Regioselective hydrolysis of ketenimines derived from NH-acids and acetylenic esters in the presence of tert-butyl isocyanide under neutral conditions

Article abstract of DOI:10.1007/s00706-008-0954-9

The regioselective hydrolysis of ketenimines derived from NH-acids, such as 2,2,2-trichloro-N-phenylacetamide or ethyl-2-anilino-2-oxoacetates and acetylenic esters in the presence of tert-butyl isocyanide in a THF/H ₂O system (1/1) without any catalysis leads to a diastereomeric mixture of dialkyl 2-[(tert-butylamino)carbonyl]-3-[(2,2,2-trichloroacetyl) anilino]succinates and dialkyl 2-[(tert-butylamino)carbonyl]-3-[2-ethoxy-2- oxoacetyl)anilino]-succinates in good yields. Dynamic NMR effects were observed in the ¹³C NMR spectra of diethyl 2-[(tert-butylamino)carbonyl]-3- [(2,2,2-trichloroacetyl)anilino]succinate as a result of restricted rotation around the N-aryl single bond. The free energy of activation (ΔG ^#) for this process is 37.9∈kJ∈mol^-1 which leads to an observable atropisomerism.

Full text of DOI:10.1007/s00706-008-0954-9

Monatsh Chem 139, 1457–1461 (2008)
DOI 10.1007/s00706-008-0954-9
Printed in The Netherlands
Regioselective hydrolysis of ketenimines derived from NH-acids and acetylenic
esters in the presence of tert-butyl isocyanide under neutral conditions
Farough Nasiri, Samiyeh Yosefdad
Department of Chemistry, Faculty of Sciences, University of Kurdistan, Sanandaj, Iran
Received 24 March 2008; Accepted 1 May 2008; Published online 26 June 2008
# Springer-Verlag 2008
Abstract The regioselective hydrolysis of ketenimines
derived from NH-acids, such as 2,2,2-trichloro-
N-phenylacetamide or ethyl-2-anilino-2-oxoacetates
and acetylenic esters in the presence of tert-butyl iso-
cyanide in a THF=H2O system (1=1) without any
catalysis leads to a diastereomeric mixture of dialkyl
2-[(tert-butylamino)carbonyl]-3-[(2,2,2-trichloro-
acetyl)anilino]succinates and dialkyl 2-[(tert-butyl-
amino)carbonyl]-3-[2-ethoxy-2-oxoacetyl)anilino]-
succinates in good yields. Dynamic NMR effects
were observed in the 13C NMR spectra of diethyl
2-[(tert-butylamino)carbonyl]-3-[(2,2,2-trichloroace-
tyl)anilino]succinate as a result of restricted rotation
around the N-aryl single bond. The free energy of
activation (ꢀG#) for this process is 37.9 kJmolꢀ1
which leads to an observable atropisomerism.
Scheme 1
cycloadditions [2, 3], and imino-ene type reactions
[4]. There are many theoretical studies on the hydra-
tion of ketenimines but little attention has been paid
to the hydrolysis of new synthetic multifunctional
ketenimines [5–7]. On the basis of Hegarty et al.
[8] studies, the hydration of ketenimines 1 to give
hydrolysis products 2 and 3, shows dependence on
hindrence of substituted groups on ketenimines and
pH of the reaction conditions.
We have previously reported the synthesis of highly
functionalized ketenimines from the reaction of some
NH-acids and acetylenic esters in the presence of alkyl
isocyanides [9–13]. We now focused our attention on
the hydrolysis of ketenimines derived from NH-acids,
such as 2,2,2-trichloro-N-phenylacetamide or ethyl 2-
anilino-2-oxoacetates and acetylenic esters in the pres-
ence of tert-butyl isocyasnide in THF=H2O system
in neutral condition to produce new multifunctional
compounds 5a–5f in good yields (see Scheme 2).
Keywords Hydration; Heteroallenes; Hindered rotation;
Atropisomers.
