Simple synthesis of highly functionalized ketenimines

Article abstract of DOI:10.1080/00397910802219213

The 1:1 reactive intermediate generated by the addition of alkyl isocyanides to dibenzoylacetylene or dialkyl acetylenedicarboxylates was trapped by fairly strong NH acids such as isatin, phthalimide, 4-nitroimidazole, or 2-benzoylimidazole to yield highl

Full text of DOI:10.1080/00397910802219213

This article was downloaded by: [Pennsylvania State University]
On: 06 August 2013, At: 11:28
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic
Organic Chemistry
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/lsyc20
Simple Synthesis of Highly
Functionalized Ketenimines
Mohammad Bayat a , Hossien Imanieh a & Elham
Hossieninejad a
a Department of Chemistry, Imam Khomeini
International University, Qazvin, Iran
Published online: 09 Sep 2008.
To cite this article: Mohammad Bayat , Hossien Imanieh & Elham Hossieninejad (2008)
Simple Synthesis of Highly Functionalized Ketenimines, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 38:15,
2567-2574, DOI: 10.1080/00397910802219213
To link to this article: http://dx.doi.org/10.1080/00397910802219213
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or

indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Synthetic Communications1, 38: 2567–2574, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802219213
Simple Synthesis of Highly Functionalized
Ketenimines
Mohammad Bayat, Hossien Imanieh, and Elham Hossieninejad
Department of Chemistry, Imam Khomeini International University,
Qazvin, Iran
Abstract: The 1:1 reactive intermediate generated by the addition of alkyl iso-
cyanides to dibenzoylacetylene or dialkyl acetylenedicarboxylates was trapped
by fairly strong NH acids such as isatin, phthalimide, 4-nitroimidazole, or
2-benzoylimidazole to yield highly functionalized ketenimines.
Keywords: Alkyl isocyanides, dibenzoylacetylene, ketenimines, three-component
reaction
INTRODUCTION
Development of simple synthetic routes for widely used organic com-
pounds from readily available reagents is one of the major tasks in
organic chemistry.[1] A major challenge of modern organic synthesis
and drug discovery is the design of highly efficient chemical reaction
sequences, which provide a maximum of structural complexity and
diversity with just a minimum number of synthetic steps to assemble
compounds with interesting properties.[1,2]
Recently, multicomponent reactions (MCRs) have emerged as highly
valuable synthetic tools in the context of modern drug discovery. The
atom economical and convergent character, the simplicity of a one-pot
procedure, the possible structural variations, the accessible complexity
of the molecules, as well as the very large number of accessible com-
pounds are among the described advantages of MCRs.[3] Thus, they
Received in the U.K. September 18, 2007
Address correspondence to Mohammad Bayat, Department of Chemistry,
Imam Khomeini International University, P.O.Box-288, Qazvin, Iran. E-mail:
Bayat_mo@ yahoo.com
2567

2568
M. Bayat, H. Imanieh, and E. Hossieninejad
Scheme 1.
are perfectly amenable to automation for combinatorial synthesis.[4]
Among the known multicomponent reactions, isocyanide-based MCRs
such as the versatile ugi and passerini reactions are especially valu-
able.[5–7] Many different scaffolds are accessible, each with very many
examples.[8,9] Thus, they are prototypic-complexity- and diversity-
generating reactions.
ketenimines play a role as discrete but transient intermediates in
many interconversions, especially in elimination–addition processes and
in the formation of heterocyclic ring systems.[10–13] The spectroscopic
properties of ketenimines have been intensively investigated.[14] We
report a simple one-pot preparation of stable ketenimines using alkyl iso-
cyanides 1 and dibenzoylacetylene or dialkyl acetylenedicarboxylates 2 in
the presence of a NHacid 3 such as isatin, phthalimide, succinimide,
4-nitroimidazole, or 2-benzoylimidazole. This three-component conden-
sation reaction produces highly functionalized ketenimimes 4 in fairly
good yield (Scheme 1).
RESULTS AND DISCUSSION
The reaction of alkyl isocyanides 1 with dibenzoylacetylene or dialkyl
acetylenedicarboxylates 2 in the presence of NHacids 3 proceeded at
room temperature in dry diethyl ether or ethyl acetate and was completed
1
within 24 h. The IR, H NMR, and 13C NMR spectra of the crude pro-
ducts clearly indicated the formation of stable ketenimines 4 (Scheme 1).

