Aryliminopropadienone-C-Amidoketenimine-Amidinoketene-2-Aminoquinolone Cascades and the Ynamine-Isocyanate Reaction

Article abstract of DOI:10.1021/jo982471y

Imidoylketenes 11 and oxoketenimines 12 are generated by flash vacuum thermolysis of Meldrum's acid derivatives 9, pyrrolediones 17 and 18, and triazole 19 and are observed by IR spectroscopy. Ketenimine-3-carboxylic acid esters 12a are isolable at room temperature. Ketenes 11 and ketenimines 12 undergo rapid interconversion in the gas phase, and the ketenes cyclize to 4-quinolones 13. When using an amine leaving group in Meldrum's acid derivatives 9c, the major reaction products are aryliminopropadienones, ArN=C=C=C=O (15). The latter react with 1 equiv of nucleophile to produce ketenimines 12 and with 2 equiv to afford malonic acid imide derivatives 16. N-Arylketenimine-C-carboxamides 12c cyclize to quinolones 13c via the transient amidinoketenes 11c at temperatures of 25-40 °C. This implies rapid interconversion of ketenes and ketenimines by a 1,3-shift of the dimethylamino group, even at room temperature. This interconversion explains previously poorly understood outcomes of the ynamine-isocyanate reaction. The solvent dependence of the tautomerism of 4-quinolones/4-quinolinols is discussed. Rotational barriers of NMe2 groups in amidoketenimines 12c and malonioc amides and amidines 16 (24) are reported.

Full text of DOI:10.1021/jo982471y

3608
J . Org. Chem. 1999, 64, 3608-3619
Ar ylim in op r op a d ien on e-C-Am id ok eten im in e-
Am id in ok eten e-2-Am in oqu in olon e Ca sca d es a n d th e
Yn a m in e-Isocya n a te Rea ction
Curt Wentrup,* V. V. Ramana Rao, Wilhelm Frank, Belinda E. Fulloon,
Daniel W. J . Moloney, and Thomas Mosandl
Chemistry Department, The University of Queensland, Brisbane, Queensland 4072, Australia
Received December 18, 1998
Imidoylketenes 11 and oxoketenimines 12 are generated by flash vacuum thermolysis of Meldrum’s
acid derivatives 9, pyrrolediones 17 and 18, and triazole 19 and are observed by IR spectroscopy.
Ketenimine-3-carboxylic acid esters 12a are isolable at room temperature. Ketenes 11 and
ketenimines 12 undergo rapid interconversion in the gas phase, and the ketenes cyclize to
4-quinolones 13. When using an amine leaving group in Meldrum’s acid derivatives 9c, the major
reaction products are aryliminopropadienones, ArNdCdCdCdO (15). The latter react with 1 equiv
of nucleophile to produce ketenimines 12 and with 2 equiv to afford malonic acid imide derivatives
16. N-Arylketenimine-C-carboxamides 12c cyclize to quinolones 13c via the transient amidi-
noketenes 11c at temperatures of 25-40 °C. This implies rapid interconversion of ketenes and
ketenimines by a 1,3-shift of the dimethylamino group, even at room temperature. This intercon-
version explains previously poorly understood outcomes of the ynamine-isocyanate reaction. The
solvent dependence of the tautomerism of 4-quinolones/4-quinolinols is discussed. Rotational barriers
of NMe2 groups in amidoketenimines 12c and malonioc amides and amidines 16 (24) are reported.
In tr od u ction
aptitudes of the groups R follow the order NMe2 > SMe
> SH > Cl > NH2 > OMe > OH > F > H > Ph . Me
(G2(MP2,SVP) calculations). The activation barrier for
the 1,3-Cl shift in the oxoketenes 1b and 2b (R ) Cl)
was determined by dynamic 13C NMR spectroscopy in
solution as 10 kcal mol-1, and this reaction is rapid at
-30 °C.6 The calculated barrier for the corresponding 1,3-
NMe2 shift in 1b/2b is ca. 6-8 kcal mol-1. Higher barriers
for analogous shifts are expected in imidoylketenes, and
thus a value of ca. 25 kcal mol-1 is found for 1a /2a . These
are among the lowest computed activation barriers for
these types of reaction. Therefore, it is very desirable to
examine systems 1/2 with R ) NMe2 experimentally. For
1c/2c (R ) NMe2), see reference 7. The amidoketenes (1b,
R ) NMe2) are not stable at room temperature; in fact,
no example of the characterization of an amidoketene has
been reported. Amidoketenimines (1a , R ) NMe2) are
observable molecules but until now were only generated
in a few cases, by flash vacuum thermolysis (FVT) of
4-carboxamidotriazoles 3.9
There are three ways that oxoketenimines/imidoyl-
ketenes 1a /2a can be generated in FVT reactions: from
triazoles 3,1,4e,9 pyrrolediones 4,2,3,4a,4b and Meldrum’s acid
derivatives (5-methylene-1,3-dioxane-4,6-diones)1,3,4c 5.
The N-arylimidoylketenes 2a cyclize very easily to qui-
nolones 7.1,3,9 In the case of the Meldrum’s acid precur-
sors 5, a competing fragmentation can lead to the new
cumulenes, iminopropadienones, 6.10,11 The ease of this
process increases on changing the leaving group from
MeO or MeS to NMe2 in the Meldrum’s acid derivative
It was demonstrated in earlier work that oxoketen-
imines (1a ) and imidoylketenes (2a ) undergo facile
thermal 1,3-shifts of electron donating substituents
(R).1-4 Analogous rearrangements of oxoketenes (1b)5,6
and vinylketenes (1c)7 are also known. The 1,3-shifts take
place in the s-trans isomers shown, but the s-cis rotamers
are usually of lower energy.6,7b,8 According to recent ab
initio calculations on the oxoketenes 1b,6,8 the migratory
(1) Fulloon, B.; Wentrup, C. J . Org. Chem. 1996, 61, 1363.
(2) Fullon, B.; El-Nabi, H. A. A.; Kollenz, G.; Wentrup, C. Tetrahe-
dron Lett. 1995, 36, 6547.
(3) Kappe, C. O.; Kollenz, G.; Leung-Toung, R.; Wentrup, C. J . Chem.
Soc., Chem. Commun. 1992, 487.
(4) (a) Kappe, C. O.; Kollenz, G.; Wentrup, C. J . Chem. Soc., Chem.
Commun. 1992, 485. (b) Kappe, C. O.; Kollenz, G.; Netsch, K.-P.;
Leung-Toung, R.; Wentrup, C. J . Chem. Soc., Chem. Commun. 1992,
488. (c) Ben Cheikh, A.; Chuche, J .; Manisse, N.; Pommelet, J . C.;
Netsch, K.-P.; Lorencak, P.; Wentrup, C. J . Org. Chem. 1991, 56, 970.
(d) Bibas, H.; Fulloon, B. E.; Moloney, D. W. J .; Wong, M. W.; Wentrup,
C. Pure Appl. Chem. 1996, 68, 891. (e) Clarke, D.; Mares, R. W.; McNab,
H. J . Chem. Soc., Perkin Trans 1 1997, 1799.
(5) Wentrup, C.; Netsch, K.-P. Angew. Chem., Int. Ed. Engl. 1984,
23, 802. Wentrup, C.; Winter, H.-W.; Gross, G.; Netsch, K.-P.; Kollenz,
G.; Ott, W.; Biedermann, G. Angew. Chem., Int. Ed. Engl. 1984, 23,
800.
(6) Finnerty, J .; Andraos, J .; Yamamoto, Y.; Wong, M. W.; Wentrup,
C. J . Am. Chem. Soc. 1998, 120, 1701.
(7) (a) Bibas, H.; Koch, R.; Wentrup, C. J . Org. Chem. 1998, 63, 2619.
(b) Bibas, H.; Wong, M. W.; Wentrup, C. Chem. Eur. J . 1997, 3, 237.
(c) Bibas, H.; Wong, M. W.; Wentrup, C. J . Am. Chem. Soc. 1995, 117,
9582.
(8) For calculations on the 1,3-shifts in R-oxoketenes, see also: (a)
Wong, M. W.; Wentrup, C. J . Org. Chem. 1994, 59, 5279. (b) Koch, R.;
Wong, M. W.; Wentrup, C. J . Org. Chem. 1996, 61, 6809.
(9) Rao, V. V. R.; Wentrup, C. J . Chem. Soc., Perkin Trans. 1 1998,
2583.
(10) Mosandl, T.; Kappe, C. O.; Flammang, R.; Wentrup, C. J . Chem.
Soc., Chem. Commun. 1992, 1571.
(11) (a) Flammang, R.; Laurent, S.; Flammang-Barbieux, M.; Wen-
trup, C. Rapid Commun. Mass Spectrom. 1992, 6, 667. (b) Mosandl,
T.; Stadtmu¨ller, S.; Wong, M. W.; Wentrup, C. J . Phys. Chem. 1994,
98, 1080.
10.1021/jo982471y CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/29/1999

