α-Aminophosphonates and α-aminophosphine oxides by the microwave-assisted kabachnik-fields reactions of 3-amino-6-methyl-2 H-pyran-2-ones

Article abstract of DOI:10.1002/hc.21086

The microwave-assisted Kabachnik-Fields reaction of a series of 3-amino-6-methyl-2H-pyran-2-ones, paraformaldehyde, and dialkyl phosphites or diphenylphosphine oxide led to α-aminophosphonates or α- aminophosphine oxides, respectively. The α-aminophosphonates were obtained under solvent-free conditions, whereas the α-aminophosphine oxides in acetonitrile. The novel products were characterized by NMR and mass spectral data.

Full text of DOI:10.1002/hc.21086

Heteroatom Chemistry
Volume 24, Number 3, 2013
α-Aminophosphonates and
α-Aminophosphine Oxides by the
Microwave-Assisted Kabachnik–Fields
Reactions of 3-Amino-6-methyl-2
H-pyran-2-ones
Erika Ba´lint,1,2 Judit Taka´cs,1 La´szlo´ Drahos,3 Amadej Juranovicˇ,4
Marijan Kocˇevar,4 and Gyo¨rgy Keglevich1
1Department of Organic Chemistry and Technology, Budapest University of Technology and
Economics, 1521 Budapest, Hungary
2Research Group of the Hungarian Academy of Sciences, Department of Organic Chemistry and
Technology, Budapest University of Technology and Economics, 1521 Budapest, Hungary
3Hungarian Academy of Sciences, Chemical Research Center, 1525 Budapest, Hungary
4Faculty of Chemistry and Chemical Technology, University of Ljubljana, 1000 Ljubljana, Slovenia
Received 14 January 2013; revised 28 February 2013
ꢀC
spectral data.
2013 Wiley Periodicals, Inc.
ABSTRACT: The microwave-assisted Kabachnik–
Fields reaction of a series of 3-amino-6-methyl-
2H-pyran-2-ones, paraformaldehyde, and dialkyl
phosphites or diphenylphosphine oxide led to α-
aminophosphonates or α-aminophosphine oxides,
respectively. The α–aminophosphonates were ob-
tained under solvent-free conditions, whereas the α–
aminophosphine oxides in acetonitrile. The novel
products were characterized by NMR and mass
Heteroatom Chem. 24:221–225, 2013; View this
article online at wileyonlinelibrary.com. DOI
10.1002/hc.21086
INTRODUCTION
The most convenient and widespread method for
the synthesis of α-aminophosphonates involves the
condensation of a primary or secondary amine
with an aldehyde or ketone and a dialkyl phos-
phite [1–5]. This evergreen reaction leads to
α-aminophosphonates that are of real or potential
bioactivity [6–8].
Correspondence to: Gyo¨rgy Keglevich; e-mail: gkeglevich@
mail.bme.hu.
Contract grant sponsor: Slovenian–Hungarian Scientific
Research program.
The senior author of this article suggested that,
under microwave (MW) conditions, there is no
need to use environmentally unfriendly catalysts [9].
The Kabachnik–Fields (phospha-Mannich) conden-
sation was extended to heterocyclic amines [10] and
heterocyclic >P(O)H species [11]. Bis Kabachnik–
Fields reactions were also elaborated [12, 13], and
Contract grant numbers: BI-HU/11-12-005 and 2011-0637.
Contract grant sponsor: Hungarian Scientific Research Fund.
´
Contract grant numbers: OTKA K83118 and TAMOP-4.2.2.B-10/1-
2010-0009.
Contract grant sponsor: Slovenian Research Agency.
Contract grant number: P1-0230-0103.
ꢀC
2013 Wiley Periodicals, Inc.
221

222 Ba´lint et al.
TABLE 1 Condensations with 3-Amino-6-methyl-2H-pyran-
2-one (1)
the resulting bis(phosphinoxidomethyl)amines were
used in the synthesis of ring platinum complexes af-
ter double deoxygenation [13,14].
Entry
Y
T (◦C)
t (h)
Yield (%)
In the continuation, we wished to use 3-amino-
6-methyl-2H-pyran-2-ones as the starting materials
in the phospha-Mannich condensations. 2H-Pyran-
2-ones and their fused derivatives represent struc-
tural units of a wider range of natural products, their
synthetic analogues, and many other compounds
[15–19]. Furthermore, they are also very important
synthons and building blocks in organic synthesis
and have found a variety of synthetic applications:
in reactions with electrophiles and nucleophiles, as
diene components in the Diels–Alder reactions, in
photochemical reactions, etc. [20–29].
