Aminosilylation of aldehydes mediated by lithium perchlorate: Novel method for synthesis of α-silylamines

Article abstract of DOI:10.1039/a904498a

α-Silylated N,N-dialkylamines 7a-k were easily synthesized in good to excellent yields from aldehydes 1, (trimethylsilyl)dialkylamines 2, and phenyldimethylsilyllithium 4, diphenylmethylsilyllithium 5, or triphenylsilyllithium 6, in concentrated ethereal

Full text of DOI:10.1039/a904498a

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Aminosilylation of aldehydes mediated by lithium perchlorate:
novel method for synthesis of ꢀ-silylamines
M. Reza Naimi-Jamal,ab Mohammad M. Mojtahedi,b Junes Ipaktschia and
Mohammad R. Saidi*b
a Institut für Organische Chemie der Universität Giessen, Heinrich-Buff-Ring 58, D-35392,
Giessen, Germany. E-mail: junes.ipaktschi@org.chemie.uni-giessen.de
b Department of Chemistry, Sharif University of Technology, P.O. Box 11356-9516, Teheran,
I. R. of Iran. E-mail: saidi@ch.sharif.ac.ir
Received (in Cambridge, UK) 7th June 1999, Accepted 1st October 1999
α-Silylated N,N-dialkylamines 7a–k were easily synthesized in good to excellent yields from aldehydes
1, (trimethylsilyl)dialkylamines 2, and phenyldimethylsilyllithium 4, diphenylmethylsilyllithium 5, or
triphenylsilyllithium 6, in concentrated ethereal lithium perchlorate solution.
Introduction
Development of new synthetic methods for the preparation of
organosilicon compounds continues to attract much attention.
Organosilylmetallic compounds are useful reagents for con-
structing silicon–carbon bonds.1,2 For many years alkylaryl-
silyllithium compounds have been used as nucleophiles for
introducing a silyl group into a wide range of organic struc-
tures.3 On the other hand, α-silylamines are important reagents
in organic synthesis. For example, lithiated allylaminosilanes of
Scheme 1
the type A show high regioselectivity in addition reactions4,5
silyl-, diphenylmethylsilyl-, or triphenylsilyllithium proceeds
smoothly in the same manner, to give the corresponding α-silyl
amines.
Presumably due to the Lewis acidity of lithium ions and the
high polarity of the medium, the reaction of 2 with aldehydes
in a 5 M lithium perchlorate diethyl ether solution leads to the
formation of an iminium salt 3 as the intermediate,17,18 which is
trapped in situ by the organosilyllithium nucleophiles. Due to
the mild reaction conditions, no by-products are formed.
This protocol can also be applied to enolisable aldehydes
such as isobutyraldehyde, but the yields are lower for these
aldehydes. In these cases, the yield of the reaction is lowered by
the formation of enamine as side-product in the iminium ion
formation step. The results are summarized in Table 1.
To extend this method for the preparation of α-trimethyl-
silylamines, hexamethyldisilane was treated with methyllithium
solution in ether in HMPT, according to the procedure
described in the literature.19 The resulting red solution was
added to the in situ preformed iminium salts 3. After aqueous
work-up, in contrast to the above results, no α-trimethylsilyl-
amine could be detected as the product, but instead, compound
8 was isolated as the sole product in good yield. The reaction
was carried out with benzaldehyde and (o-methyl)benzaldehyde
several times, and the same results were obtained with 80 and
75% yields, respectively. Compound 8a and 8b were identified
to be phosphonic diamide, by their 1H-, 13C-NMR, IR and MS
spectra by comparison with those in the literature for 8a
(Scheme 2).20
and chiral (lithiomethyl)aminosilanes of the type B induce high
diastereoselectivity in these reactions.6 α-Silylamines were also
reacted with aldehydes in the synthesis of β-amino alcohols.7
Despite these interesting and important applications, only a few
methods are reported for preparing these compounds, such
as, reaction of amides with lithiated silanes,8–11 amination of
α-bromoalkylsilanes,7,12 reaction of Grignard reagents with
α-amino-α-cyanoalkylsilanes,13 reductive silylation of imines,14
reaction of lithiosilanes with methyleneiminium salts,15 and
reaction of lithiomethylamines with chlorosilanes.16 These
methods suffer from the difficulty of preparing the starting
materials, low yields, or are restricted to aminomethylation of
silanes.
