General synthesis of unsymmetrical tetrasubstituted oxamides via 1,1'- (1,2-dioxoethane-1,2-diyl)bis-1H-benzotriazole

Article abstract of DOI:10.1055/s-1998-2020

Aliphatic, alicyclic, and aromatic secondary amines are converted by 1,1'-(1,2-dioxoethane-1,2-diyl)bis-1H-benzotriazole, in a two-step process, into unsymmetrical tetrasubstituted oxamides in good yields. 1,1'-(1,2- Dioxoethane-1,2-diyl)bis-1H-benzotriaz

Full text of DOI:10.1055/s-1998-2020

Februrary 1998
SYNTHESIS
153
¢
General Synthesis of Unsymmetrical Tetrasubstituted Oxamides via 1,1 -(1,2-Di-
oxoethane-1,2-diyl)bis-1H-benzotriazole
Alan R. Katritzky,* Julian R. Levell, David P. M. Pleynet
Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
Fax +1(352)3929199; E-mail: KATRI,IZKY@chem.ufl.edu
Received 22 May 1997; revised 4 August 1997
Abstract: Aliphatic, alicyclic, and aromatic secondary amines are
converted by 1,1¢-(1,2-dioxoethane-1,2-diyl)bis-1H-benzotriazole, in
a two-step process, into unsymmetrical tetrasubstituted oxamides in
good yields. 1,1¢-(1,2-Dioxoethane-1,2-diyl)bis-1H-benzotriazole is
available in high yield from benzotriazole and oxalyl chloride.
Key words: unsymmetrical, tetrasubstituted, oxamides, benzotriazole
Scheme 1
Oxamides are important as intermediates in the synthesis
of a-diketones,1 and vicinal diamines,2 as ligands in or-
ganometallic complexes,3 chelating agents,4 polymer
precursors5 and polymer additives.6 Many oxamides are
biologically active as HIV-1 protease inhibitors,7 Tumor
Necrosis Factor inhibitors,8 aldose reductase inhibitors,9
cephalosporin bactericides,10 and pesticides.11 Sym-
metrical tetrasubstituted oxamides are readily obtained in
a variety of ways, including i) reaction of oxalyl chloride
with secondary amines;12 ii) oxidative coupling of sec-
ondary amines and carbon monoxide mediated by pal-
ladium,13 nickel,14 or titanium;15 iii) iron-mediated
oxidative coupling of formamides;16 iv) reaction of N,N¢-
dialkylethylenediamines with diethyl oxalate;1 v) chlo-
rination and hydrolysis of bis(amino)acetylenes;17 and vi)
rearrangement and oxidation of bithiazolium salts with
superoxide.18 However, few methods are available for the
synthesis of unsymmetrical tetrasubstituted oxamides, a
class of compounds of potential application in many of the
aforementioned areas. To our knowledge, the only general
route to N,N¢-unsymmetrical tetrasubstituted oxamides is
that of Dixneuf et al.,19 wherein the active intermediate
used is diisopropenyl oxalate, obtained by the ruthenium-
catalysed reaction of propyne with oxalic acid.19 One ex-
ample of an N,N¢-unsymmetrically tetrasubstituted
oxamide has been reported20 formed by the reaction of
carbamoyllithium (generated from the carbamoyltelluri-
um species) with a carbamoyl chloride.
Reaction of 3 with one equivalent of a secondary amine 4
in THF, at room temperature, gave intermediates 5a (R1 =
Me; R2 = Ph) and 5b (R1 = R2 = Et) in good yields. No fur-
ther substitution can be observed when an excess of 4 is
used. Intermediates 5a and b are stable to aqueous base,
allowing the byproduct, benzotriazole, to be removed by
washing with a 1 M aqueous solution of NaOH. Purifica-
tion by recrystallisation or column chromatography gives
compounds 5a and b in good to excellent yields (70–83%).