Introduction
In recent years, the synthesis applications of multi-
functional heteroallenes have been widely inves-
tigated. These heterocumulenes were particularly
useful in the synthesis of nitrogen-containing hetero-
cycles through their participation in electrocyclic
ring closures [1], intramolecular [2 þ 2] and [4 þ 2]
Correspondence: Dr. Farough Nasiri PhD, Department of
Chemistry, Faculty of Sciences, University of Kurdistan,
P.O. Box 66315-416, Sanandaj, Iran. E-mail: fnasiri@uok.
ac.ir
Results and discussion
Three-component reaction of tert-butyl isocyanide
with electron deficient acetylenic esters in the pres-

1458
F. Nasiri, S. Yosefdad
Scheme 2
ence of strong NH-acids at ambient temperature in
CH2Cl2 leads to ketenimines 4 [9, 10]. Subsequent
hydrolysis of these ketenimines in the THF=H2O
(1=1) system without any catalysis leads to a dia-
stereomeric mixture of multifunctional compounds
5a–5f in good yields (Scheme 2).
of 5a exhibited 34 resonances in agreement with the
proposed structures. In case of 5b, the major isomer
can be separated by column chromatography. We
were not able to isolate the minor isomer of 5b
in pure form; however, its NMR data can be extract
from the mixture of the two diastereomers. Partial
assignments of these resonances are given in Exper-
imental Section.
The structures of 5a–5f were deduced from their
1
elemental analysis and IR, H NMR, and 13C NMR
spectroscopic data. The mass spectra of these com-
pounds displayed molecular ion peaks at appropriate
m=z values. Due to the presence of two chirality
centers in 5, the NMR spectra of these compounds
are consistent with the presence of two diastereo-
A proposed mechanism for this reaction is out-
lined in Scheme 3 based on the previous reports
1
mers. For example the H NMR spectrum of 5a is
consistent with the presence of two diastereomers in
66:34 ratios. The 1H NMR spectrum of the diastero-
meric mixture of 5a exhibited six sharp lines for
tert-butyl (ꢀ ¼ 1.39 and 1.46 ppm) and methoxy
(ꢀ ¼ 3.81, 3.84, 3.85, and 3.86 ppm) protons. The
NH proton appeared as two broad lines at
(ꢀ ¼ 5.67, and 5.83 ppm) and the aryl moiety
appeared as multiplet at ꢀ ¼ 7.31–7.85 ppm. Two
aliphatic CH protons of 5a exhibited four dublets
3
(ꢀ ¼ 4.31, 4.38, 5.03, and 5.20 ppm, JHH ¼ 10.1 Hz).
The 13C NMR spectrum of the diasteromeric mixture
Fig. 1 Variable temperature 62.9 MHz 13C NMR spectra of
5b in CDCl3
Scheme 3

Regioselective hydrolysis of ketenimines
1459
nates and dialkyl 2-[(tert-butylamino)carbonyl]-3-
[2-ethoxy-2-oxoacetyl)anilino]succinates in good
yields. Dynamic NMR effects are observed in
the 13C NMR spectra of 5a and 5b and are attrib-
uted to restricted rotation around the aryl-nitrogen
bond.
Scheme 4
Experimental
Ketenimines were prepared by known methods [9, 10].
Melting points were measured with an Electrothermal 9100
apparatus. Elemental analyses of C, H, and N were performed
using a Heraeus CHN-O-Rapid analyzer. These results agreed
favorably with the calculated values. IR spectra were mea-
sured with a Shimadzu IR-460 spectrometer. NMR spectra
were recorded with a Bruker DRX-250 AVANCE in-
strument (250.1 MHz for 1H and 62.9 MHz for 13C) with
CDCl3 as solvent. Chemical shifts are given in ppm (ꢀ) rel-
ative to internal TMS, and coupling constant (J) are reported
in Hertz (Hz). Mass spectra were recorded with a Finnigan-
Matt 8430 mass spectrometer operating at an ionization
potential of 70 eV.
[5–8]. Initial addition of water to ketenimines 4
leads to intermediates 6. Such an addition product
may tautomerise to amide 5 (Scheme 3).
