Generation of acyloxyketenes from unstable mesoionic 1,3-dioxolium-4-olates and their reaction with ketenophiles to give [2 + 2] cycloadducts

Article abstract of DOI:10.1021/jo060074e

Fast ring opening of mesoionic 1,3-dioxolium-4-olates, generated by Rh ₂(OAc)₄-catalyzed decomposition of phenyldiazoacetic anhydride derivatives, to acyloxyphenylketenes was demonstrated by trapping the ketenes with several ketenoph

Full text of DOI:10.1021/jo060074e

Generation of Acyloxyketenes from Unstable Mesoionic
1,3-Dioxolium-4-olates and Their Reaction with Ketenophiles To
Give [2 + 2] Cycloadducts
Masashi Hamaguchi,* Naoki Tomida, Yuji Iyama, and Takumi Oshima
Department of Applied Chemistry, Graduate School of Engineering, Osaka UniVersity, Suita,
Osaka 565-0871, Japan
hamaro@chem.eng.osaka-u.ac.jp
ReceiVed January 12, 2006
Fast ring opening of mesoionic 1,3-dioxolium-4-olates, generated by Rh2(OAc)4-catalyzed decomposition
of phenyldiazoacetic anhydride derivatives, to acyloxyphenylketenes was demonstrated by trapping the
ketenes with several ketenophiles. Reactions of phenyldiazoacetic anhydride derivatives with several
ketenophiles such as dihydrofuran, carbodiimides, and imines were carried out. No 1,3-dipolar cycloadducts
of the latter with 1,3-dioxolium-4-olates were observed. Instead, only their [2 + 2]-cycloadducts with
the acyloxyketenes generated by ring-opening of the initially formed 1,3-dioxolium-4-olates were isolated.
In the reaction with cyclopentadiene, 1,3-dipolar cycloadducts with 1,3-dioxolium-4-olates were formed
as main products along with the [2 + 2]-ketene adduct. PM3 calculation of heats of formation of 2,5-
diphenyl-1,3-dioxolium-4-olate and the corresponding benzoyloxyphenylketene indicates that the ring-
opened acyloxyketenes are ca. 9 kcal/mol more stable than the corresponding 1,3-dioxolium-4-olates.
Since the synthesis of sydnones via intramolecular dehydra-
tion of N-nitroso-N-phenylglycine by Earl and Mackney1 and
the introduction of the concept of mesoionic molecules by Baker
and Ollis,2 preparation and synthetic application of many
mesoionic compounds have been reported.3 Mesoionic com-
pounds 1 cannot be represented satisfactorily by normal covalent
structures but by many resonance forms bearing positively and
negatively charged atoms.2
Typical mesoionic compounds composed of nitrogen and
oxygen atoms as ring heteroatoms are shown in Scheme 1.
Mesoionic compounds contain six ring electrons delocalizing
over p-orbitals of carbon atoms and heteroatoms, which suggests
a kind of aromaticity. However, as the energy level of p-orbitals
of an oxygen atom is lower than that of a nitrogen and a carbon
atom, resonance stability of mesoionic systems containing an
oxygen atom should be smaller than those containing nitrogen
atoms.
* To whom correspondence should be addressed. Tel/fax: +81-6-6879-4593.
(1) Earl, J. C.; Mackney, A. W. J. Chem. Soc. 1935, 899.
(2) Baker, W.; Ollis, W. D.; Poole, V. D. J. Chem. Soc. 1949, 307; 1950,
1542.
(3) (a) Ohta, M.; Kato, H. Nonbezenoid Aromatics I; Snyder, J. P., Ed.;
Academic Press: New York, 1969; 117. (b) Ollis, W. D.; Ramsden, C. A.
