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DOI: 10.1055/s-2002-32957
A New Protocol for a One-pot Synthesis of α-Amino Phosphonates by Reaction of Imines Prepared In Situ with Trialkylphosphites
Publication History
Publication Date:
25 July 2002 (online)
Abstract
Imines prepared in situ by reaction of aldehydes and ketones with primary amines in ethereal solution of LiClO4 react readily at ambient temperature with trialkylphosphite to give high yields of α-amino phosphonates.
Key words
amino phosphonate - imine - trialkylphosphite - lithium perchlorate
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References
General Procedure
for the Preparation of α-Amino Phosphonates 4. 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.
Then a primary amine
(3.0 mmol) and TMSCl (2.0 mmol) were
added via a syringe. After 10 min, trimethyl-phosphite or triethyl-phosphite
(2.5 mmol) was added and the mixture was stirred at r.t. for about
15 min. Then water (20 mL) and CH2Cl2 (20 mL)
were added. The organic phase was separated, dried over MgSO4,
and the solvent was removed. Almost pure crude product obtained.
Further purification was carried out by column chromatography on
basic alumina eluting with petroleum ether/EtOAc, if needed.
All compounds were characterized on the basis of spectroscopic data
(IR, NMR, MS) and comparison with those reported in the literature. Caution: Although we did not have any accident
while using LiClO4, it is advisable to dry lithium perchlorate
in a fume hood using a suitable lab-shield.
Selected spectral data. 4a: IR (KBr): 3304 cm-1 (NH).
1H
NMR (CDCl3, 500 MHz): δ = 3.48 (d,
3 H, J = 6.1
Hz), 3.78 (d, 3 H, J = 10.7
Hz), 4.50 (br s, 1H, NH), 4.83 (d, 1 H, J = 24.3),
6.61-6.72 (m, 3 H), 7.28-7.50 (m, 7 H). 13C
NMR (CDCl3, 125 MHz): δ = 53.68 (d,
²
J
PC = 6.6
Hz), 54.2 (d,
²
J
PC = 7.6
Hz), 55.6 (d,
¹
J
PC = 150.6
Hz), 114.2, 119.2, 123.4, 129.0, 129.8 (d, J
PC = 4.5
Hz), 130.2, 135.9 (d, J
PC = 2.5
Hz), 146.4 (d, J
PC = 14.7
Hz). 4c: IR (KBr): 3314 cm-1 (NH). 1H
NMR (CDCl3, 500 MHz): δ = 3.55 (d,
3 H, J = 10.6
Hz), 3.78 (d, 3 H, J = 10.7),
4.83 (d, 1 H, J = 24.6 Hz),
4.85 (br s, 1 H, NH), 6.62-7.46 (m, 9 H). 13C
NMR (CDCl3, 125 MHz): δ = 53.70 (d,
²
J
PC = 6.6
Hz), 54.2 (d,
²
J
PC = 6.0
Hz) 55.02 (d,
¹
J
PC = 154
Hz), 114.0, 119.1, 129.0, 129.6 (d, J
PC = 8.1),
129.9, 130.2, 134.2 (d, J
PC = 3.9
Hz), 146.4 (d, J
PC = 15.0
Hz). 4g: IR (KBr): 3325 cm-1 (NH). 1H NMR
(CDCl3, 500 MHz): δ = 3.64 (d, 3 H, J = 10.7 Hz), 3.83
(3 H, J = 10.7
Hz), 4.99 (d, 1 H, J = 25.0 Hz), 5.12 (br s,
1 H, NH), 6.62-6.73 (m, 3 H), 7.11-7.13 (m, 2
H), 7.88-8.40 (m, 4 H). 13C
NMR (CDCl3, 125 MHz): δ = 54.1 (d,
²
J
PC = 6.8
Hz), 54.6 (d,
²
J
PC = 5.9
Hz), 54.8 (d,
¹
J
PC = 155.0 Hz),
114.2 (d, J
PC = 11.2
Hz), 119.3 (d, J
PC = 11.4
Hz), 123.2, 129.7 (d, J
PC = 4.5
Hz), 130.0 (d, J
PC = 11.2
Hz), 134.3 (d, J
PC = 3.9
Hz), 139.9, 145.9 (d, J
PC = 13.8
Hz), 148.9 (d, J
PC = 2.5
Hz). 4n: IR (KBr): 3300 cm-1 (NH). 1H NMR
(CDCl3, 500 MHz): δ = 0.77 (t, 3 H, J = 6.9 Hz),
1.37 (t, 3 H, J = 7.0
Hz), 3.26 (m, 1 H), 3.79 (m, 1 H), 4.26 (m, 2 H), 5.01 (br s, 1
H, NH), 5.75 (d, 1 H, J = 24.1
Hz), 6.63-6.70 (m, 3 H), 7.06-7.09 (m, 2 H), 7.45-7.93
(m, 6 H), 8.33-8.35 (m, 1 H). 13C
NMR (CDCl3, 125 MHz): δ = 16.3 (d,
³
J
PC = 2.3
Hz) 17.0 (d,
³
J
PC = 5.8
Hz), 51.8 (d,
¹
J
PC = 151 Hz),
63.6 (d,
²
J
PC = 6.5
Hz), 63.9 (d,
²
J
PC = 5.8
Hz), 113.9, 114.1, 118.6, 123.4 (d, J
PC = 6.6
Hz), 126.2, 126.2, 126.7, 128.8, 129.0, 129.4, 129.6 (d, J
PC = 10.6
Hz), 132.0 (d, J
PC = 5.0)
134.3, 146.6 (d, J
PC = 14.5
Hz). 4u: IR (KBr): 3320 cm-1 (NH). 1H
NMR (CDCl3, 500 MHz): δ = 1.13-2.13 (m,
10 H), 3.45(br s, NH), 3.54 (d, 6 H, J = 10.2
Hz), 6.66-7.05 (m, 5 H). 13C
NMR (CDCl3, 125 MHz): δ = 20.2 (d, J
PC = 10.5
Hz), 25.6, 30.5, 53.3 (d, J
PC = 7.7 Hz), 58.1 (d, J
PC = 159.0
Hz), 118.6 (d, J
PC = 10.5
Hz), 119.6 (d, J
PC = 13.2
Hz), 129.0 (d, J
PC = 6.7
Hz), 146.1.