Iminopropadienones from dioxanediones, isoxazolopyrimidinones, pyridopyrimidinones, and pyridopyrimidinium olates

Article abstract of DOI:10.1021/jo026275+

Iminopropadienones, RN=C=C=C=O, can be generated from four different types of precursors in flash vacuum thermolysis reactions: 1,3-dioxane-4,6-diones 1, isoxazolopyrimidinones 2, pyridopyrimidinium olates 3, and pyridopyrimidinones 4. 2,6-Difluorophenyl-, 2,6-diethylphenyl-, o-tertbutylphenyl-, and mesityliminopropadienone have been directly observed by Ar matrix IR spectroscopy in one or more of these reactions. Reactions with bis-nucleophiles afford pyridopyrimidinones and perhydrodiazepinone derivatives.

Full text of DOI:10.1021/jo026275+

Im in op r op a d ien on es fr om Dioxa n ed ion es,
Isoxa zolop yr im id in on es, P yr id op yr im id in on es, a n d
P yr id op yr im id in iu m Ola tes
Majed Shtaiwi and Curt Wentrup*
Chemistry Department, School of Molecular and Microbial Sciences, The University of Queensland,
Brisbane, Qld 4072, Australia
wentrup@uq.edu.au
Received August 1, 2002
Iminopropadienones, RNdCdCdCdO, can be generated from four different types of precursors in
flash vacuum thermolysis reactions: 1,3-dioxane-4,6-diones 1, isoxazolopyrimidinones 2, pyridopy-
rimidinium olates 3, and pyridopyrimidinones 4. 2,6-Difluorophenyl-, 2,6-diethylphenyl-, o-tert-
butylphenyl-, and mesityliminopropadienone have been directly observed by Ar matrix IR
spectroscopy in one or more of these reactions. Reactions with bis-nucleophiles afford pyridopyri-
midinones and perhydrodiazepinone derivatives.
In tr od u ction
types of precursor, as well as the chemistry of two new
derivatives, the 2,6-difluoro- and 2,6-diethylphenylimi-
nopropadienones. Previous work has shown that mild
steric hindrance can protect the iminopropadienones
remarkably, thus making the neopentyl, the mesityl, and
the o-tert-butylphenyl derivatives isolable at room tem-
perature.2 It was expected that electronegative substit-
uents might increase the reactivity, and this has been
borne out with the 2,6-difluorophenyl derivative. The 2,6-
diethyl derivative, in contrast, was expected to show
“normal” reactivity, like the mesityl derivative.2
We have reported the formation of iminopropadi-
enones, RNdCdCdCdO, by flash vacuum thermolysis
(FVT) of 1,3-dioxane-4,6-dione (Meldrum’s acid) deriva-
tives1,2 1 and, in a preliminary communication, isoxazol-
opyrimidinones 2.1 Pyridopyrimidinium olates of type 3
are obtained by addition of iminopropadienones to 2-(me-
thylamino)pyridine, and in the case of the mesityl deriva-
tive, it was shown that compound 3 was again cleaved
to mesityliminopropadienone and 2-(methylamino)pyri-
dine on FVT.2 We have now found that both mesoionic
pyridopyrimidinium olates 3 and pyrimidopyrimidinones
of type 4 can be used as precursors of a variety of
aryliminopropadienones.
Resu lts a n d Discu ssion
2,6-Difluorophenyliminopropadienone 8 was generated
from three different types of precursor, the Meldrum’s
acid derivatives 5 and 5′, the isoxazolopyrimidinone 6,
and the mixture of isomeric pyridopyrimidinium olates
7a and 7b (Scheme 1). The Meldrum’s acid precursor 5
was synthesized by reaction of 5-(bismethylthiomethyl-
ene)-2,2-dimethyl-1,3-dioxane-4,6-dione with 2,6-difluo-
roaniline, and 5′ was formed by further substitution of
the SMe group by dimethylamine. Compound 6 was
obtained from 2,6-difluorobenzaldehyde by adaptation of
a standard procedure.3 A 1:1 mixture of olates 7a and
7b was obtained by reaction of 8 (generated by prepara-
tive FVT of either 5 or 6) with 2-(methylamino)pyridine
(Scheme 1). Iminopropadienone 8 is not isolable, so the
preparative chemistry of this compound is carried out by
condensing the FVT product on a coldfinger at 77 K. After
the end of the thermolysis, a solution of a trapping agent
is injected onto the coldfinger, and the product is isolated
after warming to room temperature. The two regioiso-
mers 7a and 7b were not separable by chromatography,
but the “normal” isomer 7a crystallized selectively
In this paper we report direct IR spectroscopic evidence
for the formation of iminopropadienones from the four
(1) Mosandl, T.; Kappe, C. O.; Flammang, R.; Wentrup, C. J . Chem.
Soc., Chem. Commun. 1992, 1571-1573.
(2) Bibas, H.; Moloney, D. W. J .; Neumann, R.; Shtaiwi, M.;
Bernhardt, P. V.; Wentrup, C. J . Org. Chem. 2002, 67, 2619-2631.
(3) (a) Taylor, E. C.; Garcia, E. J . J . Org. Chem. 1964, 29, 2116. (b)
Rajagopalan, P.; Talaty, C. N. Tetrahedron 1967, 23, 3541.
10.1021/jo026275+ CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/06/2002
8558
J . Org. Chem. 2002, 67, 8558-8565

Iminopropadienones from Different Precursors
SCHEME 1
from CHCl3 and was characterized by X-ray crystal-
lography. On FVT of the mixture of 7a and 7b at 550 °C,
both isomers were fully converted to 8 (Scheme 1 and
Figure 1).
dominates.2,4 The formation of a 1:1 mixture of 7a and
7b is highly unusual and indicates that the electron-
withdrawing effect of fluorine may have increased the
electrophilicity of the CdN group in 8. A similar phe-
nomenon is observed in the reaction with the unsym-
metrical N-methylethylenediamine to afford two perhy-
drodiazepinones, 10a and 10b, in a 1:1 ratio (Scheme 1).
Naturally, the reaction with the symmetrical N,N′-
dimethylethylenediamine afforded a single diazepinone,
11.
Figure 1 shows the Ar matrix IR spectra obtained from
the three precursors compared with the calculated spec-
trum at the B3LYP/6-31G** level of theory. It is clearly
seen that the same compound is obtained in all cases,
whereby the isoxazolopyrimidine (6) route is particularly
useful because the few byproducts (HCN and HNCO) do
not disturb the spectrum, and furthermore they are
rather nonnucleophilic, so they do not impede the sub-
sequent preparative reactions of the iminopropadienone.