In AdVances in Heterocyclic Chemistry; Katritzky, A. R., Boulton, A. J.,
Ed.; Academic Press: New York, 1976, Vol. 19, p 1. (c) Newton, C. G.;
Ramsden, C. A. Tetrahedron 1982, 38, 2965. (d) Osterhout, M. H.; Nadler,
W. R.; Padwa, A. Synthesis 1994, 123.
10.1021/jo060074e CCC: $33.50 © 2006 American Chemical Society
Published on Web 06/16/2006
5162
J. Org. Chem. 2006, 71, 5162-5170

Generation of Acyloxyketenes from Mesoionic 1,3-Dioxolium-4-olates
SCHEME 1
the 1,3-dioxolium-4-olates 5, giving 1,3-cycloadducts 7 and
furan derivatives 8, respectively, as shown in Scheme 2.8,9
Moreover, the reaction with electron-deficient azo compounds
gave triacylamidine derivatives 10 in good yields through several
steps from 1,3-dipolar cycloadducts 9.11 The formation of 7, 8,
and 10 indicates that generation of 5 resulted from the
intramolecular carbenoid/carbonyl reaction of phenyldiazoacetic
anhydride derivatives 6. And also we observed that as soon as
phenyldiazoacetic anhydride derivatives 6 were added to a
benzene solution of Rh2(OAc)4 without any dipolarophiles, the
solution turned to red color, which faded instantly. The very
short lifetime of the red color suggests that the reddish 1,3-
dioxolium-4-olates 5 generated are unstable and rapidly convert
to other chemical species.
TABLE 1. Heats of Formation and Heats of Hydrogenation
(kcal/mol) of Mesoionic Compounds Calculated by PM3
2
3
4
5
∆Hf (R ) H)
∆Hf of hydrogenated compounds
heats of hydrogenation
38.0
19.2
18.8
4.9
-22.0
26.9
17.9
-18.6
36.5
-16.4
-60.5
44.5
To investigate the behavior of 1,3-dioxolium-4-olates 5, we
attempted to trap the chemical species derived from 5.
According to our PM3 calculation, the heats of hydrogenation
for 2,5-diphenyl-substituted mesoionic 1,3-imidazolium-4-olate
2,4 mu¨nchnone 3,5 isomu¨nchnone 4,3d,6,7 and 1,3-dioxolium-4-
olate 58,9 increase in the order of 2, 3, 4, and 5 as shown in
Table 1. The largest heat of hydrogenation for the 1,3-dioxolium-
4-olate 5 indicates the smallest resonance stability of the system.
In fact, diphenyl-substituted mesoionic 1,3-imidazolium-4-olate
2, mu¨nchnone 3, and isomu¨nchnone 4 can be isolated as stable
crystals, but 1,3-dioxolium-4-olates 5 cannot be isolated as stable
compounds. Unstable 1,3-dioxolium-4-olate has a carbonyl ylide
resonance structure. To produce the 1,3-dioxolium-4-olate, we
used intramolecular carbenoid/carbonyl reaction method, which
has very often been reported as a traditional method for
generation of carbonyl ylides.10 So, we prepared phenyldiazo-
acetic anhydride derivatives 6 as precursors of 1,3-dioxolium-
4-olates. We previously carried out π-allyl palladium complex-
catalyzed decomposition of 6 in the presence of very reactive
olefinic and acetylenic dipolarophiles and succeeded in trapping
Results and Discussion
Preparation of Phenyldiazoacetic Anhydride Derivatives
6a-d. We prepared phenyldiazoacetic anhydride derivatives
6a-d from the reaction between triethylamine salt of phenyl-
diazoacetic acids 14 and acyl chlorides in CH2Cl2 at room
temperature as shown in Scheme 3. p-Nitro- and p-chlorophen-
yldiazoacetic acids 14a,b were prepared by diazo transfer of
the corresponding 2-methylthioethyl phenylacetates 11a,b using
12
KF-Al2O3 as base followed by isolation of sulfonium salts
13a,b after quaternarization by methyl iodide, saponification,
and then acidification. The procedure described in Scheme 3
can be applied to the synthesis of phenyl- and p-tolyldiazoacetic
acids, in which the p-toluenesulfonylhydrazones of the corre-
sponding 2-methylthioethyl benzoylformates were used for
preparation of 2-methylthioethyl phenyldiazoacetates 12.13 p-
Nitrophenyldiazoacetic acid 14a was also prepared using pyranyl
p-nitrophenylacetate as starting compounds according to the
procedure described in the literature.14
(4) (a) Hamaguchi, M.; Ibata, T. Chem. Lett. 1975 169. (b) Potts, K. T.;
Chen, S. J. J. Org. Chem. 1977, 42, 1639.
(5) Huisgen, R.; Gotthardt, H.; Bayer, H. O.; Schaefer, F. C. Angew.
Chem. 1964, 76, 185.
