Chemistry of stable iminopropadienones, RN=C=C=C=O

Article abstract of DOI:10.1021/jo0110552

The synthesis, spectroscopic properties, and chemical reactions of the stable (neopentylimino)-, (mesitylimino)-, and (o-tert-butylphenylimino)propadienones (6) are reported. Nucleophilic addition of amines affords the malonic amidoamidines 7 and 8. 3,5-Dimethylpyrazole reacts analogously to form 9b. Addition of 1,2-dimethylhydrazine produces pyrazolinones 10-12. Addition of N,N'-dimethyldiaminoethane, -propane, and -butane gives diazepine, diazocine, and diazonine derivatives 13-15, respectively (X-ray structures of 13c, 14a, and 15a are available). The mesoionic pyridopyrimidinium olates 18 are obtained by addition of 2-(methylamino)pyridine (X-ray structure of 18b available). Primary 2-aminopyridines afford the pyridopyrimidininones 20-29 and 31 (X-ray structure of 21a available), and 2-aminopyrimidines and 2-aminopyrazine afford pyrimidopyrimidinones and pyrazinopyrimidinones 33-35. Pyrimidoisoquinolinone 36 results from 1-aminoisoquinoline and pyridoquinolinone 40 from 8-aminoquinoline. 2-Aminothiazoline and 2-aminothiazole afford thiazolopyrimidinone derivatives 41-43 (X-ray structure of 43a available).

Full text of DOI:10.1021/jo0110552

J . Org. Chem. 2002, 67, 2619-2631
2619
Ch em istr y of Sta ble Im in op r op a d ien on es, RNdCdCdCdO
Herve´ Bibas, Daniel W. J . Moloney, Ralf Neumann, Majed Shtaiwi, Paul V. Bernhardt, and
Curt Wentrup*
Chemistry Department, The University of Queensland, Brisbane, Queensland 4072, Australia
wentrup@chemistry.uq.edu.au
Received November 5, 2001
The synthesis, spectroscopic properties, and chemical reactions of the stable (neopentylimino)-,
(mesitylimino)-, and (o-tert-butylphenylimino)propadienones (6) are reported. Nucleophilic addition
of amines affords the malonic amidoamidines 7 and 8. 3,5-Dimethylpyrazole reacts analogously to
form 9b. Addition of 1,2-dimethylhydrazine produces pyrazolinones 10-12. Addition of N,N′-
dimethyldiaminoethane, -propane, and -butane gives diazepine, diazocine, and diazonine derivatives
13-15, respectively (X-ray structures of 13c, 14a , and 15a are available). The mesoionic
pyridopyrimidinium olates 18 are obtained by addition of 2-(methylamino)pyridine (X-ray structure
of 18b available). Primary 2-aminopyridines afford the pyridopyrimidininones 20-29 and 31
(X-ray structure of 21a available), and 2-aminopyrimidines and 2-aminopyrazine afford pyrimi-
dopyrimidinones and pyrazinopyrimidinones 33-35. Pyrimidoisoquinolinone 36 results from
1-aminoisoquinoline and pyridoquinolinone 40 from 8-aminoquinoline. 2-Aminothiazoline and
2-aminothiazole afford thiazolopyrimidinone derivatives 41-43 (X-ray structure of 43a available).
In tr od u ction
The iminopropadienones, RNdCdCdCdO, constitute
a recently discovered class of compounds.1 While the
simple alkyl derivatives (methyl,1 isopropyl,2 and tert-
butyl2) are notoriously unstable compounds which can,
however, be isolated and characterized in low-tempera-
ture matrixes, the aryl derivatives are more stable and
undergo chemical reactions, often in good preparative
yields, under controlled conditions at temperatures around
-100 to -50 °C.3-7
We have now succeeded in preparing several imino-
propadienones that are stable at room temperature,
namely the neopentyl, mesityl,8 and o-tert-butylphenyl
derivatives. This has allowed a more thorough investiga-
tion of the preparative potential of these compounds. The
results are reported herein.
compounds 2 with dimethyl- and diethylamine affords 4
and 5, respectively. Compounds of type 2-5 can all be
used to generate iminopropadienones 6 by flash vacuum
thermolysis (FVT), but 4 is the best overall precursor,
and therefore, most experiments were performed with
these types of compounds (4a -c).
Resu lts a n d Discu ssion
FVT of 4a at 700 °C afforded CO2, acetone, and
(neopentylimino)propadienone (6a ). Collection of the
The 5-bis(methylthio)methylene derivative of Mel-
drum’s acid, 1, undergoes nucleophilic displacement of
SMe groups on reaction with amines.2-5,9 Thus, com-
pounds 2a and 3a are obtained on reaction with 1 and 2
equiv of neopentylamine, respectively. The reaction of
(1) Mosandl, T.; Kappe, C. O.; Flammang, R.; Wentrup, C. J . Chem.
Soc., Chem. Commun. 1992, 1571.
(2) Moloney, D. W. J .; Wentrup, C. J . Org. Chem. 1997, 62, 4240.
(3) Mosandl, T.; Stadtmu¨ller, S.; Wong, M. W.; Wentrup, C. J . Phys.
Chem. 1994, 98, 2005.
(4) Fulloon, B. E.; Wentrup, C. J . Org. Chem. 1996, 61, 1363.
(5) Wentrup, C.; Rao, R. V. V.; Frank, W.; Fuloon, B. E.; Moloney,
D. W. J .; Mosandl, T. J . Org. Chem. 1999, 64, 3608.
(6) (a) Plu¨g. C.; Frank, W.; Wentrup, C. J . Chem. Soc., Perkin Trans.
2 1999, 1087. (b) Andersen, H. G.; Mitschke, U.; Wentrup, C. J . Chem.
Soc., Perkin Trans. 2 2001, 602.
(7) For a review of the chemistry of carbon suboxide, C3O2, see:
Kappe, T.; Ziegler, E. Angew. Chem., Int. Ed. Engl. 1974, 13, 491.
(8) Moloney, D. W. J . Ph.D. Thesis, The University of Queensland,
Brisbane, Australia, 1997.
products in a cold trap at -50 °C allowed the subsequent
distillation of 6a as a yellow oil, which is stable at room
temperature. The IR spectrum of 6a is dominated by a
very intense and complex band centered around 2250
cm-1, as is typical of iminopropadienones (see the Sup-
porting Information).1-6
(9) Ben Cheikh, A.; Chuche, J .; Manisse, N.; Pommelet, J . C.; Netsch,
K.-P.; Lorencak, P.; Wentrup, C. J . Org. Chem. 1991, 56, 970.
10.1021/jo0110552 CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/19/2002

2620 J . Org. Chem., Vol. 67, No. 8, 2002
Bibas et al.
(Mesitylimino)propadienone 6b was similarly obtained
by FVT of 4b at 700 °C. Between 400 and 800 °C this
was the only cumulene observed by IR spectroscopy
(2234/2243/2248 (vs) cm-1; 2149 (w) cm-1 (Ar matrix)).
In CCl4 solution at room temperature, it features an
intense peak centered at 2214 cm-1. The far-IR spectrum
in polyethylene shows very low-frequency bands at 73
and 89 cm-1, which, by analogy with C3O2,10 may be due
to the bending of the cumulene chain at the central
carbon atom. However, due to the structural complexity
of 6b, further far-IR studies of simpler compounds would
be required for a rigorous assignment of the vibrational
modes. The Raman spectrum shows a relatively weak
cumulenic band at 2217-2171 cm-1. The spectra are
available in the Supporting Information.
demonstrated that the initial reaction involves formation
of an amidoketenimine by addition of dimethylamine to
the CdO group in 6b. This reaction takes place at -40
°C in CD2Cl2 solution, and the ketenimine was fully
1
characterized by H NMR and IR spectroscopy.5 Subse-
quent slow addition of a second molecule of amine gives
amidoamidines 7 and 8. Such compounds are usually
((o-tert-Butylphenyl)imino)propadienone (6c) was ob-
tained by FVT of either 2c or 4c at 700 °C and purified
by bulb-to-bulb distillation. The IR spectrum shows the
characteristic bands at 2237 (vs) and 2139 (w) cm-1 (Ar
matrix; see the Supporting Information).
The 13C NMR spectrum of 6a shows highly character-
istic carbon resonances at -11 (central cumulenic carbon,
C2), 108.5 (CdN), and 130 ppm (CdO). 6b has the
corresponding signals at -7, 112, and 133 ppm, and 6c
1
at -3.8, 108, and 130 ppm (the H and 13C NMR spectra
of 6a -c are reproduced in the Supporting Information).
Carbon suboxide, OdCdCdCdO, features analogous 13C
NMR resonances at -14.6 and 129.7 ppm.11 Calculations
at the MP2/6-31G*//HF/6-31G* level reproduce the 13C
NMR shifts of C3O2 and the iminopropadienones very
accurately.8,12 The imine carbon signal at 108-112 ppm
in the iminopropadienones is very broad and weak at
room temperature due to the adjacent nitrogen quadru-
pole moment (see e.g. Figure S2). The signal intensity
improves by recording the spectrum at -30 °C.
Compounds 6 are quite long-lived at room temperature,
even in the presence of mild nucleophiles such as alcohols
and water. Compound 6a has a half-life of almost 7 h in
the presence of a 2-fold excess of methanol.13 We have
investigated this type of reaction for other iminopropa-
dienones and found that ketenimines are formed first,
followed by addition of a second molecule of methanol to
afford malonic ester imides (eq 1).5 Compounds 6 react
obtained as the unconjugated tautomers (7); however,
workup by Kugelrohr distillation caused incomplete
tautomerization of 7a and 8a to 7a ′/8a ′. 3,5-Dimeth-
ylpyrazole reacts with 6 like an amine, forming 9b with
(mesitylimino)propadienone.
The reaction of 6 with hydrazines and bis(amines)
affords cyclic compounds. Thus, the pyrazolinone 10 is
much faster with amines than with alcohols.13 They react
virtually spontaneously with dimethyl- and diethylamine
to afford amidoamidines 7 and 8, respectively. We have
(10) Millar, F. A.; Lemon, D. H.; Witkowski, R. E. Spectrochim. Acta
1965, 21, 1709. Smith, W. H.; Leroy, G. E. J . Chem. Phys. 1966, 45,
1767.
(11) Williams, E. A.; Cargoli, J . D.; Ewo, A. J . Chem. Soc., Chem.
Commun. 1975, 367.
obtained from 6a and 1,2-dimethylhydrazine at room
temperature. Pyrazolinone 11 is obtained from 6b with
hydrazine, and pyrazolinones 12b,c are obtained with
methylhydrazine, respectively. N,N′-Dimethyl-1,2-diami-
noethane, -1,3-diaminopropane, and -1,4-diaminobutane
afford the perhydrodiazepine, -diazocine, and -diazonine
derivatives 13a -c, 14, and 15, respectively. Compound
13a undergoes partial tautomerization to the conjugated
(12) Koch, R.; Wentrup, C. Unpublished results.
(13) More detailed kinetics of the reactions with alcohols and amines
are under investigation. It is known that ketenes react faster with
amines than with alcohols, and a nucleophilicity series has been
published: De Lucas, N. C.; Netto-Ferreira, J .-C.; Andraos, J .; Scaiano,
J . C. J . Org. Chem. 2001, 66, 5016. Acetylketene reacts with propanol
and propanamine to give a product ratio of 1:2.3: Birney, D. M.; Xu,
X.; Ham, S.; Huang, X. J . Org. Chem. 1997, 62, 7114.

Chemistry of Stable Iminopropadienones
J . Org. Chem., Vol. 67, No. 8, 2002 2621
Sch em e 1
13a ′ on workup involving Kugelrohr distillation. o-
Phenylenediamine reacted similarly with 6b to afford the
benzodiazepine derivative 16. The structures of com-
pounds 13c, 14a , and 15a were confirmed by X-ray
crystallography (see the Supporting Information). Com-
pounds 6b,c also reacted with N,N′-dimethyl-1,3-diami-
nopropane to afford diazocine derivatives (14b,c), but
these have so far only been obtained as oils that were
difficult to purify. No cyclic amidoamidines of structures
related to 13-15 are known in the literature.
The reactions of iminopropadienones with N-hetero-
cyclic amines is particularly interesting, because of the
possibility of forming mesoionic (zwitterionic) com-
pounds.6b,14 Compounds 6 react with 2-(methylamino)-
pyridine to afford pyridopyrimidinium olates 18 as red-
orange solids (Scheme 1). The atom connectivity in 18a
was established by 2D 13C NMR experiments (HMBC and
HSQC) and by X-ray crystallography for 18b (data in the
Supporting Information). The structures of many me-
soionic compounds show distortions toward ketene va-
lence isomers, with long N-CO bonds and acute OCN
angles.14 Compound 18b features a characteristically long
N-CO bond (1.49 Å) and tilting of the CdO group toward
the ring junction at N5a ( O4-C4-N5 ) 116°). A
mechanism for the formation of 18 is given in Scheme 1.
It is known that ketenes react with pyridine, even at very
low temperatures (e.g. 40 K), to produce ketene-pyridine
zwitterions.15 Furthermore, carbon suboxide, OdCdCd
CdO, reacts with pyridine and other amine nucleophiles
in low-temperature matrixes to give, first, observable van
der Waals complexes,16 which can be transformed into
covalent zwitterions of the type OdCdCdC(O-)Nu+.17 It
is postulated that the corresponding zwitterion 17 can
form by interaction of 2-(methylamino)pyridine with 6.
Addition of the exocyclic amino group to the imine carbon
atom in 17 affords the mesoionic heterocycle 18. It would
be possible to bypass 17 by postulating that the exocyclic
amino group reacts with the less electrophilic CdN
carbon of the cumulene 6, but this goes against all our
knowledge of the initial stages of these and similar
reactions.5,16,17 This reaction is reversible: FVT of 18b
at 350 °C regenerates 2-(methylamino)pyridine and 6b,
as proved by the IR spectrum of the products in Ar matrix
at 10 K. However, the mechanisms of the synthesis and
fragmentation of 18c are likely to involve different
intermediates. A rational mechanism for the FVT reac-
tion is given in Scheme 1, and this is based on a previous
investigation of ring opening and fragmentation in six-
membered mesoionic compounds.18 The 1,2-dihydro-2-
(methylimino)pyridine initially formed in this mechanism
undergoes rapid tautomerization to the observed 2-(me-
thylamino)pyridine.18
The corresponding reactions of 6 with primary 2-ami-
nopyridines would proceed via the analogous zwitterions
17′ to the mesoions 19, followed by tautomerization to
the pyridopyrimidinones 20-24 as final products (Scheme
2). These are indeed the major or exclusive products when
the reactions are performed in methylene chloride solu-
(14) Plu¨g, C.; Wallfisch, B.; Andersen, H. G.; Bernhardt, P. V.; Baker,
L. J .; Clark, G. R.; Wong, M. W.; Wentrup, C. J . Chem. Soc., Perkin
Trans. 2 2000, 2096.
(15) Qiao, G. G.; Andraos. J .; Wentrup, C. J . Am. Chem. Soc. 1996,
118, 5634. Visser, P.; Zuhse, R.; Wong, M. W.; Wentrup, C. J . Am.
Chem. Soc. 1996, 118, 12598. Kollenz, G.; Holzer, S.; Kappe, C. O.;
Dalvi, T. S.; Fabian, W. M. F.; Sterk, H.; Wong, M. W.; Wentrup, C.
Eur. J . Org. Chem. 2001, 1315.
(16) Couturier-Tamburelli, I.; Aycard, J .-P.; Wong, M. W.; Wentrup,
C. J . Phys. Chem. A 2000, 104, 3466.
(17) Sessouma, B.; Couturier-Tamburelli. I.; Monnier, M.; Wong, M.
W.; Wentrup, C.; Aycard, J . P. J . Phys. Chem. A, in press.
(18) Fiksdahl, A.; Plu¨g, C.; Wentrup, C. J . Chem. Soc., Perkin Trans.
2 2000, 1841.

