Imidoylketene-oxoketenimine interconversion. Rearrangement of a carbomethoxyketenimine to a methoxyimidoylketene and 2-methoxy-4-quinolone

Article abstract of DOI:10.1021/jo951832w

FVP of triazole 13 produces the isolable ketenimine 11 together with indole 15. 11 undergoes reversible interconversion with imidoylketene 10 above 380 °C. The latter cyclizes to quinolone 12. Meldrum's acid derivative 16 produces the same ketene 10 above 200 °C, and the latter isomerizes to ketenimine 11 at 200 °C by a 1,3-shift of a MeO group. A competing elimination of MeOH from 16 produces (phenylimino)propadienone 20.

Full text of DOI:10.1021/jo951832w

J . Org. Chem. 1996, 61, 1363-1368
1363
Im id oylk eten e-Oxok eten im in e In ter con ver sion . Rea r r a n gem en t
of a Ca r bom eth oxyk eten im in e to a Meth oxyim id oylk eten e a n d
2-Meth oxy-4-qu in olon e
Belinda E. Fulloon and Curt Wentrup*
Department of Chemistry, The University of Queensland, Brisbane, Qld 4072, Australia
Received October 11, 1995X
FVP of triazole 13 produces the isolable ketenimine 11 together with indole 15. 11 undergoes
reversible interconversion with imidoylketene 10 above 380 °C. The latter cyclizes to quinolone
12. Meldrum’s acid derivative 16 produces the same ketene 10 above 200 °C, and the latter
isomerizes to ketenimine 11 at 200 °C by a 1,3-shift of a MeO group. A competing elimination of
MeOH from 16 produces (phenylimino)propadienone 20.
In tr od u ction
order CH3 , Ph < H < OH < MeO < NH2 <SH < NHMe
6,7
MeS < NMe2.
The interconversion of R-oxoketenes involves a degen-
erate intramolecular 1,3-shift of the group R (1a / 2a ).1
This rearrangement was first reported for benzoylketene
(1a , R ) Ph) and established by 13C scrambling in the
specifically labeled ketene, both by direct IR spectroscopic
observation of the ketenes and by 13C NMR analysis of
the trapping product with methanol, methyl benzoylac-
etate. In this case, the interconversion 1a / 2a is
complete under flash vacuum pyrolysis (FVP) conditions
at 800 °C (ca. 10-4 mbar; contact times ≈ ms).1 An
analogous 13C labeling experiment demonstrated that a
methyl group does not undergo this 1,3-shift in acetyl-
ketene (1a , R ) CH3) at FVP temperatures up to 1100
°C.2
We have recently found that a similar interconversion
of vinylketenes and oxoallenes (1c / 2c) becomes observ-
able when an electron-donating group is employed (R )
OMe, NMe2, or Cl).8 Further calculations confirmed the
very facile 1,3-migration of halogen atoms (Br > Cl ∼
NMe2).8b
Although predicted by theory to be facile, there has
been little or no direct evidence for the interconversion
of carboxylic acid derivatives of ketenes and ketenimines
(1b / 2b, R ) OR′ or Cl), except for the thioesters4 (R )
SMe). McNab et al. concluded from 13C labeling studies
of the rearrangement of pyrazolyltriazole 3 to pyrazol-
opyrimidinone 6 that a ketenimine-imidoylketene rear-
rangement 4 f 5 was involved.9
The same type of rearrangement interconverts imi-
doylketenes and oxoketenimines (1b / 2b).3-5 For R )
aryl, FVP temperatures of 600-700 °C are required,4,5
but the reaction is dramatically accelerated for R ) SMe
(ca. 400 °C) and, by implication, also for R ) NMe2.3,4
Ab initio calculations have provided a comprehensive
rationale for these observations.6 The most important
factor governing the 1,3-shift of the group R is electron
donation from this group into the ketene LUMO, which
has a large coefficient at the central ketene C atom to
which the migration takes place. Thus, the accelerated
migration of electron-donating groups is readily under-
stood. The calculated migratory aptitudes follow the
An analogous mechanism was postulated for the
conversion of ethyl 1-phenyltriazole-4-carboxylate (7) to
2-hydroxy-4-quinolone (8),9 thought to arise by ethene
elimination from an initially formed 2-ethoxyquinolone.