The mechanism of formation of RNCCCO from 6 is
believed to involve breakage of the N-O bond to generate
a putative vinylnitrene, which, when R ) aryl, undergoes
a 1,2-shift of R from C to N. The resulting ketenimine
undergoes a cycloreversion to HCN, HNCO, and RNC-
CCO.1
The chemistry of the difluoro compound 8 is contrasted
with that of the diethyl analogue 13 in Scheme 2. 13 Was
obtained by FVT of the Meldrum’s acid derivatives 12
and 12′, themselves synthesized by reaction of 2,6-
diethylphenyl isothiocyanate with Meldrum’s acid, fol-
lowed by S-methylation with methyl iodide and nucleo-
philic replacement of the methylthio group with dimethyl-
amine. The iminopropadienone 13 was identified by its
Ar matrix IR spectrum (Figure S1). Like 8, 13 is not
isolable at room temperature, and the preparative chem-
istry was performed as outlined above. Reaction with
diethylamine gave the malonic imide derivative 15. With
2-(methylamino)pyridine, only one product, 14, corre-
sponding to the “normal” mode of addition, was obtained.
Also with N-methylethylenediamine, only one product,
16, was obtained, corresponding to addition of the more
nucleophilic NMe group to the CdO function. N,N′-
dimethylethylenediamine afforded the diazepinone de-
rivative 17. Thus, the diethyl derivative 13 exhibits the
The chemistry of 8 is unusual in several respects. The
normal mode of reaction of iminopropadienones with bis-
nucleophiles is a rapid reaction with the strongest
nucleophile at the highly electrophilic CdO group, fol-
lowed by a slower reaction at the less electrophilic CdN
group.2 With mononucleophiles, this leads to malonic acid
imide derivatives (e.g. 9, Scheme 1, and 15, Scheme 2),
and with bis-nucleophiles, heterocyclic compounds are
generated. In some cases minor amounts of the products
of the opposite mode of addition are formed, correspond-
ing to initial addition of the weaker nucleophile to the
CdO group or initial addition of the stronger nucleophile
to the CdN group, but the “normal” mode always
(4) Andersen, H. G.; Mitschke, U.; Wentrup, C. J . Chem. Soc., Perkin
Trans. 2, 2001, 602-607.
J . Org. Chem, Vol. 67, No. 24, 2002 8559

Shtaiwi and Wentrup
SCHEME 2
SCHEME 3
F IGURE 1. IR spectra of 2,6-diflourophenyliminopropadi-
enone 8 (a) generated by FVT of dioxanedione 5′ (Ar matrix,
8 K), (b) by FVT of the 1:1 mixture of pyridopyrimidinium
olates 7a and 7b (Ar matrix, 8 K), (c) by FVT of isoxazolopy-
rimidinone 6 (Ar matrix, 8 K), (d) DFT-calculated spectrum
(B3LYP/6-31G**; scaling factor 0.9613). 2,6-Difluorophenylim-
inopropadienone 8: 2247, 2145, 2137, 1636, 1483, 1017 cm-1
.
(A) acetone: 1720, 1364, 1217, 1092 cm-1. (C) carbon dioxide:
2345, 2340, 663 cm-1. (D) dimethylamine: 2975, 2832, 1148
cm-1. (M) 2-(methylamino)pyridine: 1612, 1602, 1578, 1524,
1511, 1421, 771 cm-1. (H) HNCO: 2259 cm-1 (also present but
not shown 3518, 3507, 770 cm-1).
normal reactivity pattern similar to the neopentyl, the
o-tert-butylphenyl (19a ), and the mesityl (19b) deriva-
tives.2
In the case of the mesityl derivative 19b, obtained from
the Meldrum’s acid derivative 18b, it has already been
shown that the olate 21b regenerates the iminopropa-
dienone.2 This also happens on FVT of the pyridopyri-
midinone 20b (Scheme 3 and Figure S2). Unlike the
difluorophenyl case described above, the isoxazolopyri-
midinone 22b is not a good iminopropadienone precur-
sor: while 19b can be identified by its strong abosorption
Compound 19a was prepared by FVT of the Meldrum’s
acid derivative 18a as previously described.2 Reaction
with 2-aminopyridine and 2-(methylamino)pyridine af-
forded the pyridopyrimidinone 20a and the olate 21a ,
respectively (Scheme 3). FVT of both 20a and 21a
regenerated the iminopropadienone 19a (Figure 2).
8560 J . Org. Chem., Vol. 67, No. 24, 2002

Iminopropadienones from Different Precursors
at 2240 cm-1, the yield was low, and unidentified byprod-
ucts were formed.5
Th e 2,4- a n d 2,5-d im eth oxyim in op r op a d ien on es
23 and 24 have also been prepared by FVT of the
corresponding Meldrum’s acid derivatives. The prepara-
tive procedures and matrix IR spectra are presented in
the Supporting Information (Figures S3 and S4).
Mech a n ism of Clea va ge of P yr id op yr im id in on es.
What is the mechanism of formation of iminopropadi-
enones from the neutral and mesoionic pyridopyrimidi-
nones? It is known that 2-substituted pyridopyrimidin-
4-ones of type 25 (X ) Cl, MeS, or NMe2) undergo
elimination of HX under FVT conditions to generate
2-pyridyliminopropadienone 29.4,6 The reaction is be-
lieved to take place via the intermediates 26-28, as
indicated in Scheme 4. Why is this pathway not followed
in the case of the pyridopyrimidinones 20? An explana-
tion is given in Scheme 4. In 2-aminopyridopyrimidinones
25, where X ) NHR, tautomerization can populate the
mesoionic form 30. This type of tautomerization is known
for the corresponding hydroxy derivatives (i.e. 25, X )
OH).7 It is also known that the non-mesoionic pyridopy-
rimidinones have somewhat lower energies than the
mesoionic ones, but the difference is not large.4 Ring
opening4,6,8 of mesoion 30 will lead to the transient ketene
31, which can undergo a cycloelimination to 1H-2-
iminopyridine 33 and the iminopropadienones 32 (19).
