An efficient and mild bismuth triflate-catalysed three-component Mannich-type reaction

Article abstract of DOI:10.1039/b710794c

In the presence of a catalytic amount of Bi(OTf)₃·4H ₂O, aldehydes together with amines react with silyl enolates to afford the corresponding Mannich-type adducts smoothly. A wide variety of silyl enolates derived from ketones, as well as esters and thioesters, react rapidly to afford the β-amino ketones or the β-amino esters in high yields (up to 94%). The Royal Society of Chemistry.

Full text of DOI:10.1039/b710794c

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Volume 5 | Number 19 | 7 October 2007 | Pages 3057–3220
ISSN 1477-0520
ARTICLE
T. Ollevier and E. Nadeau
ARTICLE
S. M. Hecht et al.
An efficient and mild bismuth triflate- Positional assignment of differentially
catalysed three-component Mannich- substituted bisaminoacylated
type reaction
pdCpAs

PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
An efficient and mild bismuth triflate-catalysed three-component
Mannich-type reaction
Thierry Ollevier* and Etienne Nadeau
Received 16th July 2007, Accepted 10th August 2007
First published as an Advance Article on the web 30th August 2007
DOI: 10.1039/b710794c
In the presence of a catalytic amount of Bi(OTf)3·4H2O, aldehydes together with amines react with silyl
enolates to afford the corresponding Mannich-type adducts smoothly. A wide variety of silyl enolates
derived from ketones, as well as esters and thioesters, react rapidly to afford the b-amino ketones or the
b-amino esters in high yields (up to 94%).
compounds. We wish to disclose our results in this area, namely,
Introduction
the development of an efficient bismuth-catalysed Mannich-type
three-component reaction that combines an aldehyde, an amine,
and a silyl enolate to give compounds with a b-amino carbonyl
core structure. b-Amino esters and ketones are obtained efficiently
in the presence of 1–2 mol% of Bi(OTf)3·4H2O. Since the original
communication of our work,17 the scope and generality of the
reaction have been broadened. A large selection of carbonyl
compounds and silyl enolates have been examined, and recycling
studies are also included in this study. In addition, further insights
regarding the mechanism are presented.
The development of new methods for the synthesis of b-amino
carbonyl derivatives is an important area of synthetic research,
because b-amino ketones and esters are extremely important as
biologically active molecules.1 The Lewis acid-mediated reactions
of imines with silyl enolates are among the most efficient methods
for the synthesis of b-amino carbonyl compounds. Although
a wide range of catalytic methods has been developed for
the synthesis of b-amino carbonyl compounds,2 none are both
broadly applicable and amenable to large-scale organic synthesis.
Moreover, many imines tend to be unstable during purification
by chromatography, distillation, or prolonged storage. Thus, it
is desirable from a synthetic point of view that imines, formed
in situ from aldehydes and amines, immediately react with silyl
enolates and provide b-amino carbonyl compounds in a one-pot
process.3 Nevertheless, most Lewis acids can not be used in this
reaction because they decompose or deactivate in the presence of
the amines and water produced during imine formation. Recently,
synthetic methods involving rare-earth and lanthanide triflates as
catalysts for Mannich-type reactions have been reported.4 High
catalytic activity, low toxicity, moisture and air tolerance make
lanthanide triflates attractive catalysts. However, the high cost of
these catalysts restricts their use.
Bismuth compounds too have attracted recent attention due
to their low toxicity, low cost, and stability.5 Bismuth salts
have been reported as catalysts for the opening of epoxides,6
allylation of imines,7 Mukaiyama-aldol reactions,8 formation and
deprotection of acetals,9 Friedel–Crafts reactions,10 Diels–Alder
reactions,11 Fries rearrangements,12 Claisen rearrangements,13 and
intramolecular Sakurai cyclizations.14 Bi(OTf)3 is particularly
attractive because it is commercially available or can be easily
prepared from readily available starting materials.15
Results and discussion
Catalyst screening
Initial investigations of the Mannich-type reaction of silyl enolates
with benzaldehyde and aniline employed a series of bismuth(III)
salts (Scheme 1, Table 1). These results were promising, as the
corresponding b-amino ketone could be obtained in moderate
to good yield with bismuth halides except with bismuth fluoride
(Table 1, entries 1–4). Bismuth nitrate smoothly afforded the
expected product (Table 1, entry 5). While bismuth acetate gave
no conversion, bismuth trifluoroacetate provided the product in
only moderate yield (Table 1, entries 6 and 7). Phenyl bismuth
ditriflate and diphenyl bismuth triflate appeared to be more
efficient catalysts than all previously tested ones (Table 1, entries 8
and 9). Bismuth(III) triflate led to the expected product in a good
yield and in a short reaction time without any difference between
the anhydrous and the hydrated form (Table 1, entries 10 and 11).
As a part of our ongoing interest in bismuth(III)-catalysed
Mannich-type and aza-Sakurai reactions,7,16 we report herein our
results in the three-component bismuth(III)-catalysed Mannich-
type reaction. A major merit of the three-component reaction is
indeed that many unique structures can be afforded rapidly when
three or more reactants are combined in a single step to afford new
Scheme
1
Mannich-type reaction of benzaldehyde, aniline, and
(1-phenylvinyloxy)trimethylsilane catalysed by BiX3 salts.
Solvent screening
With Bi(OTf)3·4H2O identified as an effective catalyst for the
Mannich-type reaction, optimisation of reaction conditions us-
ing various solvents was undertaken (Scheme 1, Table 2).