1
OEt
OBu
Ph
120
120
100
2.5
2.5
3
74 (2a)
88 (2b)
98 (2c)
2
3a
aIn acetonitrile.
Me
R
O
O
Y
Y
O
H
+
+
(HCHO)n
P
NH2
O
R = Me (3), Ph (4)
MW
T, t
No solvent
O
RESULTS AND DISCUSSION
Me
O
O
1
4
The starting materials 1 [30], 3, and 4 [31] were pre-
pared as described earlier.
6
5
2
3
Y
R
NH CH2
P
Y
O
R = Me (5), Ph (6)
Y = OMe (a), OEt (b), OBu (c), Ph (d)
Kabachnik–Fields Reaction of
3-Amino-6-methyl-2H-pyran-2-one
Formaldehyde and >P(O)H Reactants under
MW Conditions
SCHEME 2
In the first approach, the 5-unsubstituted 3-amino-
6-methyl-2H-pyran-2-one (1) was reacted with an
equivalent amount of paraformaldehyde and dialkyl
(diethyl or dibutyl) phosphites or diphenylphos-
phine oxide to afford the phosphonomethyl- or phos-
phinoylmethyl derivatives 2a/2b and 2c, respectively
(Scheme 1 and Table 1). The phosphinoylmethyla-
tion required somewhat milder conditions, although
it had to be carried out in acetonitrile as the solvent
due to the heterogenity. The other reactions did not
require the use of solvent. Products 2a–c were ob-
tained in 74–98% yields after chromatography.
Kabachnik–Fields Reaction of
5-Acetyl-3-amino-6-methyl-2H-pyran-2-one and
3-Amino-5-benzoyl-6-methyl-2H-pyran-2-one
Under MW Conditions
The Kabachnik–Fields condensations were extended
to the 5-acyl-substituted 3-amino-2H-pyran-2-ones
(3 and 4), as well. Reactions of the 5-acetyl start-
ing material (3) with paraformaldehyde and dialkyl
phosphites or diphenylphosphine oxide provided
products 5a–-c and 5d, respectively. The similar re-
action of the 5-benzoyl starting material furnished
products 6a and 6d (Scheme 2 and Table 2). The
phosphonomethyl products (5a–c and 6a) were ob-
tained without the use of any solvent, whereas the
phosphinoxidomethyl derivatives (5d and 6d) had
Me
O
O
Y
Y
O
H
(HCHO)n
+
+
P
NH2
1
TABLE 2 Condensations with 5-Keto-3-amino-6-methyl-2H-
pyran-2-ones 3 and 4
MW
T, t
No solvent
Entry
R
Y
T (◦C)
t (h)
Yield (%)
Me
O
O
1
2
Me
Me
Me
Me
Ph
Ph
OMe
OEt
OBu
Ph
OEt
Ph
120
120
120
100
120
100
1.5
2
2
2
4
90 (5a)
74 (5b)
91 (5c)
98 (5d)
61 (6a)
97 (6d)
1
4
6
5
2
3
O
Y
Y
3
P
NH CH2
2
4a
5
6a
2
Y = OEt (a), OBu (b), Ph (c)
SCHEME 1
aIn acetonitrile.
Heteroatom Chemistry DOI 10.1002/hc

α-Aminophosphonates and α-Aminophosphine Oxides by Microwave-Assisted Kabachnik–Fields Reactions 223
to be prepared in acetonitrile solution. After chro-
matography, the yields remain within the range of
61–98%.
0.25 mmol (0.0075 g) of paraformaldehyde, and 0.25
mmol of the >P(O)H species (0.023 mL of dimethyl
phosphite, 0.0325 mL of diethyl phosphite, 0.0488
mL of dibutyl phosphite, or 0.05 g of diphenylphos-
phine oxide) was heated at 120◦C in a closed vial in
a CEM Discover microwave reactor equipped with
a pressure controller for 1.5–2 h. The reaction with
diphenylphosphine oxide was carried out in 1.5 mL
of acetonitrile. The water formed was removed in
vacuum. Column chromatography (silica gel, 3%
methanol in dichloromethane) of the residue af-
forded the products (2a–c, 5a–d, and 6a, 6d) as oils.
