Amine-catalyzed aldol condensation in the presence of lithium perchlorate

Article abstract of DOI:10.1055/s-2006-926346

A catalytic aldol condensation in the presence of lithium perchlorate and tertiary amines is described giving pure products in high yields. The aldol condensation can be performed even in the presence of hydrated lithium perchlorate. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-926346

PAPER
1099
Amine-Catalyzed Aldol Condensation in the Presence of Lithium Perchlorate
Amine-Catalyzed
l
Aldol
C
i
onden
n
sation e Arnold, Morris Markert, Rainer Mahrwald*
Institute of Chemistry, Humboldt-Universität, Brook-Taylor-Straße 2, 12489 Berlin, Germany
Fax +49(30)20936940; E-mail: rainer.mahrwald@rz.hu-berlin.de
Received 27 July 2005; revised 20 October 2005
O
O
LiClO4
Abstract: A catalytic aldol condensation in the presence of lithium
PhCHO
+
perchlorate and tertiary amines is described giving pure products in
high yields. The aldol condensation can be performed even in the
presence of hydrated lithium perchlorate.
Ph
Ph
Et3N, r.t.
2a
1a
Scheme 1
Key words: aldol reactions, aldehydes, ketones, catalysis, amines
Table 1 Reactions of Benzaldehyde with Acetone in the Presence
of LiClO4 and Et3Na
a,b-Unsaturated carbonyl compounds, diarylylidene or
dialkylidene carbonyl compounds, are very important pre-
cursors in the perfume industry,1 for bioactive pyrim-
idines,2 as agrochemicals, and as liquid crystal polymers.3
Moreover, a,b-unsaturated carbonyl compounds are im-
portant structural elements in the curcumin family of nat-
ural products which exhibit certain anti-cancer
properties.4 They were used in the indium-catalyzed syn-
thesis of substituted vinylcyclopropanones5 or the gold-
catalyzed alkylation of indoles.6 Many of these substances
are widely used as ligands in palladium-catalyzed cou-
pling processes,7 moreover, some of these ligands are ex-
tremely expensive.8
Entry
LiClO4 (mol%)b Et3N (mol%)b
Time
2 min
2 min
2 h
Yield (%)
1
2
3
4
5
6
100
50
10
10
10
10
1
94
89
87
96
91
95
20
10
16 h
24 h
17 h
100
100c
10
a Procedure A.
b Relative to benzaldehyde.
c LiClO4·3H2O.
Recently, several methods appeared describing the syn-
thesis of arylidene- or alkylideneketones. Several metal
salts were employed as reagents in these reactions,9 how-
ever, often higher temperatures and long reaction times
are necessary for complete conversion and hence forma-
tion of byproducts increased. In addition, most of these re-
actions were accompanied by low chemoselectivity, also
self-condensations were observed rather than cross-aldol
condensations, which caused problems in their purifica-
tion.
reduced. Dibenzylacetone was isolated in up to 91% yield
in the presence of 1 mol% Et3N (Table 1, entry 5).
To ensure complete conversion, relatively long reaction
times, 16–24 hours at room temperature, were required.
Initial experiments were carried out in the presence of an-
hydrous LiClO4; however, later we realized the outcome
of the reaction was not influenced by water: even with a
two-phase system quantitative yields were obtained
(Table 1, entry 6, 0.5 mL of water added).
During our ongoing studies of aldol processes in the pres-
ence of LiClO410 we developed a very mild, easy, and cat-
alytic process for the synthesis of arylidene and alkylidene
carbonyl compounds, which we describe herein.
O
While investigating aldol addition processes, we observed
that ketones and aldehydes react in the presence of LiClO4
and catalytic amounts of tertiary amines to yield aldol
condensation products. The reaction was carried out neat
in the presence of 10 mol% Et3N at room temperature
(Scheme 1).