De´partement de Chimie, Universite´ Laval, Que´bec, G1K 7P4, Canada.
E-mail: thierry.ollevier@chm.ulaval.ca; Fax: +1 418 6567916; Tel: +1 418
6565034
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Table 1 Mannich-type reaction of benzaldehyde, aniline, and (1-phenyl-
vinyloxy)trimethylsilane using Bi(III) salts as the catalysta
Entry
Catalyst
Time/h
Yield (%)b
1
2
3
4
5
6
7
8
9
BiF3
BiCl3
BiBr3
BiI3
Bi(NO3)3·5H2O
Bi(OAc)3
Bi(OCOCF3)3
Ph2Bi(OTf)
PhBi(OTf)2
Bi(OTf)3·4H2O
Bi(OTf)3
24
0
59
72
62
67
0
36
85c
89c
89c
90c
1.5
0.3
7.5
0.2
23
0.8
0.3
0.1
0.1
0.1
Scheme 2 Bi(OTf)3·4H2O-catalysed Mannich-type reaction involving
various aldehydes, amines, and silyl enolates.
clopentanone or cyclohexanone afforded the b-amino ketones in
good yields (Table 3, entries 5 and 6).
Other aldehydes were tested and, generally, moderate to excel-
lent yields of b-amino ketone were obtained with silyl enol ethers
and 1 mol% of Bi(OTf)3·4H2O at 25 ◦C in acetonitrile. Aromatic
aldehydes reacted smoothly to give the corresponding b-amino
ketone derivatives 4 in high yield (Table 3, entries 7–14). The
reaction worked well with a variety of aldehydes including those
bearing an electron-withdrawing group, and the corresponding
b-amino ketones 4 were obtained with very good yields. Several
electron-rich aromatic aldehydes led to the desired products in
good yields (Table 3, entries 11 and 12). 4-Acetylbenzaldehyde led
to the expected product with complete chemoselectivity toward
the aldehyde (Table 3, entry 13). Only a moderate yield was
obtained with 1-naphthylcarboxaldehyde as the substrate (Table 3,
entry 14). With a heterocyclic aldehyde (e.g., furfural) the b-amino
ketones were obtained in good yield (Table 3, entries 15–17).
However, the reaction with 3-pyridylcarboxaldehyde gave a lower
yield due to low conversion (Table 3, entry 18). A conjugated
aldehyde was a good substrate as well (Table 3, entry 19).
Aliphatic aldehydes did not react under such conditions (probably
due to self-condensation), except cyclohexane carboxaldehyde
and pivaloyl aldehyde, which afforded product 4 in good yields
(Table 3, entries 20 and 21). For enolizable aliphatic aldehydes,
it was possible to obtain the corresponding b-amino ketones by
a slight modification of the reaction conditions. Decreasing the
reaction temperature to 0 ◦C and adding the aldehyde as the
last reagent provided moderate to good yields of the expected
products (Table 3, entries 22–24). Interestingly, we never observed
side reaction products such as aldol and deamination products.
10
11
a Reagents and conditions: benzaldehyde 1a (1.0 equiv.), aniline 2a
(1.0 equiv.), (1-phe◦nylvinyloxy)trimethylsilane 3a (1.0 equiv.), BiX3
(1 mol%), MeCN, 25 C. b Isolated yield. c 1.2 equiv. of (1-phenylvinyloxy)-
trimethylsilane was used.
Table 2 Mannich-type reaction of benzaldehyde, aniline, and (1-phenyl-
vinyloxy)trimethylsilane in different solventsa
Entry
Solvent
Catalyst loading (x mol%)
Time/h
Yield (%)b
1
2
3
4
5
6
7
8
9
PhMe
Et2O
1
1
1
1
1
1
0.5
2
5
3.5
2.5
1.5
0.1
3
0.5
21
54
72
60
71
80
82c
68
84
85
CH2Cl2
MeNO2
EtOH
MeCN
MeCN
MeCN
MeCN
0.5
0.1
a Reagents and conditions: benzaldehyde 1a (1.0 equiv.), aniline
2a (1.0 equiv.), (1-phenylvinyloxy)trimethylsilane 3a (1.0 equiv.),
Bi(OTf)3·4H2O (x mol%), 25 ◦C. b Isolated yield. c On a 0.1 mol ben-
zaldehyde scale, the yield was 85%.
Benzaldehyde, aniline and (1-phenylvinyloxy)trimethylsilane were
chosen as representative substrates. Among various solvents
tested, toluene, diethyl ether, dichloromethane, and nitromethane
gave moderate yields of the expected product (Table 2, entries 1–
4). Ethanol afforded the product in good yield (Table 2, entry 5).
The best solvent was found to be acetonitrile, giving 1,3-diphenyl-
3-(N-phenylamino)propan-1-one 4a in 82% yield. Scaling up the
reaction to 0.1 mol afforded 4a in 85% yield (Table 2, entry 6). With
further optimization of the reaction conditions, we found that a
lower catalyst loading gave decreased yields (Table 2, entry 7).
Increasing the catalyst loading did not significantly affect the yield
(Table 2, entries 8 and 9).
Silyl ketene acetals as the nucleophilic partner
Several examples of Bi(OTf)3-catalysed Mannich-type reactions
with various silyl ketene acetals are summarized in Table 4
(Scheme 2). Due to rapid hydrolysis of silyl ketene acetals under
our standard conditions, it was necessary to optimize the reaction
parameters. It was found that using 2 mol% of catalyst in THF
◦
at −78 C gave the best yields. Thus, silyl ketene acetals derived
from various esters were reacted with an equimolar mixture of
benzaldehyde and aniline. The corresponding b-amino esters 4
were obtained in good yields (Table 4). Silyl enolates derived from
esters as well as thioesters reacted smoothly to give the adducts.