Aryliminopropadienone-Amidoketenimine-Amidinoketene Cascades
J . Org. Chem., Vol. 64, No. 10, 1999 3609
1a). The ketenimine peak increased in intensity at 300-
400 °C, but already at 400 °C phenyliminopropadienone
15H (2222, 2140 cm-1) started to form. This was virtually
the only observable product at 600 °C, apart from CO2,
acetone, MeSH, and quinolone 13Hb, all of which were
identified by comparison with authentic materials. A
representative series of spectra of the ketene region is
shown in Figure 1. An Ar matrix IR spectrum of 15H
was identical with that published previously.11b Qui-
nolone 13Hb was obtained in 70% yield by preparative
FVT of 9Hb. It has been obtained previously as the
product of thermolysis of 9Hb in diphenyl ether at 240
°C.14 Generally, the MeS derivatives of 9 give very good
yields of quinolones but poor yields of ArNCCCO (15);
route a in Scheme 1 dominates.
The same ketene and ketenimine 11Hb and 12Hb
were also obtained on FVT of the pyrroledione 17 and
observed by IR spectroscopy.3 Importantly, there was no
5, so much so that in the latter case, iminopropadienone
formation becomes almost the only reaction. Another type
of precursor, the isoxazolopyrimidinone 8, leads directly
to 6 on FVT.10,11 The iminopropadienones 6 can be
isolated in good yields at 77 K, using either 5 or 8 as
precursor. Aryliminopropadienones usually undergo chemi-
cal reactions at temperatures of -100 to -50 °C; only in
special cases are they isolable at room temperature.12
Here, we report full details of the synthesis of arylimi-
nopropadienones 6 (15), as well as their conversion to
amidoketenimines 1a (12) in solution at low temperature.
This is followed by facile rearrangement to 2-amino-4-
quinolones13 at or near room temperature, thereby indi-
cating a rapid equilibration of amidoketenimines 1a (12)
with amidinoketenes 2a (11). The results have implica-
tions also for the mechanism of the reaction between
ynamines and isocyanates.
corresponding formation of iminopropadienone 15H in
this case, either at 400 °C or at higher temperatures.
Above 600 °C, there was simply disappearance of both
11Hb and 12Hb and virtually quantitative formation of
quinolone 13Hb instead (90%). Therefore, 11 and 12
cannot be the source of iminopropadienones 15 from
Meldrum’s acid derivatives 9. Instead, 15 must be formed
via initial elimination of HX to yield a transient keten-
imine 14, which undergoes a cycloreversion to 15, CO2,
and acetone (route b, Scheme 1). The transients 14 are
often formed in quantities too small for reliable identi-
fication by IR spectroscopy, but they have been detected
unambiguously by on-line mass spectrometry (a ther-
mally produced m/z 245 at 350 °C in the case of 14H).10,15
Thus, Meldrum’s acid derivatives 9Ha ,b yield imino-
propadienone 15H and quinolones 13Ha ,b as the ulti-
mate products, formed via two different pathways, routes
a and b in Scheme 1. The pyrroledione 17 gives only
quinolone 13Hb because of the dynamic equilibrium
between ketene and ketenimine (11Hb/12Hb), with all
of the ketene cyclizing to the quinolone. Similarly,
5-methoxypyrroledione (4, R ) OMe) affords 13Ha .2
Quite a different situation occurs when a dimethyl-
amino group is used as the leaving group in the Mel-
drum’s acid precursor 9Hc. At first sight, there is little
or no quinolone formation, but as we shall see, this
depends on how the experiment is carried out. Only
minor amounts of ketene and ketenimine 11Hc and
12Hc are formed in this case, and therefore also only
Resu lts a n d Discu ssion
1. F VT Exp er im en ts. We will describe the differently
substituted starting materials and products in Scheme
1 as the H series (R1 ) H), the M series (R1 ) Me), and
the X series (R1 ) methoxy). To investigate the primary
reaction products from the FVT of the Meldrum’s acid
precursors 9, the products were isolated either neat at
77 K or in Ar matrix at 14 K for IR spectroscopy.
In the 9H series, the familiar ketene and ketenimine
11Ha and 12Ha were formed (2135 and 2050 cm-1
,
respectively, at 77 K) starting at ca. 200 °C, and both of
these intermediates were replaced by PhNCCCO (15H)
above 500 °C.1 Compound 15H can be trapped with added
MeOH on the coldfinger to yield 16Ha in 30-67% yield.1
The ketenimine 12Ha has been isolated and character-
ized,1,2 and FVT of this compound did not produce 15H.
Using the SMe leaving group in the 9Hb series, weak
signals due to a ketene and a ketenimine, assigned to
11Hb and 12Hb, were observed on FVT at 260 °C (Figure
(12) Moloney, D. W. J . Ph.D. Thesis, The University of Queensland,
1997. Moloney, D. W. J .; Wentrup, C. To be submitted for publication.
(13) The term 4-quinolone as used in this paper includes the
4-hydroxyquinoline tautomers. Only one tautomer is observed by NMR
in each case, but different tautomers predominate in different solvents.
This subject is expounded in Section 5. For early literature, see:
Elguero, J .; Marzin, C.; Katritzky, A. R.; Linda, P. The Tautomerism
of Heterocycles; Academic: New York, 1976; p 87 and references
therein.
(14) Ye, F.-C.; Chen, B.-C.; Huang, X. Synthesis 1989, 317.
(15) (a) Moloney, D. W. J .; Wong, M. W.; Flammang, R.; Wentrup,
C. J . Org. Chem. 1997, 62, 4240. (b) Flammang, R.; Wentrup, C.
Unpublished results.

3610 J . Org. Chem., Vol. 64, No. 10, 1999
Wentrup et al.
Sch em e 1
(R ) NMe2, Ar ) Ph).9 A very weak absorption at 2137
cm-1 may be due to formation of a trace of the ketene
11Hc. As we have concluded before,9 this ketene was not
identifiable with any degree of certainty from the triazole
route as a result of the facts that the ketenimine is the
primary product in that case, a high temperature (500
°C) was required, and the cyclization to quinolone 13Hc
is very facile. In the case of the Meldrum’s acid aminal
9Hc, a strong signal due to PhNCCCO (15H) appeared
already at 360 °C, and the putative ketene and keten-
imine signals disappeared completely above 360 °C (Ar
matrix) or at 500 °C (neat isolation at 77 K). The
conversion of the starting material (9Hc) is only complete
at ca. 600 °C. On preparative FVT of 9Hc at 600 °C,
PhNCCCO (15H) is isolated on a 77 K coldfinger, where
it can be trapped with alcohols to give malonic ester
imides 16c,d , with added dimethylamine to give 16e, and
with added diethylamine to give 16f and 16g in total
yields up to 84%. This trapping reaction is described more
fully in Section 2. The quinolone 13Hc is very involatile
and also very insoluble in solvents other than DMSO or
DMF, and therefore this compound is never present on
the coldfinger or in the solutions of this material for NMR
spectroscopy. However, 13Hc deposited in yields of 15-
20% in the air-cooled part of the apparatus before the
coldfinger, immediately outside the oven in the 600 °C
preparative FVT experiment. This compound must be
formed by cyclization of ketene 11Hc in the gas phase
and therefore represents the fraction of the reaction
taking place via path a (Scheme 1). Therefore, the reason
F igu r e 1. Partial FTIR spectra (1900-2400 cm-1 range) of
the products (77 K) of FVT of 9Hb at 260-600 °C (a-d). K )
ketene 11Hb (2121, 2106 (sh) cm-1). I ) ketenimine 12Hb
(2040 cm-1). P ) phenyliminopropadienone 15H (2222 (vs),
2140 (sh) cm-1).
little 2-dimethylaminoquinolone 13Hc is produced. In-
stead, there is immediate formation of phenyliminopro-
padienone 15H, dimethylamine, CO2, and acetone, as
observed in the IR spectra at 77 K and at 14 K. The
ketenimine 12Hc was observable only at FVT tempera-
tures of 310-360 °C (2035-2051 vw cm-1 in Ar matrix,
15 K; 2033/2042 vw cm-1 neat, 77 K). The position and
shape of this complex peak was the same as observed
previously for the ketenimine formed from the triazole 3

Aryliminopropadienone-Amidoketenimine-Amidinoketene Cascades
J . Org. Chem., Vol. 64, No. 10, 1999 3611
F igu r e 2. Partial FTIR spectra (1900-2400 cm-1 range) of the products (77 K) of FVT of 9Ma at 150-500 °C (a-e) and of
triazole 19 at 300-500 °C (f-h). K ) ketene 11Ma (2136, 2119 (sh) cm-1). I ) ketenimine 12Ma (2046 cm-1). P )
4-methylphenyliminopropadienone 15M (2221, 2182 (sh) cm-1).
that the intermediates 11c/12c cannot be observed above
ca. 360 °C (where very little reaction has taken place) is
not that they are not formed but that 11c cyclizes very
easily to 13c.
The methyl (M) series, using the p-tolylaminomethyl-
ene-Meldrum’s acid precursors 9M, gave results analo-
gous to those reported for the H series above. The ketene
11Ma was already detectable at a FVT temperature as
low as 150 °C (Figure 2a), and the ketenimine 12Ma
appeared from at least 200 °C (Figure 2b)). The signal
for iminopropadienone, 4-MePhNCCCO (15M) became
strong already at 300 °C, and this was the only cumulene
signal remaining at 500 °C (Figure 2c-e). Preparative
FVT of 9Ma at 500 °C with subsequent trapping of 15M
with MeOH on the coldfinger gave a 38% yield of malonic
ester imide 16Ma and a 55% yield of quinolone 13Ma .
The ketenimine 12Ma was isolable in 34% yield from
FVT at 300 °C. FVT of the isolated and distilled keten-
imine 12Ma at 400 °C gave a small amount of ketene
11Ma , together with mostly unchanged 12Ma , as ob-
served by IR spectroscopy, and a little quinolone 13Ma .
Importantly, the FVT of 12Ma did not give any iminopo-
padienone, 15M.
The same ketene and ketenimine, 11Ma and 12Ma ,
but not the iminopropadienone 4-MePhNCCCO (15M),
were also obtained on FVT of the pyrroledione 18 and
the triazole 19 (Figure 2f-h), whereby the latter also
gave some indole 20 (9-17%). The formation of indoles
has been described elsewhere.1 Compounds 11Ma and
12Ma had the same spectral characteristics as described
above. The ketenimine 12Ma was isolable in 24% yield
from the triazole and in 32% yield from the pyrroledione
(using FVT at 500 °C). Quinolone 13Ma was isolated in
74% yield from the triazole and in up to 84% yield from
the pyrroledione (using FVT at 600 °C).
The methylthio-substituted Meldrum’s acid precursor
9Mb was investigated cursorily. The ketenimine 12Mb
was observed at 2048 cm-1 (Ar, 12 K), and 4-MePhNC-
CCO (15M) had an IR spectrum identical to that de-
scribed above.
The dimethylamino analogue 9Mc afforded strong IR
signals due to 4-MePhNCCCO (15M) already at a FVT
temperature of 300 °C. An Ar matrix IR spectrum is
shown in the Supporting Information. A ketenimine was
hardly detectable in this case (a very weak and diffuse
peak was present at 2050 cm-1 (neat) in the 300 °C
experiment). As we shall see in Section 3, the ketenimine
12Mc can be synthesized from 15M by addition of
dimethylamine.
In the methoxy (X) series, the elimination of CO2 and
acetone from 9Xa started at ca. 300 °C, and both a
ketenimine 12Xa (2047 neat, 2050 Ar cm-1) and a ketene
(2138 (vw) neat, 2142 (vw) Ar cm-1), presumably 11Xa ,
were observable at 77 K. At 400 °C, a much stronger
signal due to the ketenimine 12Xa , together with a very
weak signal due to the ketene, and new bands in the 2200
cm-1 region were observed (Figure 3a). The latter are
ascribed to 4-MeOPhNCCCO (15X), and these became
very strong at 500 °C and higher temperatures (Figure
3b,c). In an Ar matrix, this signal appeared as a char-
acteristic, complex band with maxima at 2252 (s), 2246
(vs), 2239 (s), 2235 (s), and 2137 (w) cm-1 (spectrum
shown in the Supporting Information). Bands due to CO2
and acetone were also recorded. The ketene 11 and
ketenimine 12 were absent above 600 °C as a result of