(6) Wong, M. W.; Wentrup, C. J . Org. Chem. 1994, 59, 5279.
(7) (a) Related isomerization of thioacyl isocyanates to acyl isothio-
cyanates, and of guanyl isocyanate to carbamoylcarbodiimide have been
reported by Goerdeler et al.;7b the migratory aptitudes were similar
to the ones calculated by us:6 (Alk)2N, Alk(Ar)N > ArS > AlkS . ArO
> AlkO. (b) Goerdeler, J .; J onas, G. Chem. Ber. 1966, 99, 3572.
Goerdeler, J .; Bartsch, H.-J . Chem. Ber. 1985, 118, 2294, 4196.
Goerdeler, J .; Raddatz, S. Chem. Ber. 1980, 113, 1095.
(8) (a) Bibas, H.; Wong, M. W.; Wentrup, C. J . Am. Chem. Soc. 1995,
117, 9582. (b) Wong, M. W.; Wentrup, C. To be published.
(9) Clarke, D.; Mares, R. W.; McNab, H. J . Chem. Soc., Chem.
Commun. 1993, 1026.
X Abstract published in Advance ACS Abstracts, February 1, 1996.
(1) Wentrup, C.; Netsch, K.-P. Angew. Chem., Int. Ed. Engl. 1984,
23, 802.
(2) Sankar, I. V.; McCluskey, A.; Wentrup, C. Unpublished results.
(3) Ben Cheikh, A.; Chuche, J .; Manisse, N.; Pommelet, J . C.; Netsch,
K.-P.; Lorencak, P.; Wentrup, C. J . Org. Chem. 1991, 56, 970.
(4) Kappe, C. O.; Kollenz, G.; Leung-Toung, R.; Wentrup, C. J . Chem.
Soc., Chem. Commun. 1992, 487.
(5) Kappe, C. O.; Kollenz, G.; Netsch, K.-P.; Leung-Toung, R.;
Wentrup, C. J . Chem. Soc., Chem. Commun. 1992, 488.
0022-3263/96/1961-1363$12.00/0 © 1996 American Chemical Society

1364 J . Org. Chem., Vol. 61, No. 4, 1996
Fulloon and Wentrup
By using the pyrroledione precursor 9, we were able
to observe both the imidoylketene 10 and the ketenimine
11, which are related through a 1,3-shift of the methoxy
group, taking place at ca. 350 °C under FVP conditions;
this interconversion is so facile that it competes with the
cyclization of ketene 10 to 2-methoxy-4-quinolone (12).10
F igu r e 1. Partial FTIR spectra (1900-2200 cm-1 range) of
the products (77 K) of FVP of 13. K ) ketene 10 (2135 cm-1);
I ) ketenimine 11 (2050 cm-1).
Sch em e 1
We now report further studies of these ketene and
ketenimine intermediates, demonstrating the extraordi-
narily facile 1,3-shift of the methoxy group at a temper-
ature as low as 200 °C under FVP conditions and even
proceeding in solution in boiling diphenyl ether (242 °C).
Resu lts a n d Discu ssion
Preparative FVP of triazole 13 with isolation of the
products on a liquid N2 cooled cold finger resulted in three
products: the ketenimine 11, the indole 15, and the
quinolone 12 (Scheme 1). In parallel experiments, the
FVP products were isolated on a BaF2 disk at 77 K for
IR spectroscopic observation of the primary reaction
products. N2 elimination from 13 commenced at 380 °C,
and both a ketenimine 11 and a ketene 10 were im-
mediately observable as very weak peaks by IR spectros-
copy. At 450 °C, a much stronger signal due to the
ketenimine 11, together with a weak signal due to the
ketene 10, were observed (Figure 1a). The ketenimine
was isolable as a neat liquid by Kugelrohr distillation of
the product of the preparative pyrolyses; a 29% isolated
yield was obtained at 600 °C. The residue from the
distillation was separated by column chromatography to
give indole 15 (13%) and quinolone 12 (44%). Analogous
FVP of 13 at 800 °C gave 15 (4%) and 12 (93%). The
ketenimine was no longer present. The yields are sum-
marized in Table 1.