The following products were thus prepared.
Products 2a–c, 5a–d, 6a, 6d, 7, and 8 were char-
1
acterized by 31P, 13C, and H NMR, as well as high-
resolution mass spectral data.
We tried to prepare bis(phospha-Mannich
adducts) by applying the formaldehyde and the
>P(O)H species in twofold quantities, but we failed.
When α-aminophosphonate 2a was further at-
tempted to react in the Kabachnik–Fields reaction,
it also remained unsuccessful.
Comparative Thermal Experiments
Diethyl [(6-Methyl-2-oxo-2H-pyran-3-yl)amino]
methylphosphonate (2a). Yield 74%; 31P NMR δ:
(CDCl3) 22.5; 13C NMR (CDCl3) δ: 16.5 (J = 5.6,
CH2CH3), 18.8 (C6 CH3), 39.6 (J = 158.8, CH2P),
62.6 (J = 6.8, OCH2), 103.6 (C5), 108.4 (J = 1.8, C4),
131.7 (J = 7.7, C3), 148.9 (C6), 160.9 (C O); 1H NMR
(CDCl3) δ: 1.33 (t, J = 7.1, 6H, CH2CH3), 2.17 (s, 1H,
NH), 2.17 (s, 3H, C6 CH3), 3.39 (d, J = 6.0) and 3.43
(d, J = 6.0) (2H, CH2), 4.07–4.23 (m, 4H, OCH2),
5.89 (d, J = 7.1, 1H, C5H),* 6.11 (d, J = 7.1, 1H,
To evaluate the potential of MW irradiation, com-
parative thermal experiments were also carried out
in a few cases. Hence, the experiments presented in
Table 1, entry 1, Table 2, entry 2, and Table 2, entry 5
were repeated under conventional heating at 120◦C
for 2.5, 2 and 4 h, respectively. The corresponding
products 2a, 5b, and 6a were obtained in yields of
49%, 51%, and 38%, respectively. The 23–25% lower
yields of the thermal control experiments indicate
the advantage of the MW technique regarding effi-
ciency.
C4H),* *may be reversed; [M + H]+
= 276.1004,
found
C11H19NO5P requires 276.1001; [M + Na]+
=
found
298.0824, C11H18NO5NaP requires 298.0820.
In summary, nine new N-(2H-pyranonyl)-
α-aminophosphonates or -α-aminophosphine oxides
were synthesized under MW conditions, in most
cases under solvent-free conditions.
Dibutyl [(6-Methyl-2-oxo-2H-pyran-3-yl)amino]
methylphosphonate (2b). Yield 88%; 31P NMR δ:
(CDCl3) 22.5; 13C NMR (CDCl3) δ: 13.6 (CH3(CH2)3),
18.7 (CH3CH2CH2), 18.8 (C6 CH3), 32.5 (J = 5.7,
CH2CH2O), 39.5 (J = 158.6, CH2P), 66.3 (J = 7.0,
OCH2), 103.6 (C5), 108.3 (J = 1.8, C4), 131.7 (J =
EXPERIMENTAL
General
1
7.3, C3), 148.9 (C6), 160.9 (C O); H NMR (CDCl3)
31P, 13C, and 1H NMR spectra were obtained in
CDCl3 solution on a Bruker AV-300 spectrometer
operating at 121.5, 75.5, and 300 MHz, respectively.
Chemical shifts are downfield relative to 85% H3PO4
and TMS. Mass spectra were obtained using a Q-
TOF Premier mass spectrometer in positive elec-
trospray mode. The reactions were carried out in a
300 W CEM Discover (CEM Microwave Technology
Ltd., Buckingham, UK) focused microwave reactor
equipped with a pressure controller applying 50–80
W under isothermal conditions.
δ: 0.92 (t, J = 7.3, 6H, CH3(CH2)3), 1.30–1.46 (m,
4H, CH2), 1.55–1.72 (m, 4H, CH2), 2.17 (s, 3H,
C6 CH3), 2.19 (s, 1H, NH), 3.39 (d, J = 6.0) and 3.43
(d, J = 6.0) (2H, CH2P), 3.99–4.17 (m, 4H, OCH2),
5.89 (d, J = 7.1, 1H, C5H),* 6.10 (d, J = 7.1, 1H,
C4H),* *may be reversed; [M + H]+
= 332.1633,
found
C15H27NO5P requires 332.1627; [M + Na]+
=
found
354.1451, C15H26NO5NaP requires 354.1446.