3612 J . Org. Chem., Vol. 64, No. 10, 1999
Wentrup et al.
For example, when 15X, generated by FVT of 9Xc at 600
°C, was slowly warmed from -196 °C, reaction with the
cocondensed dimethylamine took place at ca. -70 °C with
irreversible formation of ketenimine 12Xc, which per-
sisted on further warmup till 0 °C (Figure 4). This
ketenimine was also observed by IR and NMR spectros-
copy in solution by injecting CD2Cl2 on the 77 K coldfin-
ger containing 15X and allowing the material to thaw
and flow into a precooled NMR tube at -80 to -70 °C.
The 1H NMR spectrum at -70 °C displayed characteristic
signals due to ketenimine 12Xc at δ 2.93, 2.98, 3.75, and
5.05 ppm, corresponding to the two NMe signals due to
slow rotation of the NMe2 group, the OMe group, and the
CdCH function, respectively.16 On slow warming of this
solution to room temperature, coalescence of the two
methyl signals of the NMe2 group took place at -10 °C,
from which the free energy of activation for rotation about
the amide C-N bond is calculated17 as ∆Gq ) 13.6 kcal/
mol.
F igu r e 3. Partial FTIR spectra (1900-2400 cm-1 range) of
the products (77 K) of FVT of 9Xa at 400-800 °C (a-c). K )
ketene 11Xa (2138 cm-1). I ) ketenimine 12Xa (2047 cm-1).
P ) 4-methoxyphenyliminopropadienone 15X (2257, 2237 (sh),
2184 cm-1).
the formation of the involatile quinolone 13Xa , which was
isolated in 34% yield from a preparative FVT experiment
and in 24% yield from refluxing diphenyl ether (vide
infra). Trapping of 15X with methanol on the coldfinger
afforded the malonic ester imide 16Xa in 47% yield.
An analogous FVT experiment with 9Xb (500 °C/14 K
Ar) produced the same IR spectrum of 4-MeOPhNCCCO
(15X) as reported above.
Similar FVT of 9Xc was studied between 300 and 800
°C. At 300 °C, the IR spectrum showed extremely weak
bands at 2039, 2049, and 2127 cm-1 possibly due to 12Xc
and/or 14X and 11Xc, but already at this temperature,
weak bands ascribed to 4-MeOPhNCCCO (15X) were
present. At FVT temperatures of 400 °C and above, this
was the only cumulene observed, the other ketenimine
absorptions having completely disappeared. The IR spec-
trum of 15X in an Ar matrix displayed the characteristic
multiplet structure described above. Trapping of 15X
with added dimethylamine on the coldfinger afforded the
malonic amidoamidine derivative 16Xe in 67% yield.
Because of its involatility, no quinolone was present on
the coldfinger, but a ca. 20% yield of quinolone 13Xc
condensed in the air-cooled part of the apparatus im-
mediately after the exit of the pyrolysis oven. Thus, the
67% yield of 16Xe represents the yield of 4-MeOPhNC-
CCO (15X) arriving on the coldfinger, and the 20% yield
of quinolone 13Xc represents the cyclization of ketene
11Xc in the gas phase.
Thus, in general, with HNMe2 as the leaving group,
route b in Scheme 1 dominates the reaction. The imino-
propadienones ArNCCCO (15) are obtained essentially
pure on the liquid N2 cooled coldfinger. This is found in
the H, M, and X series.
2. F or m a tion of Keten im in es a n d Ma lon ic Acid
Der iva tives. When the Meldrum’s acid derivatives 9c
having amine leaving groups are used in FVT experi-
ments, we know from direct IR spectroscopic observation
at either 77 K or in Ar matrixes that the products
arriving on the cold targets are iminopropadienones,
ArNCCCO (15), together with HNMe2. Subsequent war-
mup caused formation of ketenimines 12c (R2 ) NMe2).
The IR spectrum of the cold CD2Cl2 solution revealed
a strong band at 2036 cm-1 (also present in CH2Cl2
solution), ascribed to ketenimine 12Xc and persisting till
room temperature.
Similar reactions of iminopropadienones 15H and 15M
afforded ketenimines 12Hc and 12Mc. According to IR
spectroscopy, 12Mc started forming at -90 °C (2030
cm-1, neat). FVT of 9Hc at 500 °C gave a very strong
band due to PhNCCCO (15H, 2222 cm-1), together with
a very weak one due to ketenimine 12Hc (2042, 2033
cm-1, neat, 77 K). On warming this mixture to -100 °C,
the band due to PhNCCCO started to decrease, and that
due to ketenimine 12Hc increased strongly as a result
of reaction with dimethylamine.
1
The H and 13C NMR spectra of 12Hc are reported in
the Experimental Section and shown in the Supporting
Information. From the coalescence of the methyl signals
of the dimethylamino group in 12Hc at -10 °C, ∆Gq )
13.0 kcal/mol was calculated. Dimethylamides normally
have rotational barriers of ca. 16-20 kcal mol-1 as a
result of the partial double bond character of the C-N
bond in the zwitterionic resonance structure.17,18 The low
value for the keteniminecarboxamide 12Hc and the
mesityl analogue 23 described below can be attributed
(16) NMR data for ketenimines: see ref 1, and the Supporting
Information to ref 1 and to this paper, and (a) Firl, J .; Runge, W.;
Hartmann, W.; Utikal, H.-P. Chem. Lett. 1975, 51. (b) Eberl, K.;
Roberts, J . D. Org. Magn. Reson. 1981, 17, 180.
(17) Free energy of activation calculations according to, e.g., Bovey,
F. A. Nuclear Magnetic Resonance Spectroscopy; Academic Press: San
Diego, 1988. The estimated error is 1 kcal/mol.
(18) Kessler, H. Angew. Chem., Int. Ed. Engl. 1970, 9, 219.

Aryliminopropadienone-Amidoketenimine-Amidinoketene Cascades
J . Org. Chem., Vol. 64, No. 10, 1999 3613
corresponding esters 12a (R2 ) OMe) are much more
stable, usually distillable liquids.1,2
Ketenimines 12 and 23 react with nucleophiles at or
below room temperature to afford malonic ester imides
16 (24). For example, addition of excess dimethylamine
to a solution of 12Xc gives 16e quantitatively. Addition
of ethanol in CHCl3 affords 16d quantitatively. To pre-
pare compounds 16, the easiest would seem to be injec-
tion of the nucleophile R3H on the cold (77 K) ther-
molysate from 9 (Scheme 1). Thus, injection of MeOH on
the thermolysate from 9a affords 16a . The thermolysate
from 9c affords 16e with HNMe2. Whenever HNMe2 is
used as the leaving group, subsequent injection of
methanol will, however, afford 16c, and ethanol will give
16d . In other words, the cocondensed dimethylamine
reacts first, at the ketene terminus of the iminopropa-
dienone 15, to produce amidoketenimine 12c. That 16 is
formed via 15 (route b, Scheme 1) and not directly from
12 (route a, Scheme 1) under such conditions is shown
by the fact that one can remove part of the cocondensed
HNMe2 from the pyrolysates by intermittant warming
of the coldfinger to ca. -80 °C while pumping in high
vacuum. Subsequent addition of a second nucleophile
(e.g., MeOH) then provides a mixture of products, e.g.,
16c due to reaction with residual HNMe2 and then MeOH
and 16a due to reaction with MeOH only. If an excess of
diethylamine is cocondensed with the pyrolysate, HNEt2
can compete with HNMe2, and the product with two
diethylamino groups, 16g, will dominate. Added amine
also competes efficiently with cocondensed methanol.
Thus, the pyrolysate from 9Xa reacts with HNMe2 to give
16Xe.
F igu r e 4. Partial FTIR spectra (1900-2400 cm-1 range) of
the products of FVT of 9Xc at 600 °C, recorded at -196 °C (a)
and after warmup to -70 °C (b) and -50 °C (c). I ) ketenimine
12Xc (2034 cm-1). P ) 4-methoxyphenyliminopropadienone
15X (2257 cm-1).
to a contribution from the resonance structure 21c,19
which reduces the C-N double bond character expressed
in structure 21b. Such an effect is not present in
allenecarboxamides,7b,20 which normally exhibit two dis-
tinct resonances for the two N-alkyl groups at room
temperature, thus suggesting normal rotational barriers.
The synthesis and chemistry of the mesityl-NCCCO
compound 22 is described in other work.12 This derivative
reacts in the same manner to give a ketenimine 23. The
The malonic acid derivatives 16 and 24 exist only in
the tautomeric forms shown according to NMR spectros-
copy. In the 1H NMR spectra of the amidoamidines 16e-
g, the amidine function appears at lowest field, and the
two methyl or alkyl groups are equivalent at room
temperature as a result of rapid rotation. The higher field
amide function appears as two nonequivalent methyl
groups as a result of slow rotation. For example, the
spectrum of 16Xe exhibits two singlets at δ 2.68 (3H) and
2.84 (3H) (OC-NMe2) and a singlet at δ 3.09 (6H) (Nd
C-NMe2). We have measured the high and low coales-
cence temperatures and derived17 the rotational barriers
for some of these amidoamidines and find that they are
in the order of 11-13 kcal mol-1 for the amidines and
ca. 18 kcal/mol for the amides (e.g., for 24, 11.0 and 18.3
kcal mol-1, respectively). The lower barriers for the
amidine functions are to be expected because of the lower
electronegativity of N compared to O, which will reduce
the C-N double bond character. These barriers are
diagnostically valuable as a means of secure assignment
of structures to compounds of the type 16 and hence
asserting the sequence and positions of addition of the
nucleophiles.
closeness of the two NMe signals causes a low coalescence
temperature of -25 °C, but the free energy of activation
is similar to the above: ∆Gq ) 13.2 kcal mol-1
.
The formation of malonic imide derivatives of type 16
from ketenimines is thermally reversible in some cases
when the leaving group is an amine. Thus, FVT or GC-
MS (injector temp 200 °C) of 16Xe afforded quinolone
13Xc. Work to be published on other substances indicates
that HNMe2 is eliminated from the amido group, gener-
ating the imidoylketene, which then cyclizes to the
quinolone.
The amidoketenimines 12c (R2 ) NMe2) are not
usually isolable as pure compounds. Their further fate
at room temperature in the absence of nucleophiles, viz.,
quinolone formation, is described in Section 3. The
(19) For the importance of resonance structure 21c, see ref 16b and
J ochims, J . C.; Lambrecht, J .; Burkert, U.; Zsolnai, L.; Huttner, G.
Tetrahedron 1984, 40, 839. Wolf, R.; Stadtmu¨ller, S.; Wong, M. W.;
Barbieux-Flammang, M.; Flammang, R.; Wentrup, C. Chem. Eur. J .
1996, 2, 1318.
16Xe f 11Xc + HNMe2 f 13Xc + HNMe2
(20) Himbert, G. J ustus Liebigs Ann. Chem. 1979, 829.