No adducts between aldehydes and the silyl enolates were observed
in any reaction according to NMR analysis of the crude reaction
mixture. As for the diastereoselectivity of the reaction, good results
were obtained with the following substrates. ((E)-1-Methoxyprop-
1-enyloxy)trimethylsilane afforded the expected product with syn
stereoselectivity (Table 4, entry 4). Moderate syn selectivity was
observed with ((E)-1-alkoxy-2-phenylvinyloxy)trimethylsilane
(Table 4, entries 5 and 6). The geometry of the silyl ketene
Generality of the reaction
Several examples of Bi(OTf)3-catalysed Mannich-type reactions
with various silyl enol ethers are summarized in Table 3. Silyl
enol ethers derived from aromatic ketones and from aliphatic
ketones were reacted with an equimolar mixture of aldehyde 1
and aniline 2a (Scheme 2). The corresponding b-amino ketones
4 were obtained in good yields (Table 3, entries 1–4) from
aromatic-derived silyl enol ethers except for the more hindered
isobutyrophenone derivative. Silyl enol ethers derived from cy-
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Table 3 Mannich-type reaction with silyl enol ethers derived from ketonesa
Entry
1
Aldehyde
Silyl enol ether
Time/h
0.1
Yield (%)b
89
syn/anti
—
2
3
2
94
50 : 50
—
37
45c
4
0.5
82
—
5
6
1.5
0.5
80
81
68 : 32
61 : 39
7
8
9
0.8
1.5
0.5
82
83
88
—
d
—
—
—
10
0.5
87
11
12
13
1
81
86
92
—
—
—
0.7
0.1
14
1
44
—
—
15
16
17
1
3
1
76
80
78
e
—
58 : 42
18
19
4.5
1.5
49
72
—
—
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Table 3 (Contd.)
Entry
20
Aldehyde
Silyl enol ether
Time/h
0.8
Yield (%)b
77
syn/anti
—
21
22
23
24
1
17
18
3
54
—
—
—
61f
51f
70f
g
—
◦
a Reagents and conditions: aldehyde 1 (1.0 equiv.), aniline 2a (1.0 equiv.), silyl enol ether 3 (1.0–1.2 equiv.), Bi(OTf)3·4H2O (1 mol%), 25 C. b Isolated
yield. c Bi(OTf)3·4H2O (5 mol%). d dr = 66 : 34. e dr = 61 : 39. f Reaction carried out at 0 ◦C. g dr = 85 : 15
acetal did not influence the diastereoisomeric ratio, as (E)- and
(Z)-1-((ethylthio)prop-1-enyloxy)trimethylsilane afforded the b-
aminothioester with the same syn/anti ratios (Table 4, entries 8 and
9). The relative stereochemistry was confirmed by base-cyclization
to the corrersponding b-lactam and comparison of the vicinal
proton–proton coupling constants with those in the literature
(Scheme 3).18
amino carbonyl compound (Table 5, entry 8). The reaction of the
same silyl enol ether with benzaldehyde and a-methylbenzylamine
gave no conversion (Table 5, entry 9). For the reactions with
a silyl ketene acetal, yields proved to be more dependent on
aniline substitution. An excellent yield was obtained with an
electron-poor aniline, but lower yields were observedwith electron-
rich anilines (Table 5, entries 10–12). Changing p-anisidine for a
more sterically hindered o-anisidine also led to a decreased yield
(Table 5, compare entries 11 and 12).
Effect of additives
It is interesting to note that the ‘two-pot’ version of this reaction,
i.e. with prior formation and isolation of the imine, always
occurred in very low conversions in our hands (Scheme 4, Table 6).
Knowing that the main difference between the two-pot and the
one-pot strategy is the in situ formation of water in the latter,
the addition of a variety of acidic additives was examined. When
the model reaction was studied with N-benzilideneaniline 5, b-
aminoketone 4a was obtained in low yield using 1 mol% of
Bi(OTf)3·4H2O (Table 6, entry 1). However, addition of one equiv-
alent of water or hexafluoroisopropanol provided the expected
product (Scheme 4, Table 6, entries 2 and 3) in the usual high
yields obtained in the three-component system.
Scheme 3 Determination of the relative stereochemistry of a b-amino
thioester.
Generally, good yields of b-amino ester were obtained with
aromatic aldehydes as well as an a,b-unsaturated aldehyde
(Table 4, entries 12–16). Interestingly, we noted that the reaction
was sterically sensitive, as ortho substitution led to a decreased
conversion (compare entries 13 and 14). Aliphatic aldehydes also
afforded the corresponding amino esters 4 in moderate to good
yields. In all cases, the corresponding aldol derivative was never
observed as a by-product.
Reaction scope: amine substrate
The scope of our method could be extended to other amines. Ben-
zaldehyde was chosen in our model reaction (Scheme 2). Ortho-
and para-anisidines gave good yields of the corresponding b-amino
carbonyl compounds (Table 5, entries 1 and 2), which are known
to be cleavable under oxidative conditions.19 Other substituted
anilines also afforded the b-amino carbonyl compounds in high
yields (Table 5, entries 3–5). The reaction with o-anisidine or 2-
aminophenol and silyl enol ether derived from propiophenone
proceeded smoothly, albeit with almost no diastereoselectivity
(Table 5, entries 6 and 7). Using benzyl carbamate instead of
an aniline gave only a moderate yield of the Cbz-protected b-
Scheme 4 Use of additives in the Bi(OTf)3·4H2O-catalysed Mannich-type
reaction.