O
LiClO4
+
PhCHO
Ph
Ph
Et3N
R1
R2
R1
R2
1a–h
2a–h
Scheme 2
In order to test the catalytic potential of this transforma-
tion we reacted acetone and benzaldehyde with different
ratios of LiClO4 and Et3N (Table 1). Excellent yields were
achieved even when the amounts of Et3N and LiClO4 were
With optimized conditions in hand (anhyd LiClO4, r.t.) we
began to study the scope of the reaction (Scheme 2). Ini-
tially we carried out the reaction with benzaldehyde and
varied the ene component (Table 2). As discussed above,
the reaction of benzaldehyde with acetone is very fast and
quantitative; the same is true for the reaction of benzalde-
SYNTHESIS 2006, No. 7, pp 1099–1102
x
x
.
x
x
.2
0
0
6
Advanced online publication: 27.02.2006
DOI: 10.1055/s-2006-926346; Art ID: T10105SS
© Georg Thieme Verlag Stuttgart · New York

1100
A. Arnold et al.
PAPER
Next, we tested the range of aldehydes applicable to this
transformation with acetone employed as the ene compo-
nent in every reaction (Scheme 3, Table 3). Aromatic al-
dehydes 3a, 3b, 3c, and 3f reacted under these conditions
to give the expected unsaturated ketones 4a, 4b, 4c, and
4f. The reactions were very fast and quantitative (with the
exception of cinnamaldehyde 3f, ca. 60%). Even aliphatic
enolizable aldehydes reacted under these conditions,
isobutyraldehyde 3h reacted with acetone to give com-
pound 4h in quantitative yields. As expected, p-hydroxy-
benzaldehyde 3e did not react under these conditions
(Table 3, entry 5).
Table 2 Reaction of Benzaldehyde with a Range of Ketones in the
Presence of LiClO4 and Et3Na
Entry
R1
R2
H
Compd
2a
Yield (%)
1
2
3
4
5
6
7
8
9
H
94
91
93
48
45
–
-(CH2)2-
-(CH2)3-
H
2b
2c
Me
Me
H
2db
2eb
2f
Me
OH
O
O
OMe
OH
H
2g
–
LiClO4
Et3N
+
RCHO
R
R
OH
OAc
2h
–
3a–h
OAc
2i
–
5a–h
a General Procedure A.
b General Procedure B.
Scheme 4
Table 4 Reactions of a Range of Aldehydes with Cyclopentanone
in the Presence of LiClO4 and Et3Na
hyde with cyclopentanone and cyclohexanone: quantita-
tive yields were obtained within three minutes at room
temperature. Highly substituted acetone derivates re-
quired longer reaction times or additional heating to force
the reaction to go to completion (General Procedure B, for
compounds 2d and 2e). Oxygen-substituted acetone de-
rivatives were unsuitable for these reactions. None of the
expected products could be detected in reactions with hy-
droxyacetone, dihydroxyactone, diacetoxyacetone, or
methoxyacetone (Table 2, entries 6–9); products derived
from acetalization were isolated.
Entry
R
Compd
5a
Time
1 min
4 min
1 min
4 d
Yield (%)
1
2
3
4
5
6
7
8
p-NO2C6H4
p-ClC6H4
p-MeOC6H4
3,4-(MeO)2-C6H3
p-HOC6H4
C6H5CH=CH
c-Hex
74
97
5b
5c
100
100
–
5d
5e
4 d
5f
3 min
24 h
4 d
90
5g
95
O
O
LiClO4
Et3N
i-Pr
5h
100
+
R
R
RCHO
a General Procedure A.
4a–h
3a–h
Scheme 3
Finally, we reacted a range of aldehydes with cyclopen-
tanone as the ene component and found cyclopentanone to
be an even better ene component than acetone (Scheme 4,
Table 4). Overall, reactions were faster, yields were high-
er, and the range of suitable aldehydes increased, in par-
ticular, the reactions of both 3,4-dimethoxybenzaldehyde
(3d; compare Table 3, entry 4 with Table 4, entry 4) and
cyclohexylcarboxyladehyde (3g; compare Table 3, entry
7 with Table 4, entry 7) were much improved. As expect-
ed, p-hydroxybenzaldehyde 3e did not react at all under
these conditions (Table 4, entry 5). Also the self-conden-
sation of cyclopentanone was very slow, after a reaction
time of 11 days at room temperature cyclopentylidenecy-
clopentanone was obtained in 70% yield. This is in con-
trast with the acetone series (Table 3), where we did not
observe self-condensation of acetone.