(6) (a) Hamaguchi, M.; Ibata, T. Tetrahedron Lett. 1974, 4475. (b) Ibata,
T.; Hamaguchi, M.; Kiyohara, H. Chem. Lett. 1975, 21. (c) Hamaguchi,
M.; Ibata, T. Chem. Lett. 1975, 499. (d) Hamaguchi, M. J. Chem. Soc.,
Chem. Commun. 1978, 247. (e) Hamaguchi, M.; Ibata, T. J. Chem. Soc.,
Chem. Commun. 1980, 230.
(7) (a) Freeman, J. P.; Haddadin, M. J.; Rastatter, W. H.; Chancellor, T.
Tetrahedron Lett. 1982, 23, 815. (b) Haddadin, M. J.; Kattarn, A. M.;
Freeman, J. P. J. Org. Chem. 1982, 47, 723.
Rh2(OAc)4-Catalyzed Decomposition of 6a-d in the Pres-
ence of Dihydrofuran. A benzene solution of p-nitrophenyl-
diazoacetic p-chlorobenzoic anhydride 6a, a catalytic amount
of Rh2(OAc)4, and 20 molar equiv of dihydrofuran 16 was
stirred at 30 °C for 5 h (Scheme 4). The NMR spectrum of the
reaction mixture showed almost quantitative formation of a
single product.
As dihydrofuran is known to be a dipolarophile, we expected
that the product might be the 1,3-dipolar cycloadduct 17a.
However, the IR spectrum exhibited two strong carbonyl
absorptions at 1789 and 1716 cm-1, which suggests a cyclobu-
tanone derivative, namely, the [2 + 2] ketene adduct 18a bearing
a four-membered cyclic ketone and an ester group. Configura-
tion of the cyclobutanone 18a was determined on the basis of
the NMR spectrum.
In the NMR spectrum of 18a, the Ha proton (δ 3.17, ddd) of
OCH2 appeared at 0.7 ppm higher field than Hb (δ 3.89, ddd)
due to the shielding effect of the endo-p-nitrophenyl group.15
The bridgehead proton corresponding to the Hc proton of
bicyclic cyclobutanone bearing an endo-phenyl group was
reported to appear around 4.35 ppm.15,17a Rh2(OAc)4-catalyzed
decomposition of phenyldiazoacetic anhydride 6b and 6d in the
(8) Hamaguchi, M.; Nagai, T. J. Chem. Soc., Chem. Commun. 1985,
190.
(9) Hamaguchi, M.; Nagai, T. J. Chem. Soc., Chem. Commun. 1985,
1319.
(10) (a) Mehta, G.; Muthusamy, S. Tetrahedron 2002, 58, 9477. (b)
Padwa, A.; HelV. Chim. Acta 2005, 88, 1357. (c) Osterhout, M. H.; Nadler,
W. R.; Padwa, A. Synthesis 1994, 123. (d) Hodgson, D. M.; Glen, R.; Grant,
G. H.; Redgrave, A. J. J. Org. Chem. 2003, 68, 581. (e) Muthusamy, S.;
Babu, S. A.; Gunanathan, C.: Ganguly, B.; Suresh, E.; Dastidar, P. J. Org.
Chem. 2002, 67, 8019. (f) Padwa, A.; Sheeman, S. M.; Straube, C. S., J.
Org. Chem. 1999, 64, 8648. (g) Padwa, A.; Precedo, L.; Semones, M. A.
J. Org. Chem. 1999, 64, 4079. (h) Padwa, A.; Price, A. T. J. Org. Chem.
1998, 63, 556. (i) Padwa, A.; Price, A. T. J.; Zhi, L. J. Org. Chem. 1996,
61, 2283. (j) Padwa, A.; Zhi, L. J. Am. Chem. Soc. 1992, 114, 593. (k)
Padwa, A.; Snyder, J. P.; Curtis, E. A.; Sheeman, S. M.; Worsencroft, K.
J.; Kappe, C. O. J. Am. Chem. Soc. 2000, 122, 8155. (l) Padwa, A.;
Hasegawa, T.; Liu, B.; Zhang, Z. J. Org. Chem. 2000, 65, 7124. (m)
Kitagaki, S.; Yasugahira, M.; Anada, M.; Nakajima, M.; Hashimoto, S.