As demonstrated, an aqueous solution of Bi(OTf)3 is acidic,15a,20
so the true catalyst is apparently HOTf released from the hydrol-
ysis of Bi(OTf)3·4H2O. The observation that the same reaction
still occurs in the presence of hindered 2,6-di-tert-butylpyridine
(1 equiv. of PhCHO 1a, 1 equiv. of PhNH2 2a, 1 equiv. of
(1-phenylvinyloxy)trimethylsilane 3a, 1 mol% of Bi(OTf)3·4H2O,
3 mol% of 2,6-di-tert-butylpyridine, 25 ◦C, 0.3 h, 80% of 4a)
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Table 4 Mannich-type reaction with silyl ketene acetals derived from esters or thioestersa
Entry
1
Aldehyde
Silyl ketene acetal
Time/h
3.5
Yield (%)b
84
syn/anti
—
2
3
1.5
0.8
83
85
—
—
4
5
E/Z = 80 : 20
2.5
2.5
80
81
74 : 26
78 : 22
E/Z = 78 : 22
E/Z = 69 : 31
6
7
24
60
59
62 : 38
—
1.7
8
E/Z = 5 : 95
E/Z = 99 : 1
1
89
76 : 24
9
1.8
1
83
85
78 : 22
—
10
11
12
1
2
90
82
—
—
13
14
15
16
17
18
1
76
34
70
61
38
89
—
—
—
—
—
—
3.5
2
2.5
1
1.3
a Reagents and conditions: aldehyde 1 (1.0 equiv.), aniline 2a (1.0 equiv.), silyl ketene acetal 3 (1.2 equiv.), Bi(OTf)3·4H2O (2 mol%), THF, −78 ◦C. b Isolated
yield.
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Table 5 Bi(OTf)3·4H2O-catalysed Mannich-type reaction with aminesa
2a, 1 equiv. of (1-phenylvinyloxy)trimethylsilane 3a, 3 mol%
of 2,6-di-tert-butylpyridinium triflate, 25 ◦C, 0.3 h, 80% of
4a). However, replacing Bi(OTf)3·4H2O by HOTf as catalyst
for the three-component model reaction showed that HOTf is
indeed as effective as Bi(OTf)3·4H2O at catalysing the Mannich-
type reaction (1 equiv. of PhCHO 1a, 1 equiv. of PhNH2 2a,
1 equiv. of (1-phenylvinyloxy)trimethylsilane 3a, 3 mol% of HOTf,
25 ◦C, 0.3 h, 80% of 4a). The HOTf-catalysed Mannich-type
reaction on the preformed imine affords the same product in
good yield (1 equiv. of N-benzylideneaniline 5, 1 equiv. of (1-
phe◦nylvinyloxy)trimethylsilane 3a, 1 equiv. H2O, 3 mol% of HOTf,
25 C, 0.1 h, 77% of 4a) (compare with Table 6, entry 2).21
Moreover, the competition between the Mannich-type and the
Mukaiyama aldol reaction was studied using Bi(OTf)3·4H2O
and HOTf with (Z)-(1-phenylprop-1-enyloxy)trimethylsilane 3b
as the nucleophile (Scheme 5). In both cases, only the Mannich-
type reaction occurred without formation of the corresponding
aldol. The b-amino ketone 4b was obtained in both cases with
the same chemical yield, the same diastereoselectivity (1 mol%
Bi(OTf)3·4H2O, 0.7 h, 82% of 4b, dr = 51 : 49; 3 mol% HOTf,
0.6 h, 85% of 4b, dr = 50 : 50), and the same chemoselectivity.
This result, in addition to the previous one, indicates that, most
probably, Bi(OTf)3·4H2O is hydrolysed under these conditions,
affording triflic acid, which could be the real catalytic species.
Since HOTf is very corrosive and difficult to handle, the practical
use of Bi(OTf)3·4H2O makes our method particularly valuable.
Entry
1
Amine
Silyl enolate
Time/h
2
Yield (%)b
78
2
3
4
5
6
7
1
79
0.5
0.5
2
88c
85c
78c
92 d
88e
1
4
8
9
0.8
21
49c
0
10
0.8
90
Scheme 5 Competition studies for diastereoselective Mannich-type reac-
tion catalysed by Bi(OTf)3·4H2O or HOTf.
11
12
2
70
55
22
Catalyst recycling
From an environmental point of view, it is desirable to mini-
mize the amount of waste for each organic transformation. In
this context, we recycled the catalyst solution for subsequent
runs. We chose the reaction between benzaldehyde, aniline,
and (1-phenylvinyloxy)trimethylsilane. As the corresponding b-
aminoketone was insoluble in acetonitrile, it could be easily
recovered by simple filtration. The catalyst solution was recycled
for subsequent cycles. Up to four runs could be achieved without
noticeable decrease in yield (Scheme 6).
a Reagents and conditions: benzaldehyde1a (1.0 equiv.), amine2 (1.0 equiv.),
silyl enolate 3 (1.2 equiv.), Bi(OTf)3·4H2O (1 mol%), MeCN, 25 ◦C
(entries 1–9) or Bi(OTf)3·4H2O (2 mol%), THF, −78 ◦C (entries 10–12).
b Isolated yield. c Reaction at 0 ◦C. d dr = 60 : 40. e dr = 50 : 50.