Ta ble 1. P r od u cts of F VP of Keten e/Keten im in e
P r ecu r sor s a s a F u n ction of Tem p er a tu r e
yield, %a
precursor
temp, °C
11
12
15
21b
9c
500
800
500
700
600
800
350
600
700
800
30
64
97
75
91
44
93
48d
67
50
33
9c
11
11
13
13
16
16
16
16
29
26
13
4
33
50
67
a
Absolute yields by isolation. The ratios of 12 and 21 were
b
determined by 1H NMR spectroscopy. By trapping of 20 with
d
MeOH on the cold finger. c Data from ref 10. 20% starting
material 16 was recovered.
The formation of indoles from triazoles has been
investigated previously under both thermal and photo-
chemical conditions.11 The cyclization of an initially
formed imidoylcarbene 14 to give indole 15 is the fully
expected normal outcome.11,12 The 1,2-H shift in imi-
doylcarbenes to give ketenimines is also well docu-
(11) Gilchrist, T. L.; Rees, C. W.; Thomas, C. J . Chem. Soc., Perkin
Trans 1 1975, 8. Mitchell, G.; Rees, C. W. J . Chem. Soc., Perkin Trans
1 1987, 413.
(10) Fulloon, B.; El-Nabi, H. A. A.; Kollenz, G.; Wentrup, C.
Tetrahedron Lett. 1995, 36, 6547.

Imidoylketene-Oxoketenimine Interconversion
J . Org. Chem., Vol. 61, No. 4, 1996 1365
mented.12 The surprising observation is that, as soon as
the ketenimine 11 starts to form (380-450 °C), it
isomerizes to the ketene 10. As shown in Figure 1, the
ketene peak (K) is present throughout the temperature
range 450-600 °C. It never increases significantly in
intensity because the ketene is removed from the equi-
librium by cyclization to the quinolone 12, which is
always formed, even under the mildest conditions of FVP,
where very little decomposition of 13 occurs. Compounds
10 and 11 are much more volatile than quinolone 12 and
therefore are deposited on the cold disk (77 K) free of
any quinolone until a FVP temperature of 800 °C. At
lower FVP temperatures (400-700 °C), the quinolone
(with small amounts of indole 15) condenses on the cool
surface between the pyrolysis zone and the deposition
disk.
Sch em e 2
We conclude from these experiments that an equilib-
rium between ketenimine 11 and ketene 10 is established
as soon as 11 is formed (g400 °C). While 10 is only
observable by low temperature spectroscopy (up to +15
°C), its structure is given by that of the derived quinolone
12 as well as by independent generation from the
pyrroledione 9.10 9 gave only ketene 10 at 300 °C, but
the ketenimine 11 dominated in the IR spectrum already
at 350 °C. A ketene:ketenimine ratio similar to that
shown in Figure 1b was achieved from 9 at 500 °C.
Ketenimine 11 was isolable in 30% yield following FVP
of 9 at 500 °C; quinolone 12 was obtained in 64% yield
under these conditions, and in 97% yield at 800 °C.10 The
combined results from 13 and 9 demonstrate that the
interconversion of ketenimine 11 and ketene 10 takes
place in both directions, starting at 350 °C or lower.