2622 J . Org. Chem., Vol. 67, No. 8, 2002
Bibas et al.
Sch em e 2
portions of the “abnormal” isomers 26-29 were found to
increase when the reactions were performed in refluxing
toluene, but 20a -23a always remained the major isomer.
Control experiments excluded the possibility of a rear-
rangement of 22a to 28. The formation of 26-29 is
postulated to result from initial attack of the exocyclic
amino group of the pyridine on the carbonyl group of 6,
leading to the zwitterions 25. Subsequent attack of the
pyridine nitrogen lone pair on the imine carbon in 25
gives 26-29. In most cases, other possible tautomers of
20-30 are not observed, but in the case of 2-amino-3-
methylpyridine, a small amount of the hydroxy tautomer
31a was formed as well.
Compounds of type 20-24 are structurally interesting
because, even though they are not mesoionic, they exist
in a highly zwitterionic form, as expressed by resonance
structure 32.14 The X-ray structure analysis of 21a
confirmed that this is the case, with short C10-N1 and
N1-C2 bonds, long C2-C3 and C3-C4 bonds, an unusu-
ally long C4-N5 bond, and the CdO group at C4 tilted
toward the ring junction at N5 (C10-N1 ) 1.322 Å, N1-
C2 ) 1.353 Å, C2-C3 ) 1.383 Å, C3-C4 ) 1.380 Å, C4-
N5 ) 1.446 Å, N5-C10 ) 1.376 Å; C10-N1-C2 )
117.3°, N1-C2-N2 ) 115.9°, N1-C2-C3 ) 123.0°, C2-
C3-C4 ) 121.5°, C3-C4-N5 ) 114.1°, O4-C4-N5 )
116.8°). Full data are reported in the Supporting Infor-
mation.
2,3-Diaminopyridines react just like 2-aminopyridine,
by using the pyridine ring nitrogen and the amino group
in the 2-position, thus affording 33 with 6b.
2-Aminopyrimidines and 2-aminopyrazine react in a
similar manner with 6 to give pyrimido- and pyrazinopy-
rimidinones 34 and 35. These rings are less nucleophilic
tion at room temperature, but small amounts of the
alternate addition products 26-29 were also obtained
from (neopentylimino)propadienone 6a . 2-Amino-6-me-
thylpyridine gave only 24; compound 30 was not formed.
Usually, the pyridine nitrogen atom is the most nucleo-
philic center in 2-aminopyridines, and the CdO group is
more electrophilic than the CdN group in iminopropa-
dienones, but the formation of both types of addition
products, corresponding to the two alternate modes of
nucleophile/electrophile interaction, has been described
in a previous case.6b Moreover, the orientation of addition
can be modulated by electronic substituent effects in the
aromatic ring in (phenylimino)propadienones.19 The pro-
(19) Shtaiwi, M.; Wentrup, C. Unpublished results. Shtaiwi, M.
Ph.D. Thesis, The University of Queensland, Brisbane, Australia, 2002.

Chemistry of Stable Iminopropadienones
J . Org. Chem., Vol. 67, No. 8, 2002 2623
Sch em e 3
than pyridine and react much more slowly. 1-Aminoiso-
quinoline reacts at room temperature to afford the
cyclization products 36a ,b.
(see the Supporting Information). As mentioned above,
the “normal” pyridopyrimidinones of types 20-24 are
highly zwitterionic, as expressed in the canonical struc-
ture 32. The bond lengths in 43a suggest a different kind
of zwitterionic contribution involving the exocyclic amino
group, as expressed in canonical structure 44 (bond
lengths (Å): C2-C3 ) 1.320, C8a-N8 ) 1.296, N8-C7
) 1.398, C7-C6 ) 1.416, C6-C5 ) 1.372, C5-N4 )
1.400, N4-C8a ) 1.374; exocyclic NH-C5 ) 1.330,
exocyclic NH-CH2 ) 1.457).
The reaction with 8-aminoquinoline in refluxing THF
affords compound 40a , the formation of which is ratio-
nalized in Scheme 3. Initial addition to 6a by using the
pyridine type lone pair leads to zwitterion 37. Cyclization
affords the new zwitterion 38, which can be regarded as
an intramolecular ketene-pyridine zwitterion.6b,15 Such
zwitterions can be in equilibrium with the ketene valence
isomer 39. The cyclization of 39 onto the C7 of the
quinoline system can be described as an electrophilic
aromatic substitution by a ketene. Another cyclization
reaction analogous to 39 f 40 has been reported re-
cently.18 Again, it would be possible to bypass 37 and 38
by postulating direct formation of 39. However, this
would involve the initial attack of an amino group on the
less electrophilic and more hindered CdN carbon in 6a
and go against our current knowledge of the reactivity
of iminopropadienones.
Thiazole forms a van der Waals complex with C3O2 in
the same manner as pyridine,16,17 involving an interaction
between the nitrogen lone pair and the cumulene sys-
tem.20 Therefore, it may be expected that thiazoles and
thiazolines react with ketenes in much the same manner
as pyridines and that reaction with 6 will proceed
analogously to Schemes 1 and 2. 2-Aminothiazoline
afforded the expected addition products 41a -c in meth-
ylene chloride solution at room temperature. Similarly,
2-aminothiazole yielded compounds 42a -c under the
same reaction conditions, but in refluxing toluene a small
amount of the “abnormal” tautomer 43a was formed as
well. The mechanism for its formation is expected to be
analogous to the formation of 26-30 in Scheme 2. The
structure of 43a was confirmed by X-ray crystallography
Con clu sion
Whereas simple alkyliminopropadienones are highly
unstable and have the character of reactive intermedi-
ates, the neopentyl, mesityl, and o-tert-butylphenyl de-
rivatives 6 are sufficiently stable to permit isolation at
room temperature. This may appear somewhat surpris-
ing, since the steric hindrance exerted by these substit-
uents, especially to attack on the cumulenic carbonyl
groups, would seem to be very modest. Cumulenes 6
undergo a multitude of nucleophilic addition reactions,
usually initiated by attack of amines on the cumulenic
carbonyl group, to generate zwitterion intermediates.
Subsequent ring closure reactions lead to a multitude of
heterocyclic compounds containing five-, six-, seven-,
eight-, and nine-membered rings, including pyrazolino-
nes, pyridopyrimidinones and mesoionic pyridopyrimi-
dinium olates, pyrimidopyrimidinones, pyrazinopyrimi-
dinones, and perhydrodiazepinone, -diazocinone, and
-diazoninone derivatives.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. NMR spectra were recorded at
200 MHz for 1H and 50.3 MHz for 13C unless otherwise
indicated. 2D H-13C COSY spectra were recorded using the
1
HMBC or HSQC sequences. Mass spectra were obtained at
70 eV electron ionization. GC-MS employed a BP-4 capillary
column (30 m × 0.25 mm; He carrier gas at 20 psi head
pressure; injector 200 °C; detector 280 °C; column temperature
100-270 °C, programmed at 16 °C/min). Flash, column, and
thin-layer chromatography were performed on silica gel. IR
spectra were recorded on FT-IR spectrometers, usually at
0.5-1 cm-1 resolution. Melting points are uncorrected. The
(20) Couturier-Tamburelli. I.; Sessouma, B.; Aycard, J .-P. J . Mol.
Struct. 2001, 560, 197.

2624 J . Org. Chem., Vol. 67, No. 8, 2002
Bibas et al.
apparatus used for flash vacuum thermolysis and matrix
isolation has been described.21
(Neop en tylim in o)p r op a d ien on e (6a ). This compound
was prepared by preparative FVT as follows. In the course of
ca. 1 h compound 4a (100 mg, 0.35 mmol) was sublimed at
150-180 °C/10-4 mbar through an unpacked 300 × 20 mm
(i.d.) horizontal quartz tube heated to 700 °C in a tube furnace
(heating zone 250 mm). The iminopropadienone was collected
5-[((2,2-Dim eth ylpr opyl)am in o)(m eth ylth io)m eth ylen e]-
2,2-d im eth yl-1,3-d ioxa n e-4,6-d ion e (2a ). 2,2-Dimethylpro-
pylamine (6.53 g, 75 mmol) and 5-(bis(methylthio)methylene-
1,3-dioxane-4,6-dione (1;4 18.6 g, 75 mmol) were dissolved in
130 mL of THF and stirred for 2 days at room temperature.
The solvent was reduced to half its volume under vacuum, and
diethyl ether (100 mL) was added. A yellow precipitate formed
immediately. The solution was decanted and the residue
recrystallized from THF/diethyl ether to yield 18.3 g (85%) of
2a. Use of CH3CN or EtOH as solvent gave yields of 71 and
75%, respectively. The compound was sublimed at 100 °C/10-7
in
a U-tube cooled to -50 °C with dry ice/acetone and
connected via an uncooled cold finger to a vacuum line
equipped with an oil diffusion pump. After completion of the
thermolysis, the dry ice/acetone bath was removed, and the
U-tube was warmed to room temperature. The pump was
isolated, and the cold finger was cooled to 77 K with liq. N2.
As soon as the U-tube containing the iminopropadienone was
heated with a heat gun to a maximum of 150 °C, a yellow oil
distilled and deposited on the cold finger as a pale yellow layer.
The system pressure was equalized with N2, the cold finger
was warmed to room temperature, and the iminopropadienone
was collected in a receiving NMR tube by rinsing the cold
finger with a suitable solvent: 1H NMR (CD3OD) δ 1.00 (s, 9
H, t-Bu), 3.38 (s, 2 H, NCH2); 13C NMR (CD3OD) δ -11.0, 27.1,
33.9, 57.5, 108.5, 130.0 (see the Supporting Information for
the spectra); MS m/z 137.0843, calcd for C8H11NO 137.0841.
Ma t r ix Isola t ion of (Neop en t ylim in o)p r op a d ien on e
(6a ). In the course of 5 min, Meldrum’s acid derivative 3a was
sublimed at 80 °C/4 × 10-6 mbar under an argon stream,
pyrolyzed at 700 °C, and deposited on a CsI window in the
cryostat at 7 K: IR (Ar matrix, 7 K) 2975 (m), 2313 (m), 2250
1
mbar prior to use in FVT experiments: mp 130 °C; H NMR
(CDCl3) δ 1.05 (s, 9 H), 1.73 (s, 6 H), 2.58 (s, 3 H), 3.11 (d, 2 H,
3J ) 5.62 Hz); 13C NMR (CDCl3) δ 18.2, 26.0, 27.2, 31.9, 57.6,
82.9, 102.5. 163.8, 178.7. Anal. Calcd for C13H21NO4S: C, 54.33;
H, 7.37; N, 4.87. Found: C, 54.45; H, 7.59; N, 4.81.
5-[(Bis((2,2-d im eth ylp r op yl)a m in o)m eth ylen e]-2,2-d i-
m eth yl-1,3-d ioxa n e-4,6-d ion e (3a ). A mixture of 2,2-dim-
ethylpropylamine (1.31 g, 15 mmol) and 1 (1.21 g, 5 mmol) in
30 mL of ethanol was refluxed for 5 h. The solvent was reduced
to half its volume under vacuum, and diethyl ether (20 mL)
was added. After the mixture was cooled to 0 °C in
a
refrigerator for 2 days, yellow crystals formed. The solution
was decanted and the residue recrystallized from THF/diethyl
ether to yield 0.78 g (2.4 mmol, 48%) of 3a as a colorless
powder. Compound 3a can also be purified by chromatography
on silica gel/diethyl ether (Rf ) 0.68): mp 148 °C; 1H NMR
(vs), 2216 (s) cm-1
.
Kin etics of Rea ction of 6a w ith Meth a n ol. (Neopentyl-
imino)propadienone (6a ) obtained from Meldrum’s acid deriva-
tive 3a (100 mg, 0.3 mmol) and isolated in a dry ice/acetone
cold trap was warmed to 0 °C, and 1 mL of CD2Cl2 was injected
through a septum onto the cold finger to rinse 6a into an NMR
tube cooled in liquid N2. A solution of 0.03 mL (0.74 mmol) of
methanol in 1 mL of CD2Cl2 was added, and the tube was
placed in the NMR spectrometer. The reaction was monitored
during a period of 832 min (ca. 2 half-lives) in intervals of 6
min by integration of the N-methylene protons. By plotting
-ln [np-NCCCO] versus time, a straight line was obtained,
indicating a first-order reaction kinetics with respect to the
decreasing concentration of 6a . Regression analysis yielded
-ln [npNCCCO] ) 0.0017t + 0.0509, R2 ) 0.9905, rate
constant k1 ) 2.83 × 10-5 s-1, and t1/2 ) 408 min.
3
(CDCl3) δ 0.96 (s, 18 H), 1.61 (s, 6 H), 3.10 (d, 2 H, J ) 4.88
Hz), 9.83 (s, br, 2H); 13C NMR (CDCl3) δ 25.7, 26.7, 32.2, 58.1,
73.7, 101.6, 165.2, 166.3. Anal. Calcd for C17H30N2O4: C, 62.55;
H, 9.26; N, 8.58. Found: C, 62.59; H, 9.57; N, 8.22.
5-[(Dim eth yla m in o)(2,2-(d im eth ylp r op yl)a m in o)m eth -
ylen e]-2,2-d im eth yl-1,3-d ioxa n e-4,6-d ion e (4a ). Compound
2a (10 g, 35 mmol) was dissolved in 40 mL of dry THF. A
stream of gaseous dimethylamine was bubbled via a pipet
through the stirred solution at such a rate that the gas was
just absorbed. After approximately 20 min, a colorless pre-
cipitate had formed. The addition of HNMe2 was stopped, and
the reaction mixture was stirred for another 1h. The precipi-
tate was filtered, and the yellow solution was collected and
treated with HNMe2 as described above for another 20 min.
After the mixture was stirred for a further 2 h, the pale yellow
precipitate was filtered, and the combined solid fractions were
recrystallized from hot THF to afford 7.56 g (26.6 mmol, 76%)
of 4a: mp 202 °C dec; 1H NMR (CDCl3) δ 0.94 (s, 9 H), 1.66 (s,
6 H), 2.87 (d, 2 H, 3J ) 6.11 Hz), 3.15 (s, 6 H), 7.45 (s, br, 1 H);
13C NMR (CDCl3) δ 26.4, 27.1, 31.8, 40.6, 57.6, 70.6, 102.5,
163.4, 164.6. Anal. Calcd for C14H24N2O4: C, 59.14; H, 8.51;
N, 9.85. Found: C, 58.89; H, 8.73; N, 9.61.
1,3-Bis(d im eth yla m in o)-3-((2,2-d im eth ylp r op yl)im in o-
)p r op a n -1-on e (7a ) a n d 1,3-Bis(d im eth yla m in o)-3-((2,2-
d im eth ylp r op yl)a m in o)p r op en -1-on e (7′a ). (Neopentylim-
ino)propadienone (6a ) obtained from Meldrum’s acid derivative
4a (300 mg, 1.1 mmol) was isolated on a cold finger as above,
and 10 mL of a 1 N solution of dimethylamine in THF was
injected through a septum onto the cold thermolysate. The red-
brown reaction mixture was warmed to room temperature.
After evaporation of the solvent, a 1H NMR spectrum of the
crude oil indicated an almost pure sample of 7a /7′a in a 1:0.4
ratio. Kugelrohr distillation at 135 °C/10-4 mbar yielded 7a /
7′a in a 0.7:1 ratio as a yellow oil. Yield: 145 mg (0.64 mmol,
61%). 7a : 1H NMR (CDCl3) δ 0.90 (s, 9 H), 2.83 (s, 2 H), 2.94
(s, br), 2.97 (s, br), 3.05 (s, br), 3.53 (s, br, 2 H). 7′a : 1H NMR
(CDCl3) δ 0.94 (s, 9 H), 2.67 (s, 6 H), 2.81 (d, 2 H), 2.92 (s, 6
H), 4.09 (s, 1 H), 8.99 (t, br, 1 H). 7a /7′a : 13C NMR (CDCl3) δ
27.4, 27.7, 32.2, 32.5, 32.4, 33.6, 36.4, 37.3, 38.6, 40.4, 56.9,
60.9, 69.4, 154.9, 166.9, 168.1, 171.3. Anal. Calcd for
5-[(Dieth yla m in o)(2,2-(d im eth ylp r op yl)a m in o)m eth yl-
en e]-2,2-d im eth yl-1,3-d ioxa n e-4,6-d ion e (5a ). Compound
2a (0.28 g, 1 mmol) and diethylamine (0.4 g, 5.5 mmol) were
dissolved in 10 mL of freshly distilled dry THF, and the
mixture was heated under reflux. Further diethylamine (0.5
g) was added after 3 h and again after 10 h. After 17 h the
reaction was completed, and the solvent was evaporated under
vacuum. The oily yellow residue was dissolved in methylene
chloride (5 mL). Petroleum ether was added to precipitate 0.24
g (0.77 mmol, 77%) of 5a as a pale yellow powder. To obtain
analytical purity the crude product was sublimed at 120 °C/
10-2 mbar to yield 0.22 g (0.71 mmol, 71%) of 5a as a colorless
C
12H25N3O: C, 63.40; H, 11.08; N, 18.48. Found: C, 63.11; H,
11.37; N, 18.60.
1
1,3-Bis(d ieth yla m in o)-3-((2,2-d im eth ylp r op yl)im in o)-
p r op a n -1-on e (8a ) a n d 1,3-Bis(d ieth yla m in o)-3-((2,2-d i-
m eth ylp r op yl)a m in o)p r op en -1-on e (8′a ). (Neopentylimi-
no)propadienone (6a ) obtained from Meldrum’s acid derivative
4a (300 mg, 1.1 mmol) was isolated on a cold finger as above,
10 mL of a 1 N solution of diethylamine in THF was injected,
and the red-brown reaction mixture was warmed to room
temperature. The solvent was evaporated, and the crude oil
was distilled at 150-155 °C/10-4 mbar to yield 8a and 8′a in
a 1:0.83 ratio as a yellow oil. Yield: 203 mg (0.72 mmol, 65%).
8: 1H NMR (CDCl3) δ 0.87 (s, 9 H), 2.81 (s, 2 H), 3.35 (s, 2 H).
8′: 1H NMR (CDCl3) δ 0.9 (s, 9 H), 2.80 (d, 2 H), 2.99 (q, 4 H),
compound: mp 172 °C; H NMR (CDCl3) δ 0.94 (s, 9 H), 1.32
3
(t, 6 H), 1.71 (s, 6 H), 2.03 (s, br, 1 H), 3.08 (d, 2 H, J ) 5.86
Hz), 3.53 (q, 4 H); 13C NMR (CDCl3) δ 13.2 (br), 26.5, 27.1,
31.9, 43.8-46.8 (br), 57.2, 70.5-70.7, 102.3, 163.5, 164.6. The
broad signals are ascribed to hindered rotation (CH3 group at
δ 13.2) or the presence of the nitrogen quadrupole moment
(NCH2 signal at δ 43.8-46.8). Anal. Calcd for C16H28N2O4: C,
61.51; H, 9.03; N, 8.97. Found: C, 61.49; H, 9.30; N, 8.78.
(21) Kuhn, A.; Plu¨g, C.; Wentrup, C. J . Am. Chem. Soc. 2000, 122,
1945. Wentrup, C.; Blanch, R.; Briehl, H.; Gross, G. J . Am. Chem. Soc.
1988, 110, 1874.