Table 6 Mannich-type reaction of N-benzilideneaniline and (1-phenyl-
vinyloxy)trimethylsilanea
Entry
Additive
Time/h
Yield (%)b
1
2
3
—
H2O
2
0.1
0.1
26
84
74
Scheme 6 Recycling of the catalyst solution.
a Reagents and conditions: benzilideneaniline
5
(1.0 equiv.), (1-
phenylvinyloxy)trimethylsilane 3a (1.0 equiv.), Bi(OTf)3·4H2O (1 mol%),
additive (1 equiv.), MeCN, 25 ◦C. b Isolated yield.
Conclusions
does not indicate unambiguously that a Brønsted acid is not
involved in the process, because the pyridinium salt itself also
mediates the reaction (1 equiv. of PhCHO 1a, 1 equiv. of PhNH2
As an improvement over other catalyst systems, Bi(OTf)3·4H2O is
a versatile catalyst for the Mannich-type reaction of a variety
of silyl enolates with imines generated in situ. The reaction
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affords up to 94% yields of b-amino carbonyl compounds in
short reaction times, and using only 1–2 mol% of the catalyst.
This method offers several advantages including mild reaction
conditions, a highly catalytic process, and no by-products. The
conditions are suitable for a variety of aldehydes, aromatic amines
and silyl enolates. Also, the practical use of Bi(OTf)3·4H2O is
highly valuable as a surrogate for HOTf since the latter is very
corrosive and difficult to handle. Moreover, our protocol does
not require prior isolation of the imine. The b-amino carbonyl
compound is directly obtained, usually as a crystalline product, in
a one-pot process. Because of its numerous benefits, this method
for the one-pot synthesis of b-amino esters and ketones using
bismuth triflate catalysis should find utility in the synthesis of
biologically active compounds.
room temperature until the reaction was complete as indicated
by TLC. The reaction was quenched with water (8 mL) and
extracted with diethyl ether (3 × 40 mL). The organic phase was
washed with water and saturated aqueous sodium chloride, dried
over magnesium sulfate, and concentrated under vacuum (rotary
evaporator). When the crude product was a solid, it was triturated
with hexane (20 mL) and filtered; otherwise, it was purified
by column chromatography (eluent hexane–ethyl acetate). The
spectral data for known compounds match with those reported in
the literature.17a,22
General procedure for the bismuth triflate-catalysed
three-component reaction with silyl ketene acetals
Under an inert atmosphere of argon, the silyl ketene acetal
(1.2 mmol) in 1 mL of dry THF was added dropwise to a solution
of Bi(OTf)3·4H2O (2 mol%), the aldehyde (1 mmol), and the
amine (1 mmol) in 1 mL of dry THF at −78 ◦C. The mixture
was stirred at −78 ◦C for 0.15 h and then allowed to reach
room temperature. The mixture was stirred until the reaction
was completed as indicated by TLC. The reaction was quenched
with water (4 mL) and extracted with diethyl ether (3 × 20 mL).
The organic phase was washed with water and saturated aqueous
sodium chloride, dried over magnesium sulfate, and concentrated
under vacuum (rotary evaporator). When the crude product was a
solid, it was triturated with hexane (10 mL) and filtered; otherwise,
it was purified by column chromatography (eluent hexane–ethyl
acetate). The spectral data for known compounds match with
those reported in the literature.3g,17b,22c,23
Experimental
All reactions were carried out in flame-dried test tubes cooled
under an atmosphere of argon. Dichloromethane and acetoni-
trile were distilled from calcium hydride. Tetrahydrofuran and
ether were distilled from sodium/benzophenone. Toluene was
distilled from sodium. Benzaldehyde, cyclohexylcarboxaldehyde,
n-butyraldehyde, and isobutyraldehyde were distilled before use.
Other reagents and solvents were used as received. Flash column
chromatography was performed using silica gel (230–400 mesh)
under pressure. Analytical thin layer chromatography (TLC)
was carried out using 250 lm commercial silica gel plates, and
visualised by ultra-violet irradiation (254 nm) or by staining
with aqueous potassium permanganate and developed with
appropriate heating. Melting points were recorded on a Mel-
Temp apparatus, and are uncorrected. Infra-red spectra were
obtained on a FT-IR spectrometer and are reported in cm−1.
Mass spectra were obtained on a Waters instrument, by electron
impact or electrospray ionisation techniques, at the Department
of Chemistry, Universite´ de Sherbrooke, Sherbrooke, Canada. 1H
NMR spectra were recorded at ambient temperature on Varian
DPX-400 spectrometer at 400 MHz with tetramethylsilane (TMS)
as the internal reference (dH = 0 ppm); chemical shifts (d) are given
in parts per million (ppm) and coupling constants (J) are given
in Hertz (Hz). The proton spectra are reported as follows: d/ppm
(number of protons, multiplicity, coupling constant J/Hz). 13C
NMR spectra were recorded at ambient temperature on the same
spectrometer at 100 MHz, with the central peak of CHCl3 as the
internal reference (dC = 77.0 ppm). For 19F NMR, CFCl3 was
used as the internal standard (d = 0). DEPT and two-dimensional
(COSY, HMQC, HMBC) NMR spectroscopy were used, where
appropriate, to aid the assignments of signals in the 1H and
13C NMR spectra. Where a compound was characterised as an
inseparable mixture of diastereoisomers, the NMR data for the
major (maj) and minor (min) isomers have been reported as far as
was discernable from the spectrum of the mixture.