Compound 33 tautomerizes to 2-aminopyridine.9
How ever , w h en X * NHR or OH, ta u tom er iza tion
of 25 cannot take place, and the normal ring opening
yields 26 and hence 27 and 28, and 1,4-elimination leads
to the observed product, 2-pyridyliminopropadienone 29.
We find that the meosionic 1-methylpyridopyrimidinones
usually undergo cleavage to RNCCCO at FVT tempera-
tures of ca. 350-550 °C. The nonmesoionic 2-aminopy-
ridopyrimidinones require much higher temperatures, on
the order of 800 °C. Thus, provided the initial barrier to
tautomerization (25 f 30) can be overcome, the me-
soionic pathway will dominate.
F IGURE 2. IR spectra of 2-tert-butylphenyliminopropadi-
enone 19a (a) generated by FVT of dioxanedione 18a (Ar
matrix, 8 K), (b) by FVT of pyridopyrimidinone 20a (Ar matrix,
8 K), (c) by FVT of pyridopyrimidinium olate 21a (Ar matrix,
8 K), and (d) DFT-calculated spectrum (B3LYP/6-31G**;
scaling factor 0.9613). 2-tert-Butylphenyliminopropadienone
19a : 2790, 2237, 2138, 1624, 1354, 730, 530 cm-1. (A)
acetone: 1720, 1364, 1217, 1092 cm-1. (D) dimethylamine:
2975, 2832, 1148, 1021 cm-1. (C) carbon dioxide: 2341, 663
cm-1. (M) 2-(methylamino)pyridine: 1612, 1602, 1578, 1524,
1511, 1421, 771 cm-1. (P) 2-aminopyridine: 1611, 1608, 1575,
Thus, by proper choice of leaving groupssecondary or
tertiary aminesit is possible to synthesize a range of
(substituted) phenyl- and pyridyliminopropadienones,
and the pyridopyrimidionones 25 emerge as a very
versatile group of precursors. This is particularly impor-
tant, because it is not possible to obtain 2-pyridylimino-
propadienones from Meldrum’s acid precursors.5,10
1484, 1445, 1317, 1273, 1149, 735 cm-1
.
Con clu sion
Meldrum’s acid derivatives, isoxazolopyrimidinones,
pyridopyrimidinones, and pyridopyrimidinium olates can
all be used as precursors of iminopropadienones, RNC-
CCO. There are two mechanisms of fragmentation of
pyridopyrimidinones 25, which, by using either tertiary
or secondary amine substituents, can be harnessed at will
to produce either 2-pyridyliminopropadienone or arylimi-
nopropadienones. 2,6-Difluorophenyliminopropadienone
shows unusual reactivity, being indiscriminate in its
reactions with nucleophiles at the CdO vs CdN bonds.
The origin of this effect is the subject of an ongoing
investigation.
(5) Neumann, R.; Borget, F.; Wentrup, C. Unpublished results.
(6) Plu¨g. C.; Frank, W.; Wentrup, C. J . Chem. Soc., Perkin Trans.
2, 1999, 1087-1093.
(7) 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, 2002, 2096-2108.
(8) Fiksdahl, A.; Plu¨g, C.; Wentrup, C. J . Chem. Soc., Perkin Trans.
2, 2000, 1841-1845.
(9) Alkorta, I.; Elguero, J . J . Org. Chem. 2002, 67, 1515-1519.
(10) Isoxazolopyrimidinones are excellent precursors of pyridylimi-
nopropadienones: Kokas, O. J .; Wentrup, C. Unpublished results.
J . Org. Chem, Vol. 67, No. 24, 2002 8561

Shtaiwi and Wentrup
bottom flask or heated in a minireactor at 90 °C under high
pressure (1000 psi) for 6 h. (CAUTION: The heating in a
closed system or under pressure should be carried out in an
apparatus equipped with a proper safety valve.) The resulting
solution was concentrated by evaporating some of the solvent
to precipitate white crystals, which were collected by filtration
and recrystallized from hot THF to give 6.9 g (yield 70%) in
the first case and 8.8 g (yield 90%) in the second case as
colorless crystals: mp 186-188 °C; 1H NMR (400 MHz, CDCl3)
δ ) 1.67 (s, 6 H), 2.89 (s, 6 H), 6.96 (t,3J ) 8.4 Hz, 2H), 7.17-
7.22 (m, 1H) 9.23 (s, br, 1 H, NH); 13C NMR (100 Hz,CDCl3) δ
SCHEME 4
26.2, 41.4, 76.2, 102.3, 112.1, 116.7, 127.7, 157.3 (dd, J CF
)
252 Hz), 164.3, 165.2. Anal. Calcd for C19H26N2O4: C, 55.21;
H, 4.94; N, 8.59. Found: C, 55.11; H, 5.00; N, 8.55.
2,6-Dieth ylp h en yl isoth iocya n a te was prepared by the
procedure of Habib et al.12 with modifications. 2,6-Diethyla-
niline (15.0 g, 100 mmol) and phenyl isothiocyanate (29.7 g,
220 mmol) were heated under reflux for 24 h, whereupon a
white flaky crystalline sublimate of diphenylthiourea appeared
in the condenser. The mixture was cooled, quenched with 100
mL of petroleum spirit (bp 60-90 °C), filtered, and the filtrate
was evaporated to dryness. The product was purified by
vacuum distillation (1 × 10-4 mbar) to afford 17.2 g of colorless
oil (90%): bp 178 °C; IR (KBr) ν 3064, 2087, 1801, 1593 cm-1
.
1H NMR (200 MHz, CDCl3) δ 1.44 (t, 3J ) 7.5 Hz, 6H), 2.90
(q, 3J ) 7.5 Hz, 4H), 7.22-7.38 (m, 3H); 13C NMR (50 Hz,
CDCl3) δ 14.2, 25.6, 126.4, 127.3, 128.1, 134.9, 140.8.