Tetrahedron Lett. 2000, 41, 5931. (n) Hodgston, D. M.; Villalonga-Barber,
C. Tetrahedron Lett. 2000, 41, 5597. (o) Kataoka, O.; Kitagaki, S.;
Watanabe, N.; Kobayashi, J.; Nakamura, S.; Shiro, M.; Hashimoto, S.
Tetrahedron Lett. 1998, 39, 2371. (p) Kitagaki, S.; Anada, M.; Kataoka,
O.; Matsuno, K.; Umeda, C.; Watanabe, N.; Hashimoto, S. J. Am. Chem.
Soc. 1999, 121, 1417. (q) Hamaguchi, M.; Ibata, T. Chem. Lett. 1976, 287.
(r) Ibata, T.; Motoyama, T.; Hamaguchi, M. Bull. Chem. Soc. Jpn 1976,
49, 2298.
(11) Hamaguchi, M.; Tomida, N.; Mochizuki, E.; Oshima, T. Tetrahedron
Lett. 2005, 46, 1259.
(12) Yamawaki, J.; Ando, T. Chem. Lett. 1979, 755.
(13) Unpublished results.
(14) Schank, K. Ann. 1969, 723, 205.
J. Org. Chem, Vol. 71, No. 14, 2006 5163

Hamaguchi et al.
SCHEME 2
SCHEME 3
TABLE 2. Yields and Chemical Shifts of Ha, Hb, Hc, and Hd
presence of dihydrofuran also gave single [2 + 2] ketene adducts
18b and 18d in good yields (Table 2). Reaction of acetic
p-nitrophenyldiazoacetic anhydride 6c with dihydrofuran also
gave a single product, the bicyclic cyclobutanone 18c. The
structure of 18c was confirmed by X-ray analysis.16 The IR and
NMR spectra of 18c showed very pattern similar to those of
18a,b,d as shown in Table 2. In particular, similarities of signals
of furan ring protons of 18a-d strongly support endo-phenyl
Protons of Cyclobutanones 18 from Acyloxyketenes 15 and
Dihydrofuran
chemical shift/δ
isolated yields/%
Ha
Hb
Hc
Hd
18a
18b
18c
18d
86
90
74
84
3.17
3.16
3.10
3.13
3.89
4.88
4.84
4.86
4.49
4.49
4.37
4.41
5.36
5.35
5.22
5.33
(15) Naidorf-Meir, S. Hassner, A. J. Org. Chem. 1992, 57, 5102. NMR
spectrum of the adduct between dihydrofuran and phenylchloroketene
showed very similar pattern. Chemical shifts of the furan ring protons of
the adduct: δ 5.08 (d, J ) 6 Hz, H-l), 4.35 (dddt, J ) 9.5, 6, 1.5, 0.5 Hz,
H-5), 3.95 (ddd, J ) 10, 8, 2 Hz, H-3 eq), 3.40 (dddt, J ) 11, 9.6, 0.5 Hz,
H-3 ax), 2.27 (ddddd, J ) 13, 7, 4.5, 2, 0.5 Hz, H-4 eq), 2.04 (dddd, J )
13, 10.5, 9, 8 Hz, H-4 ax).
(16) (a) Hamaguchi, M.; Tomida, N.; Mochizuki, E.; Oshima, T.
Tetrahedron Lett. 2003, 44, 7945. (b) Crystallographic data for compound
18c have been deposited with the Cambridge Crystallographic Data Centre
as supplementary publication number CCDC 218209. Copies of the data
can be obtained, free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44(0)-1223-336033 or e-mail: deposit@
ccdc.cam.ac.uk).
(17) (a) Brady, W. T.; Parry, F. H., III; Roe, R., Jr.; Hoff, E. F., Jr.
Tetrahedron Lett. 1970, 819. (b) Brady, W. T.; Roe, R., Jr. J. Am. Chem.
Soc. 1970, 92, 4618. (c) Brady, W. T.; Hoff, E. F., Jr. J. Org. Chem. 1970,
35, 3733. (d) Brook, P. R.; Duke, A, J.; Duke, J, R. C. J. Chem. Soc.,
Chem. Commun. 1970, 574. (e) Brook, P. R.; Harrison, J. M.; Duke, A, J.