Chemistry of Stable Iminopropadienones
J . Org. Chem., Vol. 67, No. 8, 2002 2625
4.18 (s, 1 H). 1H NMR signals common to 8a and 8′a : δ 1.00-
1.21 (m, 24 H, CH3), 3.23-3.35 (m, 12 H NCH2), 8.98 (t, br, 1
H). 8, 8′: 13C NMR (CDCl3) δ 11.9, 12.1, 13.4, 14.0, 14.2, 27.4,
27.8, 32.0, 32.0, 32.5, 40.4, 40.9, 42.3, 56.5, 60.9, 72.4, 150.5,
153.9 166.3, 169.9.
Calcd for C13H25N3O: C, 65.23; H, 10.53; N, 17.56. Found: C,
65.53; H, 10.94; N, 17.47. For the X-ray structure, see the
Supporting Information.
1,5-Dim eth yl-4-((2,2-d im eth ylp r op yl)im in o)p er h yd r o-
[1,5]d ia zon in -2-on e (15a ). (Neopentylimino)propadienone
(6a ) obtained from Meldrum’s acid derivative 4a (300 mg, 1.1
mmol) was isolated in a cold trap as above and dissolved in
50 mL of dry CH2Cl2, and a solution of N,N′-dimethylbuty-
lenediamine (41 mg, 0.35 mmol), dissolved in 40 mL of dry
diethyl ether, was added via an automatic syringe pump over
the course of 16 h. The reaction mixture was stirred for another
5 h at room temperature and was then concentrated to
dryness. A 10 mL portion of methanol was added, and the
solution was filtered through cotton wool. After evaporation
of the solvent under vacuum, the brown oil was subjected to
bulb to bulb distillation at 170-200 °C/10-5 mbar to afford a
yellow oil. Subsequently, a very slow Kugelrohr distillation
at 80-100 °C/7 × 10-6 mbar gave 15a as a colorless semisolid
1,2-Dim eth yl-5-((2,2-d im eth ylp r op yl)a m in o)p yr a zolin -
3-on e (10a ). (Neopentylimino)propadienone (6a ) obtained
from Meldrum’s acid derivative 4a (100 mg, 0.36 mmol) was
isolated on a cold finger as above and dissolved in 10 mL of
dry CH2Cl2. A solution of 1,2-dimethylhydrazine in 10 mL of
dry THF, previously prepared from 1,2-dimethylhydrazine
dihydrochloride (40 mg, 0.3 mmol) and dry triethylamine (100
mg, 1 mmol), was added. The reaction mixture was stirred for
3 h at room temperature and was then concentrated to
dryness. The brown residue was chromatographed (silica gel,
CH2Cl2/MeOH ) 100:15, Rf ) 0.75) to afford 26 mg (37%) of
10a as a yellow oil: 1H NMR (CDCl3) δ 0.90 (9 H), 2.80 (s, 2
H), 2.98 (s, 3 H), 3.01 (s, 3 H), 4.45 (s, 1 H), 4.80 (t, br, 1 H);
13C NMR (CDCl3) δ 27.2, 31.3, 32.3, 36.7, 56.2, 75.5, 164.4,
172.0.
1,4-Dim eth yl-7-((2,2-d im eth ylp r op yl)im in o)p er h yd r o-
[1,4]d ia zep in -5-on e (13a ) a n d 1,4-Dim et h yl-7-((2,2-d i-
methylpropyl)amino)-1,2,3,4-tetrahydro-5H-1,4-diazepin-5-one
(13′a ). (Neopentylimino)propadienone (6a ) obtained from Mel-
drum’s acid derivative 4a (300 mg, 1.1 mmol) was isolated in
a cold trap and dissolved in 25 mL of dry CH2Cl2, and a
solution of N,N′-dimethylethylenediamine (90 mg, 1 mmol) in
dry diethyl ether (20 mL) was added via a dropping funnel
within 1 h. The reaction mixture was stirred for another 6 h
at room temperature and was then concentrated to dryness.
The brown oily residue was distilled in a Kugelrohr apparatus
at 150-160 °C/10-5 mbar to afford 141 mg (0.63 mmol, 57%)
of 13a and 13′a in the ratio 1:0.13 as a colorless solid. For
further purification 13a /13′a was dissolved in 10 mL of diethyl
ether and precipitated by addition of a few drops of hexane:
mp 90-91 °C; GC retention time 9.6 min. 13: 1H NMR (CDCl3,
400 MHz) δ 0.83 (s, 9 H, t-Bu), 2.84 (s, 3 H, NMe), 2.88 (s, 3
H, NMe), 2.94 (s, 2 H, CH2), 3.37-3.40 (m, 2 H, NCH2), 3.46-
3.49 (m, 2 H, NCH2), 3.54 (s, 2 H, 6-H); 13C NMR (CDCl3,
100.62 MHz) δ 27.5 (CMe3), 32.5 (CMe3), 35.4 (NMe), 36.0 (C-
6), 36.7 (NMe), 49.8 (NMe), 50.1 (NCH2), 61.4 (NCH2), 153.1
(C-5), 166.6 (C-7). 13′: 1H NMR (CDCl3, 400 MHz) δ 0.88 (s, 9
H, t-Bu), 2.75 (s, 2 H, NCH2), 2.84 (s, 3 H, NMe), 2.92 (s, 3 H,
NMe),), 3.33 (s, br, 4 H, 2x NCH2), 4.3 (s, 1 H, 6-Holefin); 13C
NMR (CDCl3, 100.62 MHz) δ 27.4 (CMe3), 31.6 (CMe3), 36.7
(NMe), 38.6 (NMe), 52.9 (NCH2), 55.7 (NCH2), 78.1 (C-6) 156.9
(C-7), 168.5 (C-5) ppm. The 13C NMR assignments are sup-
ported by an HSQC spectrum. 13, 13′: IR (KBr) 1651 (s), 1636
(vs), 1622 (s) cm-1. Anal. Calcd for C12H23N3O: C, 63.96; H,
10.29; N, 18.65. Found: C, 63.83; H, 10.56 N, 18.80.
1
compound: yield 20 mg (0.08 mmol, 23%); H NMR (CDCl3,
400 MHz) δ 0.94 (s, 9 H), 1.63-1.65 (m, 2 H), 1.69-1.73 (m, 2
H), 2.89 (s, 3 H), 2.14 (s, 3 H), 3.43 (s, 2 H), 3.58 (t, 2 H), 3.66
(t, 2 H), 3.8 (s, 2 H, 3-H); 13C NMR (CDCl3, 100.62 MHz) δ
24.2, 24.8, 27.7, 31.0, 38.3, 32.7, 34.2, 47.1, 48.7, 60.2, 156.2,
167.4. Anal. Calcd for C14H27N3O: C, 65.23; H, 10.53; N, 17.56.
Found: C, 66.15; H, 10.86 N, 16.03. For the X-ray structure,
see the Supporting Information.
1-Met h yl-2-((2,2-d im et h ylp r op yl)im in o)-1,2-d ih yd r o-
p yr id o[1,2-a ]p yr im id in -5-iu m -4-ola te (18a ). (Neopentyl-
imino)propadienone (6a ) obtained from Meldrum’s acid de-
rivative 4a (300 mg, 1.1 mmol) was isolated in a cold trap as
above, and a solution of 2-(methylamino)pyridine (119 mg; 1.1
mmol) in 15 mL of dry CH2Cl2 was added. The red-brown
solution was transferred to a round-bottom flask, heated for
15 min under reflux, and stirred at room temperature over-
night. The solvent was evaporated, and the brown residue was
flash-chromatographed using diethyl ether/methanol (100:10)
as the mobile phase to remove unreacted starting material and
impurities. 18a was obtained as a red solid in 32% yield (86
mg, 0.35 mmol) by washing the column with a diethyl ether/
methanol (100:70) mixture: mp 155-160 dec; 1H NMR (CDCl3)
δ 0.93 (s, 9 H, t-Bu), 2.74 (s, 2 H, NCH2), 3.68 (s, 3 H, NMe),
5.02 (s, 1 H, 3-H), 7.02 (dt, 3J ) 7.1 Hz, 4J ) 1.2 Hz, 7-H),
7.19 (d, 1 H, 9-H), 7.89 (dt, 3J ) 6.8 Hz, 4J ) 1.7 Hz, 1 H,
1
8-H), 9.17 (dd, 3J ) 6.8 Hz, 4J ) 1.5 Hz, 1 H, 6-H) ppm; H
NMR (CD3CN, DMSO, 400.13 MHz) δ 0.88 (s, 9 H, t-Bu), 3.13
(d, 3J ) 6.5 Hz, 2 H, NCH2), 3.75 (s, 3 H, NMe), 5.81 (s, 1 H,
3-H), 7.65 (t, 7-H), 7.99 (t, br, 1 H, NH), 8.11 (d, 1 H, 9-H),
8.45 (dt, 3J ) 7.0 Hz, 4J ) 1.7 Hz, 1 H, 8-H), 9.17 (dd, 3J ) 6.8
Hz, 4J ) 1.2 Hz, 1 H, 6-H); 13C NMR (CDCl3, 50.32 MHz) δ
27.9 (CMe3), 30.3 (NMe), 32.3 (CMe3), 60.2 (NCH2), 75.0 (C-
3), 112.1 (C-9), 113.1 (C-7), 132.0 (C-6), 142.3 (C-8), 148.4 (C-
9a), 149.9 (C-2), 151.2 (C-4); 13C NMR (CD3CN, DMSO, 100.6
MHz) 27.3 (CMe3), 33.6 (NMe), 35.7 (CMe3), 52.8 (NCH2), 78.2
(C-3), 116.6 (C-9), 118.8 (C-7), 130.9 (C-6), 145.5 (C-8), 147.5
(C-9a), 153.3 (C-2), 154.8 (C-4) ppm (the 13C NMR assignments
are supported by HMBS and HSQC spectra); IR (KBr) 2959
(s), 2871 (sh), 1638 (vs, br), 1546 (s), 1478 (s), 1397 (s), 1369
(m), 1253 (m), 1207 (m), 1094 (m) cm-1. Anal. Calcd for
1,5-Dim eth yl-4-((2,2-d im eth ylp r op yl)im in o)p er h yd r o-
[1,5]d ia zocin -2-on e (14a ). (Neopentylimino)propadienone
(6a ) obtained from Meldrum’s acid derivative 4a (300 mg, 1.1
mmol) was isolated in a cold trap as above and dissolved in
50 mL of dry CH2Cl2, and a solution of N,N′-dimethylpropy-
lenediamine (36 mg, 0.35 mmol) in dry diethyl ether (40 mL)
was added via an automatic syringe pump (flow rate 2.5 mL/
h) within 16 h. The reaction mixture was stirred for another
5 h at room temperature and was then concentrated to
dryness. A 10 mL portion of methanol was added, and the
solution was filtered through cotton wool. After evaporation
of the solvent under vacuum, the brown oil was subjected to a
bulb to bulb distillation at 170-200 °C/10-5 mbar to afford a
yellow oil. A subsequent Kugelrohr distillation at 160 °C/7 ×
10-6 mbar gave 14a as a colorless solid. Recrystallization in
the cold from diethyl ether/hexane yielded 23 mg (0.08 mmol,
C
14H19N3O: C, 68.54; H, 7.81; N, 17.13. Found: C, 68.45; H,
7.90; N, 16.84.
2-((2,2-Dim eth ylp r op yl)a m in o)p yr id o[1,2-a ]p yr im id in -
4-on e (20a ) a n d 4-((2,2-Dim eth ylp r op yl)a m in o)p yr id o-
[1,2-a ]p yr im id in -2-on e (26). Meth od A. (Neopentylimino)-
propadienone (6a ) obtained from Meldrum’s acid derivative
4a (200 mg, 0.6 mmol) was isolated in a cold trap as above
and dissolved in 50 mL of dry CH2Cl2. This solution was
treated with a solution of 2-aminopyridine (56 mg, 0.6 mmol)
in 10 mL of CH2Cl2. The reaction mixture was stirred at room
temperature overnight. The solvent was evaporated under
vacuum, and the oily residue was chromatographed (MeOH/
diethyl ether 2.5:100, Rf ) 0.44) to afford 99 mg (0.43 mmol,
73%) of 20a as a pale brown solid.
1
24%) of 14a : mp 89-90 °C; GC retention time 10.1 min; H
NMR (CDCl3, 400 MHz) δ 0.89 (s, 9 H, t-Bu), 1.75 (quin, 2 H,
3-H), 2.83 (s, 3 H, NMe), 2.95 (s, 3 H, NMe), 3.00 (s, 2 H,
NCH2), 3.3-3.4 (mc, 4 H, 2x NCH2), 3.52 (s, 2 H, 3-H) ppm;
13C NMR (CDCl3, 100.62 MHz) δ 27.1 (C-7) 27.8 (CMe3), 32.7
(CMe3), 34.5 (C-3), 36.2 (NMe), 36.4 (NMe), 47.3 (NCH2), 47.2
(NCH2), 62.0 (NCH2), 155.5 (C-4), 169.1 (C-2) ppm (the 13C
NMR assignments are supported by an HSQC spectrum); MS
m/z 257.2093 (M+ + H2O), calcd for C8H12NO2 257.2096. Anal.
Meth od B. Iminopropadienone 6a similarly obtained from
Meldrum’s acid derivative 4a was treated with a solution of
2-aminopyridine (56 mg, 0.6 mmol) in 15 mL of toluene, and