5-[(2,6-Dieth yla 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 12. A solution of 14.4 g (100
mmol) of isopropylidene malonate (Meldrum’s acid) and 28 mL
triethylamine (200 mmol) in 70 mL of dry acetonitrile was
stirred for 30 min, then 19.1 g (100 mmol) of 2,6-diethylphenyl
isothiocyanate was added, and the mixture was heated at 60
°C for 12 h. A total of 7.0 mL (100 mmol) of idomethane was
added dropwise to the mixture at room temperature and the
resulting solution was then stirred for 48 h. The resulting
solution was concentrated under reduced pressure, then 5 mL
of n-hexane was added to precipitate yellow crystals, which
were collected by filtration and recrystallized from hot THF
to give 21.0 g (yield 60%) as pale yellow crystals: mp 150-
3
151 °C; 1H NMR (400 MHz, CDCl3) δ 1.19 (t, J ) 7.6 Hz, 6H,
CH3CH2), 1.75 (s, 6 H, CMe2), 2.35 (s, 3 H, SCH3), 2.49-2.62
3
3
(m, 4H, CH3CH2), 7.17 (d, J ) 7.9 Hz, 2H), 7.31 (t, J ) 7.6
Hz, 1H), 12.2 (s, br, 1H, NH). 13C NMR (100 Hz,CDCl3) δ 14.2
(CH3CH2), 18.3 (SCH3), 24.6 (CH3CH2), 26.2 (CMe2), 84.1 (Cd
CCO), 102.9 (CMe2), 126.6, 129.3, 134.0, 140.8, 163.9(CO),
180.1 (CdC-CO) (the assignment of the peaks was supported
Exp er im en ta l Section
The FVT apparatus and general equipment were as previ-
ously reported.2,4
by HSQC and HMBC experiments). Anal. Calcd for C18H23
-
NO4S: C, 61.87; H, 6.63; N, 4.01. Found: C, 61.78; H, 6.69;
N, 3.96.
Meld r u m ’s Acid Rou te. 5-[(2,6-Diflu or oa n ilin 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 5.
A solution of 12.4 g (50 mmol) of 5-[bis(methylthio)methylene]-
2,2-dimethyl-1,3-dioxane-4,6-dione11 and 7.1 g (55 mmol) of
2-tert-butylaniline in 100 mL of ethanol was refluxed for 24
h. The resulting solution was concentrated under reduced
pressure, then 5 mL of n-hexane was added to precipitate
white crystals, which were collected by filtration and recrystal-
lized from hot THF to give 7.5 g (yield 45%) as colorless
5-[(2,6-Dieth yla n ilin o)(d im eth 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 12′ was prepared from 12
(12.2 g, 35 mmol) as described for 5′ above to give 8.5 g (yield
70%) by the first method and 10.9 g (yield 90%) by the second
1
method as colorless crystals: mp 199-200 °C; H NMR (400
3
MHz, CDCl3) δ 1.18 (t, J ) 7.7 Hz, 6H), 1.73 (s, 6 H), 2.40-
2.63 (m, 4H), 2.66 (s, 6 H), 7.12 (d, 3J ) 7.4 Hz, 2H), 7.21(t, 3J
) 7.4 Hz, 1H), 9.65 (s, br, 1H, NH); 13C NMR (100 Hz,CDCl3)
δ 14.0, 24.3, 26.1, 41.2, 75.3, 102.0, 126.6, 127.9, 135.1, 140.1,
164.6, 164.8. Anal. Calcd for C19H26N2O4: C, 65.87; H, 7.56;
N, 8.09. Found: C, 65.71; H, 7.78; N, 7.94.
1
crystals: mp 145-146 °C; H NMR (400 MHz, CDCl3) δ 1.78
(s, 6 H), 2.47 (s, 3 H), 7.02-7.37 (m, 2H), 7.34-7.43 (m, 1H),
12.2 (s, br, 1 H, NH); 13C NMR (100 Hz, CDCl3) δ 18.2 (SCH3),
26.2, 87.4, 103.3, 111.8, 115.0, 129.8, 157.6 (dd, J CF ) 252 Hz),
163.5, 180.4. Anal. Calcd for C18H23NO4S: C, 51.06; H, 3.98;
N, 4.25. Found: C, 50.93; H, 4.04; N, 4.04.
F VT w ith Ar gon Ma tr ix Isola tion . 2,6-Diflu or op h e-
n ylim in op r op a d ien on e 8. 5-[(2,6-Diflu or oa n ilin o)(d i-
methylamino)methylene]-2,2-dimethyl-1,3-dioxane-4,6-dione
5′ (10 mg, 0.03 mmol) was sublimed at 70 °C through the FVT
tube at 400-700 °C with Ar matrix isolation of 8 on a BaF2
disk at 8 K over the course of 30 min: IR (Ar, 8 K) 2790 w,
5-[(2,6-Diflu or oa n ilin o)(d im et h 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 5′ was prepared from
compound 5 (10.0 g, 30.4 mmol) dissolved in 50 mL of THF,
previously dried over sodium. A stream of gaseous dimethy-
lamine was bubbled via a pipet through the stirred solution
at such a slow rate that the gas just absorbed; the solution
was then either heated at 50 °C for 24 h in a closed round-
2247 vs, 2145 w, 2137 w, 1636 m, 1483 w, 1017 w, 778 w cm-1
.
Also present were the following peaks: 1768 w, 1722 m, 1362
m, 1218 m, 1092 m cm-1 (acetone); 2976 w, 2831 w, 1483 w,
(11) Fulloon, B. E.; Wentrup, C. J . Org. Chem. 1996, 61, 1363.
8562 J . Org. Chem., Vol. 67, No. 24, 2002
(12) Habib, N. S.; Rieker, A. Synthesis 1984, 825.

Iminopropadienones from Different Precursors
4
3
4
1148 w, 1021 w cm-1 (dimethylamine); 2346, 2340, 664 m cm-1
(carbon dioxide).
Hz, J ) 1.8 Hz, 1H), 10.0 (dd, J ) 7.0 Hz, J ) 1.2 Hz, 1H);
13C NMR (100 Hz, CDCl3) δ 29.4, 31.4, 77.1, 78.4, 111.5, 111.7,
112.7, 113.1, 114.6, 115.0, 121.7, 122.1, 126.6, 127, 132.1,
133.1, 142.3, 142.9, 147.3, 147.4, 149.1, 152.8, 155.8 (dd, J CF
) 244 Hz), 156.2 (C-F, dd, J CF ) 244 Hz). Anal. Calcd for
2,6-Dieth ylp h en ylim in op r op a d ien on e 13. 5-[(2,6-Dieth-
ylanilino)(dimethylamino)methylene]-2,2-dimethyl-1,3-dioxane-
4,6-dione 12′ (10 mg, 0.03 mmol) was sublimed at 85 °C
through the FVT tube at 400-700 °C with Ar matrix isolation
of 13 on a BaF2 disk at 8 K over the course of 30 min:
IR (Ar, 8 K) 2943 w, 2791 w, 2244 vs, 1627 m, 1354 w, 731
m cm-1; peaks due to acetone, dimethylamine, and carbon
dioxide were also present (see above).
