydes and aldimines using allyltributylstannane has been presented. The reaction proceeds rapidly and yields corresponding homoallylic alcohols and homoallylic amines in good yields. The bismuth tr

Full text of DOI:10.1055/s-2002-34239

1694
LETTER
Highly Efficient Allylation of Aldehydes and Three-Component Synthesis of
Homoallylamines Using Bismuth Triflate Catalyst
Highly Efficient
A
llylation of
yAldehydes apati M. Choudary,* Sridhar Chidara, Ch. V. Raja Sekhar
Indian Institute of Chemical Technology, Hyderabad – 500 007, India
Fax +91(40)7160921; E-mail: choudary@iict.ap.nic.in
Received 1 August 2002
Initially, we studied the allylation of p-chlorobenzalde-
hyde with allyltributylstannane using 2 mol% of bismuth
triflate and acetonitrile as a solvent at room temperature.14
The reaction is very sluggish and a conversion of 20% was
Abstract: Bismuth triflate catalyzed allylation of a variety of alde-
hydes and aldimines using allyltributylstannane has been presented.
The reaction proceeds rapidly and yields corresponding homoallylic
alcohols and homoallylic amines in good yields. The bismuth tri-
flate displays manifold activity over the La, Yb, and Sc triflates. The observed after 12 hours. However, when 1 equivalent of
catalyst is reused for allylation of aldehydes and aldimines without
significant loss of catalytic activity for four cycles.
benzoic acid as an additive was employed, p-chloroben-
zaldehyde reacted with allyltributylstannane rapidly and
Key words: allylation, aldehydes and aldimines, bismuth triflate,
Bronsted acids, turnover frequency
gave the corresponding homoallyl alcohol in good yields
(90%). Encouraged by this result, we have carried out the
allylation of a variety of aldehydes in order to understand
the scope and reactivity. The results are summarized in
Over the past two decades, the Lewis acid (LA) catalyzed Table 1. It is clear from Table 1 that the reaction was com-
allylation of aldehydes1 and aldimines2 has become an im- pleted in 5–30 minutes. Interestingly, when p-nitrobenz-
portant carbon-carbon bond forming reaction in organic aldehyde or 3,4,5-trimethoxy benzaldehyde was used, the
synthesis. This is mainly because this reaction adds a new reaction was completed in about 5 minutes.
functionality into the substrate that can be extended to fur-
It is very amazing to note that the allylation of all the al-
ther organic transformations. Furthermore, allylation of
dehydes catalyzed by bismuth triflate proceeded with very
aldimines provides a useful synthetic methodology for ho-
high turnover frequency (TOF), 5–22 times over lantha-
moallylic amines, which are useful building blocks for
num triflate13 under identical conditions as can be seen in
natural products.
Table 1. These results strongly suggest that bismuth tri-
There are several different metal-based LA catalysts flate is a more efficient LA catalyst than lanthanum tri-
available for this reaction.3 Lately, synthetic methodology flates for the allylation of aldehydes. The catalyst, which
involving lanthanide triflates in combination with rate ac- was precipitated at the end of the reaction, was filtered
celerating agents4 such as benzoic acid and sodium dode- and reused for allylation reaction without significant loss
cyl sulfate (SDS)5 as catalysts for allylation of aldehydes of activity for four cycles (Table 1, entry 1).
and aldimines has received considerable attention. High
The present catalytic system exhibited high chemoselec-
catalytic activity, low toxicity, moisture and air tolerance
tivity towards aldehydes in the presence of ketones when
and their recyclability make use of lanthanide triflates at-
the allylation was conducted in a binary substrate system,
tractive alternatives to LA’s such as InCl3 or AlCl3. How-
p-chlorobenzaldehyde and acetophenone; aldehyde was
ever, unfortunately, lanthanide triflates are rather
allylated to the extent of 90%, whereas 5–10% of ketone
expensive and thus, their use in large-scale synthetic
was allylated at the same time.
methodology is very limited. Thus, more cheaper and ef-
We have also evaluated the use of bismuth triflate–benzo-
ficient LA catalysts are desirable for allylation reactions.
ic acid catalytic system for the one-pot synthesis of ho-
In this direction, bismuth triflate is the center of focus to
moallylamines in acetonitrile as solvent.15 As was the case
with the allylation of p-chlorobenzaldehyde; the one-pot
reaction of p-chlorobenzaldehyde, o-chloroaniline and al-
lyltributylstannane also required 1 equivalent of the ben-
zoic acid as an additive. This reaction was completed in
45 minutes and the corresponding homoallylamine prod-
uct was isolated in 65% yield using flash chromatography
(10% ethyl acetate–hexane). A variety of aldehydes and
amines have been examined in an effort to understand the
generality of this reaction, and the results from this study
are shown in Table 2. It is clearly seen from Table 2 that
moderate to good yields (60–90%) were obtained for all
substrates, and the reactions were completed within 45
minutes. When p-nitrobenzaldehyde or p-nitroaniline was
organic chemists.6–10
In view of this, we have examined bismuth triflate as a LA
catalyst for the allylation of aldehydes and aldimines (as
an one-pot synthesis) in our laboratory. We are particular-
ly interested in bismuth triflate, because it is inexpensive11
and can be easily prepared in laboratory from commer-
cially available bismuth (III) oxide and triflic acid.12 The
results from our study are presented herein.
Synlett 2002, No. 10, Print: 01 10 2002.
Art Id.1437-2096,E;2002,0,10,1694,1696,ftx,en;D12402ST.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