It is necessary also to consider an alternative Wolff
rearrangement in imidoylcarbene 14 which, by a 1,2-shift
of the methoxy group would give ketene 10′, isomeric
with 10. Cyclization of ketene 10′ would yield the
quinolone 12′, isomeric with 12.
probably via the tautomer4,14b,16 17 (Scheme 2), starting
already at 200 °C. The first detectable intermediate is
the imidoylketene 10 (2135 cm-1). A methyleneketene
18, which could have formed directly from 16 by loss of
acetone and CO2, was not detectable. Importantly, even
at the lowest temperature where 16 reacts (200 °C), there
was already formation of a small amount of the keten-
imine 11 (2050, 1712, 1696 cm-1) (Figure 2a). The
amount of ketenimine rapidly increased, and that of the
ketene decreased as a function of temperature, so that
at 400 °C their ratio approached that seen earlier using
13 and 9 as precursors (Figure 2c). At the same time,
quinolone 12 was being formed; this was isolable in 48%
yield at 350 °C and in 67% yield at 600 °C. The
ketenimine 11 was again isolated by distillation (26%
from FVP at 350 °C). 10 and 11 were shown by spectral
comparison to be identical with the materials described
above.
1
A careful search by 500 MHz H NMR failed to reveal
the presence of 12′ (a known compound13 ) in either the
crude product of FVP of 13 or in the chromatography
fraction containing all of quinolone 12. Therefore, if this
Wolff rearrangement takes place at all, it could only be
to the extent of a few percent.
It is seen in Figure 2 that a new peak starts appearing
in the IR spectrum near 2200 cm-1 at 400 °C. At 700 °C
this species has replaced everything else in the ketene
region, giving rise to a very strong and complex signal
with maxima at 2222 and 2140 cm-1 (Figure 2d,e). This
new compound is (phenylimino)propadienone (20), formed
in a competing elimination of MeOH from 16, a reaction
that starts at 400 °C (Scheme 2). Cumulene 20 was
identified by comparison of its IR spectrum, both as a
neat film at 77 K and in Ar matrix at 12 K (2247 (vs),
2140 (w) cm-1), with samples prepared from other
precursors.17 Furthermore, trapping of 20 with MeOH
produced the malonic ester imide 21. The yield of 21
increased, and that of quinolone 12 decreased with rising
It was shown previously that 5-aminomethylene de-
rivatives of Meldrum’s acid (2,2-dimethyl-1,3-dioxane-4,6-
dione) are excellent precursors of imidoylketenes.3,4,14a
The requisite methoxy-substituted Meldrum’s acid 16
was prepared by displacement of the methylthio ana-
logue4 with methanol in the presence of a HgO/HgCl2
catalyst (either HgO or HgCl2 alone15 does not suffice).
FVP of 16 proceeds with elimination of acetone and CO2,
(12) Wentrup, C. Adv. Heterocycl. Chem. 1981, 28, 232-361, in
particular pp. 252-257 and references therein.
(13) Albini, A.; Fasani, E.; Dacrema, L. M. J . Chem. Soc., Perkin
Trans. 1, 1980, 2738.
(14) (a) Briehl, H.; Lukosch, A.; Wentrup, C. J . Org. Chem. 1984,
49, 2772. (b) Wentrup, C.; Briehl, H.; Lorencak, P.; Vogelbacher, U.
J ., Winter, H.-W.; Maquestiau, A.; Flammang, R. J . Am. Chem. Soc.
1988, 110, 1337.
(16) Cf. also Wentrup, C.; Gross, G.; Berstermann, H.-M.; Lorencak,
P. J . Org. Chem. 1985, 50, 2877. Wentrup, C.; Lorencak, P. J . Am.
Chem. Soc. 1988, 110, 1880.
(15) Ye, F.-C.; Chen, B.-C.; Huang, X. Synthesis 1989, 317.

1366 J . Org. Chem., Vol. 61, No. 4, 1996
Fulloon and Wentrup
F igu r e 2. Partial FTIR spectra (1900-2200 cm-1 range) of the products (77 K) of FVP of 16. K ) ketene 10 (2135 cm-1); I )
ketenimine 11 (2050 cm-1); P ) propadienone 20 (2222, 2140 cm-1).
F igu r e 3. FTIR spectrum of ketenimine 11 in CCl4. Inset: partial FTIR spectrum (77 K) showing the formation of a small
amount of ketene 10 (K, 2135 cm-1) on FVP of 11 (I, 2050 cm-1) at 450 °C.
temperature, in agreement with the results of the IR
spectroscopic observation. The yields are reported in
Table 1.
ment 10 f 11 is 155 kJ mol-1; for 11 f 10 it is ca. 165
kJ mol-1 8b
.