Highly Functionalized Ketenimines
2569
Scheme 2.
The structures of 4 were deduced from their elemental analyses, mass
1
spectrometric data, and their H NMR, 13C NMR and IR spectra. The
1H NMR spectra of 4a (CDCl3) showed four sharp lines for tert-butyl
(d ¼ 1.41 ppm), methoxy (d ¼ 3.63 and 3.71 ppm), and methine
(d ¼ 5.67 ppm) protons, with the aromatic protons at d ¼ 7.04–7.59 ppm.
The 13C NMR spectrum of 4a showd signals for tert-butyl
(d ¼ 29.68 ppm), methoxy (d ¼ 52.1 and 52.3 ppm), and methine
(d ¼ 52.11 ppm) carbons in agreement with proposed structure. Partial
assignments of these resonances are given in the methods and marterials
section.
The 1H NMR spectra of 4b–i are similar to that of 4a, except for the
signals of cyclohexyl, ester, and aromatic moieties. The structural assign-
ments of 4b–i made on the basis of their NMR spectra were supported by
their IR spectra. Ketenimines show a strong absorption band at about
2035–2086 cmꢀ1 in all compounds.
On the basis of the well-established chemistry of isocynides,[15–16] it is
reasonable to assume that compound 4 results from initial addition of
alkyl isocyanide to the dibenzoylacetylene or dialkyl acetylenic ester
and subsequent protonation of the 1:1 adduct by the NHacid. Then,
the positively charged ion is attacked by the nitrogen atom of the anion
of the NHacid to form ketenimine 4 (Scheme 2).
In conclusion, the three-component reaction of alkyl isocyanides
with electron-deficient acetylenic esters or dibenzoylacetylene in the pres-
ence of NHacids provides a simple entry into the synthesis of polyfunc-
tionalized ketenimines of potential synthetic interest. Not only is the
reaction performed under neutral conditions, but also the substances
can be mixed without any activation or modification.
MATERIALS AND METHODS
Dialkyl acetylenedicarboxylates, tert-butyl isocyanide, and other reagents
and solvents used in this work were obtained from Fluka (Buchs,
Switzerland) and used without further purification. Dibenzoylacetylene,
4-nitroimidazole,[17,18] and 2-benzoylimidazole[19] were prepared accord-
ing to the published procedures. NMR spectra were recorded with a

2570
M. Bayat, H. Imanieh, and E. Hossieninejad
1
Bruker DRX-500 Avance instrument (500.1 MHz for H and 125.7 MHz
for 13C) with CDCl3 as solvent. Chemical shifts are given in parts per
million (d) relative to internal tetramethylsilane (TMS), and coupling
constant (J) are reported in hertz (Hz). Melting points were measured
with an electrotherma1 9100 apparatus. Elemental analyses for C, H,
and N were performed using a Heraeus CHN-O-Rapid Analyzer. These
results agreed favorably with the calculated values. Mass spectra were
recorded with a Shimadzu QP-GC Mass 1100-EX spectrometer operating
at an ionization potential of 70 eV. IR spectra were measured with
Bucksience 5000 spectrometer.
Preparation of Dimethyl 2-[(Tert-butylimino)-methylene]-3-(2,3-dioxo-
2,3-dihydro-indol-1-yl)-butanedioate (4a): Typical Procedure
To a magnetically stirred solution of 0.147 g of isatin (1 mmol) and
0.142 g of dimethyl acetylendicarboxylate (1 mmol) in 5 mL of ethyl acet-
ate, 0.083 g of tert-butyl isocyanide (1 mmol) in 2 mL of ethyl acetate was
added dropwise at 0 ꢁC over 20 min. The reaction mixture was then
allowed to warm up to room temperature and stand for 24 h. The solvent
was removed under reduced pressure, and the residue was purified by
silica-gel (Merck silica gel 60, 70–230 mesh) column chromatography
using hexane–ethyl acetate (8:2) as eluent. The solvent was removed
under reduced pressure to afford the product.
Orange crystals: yield 0.34 g (93%), mp 132–134 ꢁC. IR(KBr) (nmax
=
cmꢀ1): 2086 (C C N), 1740, 1738, and 1680 (C O). H NMR: d ¼ 1.41
(9H, s, CMe3), 3.63 and 3.71 (6H, 2 s, 2OMe), 5.67 (1H, s, CH), 7.05–7.15
(2H, m, arom.), 7.51–7.60 (2H, m, arom.). 13C NMR: d ¼ 30.14 (CMe3),
51.84 and 53.27 (2OMe), 52.11 (CH), 59.14 (CMe3), 62.81 (C ¼ C ¼ N),
111.60, 117.96, 123.80, 125.30, 138.53, 150.14 (arom. carbons), 157.93
(C ¼ C ¼ N), 161.60, 167.36, 169.90, and 182.69 (4C ¼ O). MS (EI,
70 eV): m=z (%) ¼ 373 (Mþ þ 1, 46), 317 (88), 284 (19), 226 (77), 185
(31), 146 (40), 119 (33), 91 (23), 57 (100). Anal. calcd. for C19H20N2O6
(372.87): C, 61.28; H, 5.41; N, 7.25%. Found: C, 61.4; H, 5.2; N, 7.1%.
1
=
=
=
Diethyl 2-[(Tert-butylimino)-methylene]-3-(2,3-dioxo-2,3-dihydro-indol-1-
yl)-butanedioate (4b)
To a magnetically stirred solution of 0.147 g of isatin (1 mmol) and
0.170 g of diethyl acetylendicarboxylate (1 mmol) in 5 mL of ethyl acetate,
0.083 g of tert-butyl isocyanide (1 mmol) in 2 mL of ethyl acetate was
added dropwise at 0 ꢁC over 20 min. The reaction mixture was then
allowed to warm up to room temperature and stand for 24 h.