3-[(Diphenylphosphinoyl)methylamino]-6-methyl-
2H-pyran-2-one (2c). Yield 98%; 31P NMR δ:
(CDCl3) 30.0; 13C NMR (CDCl3) δ: 18.9 (C6 CH3),
44.2 (J = 79.4, CH2P), 103.8 (C5), 109.3 (C4), 129.0
(J = 11.8, C2’),* 130.7 (J = 99.1, C1’), 131.3 (J =
9.3, C3’),* 131.9 (J = 6.5, C3), 132.6 (J = 2.7, C4’),
149.2 (C6), 160.9 (C O), *may be reversed; 1H NMR
(CDCl3) δ: 1.95 (s, 1H, NH), 2.09 (s, 3H, C6 CH3),
3.88 (d, J = 7.5, 2H, PCH2), 5.78 (d, J = 7.2, 1H,
General Procedure for the Preparation of Dialkyl
[(2-Oxo-2H-pyran-3-yl)amino]-
methylphosphonates and
3-[(Diphenylphosphinoyl)methylamino]-2H-
pyran-2-ones
A mixture of 0.25 mmol of the pyran-2-one deriva-
tive (0.031 g of 1, 0.042 g of 3 or 0.057 g of 4),
C5H),* 6.13 (d, J = 7.2, 1H, C4H),* 7.39–7.81 (m, 10H,
*
ArH), may be reversed; [M + H]+
= 340.1107,
found
Heteroatom Chemistry DOI 10.1002/hc

224 Ba´lint et al.
C19H19NO3P requires 340.1103; [M + Na]+
=
1
be reversed; H NMR (CDCl3) δ: 1.78 (s, 1H, NH),
found
2.43 (s, 3H, CH3C O),* 2.48 (s, 3H, C6 CH3),* 3.96
(d, J = 6.6) and 3.98 (d, J = 6.5) (2H, CH2), 6.60
(s, 1H, C4H), 7.45–7.84 (m, 10H, ArH), *may be
362.0926, C19H18NO3NaP requires 362.0922.
Dimethyl [(5-Acetyl-6-methyl-2-oxo-2H-pyran-3-
yl)amino]methylphosphonate (5a). Yield 90%; 31P
NMR δ: (CDCl3) 22.3; 13C NMR (CDCl3) δ: 19.6
(C6 CH3), 29.9 (CH3C O), 39.2 (J = 159.9, CH2),
53.5 (J = 6.8, OCH3), 107.7 (J = 2.0, C4), 117.6 (C5),
131.1 (J = 6.5, C3), 155.8 (C2 O),* 159.3 (C6),* 196.5
reversed; [M + H]+
= 382.1219, C21H21NO4P
found
requires 382.1208; [M + Na]+
= 404.1039,
found
C21H20NO4NaP requires 404.1028.
*
1
(C O), may be reversed; H NMR (CDCl3) δ: 1.25
(s, 1H, NH), 2.47 (s, 3H, CH3C O),* 2.51 (s, 3H,
C6 CH3),* 3.50 (d, J = 6.1) and 3.54 (d, J = 6.1)
(2H, CH2), 3.81 (d, J = 6.1, 6H, OCH3), 6.55 (s, 1H,
Diethyl [(5-Benzoyl-6-methyl-2-oxo-2H-pyran-3-
yl)amino]methylphosphonate (6a). Yield 61%; 31P
NMR δ: (CDCl3) 22.1; 13C NMR (CDCl3) δ: 16.5
(J = 5.8, CH2CH3), 18.5 (C6 CH3), 39.6 (J = 158.7,
CH2), 62.7 (J = 6.9, OCH2), 107.9 (J = 1.9, C4),
117.3 (C5), 128.8 (C2"),a 129.6 (C3"),a 133.0 (C3),
133.5 (C4"), 152.4 (C2 O),b 159.4 (C6),b 194.0 (C O),
a,bmay be reversed; 1H NMR (CDCl3) δ: 1.33 (t,
J = 7.0, 6H, CH2CH3), 1.71 (s, 1H, NH), 2.17 (s, 3H,
C6 CH3), 3.36 (d, J = 6.0) and 3.41 (d, J = 6.0) (2H,
CH2), 4.09–4.21 (m, 4H, OCH2), 6.20 (s, 1H, C4H),
C4H), *may be reversed; [M + Na]+
= 312.0612,
found
C11H16NO6NaP requires 312.0613.