J. Chem. Soc., Chem. Commun. 1970, 589. (f) DoMinh, T.; Strausz, O. P.
J. Am. Chem. Soc. 1970, 92, 1766. (g) Roberts, M. R. S.; Dieffenbacher,
A.; Dreiding, A. S. HelV. Chim. Acta 1970, 53, 417. (h) Woodward, R. B.;
Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1969, 8, 847.
groups in 18a-d. The predominant formation of cyclobutanones
18a-d indicates that 1,3-dioxolium-4-olates 5a-d initially
formed by intramolecular carbenoid/carbonyl reaction undergo
ring-opening to acyloxyketenes 15a-d faster than 1,3-dipolar
cycloaddition with dihydrofuran, and the resultant acyloxy-
ketenes 15a-d undergo [2 + 2] cycloaddition with dihydro-
furan. The bicyclic cyclobutanones 18a-d bearing the endo-
p-nitrophenyl group should be sterically more crowded than the
other isomer bearing the exo-p-nitrophenyl group. The formation
of sterically crowded cyclobutanones in the [2 + 2] cycload-
dition of unsymmetrical ketenes with the ketenophiles has been
reported.17 The predominant formation of sterically crowded
cyclobutanones in the [2 + 2] cycloaddition of ketenes has been
explained by kinetic control, that is, initial crosswise approach
of both components with minimum steric repulsion of a bulky
substituent of ketene with a ketenophile ([π2s + π2a]) followed
by bond formation in a way of smooth increase in overlap as
5164 J. Org. Chem., Vol. 71, No. 14, 2006

Generation of Acyloxyketenes from Mesoionic 1,3-Dioxolium-4-olates
TABLE 3. Ratios of 20, 21, and 22 in the Reaction with
Cyclopentadiene 19a
SCHEME 4
X
R
20/%
21/%
22/%
a
b
c
NO2
NO2
NO2
Cl
p-ClC6H4
p-CH3OC6H4
CH3
21
31
17
13
55
50
55
60
24
19
28
27
d
p-ClC6H4
1
a Determined by H NMR.
3). The structure of 20a was determined on the basis of IR
spectrum showing two carbonyl absorptions at 1787 and 1717
cm-1 and NOE difference analysis. NOE (1.5%) of the olefinic
proton Hb at higher field was observed on irradiation of the
nitrophenyl proton Ha, indicating endo-p-nitrophenyl group. 1,3-
Cycloadducts 21a and 22a were decomposable over silica gel
in chromatography. We succeeded in crystallization of major
component 21a by treatment of the reaction mixtures with ether.
IR spectrum of the major adduct 21a exhibited a single carbonyl
absorption at 1793 cm-1, which is characteristic of a strained
bicyclic lactone, namely, a 1,3-dipolar cycloadduct between 1,3-
dioxolium-4-olate 5a and cyclopentadiene 19. The configuration
of 21a was determined by NOE difference analysis. NOE of
the signals of Ha (1.6%), Hc (6.5%), and Hg (4.9%) was
observed on the irradiation of the signal of the olefinic proton
Hb. Small coupling constant between Hg and Hf also supports
the exo-adduct 21a. Although [2 + 2] ketene adducts 20b,c,d
in the reaction of 6b-d with 19 were isolated without
decomposition by column chromatography, major products
21b,c,d decomposable in column chromatography were isolated
by treatment of the reaction mixture with ether. In the reaction
of 6c, isomeric 1,3-cycloadducts 21c and 22c were isolated in
a pure state by fractional recrystallization. Although the other
adducts 22a,b,d could not be isolated, their NMR spectra were
analyzed from the NMR spectra of the filtrate containing
20a,b,d, 21a,b,d, and 22a,b,d after isolation of 21a,b,d. 1HNMR
and difference NOE analysis of pure 21c and 22c were inspected
in detail, leading to the structural determination as shown in
Scheme 6. Chemical shifts and coupling patterns of 21a,b,d
and 22a,b,d closely resemble 21c and 22c, respectively, as
shown in Tables 4 and 5. Formation of 21 and 22 can be
rationalized by the fact that cyclopentadiene 19 is a reactive
the new σ-bonds leads to the prediction that the larger substituent
of the ketene will be endo in the cycloadduct.17d,e
Rh2(OAc)4-Catalyzed Decomposition of 6a-d in the Pres-
ence of Cyclopentadiene. Cylopentadiene 19 is one of the most
well-known ketenophiles, which has very often been used in
the reaction with ketenes. However, on decomposition of
diazoacetic anhydride 6a in the presence of 5 molar equiv of
cyclopentadiene 19, only [2 + 2] ketene adducts 20a was
isolated in a low yield by column chromatography on silica
gel. However, NMR spectrum of the reaction mixture showed
formation of 1,3-dipolar cycloadducts 21a and 22a between 1,3-
dioxolium-4-olate 5a and 19 in a ratio of ca. 2:1 as main
products along with 20a as a minor product (Scheme 5, Table
SCHEME 5
J. Org. Chem, Vol. 71, No. 14, 2006 5165

Hamaguchi et al.