Highly Functionalized Ketenimines
2571
Orange crystals: yield 0.38 g (95%), mp 102–104 ꢁC. IR(KBr) (nmax
=
cmꢀ1): 2079 (C C N), 1741, 1738, and 1678 (C O). H NMR: d ¼ 1.11
(6H, 2 t,3JHH ¼ 7.1 Hz, 2 Me), 1.35 (9H, s, CMe3), 3.95 and 4.13 (4H, 2q,
3JHH ¼ 7.1 Hz, 2OCH2), 5.62 (1H, s, CH), 6.98–7.05 (2H, m, arom.),
7.44–7.50 (2H, m, arom.). 13C NMR: d ¼ 13.91 and 14.30 (2Me), 30.0,
(CMe3), 52.05 (CH), 59.68 (CMe3), 60.17 and 62.40 (2OCH2), 62.60
(C ¼ C ¼ N), 111.59, 117.76, 123.72, 125.10, 138.39, and 150.21 (arom.
carbons), 157.74 (C ¼ C ¼ N), 162.78, 166.65, 169.17, and 182.60
1
=
=
=
(4C O). MS (EI, 70 eV): m=z (%) ¼ 401 (Mþ þ 1, 77), 345 (85), 298
=
(37), 254 (72), 198 (52), 171 (81), 146 (48), 119 (44), 57 (100). Anal. Calcd.
for C21H24N2O6 (400.43): C, 62.98; H, 6.04; N, 7.01%. Found: C, 62.5;
H, 6.1; N, 6.7%.
Diethyl 2-[(Cyclohexylimino)-methylene]-3-(2,3-dioxo-2,3-dihydro-
indol-1-yl)-butanedioate (4c)
To a magnetically stirred solution of 0.147 g of isatin (1 mmol) and
0.170 g of diethyl acetylendicarboxylate (1 mmol) in 5 mL of ethyl acetate,
0.110 g of cyclohexyl isocyanide (1 mmol) in 2 mL of ethyl acetate was
added dropwise at 0 ꢁC over 20 min. The reaction mixture was then
allowed to warm up to room temperature and stand for 24 h.
Red crystals: yield 0.38 g (90%), mp 126–128 ꢁC. IR(KBr)
1
(nmax=cmꢀ1): 2078 (C C N), 1743, 1721, and 1687 (C O). H NMR:
=
=
=
3
3
d ¼ 1.01 (3H, t, JHH ¼ 7.2 Hz, CH3), 1.22 (3H, t, JHH ¼ 7.2 Hz,
CH3), 1.09–1.18 (10H, m, 5CH2), 4.09 (2H, q,3JHH ¼ 7.2 Hz, OCH2),
4.18 (2H, q,3JHH ¼ 7.2 Hz, OCH2), 5.68 (1H, s, CH), 7.03–7.19 (2H, m,
arom.), 7.51–7.57 (2H, m, arom.). 13C NMR: d ¼ 13.92 and 14.32
(2CH3), 23.64, 25.16, 25.41, 32.98, and 33.05 (5CH2), 52.28 (CH), 58.10
( ¼ N-CH), 60.52 and 62.53 (2OCH2), 77.53 (C ¼ C ¼ N), 111.66,
117.85, 123.70, 125.21, 138.64, and 150.30 (arom. carbons), 157.96
=
(C ¼ C ¼ N), 162.17, 166.89, 169.40, and 182.81 (4C O). MS (EI,
70 eV): m=z (%) ¼ 426 (Mþ , 6), 298 (100), 280 (25), 251 (52), 198 (16),
170 (33), 148 (43), 119 (39), 98 (35), 55 (31). Anal. calcd. for
C23H26N2O6 (426.46): C, 64.77; H, 6.14; N, 6.56%. Found: C, 64.9; H,
6.2; N, 6.7%.
Dimethyl 2-[(Tert-butylimino)-methylene]-3-(2,3-dioxo-1,3-dihydro-
isoindol-2-yl)-butanedioate (4d)
To a magnetically stirred solution of 0.147 g of phthalimide (1 mmol) and
0.142 g of dimethyl acetylendicarboxylate (1 mmol) in 5 mL of ethyl
acetate, 0.083 g of tert-butyl isocyanide (1 mmol) in 2 mL of ethyl acetate