Scheme 2
Table. Preparation of Unsymmetrical Tetrasubstituted Oxamides
Ox- R1
amide
R2
R3
R4
Yielda mp
(%)
(°C)
7a
7b
7c
7d
7e
7f
Me Ph
Me Ph
Me Ph
Me Ph
Me
Me
Ph
Bu
75
oil
oil
107–108
140–142
oil
oil
126–128
70–71
CH2CH(OMe)2 63
Ph
47b
70
75
–CH2CH2(o-C6H4)CH2–
Et
Et
Et
Et
Et
Et
Et
Et
Me
Me
Ph
Bu
CH2CH(OMe)2 68
Ph
44b,c
55
7g
7h
We recently introduced 1,1¢-carbonylbisbenzotriazole as
an efficient intermediate in the synthesis of unsymmetri-
cal tetrasubstituted and other ureas,21 and now report our
results utilising 1,1¢-(1,2-dioxoethane-1,2-diyl)bis-1H-
benzotriazole for the related synthesis of unsymmetrical
tetrasubstituted oxamides.
–CH2CH2(o-C6H4)CH2–
a Of recrystallised or Kugelrohr distilled materials, based on 5.
b Requires 5 d reflux or is isolated in considerably reduced yield.
c
Slowly decomposes on silica gel column.
1,1¢-(1,2-Dioxoethane-1,2-diyl)bis-1H-benzotriazole (3)
has previously been reported as a ligand for uranium
coordination22 and as an oil soluble corrosion inhibitor,23 its
synthesis being effected in 86% yield by reaction of benzo-
triazole with oxalyl chloride in dry THF, in the presence of
triethylamine.22 This has been improved by direct reaction
of two molar equivalents of benzotriazole (1) with one mo-
larequivalentofoxalylchloride(2), indiethyletheratroom
temperature over 16 hours, The product precipitating out of
Reaction of 5 with the sodium salt of secondary amines 6
in refluxing THF gave the desired oxamides 7a–h in 44–
75% yields, after aqueous workup, column chromatogra-
phy, and recrystallisation or Kugelrohr distillation. The
reaction is successful for the synthesis of a variety of
unsymmetrical tetrasubstituted oxamides derived from
aliphatic, alicyclic, and aromatic secondary amines.
1
the solution was filtered off and washed with diethyl ether Amides often show two distinct H and 13C NMR reso-
to give analytically pure material in greater than 90% yield.
nances for all of the non-equivalent nucleii of 2 rota-

154
Papers
SYNTHESIS
mers.24 N,N¢-Unsymmetrically substituted oxamides have CH2 group of the tetrahydroisoquinoline, are at d = 3.93
and 3.78 for the minor rotamers, and the overlapped triplets
due to the major rotamers appear at d= 3.59 and 3.57 (when
the 1H NMR spectrum is measured in DMSO-d6 the two
triplets are more distinct from each other, appearing at d=
3.56 and 3.45). The triplets due to the benzylic CH2 group
in the position b to the nitrogen of tetrahydroisoquinoline
are overlapped at d = 2.99 and 2.97 for the minor rotamers
(no increase in separation in DMSO-d6), and at d = 2.78 and
2.45 for the major rotamers (a positive NOE is observed in
the aromatic region when irradiating at d = 2.78 and 2.45).
The temperature study in DMSO-d6 (Figure) shows the co-
alescence of the signals due to the benzylic CH2 in the po-
sition a to the nitrogen of the tetrahydroisoquinoline (ca.
d = 4.3-4.7), and the signals due to the non-benzylic CH2
group of the tetrahydroisoquinoline (ca. d = 3.5–3.9).
two such amide linkages and, therefore, would be expect-
1
ed to show different resonances in the H and 13C NMR
for all of the non-equivalent nuclei of the four possible
rotamers. A further complication is that the four rotamers
are not present in equimolar amounts due to their differing
relative thermodynamic stability. Many of the 1H and 13
C
NMR of 7 are complex even when the purity of the prod-
ucts has been confirmed by combustion analyses.