Table 3 Reactions of a Range of Aldehydes with Acetone in the
Presence of LiClO4 and Et3Na
Entry
R
Compd
4a
Time
30 min
4 min
5 min
4 d
Yield (%)
1
2
3
4
5
6
7
8
p-NO2C6H4
p-ClC6H4
p-MeOC6H4
62
94
92
50
–
4b
4c
3,4-(MeO)2C6H3 4d
p-HOC6H4
C6H5CH=CH-
c-Hex
4e
2 d
4f
30 min
4 d
57
12
97
4gb
4h
In conclusion, we have demonstrated convincingly that
LiClO4 and amines can be used as catalysts in aldol con-
densation processes. This method works even in the pres-
i-Pr
4 d
a General Procedure A.
b General Procedure B.
Synthesis 2006, No. 7, 1099–1102 © Thieme Stuttgart · New York

PAPER
Amine-Catalyzed Aldol Condensation
1101
(1E,4E)-1,5-Bis(4¢-nitrophenyl)penta-1,4-dien-3-one (4a)9h
ence of enolizable aldehydes resulting in quantitative
yields. The mild, very rapid, and clean performance of
these reactions is an advantage over previously described
procedure. Products were obtained with a high degree of
purity and no chromatographic procedures were necessary
for further purification. Analytically pure compounds
were obtained by one recrystallization of the crude reac-
tion mixture.
1H NMR: d = 8.27 (d, J = 15.6 Hz, 2 H), 7.90 (d, J = 7.6 Hz, 4 H),
7.69 (m, J = 8.2 Hz, 4 H), 7.27 (d, J = 15.6 Hz, 2 H).
13C NMR: d = 189.2, 149.5, 142.5, 142.2, 131.0, 131.4, 125.4.
(1E,4E)-1,5-Bis(4¢-chlorophenyl)penta-1,4-dien-3-one (4b)9h
1H NMR: d = 7.69 (d, J = 15.9 Hz, 2 H), 7.57 (d, J = 8.5 Hz, 4 H),
7.42 (t, J = 5.8 Hz, 4 H), 6.98 (d, J = 15.9 Hz, 2 H).
13C NMR: d = 189.3, 142.7, 136.1, 133.5, 129.5, 129.2, 125.1.
(1E,4E)-1,5-Bis(4¢-methoxyphenyl)penta-1,4-dien-3-one (4c)9h
1H NMR: d = 7.70 (d, J = 15.8 Hz, 2 H), 7.54 (m, J = 8.5 Hz, 4 H),
6.94 (d, J = 15.8 Hz, 2 H), 6.90 (d, J = 7.2 Hz, 4 H), 3.81 (s, 6 H).
13C NMR: d = 204.3, 160.0, 140.5, 128.4, 126.8, 121.9, 112.7, 53.7.
Aldehydes were distilled before use. Products were purified by re-
crystallization (CH2Cl2) with the exception of 2e (flash chromatog-
raphy, hexane–EtOAc, 8:2). LiClO4 was dried at 120 °C in vacuo
for 10 h before use.11
1H NMR and 13C NMR spectra were recorded at 300 and 75 MHz,
respectively, in CDCl3, on a AC-300 spectrometer. Chemical shifts
are given in ppm. TLC was carried out with Merck Silica Gel 60
F254 TLC plates. Yields are not optimized and are relative to the
amount of aldehyde.
(1E,4E)-1,5-Bis(3¢,4¢-dimethoxyphenyl)penta-1,4-dien-3-one
(4d)14
1H NMR: d = 7.61 (d, J = 15.8 Hz, 2 H, =CH), 7.12 (dd, J = 1.9, 8.3
Hz, 2 H, o-Ph), 7.06 (d, J = 1.9 Hz, 2 H, m-Ph), 6.88 (d, J = 15.8
Hz, 2 H, =CH), 6.80 (d, J = 8.3 Hz, 2 H, o-Ph), 3.86 (s, 6 H, OMe),
3.84 (s, 6 H, OMe).
General Procedure A
To a solution of LiClO4 (1.1 g, 10 mmol), aldehyde (10 mmol), and
ketone (5 mmol), Et3N (0.14 mL, 1 mmol) was added. The reaction
mixture was stirred at r.t. and monitored by TLC. When the reaction
was complete a sat. aq solution of NH4Cl (30 mL) was added and
the resulting mixture was extracted with CH2Cl2 (100 mL). The or-
ganic layer was dried over MgSO4 and the solvent was removed in
vacuo to give the crude product.