3614 J . Org. Chem., Vol. 64, No. 10, 1999
Wentrup et al.
The other compounds 16 described in this paper were
stable under GC-MS conditions.
3. Rea r r a n gem en t of Keten im in es to Qu in olon es.
The amidoketenimines 12c and 23 are observable by
NMR in solution at room temperature as described above.
However, the signals of 12Hc disappeared in the course
of 24 h at room temperature in CDCl3 or CD2Cl2 solution,
and at the same time, quinolone 13Hc precipitated from
the solution, from which it was isolated in 20% yield
based on the Meldrum’s acid precursor, 9Hc. The yield
was improved to 25% by refluxing the methylene chloride
solution for 1 h. The ketenimine 12Xc disappeared from
the NMR spectrum in 3 days at room temperature,
mainly polymerizing and giving only a trace of quinolone,
but at 40 °C the quinolone 13Xc was formed in 15% yield
and at 83 °C in 20% yield (38% yield of the material
arriving on the coldfinger). We know from the low-
temperature IR and NMR studies that no quinolone was
present in these solutions initially. They must therefore
have formed by rearrangement of the ketenimines or
molecules derived therefrom. The structures of the qui-
nolones are without doubt, being identical with the
materials obtained from two other routes (the triazole
route9 and the ynamine-isocyanate route; see Section 5).
Imidoylketenes 11 cyclize very readily to quinolones at
or near room temperature.9,21 Therefore, our results
strongly support the hypothesis of an equilibrium be-
tween amidoketenimine 12 and imidoylketene 11, taking
place via a 1,3-shift of the NMe2 group. This equilibrium
is fast at room temperature:
This can explain why 12Hc rearranges to quinolone
at room temperature, whereas 12Xc requires ca. 40 °C.
4. P r ep a r a tion of Qu in olon es in Solu tion a n d
Assign m en t of Str u ctu r e. Several quinolones in the
13H and 13X series were prepared in yields of 24-76%
by refluxing the Meldrum’s acid derivatives 9 in diphenyl
ether. The yields obtained on preparative FVT of 9 at
600-700 °C are often as good. The formation of quino-
lones 13Ha and 13Hb in refluxing diphenyl ether solu-
1
tion was reported previously.1,14 The H NMR spectra of
3-unsubstituted quinolones display characteristic signals
for H(C-3) at ca. δ 6 ppm, and these are particularly
broad in DMSO-d6 solution. The 13C NMR signal for C-3
appears in the region of δ 90-105 ppm. The sequence of
1
the H NMR signals for H(C-5) and H(C-8) is reversed
when going from DMSO-d6 to CDCl3 (or more conve-
niently, for better solubility CDCl3/CD3OD mixed sol-
vent). This solvent change also causes C-8 to move to
higher field. In DMSO-d6, C-2 usually appears at lower
field than C-4 (when the 2-substituent is MeO, MeS, or
NMe2). The signals due to the quaternary carbons C-2
and C-8a are often very weak and broad as a result of
the neighboring nitrogen quadrupole moment. In DMSO-
d6 solution in particular, the appearance of the spectra
(chemical shifts and broadness of both proton and carbon
signals) is highly dependent on the amount of water
present; the tautomeric mixture undoubtedly depends on
solvent polarity, water content, and other factors. In
DMSO-d6 solution, all of the signals due to quaternary
carbons and also often that of C-8 are particularly weak
and broad; it can help to heat the sample to 80 °C. The
ensemble of data strongly indicates that there is a
preponderance of the 4-hydroxyquinoline tautomer in
DMSO solution and of the 1H-quinoline-4-one tautomer
in CDCl3/CD3OD (eq 2).
The ketene 11 is not observed in the equilibrium by
NMR or IR spectroscopy at room temperature because
the ketenimine is more stable by ca. 5 kcal/mol according
to calculations.22 As described above, this ketene is
observed by low temperature IR spectroscopy, following
population in high-temperature FVT reactions, especially
when the NMe2 group is replaced by OMe (11a ), in which
case the cyclization to quinolones becomes slower.
The alkoxyimidoylketenes/oxoketenimines 11a /12a do
not undergo such facile cyclization to quinolones. The
ketenimines are isolable at room temperature, and qui-
nolones are formed only on heating to 100 °C or by FVT
at 200 °C. The dimethylamino group in amidinoketenes
helps make the aromatic ring more electron rich, thus
accelerating cyclization:9
This is supported by comparisons with unpublished
data for N-alkyl-4-quinolones and O-alkyl-4-quinolinols
in our laboratory and with calculated values (increment
method). The NMR assignments made here were based
on 1H-1H coupling constants, DEPT, and 2D experi-
ments. Examples of the latter are presented in the
Supporting Information.
Also of importance is the fact that H/D exchange9 takes
place in these quinolones at H(C-3) in protic solvents, e.g.,
in the case of 13Xa in the course of several days at room
temperature in CDCl3/CD3OD solution, thus indicating
that the less favorable and not directly observed 3H
tautomer also participates.
Not surprisingly, the IR spectra of the quinolones/
quinolinols can vary widely depending on the method of
sample preparation. In some but not all cases, a carbonyl
group appears around 1640 cm-1 in the solid state (KBr)
spectra.
However, a donor group X on the aromatic ring makes
the ketene less electrophilic, thus decelerating cycliza-
tion:
(21) Bouvy, A.; J anousek, Z.; Viehe, H. G.; Arietta, J . M. Bull. Soc.
Chim. Belg. 1985, 94, 869.
(22) Finnerty, J .; Wong, M. W.; Wentrup, C. To be submitted for
publication.
5. Th e Yn a m in e-Isocya n a te Rou te to Qu in olon es.
The results described in Section 3 made us conclude that

Aryliminopropadienone-Amidoketenimine-Amidinoketene Cascades
J . Org. Chem., Vol. 64, No. 10, 1999 3615
Sch em e 2
room temperature. If no such unhindered aryl group is
available, the more stable ketenimine 27 is isolable or
undergoes further reaction to 29.
It was desirable to provide independent verification
that ketenes akin to 11 (28) would actually cyclize to
quinolones 13 (30) at room temperature. We chose the
silyl-substituted ynamines 32 of the type recently de-
scribed by Himbert27 to demonstrate this. Thus, reaction
of N,N-dimethyl-N-(trimethylsilylethynyl)amine (32a )
with phenyl isocyanate in either benzene or acetonitrile
solution at room temperature afforded quinolone 34a ()
13Hc) in ca. 25% yield. The yield is typical for this type
the ketenimine-ketene interconversion between 12c and
11c is fast at room temperature. The formation of
quinolones under these conditions then requires that the
cyclization of ketenes 11c also be rapid at room temper-
ature. There are several reports of quinolone formation
from putative imidoylketenes at elevated temperatures
(typically 100-200 °C).23 More importantly, ynamines
react with isocyanates at or near room temperature to
furnish ketenimines, 4-quinolones, and/or other prod-
ucts.21,24 There is much speculation about the mechanism
of this reaction in the literature, and it is usually
assumed that the ynamine can undergo [2+2] cycload-
dition to either the CdO (route a) or the CdN bond (route
b) of the isocyanates, leading to putative oxete 25 and
azetinone 26 intermediates (Scheme 2). The third pos-
sibility is a [2+4] cycloaddition of the ynamine to aryl
isocyanates utilizing one of the benzenoid CdC double
bonds (route c).25 Perplexingly, alkyl isocyanates ap-
peared to react by route a only, giving ketenimines 27.26
In light of our results reported in this paper, we reinter-
pret all of these ynamine-isocyanate reactions in terms
the rapid equilibrium between ketenimine 27 and ketene
28 (route d) regardless of whether path a or path b is
followed. When ketene 28 possesses an unhindered
N-aryl group, it cyclizes to the quinolone 30 at or near
of reaction.21,23-25 The analogous diethylamino compound
32b afforded 2-diethylamino-4-quinolone (34b).The tri-
methylsilyl derivative 33b was detectable by GC-MS of
the crude reaction mixture, but the trimethylsilyl group
was lost on chromatographic purification.
Con clu sion
Meldrum’s acid derivatives 9 can undergo fragmenta-
tion by two different paths, routes a and b in Scheme 1.
Route b is an almost exclusive route when the leaving
group is an amine substituent (R2 ) NMe2). This leads
via the transient ketenimine 14 to clean formation of
aryliminopropadienones, ArNdCdCdCdO (15), isolable
at 77 K and in some cases observable till room temper-
ature. Compounds 15 react with 2 equiv of nucleophiles
to afford malonic acid imide derivatives 16 and with 1
equiv to afford ketenimines 12 cleanly.
Route a (Scheme 1) leads to the interconverting imi-
doylketenes and oxoketenimines 11 and 12, the former
cyclizing to quinolones 13. This is the dominant route
when the leaving group in 9 is MeO or MeS.
The C-alkoxycarbonylketenimines 12 (R2 ) OR) are
isolable and distillable; they isomerize to ketenes 11 and
quinolones 13 on heating (ca. 200 °C in the gas phase).
The C-carboxamidoketenimines 12 (R2 ) NR2) are stable
in solution at room temperature for short periods of time
but cyclize to quinolones 13 via amidinoketenes 11 at or
near room temperature, thus implying low activation
barriers for both the interconversion between 11 and 12
and for the cyclization of 11 to 13.
(23) Potts, K. T.; Ehlinger, R.; Nichols, W. M. J . Org. Chem. 1975,
40, 2596. Kappe, T.; Zadeh, K. Synthesis 1975, 247. Moderhack, D.;
Stolz, K. Chem.-Z. 1987, 12, 372. Mass, H.; Bensimon, C.; Alper, H. J .
Org. Chem. 1998, 63, 17.
(24) (a) Kuehne, M. E.; Linde, H. J . Org. Chem. 1972, 37, 1846. (b)
Ficini, J .; Krief, A. Tetrahedron Lett. 1968, 947 (see correction of
structures in ref 24c). (c) Kuehne, M. E.; Sheehan, P. J . J . Org. Chem.
1968, 33, 4406 (regarding the ynamine-ketene reactions also reported
here, see the reassignment of the alleged oxete structures 10 in this
paper as allenes in ref 20).
(25) Ficini, J . Tetrahedron 1976, 1449.
(26) (a) Piper, J . U.; Allard, M.; Faye, M.; Hamel, L.; Chow, V. J .
Org. Chem. 1977, 26, 4261. (b) Ficini, J .; Pouliquen, J . Tetrahedron
Lett. 1972, 1139.
(27) Himbert, G.; Nasshan, H.; Gerulat, O. Synthesis 1997, 293.