Diethyl
[(5-Acetyl-6-methyl-2-oxo-2H-pyran-3-
yl)amino]methylphosphonate (5b). Yield 74%; 31P
NMR δ: (CDCl3) 20.9; 13C NMR (CDCl3) δ: 16.6 (J =
5.6, CH2CH3), 19.4 (C6 CH3), 29.7 (CH3C O), 39.7
(J = 159.0, CH2), 62.8 (J = 6.7, OCH2), 107.4 (J = 1.9,
C4), 117.4 (C5), 131.1 (J = 6.5, C3), 155.5 (C2 O),*
159.1 (C6),* 196.4 (C O), *may be reversed; 1H
NMR (CDCl3) δ: 1.26 (s, 1H, NH), 1.35 (t, J = 7.0,
6H, CH2CH3), 2.48 (s, 3H, CH3C O),* 2.52 (s, 3H,
C6 CH3),* 3.48 (d, J = 5.0) and 3.50 (d, J = 5.1)
7.44–7.85 (m, 5H, ArH); [M + H]+
= 380.1266,
found
C18H23NO6P requires 380.1263; [M + Na]+
=
found
402.1088, C18H22NO6NaP requires 402.1082.
5-Benzoyl-3-[(diphenylphosphinoyl)methylamino]-
6-methyl-2H-pyran-2-one (6d). Yield 97%; 31P NMR
δ: (CDCl3) 27.6; 13C NMR (CDCl3) δ: 18.6 (C6 CH3),
43.5 (J = 77.8, CH2), 108.3 (C4), 117.3 (C5), 128.9
(C2"),a 129.0 (J = 11.8, C2’),b 129.6 (C3"),a 131.2
(J = 9.3, C3’)b, 132.66 (C4’), 132.70 (C3), 133.5 (C4"),
152.7 (C2 O),c 159.3 (C6),c 194.0 (C O), a–cmay
(2H, CH2), 4.08–4.24 (m, 4H, OCH2), 6.58 (s, 1H,
*
C4H), may be reversed; [M + H]+
= 318.1111,
found
C13H21NO6P requires 318.1107; [M + Na]+
=
found
340.0930, C13H20NO6NaP requires 340.0926.
Dibutyl
[(5-Acetyl-6-methyl-2-oxo-2H-pyran-3-
yl)amino]methylphosphonate (5c). Yield 91%; 31P
NMR δ: (CDCl3) 22.1; 13C NMR (CDCl3) δ: 13.6
(CH3(CH2)3), 18.7 (CH3CH2CH2), 19.4 (C6 CH3),
29.6 (CH3C O), 32.6 (J = 5.7, CH2CH2O), 39.5 (J =
159.4, CH2), 66.5 (J = 6.9, OCH2), 107.3 (J = 1.9,
C4), 117.3 (C5), 131.0 (J = 7.1, C3), 155.4 (C2=O),*
159.1 (C6),* 196.3 (C O), *may be reversed; 1H
NMR (CDCl3) δ: 0.93 (t, J = 7.3, 6H, CH3(CH2)3),
1.32–1.47 (m, 4H, CH2), 1.55–1.72 (m, 4H, CH2),
2.17 (s, 1H, NH), 2.47 (s, 3H, CH3C O),* 2.52 (s,
3H, C6 CH3),* 3.46 (d, J = 6.2) and 3.51 (d, J = 6.2)
1
be reversed; H NMR (CDCl3) δ: 1.71 (s, 1H, NH),
2.16 (s, 3H, C6 CH3), 3.83 (d, J = 6.9) and 3.85 (d,
J = 7.0) (2H, CH2), 6.16 (s, 1H, C4H), 7.43–7.82 (m,
15H, ArH); [M + H]+
= 444.1366, C26H23NO4P
found
requires 444.1365; [M + Na]+
= 466.1184,
found
C26H22NO4NaP requires 466.1184.
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Heteroatom Chemistry DOI 10.1002/hc