C
15H11F2N3O: C, 62.72; H, 3.86; N, 14.63. Found: C, 62.50;
H, 4.00; N, 14.50.
4-Meth yl-7-[(2,6-d iflu or op h en yl)im in o]p er h yd r o[1,4]-
d ia zep in -5-on e 10a a n d 1-Meth yl-7-[(2,6-d iflu or op h en yl)-
im in o]p er h yd r o[1,4]d ia zep in -5-on e 10b. To iminopropa-
dienone 8, obtained from Meldrum’s acid derivative 5 (329 mg,
1.0 mmol), was injected a solution of 81.5 mg (1.1 mmol) of
N-methylethylenediamine in 30 mL of dry THF, and the
resulting mixture was stirred for 3 days. The solvent was
evaporated, and the crude product was purified by flash
chromatography (silica gel, 5% MeOH/ether) to yield 75 mg
(30%) of 10a /10b in a 1:1 ratio as a yellow oil: IR (KBr) ν 3255,
Nea t F ilm IR Sp ectr a . 2,6-Diflu or op h en ylim in op r o-
p a d ien on e 8. Compound 5′ (10 mg, 0.03 mmol) was sublimed
at 70 °C through the FVT tube at 700 °C (the system was
operated at a vacuum of 2 × 10-5), and 8 was collected as a
neat film on a BaF2 disk cooled to 50 K over the course of 15
min: IR (neat) 2224 vs, 1610 m, 754 w, 534 w cm-1. Also
present were the following peaks: 1710 m, 1365 m, 1227 m
cm-1 (acetone); 2967 w, 2822 w, 1483 w, 1143 w cm-1
(dimethylamine); 2341, 2338 cm-1 (carbon dioxide).
2,6-Dieth ylp h en ylim in op r op a d ien on e 13. Compound
12′ (10 mg, 0.03 mmol) was sublimed at 85 °C through the
FVT tube at 700 °C, and 13 was collected as a neat film at 50
1661, 1645, 1617 cm-1; H NMR (400 MHz, CDCl3) δ 3.00 (s,
1
3 H), 3.21 (s, 3 H), 3.41 (s, 2 H,), 3.47 (s, 2 H), 3.48-3.50 (m,
2H), 3.59-3.63 (m, 4H), 3.74-3.77 (m, 2H), 3.86 (br, 1H), 6.38
(br, 1H), 6.83-6.91 (m, 6H); 13C NMR (100 Hz, CDCl3) δ 35.9,
37.3, 38.0, 41.4, 42.7, 47.5, 49.6, 51.6, 110.4 (m), 111.3 (m),
K as above: IR (neat) 2224 vs, 1610 m, 754 w, 534 w cm-1
;
122.0 (t), 122.5(t), 127.2 (t), 127.8 (t), 154.2, 155.1 (dd, J
)
CF
241 Hz), 155.2 (dd, J CF ) 242 Hz), 155.8, 165.0, 167.0. HRMS
calcd for C12H13F2N3O 253.1027, found 253.1021. Anal. Calcd
for C12H13F2N3O: C, 56.91; H, 5.17; N, 16.59 Found: C, 57.12;
H, 5.29; N, 16.40
peaks due to acetone, dimethylamine, and carbon dioxide were
also present (see above).
P r ep a r a tive P yr olysis Exp er im en ts. Sta n d a r d P r oce-
d u r e for Syn th esis a n d P r ep a r a tive Tr a p p in g of Ar ylim -
in op r op a d ien on es. 5-[Arylamino)(methylthio)methylene]-
1,4-Dim eth yl-7-[(2,6-d iflu or op h en yl)im in o]p er h yd r o-
[1,4]d ia zep in -5-on e 11. To iminopropadienone 8, obtained
from Meldrum’s acid derivative 5 (329 mg, 1.0 mmol), was
injected a solution of 97.0 mg (1.1 mmol) of N,N′-dimethyl-
ethylenediamine in 30 mL of dry THF, and the resulting
mixture was stirred for 3 d. The solvent was evaporated, and
the crude product was purified by flash chromatography (silica
gel, 5% MeOH/ether), to yield 110 mg (41%) as a yellow oil:
IR (KBr) ν 1663, 1634 cm-1; 1H NMR (400 MHz, CDCl3) δ 2.97
(s, 3 H), 3.20 (s, 3 H), 3.52 (s, 2 H), 3.53-3.54 (m, 2H), 3.73-
3.76 (m, 2H), 6.85-6.87 (m, 3H); 13C NMR (50 Hz, CDCl3) δ
35.8, 37.1, 38.0, 49.4, 50.4, 111.3 (m), 122.0 (t), 127.2 (t), 155.2
2,2-dimethyl-1,3-dioxane-4,6-diones
5 or 12 or 5-[(aryl-
amino)(dimethylamino)methylene]-2,2-dimethyl-1,3-dioxane-
4,6-diones 5′ or 12′ (1.0 mmol) was sublimed at 150-180 °C/
10-4 mbar and thermolyzed at 700 °C over the course of 3 h;
the iminopropadienones 8 and 13 were collected on a coldfinger
cooled to ca. -196 °C using liquid nitrogen and connected to
an oil diffusion vacuum pump. Upon completion of the ther-
molysis, the pump was closed, the pressure was equalized with
N2, and an excess or 1 equiv of trapping agent in 15-30 mL
of dry ether, THF, or dichloromethane was injected onto the
thermolysate. This coldfinger was then allowed to warm to
room temperature. The following compounds were prepared.
3-Dim et h yla m in o-3-[(2,6-d iflu or op h en yl)]im in o-N,N-
d im eth ylp r op a n a m id e 9. Excess dimethylamine as a solu-
tion in ether (20 mL) was injected on the coldfinger containing
8 as described above, and the resulting mixture was stirred
for 12 h. The crude product was purified by flash chromatog-
raphy (silica gel, 5% MeOH in ether) to yield 100 mg (37%) of
a yellow oil: 1H NMR (400 MHz, CDCl3) δ 2.64 (s, 3H), 2.80
(s, 3H), 3.06 (s, 6H), 3.28 (s, 2H), 6.83-6.93 (m, 3H); 13C NMR
(100 Hz, CDCl3) δ 34.3, 35.6, 36.6, 39.6, 111.5, 116.0, 125.9,
156.2 (dd, J CF ) 252 Hz), 158.8, 165.8. Anal. Calcd for
(dd, J CF
) 256 Hz), 156.3, 164.9. Anal. Calcd for
C
13H15F2N3O: C, 58.43; H, 5.62; N, 15.73. Found: C, 58.49;
H, 5.59; N, 15.40.