3616 J . Org. Chem., Vol. 64, No. 10, 1999
Wentrup et al.
5-[(4-Met h oxyp h en yla m in o)(m et h ylt h io)m et h ylen e]-
2,2-d im eth yl-1,3-d ioxa n e-4,6-d ion e (9Xb) was prepared
according to the literature:14 yield 71%; mp 147-148 °C (lit.14
146-147 °C); 13C NMR (CDCl3) δ 18.7, 26.2, 55.4, 85.3, 102.9,
114.4, 126.6, 129.6, 159.0, 163.8, 178.2.
Iminopropadienones 15 are not formed from the ketenes/
ketenimines 11 or 12, or at most in only trace amounts.
Triazoles 3 (19) and pyrrolediones 4 (17, 18) afford the
interconverting ketene/ketenimines 11/12 and not, to any
significant extent, iminopropadienones 15. In the FVT
of triazoles 3 (R ) NMe2) at high temperatures, we did
observe weak bands in the IR spectra corresponding to
PhNCCCO (15H).9 Because ArNCCCO compounds are
extremely strong absorbers, these bands correspond to
only trace amounts of material.
The [2+2] cycloaddition reaction between ynamines
and isocyanates is reinterpreted: the products are de-
rived from the rapidly interconverting amidinoketene and
amidoketenimine (28-27).
The assigned structures of ketenimines and malonic
imides are strongly supported by measured rotational
barriers of dimethylamino groups. In ketenimines 12 (R
) NMe2) and 23 they are ca. 13 kcal mol-1. In the malonic
imides 16 (24) they are of the order of 18 kcal mol-1 for
the amides and 11-13 kcal mol-1 for the amidines.
5-[Met h oxy(4-m et h oxyp h en yla m in o)m et h ylen e ]-2,2-
d im eth yl-1,3-d ioxa n e-4,6-d ion e (9Xa ) was prepared as 9Ma
in 67% yield; mp 162-164 °C; IR (KBr) 1714, 1663, 1621, 1576
cm-1 1H NMR (CDCl3) δ 1.77 (s, 6H), 3.83 (s, 3H), 4.13 (s,
;
3H), 6.92 (d, 2H, J ) 6.8 Hz), 7.26 (d, 2H, J ) 6.8 Hz), 11.8
(bs, 1H, N-H); 13C NMR (CDCl3) δ 26.1, 55.4, 62.5, 75.4, 102.9,
114.4, 124.7, 127.7, 158.3, 164.1, 171.1. Anal. Calcd for C15H17
NO6: C, 58.63; H, 5.58; N, 4.56. Found: C, 58.51; H, 5.60; N,
4.51.
5-[(Dim et h yla m in o)(4-m et h oxyp h en yla m in o)m et h yl-
en e]-2,2-d im eth yl-1,3-d ioxa n e-4,6-d ion e 9Xc was prepared
as 9Mc (48 h reaction; 81% yield): mp 191-193 °C; IR (KBr)
1688, 1636, 1608, 1585 cm-1; 1H NMR (CDCl3) δ 1.53 (s, 6H),
2.92 (s, 6H), 3.73 (s, 3H), 6.89 (d, J ) 9 Hz, 2H), 7.08 (d, J )
8.9 Hz, 2H), 9.23 (bs, 1H); 13C NMR (CDCl3) δ 26.1, 41.1, 55.3,
73.9, 102.1, 114.2, 125.0, 131.6, 157.6, 163.5, 163.9. Anal. Calcd
for C16H20N2O5: C, 59.97; H, 6.30; N, 8.75. Found: C, 60.12;
H, 6.24; N, 8.72.
Meth yl 1-(4-Meth ylp h en yl)-1H-1,2,3-tr ia zole-4-ca r box-
yla te (19) was prepared from methyl propiolate (1.68 g; 0.02
mol) and p-tolyl azide (2.66 g; 0.02 mol) in ethanol (150 mL)
at reflux for 22 h. The solvent was removed by rotary
evaporation, and the resulting solid was recrystallized from
ethanol/diethyl ether to produce white crystals: yield 3.0 g
Exp er im en ta l Section
The pyrolysis apparatus and general equipment were as
previously reported for Ar matrix (12 K),28 neat film (77 K)29
deposition, and preparative scale work (77 K isolation).30 NMR
spectra are at 200 MHz for 1H and 50.3 MHz for 13C unless
otherwise indicated. Mass spectra were obtained by 70 eV
electron ionization. GC-MS employed a BP-5 capillary column
(30 m × 0.25 mm; He carrier at 20 psi head pressure; injector
200 °C; detector 280 °C; column temperature 100-125 °C,
programmed at 16 °C/min). Column chromatography was
performed on silica gel (200-400 mesh unless otherwise
stated). Melting points are uncorrected. Compounds 9Ha -
c,1,11b 9Mb,14 17,3 and 182 were prepared according to reported
procedures.
5-[(4-Met h ylp h en yla m in o)(m et h oxy)m et h ylen e ]-2,2-
d im eth yl-1,3-d ioxa n e-4,6-d ion e (9Ma ). To a solution of
5-[(4-methylphenylamino)(methylthio)methylene]-2,2-dimethyl-
1,3-dioxane-4,6-dione (9Mb) (0.154 g; 0.5 mmol) in methanol
(5 mL) was added HgO (yellow; 0.109 g; 0.5 mmol) and HgCl2
(0.135 g; 0.5 mmol) [In this type of reaction, we find that a
mixture of HgO and HgCl2 sometimes gives better yields than
either of these compounds alone1]. The mixture was refluxed
for 20 min and filtered, and the filtrate was evaporated. H2O
(10 mL) was added to the residue to assist precipitation of the
product, which was recrystallized from THF/hexane: yield 0.11
g (78%); mp 174-175 °C; 1H NMR (CDCl3) δ 1.74 (s, 6H), 2.34
(s, 3H), 4.11 (s, 3H), 7.18 (s, 4H); 13C NMR (CDCl3) δ 21.0,
26.2, 62.6, 75.2, 103.4, 123.2, 129.8, 132.3, 137.0, 164.2, 171.2;
IR (KBr) 1720, 1660 cm-1. Anal. Calcd for C15H17NO5: C, 61.83;
H, 5.89; N, 4.81. Found: C, 61.71; H, 5.85; N, 4.75.
5-[(Dim eth ylam in o)(4-m eth ylph en ylam in o)m eth ylen e]-
2,2-d im eth yl-1,3-d ioxa n e-4,6-d ion e (9Mc). To 9Ma (307 mg;
1.0 mmol) in 15 mL THF was added 2 mL of a solution of
dimethylamine in water (40% w/v), followed by HgO (216 mg;
1.0 mmol). The mixture was stirred overnight and filtered. The
filtrate was evaporated in a vacuum, and the resulting solid
was recrystallized from THF to yield colorless needles: 250
mg (79%); mp 232 °C; IR (KBr) 1640, 1611, 1587 cm-1; 1H NMR
(CDCl3) δ 1.70 (s, 6H), 2.32 (s, 3H), 2.87 (s, 6H), 6.93 (d, 2H),
7.17 (d, 2H), 9.28 (br s, 1H, exchanging with D2O); 13C NMR
(CDCl3) δ 20.9, 26.3, 41.8, 76.0, 102.2, 123.0, 130.1, 136.0,
136.2, 163.6, 164.5. Anal. Calcd for C16H20N2O4: C, 63.14; H,
6.62; N, 9.20. Found: C, 62.99; H, 6.50; N, 9.21.
1
(70%); mp 159-160 °C; H NMR (CDCl3) δ 2.41 (s, 3H), 3.97
(s, 3H), 7.29-7.62 (m, 4H), 8.45 (s, 1H); 13C NMR (CDCl3) δ
18.9, 52.3, 96.0, 125.5, 130.4, 139.8, 141.0, 161.1; IR (KBr)
1713, 1543 cm-1. Anal. Calcd for C11H11N3O2: C, 60.82; H, 5.10;
N, 19.34. Found: C, 60.79; H, 5.14; N, 19.28.
P r ep a r a tion of 2-Su bstitu ted 4-Qu in olon es 13 in Di-
p h en yl Eth er . Compounds 13Hc, 13Xa , 13Xb, and 13Xc
were obtained by refluxing 9 in Ph2O/N2 for 20-30 min.1,14
2-Dim eth yla m in o-4-qu in olon e (13Hc). White crystals
1
(70%); mp 290 °C, identified by rigorous comparison of IR, H
and 13C NMR, and mass spectra with those of the previously
characterized material.9
2,6-Dim eth oxy-4-qu in olon e (13Xa). Yellow crystals (24%);
IR (KBr) 3266, 3082, 1654, 1620, 1589 cm-1; 1H NMR (DMSO-
d6, 400 MHz) δ 3.83 (s, 3H, OMe), 3.94 (s, 3H, OMe), 6.26 (br
s, 1H, H(C-3)), 7.33 (dd, J ) 3 and 9 Hz, 1H, H(C-7)), 7.39 (d,
J ) 3 Hz, 1H, H(C-5)), 7.60 (d, J ) 9 Hz, 1H, H(C-8)), 11.3 (br
1
s, 1H); H NMR (CDCl3/CD3OD 1:1, 200 MHz) δ 3.89 (s, 3H,
OCH3), 3.97 (s, 3H, OCH3), 5.89 (s, 1H, H(C-3), slowly
exchanging with D), 7.21 (dd, J ) 3 and 9 Hz, 1H, H(C-7)),
7.37 (d, J ) 9 Hz, 1H, H(C-8)), 7.59 (d, J ) 3 Hz, 1H, H(C-5));
note that the chemical shifts of H(C-5) and H(C-8) are
interchanged in these two solvents; the assignments are based
on the observed coupling constants and a HSQC 2D 13C-1H
correlation spectra (Supporting Information); 13C NMR (CDCl3/
CD3OD 1:1) δ 55.8 (MeO), 56.3 (MeO), 89.2 (C-3), 104.7 (d,
C-5), 119.7 (d, C-8, broad), 123.3 (d, C-7), 123.8 (s, C-4a), 133.9
(s, C-8a, weak, broad), 156.5 (s), 161.8 (s), 179 (s, weak, broad);
the assignments are based on the HSQC 2D carbon-proton
correlation and a DEPT spectrum; the broad signals are
ascribed to vicinity of the 14N quadrupole moment; MS m/z
205.0729, calcd for C11H11NO3 205.0733.
6-Meth oxy-2-m eth ylth io-4-qu in olon e (13Xb).14 Yellow
solid, (49%); mp 230-232 °C (dec) (lit.14 229-230 °C); IR (KBr)
1
3189, 1612, 1576, 1537, 1500 cm-1; H NMR (DMSO-d6, 400
MHz) δ 2.56 (s, 3H, SMe), 3.82 (s, 3H, OMe), 6.20 (br s, 1H,
H(C-3)), 7.24 (dd, J ) 3 and 9 Hz, 1H, H(C-7)), 7.43 (d, J ≈ 3
Hz, 1H, H(C-5)), 7.56 (d, J ≈ 9 Hz, 1H, H(C-8), 11.84 (br s,
1H); 1H NMR (CDCl3/CD3OD 1:1, 400 MHz) δ 2.60 (s, 3H,
SMe), 3.90 (s, 3H, OMe), 6.25 (s, 1H, H(C-3)), 7.23 (dd, J ) 3
and 9 Hz, 1H, H(C-7)), 7.44 (d, J ) 9 Hz, 1H, H(C-8)), 7.60 (d,
J ) 3 Hz, 1H, H(C-5)); 13C NMR (CDCl3/CD3OD 1:1, 100 MHz)
δ 14.7 (SCH3), 55.8 (OCH3), 104.4 (C5), 104.8 (C3), 119.5 (d,
C-8), 123.7 (d, C-7), 125.2 (s), 136.2 (s), 154.0 (s), 156.9 (s),
176.9 (s). A DEPT spectrum confirmed the assignments. The
sequence of C-7 and C-8 is reversed in DMSO-d6 solution: δ
(28) Kappe, C. O.; Wong, M. W.; Wentrup, C. J . Org. Chem. 1995,
60, 1686.
(29) Briehl, H.; Lukosch, A.; Wentrup, C. J . Org. Chem. 1984, 49,
2772.
(30) Wentrup, C.; Blanch, R.; Briehl, H.; Gross, G. J . Am. Chem.
Soc. 1988, 110, 1874.