13C NMR: d = 188.6, 151.3, 149.2, 143.0, 127.8, 123.6, 123.1,
111.1, 109.8, 56.0, 55.9.
(1E,3E,6E,8E)-1,9-Diphenylnona-1,3,6,8-tetraen-5-one (4f)15
1H NMR: d = 7.51–7.44 (m, 6 H), 7.38–7.29 (m, 6 H), 6.95 (d, J =
8.8 Hz, 4 H), 6.56 (d, J = 14.9 Hz, 2 H).
13C NMR: d = 189.0, 143.0, 141.5, 136.1, 129.2, 129.0, 128.8,
127.2, 127.0.
General Procedure B
To a solution of LiClO4 (1.1 g, 10 mmol), aldehyde (10 mmol), and
ketone (5 mmol) in toluene (10 mL), Et3N (0.14 mL, 1 mmol) was
added. The reaction mixture was refluxed and monitored by TLC.
When the reaction was complete a sat. aq solution of NH4Cl (30
mL) was added and the resulting mixture was extracted with CH2Cl2
(100 mL). The organic layer was dried over MgSO4 and the solvent
was removed in vacuo to give the crude product.
MS: m/z (%) = 286 (67), 258 (18), 195 (28), 128 (100), 91 (42), 77
(49), 51 (31).
(1E,4E)-Dicyclohexylideneacetone (4g)
IR (KBr): 2923, 1728, 1664, 1631, 1611, 1333, 1313, 1276, 983
cm–1.
1H NMR: d = 6.81 (dd, J = 6.8, 15.8 Hz, 2 H), 6.25 (dd, J = 1.1, 15.8
Hz, 2 H), 2.20–1.05 (m, 22 H).
13C NMR: d = 190.3, 152.7, 126.2, 40.8, 31.8, 25.9, 25.7.
HRMS: m/z calcd for C17H26O (M+): 246.1984; found: 246.1985
(1E,4E)-Dibenzylideneacetone (2a)9h
1H NMR: d = 7.75 (d, J = 16.0 Hz, 2 H), 7.61 (m, 4 H), 7.42 (m, 6
H), 7.09 (d, J = 16.0 Hz, 2 H).
13C NMR: d = 189.0, 143.4, 134.9, 130.6, 129.0, 128.5, 125.5.
(3E,6E)-2,8-Dimethylnona-3,6-dien-5-one (4h)16
1H NMR: d = 6.85 (dd, J = 15.7, 6.4 Hz, 2 H), 6.26 (dd, J = 15.8, 1.5
Hz, 2 H), 2.47 (qd, J = 6.8, 1.5 Hz, 2 H), 1.06 (d, J = 6.8 Hz, 12 H,
Me).
Dibenzylidenecyclopentanone (2b)9g
1H NMR: d = 7.60–7.58 (m, 6 H), 7.45–7.35 (m, 6 H), 3.12 (s, 4 H).
13C NMR: d = 188.1, 144.4, 142.3, 133.3, 128.5, 127.5, 126.7, 22.6.
13C NMR: d = 190.2, 153.9, 125.7, 31.1, 21.2.
Dibenzylidenecyclohexanone (2c)10
1H NMR: d = 7.67–7.11 (m, 12 H), 2.78–2.66 (m, 4 H), 1.63–1.51
(m, 2 H).
MS: m/z (%) = 166 (13), 124 (15), 97 (97), 56 (50), 43 (71), 71
(100).
2,5-Bis(4¢-nitrobenzylidene)cyclopentanone (5a)9g
1H NMR: d = 8.32–8.26 (m, 4 H), 7.76–7.69 (m, 4 H), 7.63 (s, 2 H,
=CH), 3.18 (m, 4 H).
13C NMR: d = 196.6, 148.5, 143.0, 142.7, 133.0, 131.9, 125.2, 27.4
13C NMR: d = 190.1, 136.9, 136.2, 136.0, 130.5, 128.7, 128.5, 28.5,
23.0.
(1E)-2-Methyl-1,5-diphenylpenta-1,4-dien-3-one (2d)12
1H NMR: d = 7.62–7.20 (m, 13 H), 2.26 (d, J = 1.5 Hz, 3 H).