Since ketenimine 11 is isolable from the reactions of
13, 16, or 9, we were able to examine its own behavior
on FVP. 11 (2050 cm-1) was recovered unchanged at
temperatures below 400 °C. At 450 °C, a weak signal at
2135 cm-1 due to ketene 10 appeared (Figure 3). The
ratio of the two peaks remained essentially unchanged
between 400 and 600 °C, the reason being removal of the
ketene 10 to form quinolone 12. The latter was isolated
from these analytical pyrolyses from 450 °C onwards and
identified by comparison with the material from earlier
experiments. In a preparative FVP of 11 at 500 °C, a
75% yield of 12 was isolated; at 700 °C the yield was 91%.
The ketenimine derivative of Meldrum’s acid (19) is
not detectable in this reaction. However, by using an
analog of 16 with Me2N in place of OMe, the correspond-
ing elimination of Me2NH at 300 °C gave 19, which was
detectable by IR and MS as a fleeting intermediate,
decomposing to 20 already at 310 °C.17a
The most important conclusion from this section is that
ketene 10 isomerizes to ketenimine 11 already at 200 °C
on FVP, indicating a very low barrier for the 1,3-shift of
the MeO group. It is also remarkable that this 1,3-shift
can compete with the cyclization to quinolone 12. The
ab initio calculated activation barrier for the rearrange-
The reaction of ketenimine 11 with methanol gave
imide 21 in 83% yield (Scheme 3).
The decomposition of 13 and 16 can also be carried out
in diphenyl ether solution, as has been reported for
related Meldrum’s acid derivatives15 and pyrroldiones.10
The results are given in Table 2, with data for 9 included
(17) (a) Mosandl, T.; Kappe, C. O.; Flammang, R.; Wentrup, C. J .
Chem. Soc., Chem. Commun. 1992, 1571. (b) Mosandl, T.; Stadtmu¨ller,
S.; Wong, M. W.; Wentrup, C. J . Phys. Chem. 1994, 98, 1080. (c)
Wentrup, C.; Kappe, C. O.; Wong, M. W. Pure Appl. Chem. 1995, 67,
749.

Imidoylketene-Oxoketenimine Interconversion
J . Org. Chem., Vol. 61, No. 4, 1996 1367
in vacuo. H2O (10 mL) was added to the residue, causing
precipitation of the product, which was recrystallized from
THF/hexane: yield 0.11 g (79%), mp 162-164 °C; 1H NMR
(CDCl3) δ 1.75 (s, 6 H), 4.13 (s, 3 H), 7.26-7.43 (m, 5 H); 13C
NMR (CDCl3) δ 26.2; 62.8, 75.8, 103.1; 123.3; 127.0; 129.3;
135.0; 164.2; 171.4; IR (KBr) v 1722, 1659, 1575 cm-1; HRMS
m/ z calcd for C14H15NO5 277.0949; found: 277.0948. Anal.
Calcd for C14H15NO5: C, 60.64; H, 5.45; N, 5.05. Found: C,
60.72; H, 5.51; N, 5.03.
Sch em e 3
F VP of 13. The compound (80 mg; 0.39 mmol) was
subjected to preparative FVP at 600 °C, being sublimed into
the apparatus at 85 °C in the course of 2 h. Products were
isolated on a cold finger at 77 K. Upon completion of the
pyrolysis, the system pressure was equalized with N2, the cold
finger was allowed to warm to room temperature, and the oily
product mixture was collected in a receiving flask by washing
the cold finger with CCl4 and immediately subjected to vacuum
distillation using a Kugelrohr apparatus. Distillation at 50
°C (2.4 × 10-4 mbar) afforded 20 mg (29%) of the ketenimine
11 as a clear liquid: 1H NMR (CDCl3) δ 3.71 (s, 3 H), 4.59 (s,
1 H), 7.27-7.40 (m, 5 H); 13C NMR (CDCl3) δ 51.8, 52.3, 124.5,
128.7, 129.7, 136.5, 168.6, 176.4; IR (CCl4) v 2952, 2050, 1712,
1696 cm-1. HRMS m/ z calcd for C10H9NO2 175.06333; found:
175.0629. This compound decomposed in the course of 1-2 d
at room temperature; a satisfactory elemental analysis was
not obtainable.