The benzene region of the 13C NMR spectra of 5a
and 5b in CDCl3 at room temperature exhibits four
broad signals for the ortho and meta aromatic CH
groups (see Fig. 1). Increasing the temperature to
about 40ꢁC results in coalescence of CHmeta reso-
nances. At 55ꢁC the meta carbon atoms appear as
a relatively sharp single resonance. This dynamic
NMR effect is attributed to slow rotation around
the phenyl–N bond in 5a and 5b (Scheme 4).
Hindered rotation around the N–CO bond in 5a and
5b is ruled out, because only one signal is observed
for the para (or ipso) carbon atom of the phenyl ring
at various temperatures.
General procedure (examplified by 5a)
To a magnetically stirred solution of 0.48g 2,2,2-trichloro-N-
phenylacetamide (2mmol) and 0.28g dimethyl acetylenedi-
carboxylate (2mmol) in 6 cm3 CH2Cl2 were added drop-wise
at ꢀ10ꢁC over 10 min 0.45 g tert-butyl isocyanide (2mmol) in
2 cm3 CH2Cl2. The reaction mixture was then allowed to
warm up to room temperature and stirred for 24h. The solvent
was removed under reduced pressure and 10 cm3 THF=H2O
(50=50) were added to the reaction mixture and it was then
refluxed for 18h. The solvent was removed under reduced
pressure, and the residue was purified by silica gel (Merck
230–400 mesh) column chromatography using n-hexane=
EtOAc mixture as eluent.
Although an extensive line-shape analysis in rela-
tion to the dynamic 13C NMR effect observed for 5a
and 5b was not undertaken, the variable temperature
spectra of 5b allowed calculating the Gibbs energy
barrier (if not the enthalpy and entropy of activation)
for the dynamic NMR process. From coalescence of
the meta carbon resonances and using the expression
pffiffi
k ¼ ꢁꢀꢂ= 2, we calculated that the first-order rate
constant (k) for dynamic NMR effect in 5b is 27 sꢀ1
at 40ꢁC. Application of the absolute rate theory with
a transmission coefficient of 1 gives a Gibbs energy
of activation (ꢀG#) of 37.9 ꢂ 2 kJ molꢀ1, where
all known sources of errors are estimated and in-
cluded [14]. The experimental data available are
not suitable for obtaining meaningful values of
ꢀH# and ꢀS#, even though the errors in ꢀG# are
not large [15].
Dimethyl 2-[(tert-butylamino)carbonyl]-3-[(2,2,2-trichloro-
acetyl)anilino]succinate (5a, C19H23Cl3N2O6)
Yellow powder, mp 138–140ꢁC; yield 0.52g (54%); IR (KBr):
ꢂꢁ¼ 3495 (NH), 1753, 1678 (C¼O) cmꢀ1
.
1
Major isomer (66%); H NMR (250.1MHz, CDCl3): ꢀ ¼
1.46 (s, CMe3), 3.81, 3.85 (2s, 2OCH3), 4.38, 5.03 (2d,
3JHH ¼ 10.1 Hz, 2CH), 5.83 (s, br, NH), 7.31–7.85 (m, H–Ar)
ppm; 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 28.6 (CMe3), 52.3,
52.9 (2OCH3), 53.1, 54.7 (2CH), 67.4 (CMe3), 92.0 (CCl3),
128.6, 128.8 (2Cortho), 129.1 (Cpara), 129.2, 129.4 (2Cmeta),
142.6 (Cipso), 162.3, 164.4, 168.2, 168.9 (4C¼O) ppm.
1
In conclusion, the regioselective hydrolysis of
ketenimines derived from NH-acids such as 2,2,2-
trichloro-N-phenylacetamide or ethyl 2-anilino-2-
oxoacetates and acetylenic esters in the presence of
tert-butyl isocyanide in a THF=H2O system leads to a
diastereomeric mixture of dialkyl 2-[(tert-butylami-
no)carbonyl]-3-[(2,2,2-trichloroacetyl)anilino]succi-
Minor isomer (34%); H NMR (250.1MHz, CDCl3): ꢀ ¼
1.39 (s, CMe3), 3.84, 3.86 (2s, 2OCH3), 4.31, 5.20 (2d,
3JHH ¼ 10.1 Hz, 2CH), 5.67 (s, br, NH), 7.31–7.85 (m, H-
Ar) ppm; 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 28.5 (CMe3),
51.9, 52.8 (2OCH3), 53.6, 54.2 (2CH), 66.7 (CMe3), 92.1
(CCl3), 128.3, 128.5 (2Cortho), 129.0 (Cpara), 129.3, 129.5
(2Cmeta), 141.9 (Cipso), 162.2, 164.1, 168.0, 168.8 (4C¼O)
ppm.