SCHEME 6
SCHEME 7
TABLE 4. Chemical Shifts of Ha, Hb, Hc, Hd, He, Hf, and Hg
Protons of 1,3-Adducts 21 between 5 and Cyclopentadiene 19
chemical shift/δ
21
Ha
Hb
Hc
Hd
He
Hf
Hg
21a
21b
21c
21d
7.83
7.84
7.73
7.57
5.01
5.00
4.96
5.09
5.78
5.77
5.82
5.73
2.07
2.14
2.41
2.04
2.51
2.53
2.66
2.47
3.59
3.62
3.17
3.55
3.81
3.79
3.67
3.74
TABLE 6. Isolated Yields of Cycloadducts 24 in the Reaction of
6a-d with carbodiimides 23a and 23b
24
Ar
R
R′
isolated yields/%
TABLE 5. Chemical Shifts of Ha, Hb, Hc, Hd, He, Hf, and Hg
Protons of 1,3-Adducts 22 between 5 and Cyclopentadiene 19
24a
24b
24c
24d
24e
24f
p-NO2C6H4
p-NO2C6H4
p-NO2C6H4
p-NO2C6H4
p-NO2C6H4
p-NO2C6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-CH3OC6H4
p-CH3OC6H4
CH3
iPr
96
96
90
96
92
90
95
92
c-C6H11
iPr
chemical shift/δ
c-C6H11
iPr
c-C6H11
22
Ha
Hb
Hc
Hd-He
Hf
Hg
22a
22b
22c
22d
7.86
7.87
7.80
a
5.82
5.81
5.74
5.78
6.06
6.05
6.00
5.00
2.50-2.70
2.61-2.65
2.47-2.52
2.47-2.59
3.60
3.67
3.18
3.54
3.80
3.77
3.63
3.81
CH3
24g
24h
p-ClC6H4
p-ClC6H4
iPr
p-ClC6H4
c-C6H11
a Aromatic protons of 22d were obscured by 20d and 21d.
SCHEME 8
dipolarophile due to the strained conjugated double bonds as
well as a reactive ketenophile.
Therefore, large parts of 1,3-dioxolium-4-olate 5 generated
could undergo rapid 1,3-dipolar cycloaddition with 19 to give
isomeric 1,3-adducts 21 and 22 before the ring opening to
acyloxyketenes 15. The acyloxyketenes 15 generated from the
remaining 1,3-dioxolium-4-olate 5 would react with 19 to give
a single isomer of [2 + 2] ketene adducts 20 bearing endo-aryl
groups in low yields. Product distribution in the reaction of
6a-d with cyclopentadiene was shown in Table 3.
Rh2(OAc)4-Catalyzed Decomposition of 6a-d in the Pres-
ence of Carbodiimides 23a,b. We attempted to trap the
acyloxyketene using more reactive ketenophiles (Scheme 7).
Generation of 5a in the presence of diisopropylcarbodiimide
23a or dicyclohexylcarbodiimide 23b (DCC) resulted in quan-
titative formation of [2 + 2] cycloadducts 24a and 24b,
respectively. Other aryldiazoacetic anhydrides 6b-d with 23a,b
also gave 3-acyloxy-2-imino-4-oxoazetidine derivatives 24c-h
in high isolated yields as shown in Table 6. IR spectra of 24a-h
exhibited characteristic absorptions of 3-acyloxy-2-imino-4-
oxoazetidines at ca. 1820 (â-lactam CdO), 1720 (ester CdO),
and 1700 cm-1 (imino R′-NdC).