LETTER
Highly Efficient Allylation of Aldehydes
1695
used as the substrate, the reaction proceeded much faster
than the other substrates and gave corresponding homoal-
lylic amines in quantitative yields. Furthermore, in all
these reactions, formation of homoallylic alcohol prod-
ucts was not detected even in small amounts. The allyla-
tion of aldimines was also effected with 2 mol% of
bismuth triflate and 1 equivalent of sodium dodecyl sul-
fate (SDS) using water as a solvent to provide excellent
yields of homoallylamines. The activity expressed in
terms of turnover frequency using bismuth triflate–SDS
system in water is 42–80 fold over the scandium triflate–
SDS in water under identical conditions and 1.5–4 fold
over the bismuth triflate–benzoic system described above.
Under similar conditions, there is no reaction with alde-
hydes and allyltributylstannane using bismuth triflate–
SDS in water, indicating that the aldimines are the inter-
mediates in the three component reaction. Both the cata-
lyst systems, bismuth triflate–SDS and bismuth triflate–
benzoic acid conducted in the respective solvents, precip-
itated at the end of the reaction are recovered and reused
(Table 3, entry 1; Table 2, entry 1) for four cycles.
Table 1 Scope of Improved Allylation of Aldehydes with Bismuth
Triflate
Entry
1
Aldehyde
Time
(min)
Yielda
(%)
TOFb (h–1)
270 (26.66)
10
10
90
85
2
15
80
160 (18.20)
3
4
30
5
90
95
90 (18.75)
570 (24)
5
6
20
5
85
95
127 (20)
570 (31)
In summary, the highly efficient allylation of aldehydes
catalyzed by bismuth triflate-benzoic acid catalytic sys-
tem and one pot synthesis of homoallylamines with allyl-
tributylstannane with bismuth triflate–benzoic acid in
acetonitrile or bismuth triflate–SDS in water in good to
excellent yields under milder reaction conditions is de-
scribed. We have not only improved the product yields but
also shortened the reaction times. We have also demon-
strated the recyclablility of the catalytic system for the
synthesis of homoallylic alcohols, and thus, bismuth tri-
flate mediated allylation reaction is a simple, economical,
high yielding, and time saving methodology for allylation
of aldehydes and aldimines.
7
8
20
20
80
65
120 (8.85)
97.5 (9.7)
a Yields based on NMR
b The values in parentheses refer to the Ln(OTf)3 catalyzed reaction
conducted under identical conditions.
c Yield of the product after 4th cycle.
Table 2 Scope of Improved One-Pot Synthesis of Homoallylic Amines with Bismuth Triflate
Entry
Aldehyde and Amine
R1 = p-Cl-(C6H4)-, R2 = o-Cl
R1 = Ph, R2 = o-Cl
Time (min)
Yielda (%)
TOFb (h–1)
43.3 (18)
1
2
3
4
5
6
45
60
35
20
20
10
65 (60)c
60
30 (12.5)
R1 = p-NO2-(C6H4)-, R2 = o-Cl
R1 = p-Cl-(C6H4)-, R2 = p-NO2-
R1 = Ph, R2 = p-NO2
70
60 (22.5)
70
106 (32.5)
98.5 (24.3)
281.3 (46.6)
65
R2 = p-NO2
90
a Yields based on NMR.
b The values in parentheses refer to the Ln(OTf)3 catalyzed reaction conducted under identical conditions.
c Yield of the product after 4th cycle.
Synlett 2002, No. 10, 1694–1696 ISSN 0936-5214 © Thieme Stuttgart · New York

1696
B. M. Choudary et al.
LETTER
Table 3 Scope of Improved One-Pot Synthesis of Homoallylic Amines with Bismuth Triflate
Entry
Aldehyde and Amine
Time (min)
Yielda (%)
TOFb (h–1)
1
2
3
4
5
6
R1 = p-Cl-(C6H4)-, R2 = o-Cl
R1 = Ph, R2 = o-Cl
15
20
10
15
15
5
80 (75)c
70
160 (0.20)b
105 (0.25)b
240
R1 = p-NO2-(C6H4)- R2 = o-Cl
R1 = p-Cl-(C6H4)-, R2 = p-NO2-
R1 = Ph-, R2 = p-NO2
80
75
150
70
140
R1 = p-NO2-(C6H4)-, R2 = p-NO2
85
510
a Yields based on NMR.
b The values in parentheses refer to the Sc(OTf)3 catalyzed reaction conducted under identical conditions.
c Yield of the product after 4th cycle.
(11) Orita, A.; Tanahashi, C.; Kakuda, A.; Otera, J. Angew.
Chem. Int. Ed. 2000, 39, 2877.
(12) Repichet, S.; Zwick, A.; Vendier, L.; Le Roux, C.; Dubac, J.
Tetrahedron Lett. 2002, 43, 993.
Acknowledgement
Ch. S and Ch. V. R thank the Council of Scientific and Industrial
Research, India, for their fellowships.
(13) (a) Aspinall, H. C.; Greeves, N.; Mclver, E. G. Tetrahedron
Lett. 1998, 39, 9283. (b) Aspinall, H. C.; Bissett, J. S.;
Greeves, N.; Levin, D. Tetrahedron Lett. 2002, 43, 319.
(14) Typical Experimental Procedure for the Allylation of
Aldehydes: To a stirred solution of p-chlorobenzaldehyde (1
mmol), benzoic acid (1 mmol) and allyltributylstannane (1.2
mmol) in acetonitrile (5 mL) at r.t. was added bismuth
triflate (2 mol%). The mixture was stirred at r.t. until
reaction was completed as indicated by TLC. The catalyst,
which was precipitated at the end of the reaction, was filtered
off. The filtrate was concentrated under vacuum to obtain a
crude product and was purified by column chromatography
(10% ethyl acetate–hexane) (164 mg, 90%).
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stirred at r.t. until reaction was completed as indicated by
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Synlett 2002, No. 10, 1694–1696 ISSN 0936-5214 © Thieme Stuttgart · New York