Aryliminopropadienone-Amidoketenimine-Amidinoketene Cascades
J . Org. Chem., Vol. 64, No. 10, 1999 3617
121.8 (C-7), 122.5 (C-8, weak, broad). HSQC 1H-13C 2D
correlation spectra (for both CDCl3/CD3OD and DMSO-d6
solutions) are shown in the Supporting Information. MS m/z
221.0510, calcd for C11H11NO2S 221.0505. Anal. Calcd for
C11H11NO2S: C, 59.71; H, 4.98; N, 6.34. Found: C, 59.78; H,
5.11; N, 6.33.
propadienone (15H) was observed as a very strong peak at
2222, 2140 (sh) cm-1. A very weak peak due to ketenimine
12Hc was detectable at 2042, 2033 cm-1. On slow warmup of
this material to -100 °C, the signals due to 15H started to
decrease, and those due to ketenimine 12Hc started growing
at 2042/2033 cm-1 (neat film).
2-(N,N-d im eth yla m in o)-6-m eth oxy-4-qu in olon e (13Xc).
Light brown solid (76%), identical with previously character-
ized material.9
P r ep a r a tion of 16Hd by Tr a p p in g of Keten im in e 12Hc.
Meldrum’s acid derivative 9Hc (85 mg; 0.29 mmol) was
subjected to preparative FVT at 600 °C with isolation of the
products in a U-tube at 77 K. The system was then brought
to atmospheric pressure with N2, and the U-tube was warmed
to room temperature. [As shown above, ketenimine 12Hc
would now be present.] The content of the U-tube was
immediately dissolved in a solution of 2% EtOH in CHCl3 (50
mL), the solution was refluxed, and the solvent was then
removed by rotary evaporation. The resulting yellow oil (53
mg; 77% based on 9Hc) was shown by 1H NMR to be a mixture
of 16Hd and 16He (1:0.35), which was easily separated into
the pure constituents by chromatography through a short
column, first eluting 16Hd with CHCl3, and then 16He with
CHCl3/MeOH (10:1) (cf. spectra below). From the air- cooled
part of the apparatus, between the oven and the U-tube, was
isolated a 15-20% yield of quinolone 13Hc, identical in all
respects with the previously characterized material.9
P r ep a r a tion of Com p ou n d s 16Ha ,c,f,g by Tr a p p in g of
P h en ylim in op r op a d ien on e 15H. 15H was generated by
FVT of 9Hc (ca. 100 mg) at 600 °C. The products were isolated
on a coldfinger previously coated with the added nucleophile
(MeOH or HNEt2; ca. 2 mL) and kept at either ca. -190 or
-80 °C. The coldfinger was then allowed to warm to room
temperature, and the products were separated by column
chromatography on SiO2 (70-230 mesh), eluting with Et2O.
Meth yl 3-Meth oxy-3-(p h en ylim in o)p r op a n oa te (16Ha ).
Obtained with added MeOH. Yield 43% when using a coldfin-
ger at -80 °C; 0% at -190 °C. Yellow oil, identical with the
previously described material.1
3-Me t h oxy-3-(p h e n ylim in o)-N ,N -d im e t h ylp r op a n a -
m id e (16Hc). Obtained with added MeOH. Yield 25% at -80
°C; 73% at -190 °C. Yellow oil; IR (CCl4) 1682, 1662, 1597,
1490 cm-1; 1H NMR (CDCl3, 400 MHz) δ 2.83 (s, 3H), 2.92 (s,
3H), 3.25 (s, 2H), 3.86 (s, 3H), 6.85 (m, 2H), 7.04 (m, 1H), 7.28
(m, 2H); 13C NMR (CDCl3, 100.5 MHz) δ 35.6 (t), 37.5 (q), 53.8
(q), 121. 2 (d), 123.3 (d), 129.0 (d), 148.3 (s), 158.3 (s), 167.2
(s); MS m/z 220.1215 (calcd for C12H16N2O2 220.1212) (33%),
176 (24), 148 (13), 134 (10), 128 (16), 118 (20), 93 (59), 91 (16),
77 (18), 72 (100).
3-Dieth yla m in o-3-(p h en ylim in o)-N,N-d im eth ylp r op a n -
a m id e (16Hf). Obtained with added HNEt2. Yield 30% at -80
°C; 61% at -190 °C. Yellow oil; IR 1661, 1611, 1591 cm-1; 1H
NMR (CDCl3, 400 MHz) δ 1.21 (t, J ) 7 Hz, 6H), 2.61 (s, 3H),
2.88 (s, 3H), 3.28 (s, 2H), 3.43 (q, J ) 7 Hz, 4H), 6.72 (m, 2H),
6.91 (m, 1H), 7.20 (m, 2H); 13C NMR (CDCl3, 100.5 MHz) δ
13.44 (q), 33.1 (t), 35.6 (q), 37.1 (q), 42.1 (t), 121.4 (d), 122.4
(s), 128.7 (d), 152.1 (s), 152.9 (s); MS m/z 261.1842 (calcd for
An a lytica l F VT of 9Hb. This compound was subjected to
FVT over the temperature range 200-600 °C (sublimation
temperature 100-130 °C) with IR spectroscopic analysis of the
products at 77 K. At 200 °C, only the unchanged starting
material was obtained. At 260 °C, a ketenimine (12Hb; 2040
w cm-1) and a ketene (11Hb; 2121, 2106 w cm-1) were
observed. At 300 °C, peaks due to phenyliminopropadienone
(15H) appeared at 2222 vs, 2140 w sh cm-1. At 600 °C, both
11Hb and 12Hb had disappeared from the spectrum, and 15H
had become the main absorber, together with 2-methylthio-
4-quinolone (13Hb), which was isolated and identified by
comparison with the compound described in the following
entry.
2-Meth ylth io-4-qu in olon e (13Hb). Compound 9Hb (100
mg) was subjected to preparative FVT at 600 °C, giving 46
mg (70%) of 13Hb, which condensed in the air-cooled part of
the apparatus. 13Hb: mp 225-226 °C (lit.3 225-226 °C; lit.14
220-222 °C); IR (KBr) 3442, 1632, 1580 cm-1 1H NMR
;
(DMSO-d6) δ 2.50 (s, 3H), 6.20 (br s, 1H), 7.30 (t, 1H), 7.55
(m, 2H), 8.00 (d, 1H), 11.9 (br s, 1H); 1H NMR (CDCl3/CD3OD
1:1, 100 MHz) δ 2.55 (s, 3H), 6.24 (s, 1H, H(C-3)), 7.34
(apparent t, J ) 7.6 Hz, 1H, H(C-6)), 7.48 (apparent d, J ) 8
Hz, 1H, H(C-8)), 7.63 (complex t, apparent J ) 7.2 Hz, 1H,
H(C-7)), 8.20 (d, J ) 8 Hz, 1H, H(C-5)); 13C NMR (DMSO-d6,
80 °C) δ 13.3, 104.3, 119.9, 122.6, 122.7, 123.7, 130.6, 142.8,
154.3, 171.0; 13C NMR (CDCl3/CD3OD 1:1, 100 MHz) δ 14.6
(SCH3), 105.4 (s, C-3), 118 (d, C-8), 124.5 (d, C-6), 124.6 (s),
125.7 (d, C-5), 132.9 (d, C-7), 141.6 (s), 155.9 (s), 178.3 (s). A
DEPT spectrum confirmed the quarternary carbon assign-
ments. A HSQC 2D 1H-13C correlation is shown in the
Supporting Information. 13Hb is also obtained in ∼100% yield
by FVT of 17.3
P h en ylim in op r op a d ien on e (15H). FVT of 9Ha , 9Hb, and
9Hc (ca.10 mg portions) with Ar matrix isolation of the
products were carried out as previously described.1,11b IR of
15H (Ar, 15 K) 2247 vs, 2141 w, 1633 m, 1620 m, 1490 m,
1284 w, 1210 w, 754 w cm-1. Other signals: acetone, 3012 w,
1768 w, 1721 m, 1361 m, 1217 m, 1094 m cm-1; CO2, 2344 vs,
2340 vs cm-1; dimethylamine (using 9Hc as the precursor),
3193 w, 2973 w, 2832 w, 1482 w, 1479 w, 1159 w, 1184 w,
1025 w, 861 w cm-1
.
N-P h en ylk et en im in e-2-(N,N-d im et h ylca r b oxa m id e)
(12Hc) a n d Its Con ver sion to Qu in olon e 13Hc. Compound
9Hc (80 mg; 0.27 mmol) was subjected to preparative FVT at
700 °C/1.3 × 10-3 mbar (3 h), and the products were collected
at 77 K on a coldfinger coated with CDCl3. The system was
then brought to atmospheric pressure with N2. The coldfinger
was allowed to warm, causing the resulting solution to flow
into an NMR tube fitted below the coldfinger and cooled at
-196 °C. The NMR tube was flame sealed, and spectra were
recorded at temperatures between -50 and 27 °C. 1H NMR
(CDCl3, -50 °C) δ 3.004 (s, 3H), 3.026 (s, 3H), 5.1 (s, 1H), 7.38
(m, 5H) (acetone was present at 2.26 (s, 6H)); 13C NMR (CDCl3,
-50 °C) δ 35.3, 37.6, 53.8, 124.4, 128.3, 129.4, 136.9, 166.9,
179.6 (acetone was present at 31.2 and 208.6 ppm). The two
C
15H23N3O 261.1841) (28%), 189 (24), 120 (12), 77 (16), 72
(100).
3-Dieth yla m in o-3-(p h en ylim in o)-N,N-d ieth ylp r op a n a -
m id e (16Hg). Obtained with added HNEt2. Yield 54% at -80
°C. Yellow oil; IR (CCl4) 1654, 1612, 1591 cm-1 1H NMR
;
(CDCl3, 400 MHz) δ 0.81 (t, J ) 7 Hz, 3H), 1.09 (t, J ) 7 Hz,
3H), 1.21 (t, J ) 7 Hz, 6H), 2.90 (q, J ) 7 Hz, 2H), 3.25 (s,
2H), 3.31 (q, J ) 7 Hz, 2H), 3.43 (q, J ) 7 Hz, 4H), 6.73 (m,
2H), 6.89 (m, 1H), 7.17 (m, 2H); 13C NMR (CDCl3, 100.5 MHz)
δ 12.8 (q), 13.7 (q), 33.4 (t), 40.6 (t), 42.0 (t), 42.1 (t), 121.4 (d),
122.4 (d), 128.7 (d), 152.1 (s), 167.0 (s); MS m/z 289.2155 (calcd
for C17H27N3O 289.2154) (63%), 260 (16), 217 (49), 120 (29),
100 (100).
Tr a p p in g of 15H w ith Eth a n ol a n d Dim eth yla m in e.
Meldrum’s acid derivative 9Hc (200 mg; 0.68 mmol) was
pyrolyzed at 700 °C in the course of 3 h, using a U-tube cooled
in MeOH/liquid N2 (-96 °C) to trap the products. Upon
completion of the pyrolysis, ethanol (4 mL) was injected onto
the cold product (-96 °C), and the U-tube was purged with
N2 gas and warmed to room temperature. The resulting
solution was filtered through a plug of silica gel (ca. 1 × 1
1
CH3 signals at ca. 3 ppm in the H NMR spectrum coalesced
to a singlet at 263 K (500 MHz, ∆ν ) 10.85 Hz). After 24 h at
room temperature, all signals, except for that due to acetone,
had disappeared and quinolone 13Hc had crystallized from
the solution (20-25% yield for the two steps based on 9Hc; at
least 32% based on 12Hc.) When analogous CDCl3 (or CHCl3)
solutions were examined by IR spectroscopy at room temper-
ature, immediately after warming from -196 °C, a strong
ketenimine absorption ascribed to 12Hc was observed at 2046
cm-1. In an analogous experiment with isolation of the neat
FVT product on a BaF2 or KBr target at 77 K, phenylimino-