2626 J . Org. Chem., Vol. 67, No. 8, 2002
Bibas et al.
the reaction mixture was refluxed in a preheated oil bath for
30 min. The solution was concentrated under vacuum to half
volume, and diethyl ether was added until the solution became
cloudy. The suspension was cooled to 0 °C for several hours,
and the precipitate was collected by centrifugation, washed
with diethyl ether, and dried under vacuum to afford 21 mg
(15%) of 26 as yellow crystals (TLC with diethyl ether/MeOH
1:1; Rf ) 0.2).
toluene. The reaction mixture was refluxed in a preheated oil
bath for 30 min. The solution was concentrated under vacuum
to half-volume, and diethyl ether was added until the solution
became cloudy. The suspension was cooled to 0 °C for several
hours, and the precipitate was collected by centrifugation,
washed with diethyl ether, and dried under vacuum to afford
39 mg (0.16 mmol, 27%) of 28 as yellow crystals. The
supernatant was purified as described above to yield 50 mg
(0.2 mmol, 34%) of 22a .
The supernatant was purified in the same way as described
above for 20a to yield 73 mg (0.32 mmol, 53%) of 20a .
26: mp 216-218 °C dec; 1H NMR (CDCl3/MeOH) δ 0.86 (s,
9 H), 3.01 (s, 2 H), 5.65 (s, 1 H), 6.83 (t, 3J ) 7.2 Hz, 1 H), 7.14
1
28: mp 238-239 °C; H NMR (CDCl3, 400.13 MHz) δ 1.01
3
(s, 9 H), 2.29 (s, 3 H), 2.99 (d, J ) 3.9 Hz, 2 H), 5.70 (s, br, 1
3
4
H), 5.70 (s, 1 H), 6.60 (dd, J ) 7.3 Hz, J ) 1.7 Hz), 6.94 (s,
1 H), 8.2 (d, 3J ) 7.6 Hz); 13C NMR (CDCl3, 100.6 MHz) δ 21.1,
27.7, 32.5, 54.8, 90.2, 115.4, 122.8, 125.9, 146.7, 149.9, 151.1,
170.6.
3
3
3
(d, J ) 9.2 Hz, 2 H 9-H), 7.45 (t, J ) 7.4, 1 H), 8.22 (d, J )
7.4 Hz); 13C NMR (CDCl3) δ 27.1, 32.4, 54.4, 88.9, 113.7, 124.3,
126.1, 135.9, 150.3, 150.8, 170.3. 20a : mp 123 °C; 1H NMR
(CDCl3, 400.13 MHz) δ 0.96 (s, 9 H), 3.02 (s, br, 2 H), 4.97 (s,
br, 1 H), 5.44 (s, 1 H), 6.81 (dt, 1 H), 7.18 (d, 3J ) 8.8 Hz, 1 H),
22a : mp 179-181 °C; 1H NMR (CDCl3, 400.13 MHz) δ 0.92
(s, 9 H), 2.23 (s, 3 H), 2.98 (s, br, 2 H), 4.95 (s, br, 1 H), 5.35
3
3
4
7.53 (dt, 1 H), 8.82 (d, J ) 7.5 Hz); 13C NMR (CDCl3, 50.32
(s, 1 H), 6.63 (dd, J ) 7.4 Hz, J ) 1.7 Hz), 6.95 (s, 1 H), 8.71
(d, 3J ) 7.1 Hz); 13C NMR (CDCl3, 100.6 MHz) δ 21.3, 27.3,
32.1, 53.5, 79.5, 115.0, 121.5, 127.0, 148.8, 150.9, 158.3, 162.0.
Anal. Calcd for C14H19N3O: C, 68.54; H, 7.81; N, 17.13.
Found: C, 68.31; H, 8.01, N, 16.83.
MHz) δ 27.3, 32.1, 53.5, 79.6, 112.2, 123.6, 127.7, 136.5, 151.0,
158.4, 162.0. Anal. Calcd for C13H17N3O: C, 67.51; H, 7.41; N,
18.18. Found: C, 67.33; H, 7.66; N, 18.08.
2-((2,2-Dim eth ylp r op yl)a m in o)-9-m eth ylp yr id o[1,2-a ]-
p yr im id in -4-on e (21a ), 4-((2,2-Dim eth ylp r op yl)a m in o)-9-
m eth ylp yr id o[1,2-a ]p yr im id in -2-on e (27), a n d 4-((2,2-
Dim eth ylpr opyl)am in o)-9-m eth ylpyr ido[1,2-a ]pyr im idin -
2-ol (31). (Neopentylimino)propadienone (6a ) obtained from
Meldrum’s acid derivative 4a (200 mg, 0.6 mmol) was isolated
in a cold trap as above and treated with a solution of 2-amino-
3-methylpyridine (65 mg, 0.6 mmol) in 10 mL of CH2Cl2. The
reaction mixture was stirred at room temperature for 90 min,
and the solvent was evaporated under vacuum. A 1H NMR of
the crude product showed a mixture of 27 and 21a in a 0.3:1
ratio. The oily residue was dissolved in 10 mL of THF, and a
few drops of diethyl ether and hexane were added until the
solution became milky. The suspension was stirred for 2 h,
and the precipitate was collected by centrifugation, washed
with diethyl ether, and dried under vacuum to afford 27, which
was then recrystallized from CH2Cl2/diethyl ether to yield 25
mg (17%) as a white powder. The supernatant was cooled to 0
°C overnight in a refrigerator, and the cloudy precipitate was
isolated by centrifugation, washed with diethyl ether, and
dried under vacuum to give 31 (5 mg, 0.02 mmol, 3%) as a
red-brown solid. The supernatant was evaporated to dryness
and purified by sublimation (105 °C/10-4 mbar) to give 45 mg
(31%) of 21a as a yellow powder. 27: mp 220-228 °C dec; 1H
NMR δ 0.99 (s, 9 H), 2.28 (s, 3 H), 3.05 (s, 2 H), 5.75 (s, 1 H),
2-((2,2-Dim eth ylp r op yl)a m in o)-7-m eth ylp yr id o[1,2-a ]-
pyr im idin -4-on e (23a) an d 4-((2,2-Dim eth ylpr opyl)am in o)-
7-m eth ylp yr id o[1,2-a ]p yr im id in -2-on e (29). (Neopentyl-
imino)propadienone (6a)obtained from Meldrum’s acid derivative
4a (500 mg, 1.5 mmol) was isolated in a cold trap as above
and treated with a solution of 2-amino-5-methylpyridine (162
mg, 15 mmol) in 20 mL of dry THF. The reaction mixture was
refluxed for 6 h in a preheated oil bath. After the solvent had
been evaporated, a 1H NMR spectrum of the crude material
was taken, indicating a mixture of 29 and 23a in a 1:0.17 ratio.
Attempts to precipitate 23a from the crude mixture (in THF)
with diethyl ether failed. The crude product was chromato-
graphed (diethyl ether/methanol 100:5, Rf ) 0.5) to yield 249
mg (1.0 mmol, 68%) of 29 as a pale orange solid, while 23a
failed to elute. 23a : 1H NMR (CDCl3) δ 1.02 (s, 9 H, t-Bu), 2.20
(s, 3 H, Me), 3.16 (d, 2 H, NCH2), 5.76 (s, 1 H, 3-H), 6.9512 (d,
4
3
3J ) 9.05 Hz, 9-H), 7.28 (dd, J ) 2.44 Hz, J ) 8.79 Hz,8-H),
8.55 (s, 6-H). 29: mp 138-140 °C; GC/MS 13.5 min; 1H NMR
(CDCl3) δ 0.93 (s, 9 H, t-Bu), 2.26 (s, 3 H, Me), 2.99 (d, 2 H,
3
NCH2), 5.10 (tr, br, 1 H, NH), 5.42 (s, 1 H, 3-H), 7.12 (d, J )
9.03 Hz, 9-H), 7.40 (dd, 4J ) 4.18 Hz, 3J ) 9.03 Hz, 8-H), 8.65
(s, 6-H). 13C NMR (CDCl3) δ 17.9 (Me), 27.3 (CMe3), 32.1
(CMe3), 53.4 (NCH2), 80.0 (C-3), 122.3 (C-7), 122.7 (C-9), 125.2
(C-6), 139.7 (C-7), 149.6 (C-9a), 158.1 (C-2), 161.4 (C-4) ppm
(the assignments are supported by a HMBC spectrum). Anal.
Calcd for C14H19N3O: C, 68.54; H, 7.81; N, 17.13. Found: C,
68.36; H, 8.05; N, 17.09.
3
6.64 (t, J ) 6.24 Hz, 1 H), 6.79 (s, br, 1 H), 7.25 (d, 1 H), 8.50
(d, 3J ) 7.04 Hz); 13C NMR (CD3CN, CDCl3, 100.62 MHz) δ
18.4, 27.2, 32.3, 54.4, 88.5, 112.9, 124.6, 133.2, 133.8, 150.3,
150.6, 169.5. 31: 1H NMR (CDCl3, 400.13 MHz) δ 0.99 (s, 9
2-((2,2-Dim eth ylp r op yl)a m in o)-6-m eth ylp yr id o[1,2-a ]-
p yr im id in -4-on e (24a ). (Neopentylimino)propadienone (6a )
obtained from Meldrum’s acid derivative 4a (100 mg, 0.3
mmol) was isolated in a cold trap as above and treated with a
solution of 2-amino-6-methylpyridine (32 mg, 0.3 mmol) in 10
mL of CH2Cl2. The reaction mixture was stirred at room
temperature, and the course of the reaction was monitored by
GC/MS. After 5 days the solvent was evaporated under
vacuum and the oily residue was chromatographed on (diethyl
ether/MeOH 100:5, Rf ) 0.41) to afford 21 mg (0.08 mmol, 28%)
of 24a as a pale brown solid: mp 156-158 °C; 1H NMR (CDCl3)
δ 0.96 (s, 9 H), 2.96 (d, 2 H), 2,97 (s, 3 H), 5.03 (t, br, 1 H),
3
H), 2.41 (s, 3 H), 3.15 (s, 2 H), 6.18 (s, 1 H), 6.96 (t, J ) 7.1
3
3
Hz, 1 H), 7.48 (d, J ) 6.9, 1 H), 7.77 (s, br, 1 H), 8.95 (d, J )
7.1 Hz, 1 H). 21a : mp 183-184 °C; GC/MS 12.97 min; 1H NMR
(CDCl3, 400.13 MHz) δ 0.97 (s, 9 H), 2.41 (s, 3 H), 3.08 (d, 2
3
H), 4.96 (t, br, 1 H), 5.45 (s, 1 H), 6.74 (t, J ) 6.8 Hz, 1 H),
7.41 (s, 1 H), 8.77 (d, J ) 6.6 Hz); 13C NMR (CDCl3) δ 18.0,
3
27.7, 32.3, 53.2, 80.2, 111.6, 125.6, 132.0, 135.0, 150.6, 159.0,
161.5. Anal. Calcd for C14H19N3O: C, 68.54; H, 7.81; N, 17.13.
Found: C, 68.34; H, 8.08; N, 16.95. For the X-ray structure of
21a see the Supporting Information.
2-((2,2-Dim eth ylp r op yl)a m in o)-8-m eth ylp yr id o[1,2-a ]-
pyr im idin -4-on e (22a) an d 4-((2,2-Dim eth ylpr opyl)am in o)-
8-m et h ylp yr id o[1,2-a ]p yr im id in -2-on e (28). Met h od A.
(Neopentylimino)propadienone (6a ) obtained from Meldrum’s
acid derivative 4a (100 mg, 0.3 mmol) was isolated in a cold
trap as above and treated with a solution of 2-amino-4-
methylpyridine (32 mg, 0.3 mmol) in 10 mL of CH2Cl2. The
reaction mixture was stirred at room temperature for 5 h. The
solvent was evaporated under vacuum, and the oily residue
was chromatographed (MeOH:diethyl ether 5:100) to afford 45
mg (61%) of 22a as a pale brown solid.
3
3
5.27 (s, 1 H), 6.43 (d, J ) 6.8 Hz), 7.03 (d, J ) 8.81 H), 7.29
(dd, J ) 6.8 Hz, J ) 8.8 Hz, 1 H); 13C NMR (CDCl3) δ 24.8,
27.3, 32.1, 53.5, 81.2, 116.3, 122.0, 136.2, 144.7, 153.0, 160.1,
162.3. Anal. Calcd for C14H19N3O: C, 68.54; H, 7.81; N, 17.13.
Found: C, 68.69; H, 8.17; N, 17.11.
3
3
2-((2,2-Dim eth ylp r op yl)a m in o)-8-m eth ylp yr im id o[1,2-
a ]p yr im id in -4-on e (34a ). (Neopentylimino)propadienone (6a )
obtained from Meldrum’s acid derivative 4a (100 mg, 0.3
mmol) was isolated in a cold trap as above and treated with a
solution of 2-amino-4-methylpyrimidine (33 mg, 0.3 mmol) in
15 mL of dry THF. The reaction mixture was refluxed for 30
min. The solvent was evaporated, and the brown residue was
flash chromatographed using a diethyl ether/methanol mixture
(100:15, Rf ) 0.58) as the mobile phase. The crude product
Meth od B. (Neopentylimino)propadienone (6a ) obtained
from Meldrum’s acid derivative 4a (200 mg, 0.6 mmol) was
isolated in a cold trap as above and treated with a solution of
2-amino-3-methylpyridine (65 mg, 0.6 mmol) in 15 mL of