The complex nature of the NMR spectra of N,N¢-unsym-
metrically substituted oxamides has not been previously
noted, an indication of the absence of a previous system-
atic investigation of these compounds. The paucity of
published data is also presumably due to the previous lack
of simple methodology for the synthesis of these mole-
cules. Detailed systematic investigation of the spectral
temperature variation could allow insight into the rota-
tional energy barriers in these systems.
Scheme 3
Inconclusion,1,1¢-(1,2-dioxoethane-1,2-diyl)bis-1H-benzo-
triazole is a stable solid, easily obtained on a large scale by a
simple, high-yieldingreaction. Itisanefficientstartingma-
terialforthesynthesisofunsymmetricaltetrasubstitutedox-
amides, by two successive reactions with a variety of alkyl,
arylandcyclicsecondaryamines.Theonlybyproductisben-
zotriazole, which is easily rmoved and unreactive towards
sensitive substrates. Thus, the method should be applicable
for the introduction of the oxamide group into biologically
active or acid/base-sensitive compounds.
Melting points were determined on a Koefler hot stage apparatus, and
are uncorrected.1H NMR spectra and NOE-difference experiments
were recorded at 300 MHz on a Varian VXR-300 spectrometer, with
TMS as internal reference, spectral signals for minor rotamers of the
oxamides are in square brackets.13C NMR spectra were recorded at
75 MHz on the same instrument, using the solvent as internal refer-
ence. All reagents were purchased from Aldrich and used without
further purification. THF was distilled under N2 from sodium/
benzophenone directly prior to use.
1,1¢-(1,2-Dioxoethane-1,2-diyl)bis-1H-benzotriazole (3):
Oxalyl chloride (6.35 g, 50 mmol) was dissolved in toluene (50 mL),
and added dropwise, at r.t., to a vigorously stirring solution of benzo-
triazole (11.9 g, 100 mmol) in Et2O (500 mL). The mixture was left
stirring at this temperature for 16 to 24 h under the protection of a
CaCl2 drying tube (72 h gives the same yield, but less than 12 h results
in the isolation of some byproduct benzotriazole hydrochloride). The
product was filtered off, washed with Et2O (3 ´ 75 mL), and air dried
to give analytically pure 3 (13.80 g, 92%) as white powder crystals;
mp 163–164°C (Lit.22 163–164 °C). [The use of anhydrous solvents
and an argon atmosphere does not result in a significant increase in
the isolated yield].
Figure. Temperature ramped coalescence: 1H NMR of 7d
Compound 7d was further investigated, as an illustrative
example, using NOE difference experiments and temper-
ature ramped coalescence studies (Figure); the four differ-
ent rotamers are depicted in Scheme 3. Indeed, four
distinct signals due to the regiomeric hydrogens, which
are not equivalent in the different rotamers, can be identi-
fied for the majority of the proton-containing groups. The
two minor rotamers show singlets at d = 4.84 and 4.70 due
to the benzylic CH2 in the position a to the nitrogen of the
tetrahydroisoquinoline; the two major rotamer signals are
at d = 4.58 and 4.48. The triplets, due to the non-benzylic
1H NMR: d = 8.39 (d, J = 8.2 Hz, 2H), 8.20 (d, J = 8.3 Hz, 2H), 7.82
(t, J = 8.2 Hz, 2H), 7.65 (t, J = 8.2 Hz, 2H).
13C NMR: d = 158.0, 146.3, 131.5, 130.3, 127.7, 120.9, 114.0.
C14H8N6O2 calcd
(292.26) found
C
57.54
57.10
H
2.76
2.76
N
28.76
28.92

February 1998
SYNTHESIS
155
1-[2-[Methyl(phenyl)amino]-1,2-dioxoethyl)]-1H-benzotriazole
(5a):
N¢-(2,2-Dimethoxyethyl)-N,N¢-dimethyl-N-phenyloxamide (7b): col-
ourless oil; bp 210–215 °C/1.32 mbar.
1H NMR: d = 7.43–7.27 (m, 5H), [4.64], [4.57], [4.50], 3.98 (4 ´ t, J
= 5 Hz, 1H); 3.61–3.19 (m, 1 1H), [3.17], [3.10], 2.98, [2.77] (4 ´ s,
3H).