2,2-Dimethyl-1,3-diphenyl-3-(N -phenylamino)propan-1-one.
(Table 3, entry 3): Yield 45%; white solid; mp 117–118 ◦C; Rf
0.54 (hexane–ethyl acetate = 4 : 1); IR (KBr): m = 3389, 1656;
1H NMR (CDCl3): d = 7.20–7.40 (10H, m), 7.01 (2H, m), 6.59
(1H, tt, J = 7.3, 1.0 Hz), 6.43 (2H, m), 4.76 (1H, s), 4.67 (1H, s),
1.32 (3H, s), 1.23 (3H, s); 13C NMR (CDCl3): d = 210.7, 146.2,
140.1, 138.6, 130.4, 129.2, 129.0, 128.3, 127.8, 126.9, 118.1, 114.1,
63.7, 52.3, 25.5, 20.5; HRMS: Calc. for C23H23NO (M+) 329.1780,
found 329.1783.
3-(4-Chlorophenyl)-2-methyl-1-phenyl-3-(N-phenylamino)propan-
1-one. (Table 3, entry 8): Yield 83%; major/minor = 66 : 34;
◦
white solid; mp 146–149 C; Rf 0.44 (hexane–ethyl acetate = 4 :
1); IR (KBr): m = 3417, 3394, 1670; 1H NMR (CDCl3): d = 7.92
(maj, 2H, m), 7.75 (min, 2H, m), 7.18–7.59 (7H, m), 7.02–7.09
(2H, m), 6.64 (1H, t, J = 7.3 Hz), 6.51 (min, 2H, d, J = 7.8 Hz),
6.44 (maj, 2H, m), 4.71 (maj, 1H, d, J = 5.3 Hz), 4.69 (min, 1H,
d, J = 7.4 Hz), 4.58–4.92 (1H, br s), 3.90–3.99 (1H, m), 1.31 (min,
3H, d, J = 7.0 Hz), 1.22 (maj, 3H, d, J = 7.0 Hz); 13C NMR
(CDCl3): d = 203.9, 202.6, 147.0, 146.8, 140.5, 140.3, 137.1, 136.3,
133.7, 133.6, 133.2, 129.4, 129.2, 129.08, 129.05, 129.0, 128.9,
128.51, 128.47, 128.4, 118.2, 118.0, 114.1, 113.8, 60.9, 59.0, 46.9,
46.4, 16.9, 11.9; HRMS: Calc. for C22H20ClNO (M+) 349.1233,
found 349.1241.
General procedure for the bismuth triflate-catalysed
three-component reaction with silyl enol ethers
3-(4-Acetylphenyl)-1-phenyl-3-(N-phenylamino)propan-1-one.
(Table 3, entry 13): Yield 92%; yellowish solid; mp 168–169 ◦C; Rf
0.18 (hexane–ethyl acetate = 4 : 1); IR (KBr): m = 3404, 1672; 1H
NMR (CDCl3): d = 7.89–7.93 (4H, m), 7.54–7.60 (3H, m), 7.45
(2H, t, J = 7.7 Hz), 7.07–7.11 (2H, m), 6.68 (1H, t, J = 7.3 Hz),
6.52–6.55 (2H, m), 5.06 (1H, dd, J = 7.2, 5.4 Hz), 4.64 (1H, br s),
Under an inert atmosphere of argon, the silyl enol ether (2.4 mmol)
in 2 mL of dry acetonitrile was added in one portion to a solution
of Bi(OTf)3·4H2O (1 mol%), the aldehyde (2 mmol), and the amine
(2 mmol) in 2 mL of dry acetonitrile. The mixture was stirred at
3132 | Org. Biomol. Chem., 2007, 5, 3126–3134
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©

3.52 (1H, dd, J = 16.5, 5.4 Hz), 3.46 (1H, dd, J = 16.5, 7.2 Hz),
2.57 (3H, s); 13C NMR (CDCl3): d = 198.0, 197.9, 148.8, 146.9,
136.7, 136.6, 133.9, 129.4, 129.2, 129.0, 128.4, 126.9, 118.4, 114.1,
54.7, 46.1, 26.9; HRMS: Calc. for C23H21NO2 (M+) 343.1572,
found 343.1576.
16.5, 6.5 Hz), 3.10 (maj, 1H, dd, J = 16.8, 4.5 Hz), 2.96 (min,
1H, dd, J = 16.5, 6.0 Hz), 2.81 (maj, 1H, dd, J = 16.8, 6.2 Hz),
1.41 (maj, 3H, d, J = 7.2 Hz), 1.37 (min, 3H, d, J = 7.0 Hz); 13
C
NMR (CDCl3): d = 199.9, 199.5, 147.8, 147.4, 143.9, 142.7, 137.4,
137.0, 133.4, 133.2, 129.6, 128.84, 128.80, 128.7, 128.6, 128.3,
128.2, 128.1, 127.1, 127.0, 117.7, 117.6, 113.80, 113.77, 56.2, 54.7,
43.9, 42.5, 41.1, 40.2, 19.0, 17.0; HRMS: Cald for C23H23NO (M+)
329.1780, found 329.1783.