Chemistry of Stable Iminopropadienones
J . Org. Chem., Vol. 67, No. 8, 2002 2627
Ta ble 1
was recrystallized from THF to give 36 mg (42%): mp 242 °C;
GC retention time 14.2 min; 1H NMR (CDCl3) δ 0.96 (s, 9 H),
2.59 (s, 3 H), 2.98-3.04 (s, br, 2 H), 5.23 (s, br, 1 H), 5.36 (s,
1 H), 6.74 (d, 3J ) 7.1 Hz), 8.96 (d, 3J ) 7.1 Hz, 1 H); 13C NMR
(CDCl3) δ 25.5, 27.3, 32.1, 53.6, 78.7, 110.1, 135.8, 158.0, 163.5,
173.3.
4-/2-pyrimidinone ratio
CH2Cl2, room
temp, 5 h
toluene, reflux,
30 min
reagent
2-aminopyridine
2-amino-4-methylpyridine
2-aminothiazole
1/0.3a 20a /26
1/0.25b 22a /28
1/0a 42a /43a
1/0.6a 20a /26
1/0.72b 22a /28
1/0.5a 42a /43a
2-((2,2-Dim eth ylp r op yl)a m in o)p yr a zin o[1,2-a ]p yr im i-
d in -4-on e (35a ). (Neopentylimino)propadienone (6a ) obtained
from Meldrum’s acid derivative 4a (200 mg, 0.6 mmol) was
isolated in a cold trap as above and treated with a solution of
2-aminopyrazine (70 mg, 0.7 mmol) in 15 mL of dry THF. The
reaction mixture was heated under reflux for 4 h. The solvent
was evaporated, and the brown residue was flash-chromato-
graphed using a diethyl ether/methanol mixture (100:15, Rf
) 0.42) as the mobile phase. The crude product was recrystal-
lized from THF to give 61 mg (37%) as a beige powder: mp
a
b
By integration of tert-butyl signals. By integration of
pyridylmethyl signals.
4.98 (s, 1 H); 13C NMR (CDCl3, 100.62 MHz) δ 26.4, 27.3, 32.0,
48.3, 53.8, 79.9, 162.2, 163.0, 164.0.
7-((2,2-Dim eth ylp r op yl)a m in o)[1,3]th ia zolo[3,2-a ]p yr i-
m id in -5-on e (42a ) a n d 5-((2,2-Dim eth ylp r op yl)a m in o)-
[1,3]th iazolo[3,2-a ]pyr im idin -7-on e (43a). Meth od A. (Neo-
pentylimino)propadienone (6a ) obtained from Meldrum’s acid
derivative 4a (200 mg, 0.6 mmol) was isolated in a cold trap
as above and treated with a solution of 2-aminothiazole (61
mg, 0.6 mmol) in 10 mL of THF. The reaction mixture was
refluxed for 1 h. The solvent was evaporated under vacuum,
and the oily residue was chromatographed (MeOH/diethyl
ether ) 10:100) to afford 65 mg of 42a (46%) as a pale brown
solid.
Meth od B. (Neopentylimino)propadienone (6a ) obtained
from Meldrum’s acid derivative 4a (200 mg, 0.6 mmol) was
isolated in a cold trap as above, treated with a solution of
2-aminothiazole (61 mg, 0.6 mmol) in 15 mL of toluene, and
refluxed for 30 min. The solution was concentrated under
vacuum to half-volume, and diethyl ether was added until the
solution turned cloudy. After the mixture was cooled for 48 h
at 0 °C, the precipitate was collected by centrifugation, washed
with diethyl ether, and dried under vacuum. Recrystallization
from ethanol afforded 19 mg (13%, 0.08 mmol) of 43a as yellow
crystals. The supernatant was purified as described above to
yield 41 mg (35%) of 42a .
1
166 °C, GC retention time 12.3 min; H NMR (CDCl3, 400.13
MHz) δ 0.98 (s, 9 H), 3.06 (d, 2 H), 5.12 (s, br, 1 H), 5.54 (s, 1
3
3
H), 7.87 (d, J ) 4.7 Hz), 8.51 (d, J ) 4.7 Hz, 1 H), 8.69 (s, 1
H); 13C NMR (CDCl3) δ27.3, 32.2, 53.5, 82.7, 117.6, 129.2,
144.4, 151.0, 156.9, 162.3.
4-((2,2-Dim eth ylp r op yl)a m in o)p yr im id o[2,1-a ]isoqu in -
olin -4-on e (36a ). (Neopentylimino)propadienone (6a ) obtained
from Meldrum’s acid derivative 4a (100 mg, 0.3 mmol) was
isolated in a cold trap as above, treated with a solution of
1-aminoisoquinoline (51 mg, 0.32 mmol) in 10 mL of dry CH2-
Cl2, and stirred at room temperature for 16 h. The solvent was
evaporated, and the brown oil was chromatographed (diethyl
ether/methanol 100:7, Rf )0.68) to afford 36, which was
recrystallized from boiling THF to give 28 mg (0.1 mmol,
31%): mp 170 °C; GC retention time 17.2 min; 1H NMR (CD3-
OD, 400.13 MHz) δ 1.00 (s, 9 H), 3.06-3.1 (d, br, 2 H), 5.16
(tr, 1 H), 5.50 (s, 1 H), 6.99d, 3J ) 7.92 Hz), 7.57 (dt, 1 H),
3
7.59 (d, 1 H), 7.67 (dt, 1 H), 8.63 (d, J ) 7.62 Hz), 8.81 (d, 1
H); 13C NMR (CDCl3, 100.62 MHz) δ 27.4, 32.3, 53.4, 80.8,
112.0, 122.1, 126.0, 126.3, 126.9, 127.9, 132.2, 134.2, 149.6,
159.5, 161.5. Anal. Calcd for C17H19N3O: C, 72.56; H, 6.81; N,
14.94. Found: C, 71.93; H, 6.73 N, 13.61.
42a : mp 82 °C; GC retention time 12.6 min; 1H NMR
(CDCl3, 400 MHz) δ 0.94 (s, 9 H), 2.97 (d, J ) 5.3 Hz, 2 H),
4.89 (t, br, 1 H), 5.2 (s, 1 H), 6.64 (d, J ) 4.7 Hz), 7.78 (d, J
) 4.7 Hz); 13C NMR (CDCl3, 100.62 MHz) δ 27.3, 32.1, 53.7,
78.9, 107.1, 122.2, 159.1, 162.4, 162.9. Anal. Calcd for C11H15N3-
OS: C, 55.67; H, 6.37; N, 17.17 Found: C, 55.58; H, 6.47; N,
17.72.
3
1,4-D ih y d r o -2-[(2,2-d im e t h y lp r o p y l)a m in o ][1,10]-
p h en a n th r olin -4-on e (40). (Neopentylimino)propadienone
(6a ) obtained from Meldrum’s acid derivative 4a (300 mg, 1.1
mmol) was isolated in a cold trap as above and treated with a
solution of of 8-aminoquinoline (144 mg, 1 mmol) in 10 mL of
THF. The brown reaction mixture was heated under reflux
for 6 h (no reaction took place in CH2Cl2 at room temperature).
After evaporation of the solvent 40 was chromatographed
using a diethyl ether/methanol gradient (0% to 10% methanol,
Rf ) 0.52 using 10% methanol in diethyl ether) and recrystal-
lized from THF to give 78 mg (28%) of a colorless solid: mp
3
3
1
43a : mp 276 °C dec; H NMR (DMSO-d6, 333 K) δ 0.96 (s,
3
9 H), 2.99 (d, J ) 4.9 Hz, 2 H), 5.31 (s, 1 H), 6.8 (s, br, 1 H),
3
3
7.26 (d, J ) 5.12 Hz), 8.12 (d, J ) 5.12 Hz); 13C NMR (CD3-
CN, DMSO-d6) δ 27.0, 32.5, 53.0, 82.4, 108.4, 120.9, 149.6,
162.8, 168.0. Anal. Calcd for C11H15N3OS: C, 55.67; H, 6.37;
N, 17.71. Found: C, 55.37; H, 6.40 N, 17.42. For the X-ray
structure, see the Supporting Information.
1
288-312 °C dec; H NMR (CD3OD, 500 MHz) δ 1.06 (s, 9 H,
t-Bu), 3.06 (s, 2 H, NCH2), 5.82 (s, 1 H, 3-H), 7.61 (dd, 8-H),
8.9 (d, 3J ) 3.3 Hz, 9-H); 13C NMR (CD3OD, 125.7 MHz) δ 27.2
(CMe3), 32.9 (CMe3), 54.8 (NCH2), 91.3 (C-3), 121.1 (C-4a),
121.9 (C-6), 123.1 (C-5), 124.6 (C-8), 130.5 (C-6a), 136.9 (C-
10b), 137.4 (C-7), 139.2 (C-10a), 150.4 (C-9), 155.7 (C-2), 178.4
(C-4) (HMBC and HSQC spectra supported the assignments).
Anal. Calcd for C17H19N3O: C, 72.56; H, 6.81; N, 14.94.
Found: C, 71.80; H, 6.97; N, 14.19.
Tem p er a tu r e Effect on Isom er Ra tio in Rea ction s of
6a w ith 2-Am in op yr id in es a n d 2-Am in oth ia zole. For each
of the following experiments, iminopropadienone 6a obtained
from Meldrum’s acid derivative 3a (50 mg, 0.15 mmol) was
isolated at -78 °C and subsequently treated with 2-aminopy-
ridine (0.28 mmol, 28 mg), 2-amino-4-methylpyridine (0.28
mmol, 32 mg), or 2-aminothiazole (0.28 mmol, 30 mg), dis-
solved in either methylene chloride or toluene (the use of
nitrobenzene at reflux caused mainly decomposition). The
reaction mixture was stirred at room temperature for 5 h when
methylene dichloride was used as solvent and for 30 min under
reflux in toluene. The solvents were evaporated under vacuum,
and the samples were analyzed by 1H NMR spectroscopy to
give the results shown in Table 1.
Attem p ted Isom er iza tion of 2-((2,2-Dim eth ylp r op yl)-
a m in o)-8-m eth ylp yr id o[1,2-a ]p yr im id in -4-on e (22a ) in to
4-((2,2-Dim eth ylp r op yl)a m in o)-8-m eth ylp yr id o[1,2-a ]p y-
r im id in -2-on e (28). 2-((2,2-Dimethylpropyl)amino)-8-meth-
ylpyrido[1,2-a]pyrimidin-4-one (22a ) (10 mg) was dissolved in
1 mL of toluene-d8 and placed in a NMR tube. The NMR tube
was sealed and placed in the 200 MHz spectrometer. The probe
7-((2,2-Dim eth ylpr opyl)am in o)-2,3-dih ydr o[1,3]th iazolo-
[3,2-a ]p yr im id in -5-on e (41a ). (Neopentylimino)propadienone
(6a ) obtained from Meldrum’s acid derivative 4a (200 mg, 0.6
mmol) was isolated in a cold trap as above and treated with a
solution of 2-aminothiazole (62 mg, 0.6 mmol) in 10 mL of CH2-
Cl2. The yellow solution was stirred for 15 min at room
temperature. The solvent was partly evaporated under vacuum,
and diethyl ether was added to precipitate a brown solid. The
solvent was decanted, and the residue was dissolved in a few
drops of CH2Cl2. After a few drops of diethyl ether were slowly
added, the solution turned into a milky suspension. After the
mixture was cooled at 0 °C for 2 days, pale brown crystals
formed. Yield: 90 mg (62%). For further purification 41a was
chromatographed using diethyl ether/methanol (100:10) as the
mobile phase (Rf ) 0.78): mp 112-114 °C; GC retention time
1
was heated to 95 °C, and H NMR spectra were recorded over
a period of 12 h in intervals of 1 h. No change in the NMR
patterns occurred, and the solution was therefore heated in
1
13.7 min; H NMR (CDCl3, 400 MHz) δ 0.91 (s, 9 H), 2.85 (d,
3J ) 6.1 Hz, 2 H), 3.36 (t, 2 H), 4.34 (t, 2 H), 4.98 (t, br, 1 H),