3618 J . Org. Chem., Vol. 64, No. 10, 1999
Wentrup et al.
cm), excess solvent was evaporated, and the products were
separated by preparative gas chromatography on an OV-101
column (isothermal, 130 °C) to give 16Hb, 16Hd , and 16He.
the spectrum, being absent or obscured by 15M. By 500 °C,
only peaks due to 15M and quinolone 13Ma remained.
Meth yl N-(4-Meth ylp h en yl)k eten im in e-2-ca r boxyla te
(12Ma ) a n d 2-Meth oxy-6-m eth ylqu in olin e-4-on e (13Ma ).
Compound 9Ma (68 mg) was subjected to preparative FVT at
300 °C. The product was collected in a 77 K U-tube, dissolved
in CCl4, and purified by Kugelrohr distillation (60 °C/7 × 10-5
mbar) to give a clear oil, identified as 12Ma (15 mg; 34%): IR
(CCl4) 2046, 1718, 1437, 1240, 1152 cm-1; 1H NMR (CDCl3) δ
2.35 (s, 3H), 3.70 (s, 3H), 4.55 (s, 1H), 7.18 (s, 4H); 13C NMR
(CDCl3) δ 21.2, 51.7, 52.1, 124.6, 130.3, 139.59, 139.61, 168.8,
175.6; MS m/z 189.0793, calcd for C11H11NO2 189.0789. Chro-
matography of the remaining material on SiO2, eluting with
ether/hexane, afforded quinolone 13Ma (10 mg; 23%): mp
292-294 °C; IR (KBr) 3369, 1634, 1591 cm-1; 1H NMR (DMSO-
d6) δ 2.36 (s, 3H), 3.49 (s, 3H), 5.83 (s, 1H), 7.33-7.67 (m, 3H),
11.25 (s, 1H); 13C NMR (DMSO-d6) δ 20.7, 58.8, 98.4, 114.9,
116.3, 123.2, 130.6, 138.5, 162.9, 189.9; MS m/z 189.0790, calcd
for C11H11NO2 189.0789. Anal. Calcd for C11H11NO2: C, 69.81;
H, 5.86; N, 7.41. Found: C, 70.01; H, 6.16; N, 7.20.
Eth yl 3-Eth oxy-3-(p h en ylim in o)p r op a n oa te (16Hb).
Yellow oil, Rt 15 min, 34 mg (21%); IR (CHCl3) 1735, 1674,
1
1579 cm-1; H NMR (CDCl3) δ 1.17 (t, 3H), 1.27 (t, 3H), 3.12
(s, 2H), 4.07 (q, 2H), 4.22 (q, 2H), 6.73 (m, 2H), 6.97 (m, 1H),
7.21 (m, 2H); 13C NMR (CDCl3) δ 14.0, 36.5, 61.2, 62.2, 121.0,
123.3, 129.0, 148.1, 156.5, 167.9; MS m/z 235.1236 (calcd for
C
13H17NO3 235.1236) (60%), 207 (40), 190 (27), 120 (46), 104
(55), 93 (100), 77 (45). Anal. Calcd for C13H17NO3: C, 66.36;
H, 7.28; N, 5.95. Found: C, 66.39, H, 7.12; N, 6.10.
3-E t h o x y -3-(p h e n y lim in o )-N ,N -d im e t h y lp r o p a n a -
m id e (16Hd ). Yellow oil, Rt 37 min, 66 mg (40%); IR (CHCl3)
1
1647, 1597, 1489 cm-1; H NMR (CDCl3) δ 1.35 (t, 3H), 2.83
(s, 3H), 2.91 (s, 3H), 3.23 (s, 2H), 4.30 (q, 2H), 6.83 (m, 2H),
7.03 (m, 1H), 7.26 (m, 2H); 13C NMR (CDCl3) δ 14.1, 35.5, 35.7,
37.5, 62.1, 121.1, 123.1, 129.0, 148.3, 157.6, 167.2; MS m/z
234.1370 (calcd for C13H18N2O2 234.1370) (22%), 120 (22), 93
(52), 87 (55), 77 (35), 72 (100). Anal. Calcd for C13H18N2O2: C,
66.64; H, 7.47; N, 11.96. Found: C, 66.56; H, 7.76; N, 11.77.
Meth yl 3-Meth oxy-3-(4-m eth ylph en ylim in o)pr opan oate
(16Ma ) a n d Qu in olon e 13Ma . FVT of 9Ma was carried out
at 500 °C. MeOH was then injected onto the coldfinger, the
mixture was allowed to thaw, and the resulting solution was
condensed and distilled (80 °C/5.5 × 10-5 mbar) to give a yellow
3-Dim et h yla m in o-3-(p h en ylim in o)-N,N-d im et h ylp r o-
p a n a m id e (16He). Yellow oil, Rt 49 min, 31 mg (19%); IR
(CHCl3) 1652, 1615, 1591, 1481 cm-1; 1H NMR (CDCl3) δ 2.64
(s, 3H), 2.87 (s, 3H), 3.03 (s, 6H), 3.30 (s, 2H), 6.72 (m, 2H),
6.91 (m, 1H), 7.18 (m, 2H); 13C NMR (CDCl3) δ 33.5, 35.7, 37.2,
38.4, 122.0, 123.1, 129.0, 151.1, 155.0, 167.6; MS m/z 233.1530
(calcd for C13H19N3O 233.1530) (26%), 189 (22), 77 (40), 72
(100). Anal. Calcd for C13H19N3O: C, 66.92; H, 8.21; N, 18.01.
Found: C, 66.84; H, 8.15; N, 17.85.
4-Meth ylph en ylim in opr opadien on e (15M). FVT of 9Mb
a n d 9Mc. These precursors were both subjected to FVT at 700
°C with Ar matrix isolation of the products on a BaF2 disk. IR
of 15M (Ar, 15 K) 2944 w, 2794 w, 2248 vs, 2142 w, 1634 w,
1429 w, 1354 w, 728 w cm-1. Other peaks: acetone, CO2, and
dimethylamine, as reported for 15H above; methanethiol, 2948
m, 2603 w, 1445 m, 800 w cm-1. When 9Mb was used as the
precursor, a weak band ascribed to a ketenimine was observed
at 2048 cm-1 for FVT temperatures of 300-500 °C; it had
disappeared at 600 °C. When 9Mc was used as the precursor,
15M was formed immediately, at 300 °C, with no other
intermediates reliably detectable. When 9Mc was the precur-
sor and 15M was isolated together with Me2NH at 77 K,
subsequent warmup to -90 °C caused slow reaction of the two
products with formation of ketenimine 12Mc (2030 cm-1, neat).
When the cocondensed Me2NH was partially removed by
evaporation, 15M remained observable up to 0 °C.
oil, identified as 16Ma (18 mg; 38%: IR (CCl4) 1750, 1680 cm-1
;
1H NMR (CDCl3) δ 2.28 (s, 3H), 3.21 (s, 2H), 3.67 (s, 3H), 3.82
(s, 3H), 6.65-7.09 (m, 4H); 13C NMR (CDCl3) δ 20.7, 35.9, 52.3,
53.7, 120.8, 128.6, 145.3, 156.8, 168.3; MS m/z 221.1054, calcd
for C12H15NO3 221.1052. Anal. Calcd for C12H15NO3: C, 65.13;
H, 6.84; N, 6.33. Found: C, 64.98; H, 6.72; N, 6.12. An
involatile solid depositing in the air-cooled part of the ap-
paratus was identified as quinolone 13Ma (22 mg; 55%) by
NMR.
Tr a p p in g of Keten im in e 12Ma . Compound 16Ma was ob-
tained in 83% yield by stirring the distilled ketenimine 12Ma
(17 mg) with excess MeOH at room temperature for 16 h.
Isom er iza tion of Keten im in e 12Ma . The freshly distilled
ketenimine was subjected to FVT at 400 °C, and the neat
pyrolysate was isolated at 77 K on KBr: IR (77 K) 2046, 1711,
1699, 1441, 1242 cm-1 due to 12Ma . A new, weak band at 2136
cm-1 is ascribed to ketene 11Ma . A white solid depositing in
the air-cooled part of the apparatus was identified as quinolone
13Ma .
P r ep a r a tive F VT of Tr ia zole 19. (a) 19 (80 mg) was
thermolyzed at 500 °C (sublimation temperature 95 °C) for 2
h. Kugelrohr distillation of the product mixture afforded
1
ketenimine 12Ma (17 mg; 24%), identified by IR, H and 13C
An a lytica l F VT of Tr ia zole 19. The compound was
sublimed at ca. 85 °C and pyrolyzed over the temperature
range 200-700 °C/3 × 10-5 mbar with isolation of the products
at 77 K (neat) for IR spectroscopy. At a FVT temperature of
200 °C, only the unchanged starting material was observed
(3140, 1717, 1548, 1520, 1269, 1153, 1039 cm-1). At temper-
atures of 300-500 °C, the oxoketenimine 12Ma was observed
(2046, 1712, 1697, 1442, 1241, 1153 cm-1) together with the
imidoylketene 11Ma (2136 (w), 2119 (w sh) cm-1). At 500 °C,
the intensities of these two bands decreased but remained in
approximately the same ratio. Also at 500 °C, new peaks
emerged corresponding to quinolone 13Ma (1643, 1610 cm-1).
At 600 °C, the latter was the only species still observed. The
quinolone was also isolated from the cryostat and identified
NMR, and MS. The residue from the distillation was separated
into two compounds by column chromatography (hexane/
CHCl3 60:40). The first was identified as m eth yl 5-m eth ylin -
d ole-3-ca r boxyla te (20): 12 mg (17%); Rf ) 0.31; mp 160-
161 °C; IR (KBr) 3236, 1667, 1529 cm-1;1H NMR (CDCl3) δ
2.47 (s, 3H), 3.91 (s, 3H), 7.05-7.97 (m, 3H), 7.85 (d, 1H), 8.53
(br s, 1H); 13C NMR (CDCl3) δ 21.6, 51.0, 108.3, 111.1, 121.1,
124.8, 126.0, 131.0, 134.3, 165.7; MS m/z 189.0790, calcd for
C
11H11NO2 189.0789. Anal. Calcd for C11H11NO2: C, 69.81; H,.
5.86: N, 7.41. Found: C, 69.66; H, 5.70; N, 7.42. The second
compound was identified as quinolone 13Ma (28 mg; 40%; Rf
) 0.10; mp 292-294 °C). (b) Analogous FVT of triazole 19 (65
mg) at 600 °C afforded indole 20 (5 mg; 9%) and quinolone
13Ma (41 mg; 74%).
1
by GC-MS and H NMR. The absence of quinolone 13Ma from
the IR spectrum at FVT temperatures below 500 °C is due
merely to its involatility.
4-Meth oxyph en ylim in opr opadien on e (15X). Compounds
9Xa , 9Xb, and 9Xc were each subjected to FVT at 700 °C with
isolation of the products in Ar matrix on a BaF2 disk. IR of
An a lytica l F VT of 9Ma . Compound 9Ma was sublimed at
ca. 95 °C/1.5 × 10-5 mbar. No reaction was observable using
FVT temperatures below 150 °C. From 150 to 400 °C, the IR
spectra (neat film, 77 K) revealed the imidoylketene (2135,
2119 (sh) cm-1); from ca. 200 to 400 °C, the oxoketenimine
appeared (2046 cm-1); and from ca. 300 °C, 4-methylphen-
yliminopropadienone was present (15M; 2221 (vs) and 2182
(sh, w) cm-1, 77 K, neat). At 400 °C, the peak due to the
oxoketenimine decreased, and those due to 15M increased in
intensity. The imidoylketene was now no longer detectable in
15X (Ar, 15 K) 2252 (s), 2246 (vs), 2239 (s), 2137 (w) cm-1
.
Other peaks: acetone, CO2, methanethiol, and dimethylamine,
as described above.
P r ep a r a tive F VT of 9Xa . (a) (150 mg) was performed at
700 °C and the intermediates on the 77 K coldfinger were
trapped with MeOH. The resulting material was washed with
CHCl3-MeOH (1:1) and separated by column chromatography
to afford 16Xa (54 mg; 47%) and 13Xa (34 mg; 34%). Spectral
data for 16Xa : 1H NMR (CDCl3, 400 MHz) δ 3.17 (s, 2H), 3.63
(s, 3H), 3.71 (s, 3H), 3.76 (s, 3H), 6.75 (m, 4H); 13C NMR