1-Phenyl-3-(N-phenylamino)-3-(3-pyridyl)propan-1-one. (Table 3,
entry 18): Yield 49%; yellowish solid; mp 138–139 ◦C; Rf 0.16
1
(hexane–ethyl acetate = 1 : 1); IR (KBr): m = 3255, 1680; H
NMR (CDCl3): d = 8.70 (1H, d, J = 2.1 Hz), 8.46 (1H, dd, J =
4.7, 1.6 Hz), 7.86–7.89 (2H, m), 7.75 (1H, dt, J = 7.8, 1.8 Hz), 7.55
(1H, tt, J = 7.4, 1.5 Hz), 7.40–7.45 (2H, m), 7.20 (1H, ddd, J =
7.9, 4.8, 0.5 Hz), 7.05–7.10 (2H, m), 6.67 (1H, tt, J = 7.3, 1.0 Hz),
6.53 (2H, dd, J = 8.6, 1.0 Hz), 5.05 (1H, dd, J = 6.1, 6.1 Hz),
4.63 (1H, br s), 3.43–3.52 (2H, m); 13C NMR (CDCl3): d = 197.8,
149.0, 148.8, 146.7, 138.5, 136.6, 134.5, 133.9, 129.5, 129.0, 128.4,
123.9, 118.5, 114.1, 52.6, 45.9; HRMS: Calc. for C20H18N2O (M+)
302.1419, found 302.1425.
Methyl 1-(phenyl-N-phenylaminomethyl)cyclohexanecarboxy-
late. (Table 4, entry 7): Yield 59%; white crystals; mp 98–99 ◦C;
Rf 0.70 (hexane–ethyl acetate = 4 : 1); IR (KBr): m = 3378, 1721;
1H NMR (CDCl3): d = 7.19–7.29 (5H, m), 7.02 (2H, dd, J = 8.7,
7.3 Hz), 6.57 (1H, tt, J = 7.2, 1.1 Hz), 6.45 (2H, dd, J = 8.7,
1.1 Hz), 5.01 (1H, br s), 4.32 (1H, s), 3.63 (3H, s), 2.40 (1H, d, J =
14.1 Hz), 2.01 (1H, dd, J = 12.9, 2.9 Hz), 1.56–1.68 (3H, m), 1.04–
1.44 (5H, m); 13C NMR (CDCl3): d = 175.8, 147.2, 139.6, 129.2,
128.5, 128.1, 127.7, 117.2, 113.3, 65.3, 52.2, 52.0, 33.8, 30.6, 25.7,
23.8, 23.3; HRMS: Calc. for C21H25NO2 (M+) 323.1885, found
323.1888.
4,4-Dimethyl-1-phenyl-3-(N -phenylamino)pentan-1-one.
◦
(Table 3, entry 21): Yield 54%; yellowish solid; mp 102–103 C;
Rf 0.57 (hexane–ethyl acetate = 4 : 1); IR (KBr): m = 3386, 1663;
1H NMR (CDCl3): d = 7.85–7.87 (2H, m), 7.53 (1H, tt, J = 7.3,
1.5 Hz), 7.40–7.44 (2H, m), 7.05–7.09 (2H, m), 6.56–6.68 (3H, m),
4.02 (1H, dd, J = 7.1, 5.1 Hz), 3.30 (1H, dd, J = 16.0, 5.1 Hz),
2.97 (1H, dd, J = 16.0, 7.1 Hz), 1.01 (9H, s); 13C NMR (CDCl3):
d = 199.8, 148.3, 137.5, 133.2, 129.4, 128.8, 128.3, 117.3, 113.4,
58.6, 40.9, 36.1, 26.9; HRMS: Calc. for C19H23NO (M+) 281.1780,
found 281.1783.
Methyl 2,2-dimethyl-3-(N-phenylamino)-3-o-tolylpropanoate.
(Table 4, entry 14): Yield 34%; yellowish solid; mp 129–130 C;
◦
Rf 0.70 (hexane–ethyl acetate = 4 : 1); IR (KBr): m = 3371, 1714;
1H NMR (CDCl3): d = 7.19–7.22 (1H, m), 7.09–7.15 (3H, m),
7.01–7.07 (2H, m), 6.56–6.61 (1H, m), 6.43–6.46 (2H, m), 4.88
(1H, d, J = 7.1 Hz), 4.83 (1H, d, J = 7.1 Hz), 3.67 (3H, s), 2.54
(3H, s), 1.29 (3H, s), 1.20 (3H, s); 13C NMR (CDCl3): d = 177.5,
147.4, 138.1, 136.8, 130.8, 129.4, 127.4, 126.2, 117.5, 113.4, 59.4,
52.4, 48.5, 25.0, 20.67, 20.65; HRMS: Calc. for C19H23NO2 (M+)
297.1729, found 297.1735.
1-Phenyl-3-(N-phenylamino)hexan-1-one. (Table 3, entry 22):
Yield 61%; yellowish oil; Rf 0.56 (hexane–ethyl acetate = 4 : 1); IR
(film): m = 3395, 1679; 1H NMR (CDCl3): d = 7.90–7.94 (2H, m),
7.55 (1H, tt, J = 7.4, 1.5 Hz), 7.42–7.46 (2H, m), 7.13–7.18 (2H,
m), 6.66–6.70 (1H, m), 6.63 (2H, dd, J = 8.6, 1.0 Hz), 4.05 (1H,
ddt, J = 7.0, 7.0, 4.8 Hz), 3.76 (1H, br s), 3.27 (1H, dd, J = 16.5,
4.8 Hz), 3.16 (1H, dd, J = 16.5, 7.0 Hz), 1.35–1.72 (4H, m), 0.92
(3H, t, J = 7.3 Hz); 13C NMR (CDCl3): d = 199.7, 147.4, 137.4,
133.4, 129.6, 128.8, 128.3, 117.6, 113.6, 50.1, 43.0, 37.8, 19.8, 14.2;
HRMS: Calc. for C18H21NO (M+) 267.1623, found 267.1630.