2628 J . Org. Chem., Vol. 67, No. 8, 2002
Bibas et al.
1
an oil bath at 140 °C for another 12 h. The H NMR remained
to give 12b as a pale brown solid (yield 70%): mp 138-140
1
unchanged. Consequently, no equilibrium between 22a and
28 was achieved under these conditions.
°C; H NMR (CDCl3, 400 MHz) δ 6.91 (s, 1 H), 5.90 (s, 1 H),
3.16 (s, 2 H), 3.15 (s, 3 H), 2.27 (s, 3 H), 2.23 (s, 6 H); 13C NMR
(CDCl3) δ 168.1, 154.7, 137.2, 135.5, 132.4, 129.3, 36.7, 31.1,
20.9, 18.2. Anal. Calcd for C13H17N3O: C, 67.49; H, 7.41; N,
18.18. Found C, 67.20; H, 7.46; N, 18.16.
Sta n d a r d P r oced u r e for Syn th esis a n d Ch em istr y of
(Mesit ylim in o)p r op a d ien on e (6b ). 5-[(Dimethylamino)-
(mesitylamino)methylene]-2,2-dimethyl-1,3-dioxane-4,6-di-
one (4b;22 100 mg, 0.3 mmol) was subjected to FVT at 700 °C/
1.5 × 10-5 mbar over the course of 4 h, collecting the product
in an ice-cooled U-tube. Upon completion of the thermolysis,
the apparatus was flushed with N2, and an excess or 1 equiv
of trapping agent in dilute solution (4 mL of dry CCl4 or CH2-
Cl2) was injected through a septum onto the cold thermolysate.
After the mixture stood for a further 30 min in the ice bath,
the U-tube was warmed to room temperature, and the solvent
was removed by rotary evaporation.
(Mesitylim in o)p r op a d ien on e (6b). After thermolysis of
4b as above, 4 mL of CCl4 was injected to give 6b in 72-80%
yield as a white solid (color changed rapidly to brown): mp
12 °C dec. Spectroscopy was performed immediately: 1H NMR
(CDCl3) δ 2.25 (s, 3H), 2.29 (s, 6H), 6.74 (s, 2H); 13C NMR
(CDCl3) δ -6.8, 18.6, 21.1, 111.6, 126.2, 128.8, 132.5, 135.0,
137.3; IR (CCl4) 2983, 2921, 2857, 2214, 2181, 1615, 1474,
1379, 1264, 1204, 855 cm-1; IR (Ar, 14 K) 2248, 2243, 2234,
2149, 1583, 1483, 1440, 1145, 1032 cm-1; far-IR (LLD poly-
ethylene) 73, 90 cm-1; Raman (CCl4) 2925, 2217, 2204, 2180,
2171, 1610, 1475, 1309, 1207, 1151, 577 cm-1 (see the Sup-
porting Information for IR, Raman, and NMR spectra); MS
m/z 308 (M+, 2), 292 (2), 247 (6), 213 (5), 173 (3), 141 (53), 135
(100), 120 (98), 112 (69), 85 (96), 70 (15), 56 (15), 42 (39); HRMS
m/z calcd for C12H11NO 185.0841, found 185.0480.
N,N-Diet h yl 3-(Diet h yla m in o)-3-(m esit ylim in o)p r o-
p a n a m id e (8b). Diethylamine in dichlorormethane was added
to 6b. The resulting yellow solution was filtered through a
pipet containing cotton wool, and the solvent was evaporated
to give 39 mg of 8b as a yellow oil. According to the 1H and
13C NMR spectra, the product was >98% pure: 1H NMR
(CDCl3, 400 MHz) δ 0.72 (t, 3 H, J ) 7.2 Hz), 1.00 (t, 3 H, J )
7.1 Hz), 1.20 (t, 6 H, J ) 7.0), 1.96 (s, 6 H), 2.16 (s, 3 H), 2.69
(q, 2 H, J ) 7.2 Hz), 3.06 (s, 2 H), 3.20 (q, 2 H, J ) 7.1 Hz),
3.46 (q, 4 H, J ) 7.0 Hz), 6.72 (s, 2 H); 13C NMR (CDCl3, 100
MHz) δ 166.2, 152.5, 146.5, 130.4, 129.1, 128.4, 42.2, 42.0, 40.7,
31.9, 20.6, 18.4, 13.7, 13.6, 12.8. Anal. Calcd for C20H33N3O:
C, 72.42; H, 10.03; N, 12.68. Found: C, 72.47; H, 10.04; N,
12.60.
1,3-Bis(3,5-dim eth ylpyr azolyl)-3-(m esitylim in o)pr opan -
1-on e (9b). 3,5-Dimethylpyrazole in dichloromethane was
added to 6b, and the solution was evaporated. NMR data
showed the formation of only 9b (>95% purity according to
NMR). Dilution (1 equiv of trapping agent in 80 mL of
dichloromethane) gave the same results: 1H NMR (CDCl3) δ
6.78 (s, 2 H), 5.86 (s, 1 H), 5.82 (s, 1 H), 4.34 (s, 2 H), 2.61 (s,
3 H), 2.34 (s, 3 H), 2.16 (s, 3 H), 2.11 (s, 3 H), 2.04 (s, 6 H),
2.01 (s, 3 H); 13C NMR (CDCl3) δ 168.2, 151.9, 151.8, 149.2,
143.9, 143.3, 142.6, 132.4, 128.7, 126.8, 111.0, 109.9, 37.3, 20.6,
18.3, 15.6, 14.2, 13.7, 13.6. HRMS m/z calcd for C22H27N5O
377.2210, found 377.2211.
1,4-Dim eth yl-7-(m esitylim in o)p er h yd r o[1,4]d ia zep in -
5-on e (13b). Iminopropadienone 6b obtained from 4b (332 mg,
1.0 mmol) was treated with a solution of 97.0 mg (1.1 mmol)
of N,N′-dimethylethylenediamine in 30 mL of diethyl ether,
which was added dropwise to the stirred solution over a period
of 6 h. The resulting mixture was stirred for 3 days. The
solvent was evaporated, and the crude product was purified
by flash chromatography (5% MeOH/ether) to give 150 mg
(yield 55%) as a yellow oil which was difficult to purify to
analytical accuracy: 1H NMR (400 MHz, CDCl3) δ1.91 (s, 6
H), 2.92 (s, NMe, 3 H), 3.14 (s, 3 H, NMe), 3.28 (s, 2 H), 3.49-
3.51 (m, 2H), 3.63-3.66 (m, 2H), 6.77 (s, 2H); 13C NMR (100
MHz, CDCl3) δ 18.1, 20.7, 35.6, 37.4, 37.5, 50.0, 50.1, 128.5,
129.3, 134.6, 143.8, 153.1, 165.6.
4-(Me s it y lim in o )-2,3,4,5-t e t r a h y d r o b e n zo [b ][1,4]-
d ia zep in -2-on e (16). Iminopropadienone 6b obtained from
4b (332 mg, 1.0 mmol) was treated with 119.0 mg (1.1 mmol)
of 1,2-phenylenediamine in 15 mL of dry THF, and the
resulting mixture was stirred for 3 h. The solvent was
evaporated, and the crude product was sublimed to remove
excess 1,2-phenylenediamine and then purified by flash chro-
matography (5% MeOH/ether), sublimed, and washed with
ethyl acetate to give 160 mg (yield 55%) as white crystals: mp
1
238-239 °C; H NMR (400 MHz, CDCl3) δ 2.20 (s, 6 H), 2.30
3
(s, 3 H,), 3.20 (s, 2 H), 6.95 (s, 2 H), 7.19 (dd, J ) 7.6 Hz,4J )
3
4
1.0 Hz, 1 H), 7.26-7.36 (m, 2 H), 7.54 (dd, J ) 7.9 Hz, J )
1.4 Hz, 1 H), 8.58 (s, 2 H); 13C NMR (100 MHz, CDCl3) δ 18.4,
21.0, 34.9, 122.7, 124.3, 126.8, 127.2, 128.4, 128.7, 129.2, 129.8,
135.7, 139.9, 160.9, 163.1. Anal. Calcd for C18H19N3O: C, 73.69;
H, 6.53; N, 14.32. Found: C, 73.84; H, 6.64; N, 14.05.
1-Met h yl-2-(m esit yla m in o)p yr id o[1,2-a ]p yr im id in -5-
iu m -4-olate (18b). 2-(Methylamino)pyridine in dichloromethane
was added to 6b to give, after evaporation of the solvent and
recrystallization of the crude product with methanol, 50 mg
of 18b as an orange solid (yield 79%): mp 237-240 °C; 1H
NMR (DMSO-d6, 400 MHz) δ 9.00 (apparent d, 1H), 8.22 (appt
t, 1 H), 7.71 (appt d, 1 H), 7.33 (appt t, 1 H), 6.80 (s, 2 H), 4.08
(s, 1 H), 3.80 (s, 3 H), 2.19 (s, 3 H), 1.94 (s, 6 H); 13C NMR
(DMSO-d6) δ 150.7 (C-4), 149.0 (C-9a or C-2), 148.2 (C-2 or
C-9a), 145.0 (C-N), 143.6 (C-8), 130.7 (C-6), 129.6 (C-CH3),
128.4 (2x CH), 128.1 (2 × C-CH3), 114.9 (C-7), 114.1 (C-9),
73.6 (C-3), 30.7 (CH3-N), 20.4 (CH3), 17.7 (2 × CH3) (the NMR
assignments are supported by HSQC and HMBC spectra); IR
(KBr) 1710, 1638, 1616, 1603, 1561, 1415 1385 cm-1; IR (Ar,
14 K) 1738, 1636, 1624, 1609, 1590, 1568, 1533, 1485, 1468,
1443, 1434, 1412, 1383, 1366, 1351, 1323, 1306, 1265, 1229,
1201, 1176, 1168, 1155, 1139, 1051, 1035, 1007, 930, 853, 778,
767, 742, 663, 552, 469 cm-1 (for medium effects on the IR
spectra of mesoionic compounds, see ref 12). Anal. Calcd for
C
18H19N3O: C, 73.68; H, 6.53; N, 14.33. Found: C, 73.86; H,
6.54; N, 14.27. For the X-ray structure, see the Supporting
Information.
3-(Mesityla m in o)p yr a zolin -5-on e (11). Addition of an
excess of anhydrous hydrazine in dichloromethane to 6b
resulted in the formation of an insoluble white solid. Filtration
and washing with dichloromethane and acetone gave 35 mg
F la sh Va cu u m Th er m olysis of 18b: F or m a tion of 6b
a n d 2-(Meth yla m in o)p yr id in e. FVT of 18b was carried out
with deposition of the thermolysate in an Ar matrix at ca. 10
K. At 350 °C, only starting material was isolated (deposition
for 10 min using 70 mbar of Ar; vacuum 5 × 10-5 mbar). At
450 °C, 18b decomposed to give 6b with the characteristic
bands at 2248, 2243, and 2235 cm-1 and 2-(methylamino)-
pyridine, which was identified by comparison with the IR
spectrum of an authentic sample.
2-(Mesit yla m in o)p yr id o[1,2-a ]p yr im id in -4-on e (20b ).
2-Aminopyridine in dichloromethane was added to 6b, and the
solvent was evaporated to give a brownish solid. The starting
material was removed by sublimation, and the crude product
was washed with cold ether to give 40 mg of 20b as a pale
yellow solid (yield 66%): mp 240-242 °C; 1H NMR (CDCl3,
400 MHz) δ 8.89 (broad d, 1H, J ) 7.0 Hz), 7.59 (ddd, 1H, J )
9.0, 7.0, 1.7 Hz), 7.23 (broad d, 1H, J ) 9.0 Hz), 6.95 (s, 2H),
1
of 11 as a white solid (yield 72%): mp 268-270 °C; H NMR
(DMSO-d6) δ 9.92 (s, 1 H), 7.80 (s, 1 H), 6.83 (s, 2 H), 3.27 (s,
2 H), 2.19 (s, 3 H), 2.12 (s, 6 H); 13C NMR (DMSO-d6) δ 171.5,
154.6, 135.0, 134.7, 134.0, 128.4, 36.0, 20.5, 18.1. Anal. Calcd
for C12H15N3O: C, 66.38; H, 6.96; N, 19.35. Found: C, 66.11;
H, 6.91; N, 19.19.
1-Meth yl-3-(m esityla m in o)p yr a zolin -5-on e (12b). Ad-
dition of an excess of anhydrous methylhydrazine in dichlo-
romethane to 6b resulted in the formation of a yellow solution.
Evaporation of the solvent gave a brownish solid which was
purified by recrystallization (THF/pentane) or by sublimation
(22) Bernhardt, P. V.; Koch, R.; Moloney, D. W. J .; Shtaiwi, M.;
Wentrup, C. J . Chem. Soc., Perkin Trans. 2, in press.