2572
M. Bayat, H. Imanieh, and E. Hossieninejad
was added dropwise at 0 ꢁC over 20 min. The reaction mixture was then
allowed to warm up to room temperature and stand for 24 h.
Colorless oil: yield 0.32 g (87%). IR(KBr) (nmax=cmꢀ1): 2086
1
=
=
=
(C C N), 1738, and 1678 (C O). H NMR: d ¼ 1.49 (9H, s, CMe3),
3.85 and 3.89 (6H, 2 s, 2OMe), 6.12 (1H, s, CH), 7.75–8.15 (4H, m,
arom.). 13C NMR: d ¼ 30.10, (CMe3), 51.05 and 53.12 (2OMe), 59.10
(CMe3), 60.61 (C ¼ C ¼ N), 123.71, 128.60, 131.61, 132.10, 134.31 and
134.62 (arom. carbons), 163.90 (C ¼ C ¼ N), 167.61, 168.20 and 169.63
þ
=
(4C O). MS (EI, 70 eV): m=z (%) ¼ 372 (M , 6), 316 (64), 271 (35),
242 (24), 146 (100), 73 (45), 57 (70). Anal. Calcd. for C19H20N2O6
(372.37): C, 61.28; H, 5.41; N, 7.52%. Found: C, 61.9; H, 5.1; N, 7.2%.
2-[(Cyclohexylimino)-methylene]-3-(4-nitro-1H-imidazol-1-yl)-1,4-
diphenyl-1,4-butanedione (4e)
To a magnetically stirred solution of 0.113 g of 4-nitroimidazole (1 mmol)
and 0.234 g of dibenzoylacetylene (1 mmol) in 10 mL of dry diethyl ether,
0.110 g of cyclohexyl isocyanide (1 mmol) in 2 mL of dry diethyl ether was
added dropwise at 0 ꢁC over 20 min. The reaction mixture was then
allowed to warm up to room temperature and stand for 24 h.
Pale yellow powder: yield 0.43 g (95%), mp 146–148 ꢁC. IR(KBr)
(nmax=cmꢀ1): 2035 (C C N), 1687 (C O), 1277 and 1594 (NO2).
1H NMR: d ¼ 1.16–1.67 (10H, m, 5CH2), 3.68 (1H, m, ¼ N-CH), 7.15
(1H, s, CH ofbutanedione), 7.37–7.66 (10H, m, arom.), 7.69 (1H, s,
CH of imidazole), 8.05 (1H, s, CH of imidazole). 13C NMR: d ¼ 23.44,
24.60, 32.83, and 33.04 (5CH2), 59.12 ( ¼ NCH), 61.01 (CH ofbutane-
dione), 68.95 (C ¼ C ¼ N), 119.81 (C5 of imidazole), 127.40, 128.45,
128.67, 129.27, 132.10, and 134.94 (arom. carbons), 133.08 and 138.40
(2Cipso of 2C6H5), 136.27 (C2 of imidazole), 147.92 (C4 of imidazole),
=
=
=
=
155.33 (C ¼ C ¼ N), 190.41 and 191.48 (2C O). MS (EI, 70 eV): m=z
(%) ¼ 456 (Mþ , 11), 345 (21), 303 (11), 269 (24), 262 (47), 263 (53),
106. (21), 105 (100), 98, (22), 76, (84). Anal. Calcd. for C26H24N4O4
(456.50): C, 68.41; H, 5.30; N, 12.27%. Found: C, 68.2; H, 5.8; N, 12.1%.
2-[(Tert-butylimino)-methylene]-3-(2-phenyl-methanone-2-H-imidazol-2-
yl)-1,4-diphenyl-1,4-butanedione (4f)
To a magnetically stirred solution of 0.172 g of 2-benzoylimidazole
(1 mmol) and 0.234 g of dibenzoylacetylene (1 mmol) in 10 mL of dry
diethyl ether 0.083 g of tert-butyl isocyanide (1 mmol) in 2 mL of dry
diethyl ether was added dropwise at 0 ꢁC over 20 min. The reaction