1-Meth yl-2-[(2,6-d ieth ylp 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 14. 2-(Methylamino)-
pyridine (119 mg, 1.1 mmol) in 15 mL of dry CH2Cl2 was
injected onto the coldfinger containing 13 (obtained from
Meldrum’s acid derivative 12 (349 mg, 1.0 mmol) as described
above), and the resulting mixture was stirred for 24 h. The
solvent was evaporated, and the crude product was purified
by flash chromatography (silica gel, 50% MeOH/ether) to 180
mg (yield 59%) of a yellow solid: mp 157-158 °C; IR (KBr) ν
C
13H17F2N3O: C, 57.98; H, 6.36; N, 15.60. Found: C, 57.59;
1717, 1636, 1617, 1559 cm-1
;
1H NMR (400 MHz, CDCl3) δ
H, 6.35; N; 15.40.
3
1.12 (t, J ) 7.7 Hz, 6H) 2.38-2.48 (m, 4H), 3.90 (s, 3H), 4.62
(s, 1H), 6.94 (t, 3J ) 7.4 Hz, 1H), 7.03 (d, 3J ) 7.3 Hz, 2H),
7.13 (t, 3J ) 7.0 Hz, 1H), 7.39 (d, 3J ) 8.8 Hz, 1H), 8.00 (td, 3J
) 7.0 Hz, 4J ) 1.5 Hz, 1H), 9.23 (dd, 3J ) 6.6 Hz, 4J ) 1.5 Hz,
1H); 13C NMR (100 Hz,CDCl3) δ 14.1, 24.5, 31.4, 67.4, 112.7,
114.2, 122.7, 126.0, 132.0, 135.0, 142.8, 144.8, 148.3, 149.3,
151.3. Anal. Calcd for C19H21N3O: C, 74.24; H, 6.89; N, 13.67.
Found: C, 74.50; H, 6.91; N, 13.67.
1-Meth yl-2-[(2,6-d iflu or op 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 7a a n d 1-Meth yl-4-
[(2,6-d iflu or op h en yl)im in o]-1,2-d ih yd r op yr id o[1,2-a ]p y-
r im id in -1-iu m -2-ola te 7b. 2-(Methylamino)pyridine (119 mg;
1.1 mmol) in 15 mL of dry THF was injected onto the coldfinger
covered with iminopropadienone 8 obtained from Meldrum’s
acid derivative 5 (329 mg, 1.0 mmol), and the resulting mixture
was stirred for 24 h. The solvent was evaporated, and the crude
product was purified by flash chromatography (silica gel, 50%
MeOH/ether) to afford 150 mg (yield 52%) of 7a /7b in a 1:1
ratio as a yellow solid (mp 180-185 °C). Compound 7a
crystallized from the CDCl3 solution in the NMR tube after
prolonged storing at room temperature: mp 208-209 °C. X-ray
data for this compound are given in the Supporting Informa-
tion (Figure S5 and Tables S1-S5). The following data are
for the mixture of 7a and 7b: IR (KBr) ν 1717, 1665, 1623
Dieth yl 3-Dieth yla m in o-3-(2,6-d ieth ylp h en yl) Im in o-
p r op a n a m id e 15. Diethylamine (0.21 mL, 2.0 mmol) in 15
mL of dry CH2Cl2 was injected onto the coldfinger containing
13 obtained from 12 as above, and the resulting mixture was
stirred for 12 h. The crude product was purified by flash
chromatography (silica gel, 3% MeOH in ether) to yield 200
mg (58%) of a white solid: mp 92-93 °C; 1H NMR (400 MHz,
3
3
CDCl3) δ 0.70 (t, J ) 7.2 Hz, 3H), 0.99 (t, J ) 7.2 Hz, 3H),
1
3
3
cm-1; H NMR (400 MHz, CDCl3) δ 3.67 (s, 3H), 3.92 (s, 3H),
1.12 (t, J ) 7.2 Hz, 6H), 1.22 (t, J ) 7.2 Hz, 6H), 2.47-2.53
3 3
4.89 (s, 1H), 4.93 (s, 1H), 6.87-6.93 (m, 6H), 7.22 (td, 3J ) 7.0
(m, 4H), 2.64 (q, J ) 7.2 Hz, 2H), 3.08 (s, 2H), 3.19 (q, J )
6.6 Hz, 2H), 3.46-3.51 (m, 4H), 6.83 (t, 3J ) 7.5 Hz, 1H), 6.96
4
3
4
Hz, J ) 1.2 Hz, 1H), 7.31 (td, J ) 7.0 Hz, J ) 1.2 Hz, 1H),
7.42 (t, 3J ) 7.4 Hz, 2H), 8.03-8.12 (m, 2H), 9.28 (dd, 3J ) 6.8
(d, J ) 7.5 Hz, 2H). 13C NMR (100 Hz, CDCl3) δ 12.9, 13.0,
3
J . Org. Chem, Vol. 67, No. 24, 2002 8563

Shtaiwi and Wentrup
13.6, 13.7, 24.3, 32.2, 40.8, 42.1, 42.5, 125.6, 127.6, 135.9 141.9,
153.1, 165.1. Anal. Calcd for C21H35N3O: C, 73.00; H, 10.21;
N, 12.16. Found: C, 73.05; H, 10.01; N, 12.11.
MHz, MeOD) δ 5.02 (s, 2H), 6.42 (s, 2H), 7.05-7.7.28 (m, 2
H), 7.53-7.65 (m, 1H); 13C NMR (100 Hz, MeOD) δ 88.5, 106.7
(t), 112.0 (m), 132.7 (t), 151.1, 159.9 (dd, J CF ) 250 Hz), 163.3,
170.8.