13C NMR: d = 192.6, 143.3, 138.6, 138.4, 135.9, 135.0, 134.5,
130.3, 129.7, 128.8, 128.4, 128.2, 121.8, 13.7.
2,5-Bis(4¢-chlorobenzylidene)cyclopentanone (5b)9g
1H NMR: d = 7.47–7.45 (m, 6 H), 7.35–7.33 (m, 4 H), 3.00 (m, 4 H).
13C NMR: d = 195.9, 137.5, 135.4, 134.2, 132.7, 131.8, 129.1, 26.4.
2,4-Dimethyl-1,5-diphenylpenta-1,4-dien-3-one (2e)13
1H NMR: d = 7.48–7.36 (m, 12 H), 2.07 (d, J = 1.1 Hz, 6 H).
2,5-Bis(4¢-methoxybenzylidene)cyclopentanone (5c)9g
1H NMR: d = 7.59–7.51 (m, 6 H), 6.97–6.89 (m, 4 H), 3.83 (s, 6 H,
OMe), 3.06 (m, 4 H).
13C NMR: d = 195.7, 149.9, 137.4, 130.0, 128.7, 128.4, 128.1, 10.9.
13C NMR: d = 196.3, 160.5, 135.3, 133.3, 132.5, 128.7, 114.3, 55.4,
26.4.
Synthesis 2006, No. 7, 1099–1102 © Thieme Stuttgart · New York

1102
A. Arnold et al.
PAPER
2,5-Bis(3¢,4¢-dimethoxybenzylidene)cyclopentanone (5d)17
1H NMR: d = 7.55 (s, 2 H), 7.22 (dd, J = 1.9, 8.3 Hz, 2 H), 7.12 (d,
J = 1.9 Hz, 2 H), 6.92 (d, J = 8.3 Hz, 2 H), 3.92 (s, 12 H), 3.10 (s, 4
H).
13C NMR: d = 196.1, 150.3, 148.9, 135.4, 133.7, 129.0, 124.6,
113.4, 111.2, 56.0, 55.9, 26.5.
(2) Deli, J.; Lorand, T.; Szabo, D.; Foldesi, A. Pharmazie 1984,
39, 539.
(3) Kishore, G.; Kishore, K. Polymer 1995, 36, 1903.
(4) (a) Adams, K. B.; Ferstl, E. M.; Davis, M. C.; Herold, M.;
Kurtkaya, S.; Camalier, R. F.; Hollingshead, M. G.; Kaur,
G.; Sausville, E. A.; Rickles, F. R.; Snyder, J. P.; Liotta, D.
C.; Shoji, M. Bioorg. Med. Chem. 2004, 12, 3871.
(b) Robinson, T. P.; Hubbard, R. B.; Ehlers, T. J.; Arbiser, J.
L.; Goldsmith, D. J.; Bown, J. P. Bioorg. Med. Chem. 2005,
13, 4007.
(5) Clarke, T. P.; Höppe, H. A. F.; Lloyd-Jones, G. C.; Murray,
M.; Peakman, T. M.; Stentiford, R. A.; Walsh, K. E.;
Worthington, P. A. Eur. J. Org. Chem. 2000, 963.
(6) Arcadi, A.; Bianchi, G.; Chiarini, M.; Dànniballe, G.;
Marinelli, F. Synlett 2004, 944.
2,5-Bis(3´-phenylallylidene)cyclopentanone (5f)9d
1H NMR: d = 7.49 (d, J = 7.0 Hz, 4 H), 7.38–7.26 (m, 8 H), 6.97 (d,
J = 6.8 Hz, 4 H), 2.90 (s, 4 H).
13C NMR: d = 188.7, 141.3, 139.8, 136.6, 132.7, 129.0, 128.8,
127.2, 124.7, 23.9.
MS: m/z (%) = 312 (80), 286 (42), 105 (82), 77 (77), 51 (37), 91
(100).
(7) Fairlamb, I. J. S.; Kapdi, A. R.; Lee, A. F. Org. Lett. 2004,
2,5-Dicyclohexylidenecyclopentanone (5g)18
6, 4435.
1H NMR: d = 6.44 (d, J = 9.4 Hz, 2 H), 2.55 (s, 4 H), 2.21–2.08 (m,
2 H, CH), 1.73–1.54 (m, 8 H), 1.31–1.04 (m, 12 H).
(8) Compound 4d: 1 g costs 600 $ (TRC Biomedical Research
Chemicals).