Chemistry of Stable Iminopropadienones
J . Org. Chem., Vol. 67, No. 8, 2002 2629
6.88 (td, 1H, J ) 7.0, 1.3 Hz), 6.52 (s, 1H, NH), 5.06 (s, 1H),
2.31 (s, 3H), 2.21 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ 161.3,
158.5, 151.4, 137.6, 136.7, 136.6, 131.7, 129.3, 127.8, 123.7,
112.5, 80.5, 20.9, 18.0; IR (KBr) 3230, 1661, 1642, 1568, 1544
cm-1. Anal. Calcd for C17H17N3O: C, 73.08; H, 6.14; N, 15.05.
Found C, 72.68; H, 6.17; N, 14.93.
9-Am in o-2-(m esit yla m in o)p yr id o[1,2-a ]p yr im id in -4-
on e (33). 2,3-Diaminopyridine in dichloromethane was added
to 6b. Evaporation of the solvent and purification of the crude
product by chromatography through a short column, with ethyl
acetate as eluent, gave 40 mg of 33 as a pale brown solid (yield
63%): mp 230-232 °C; 1H NMR (CDCl3, 400 MHz) δ 8.35 (dd,
1H, J ) 7.0 Hz, 1.4 Hz), 6.94 (s, 2H), 6.79 (dd, 1H, J ) 7.0, 1.4
Hz), 6.73 (t, 1H, J ) 7.0 Hz), 6.12 (s, 1H, NH), 5.04 (s, 1H),
4.77 (s, 2H, NH2), 2.30 (s, 3H), 2.21 (s, 6H); 13C NMR (CDCl3,
100 MHz) δ 159.9 (C-4), 159.2 (C-9a or C-2), 144.0 (C-2 or
C-9a), 138.6 (C-9), 137.4 (C-N), 136.6 (2 × C-CH3), 131.8 (C-
CH3), 129.3 (2 × CH), 116.6 (C-6), 112.9 (C-8), 112.1 (C-7), 80.7
(C-3), 20.9 (CH3), 18.1 (2 × CH3) (the NMR assignments are
supported by a HSQC spectrum); HRMS m/z calcd for
(m, 1H), 7.33 (td, 3J ) 7.3 Hz, 4J ) 1.4 Hz, 1H), 7.50 (dd, 3J )
8.1 Hz, 4J ) 1.5 Hz), 12.8 (s, br, 1 H, NH); 13C NMR (100 MHz,
CDCl3) δ 18.3, 26.1, 30.3, 34.9, 85.2, 102.7, 126.7, 127.5, 128.9,
129.2, 135.2, 144.8, 163.8, 178.3. Anal. Calcd for C18H23NO4S:
C, 61.87; H, 6.63; N, 4.01. Found: C, 61.62; H, 6.64; N, 4.04.
5-[(2-ter t-Bu t yla n ilin o)(d im et h yla m in o)m et h ylen e]-
2,2-dim eth yl-1,3-dioxan e-4,6-dion e (4c). Compound 2c (12.2
g, 35 mmol) was dissolved in 50 mL of dry THF. A stream of
gaseous dimethylamine was bubbled via a pipet through the
stirred solution at such a rate that the gas just absorbed, and
the solution was then heated at 50 °C for 24 h in a closed flask.
The resulting solution was concentrated, causing precipitation
of white crystals, which were collected by filtration and
recrystallized from THF to give 9.1 g (75%) of colorless
1
crystals: mp 117-118 °C; H NMR (400 MHz, CDCl3) δ 1.42
3
4
(s, 9 H), 1.74 (s, 6 H), 2.79 (s, 6 H), 6.88 (dd, J ) 7.5 Hz, J )
3
4
1.8 Hz, 1 H), 7.14-7.22 (m, 2 H), 7.44 (dd, J ) 7.5 Hz, J )
1.8 Hz, 1 H) 10.2 (s, br, 1 H); 13C NMR (100 MHz, CDCl3) δ
26.2 (CH3), 30.3 (CH3 in tBu), 35.1 (C in tBu), 41.7 (NCH3),
76.5 (C(CO)), 102.0 (C(O)), 124.3 (aryl-C3), 126.4 (aryl-C5),
126.9 (aryl-C4), 127.7 (aryl-C6), 137.1 (aryl-C2), 142.5 (aryl-
C1), 162.8 (C(N)N), 164.7 (CO) (the assignments are supported
by HSQC and HMBC spectra). Anal. Calcd for C19H26N2O4:
C, 65.88; H, 7.56; N, 8.09. Found: C, 65.70; H, 7.50; N, 8.01.
5-[(2-ter t-Bu tyla n ilin o)(d ieth yla m in o)m eth ylen e]-2,2-
d im eth yl-1,3-d ioxa n e-4,6-d ion e (5c). A solution consisting
of 10 g (35 mmol) of 2c and 10 mL (97 mmol) of diethylamine
in 50 mL of dry acetonitrile was refluxed for 40 h. Concentra-
tion of the resulting solution caused precipitation of white
crystals, which were filtered and recrystallized from THF to
give 10.5 g (80%) of colorless crystals: mp 198-199 °C; 1H
C
17H18N4O 294.1481, found 294.1478.
2-(Mesitylam in o)pyr im ido[1,2-a ]pyr im idin -4-on e (34b).
2-Aminopyrimidine in dichloromethane was added to 6b to
give, after evaporation of the solvent and purification of the
crude product by chromatography (CHCl3/MeOH 40:1), 45 mg
of 34b as a pale brown solid (yield 74%): mp 193-195 °C; 1H
NMR (CDCl3, 400 MHz) δ 9.11 (dd, 1H, J ) 6.8, 1.8 Hz), 8.82
(dd, 1H, J ) 3.9, 1.8 Hz), 6.91 (s, 2H), 6.89 (dd, J ) 6.8, 3.9
Hz), 6.87 (s, 1H), 4.97 (s, 1 H), 2.26 (s, 3 H), 2.17 (s, 6 H); 13C
NMR (CDCl3, 400 MHz) δ 162.7, 162.6, 158.1, 152.1, 137.9,
137.0, 136.4, 131.2, 129.4, 109.3, 80.0, 20.9, 18.0; IR (KBr)
3285, 3229, 1674, 1558, 1484, 1413, 1285, 804, 784 cm-1
;
NMR (400 MHz, CDCl3) δ 1.11 (t, J ) 7.2 Hz, 6 H), 1.40 (s, 9
3
HRMS m/z calcd for C16H16N4O 280.1319. found 280.1321.
H), 1.70 (s, 6 H), 3.17-3.18 (m, 4 H), 7.08-7.10 (m, 1 H), 7.15-
7.18 (m, 2 H), 7.44-7.46 (m, 1 H), 10.1 (s, br, 1 H) ppm; 13C
NMR (100 MHz, CDCl3) δ 12.4, 26.3, 35.1, 44.2, 76.4, 102.0,
124.1, 126.5, 126.8, 127.8, 137.5, 142.4, 163.1, 164.8. Anal.
Calcd for C20H30N2O4: C, 61.87; H, 6.63; N, 4.01. Found: C,
61.77; H, 6.60; N, 3.98.
2-(Mesit yla m in o)isoq u in olin o[1,2-a ]p yr im id in -4-on e
(36b). 1-Aminoisoquinoline in dichloromethane was added to
6b to give, after evaporation of the solvent and purification
by chromatography (CHCl3), 60 mg of 36b as a cream-colored
solid (yield 84%): mp 288-290 °C; 1H NMR (CDCl3, 400 MHz)
δ 8.91 (br d, 1 H), 8.67 (d, 1H, J ) 7.6 Hz), 7.74 (ddd, J ) 8.0,
7.0, 1.3 Hz, 1 H), 7.67-7.60 (m, 2 H), 7.05 (d, 1 H, J ) 7.6
Hz), 6.94 (s, 2 H), 6.28 (s, 1 H), 5.09 (s, 1 H), 2.30 (s, 3 H), 2.22
(s, 6 H); 13C NMR (CDCl3, 100 MHz) δ 160.6, 159.7, 150.2,
137.6, 136.5, 134.4, 132.5, 131.7, 129.3, 128.0, 127.1, 126.4,
126.0, 122.2, 112.3, 81.5, 21.0, 18.1; HRMS m/z calcd for
((2-ter t-Bu tylph en yl)im in o)pr opadien on e (6c). This com-
pound was prepared by preparative FVT as follows: 100 mg
(0.29 mmol) of 4c was sublimed at 150-180 °C/10-4 mbar and
thermolyzed at 700 °C; the iminopropadienone 6c was collected
on a cold finger cooled to -30 °C using acetone/liquid nitrogen
solution; this cold finger was connected via an uncooled cold
finger to the oil diffusion vacuum pump. Upon completion of
the thermolysis, the pump was closed, and the first cold finger
was warmed to 20 °C for 30 min and then heated with a heat
gun to distill 6c to the second cold finger, which was cooled to
77 K in liquid nitrogen. This cold finger was now warmed to
room temperature while the pressure was equalized with N2,
and iminopropadienone 6c was rinsed into a receiving NMR
tube with CDCl3. The compound was stable for ca. 2 h at room
C
21H19N3O 329.1410, found 329.1421.
2,3-Dih yd r o-7-(m esityla m in o)[1,3]th ia zolo[3,2-a ]p yr i-
m id in -5-on e (41b). 2-Aminothiazoline in dichloromethane
was added to 6b to give, after evaporation of the solvent and
chromatography (CHCl3), 50 mg of 41b as a cream-colored solid
(yield 74%): mp 114-120 °C; 1H NMR (CDCl3) δ 6.89 (s, 2 H),
6.10 (s, 1 H), 4.59 (s, 1 H), 4.37 (t, 2 H, J ) 7.6 Hz), 3.40 (t, 2
H, J ) 7.6 Hz), 2.26 (s, 3 H), 2.15 (s, 6 H); 13C NMR (CDCl3)
δ 164.7, 162.2, 162.1, 137.6, 136.2, 131.5, 129.2, 81.0, 48.3, 26.5,
20.9, 18.0. Anal. Calcd for C15H17N3OS: C, 62.69; H, 5.97; N,
14.63. Found: C, 62.72; H, 6.16; N, 14.09.
7-(Mesit yla m in o)[1,3]t h ia zolo[3,2-a ]p yr im id in -5-on e
(42b). 2-Aminothiazole in dichloromethane was added to 6b
to give, after evaporation of the solvent and chromatography
(CHCl3), 45 mg of 42b as a cream-colored solid (yield 74%):
mp 198-202 °C; 1H NMR (CDCl3) δ 7.81 (d, 1 H, J ) 4.9 Hz),
6.91 (s, 2 H), 6.69 (d, 1 H, J ) 4.9 Hz), 6.35 (s, 1 H), 4.80 (s, 1
H), 2.27 (s, 3 H), 2.17 (s, 6 H); 13C NMR (CDCl3) δ 163.2, 161.4,
159.1, 137.7, 136.4, 131.5, 129.3, 122.2, 107.6, 79.5, 20.9, 18.0.
Anal. Calcd for C15H15N3OS: C, 63.14; H, 5.30; N, 14.74.
Found: C, 63.24; H, 5.44; N, 14.58.
5-[(2-ter t-Bu tyla n ilin o)(m eth ylth io)m eth ylen e]-2,2-d i-
m eth yl-1,3-d ioxa n e-4,6-d ion e (2c). A solution consisting of
10 g (40 mmol) of 1 and 7.5 g (50 mmol) in 50 mL of dry
acetonitrile was refluxed for 30 h. The resulting solution was
concentrated under reduced pressure, and 5 mL of n-hexane
was added to precipitate white crystals, which were collected
by filtration and recrystallized from hot THF to give 9.1 g
(65%) as colorless crystals: mp 148-149 °C; 1H NMR (400
MHz, CDCl3) δ 1.40 (s, 9 H, t-Bu), 1.78 (s, 6 H, CMe2), 2.32 (s,
3 H, SCH3), 7.18 (dd, 3J ) 7.8 Hz, 4J ) 1.6 Hz, 1H), 7.22-7.26
temperature: IR (CHCl3) 2794 m, 2219 s, 2189 s, 1603 m cm-1
;
1H NMR (400 MHz, CDCl3) δ 1.40 (s, 9 H), 7.07-7.09 (m, 1
H), 7.11-7.15 (m, 2 H), 7.32-7.34 (m, 1 H); 13C NMR (100
MHz, CDCl3) δ -3.81, 29.7, 35.0, 107.6, 126.8, 127.2, 127.5,
128.6, 130.4, 132.6, 144.9 (see Supporting Information for
NMR and matrix IR spectra).
Ma tr ix Isola tion of ((2-ter t-Bu tylp h en yl)im in o)p r op a -
d ien on e (6c). Compound 4c (10 mg, 0.03 mmol) was sublimed
at 50 °C through the FVT tube at 700 °C with Ar matrix
isolation of the product on a BaF2 disk at 7 K over the course
of 15 min: IR (Ar, 7K) 2790 w, 2237 vs, 2138 w, 1624 m, 1354
w, 663 m cm-1, Other IR peaks: acetone 1769 w, 1722 m, 1362
m, 1217 m, 1092 m cm-1; dimethylamine 2975 w, 2832 w, 1486
w, 1148 w, 1021 w cm-1; carbon dioxide 2346, 2340 cm-1
.
N,N-Dieth yl 3-(Dieth yla m in o)-3-((2-ter t-bu tylp h en yl)-
im in o)p r op a n a m id e (8c). Iminopropadienone 6c obtained
from Meldrum’s acid derivative 5c (374 mg, 1.0 mmol) as above
was treated with 0.21 mL (2.0 mmol) of diethylamine in 15
mL of dry CH2Cl2, and the resulting mixture was stirred for
12 h. The crude product was purified by flash chromatography
(3% MeOH in ether) to yield 200 mg (58%) of a white solid:
3
mp 82-83 °C; 1H NMR (400 MHz, CDCl3) δ 0.819 (t, J ) 7.2
3
3
Hz, 3 H), 1.09 (t, J ) 6.9 Hz, 3 H), 1.20 (t, J ) 7.2 Hz, 6 H),