Highly Functionalized Ketenimines
2573
mixture was then allowed to warm up to room temperature and stand
for 24 h.
Pale yellow powder: yield 0.44 g (92%), mp 160–163 ꢁC. IR(KBr)
(nmax=cmꢀ1): 2080 (C C N), 1682 and 1609 (2C O), 1277 and 1594
=
=
=
1
(NO2). H NMR: d ¼ 1.07 (9H, s, CMe3), 7.34 (1H, s, CH of midazole),
7.37–7.62 (11H, m 3C6H5), 7.56 (1H, s, CH of imidazole), 7.97 (1H, s, CH
3
of butanedione), 8.15 (2H, d, JHH ¼ 7.6 Hz, 2CHortho of C6H5), 8.21
3
(2H, d, JHH ¼ 7.6 Hz, 2CHortho of C6H5). 13C NMR: d ¼ 29.90
(CMe3), 59.78 (CMe3), 63.54 (CH of butanedione), 70.43 (C ¼ C ¼ N),
124.35 (CH of imidazole), 127.37, 127.95, 128.27, 128.68 and 128.95
(arom. carbons), 129.36 (CH of imidazole), 130.89, 131.65, 132.54 and
133.83 (arom. carbons), 134.35, 137.26 and 138.97 (3Cipso of 3C6H5),
142.71 (C2 of imidazole), 159.84 (C ¼ C ¼ N), 184.34, 190.81 and
192.96 (3C O). MS (EI, 70 eV): m=z (%) ¼ 490 (Mþ þ 1, 5), 345 (21),
=
303 (11), 269 (25), 246 (10), 129 (14), 106 (20), 105 (100), 98 (22), 76
(84), 52 (30). Anal. Calcd. for C31H27 N3 O3 (489.57): C, 76.05; H,
5.55; N, 8.58%. Found: C, 76.5; H, 5.1; N, 8.2%.
Di-tert-butyl-2-[(cyclohexylimino)-methylene]-3-(2,5-dioxo-pyrrolidin-1-
yl)butanedione (4g)
To a magnetically stirred solution of 0.099 g of succinimide (1 mmol) and
0.226 g of di-tert-butyl acetylendicarboxylate (1 mmol) in 10 mL of dry
diethyl ether, 0.110 g of cyclohexyl isocyanide (1 mmol) in 2 mL of dry
diethyl ether was added dropwise at 0 ꢁC over 20 min. The reaction mix-
ture was then allowed to warm up to room temperature and stand for 24 h.
Pale yellow oil: yield 0.36 g (85%). IR(KBr) (nmax=cmꢀ1): 2065
1
=
=
=
(C C N), 1730 and 1687 (C O). H NMR: d ¼ 1.35 and 1.64 (18H,
2 s, 2CMe3), 1.24–1.48 (10H, m, CH2), 2.42 (4H, s, 2CH2), 3.64 (1H,
m, CHN), 6.52 (1H, s, CH).13C NMR: d ¼ 24.71, 25.12, 25.28, 27.92,
32.34 and 33.09 (7CH2), 27.91 and 28.20 (2CMe3), 52.48 (CH), 60.12
(CHN), 63.34 (C ¼ C ¼ N), 81.50 and 82.09 (2OCMe3), 158.19
=
(C ¼ C ¼ N), 167.66, 168.14, 170.85 (3C O). MS (EI, 70 eV):
m=z (%) ¼ 434 (Mþ , 2), 336 (8), 292 (25), 142 (38), 98 (100), 82 (54),
56 (46). Anal. Calcd. for C23H34N2O6 (434.53): C, 63.57; H, 7.88; N,
6.44%. Found: C, 64.4; H, 6.2; N, 6.1%.
REFERENCES
1. Schreiber, S. L. Target-oriented and diversity-oriented organic synthesis in
drug discovery. Science 2000, 287, 1964–1969.
2. Domling, A. Recent advances in isocyanide-based multicomponent chemis-
try. Curr. Opin. Chem. Boil. 2002, 6, 297–305.