(9) (a) Ti(OR)4: Mahrwald, R.; Schick, H. Synthesis 1990, 592.
(b) RuCl3: Iranpoor, N.; Kazemi, F. Tetrahedron 1998, 54,
9475. (c) SmI3: Bao, W. L.; Zhang, Y. M. Youji Huaxue
1998, 18, 272. (d) FeCl3: Zhang Fan, X. S.; Niu, H. Y.;
Wang, J. J. Green Chem. 2003, 5, 267. (e) BF3·Et2O:
Huang, D. F.; Wang, J. X.; Hu, Y. L. Chem. Lett. 2003, 14,
333. (f) InCl3: Deng, G.; Ren, T. Synth. Commun. 2003, 33,
2995. (g) Yb(OTf)3: Wang, L.; Scheng, J.; Han, H. T.; Fan,
Z.; Qian, C. Synthesis 2004, 3060. (h) For NaOH/H2O-
system, see: Fairlamb, I. J. S. SyntheticPages 2004, 221.
(10) Markert, M.; Mahrwald, R. Synthesis 2004, 1429.
(11) For safety information, see: Armarego, W. L. F.; Perrin, D.
D. Purification of Laboratory Chemicals; Butterworth-
Heinemann: Oxford, 1997.
13C NMR: d = 195.7, 142.1, 137.2, 38.7, 31.6, 25.8, 25.5, 23.2.
MS: m/z (%) = 272 (100), 229 (15), 177 (73), 41 (61).
2,5-Diisobutylidenecyclopentanone (5h)
IR (KBr): 2872, 2731, 2670, 1708, 1644, 1465, 1385, 1167, 962
cm–1.
1H NMR: d = 6.43 (d, J = 9.8 Hz, 2 H), 2.55 (s, 4 H, CH2), 2.52–
2.37 (m, 2 H, CH), 0.98 (d, J = 6.8 Hz, 12 H, Me).
13C NMR: d = 195.8, 143.8, 136.7, 28.9, 23.0, 21.6.
MS: m/z (%) = 192 (42), 177 (74), 43 (100).
HRMS: m/z calcd for C13H20O (M+): 192.1514; found: 192.1515.
(12) Ramalingam, K.; Berlin, K. D.; Satyamurthy, N.;
Sivakumar, R. J. Org. Chem. 1979, 44, 471.
(13) Shoppee, C. W.; Cooke, B. J. A. J. Chem. Soc., Perkin
Trans. 1 1973, 1026.
(14) (a) Wattanasin, S.; Murphy, W. S. Synthesis 1980, 647.
(b) Suarez, J. A. Q.; Peseke, K.; Kordian, M.; Carvalho, J.
E.; Kohn, L. K.; Antonio, M. A.; Brunhari, H. PCT Int. Appl.
2004047716, 2004 (4d, 87% yield).
2-Cyclopentylidenecyclopentanone19
1H NMR: d = 2.68 (m, 2 H), 2.52 (m, 2 H), 2.28 (m, 2 H), 2.23 (m,
2 H), 1.85 (m, 2 H), 1.66 (m, 4 H).
13C NMR: d = 206.9, 158.3, 127.9, 39.7, 34.3, 32.5, 29.6, 27.0, 25.3,
20.1.
Acknowledgment
(15) Thiele, G.; Streitwieser, A. J. Am. Chem. Soc. 1994, 116,
446.
The authors would like to thank the Deutsche Forschungsgemein-
schaft for its financial support.
(16) (a) Ocafrain, M.; Devaud, M.; Troupel, M.; Perichon, J. J.
Chem. Soc., Chem. Commun. 1995, 2331. (b) Binder, J.;
Zbiral, E. Tetrahedron Lett. 1984, 25, 4213.
(17) Frey, H.; Behmann, G.; Kaupp, G. Chem. Ber. 1987, 120,
387.
(18) Kaupp, G.; Frey, H.; Behmann, G. Chem. Ber. 1988, 121,
2127.
(19) Eldin, S.; Whalen, D. L.; Pollack, R. M. J. Org. Chem. 1993,
58, 7100.
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Synthesis 2006, No. 7, 1099–1102 © Thieme Stuttgart · New York