1460
F. Nasiri, S. Yosefdad
1
Minor isomer (17%); H NMR (250.1MHz, CDCl3): ꢀ ¼
Diethyl 2-[(tert-butylamino)carbonyl]-3-[(2,2,2-trichloro-
acetyl)anilino]succinate (5b, C21H27Cl3N2O6)
Yellow oil, yield 0.53g (52%).
1.01 (t, 3JHH ¼ 7.0 Hz, OCH2CH3), 1.27 (s, CMe3), 3.69, 3.70
3
(2s, 2OCH3), 4.05 (q, JHH ¼ 7.0 Hz, OCH2CH3), 4.29, 5.21
(2d, 3JHH ¼ 10.0Hz, 2CH), 5.78 (s, br, NH), 7.24–7.51 (m, H–
Ar) ppm; 13C NMR (62.9MHz, CDCl3): ꢀ ¼ 13.6 (CH3), 28.4
(CMe3), 51.8, 52.8 (2OCH3), 53.0, 53.5 (2CH), 61.9 (OCH2),
62.1 (CMe3), 122.8 (C–Br), 128.9, 132.5 (4CH), 139.7 (N-
Cipso), 161.1, 162.0 , 163.7, 167.8, 168.5 (5C¼O) ppm.
Major isomer (75%), white powder, mp 126–127ꢁC;
IR (KBr): ꢂꢁ¼ 3460 (NH), 1747, 1682 (C¼O) cmꢀ1
.
1H
NMR (250.1MHz, CDCl3): ꢀ ¼ 1.28, 1.34 (2t, 3JHH ¼ 7.3 Hz,
2OCH2CH3), 1.43 (s, CMe3), 4.20–4.37 (m, 2OCH2CH3),
3
4.36, 4.97 (2d, JHH ¼ 10.3Hz, 2CH), 5.82 (s, br, NH),
7.33–7.85 (m, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3):
ꢀ ¼ 14.0 (2OCH2CH3), 28.6 (CMe3), 52.2, 54.8 (2CH), 61.7,
62.3 (2OCH2CH3), 67.4 (CMe3), 92.0 (CCl3), 128.4, 129.1
(2Cortho), 129.0 (Cpara), 129.3, 129.5 (2Cmeta), 142.7 (Cipso),
162.2, 164.7, 167.7, 168.4 (4C¼O) ppm.
Dimethyl 2-[(tert-butylamino)carbonyl]-3-[(2-ethoxy-2-
oxoacetyl)-4-nitroanilino]succinate (5e, C21H27N3O10)
Yellow powder, mp 110–112ꢁC, yield 0.49g (51%); IR (KBr):
ꢂꢁ¼ 3370 (NH), 1746, 1671 (C¼O) cmꢀ1
.
Minor isomer (25%); 1H NMR (250.1 MHz, CDCl3):
ꢀ ¼ 1.22–1.42 (m, 2OCH2CH3, CMe3), 4.20–4.37 (m,
Major isomer (81%); 1H NMR (250.1MHz, CDCl3):
3
ꢀ ¼ 1.11 (t, JHH ¼ 7.0 Hz, OCH2CH3), 1.41 (s, CMe3), 3.83,
3
3
2OCH2CH3, CH), 5.11 (d, JHH ¼ 10.0Hz, CH), 5.64 (s, br,
3.84 (2s, 2OCH3), 4.11 (q, JHH ¼ 7.0 Hz, OCH2CH3), 4.44,
NH), 7.19–7.85 (m, H–Ar) ppm; 13C NMR (62.9 MHz,
CDCl3): ꢀ ¼ 13.8 (2OCH2CH3), 30.3 (CMe3), 51.9, 54.7
(2CH), 61.3, 63.0 (2OCH2CH3), 67.3 (CMe3), 92.8 (CCl3),
128.3, 129.8 (2Cortho), 129.2 (Cpara), 129.7, 129.9 (2Cmeta),
142.7 (Cipso), 162.1, 164.6, 167.5, 168.3 (4C¼O) ppm.