4-Met h yl-7-[(2,6-d iet h ylp h en yl)im in o]p er h yd r o[1,4]-
d ia zep in -5-on e 16. To iminopropadienone 13, obtained from
12 as above, was injected a solution of 81.5 mg (1.1 mmol) of
N-methylethylenediamine in 30 mL of dry THF, and the
resulting mixture was stirred for 3 days. The solvent was
evaporated and the crude product was purified by flash
chromatography (silica gel, 5% MeOH/ether) to yield 70 mg
3-(2,6-Diflou r oph en yl)isoxazolo[5,4-d]pyr im idin e-4(5H)-
on e 6 was prepared by adaptation of the method of Taylor
and Garcia.3a
The foregoing isoxazolecarboxamide (2.12 g, 8.8
mmol) and 15 g (100 mmol) of triethyl orthoformate were
dissolved in 28 mL of acetic anhydride and heated under reflux
for 24 h. The mixture was evaporated and ethanol was added
to the residue. 15 mL of n-hexane was added, the solution
turned cloudy. The mixture was filtered off after it was frozen
for 4 days at -20 °C to yield 1.3 g (60%): mp 258-260 °C; IR
1
(26%) as a yellow oil: IR (KBr) ν 3340, 1646 cm-1; H NMR
3
(400 MHz, CDCl3) δ 1.13 (t, J ) 7.7 Hz, 6H), 2.37-2.47 (m,
4H), 3.01 (s, 3 H), 3.43-3.71 (m, 4H), 3.82 (s, 2 H), 4.50 (br,
1H), 6.97(t, 3J ) 7.0 Hz, 1H), 7.06 (d, 3J ) 0.0 Hz, 2H); 13C
NMR (100 Hz, CDCl3) δ 14.0, 24.5, 35, 41.4, 43.8, 52.2, 123.2,
126.3, 134.7, 144.3, 150.9, 167.7. HRMS calcd for C16H23N3O
273.1841, found 273.1840. Anal. Calcd for C16H23N3O: C,
70.30; H, 8.48; N, 15.37 Found: C, 70.21; H, 8.24; N, 15.20
1,4-Dim et h yl-7-[(2,6-d iet h ylp h en yl)im in o]p er h yd r o-
[1,4]d ia zep in -5-on e 17. To iminopropadienone 13, obtained
from 12 as above, was injected a solution of 97.0 mg (1.1 mmol)
N,N′-dimethylethylenediamine in 30 mL of dry THF, and the
resulting mixture was stirred for 3 d. The solvent was
evaporated and the crude product was purified by flash
chromatography (silica gel, 5% MeOH/ether), to yield 150 mg
(yield 52%) as a white crystals: mp 125-126 °C; IR (KBr) ν
(KBr) 3445, 1761, 1633 cm-1
C NMR
(100 Hz, MeOD) 103.7, 106.7 (t), 113.0 (m), 134.4 (t), 151.3,
;
1H NMR (200 MHz, MeOD)
7.16-7.28 (m, 2 H), 7.60-7.75 (m, 1H), 8.36 (s, 1H); 13
153.3, 158.8, 161.9 (dd, J CF
) 253 Hz), 177.3. Anal. Calcd for
C
11H5F2N3O2: C, 53.02; H, 2.02; N, 16.86. Found: C, 53.32;
H, 2.09; N, 16.60.
Ma tr ix Isola tion of 2,6-Diflu or op h en ylim in op r op a d i-
en on e 8 Gen er a ted fr om 6. 3-(2,6-Difluorophenyl)isoxazolo-
[5,4-d]pyrimidine-4(5H)-one 6 (10 mg, 0.04 mmol) was sub-
limed at 100 °C through the FVT tube at 700 °C with Ar matrix
isolation of 8 on a BaF2 disk at 8 K over the course of 20 min:
IR (Ar, 8 K) 2247 vs, 2145 w, 2137 w, 1636 m, 1483 w, 1017
m, 778 w cm-1. Also present were the following peaks: 3518
w, 3507 w, 2259 m, 770 w cm-1 (hydrogen isocyanate, HNCO).
F VT of P yr id op yr im id in on es. 2-ter t-Bu tylp h en ylim i-
n opr opadien on e 19a Gen er ated fr om 2-[(2-ter t-Bu tylph e-
n yl)a m in o]p yr id o[1,2-a ]p yr im id in -4-on e 20a . Compound
20a 2 (10 mg, 0.025 mmol) was sublimed at 140 °C through
the FVT tube at 850 °C with Ar matrix isolation of 19a on a
BaF2 disk at 8 K over the course of 10 min: IR (Ar, 8 K) 2237
vs, 2138 w, 1624 m, 1354 w, 730 w cm-1. Also present were
the following peaks: 3535 w, 3429 w, 3074 w, 1611 s, 1608 s,
1575 w, 1484 m, 1445 m, 1317 w, 1273 w, 1149 w, 735 m cm-1
(2-aminopyridine).
1
1627, 1586 cm-1; H NMR (400 MHz, CDCl3) δ 1.11 (t, 3J )
7.6 Hz, 6H), 2.20-2.42 (m, 4H), 2.96 (s, 3 H), 3.14 (s, 3 H),
3.31 (s, 2 H), 3.52-3.56 (m, 2H), 3.64-3.70 (m, 2H), 6.86-
6.94 (m, 1H), 7.00-7.04 (m, 2H); 13C NMR (100 Hz, CDCl3) δ
13.6, 24.4, 35.6, 37.2, 37.9, 49.8, 50.2, 122.4, 125.6, 133.9, 146.1,
151.9, 165.9. Anal. Calcd for C17H25N3O: C, 71.04; H, 8.77; N,
14.62. Found: C, 69.95; H, 8.74; N, 14.40.
Isoxa zolop yr im id in on e Rou te. 2,6-Diflu or op h en ylca r -
ba ld oxim e. A solution of 19.6 g (0.14 mol) of 2,6-difluoroben-
zaldyhyde in 200 mL of ethanol was added under vigorous
stirring at 60 °C to a 1 L aqueous solution of 15.0 g (0.16 mol)
of sodium acetate and 11.0 g (0.16 mol) of hydroxylamine
hydrochloride. The mixture was refluxed for 6 h and then
cooled in a refrigerator overnight to precipitate 13.3 g of fine,
Mesitylim in op r op a d ien on e 19b Gen er a ted fr om (2-
Mesityla m in o]p yr id o[1,2-a ]p yr im id in -4-on e 20b. Com-
pound 20b2 (10 mg, 0.025 mmol) was sublimed at 140 °C
through the FVT tube at 850 °C with Ar matrix isolation of
19b on a BaF2 disk at 8 K over the course of 10 min: IR (Ar,
1
long white crystals (yield 60.5%): mp 114-116 °C; H NMR
(400 MHz, CDCl3) δ 6.87-6.93 (m, 2 H), 7.20-7.7.30 (m, 1H),
8.27 (s, 1 H), 10.1 (s, 1 H); 13C NMR (100 Hz, CDCl3) δ 109.6
(t), 112.0 (m), 131.0 (t), 140.4, 157.6 (dd, J CF ) 256 Hz).