Rh2(OAc)4-Catalyzed Decomposition of 6a in the Presence
of the Imine 25. A benzene solution of 6a, a catalytic amount
of Rh2(OAc)4, and 5 equiv of N-p-chlorobenzylidene-p-toluidine
25 was stirred at 50 °C for 2 h. The reaction mixture was
chromatographed over silica gel to give the â-lactams 26 and
27 in a ratio of 7:3 (54% isolated yield) (Scheme 8). Structures
of 26 and 27 were determined on the basis of their NMR spectra.
p-Nitrophenyl and p-chlorophenyl protons of 26 appeared at
higher field than the corresponding protons of 27.
Rh2(OAc)4-Catalyzed Decomposition of 6a-d in the Pres-
ence of Methanol. Generation of 5a from Rh2(OAc)4-catalyzed
decomposition of diazoacetic anhydride 6a in the presence of
5-fold molar excesses of methanol resulted in almost quantitative
formation of methyl R-p-chlorobenzoyloxy-p-nitrophenylacetate
28a (isolated yield 92%). Phenyldiazoacetic anhydride deriva-
tives 6b-d also gave the same results (Scheme 9).
In previous papers describing isolation of 1,3-dipolar cy-
cloadducts 7 and furans 8 in the reaction of 6 with olefinic and
acetylenic dipolarophiles, we used a π-allyl palladium complex
as a catalyst.8,9 To investigate the effects of catalysts on
formation of 1,3-dioxolium-4-olates 5 or the acyloxyketenes,
Rh2(OAc)4-catalyzed decomposition of 6 in the presence of
reactive olefinic and acetylenic dipolarophiles was carried out,
giving the same results as the case of the Pd catalyst, which
indicates that the rhodium carbenoid also attacks the intramo-
5166 J. Org. Chem., Vol. 71, No. 14, 2006

Generation of Acyloxyketenes from Mesoionic 1,3-Dioxolium-4-olates
SCHEME 9
SCHEME 10
TABLE 7. Heats of Formation of 1,3-Dioxolium-4-olates 5 and the
Corresponding Acyloxyketenes 15
∆Hfa/kcal mol-1
entry
Ar
Ph
Ph
CH3
R
5
15
∆∆Hf/kcal mol-1
captured by various ketenophiles to give [2 + 2] cycloadducts
such as cyclobutanones 18, 20, 4-iminoazetidine-2-ones 24, and
â-lactams 26, 27. However, in the reaction with cyclopentadiene
19, large parts of 1,3-dioxolium-4-olates 5 were trapped before
the ring-opening to acyloxyketenes 15 by 19 as reactive
dipolarophile to give 1,3-adducts 21, 22 as main products and
[2 + 2] ketene adduct 20 as minor product.
1
2
3
Ph
CH3
Ph
-16.4
-50.5
-48.8
-25.4
-60.0
-58.3
9.0
9.5
9.5
a Calculated by PM3.
lecular carbonyl oxygen atom to initially produce the 1,3-
dioxolium-4-olate 5.
Experimental Section
Transient appearance and rapid disappearance of the red color
of the 1,3-dioxolium-4-olate 5a and the formation of the
acyloxyketene adducts 18a-d, 20a, 24a-h, 26, and 27 in the
presence of ketenophiles such as dihydrofuran, cyclopentadiene,
carbodiimides 23, and the imine 25 indicates that the initially
formed 1,3-dioxolium-4-olates 5 are too unstable to survive and
undergo rapid ring-opening to the acyloxyketenes 15, which
react with ketenophiles to give [2 + 2] cycloadducts.
PM3 calculation of heats of formation of the 2,5-diphenyl-
1,3-dioxolium-4-olate 5 and the corresponding acyloxyketene
15 indicates that the acyloxyketene 15 is 9-9.5 kcal/mol more
stable than the 1,3-dioxolium-4-olate 5 as shown in Table 7,
strongly supporting that 1,3-dioxolium-4-olates 5 undergo fast
ring opening to the acyloxyketenes 15 followed by [2 + 2]
cycloaddition with the ketenophiles.
Although ring-opening of an isolable mesoionic compound
to a ketene was observed in mu¨nchnones 3, the ring-opening
of 3 to acylaminoketenes 29 requires long heating of 3 in the
presence of ketenophiles such as imines, carbodiimides, and
enamines, resulting in formation of [2 + 2] ketene adducts 30
(Scheme 10).18 According to our PM3 calculation, the ring-
opened acylaminoketene 29 is 2.2 kcal/mol less stable than the
ring-closed mu¨nchnone 3, indicating that long heating of
mu¨nchnone was required in order to react as acylaminoketene
with ketenophiles.