3
5.06 (2d, JHH ¼ 10.5Hz, 2CH), 5.78 (s, br, NH), 7.76, 8.31
(2d, JHH ¼ 8.2 Hz, 4CH-Ar) ppm; 13C NMR (62.9 MHz,
3
CDCl3): ꢀ ¼ 13.6 (OCH2CH3), 28.4 (CMe3), 52.3, 53.1
(2OCH3), 53.4, 54.0 (2CH), 62.6 (OCH2CH3), 63.3 (CMe3),
124.8, 128.1 (4CH–Ar), 147.8, 148.5 (2C–Ar), 160.6, 162.2,
164.1, 167.4, 167.6 (5C¼O) ppm.
1
Minor isomer (19%); H NMR (250.1MHz, CDCl3): ꢀ ¼
Dimethyl 2-[(tert-butylamino)carbonyl]-3-[(2-ethoxy-2-
oxoacetyl)anilino]succinate (5c, C21H28N2O8)
Brown powder, mp 136–137ꢁC, yield 0.45g (51%); IR (KBr):
1.11 (t, 3JHH ¼ 7.0 Hz, OCH2CH3), 1.41 (s, CMe3), 3.76, 3.77
3
(2s, 2OCH3), 4.11 (q, JHH ¼ 7.0 Hz, OCH2CH3), 4.44, 5.27
3
ꢂꢁ¼ 3380 (NH), 1742, 1670 (C¼O) cmꢀ 1
.
(2d, JHH ¼ 10.0 Hz, 2CH), 5.76 (s, br, NH), 7.63, 8.31 (2d,
3JHH ¼ 8.2 Hz, 4CH–Ar) ppm; 13C NMR (62.9 MHz, CDCl3):
ꢀ ¼ 13.6 (OCH2CH3), 28.4 (CMe3), 52.1, 53.1 (2OCH3), 53.5,
54.0 (2CH), 62.6 (OCH2CH3), 63.3 (CMe3), 124.9, 128.0
(4CH–Ar), 147.7, 148.6 (2C–Ar), 160.5, 162.1, 164.1,
167.5, 167.8 (5C¼O) ppm.
Major isomer (89%); 1H NMR (250.1MHz, CDCl3):
3
ꢀ ¼ 0.94 (t, JHH ¼ 7.3Hz, OCH2CH3), 1.37 (s, CMe3), 3.77,
3
3.78 (2s, 2OCH3), 3.99 (q, JHH ¼ 7.3 Hz, OCH2CH3), 4.37,
3
5.09 (2d, JHH ¼ 10.5Hz, 2CH), 5.80 (s, br, NH), 7.34–7.51
(m, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 13.6
(OCH2CH3), 28.4 (CMe3), 52.2, 52.8 (2OCH3), 53.1, 54.1
(2CH), 61.9 (OCH2CH3), 62.8 (CMe3), 127.5 (2Cortho),
128.9 (Cpara), 129.4 (2Cmeta), 140.9 (Cipso), 161.3, 163.0,
164.3, 168.2, 168.9 (5C¼O) ppm.
Diethyl 2-[(tert-butylamino)carbonyl]-3-[(2-ethoxy-2-oxo-
acetyl)-4-nitroanilino]succinate (5f, C23H31N3O10)
Yellow powder, mp 216–218ꢁC, yield 0.53g (52%); IR (KBr):
Minor isomer (11%), 1H NMR (250.1 MHz, CDCl3):
ꢂꢁ¼ 3385 (NH), 1745, 1685 (C¼O) cmꢀ1
.