N-Methylaniline (1.20 g, 11 mmol) was added to a stirring solution of
1,1¢-(1,2-dioxoethane-1,2-diyl)bis-1H-benzotriazole (2.92 g, 10 mmol)
in anhyd THF (75 mL), under argon. The mixture was stirred at r.t.
for 72 h, the solvent removed, the residue dissolved in EtOAc and
washed with 1 M NaOH (2 ´ 50 mL) and sat. NaHCO3 (100 mL), and
dried (MgSO4). Concentration gave a pale-yellow oil which was dis-
solved in the minimum Et2O, and crystallised by addition of a small
amount of pentane. Recrystallised from Et2O/pentane to give pure
product (2.35 g, 83%) as colourless plates; mp 143–144 °C.
1H NMR: d = 8.09 (d, J = 8.1 Hz, 1H), 8.03 (d, J = 8.2 Hz, 1H), 7.60
(t, J = 8.1 Hz, 1H), 7.49 (t, J = 8.1 Hz, 1H), 7.30–7.36 (m, 2H), 7.18–
7.29 (m, 3H), 3.56 (s, 3H).
13C NMR: d = 164.7, 164.6, 141.2, 141.1, 129.2, 129. 1, 128.9, 127.9,
127.7, 126.8, 126.4, 125.9, 125.2, 125.0, 103.8, 102.9, 102.2, 102.0,
54.8, 54.7, 54.3, 54.2, 51.8, 51.7, 48.1, 47.8, 38.3, 37.6, 36.4, 35.7,
35.6, 33.2, 32.8.
C14H20N2O4 calcd
(280.32) found
C
59.97
60.31
H
7.20
7.48
N
10.00
10.23
N¢-Methyl-N,N,N¢-triphenyloxamide (7c): colourless plates; mp 107–
108 °C (Et2O/pentane).
13C NMR: d = 161.7, 161.2, 145.9, 140.2, 130.7, 130.3, 129.7, 128.8,
127.2, 126.8, 120.4, 113.7, 36.4.
1H NMR: d = 7.44–7.37 (m, 3H), 7.30–7.16 (m, 6H), 7.03–7.00 (m,
2H), 6.94-6.90 (m, 2H), 6.81 (d, J = 7.3 Hz, 2H), [3.44], 3.08 (2 ´ s,
3H).
C15H12N4O2 calcd
(280.29) found
C
64.28
64.03
H
4.32
4.30
N
19.99
20.07
13C NMR: d = 164.6, 164.3, 140.7, 140.6, 140.0, 129.6, 129.1, 129.0,
128.8, 128.4, 128.0, 127.6, 127.0, 126.8, 126.6, 126.4, 125.8, 125.3,
35.6.
1-(2-Diethylamino-1,2-dioxoethyl)-1H-benzotriazole (5b):
1,1¢-(1,2-Dioxoethane-1,2-diyl)bis-1H-benzotriazole (4.68 g, 16 mmol) C21H18N2O2 calcd
C
76.33
76.04
H
5.49
5.69
N
8.48
8.47
was dissolved in anhyd THF (40 mL) under anhyd N2 and Et2NH (330.39)
(1.76 mL, 16 mmol) was added. The mixture was stirred for 48 h. Re-
found
moval of the solvent under vacuum gave a yellow oil which was dis- 2-[2-[Methyl(phenyl)amino]-1,2-dioxoethyl]-1,2,3,4-tetrahydroiso-
solved in EtOAc, washed with 2 M NaOH and sat. NaCl, dried quinoline (7d): colourless needles; mp 140–142 °C (Et2O/pentane).
(MgSO4), filtered, and purified by flash column chromatography on 1H NMR: d = 7.44–7.26 (m, 3H), 7.23–7.01 (m, 6H), [4.84], [4.70],
silica, eluting with 50% Et2O/hexanes. Isolated as a colourless oil 4.58, 4.45 (4 ´ s, 2H), [3.93], [3.78], 3.59, 3.57 [4 ´ t (2 overlapped],
(2.75 g, 70%).