Aryliminopropadienone-Amidoketenimine-Amidinoketene Cascades
J . Org. Chem., Vol. 64, No. 10, 1999 3619
(CDCl3) δ 35.9, 52.4, 53.8, 55.4, 114.4, 121.9, 141.1, 150.5,
155.9, 168.4. MS m/z 237.0999, calcd for C12H15 NO4 237.1001.
P r ep a r a tive F VT of 9Xc. 3-Dim eth yla m in o-3-(4-m eth -
oxyph en ylim in o)-N,N-dim eth ylpr opan am ide (16Xe). Com-
pound 9Xc (100 mg) was sublimed at 130-140 °C (3 × 10-5
mbar) and thermolyzed through the oven at 700 °C onto a 77
K coldfinger. The system pressure was then equalized with
N2, and excess dimethylamine in ether was injected onto the
coldfinger. After warming to room temperature, the oily
residue was passed through a short column. Elution with
CHCl3 afforded 16Xe (55 mg; 67%): 1H NMR (CDCl3) δ 2.68
(s, 3H), 2.84 (s, 3H), 3.09 (s, 6H), 3.42 (s, 2H), 3.70 (s, 3H),
6.74 (m, 4H); 13C NMR (CDCl3) δ 34.2, 35.5, 37.3, 39.4, 55.4,
114.2, 124.8, 139.2, 156.4, 157.6, 166.6; MS m/z 263.1613, calcd
for C14H21N3O2 263.1628.
at δ 2.24 (s, 6H), 2.33 (s, 3H), 2.96 (s, 3H), 2.97 (s, 3H), 4.58
(s, 1H), 6.75 (s, 2H) (CDCl3, 500 MHz). The two singlets at
2.96 and 2.97 ppm (∆ν ) 5 Hz) coalesced on warming to 248
K. This NMR spectrum is similar to that reported for methyl
1-mesitylketenimine-3-carboxylate.31 By using IR spectral
monitoring, the formation of a ketenimine absorbing at 2088
cm-1 (neat) became noticeable from -70 °C onward. Treatment
of the NMR solution with excess HNMe2 at either -40 °C or
room temperature gave amidoamidine 24: 1H NMR (CD2Cl2,
400 MHz) δ 1.96 (s, 6H mesityl), 2.21 (s, 3H, mesityl), 2.53 (s,
3H, amide-NMe2), 2.79 (s, 3H, amide-NMe2), 3.01 (s, 6H,
amidine-NMe2), 3.13 (s, 2H, CH2), 6.75 (s, 2H,). The assign-
ment was confirmed by a DEPT spectrum and by the coales-
cence experiments described below. Addition of the shift
reagent Eu(fod)3 caused shifting but no splitting of any of the
singlets. The 6-proton amidine NMe2 signal at 3.01 ppm
decoalesced on cooling the CD2Cl2 solution to 227 K (400 MHz,
∆ν ) 49.8 Hz). The two 3-proton amide NMe signals coalesced
on heating the solution in CD2ClCD2Cl to 383 K (400 MHz,
∆ν ) 134.6 Hz).
Qu in olon es fr om th e Yn a m in e-Isocya n a te Rea ction .
(a ) 2-Dim eth yla m in o-4-qu in olon e (34a ) 13Hc). N,N-
Dimethyl-N-(trimethylsilylethynyl)amine (32a ) was prepared
from dimethylamine in the manner described for the diethyl
analogue:27 1H NMR (CDCl3) δ 0.25 (s, 9H), 2.86 (s, 6H); 13C
NMR (CDCl3) δ 0.99, 42.9, 65.4, 111.0. Equimolar amounts of
this compound (100 mg; 0.70 mmol) and phenyl isocyanate (84
mg) were stirred in benzene or MeCN solution at room
temperature under N2 for 3 d. Preparative TLC, eluting with
10% MeOH/CHCl3 afforded 30 mg (23%) of 13Hc.
(b) 2-Dieth yla m in o-4-qu in olon e (34b). N,N-Diethyl-N-
(trimethylsilylethynyl)amine (32b) was prepared according to
the literature:27 1H NMR (CDCl3) δ 0.1 (s, 9H), 1.53 (t, 6H),
2.90 (q, 4H); 13C NMR (CDCl3) δ 0.98, 12.7, 47.7, 64.2, 108.6;
IR 2142 cm-1. A 100 mg (0.59 mmol) portion of this compound
was stirred with 70 mg (0.59 mmol) of PhNCO in 10 mL of
either benzene or MeCN at room temperature for 24 h. GC-
MS of the crude product indicated the presence of 33b (m/z
288) and 34b (m/z 216). Workup as in (a) afforded 34b (20 mg
(16%) from benzene or 30 mg (26%) from MeCN): 1H NMR
(DMSO-d6) δ 1.16 (t, 6H), 3.50 (q, 4H), 5.70 (br s, 1H, typical
of H(C-3)), 7.01 (t, J ) 15 Hz, 1H), 7.43 (t, J ) 15 Hz, 1H),
7.53 (d, J ) 8 Hz, 1H), 7.90 (d, J ) 8 Hz, 1H); IR (KBr) 3263,
1637, 1596 cm-1. Anal. Calcd for C13H6N2O: C, 72.22; H, 7.40;
N, 12.96. Found: C, 72.11; H, 7.57; N, 12.62.
3-Met h oxy-3-(4-m et h oxyp h en ylim in o)-N,N-d im et h yl-
p r op a n a m id e (16Xc). Compound 9Xc (100 mg) was thermo-
lyzed as above, and the products were collected in a U-tube at
77 K. During sublimation, the U-tube temperature was
periodically raised to remove NHMe2. It was not possible to
eliminate the amine completely. After 2 h of thermolysis,
MeOH was injected onto the U-tube. After the U-tube had
warmed to room temperature under N2, column chromatog-
raphy (CHCl3) of the oily residue afforded 16Xc as a yellow
oil (40 mg; 51%): 1H NMR (CDCl3) δ 2.83 (s, 3H), 2.90 (s, 3H),
3.23 (s, 2H), 3.74 (s, 3H), 3.80 (s, 3H), 6.78 (m, 4H); 13C NMR
(CDCl3) δ 35.4, 35.5, 37.5, 53.7, 55.4, 114.2, 122.2, 141.4, 155.8,
158.5, 167.2; MS m/z 250.1313, calcd for C13H18N2O3 250.1312.
N-(4-Meth oxyp h en yl)k eten im in e-C-(N,N-d im eth ylca r -
boxa m id e) (12Xc). After similar FVT of 9Xc as above, CD2-
Cl2 was condensed on the 77 K coldfinger. On thawing, the
resulting solution flowed into a precooled NMR tube at -80
°C. The NMR tube was flame sealed under N2. Spectral data
for 12Xc: 1H NMR (CD2Cl2, -70 °C) δ 2.93 (s, 3H, NMe), 2.98
(s, 3H, NMe), 3.75 (s, 3H), 5.05 (s, 1H), 6.85 (d, 2H), 7.23 (d,
2H). The two NMe singlets coalesced on warming to -10 °C
(400 MHz, ∆ν ) 20 Hz). IR (CD2Cl2 or CH2Cl2, rt) 2036 (s)
cm-1
.
Con ver sion of Keten im in e 12Xc to Qu in olon e 13Xc. (a)
Ketenimine 12Xc was prepared in CD2Cl2 solution as in the
previous entry. Warming to room temperature resulted mainly
in polymerization of the ketenimine in the course of 3 d. Only
traces of quinolone were formed under these conditions. (b)
Warming a CD2Cl2 solution to 40 °C and maintaining it at this
temperature for 15 h resulted in a 15% isolated yield of
quinolone 13Xc. (c) Refluxing an analogous sample in 1,2-
dichloroethane at 83 °C for 24 h resulted in an improved yield
of quinolone 13Xc (20% based on the starting material 9Xc;
38% based on the material arriving on the coldfinger).
F VT of 16Xa ,c,e. Analytical and preparative FVT of
16Xa ,c,e at 600 °C and above did not give detectable keten-
imine 12X, which would not have survived this temperature.
Instead, there was formation of quinolone 13Xc from 16Xe in
the sublimation tube itself, as confirmed by TLC and 1H NMR.
13Xc was also formed from 16Xe on GC-MS (injector temp
200 °C). In contrast, 16Xa and 16Xc were stable and did not
form the corresponding quinolones 13Xa ,c under these condi-
tions.
Ack n ow led gm en t. This research was supported by
the Australian Research Council. We also thank the
Deutsche Forschungsgemeinschaft for a postdoctoral
fellowship for T.M..
Su p p or tin g In for m a tion Ava ila ble: Partial FTIR spec-
tra of the products of FVT of 17 and 18; FTIR spectra of 12Ma
and its FVT product at 400 °C, showing ketene formation; Ar
matrix FTIR spectra of 15M and 15X; 1H NMR spectra of
12Ma , 12Hc (223 and 300 K), 12Xc (203 K), 16Hc, 16Xa ,
16Xe, and 24. 13C NMR spectra of 12Ma , 12Hc, 16Hc, 16Xe
1
(DEPT), and 24 (DEPT). HSQC 2D H-13C NMR correlations
N-Mesit ylk et en im in e-2-(N,N-d im et h ylca r b oxa m id e)
(23) a n d 3-Dim et h yla m in o-3-[(2,4,6-t r im et h ylp h en yl)-
im in o]-N,N-d im eth ylp r op a n a m id e (24). N-Mesitylimino-
propadienone (22)12 (30 mg; 0.16 mmol) was treated with 1
equiv of HNMe2 (7.3 mg) in CDCl3 or CD2Cl2 (0.5 mL) in an
NMR tube at -60 °C. No significant reaction was observed
until -40°, when signals ascribed to ketenimine 23 appeared
for 13Hb, 13Xa , and 13Xb. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O982471Y
(31) Rao, V. V. R.; Fulloon, B. E.; Bernhardt, P. V.; Koch, R.;
Wentrup, C. J . Org. Chem. 1998, 63, 5779.