Methyl 2,2-dimethyl-3-(N-phenylamino)hexanoate. (Table 4,
entry 18): Yield 89%; colorless oil; Rf 0.78 (hexane–ethyl acetate =
4 : 1); IR (film): m = 3397, 1725; 1H NMR (CDCl3): d = 7.10–7.14
(2H, m), 6.59–6.63 (3H, m), 3.56–3.66 (2H, m), 3.61 (3H, s), 1.46–
1.50 (2H, m), 1.24–1.30 (2H, m), 1.22 (3H, s), 1.19 (3H, s), 0.86
(3H, t, J = 7.1 Hz); 13C NMR (CDCl3): d = 177.9, 149.5, 129.5,
116.8, 112.8, 59.5, 52.0, 48.2, 35.6, 23.1, 22.0, 20.5, 14.4; HRMS:
Calc. for C15H23NO2 (M+) 249.1729, found 249.1733.
4-Methyl-1-phenyl-3-(N-phenylamino)pentan-1-one. (Table 3,
entry 23): Yield 51%; yellowish solid; mp 74–76 ◦C; Rf 0.68
(hexane–ethyl acetate = 4 : 1); IR (KBr): m = 3392, 3370, 1668;
1H NMR (CDCl3): d = 7.90–7.93 (2H, m), 7.55 (1H, tt, J = 7.3,
1.5 Hz), 7.43–7.46 (2H, m), 7.10–7.15 (2H, m), 6.65 (1H, tt, J =
7.3, 1.1 Hz), 6.58–6.61 (2H, m), 3.93 (1H, ddd, J = 11.2, 5.9,
5.9 Hz), 3.78 (1H, br s), 3.20 (1H, dd, J = 16.4, 5.9 Hz), 3.09 (1H,
dd, 16.4, 5.9 Hz), 1.99–2.07 (1H, m), 1.03 (3H, d, J = 6.8 Hz),
0.96 (3H, d, 6.8 Hz); 13C NMR (CDCl3): d = 199.8, 147.8, 137.4,
133.4, 129.6, 128.9, 128.3, 117.4, 113.6, 55.5, 40.4, 31.9, 19.3, 18.8;
HRMS: Calc. for C18H21NO (M+) 267.1623, found 267.1627.
3-(N -2-Hydroxyphenylamino)-1,3-diphenylpropan-1-one.
(Table 5, entry 5): Yield 78%; yellowish solid; mp 112–113 ◦C; Rf
0.27 (hexane–ethyl acetate = 4 : 1); IR (KBr): m = 3550, 3392,
1683; 1H NMR (CDCl3): d = 7.92–8.00 (2H, m), 7.55 (1H, tt, J =
7.4, 1.5 Hz), 7.41–7.45 (2H, m), 7.27–7.36 (4H, m), 7.22 (1H, tt,
J = 7.1, 1.8 Hz), 6.77 (1H, dd, J = 7.6, 1.4 Hz), 6.68 (1H, ddd,
J = 7.6, 7.6, 1.4 Hz), 6.61 (1H, ddd, J = 7.6, 7.6, 1.4 Hz), 6.46
(1H, dd, J = 7.6, 1.4 Hz), 6.29 (1H, br s), 4.87 (1H, dd, J = 8.6,
4.3 Hz), 4.10 (1H, br s), 3.54 (1H, dd, J = 17.1, 8.6 Hz), 3.42
(1H, dd, J = 17.1, 4.3 Hz); 13C NMR (CDCl3): d = 199.0, 146.9,
142.9, 136.8, 134.8, 133.8, 129.0, 128.9, 128.5, 127.7, 126.8, 120.9,
120.8, 117.8, 115.0, 56.1, 46.4; HRMS: Calc. for C21H19NO2 (M+)
317.1416, found 317.1418.
1,4-Diphenyl-3-(N-phenylamino)pentan-1-one. (Table 3, en-
try 24): Yield 70%; major/minor = 85 : 15; yellowish solid; mp
110–112 ◦C; Rf 0.69 (hexane–ethyl acetate = 4 : 1); IR (KBr):
1
m = 3409, 1677; H NMR (CDCl3): d = 7.77–7.80 (min, 2H, m),
Acknowledgements
7.69–7.72 (maj, 2H, m), 7.47–7.55 (1H, m), 7.12–7.42 (9H, m),
6.61–6.69 (3H, m), 4.28–4.33 (min, 1H, m), 4.12–4.18 (maj, 1H,
m), 4.00 (maj, 1H, br s), 3.60 (min, 1H, br s), 3.22–3.27 (min, 1H,
m), 3.19 (maj, 1H, dq, J = 14.4, 7.2 Hz), 3.11 (min, 1H, dd, J =
This work was financially supported by the Natural Sciences and
Engineering Research Council of Canada (NSERC), the Fonds
Que´be´cois de la Recherche sur la Nature et les Technologies
This journal is
The Royal Society of Chemistry 2007
Org. Biomol. Chem., 2007, 5, 3126–3134 | 3133
©

(FQRNT, Que´bec, Canada), the Canada Foundation for Inno-
vation, and Universite´ Laval. E. N. thanks NSERC and FQRNT
for postgraduate fellowships. We thank Rhodia (Lyon, France)
and Sidech s.a. (Tilly, Belgium) for a generous gift of chemicals.
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3134 | Org. Biomol. Chem., 2007, 5, 3126–3134
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The Royal Society of Chemistry 2007
©