3
Major isomer (91%); 1H NMR (250.1MHz, CDCl3):
ꢀ ¼ 0.93 (t, JHH ¼ 7.3Hz, OCH2CH3), 1.34 (s, CMe3), 3.68,
3
3
3.69 (2s, 2OCH3), 3.99 (q, JHH ¼ 7.3 Hz, OCH2CH3), 4.27,
ꢀ ¼ 1.07 (t, JHH ¼ 7.3 Hz, OCH2CH3), 1.22–1.34 (m, 2CO2-
3
5.32 (2d, JHH ¼ 10.5Hz, 2CH), 5.71 (s, br, NH), 7.34–7.51
CH2CH3), 1.38 (s, CMe3), 4.07–4.34 (m, 3OCH2CH3), 4.41,
(m, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 13.4
(OCH2CH3), 28.4 (CMe3), 51.9, 52.7 (2OCH3), 52.9, 53.4
(2CH), 61.9 (OCH2CH3), 62.8 (CMe3), 127.4 (2Cortho),
128.8 (Cpara), 129.5 (2Cmeta), 140.9 (Cipso), 161.4, 162.5,
162.9, 164.1, 168.1 (5C¼O) ppm.
3
5.01 (2d, JHH ¼ 10.5Hz, 2CH), 5.87 (s, br, NH), 7.73, 8.28
(2d, JHH ¼ 7.0 Hz, 4CH–Ar) ppm; 13C NMR (62.9 MHz,
3
CDCl3): ꢀ ¼ 13.5, 13.9, 14.0 (3OCH2CH3), 28.3 (CMe3),
52.2, 54.1 (2CH), 61.9, 62.4, 62.5 (3OCH2CH3), 63.2 (CMe3),
124.7, 128.1 (4CH–Ar), 147.0, 147.3 (2C–Ar), 160.6, 162.1,
164.5, 167.3, 167.8 (5C¼O) ppm.
1
Dimethyl 2-[(4-bromo(2-ethoxy-2-oxoacetyl)anilino]-3-[(tert-
butylamino)carbonyl]succinate (5d, C21H27BrN2O8)
Minor isomer (9%); H NMR (250.1MHz, CDCl3): ꢀ ¼
3
1.07 (t, JHH ¼ 7.3 Hz, OCH2CH3), 1.22–1.34 (m, 2CO2–
3
CH2CH3), 1.38 (s, CMe3), 4.41, 5.20 (2d, JHH ¼ 10.5Hz,
Brown oil, yield 0.55 g (53%); IR (KBr): ꢂꢁ¼ 3375 (NH),
3
1742, 1679 (C¼O) cmꢀ1
.
2CH), 5.81 (s, br, NH), 7.64, 7.89 (2d, JHH ¼ 7.0 Hz, 4CH–
Ar) ppm; 13C NMR (62.9MHz, CDCl3): ꢀ ¼ 13.5, 13.9, 14.0
(3OCH2CH3), 28.3 (CMe3), 51.9, 53.7 (2CH), 62.0, 62.3, 62.5
(3OCH2CH3), 63.2 (CMe3), 125.0, 127.7 (4CH–Ar), 147.0,
147.3 (2C–Ar), 160.6, 161.8, 163.8, 167.3, 167.9 (5C¼O) ppm.
1
Major isomer (83%); H NMR (250.1 MHz, CDCl3): ꢀ ¼
3
1.05 (t, JHH ¼ 7.0 Hz, OCH2CH3), 1.35 (s, CMe3), 3.75,
3
3.76 (2s, 2OCH3), 4.03 (q, JHH ¼ 7.0 Hz, OCH2CH3),
3
4.36, 5.00 (2d, JHH ¼ 10.5 Hz, 2CH), 5.84 (s, br, NH),
7.24–7.51 (m, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3):
ꢀ ¼ 13.6 (CH3), 28.4 (CMe3), 52.1, 53.0 (2OCH3), 53.2,
54.0 (2CH), 62.2 (OCH2), 63.0 (CMe3), 123.0 (C–Br),
129.2, 132.6 (4CH), 140.7 (N–Cipso), 161.0, 162.7, 164.3,
168.0, 168.7 (5C¼O) ppm.
Acknowledgements
We are grateful to Dr. Farzad Nikpour for his assistance.

Regioselective hydrolysis of ketenimines
1461
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