The residue from the distillation was subjected to column
chromatography (ether/hexane 40:60). Two compounds were
isolated. The first fraction (Rf 0.20) was identified as methyl
indole-3-carboxylate (15) (9 mg; 13%) by comparison with an
authentic sample prepared according to ref 21: mp 144-146
°C (lit.21 144-145.6 °C); 1H NMR (CDCl3) δ 3.91 (s, 3 H), 7.38,
8.19 (m, 4 H), 7.91 (d, 1 H).
Ta ble 2. P r od u cts of Rea ction in Dip h en yl
Eth er Solu tion
yield %
precursor
temp, °C
time
19 h
15 min
2 d
15 min
1 wk
12
15
13
16
16
9
242
242
150
242
150
30
30
40
7
-
-
-
-
36a
0b
9
a
b
Data from ref. 10. Starting material recovered unchanged.
for comparison. Although the yields are much inferior
to those achieved by FVP, it is noteworthy that the
triazole 13 yields quinolone 12 in solution, thereby
implying that the ketenimine-imidoylketene rearrange-
ment (11 f 10) also takes place in solution.
The second fraction (Rf 0.07) was identified as 2-methoxy-
4-quinolone (12) (30 mg; 44%) by comparison with the material
described previously:10 mp 170-172 °C. Anal. Calcd for
C10H9NO2: C, 68.56; H, 5.18; N, 8.00. Found: C, 68.71; H,
5.17; N, 7.95.
Con clu sion
We have demonstrated a facile 1,3-shift of the methoxy
group, interconverting the imidoylketene 10 and the
isolable ketenimine 11. From the ketene side (10), this
reaction is observable already at 200 °C under FVP
conditions. From the ketenimine side, the reaction is
observable from 380 °C onward. The ketene 10 can be
detected by IR spectroscopy but readily cyclizes to qui-
nolone 12. These reactions also proceed in boiling
diphenyl ether solution. The facile methoxy group shift
is in accord with predictions from ab initio calculations
of the activation barriers for this type of reaction.6,8
The results of an analogous pyrolysis at 800 °C are given
1
in Table 1. A 20:1 ratio of 12 and 15 was determined by H
NMR spectroscopy.
F VP of 16. (a) The compound (60 mg; 0.22 mmol) was
pyrolyzed at 350 °C, being sublimed into the apparatus at 135
°C in the course of 3 h. Workup as above yielded the
ketenimine 11 (10 mg; 26%), identified by 1H NMR and IR
comparison with the previously isolated material. Column
chromatography (ether/hexane 80:40) yielded 16 (12 mg; 20%;
Rf 0.15) and 12 (18 mg; 48%; Rf 0.31). No trace of 15 was
formed. (b) In a similar pyrolysis of 16 (48 mg; 0.17 mmol) at
600 °C, the cold finger was coated with MeOH (1 mL) prior to
the experiment and again with 1 mL of MeOH after the
completion of the deposition of the pyrolysate. After warming
to rt and evaporating excess MeOH, the residue (32 mg) was
shown by 1H NMR to consist of 12 (67%) and 21 (33%). 21
was identical with the material described previously17a (see
also reaction of 11 with methanol below). (c) The results of
analogous experiments at 700 and 800 °C are given in Table
1.
F VP of 11. (a) The freshly distilled ketenimine (20 mg; 0.11
mmol) was subjected to pyrolysis at 500 °C, being distilled into
the apparatus at 50 °C (30 min). Quinolone 12 (15 mg; 75%)
was isolated from the cold finger and identified as the exclusive
product by TLC and 1H NMR comparison of previously
prepared samples. A similar experiment with 80 mg of 11 at
700 °C gave a 91% yield of 12. (b) FVP of 11 with IR
spectroscopic observation of the rearrangement product, the
ketene 10, was carried out as described in the text. Figure 3
shows that a small amount of the ketene is present above 400
°C. The degree of conversion to quinolone 12 is very low under
these conditions. 12 was identified in the white material
deposited between the pyrolysis tube and the 77 K BaF2 disk
in an experiment at 450 °C by TLC and GC comparison with
the previously described sample.