2630 J . Org. Chem., Vol. 67, No. 8, 2002
Bibas et al.
3
1.32 (s, 9 H), 2.90 (q, J ) 7.2 Hz, 2 H), 3.13 (s, 2 H), 3.31 (q,
35.7, 36.9, 37.9, 49.5, 50.6, 122.4, 123.4, 126.0, 126.5, 141.1,
148.2, 151.2, 166.1. Anal. Calcd for C17H25N3O: C, 71.04; H,
8.77; N, 14.62. Found: C, 70.94; H, 8.94; N, 13.79. For the
X-ray structure, see the Supporting Information.
3J ) 6.6 Hz, 2 H), 3.44 (q, 3J ) 6.5 Hz, 4 H), 6.57 (dd, 3J ) 7.5
4
3
4
Hz, J ) 1.4 Hz, 1 H), 6.82 (td, J ) 7.2 Hz, J ) 1.4 Hz, 1 H),
3
4
3
6.96 (td, J ) 7.5 Hz, J ) 1.4 Hz, 1 H), 7.23 (dd, J ) 7.6 Hz,
4J ) 1.4 Hz, 1 H); 13C NMR (100 MHz, CDCl3) δ 12.8, 13.6,
13.9, 29.6, 33.9, 35.1, 40.6, 41.6, 42.2, 121.3, 123.4, 125.7, 126.4,
140.7, 150.4, 151.2, 167.1. Anal. Calcd for C21H35N3O: C, 73.00;
H, 10.21; N, 12.16. Found: C, 72.91; H, 10.47; N, 11.86.
3-((2-t er t -Bu t ylp h e n yl)im in o)-1-m e t h ylp yr a zolin -5-
on e (12c). To iminopropadienone 6c, obtained from Meldrum’s
acid derivative 4c (346 mg, 1.0 mmol), was added a solution
of 50.7 mg (1.1 mmol) of methylhydrazine in 30 mL of THF
dropwise over a period of 3 h, and the resulting mixture was
stirred for 2 days. The solvent was evaporated, and the crude
product was purified by flash chromatography (5% MeOH/
ether) to yield 135 mg (55%) of a pale yellow solid: mp 160-
161 °C; 1H NMR (CDCl3) δ 1.41 (s, 9 H), 3.21 (s, 3 H), 3.30 (s,
2 H), 6.29 (s, br, 1 H), 7.10-7.26 (m, 2 H), 7.38-7.43 (m, 2 H);
13C NMR (CDCl3) δ 30.6, 31.1, 34.7, 37.4, 125.8, 126.4, 127.0,
127.1, 136.9, 142.8, 153.8, 167.8.
8-Meth yl-2-((2-ter t-bu tylp h en yl)im in o)p yr id o[1,2-a ]p y-
r im id in -4-on e (22c). Iminopropadienone 6c obtained from
Meldrum’s acid derivative 4c (346 mg, 1.0 mmol) was treated
with 119.0 mg (1.1 mmol) of 2-amino-4-picoline in 15 mL of
dry THF, and the resulting mixture was stirred for 12 h. The
solvent was evaporated, and the crude product was sublimed
to remove excess 2-amino-4-picoline. Flash chromatography
(5% MeOH/ether) yielded 200 mg (65%) as a pale yellow
1
solid: mp 229-230 °C; H NMR (400 MHz, CDCl3) δ 1.37 (s,
3
9 H), 2.32 (s, 3 H) 5.30 (s, 1 H), 6.95 (s, br, 1 H), 6.73 (d, J )
7.0 Hz, 1 H), 7.23-7.29 (m, 4 H), 7.45-7.48 (m, 1 H), 8.77 (d,
3J ) 7.0 Hz, 1 H); 13C NMR (100 MHz, CDCl3) δ 21.35, 30.7,
35.1, 81.0, 115.7, 121.4, 127.2, 127.3, 127.4, 127.6, 130.2, 136.0,
147.0, 149.5, 150.8, 158.1, 161.1. Anal. Calcd for C19H21N3O:
C, 74.24; H, 6.89; N, 13.67. Found: C, 74.49; H, 6.99; N, 13.71.
7-Meth yl-2-((2-ter t-bu tylp h en yl)im in o)p yr id o[1,2-a ]p y-
r im id in -4-on e (23c). Iminopropadienone 6c obtained from
Meldrum’s acid derivative 4c (346 mg, 1.0 mmol) was treated
with 119.0 mg (1.1 mmol) of 2-amino-5-picoline in 15 mL of
dry THF, and the resulting mixture was stirred for 12 h. The
solvent was evaporated, and the crude product was sublimed
to remove excess 2-amino-5-picoline. Flash chromatography
(5% MeOH/ether) yielded 210 mg (68%) as a pale yellow
1-Meth yl-2-((2-ter t-bu tylp h en yl)im in o)-1,2-d ih yd r op y-
r id o[1,2-a ]p yr im id in -1-iu m -4-ola te (18c). Iminopropadi-
enone 6c obtained from Meldrum’s acid derivative 4c (346 mg,
1.0 mmol) as above was treated with 119 mg (1.1 mmol) of
2-(methylamino)pyridine in 15 mL of dry CH2Cl2. The resulting
mixture was stirred for 24 h. The solvent was evaporated and
the crude product purified by flash chromatography (50%
MeOH/ether) to yield 200 mg (65%) of an orange solid: mp
198-199 °C; IR (KBr): 1716, 1694, 1636, 1615, 1560, 1473,
1
solid: mp 200-201 °C; H NMR (400 MHz, CDCl3) δ 1.39 (s,
9 H), 2.40 (s, 3 H) 5.30 (s, 1 H), 6.27 (s, br, 1 H), 7.19-7.29 (m,
1
3
1458, 1417, 1355, 1301, 1265, 1050, 771, 754 cm-1; H NMR
(400 MHz, CDCl3) δ 1.34 (s, 9 H, t-Bu), 4.97 (s, 1H, CH), 6.70
3 H), 7.49-7.52 (m, 2 H), 7.69 (d, J ) 8.0 Hz, 1 H), 8.78 (s, 1
H); 13C NMR (100 MHz, CDCl3) δ 17.9, 30.6, 35.1, 81.9, 122.7,
122.9, 125.2, 127.3, 127.4, 127.5, 130.4, 136.1, 147.1, 149.9,
158.2, 161.3. Anal. Calcd for C19H21N3O: C, 74.24; H, 6.89; N,
13.67. Found: C, 74.22; H, 7.00; N, 13.61.
3
4
3
4
(td, J ) 7.7 Hz, J ) 1.4 Hz, 1H), 6.91 (td, J ) 7.3 Hz, J )
1.5 Hz, 1H), 7.06-7.12 (m, 1H), 7.30-7.34 (m, 1H), 7.97 (td,
3J ) 7.9 Hz, J ) 2.0 Hz, 1H), 9.25 (dd, J ) 6.5 Hz, J ) 1.7
Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 30.3 (CMe3), 35.2
(CMe3), 67.1 (CH), 112.3, 113.9, 122.1, 122.6, 126.5, 126.8,
132.4, 141.6, 142.5, 148.5, 148.6, 149.3, 151.6 (CO). The
assignments are supported by a HSQC spectrum. Anal. Calcd
for C19H21N3O: C, 74.24; H, 6.89; N, 13.67. Found: C, 73.97;
H, 7.09; N, 13.54.
4
3
4
2-((2-ter t-Bu tylph en yl)im in o)pyr azin o[1,2-a ]pyr im idin -
4-on e (35c). Iminopropadienone 6c from Meldrum’s acid
derivative 4c (346 mg, 1.0 mmol) was treated with 104.6 mg
(1.1 mmol) of aminopyrazine in 15 mL of dry THF, and the
resulting mixture was stirred at room temperature for 24 h.
The solvent was evaporated, and the crude product was
sublimed to remove excess aminopyrazine and then purified
by flash chromatography (5% MeOH/ether) to yield 80 mg
2-((2-ter t-Bu tylp h en yl)im in o)p yr id o[1,2-a ]p yr im id in -
4-on e (20c). Iminopropadienone 6c obtained from Meldrum’s
acid derivative 4c (346 mg, 1.0 mmol) was isolated on a cold
finger at -30 °C. Subsequently, 103.5 mg (1.1 mmol) of
2-aminopyridine in 15 mL of dry CH2Cl2 was added to the
iminopropadienone, and the resulting mixture was stirred for
16 h. The solvent was evaporated, and the crude product was
sublimed to remove excess 2-aminopyridine and then purified
by flash chromatography (5% MeOH/ether) to yield 195 mg
1
(27%) of a pale yellow solid: mp 156-158 °C; H NMR (400
MHz, CDCl3) δ 1.40 (s, 9 H), 5.50 (s, 1 H), 6.78 (s, br, 1 H),
3
7.24-7.31 (m, 3 H), 7.49-7.51 (m, 1 H), 7.94 (d, J ) 4.7 Hz,
1 H), 8.56 (dd, 3J ) 4.7 Hz, 5J ) 1.2 Hz, 1 H), 8.77 (d, 5J ) 1.2
Hz, 1 H); 13C NMR (100 MHz, CDCl3) δ 30.6, 35.0, 84.4, 117.5,
127.4, 127.5, 127.8, 129.5, 129.7, 135.2, 144.5, 146.7, 151.0,
156.9, 161.6.
1
(66%) as a pale yellow solid: mp 190-191 °C; H NMR (400
2-((2-ter t-Bu tylp h en yl)im in o)isoqu in olin o[1,2-a ]p yr i-
m id in -4-on e (36c). Iminopropadienone 6c from Meldrum’s
acid derivative 4c (346 mg, 1.0 mmol) was treated with 158.6
mg (1.1 mmol) of 1-aminoisoquinoline in 15 mL of dry THF,
and the resulting mixture was stirred at room temperature
for 12 h. The crude product precipitated upon partial evapora-
tion of the solvent, and it was recrystallized from THF/hexane
MHz, CDCl3) δ 1.38 (s, 9 H, t-Bu), 5.38 (s, 1H, CH), 6.47 (s,
br, 1 H, NH), 6.87 (td, 3J ) 7.0 Hz, 4J ) 1.4 Hz, 1H), 7.22-
7.29 (m, 4H), 7.45-7.47 (m, 1H), 7.57 (td, 3J ) 7.7 Hz, 4J )
3
4
1.7 Hz, 1H), 8.88 (dd, J ) 7.0 Hz, J ) 1.0 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 30.7 (CMe3), 35.1 (CMe3), 81.92 (CH),
112.7, 123.9, 127.3, 127.4, 127.5, 127.9, 130.1, 136.0, 136.7,
146.7, 151.4, 158.5 (CO), 161.5 (the assignments are supported
by HSQC and HMBC spectra). Anal. Calcd for C18H19N3O: C,
73.69; H, 6.53; N, 14.32. Found: C, 73.42; H, 6.62; N, 14.25.
1,4-Dim et h yl-7-((2-ter t-b u t ylp h en yl)im in o)p er h yd r o-
[1,4]d ia zep in -5-on e (13c). Iminopropadienone 6c obtained
from Meldrum’s acid derivative 4c (346 mg, 1.0 mmol) was
treated with 97.0 mg (1.1 mmol) of N,N′-dimethylethylenedi-
amine in 30 mL of diethyl ether, which was added dropwise
to the stirred solution over a period of 6 h. The resulting
mixture was stirred at room temperature for 3 days. The
solvent was evaporated, and the crude product was purified
by flash chromatography (5% MeOH/ether), sublimed, and
then washed with ether to yield 170 mg (59%) of white
1
to yield 275 mg (80%) of a white solid: mp 260-261 °C; H
NMR (CDCl3) δ 1.43 (s, 9 H), 5.49 (s, 1 H), 6.60 (s, br, 1 H),
3
7.08 (d, J ) 7.6 Hz, 1 H), 7.23-7.36 (m, 3 H), 7.44-7.51 (m,
3
1 H), 7.60-7.80 (m, 3 H), 8.68 (d, J ) 7.6 Hz), 8.92 (br d, 1
H); 13C NMR (100 Hz, CDCl3) δ 30.6, 35.0, 82.7, 112.4, 122.2,
125.9, 126.4, 127.0, 127.2, 127.28, 127.31, 128.0, 129.9, 132.5,
134.3, 136.1, 146.4, 150.1, 159.6, 160.7. Anal. Calcd for
C
18H19N3O: C, 76.94; H, 6.16; N, 12.24. Found: C, 76.41; H,
6.16; N, 11.97.
2-((2-ter t-Bu tylp h en yl)im in o)-2,3-d ih yd r o[1,3]th ia zolo-
[3,2-a ]p yr im id in -4-on e (41c). Iminopropadienone 6c ob-
tained from Meldrum’s acid derivative 4c (346 mg, 1.0 mmol)
as above was treated with 112.4 mg (1.1 mmol) of 2-ami-
nothiazoline in 15 mL of dry THF, and the resulting mixture
was stirred for 10 h. The solvent was evaporated, and the crude
product was sublimed to remove excess trapping agent. Flash
chromatography (5% MeOH/ether) yielded 211 mg (70%) of a
pale yellow solid: mp 220-221 °C; 1H NMR (400 MHz, CDCl3)
1
crystals: mp 126-127 °C; H NMR (400 MHz, CDCl3) δ 1.30
3
(s, 9 H), 2.96 (s, 3 H), 3.14 (s, 3 H), 3.47 (s, 2 H), 3.51 (t, J )
3
3
5.3 Hz, 2 H), 3.69 (t, J ) 5.3 Hz, 2 H), 6.37 (dd, J ) 7.5 Hz,
4J ) 1.4 Hz, 1 H), 6.91 (td, 3J ) 7.2 Hz, 4J ) 1.4 Hz, 1 H), 7.09
3
4
3
4
(td, J ) 7.5 Hz, J ) 1.4 Hz, 1 H), 7.26 (dd, J ) 7.9 Hz, J )
1.8 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3) δ 29.7, 35.1,
3
3
δ 1.35 (s, 9 H), 3.44 (t, 2 H, J ) 7.3), 4.40 (t, 2 H, J ) 7.3),

Chemistry of Stable Iminopropadienones
J . Org. Chem., Vol. 67, No. 8, 2002 2631
5.01 (s, 1 H), 6.48 (s, br, 1 H), 7.16-7.23 (m, 3 H), 7.40-7.44
(m, 1 H); 13C NMR (100 MHz, CDCl3) δ 26.7, 30.6, 35.0, 48.4,
82.3, 127.2, 127.3, 127.5, 135.7, 146.6, 161.9, 162.0, 164.7.
Anal. Calcd for C16H19N3OS: C, 63.76; H, 6.35; N, 13.94.
Found: C, 63.47; H, 6.47; N, 13.85.
(CH), 107.9, 122.2, 127.3, 127.4, 127.6, 130.0, 135.8, 146.7,
159.0, 161.6, 163.0 (CO). The assignments are supported by
HSQC and HMBC spectra. Anal. Calcd for C16H17N3OS: C,
64.19; H, 5.72; N, 14.04. Found: C, 64.06; H, 5.73; N, 13.91.
2-((2-ter t-Bu tylp h en yl)im in o)[1,3]th ia zolo[3,2-a ]p yr i-
m id in e-5-on e (42c). Iminopropadienone 6c obtained from
Meldrum’s acid derivative 4c (346 mg, 1.0 mmol) was treated
with 110.2 mg (1.1 mmol) of 2-aminothiazole in 15 mL of dry
THF, and the resulting mixture was stirred for 10 h. The
solvent was evaporated, and the crude product was sublimed
to remove excess trapping agent. Flash chromatography (5%
MeOH/ether) yielded 210 mg (70%) of a pale yellow solid: mp
229-330 °C; 1H NMR (400 MHz, CDCl3) δ 1.37 (s, 9 H, t-Bu),
Ack n ow led gm en t. This work was supported by the
Australian Research Council.
Su p p or tin g In for m a tion Ava ila ble: Figures and tables
1
giving vibrational spectra of 6a -c, H and 13C NMR spectra
of 6a -c, 8a , 8′a , 9b, 10a , 12c, 13b,c, 14a , 15a , 17b, 21a , 22a ,
23a , 24a , 26a , 33b, 34a , 34b, 35a ,c, 36b, 41a , and 43a , and
X-ray structure data for 13c, 14a , 15a , 18b, 21a , and 43a .
This material is available free of charge via the Internet at
http://pubs.acs.org.
3
5.16 (s, 1H, CH), 6.59 (s, br, 1 H, NH), 6.73 (d, 1H, J ) 5.0),
3
7.23-7.24 (m, 3H), 7.43-7.47 (m, 1H), 7.82 (d, 1H, J ) 5.0);
13C NMR (100 MHz, CDCl3) δ M 30.6 (CMe3), 35.0 (CMe3), 80.8
J O0110552