2574
M. Bayat, H. Imanieh, and E. Hossieninejad
3. Trost, B. M. Atom-economy-a challenge for organic synthesis: Homogeneous
catalysts leads the way. Angew. Chem., Int. Ed. Engl. 1995, 34, 259–281.
4. Bienayme, H.; Hulme, C.; Oddon, G.; Schmitt, P. Maximizing synthetic
efficiency: Multi-component transformations lead the way. Chem. Eur.
J. 2000, 6, 3321–3329.
5. Ugi, I. From isocyanides via four-componenent condensations to antibiotic
syntheses. Angew. Chem., Int. Ed. Eng. 1982, 21, 810–812.
6. Ugi, I.; Lohberger, S.; Karl, R. In Comprehensive Organic Synthesis; B. M.
Trost, I. Fleming (Eds.); Pergamon: Oxford, 1991, vol. 2, pp. 1083–1106.
7. Domling, A.; Ugi, L. Multicomponent reactions with isocyanides. Angew.
Chem. Int. Ed. Eng. 2000, 39, 3169–3210.
8. Hulme, C.; Ma, L.; Romano, J. J.; Morton, G.; Tang, S. Y.; Cherrier, M. P.;
Choi, S.; Salvino, J.; Labaudiniere, R. Novel applications of carbon dioxide=
MeOH for the synthesis of hydantoins and cyclic ureas via the Ugi reaction.
Tetrahedron Lett., 2000, 41, 1889–1893.
9. Ballini, R.; Bosica, G.; Conforti, M. L.; Maggi, R.; Mazzacani, A.; Righi, P.;
Sartori, G. Three-component process for the synthesis of 2-amino-2-
chromenes in aqueous media. Tetrahedron Lett. 2001, 57, 1395–1398.
10. Arrieta, A.; Cossio, F. P.; Lecea, B. Competitive mechanism and origins of
stereocontrol in the [2 þ 2] thermal cycloaddition between imines and keteni-
minium cations. J. Org. Chem. 1999, 64, 1831–1842.
11. Aumann, R.; Jasper, B.; Lage, M.; Kerbs, B. Organic syntheses via transition
metal complexes: 2-(Acyloxy)-ethenyl-keteneimines by ligand disengagement
with isocyanide. Organometallics 1994, 13, 3502.
12. Getzmann, R.; Moller, M. H.; Rodewald, U.; Frohlich, R.; Grehl, M.;
Wurthwein, E. U. Metallated ketenimines: Deprotonation of N-isopropyl-
diphenyl-ketenimine and subsequent trapping reaction with electrophiles: A
theoretical and experimental study. Tetrahedron 1995, 51, 3767–3786.
13. Coyl, J. D.; Raply, P. A. Ketenimine: Geometrie und Abhangigkeit der Raze-
misierungsbarriere von Den Substituenten. Journal of the Chemical Society,
Perkin Transactions 2 1985, 1, 1957–1959.
14. Kosbahn, W.; Runge, W. Electronic spectra and electronic structures of
ketenimines and carbodiimides. Journal of the Chemical Society Perkin Trans-
actions 2 1981, 2, 270–280.
15. Marcaccini, S.; Torroba, T. The use of isocyanides in heterocyclic synthesis.
Org. Prep. Preced. Int. 1993, 25, 141–172.
16. Siddall, T. H.; prohaska, C. A. Geminal proton nonequivalences and
related phenomena in some N-substituted amides. J. Am. Chem. Soc. 1966,
88, 1172–1176.
17. Skattebol, L.; Jones, E. R. H.; Whiting, M. C. 1-Phenyl-1-penten-4-yn-3-ol.
Org. Synth. 1963, 4, 792–794.
18. Bowden, K.; Heilbron, I. M.; Jones, E. R. H.; Weedon, B. C. Researches on
acetylenic compounds, part I: The preparation of acetylenic ketones by
oxidation of acetylenic carbinols. J. Chem. Soc. 1946, 36.
19. Bastiaansen, L. A. M.; Goderoi, E. F. 2-Aroylimidazoles: A simple one-step
synthesis. Synthesis 1978, 675–676.