Exp er im en ta l Section
The pyrolysis apparatus was as previously reported for Ar
matrix (12 K),18 neat film (77 K) deposition,14a and preparative
scale work (77 K isolation).19 BaF2 disks were used for
depositions. FTIR spectra were in all cases recorded on a
Perkin Elmer 1720X spectrometer. Chromatography was on
Kieselgel 100 (Merck). Methyl 1-phenyl-1,2,3-triazole-4-
carboxylate (13) was prepared according to the literature.20
2,2-Dim et h yl-5-[m et h oxy(p h en yla m in o)m et h ylen e]-
1,3-d ioxa n e-4,6-d ion e (16) was prepared by a modification
of the procedure used by Ye et al.15 for the preparation of
different Meldrum’s acid derivatives. To a solution of 2,2-
dimethyl-5-[methylthio(phenylamino)methylene]-1,3-dioxane-
4,6-dione (0.147 g; 0.5 mmol) in MeOH (5 mL) was added
yellow HgO (0.109 g; 0.5 mmol) and HgCl2 (0.135 g; 0.5 mmol),
and the mixture was refluxed for 20 min. The mixture was
then cooled to rt and filtered, and the filtrate was concentrated
(18) Kappe, C. O.; Wong, M. W.; Wentrup, C. J . Org. Chem. 1995,
60, 1686.
(19) Wentrup, C.; Blanch, R.; Briehl, H.; Gross, G. J . Am. Chem.
Soc. 1988, 110, 1874.
(20) Abu-Orabi, S. T.; Atfah, M. A.; J ibril, I.; Mari’i, F. M.; Ail, A.
A. J . Heterocycl. Chem. 1989, 26, 1461. Huisgen, E.; Knorr, R.; Mo¨bius,
L.; Szeimies, G. Chem. Ber. 1965, 98, 4014.
(21) Peterson, P. E.; Wolf, J . P.; Niemann, J . J . Org. Chem. 1958,
23, 203. Stanovnik, B.; Tisler, M.; Carlock, J . T. Synthesis 1976, 754.

1368 J . Org. Chem., Vol. 61, No. 4, 1996
Fulloon and Wentrup
Rea ction of 11 w ith Meth a n ol. Freshly distilled 11 (20
mg) was added to MeOH (5 mL), and the mixture was allowed
to stir overnight. Evaporation of the solvent afforded 21 as a
yellow oil (20 mg; 83%). Its identity was established by
comparison with previously described material:17a 1H NMR
(CDCl3) δ 3.21 (s, 2 H), 3.68 (s, 3 H), 3.80 (s, 3 H), 6.77-7.31
(m, 5 H); 13C NMR (CDCl3) δ 35.9, 52.3, 53.8, 120.9, 123.4,
129.1, 147.9, 156.8, 168.2; IR (CCl4) v 1751, 1683, 1598, 1160
tography. After eluting remaining diphenyl ether with ether/
hexane 40:60, the products were eluted with pure ether. The
results are given in Table 2.
Ack n ow led gm en t. This research was supported by
the Australian Research Council.
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra of ketenimine 11 (2 pages). This material is contained
in libraries on microfiche, immediately follows this article in
the microfilm version of the journal, and can be ordered from
the ACS; see any current masthead page for ordering
information.
cm-1
.
P yr olysis in Dip h en yl Eth er Solu tion . The appropriate
compound (13, 16, or 9) (80 mg) was heated in boiling diphenyl
ether (242 °C) (5 mL) under N2. After a given time (see Table
2), the mixture was cooled and diluted with hexane (30 mL).
The precipitate was filtered and purified by column chroma-
J O951832W