J = 6 Hz, 2H), [3.41], 3.41, 3.37, [3.31] [4 ´ s (2 overlapped), 3H],
1H NMR: d = 8.28 (d, J = 8 Hz, 1H), 8.16 (d, J = 8 Hz, 1H), 7.73 (t, J [2.99], [2.97], 2.78, 2.45 [4 ´ t (2 overlapped), J = 6 Hz, 2H].
= 8 Hz, 1H), 7.58 (t, J = 8 Hz, 1H), 3.65 (q, J = 7 Hz, 2H), 3.36 (q, J 13C NMR: d = 164.90, 164.85, 163.6, 163.1, 141.2, 140.9, 134.2,
= 7 Hz, 2H), 1.35 (t, J = 7 Hz, 3H), 1.25 (t, J = 7 Hz, 3H).
133.5, 131.6, 131.5, 129.4, 129.2, 129.0, 128.9, 128.7, 128.4, 128.1,
13C NMR: d = 162.5, 160.9, 146.1, 130.9, 130.6, 127.0, 120.5, 113.9, 127.9, 127.2, 127.1, 126.9, 126.8, 126.7, 126.5, 126.43, 126.38,
42.6, 39.1, 13.8, 12.5.
126.2, 126.0, 125.8, 125.2, 47.6, 43.7, 43.4, 43.3, 43.1, 38.8, 35.9,
35.7, 29.3, 29.0, 28.1, 27.6.
C12H14N4O2 calcd
(246.27)
C
58.53
58.50
H
5.73
5.86
N
22.75
23.02
found
C18H18N2O2 calcd
(294.35) found
C
73.45
73.57
H
6.16
6.36
N
9.52
9.53
General Method for the Synthesis of Oxamides 7:
N¢-Butyl-N,N-diethyl-N¢-methyloxamide (7e): colourless oil; bp 130–
140 °C/0.59 mbar.
The secondary amine 6 (3.6 mmol) was dissolved in anhyd THF
(5 mL) under argon, and stirred vigorously at r.t. during the addition
of NaH (0.150 g of 60% dispersion in mineral oil, 3.6 mmol) in one
portion. The mixture was Ieft stirring at r.t. for 20 min, before being
cannulated under argon into a solution of either 5a or 5b (3 mmol)
dissolved in anhyd THF (15 mL) under argon. An additional portion
of anhyd THF (5 mL) was used to wash over any residual material.
The mixture was refluxed for 48 h (5 d for 7c, 7g) before cooling to
r.t., and quenching with 1 M aq NaOH (50 mL). The organic phase
was separated, the aqueous extracted with EtOAc (2 ´ 50 mL), the
combined organic phases washed with 1M aq NaOH (50 mL) and sat.
NaHCO3, and dried (MgSO4). The residue left from concentration
was presorbed onto silica gel (5 g) and purified by column chroma-
tography on silica gel (50 g) with 200 mL portions of EtOAc/hexanes,
ratio = 50:150; 60:140; 70:130; 80:120; 100:100; 150:50; 200:0, re-
spectively (compounds 7e and 7f were not columned because they
only showed TLC spots when concentrated, under UV or with a vari-
ety of stains, so were Kugelrohr distilled directly). The relevant frac-
tions were concentrated to leave a pale-yellow oil, which was further
purified by either Kugelrohr distillation, or recrystallisation from
Et2O/pentane to give the pure product.
1H NMR: d = 3.50–3.38 (m, 3H), 3.34–3.22 (m, 3H), 2.96 (s, 3H),
1.67–l.51 (m, 2H), 1.42–1.14 (m, 8H), 0.99–0.88 (m, 3H).
13C NMR: d = 165.1, 164.9, 164.7, 164.5, 49.7, 45.7, 42.3, 42.1, 42.1,
38.2, 34.8, 31.1, 30.0, 28.6, 19.8, 19.7, 13.9, 13.6, 13.5, 12.5, 12.4.