In this paper, we describe the one-pot three-component syn-
thesis of a variety of α-silylated N,N-dialkylamines 7a–k by the
addition of phenyldimethylsilyllithium 4, diphenylmethylsilyl-
lithium 5, or triphenylsilyllithium 6, to aldehydes 1, (enolizable
and non-enolizable) and (trimethylsilyl)dialkylamines 2, in a
5 M ethereal LiClO4 solution.
Results
Therefore, this procedure can serve as a new method for the
preparation of α-dialkylamino phosphonic diamides, 8.
Aldehyde 1, (trimethylsilyl)dialkylamines 2, and organosilyl-
lithium compounds in a 5 M ethereal LiClO4 solution, followed
by aqueous work-up, leads to the formation of α-silylated
N,N-dialkylamines 7a–k, within 30 min in good to excellent
yields (Scheme 1). Therefore, reaction of dimethylphenyl-
Experimental
Elemental Analysis: Carlo Erba Model 1104. IR spectra were
J. Chem. Soc., Perkin Trans. 1, 1999, 3709–3711
This journal is © The Royal Society of Chemistry 1999
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Table 1 α-Aminosilylation of aldehydes
removed by means of rotary evaporator. The crude material
was further purified by chromatography on basic alumina or
aqueous acid extraction, if needed.
Starting
aldehyde
α-Silyl
amine
Yield
(%)
Entry
1
(Dimethylphenylsilyl)(o-methylphenyl)-N,N-dimethylmethan-
amine 7a23
Oil; IR νmax (film)/cmϪ1 1248.4 (Si-Me), 1111.2 (Si-Ph). δH 0.01
(s, 3H), 0.47 (s, 3H), 2.19 (s, 9H, PhMe, NMe2), 3.27 (s, 1H),
7.00–7.51 (m, 9H). δC Ϫ4.57 (CH3), Ϫ2.06 (CH3), 20.38 (CH3),
47.10 (CH3), 61.56 (CH), 125.18 (CH), 125.95 (CH), 127.51
(CH), 128.11 (CH), 128.70 (CH), 130.06 (CH), 133.80 (CH),
135.00 (C), 139.08 (C), 140.93 (C). MS (70 eV) m/z (%) 283
(Mϩ, 1.8), 149 (12.5), 148 (100), 137 (5.4), 135 (3), 105 (6.6).
C18H25NSi, M 283.
74
2
3
95
95
4
83
(Diphenylmethylsilyl)phenyl(pyrrolidino)methane 7b
Oil; IR νmax (film)/cmϪ1 1426.9 (s), 1248.6 (Si-Me), 1110.8 (Si-
Ph). δH 0.41 (s, 3H), 1.57–1.67 (m, 4H), 2.32–2.45 (m, 4H), 3.44
(s, 1H), 7.00–7.80 (m, 15H). δC Ϫ4.38 (CH3), 23.46 (CH2), 55.49
(CH2), 63.98 (CH), 125.43 (CH), 127.36 (CH), 127.68 (CH),
127.72 (CH), 128.50 (CH), 128.72 (CH), 129.24 (CH), 134.72
(CH), 135.35 (C), 135.41 (CH), 137.63 (C), 142.26 (C). MS (70
eV) m/z (%) 357 (Mϩ, 1.3), 199 (2.3), 197 (2.9), 161 (13.0), 160
(100), 91 (10.7). C24H27NSi, calcd. 357.1913; found 357.1907
(HRMS). C24H27NSi (357.2): calcd. C 80.66, H 7.56, N 3.92;
found C 80.65, H 7.68, N 4.11%.