2,6-Diflu or oben zh yd r oxim oyl ch lor id e was prepared by
the method of Coda and Tacconi.13 A solution consisting 13.12
g (0.08 mol) of 2,6-difluorophenylcarbaldoxime, 130 mL of HCl
(32%), and 100 mL of glacial acetic acid was stirred for 1 h
and then cooled in an ice bath to reach 0 °C. Sodium
hypochlorite (0.11 mol as 66 mL of a 12.5% w/v solution in
water) was added dropwise using a dropping funnel to afford
a milky solution. The mixture was left stirring overnight and
then refrigerated to yield 8.5 g of a white precipitate (55.4%):
8 K) 2240 vs, 1627 m, 1583 w, 1480 m, 1092 w, 730 w cm-1
;
peaks due to 2-aminopyridine were also present (see above).
F VT of P yr id op yr im id in iu m Ola tes. 2,6-Diflu or op h e-
n ylim in op r op a d ien on e 8 Gen er a ted fr om 1-Meth yl-2-
[(2,6-d iflu or op h en yl)im in o]-1,2-d ih yd r op yr id o[1,2-a ]p y-
r im id in -1-i u m -4-ola te 7a a n d 1-Meth yl-4-[(2,6-d iflu or o-
ph en yl)im in o]-1,2-dih ydr opyr ido[1,2-a]pyr im idin -1-i u m -
2-ola te 7b. The 1:1 mixture of compounds 7a and 7b (10 mg,
0.031 mmol) was sublimed at 160 °C through the FVT tube at
550 °C with Ar matrix isolation of 8 on a BaF2 disk at 8 K
over the course of 10 min: IR (Ar, 8 K) 2247 vs, 2145 w, 2137
w, 1636 m, 1483 w, 1017 w cm-1. Also present were the
following peaks: 1612 s, 1602 s, 1578 w, 1524 m, 1511 m, 1459
m, 1421 m, 1336 m, 1329 m, 1289 m, 1156 m, 1074 m, 771 m,
734 w cm-1 [2-(methylamino)pyridine].
2-ter t-Bu tylp h en ylim in op r op a d ien on e 19a Gen er a ted
fr om 1-Meth yl-2-[(2-ter t-bu tylp h en yl)im in o]-1,2-d ih yd r o-
p yr id o[1,2-a ]p yr im id in -1-iu m -4-ola te 21a . Compound 21a 2
(10 mg, 0.031 mmol) was sublimed at 160 °C through the FVT
tube at 550 °C with Ar matrix isolation of 19a on a BaF2 disk
at 8 K over the course of 10 min: IR (Ar, 8 K) 2237 vs, 2138
w, 1624 m, 1354 w, 730 w cm-1; peaks due to 2-(methylamino)-
pyridine were also present (see above).
1
mp 104-106 °C; H NMR (400 MHz, MeOD) δ7.22-7.29 (m,
2 H), 7.59-7.67 (m, 1H); 13C NMR (100 Hz, MeOD) δ 111.7
(t), 112.3 (m), 126.1, 133.3 (t), 159.6 (dd, J CF ) 256 Hz).
5-Am in o-2,6-d iflu or op h en yl-4-isoxa zoleca r b oxa m id e
was prepared by the method of Rajagopalan and Talaty.3b
2-Cyanoacetamide (1.68 g, 20.0 mmol) in 30 mL of absolute
ethanol was added into a well-stirred solution of sodium
ethoxide, which was prepared from 0.46 g (20.0 mmol) of
sodium in 30 mL of absolute ethanol. The resulting suspension
was stirred at 0 °C in an ice bath. 2,6-Difluorobenzhydroximoyl
chloride (3.8 g; 20.0 mmol) in 30 mL of absolute ethanol was
added slowly to the mixture, which was stirred for 15 min at
0 °C and then allowed to stir for another 90 min at room
temperature. The mixture was then refluxed for 2.5 h and later
hydrolyzed by pouring it onto 25 mL of crushed ice. The
precipitate was filtered off and recrystallized from methanol/
water to afford 1.3 g (27%): mp 174-176 °C; 1H NMR (200
Refer en ce Sp ectr a . 2-Am in op yr id in e: IR (Ar, 8 K) ν
3535 m, 3429 m, 3074 w, 3031 w, 1611 vs, 1608 vs, 1586 w,
1575 m, 1497 w, 1484 s, 1445 s, 1317 m, 1273 w, 1149 w, 987
w, 846 w, 803 w, 785 w, 772 w, 765 w, 735 w, 519 w cm-1
Sublimation temperature 20 °C.
.
2-(Meth yla m in o)p yr id in e: IR (Ar, 8 K) ν 3503 w, 3481
w, 2821 w, 1612 s, 1606 s, 1602 vs, 1578 m, 1574 m, 1524 s,
(13) Coda, A. C.; Tacconi, G. Gazz. Chim. Ital. 1984, 114, 131.
8564 J . Org. Chem., Vol. 67, No. 24, 2002

Iminopropadienones from Different Precursors
1511 s, 1493 w, 1464 w, 1459 m, 1440 w, 1429 w, 1421 s, 1414
m, 1336 m, 1329 w, 1289 m, 1169 w, 1156 w, 1149 w, 1131 w,
1089 w, 1074 w, 981 w, 771 s, 734 w, 522 w cm-1. Sublimation
temperature 10 °C.
padienones; IR spectra of diethyliminopropadienone [Ar matrix
and calculated (B3LYP/6-31G**), Figure S1], mesitylimino-
propadienone (Ar matrixes, Figure S2), and dimethoxyphe-
nyliminopropadienones (Ar matrixes and neat films, Figures
S3-S4); X-ray data for pyridopyrimidinium olate 7a (Figure
S5 and Tables S1-S5); Cartesian coordinates, energies, and
calculated IR spectra of 8, 13, 19a , 23, and 24. This material
is available free of charge via the Internet at http://pubs.acs.org.
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: Experimental pro-
cedures for the preparation of the dimethoxyphenyliminopro-
J O026275+
J . Org. Chem, Vol. 67, No. 24, 2002 8565