C11H22N2O2 calcd
(214.31) found
C
61.63
61.61
H
10.35
10.55
N
13.08
13.18
N¢-(2,2-Dimethoxyethyl)-N,N-diethyl-N¢-methyloxamide (7f): colour-
less oil; bp 175–180°C/0.53 mbar.
1H NMR: d = 4.60–4.55 (m, 1H), 3.54–3.26 (m, 12H), 3.06, [3,05]
(2 ´ s, 3H), 1.25–1.16 (m, 6H).
13C NMR: d = 165.7, 165.6, 164.5, 164.4, 103.6, 102.2, 55.0, 54.5,
52.0, 48.0, 42.5, 42.1, 38.5, 38.4, 36.7, 33.3, 13.9, 13.8, 12.5, 12.4.
HRMS: m/z C11H22N2O4 (M+1) calcd: 247.1658; found: 247.1682.
N¢,N¢-Diethyl-N,N-diphenyloxamide (7g): colourless plates; mp 126–
l28 °C (Et2O/pentane).
1H NMR: d = 7.38–7.22 (m, 10H), 3.38 (q, J = 7 Hz, 2H), 3.21 (q, J
= 7 Hz, 2H), 1.23 (t, J = 7 Hz, 3H), 0.74 (t, J = 7 Hz, 3H).
13C NMR: d = 164.5, 163.5, 148.9, 140.5, 129.3, 128.9, 128.3, 126.5,
125.7, 42.2, 37.7, 13.5, 11.5.
N¢-Butyl-N,N¢-dimethyl-N-phenyloxamide (7a): colourless oil; bp
220–225 °C/0.3 mbar.
C18H20N2O2 calcd
(296.37) found
C
72.94
72.82
H
6.81
7.00
N
9.46
9.57
1H NMR: d = 7.41–7.27 (m, 5H), 3.35 (s, 3H), 3.15–3.09 (m, 2H),
2.87, [2.66], [2.31] [4 ´ s (2 overlapped), 3H], 1.70–0.72 (m, 7H).
13C NMR: d = 165. 1, 164.9, 164.2, 164.1, 141.1, 140.9, 129.05,
129.00, 128.9, 128.8, 127.8, 127.6, 126.7, 126.3, 125.9, 125.0, 49.6,
49.4, 45.6, 45.2, 37.9, 37.6, 35.5, 35.4, 34.6, 31.1, 30.5, 29.8, 29.5,
28.5, 27.9, 19.7, 19.54, 19.48, 19.2, 13.4.
2-[2-(Diethylamino)-1,2-dioxoethyl]-1,2,3,4-tetrahydroisoquinoline
(7h): colourless needles; mp 70–71 °C (Et2O/pentane).
1H NMR: d = 7.22–7.04 (m, 4H), 4.78, [4.57] (2 ´ s, 2H), [3.87], 3.65
(2 ´ t, J = 6 Hz, 2H), 3.48, [3.47] (2 ´ q, J = 7.1 Hz, 2H), 3.33, [3.24]
(2 ´ q, J = 7.1 Hz, 2H), 2.95–2.90 (m, 2H), 1.25–1.08 (m, 6H).
13C NMR: d = 164.3, 164.2, 163.8, 134.2, 133.6, 132.0, 128.9, 128.7,
C14H20N2O2 calcd
(248.33) found
C
67.70
67.75
H
8.12
8.37
N
11.29
11.50

156
Papers
SYNTHESIS
127.1, 126.69, 126.66, 126.59, 126.56, 126.0, 47.6, 43.6, 43.2, 42.32,
42.26, 39.0, 38.5, 29.3, 28.1, 14.2, 14.0, 12.6.
(12) Armbrecht, B. H.; Rice, L. M.; Grogan, C. H.; Reid, E. E. J. Am.
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C15H20N2O2 calcd
(260.34) found
C
69.19
69.39
H
7.75
7.78
N
10.77
10.83
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