5
6
70
50
7
8
80
70
9
76
(Diphenylmethylsilyl)(o-methylphenyl)-N,N-dimethylmethan-
amine 7c23
10
11
8022
85
Mp 84–85 ЊC. IR νmax (KBr)/cmϪ1 1250.7 (s, Si-Me), 1067.9
(s, Si-Ph). δH 0.50 (s, 3H), 1.90 (s, 3H), 2.20 (s, 6H), 3.60
(s, 1H), 6.8–7.8 (m, 14H). δC Ϫ5.17 (CH3), 20.16 (CH3), 47.42
(CH3), 60.42 (CH), 125.33 (CH), 125.87 (CH), 127.10
(CH), 127.79 (CH), 128.55 (CH), 128.67 (CH), 129.24 (CH),
130.05 (CH), 134.95 (CH), 135.11 (CH), 135.56 (C), 136.16 (C),
136.99 (C), 140.17 (C). MS (70 eV) m/z (%) 345 (Mϩ, 1.4), 197
(2.2), 149 (11.5), 148 (100), 132 (2.7), 118 (1.5). C23H27NSi, M
345.
(Diphenylmethylsilyl)(o-methylphenyl)-N,N-dimethylmethan-
amine, hydrochloride 7d23
Mp 189 ЊC (decomposed). IR νmax (KBr)/cmϪ1 1428 (s), 1265 (s,
Si-Me), 1106 (s, Si-Ph), 792 (s), 736 (s), 700 (s). δH 1.20 (s, 3H),
0.47 (s, 3H), 1.82 (s, 3H), 2.66 (dd, 6H, J 4.3, 15.5 Hz), 4.38
(d, 1H, J 9.8 Hz), 6.7–8.3 (m, 14H), 12.1–12.4 (br, 1H, NϩH).
δC Ϫ6.30 (CH3), 19.85 (CH3), 44.88 (CH3), 46.22 (CH3), 61.05
(CH), 127.36 (CH), 127.70 (CH), 128.24 (CH), 128.67 (CH),
128.90 (CH), 129.80 (CH), 130.67 (CH), 130.93 (CH), 131.83
(C), 132.29 (C), 133.56 (C), 134.66 (CH), 135.07 (CH), 135.76
(C).
Scheme 2
taken on Bruker IFS 25 and Matt Son 1000 Unicam FTIR
spectrophotometers. 1H and 13C NMR were recorded on Bruker
AM 400, AC 200 and AC 80 spectrometers in CDCl3. Mass
spectra were obtained on Varian MAT 311A, Varian MAT 111
or Fisson 800 Trio spectrometers. LiClO4 (Fluka) was dried
at 140 ЊC for 24 h at 10Ϫ2 Torr. The silyllithium nucleophiles
were prepared according to the procedure reported in the
literature.2,21,22
(Diphenylmethylsilyl)phenyl-N,N-dimethylmethanamine,
hydrochloride 7e
Mp 188 ЊC. δH 1.00 (s, 3H), 2.55 (d, 3H), 2.65 (d, 3H), 4.90
(d, 1H), 7.0–7.6 (m, 13H), 7.0 (m, 2H), 12.35 (br, 1H). δC Ϫ6.18
(CH3), 45.14 (CH3), 46.16 (CH3), 66.47 (CH), 127.74 (CH),
128.28 (CH), 128.83 (CH), 129.16 (CH), 129.31 (CH), 129.84
(CH), 130.66 (CH), 132.42 (CH), 133.23 (C), 133.36 (C), 134.71
(C), 134.73 (CH). C22H26ClNSi, calcd. C 71.79, H 7.13; found C
71.70, H 7.13%.
CAUTION: Although we did not have any accident using
lithium perchlorate (LiClO4), it is advisable to dry lithium
perchlorate in a hood behind a lab-shield.
General procedure for the preparation of ꢀ-silylamines from
aldehydes
The aldehyde (2 mmol) and 4 ml of 5 M LiClO4 in diethyl ether
were placed in a 50 ml flask under argon and stirred for 5 min.
(Trimethylsilyl)dialkylamine (3 mmol) was then added via
syringe. After 10 min the silyllithium nucleophile (3 mmol) was
added and stirred for 15 min at room temperature. Then, water
(about 30 ml) and diethyl ether (30 ml) were added. The organic
phase was separated, dried with MgSO4, and the solvent was
1-(Triphenylsilyl)-2-methyl-1-(pyrrolidino)propane 7f
Oil; IR νmax (film)/cmϪ1 1106.9 (Si-Ph). δH 0.91 (d, 6H, J 6.4 Hz),
1.58 (m, 4H), 2.36 (m, 1H), 2.70 (m, 4H), 3.05 (d, 1H, J 6.8 Hz)
7.20–7.70 (m, 15H). δC 22.38 (CH3), 23.94 (CH3), 24.68 (CH2),
30.30 (CH), 52.45 (CH2), 57.57 (CH), 127.49 (CH), 128.92 (C),
136.43 (CH). MS (70 eV) m/z (%) 385 (Mϩ), 342 (1.4), 276
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(33.1), 259 (16.5), 199 (65.8), 181 (8.1), 126 (100), 77 (10.4).
43.13 (CH3), 43.22 (CH3), 59.68 (CH), 60.99 (CH), 125.25
C26H31NSi, M 385.
(CH), 127.38 (CH), 130.49 (CH), 130.87 (CH), 130.90 (CH),
131.77 (CH), 131.81 (CH), 136.88 (CH), 136.98 (C). MS (70 eV)
m/z (%) 283 (Mϩ), 198 (100), 132 (2.9), 105 (3.3), 91 (1.5), 44
(4.2), 126 (100), 77 (10.4). C14H26N3OP, M 283.
(Triphenylsilyl)phenyl(pyrrolidino)methane 7g
Mp 142–144 ЊC. IR νmax (KBr)/cmϪ1 1428 (m), 1101.5 (m, Si-
Ph), 697 (s), 525 (s). δH 1.71–1.61 (m, 4H), 2.30–2.48 (m, 4H),
3.71 (s, 1H), 6.97–7.44 (m, 20H). δC 23.50 (CH2), 55.80 (CH2),
63.90 (CH), 125.56 (CH), 127.45 (CH), 127.74 (CH), 129.15
(CH), 129.21 (CH), 134.59 (CH), 136.53 (C), 141.91 (C). MS
(70 eV) m/z (%) 419 (Mϩ), 259 (3), 181 (2), 160 (100), 91 (6).
C29H29NSi (419.2) calcd. C 83.05, H 6.91, N 3.34; found C
83.13, H 7.01, N 3.54%.
Acknowledgements
M. R. Naimi-Jamal gratefully acknowledge receipt of a grant
for a study visit from Deutscher Akademischer Austauchdienst,
DAAD, and staff of Justus-Liebig-Universität Giessen. We
thank “Volkswagen-Stiftung, Federal Republic of Germany”
for financial support towards the purchase of chemicals. M. R.
Saidi thanks the Iranian National Research Council for partial
financial support.
(Triphenylsilyl)(o-methylphenyl)-N,N-dimethylmethanamine
7h23
Mp 148–150 ЊC. IR νmax (KBr)/cmϪ1 1484.9 (m), 1427.3 (s),
1105.9 (s, Si-Ph), 745.6 (s), 700.8 (s). δH 1.73 (s, 3H), 2.25 (s,
6H), 3.87 (s, 1H), 6.75–7.77 (m, 19H). δC 19.98 (CH3), 48.14
(CH3), 61.05 (CH), 125.43 (CH), 125.97 (C), 127.43 (CH),
129.22 (CH), 129.90 (CH), 134.57 (C), 136.25 (C), 136.50 (CH),
139.93 (C). MS (70 eV) m/z (%) 407 (Mϩ), 259 (3), 181 (2), 148
(100), 132 (3), 105(4). C28H29NSi (407).
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7.00–7.83 (m, 9H). δC Ϫ1.52 (CH3), 21.18 (CH3), 64.68 (CH),
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methanamine 8b
Mp 79–81 ЊC. IR νmax (KBr)/cmϪ1 1204.1 (P᎐O), 978.5. δH 2.17
᎐
(d, 3H, JP-H 8.5 Hz), 2.29 (s, 6H), 2.31 (s, 3H), 2.66 (d, 6H, JP-H
9.09 Hz), 4.21 (d, 1H, JP-H 18.4 Hz), 7.81–7.08 (m, 4H). δC 20.28
(CH3), 36.09 (CH3), 36.13 (CH3), 36.63 (CH3), 36.65 (CH3),
Paper 9/04498A
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