General Methods. Melting points were not corrected. 1H NMR
(270.05 MHz) and 13C NMR (60.40 MHz) spectra were recorded
in a CDCl3 solution using TMS as an internal standard.
Preparation of Aryldiazoacetic Acid (14). Method A: Ac-
cording to the procedure described in the literature, p-nitrophenyl-
diazoacetic acid was prepared by diazo transfer of 1-pyranyl
p-nitrophenylacetate followed by hydrolysis.14 Method B: KF-
Al2O3 (41 g) was added to an acetonitrile solution (400 mL) of
toluenesulfonyl azide (0.1 mol) and 2-methylthioethyl aryl acetate
11 (0.1 mol), prepared from the corresponding acid chloride and
2-methylthioethanol in CH2Cl2, and the resultant solution was stirred
for 120 h at room temperature. After filtration of the reaction
mixture, acetonitrile was removed under the reduced pressure and
the residue was recrystallized from ether/pentane.
2-Methylthioethyl p-nitrophenylacetate (11a): 80%; mp 42-
1
43 °C; H NMR (CDCl3) δ 8.19 (d, 2 H, J ) 8.7 Hz), 7.47 (d, 2
H, J ) 8.9 Hz), 4.30 (t, 2 H, J ) 6.7 Hz), 3.76 (s, 2H), 2.72 (t, 2
H, J ) 6.9 Hz), 2.12 (s, 3 H); IR (KBr) 2924, 2104, 1704, 1593,
1514, 1330, 1228, 1161, 1025, 851 cm-1. Anal. Calcd for C11H13O4-
NS: C, 51.7; H, 5.13; N, 5.49. Found: C, 51.50; H, 5.01; N, 5.49.
2-Methylthioethyl p-nitrophenyldiazoacetate (12a): yellow
needles; mp 51-52 °C; 1H NMR (CDCl3) δ 8.23 (d, 2 H, J ) 8.6
Hz), 7.66 (d, 2 H, J ) 8.7 Hz), 4.48 (t, 2 H, J ) 6.7 Hz), 2.82 (t,
2 H, J ) 6.7 Hz), 2.18 (s, 3 H); IR (KBr) 2926, 1731, 1605, 1519,
1348, 1164, 717 cm-1. Anal. Calcd for C11H11O4N3S: C, 46.98;
H, 3.94; N, 14.98. Found: C, 47.07; H, 3.92; N, 14.61.
2-p-Nitrophenyldiazoacetoxyethyl dimethylsulfonium iodide
1
(13a): mp 123 °C; H NMR (DMSO-d6) δ 8.27 (d, 2 H, J ) 8.7
Conclusion
Hz), 7.81 (d, 2 H, J ) 8.7 Hz), 4.73-4.68 (m, 2 H), 3.78-3.70
(m, 2 H), 2.92 (s, 6 H); IR (KBr) 2975, 2099, 1689, 1595, 1498,
1385, 1339, 1232, 1163 cm-1. Anal. Calcd for C12H14O4N3SI: C,
34.05; H, 3.33; N, 9.93. Found: C, 34.21; H, 3.28; N, 9.96.
p-Nitrophenyldiazoacetic acid (14a): 82%; mp 133-136 °C
(lit.14 mp 125 °C).
We have showed that the 1,3-dioxolium-4-olates 5 generated
from aryldiazoacetic anhydride derivatives 6 are the most
unstable mesoionic system among the related mesoionic com-
pounds, so that they cannot exist as stable compounds and
undergo rapid ring-opening to acyloxyketenes 15, which are
2-Methylthioethyl p-chlorophenylacetate (11b): colorless oil;
1
bp 145 °C/1 mmHg; H NMR (CDCl3) δ 7.30 (d, 2 H, J ) 8.6
(18) (a) Huisgen, R.; Funke, E.; Schaefer, F. C.; Knorr, R. Angew. Chem.,
Int. Ed. Engl. 1967, 6, 367. (b) Bayer, H. O.; Huisgen, R.; Knorr, R.;
Schaefer, F. C. Chem. Ber. 1971, 104, 3222.
Hz), 7.21 (d, 2 H, J ) 8.6 Hz), 4.27 (t, 2H, J ) 6.9 Hz), 3.61 (s,
2H), 2.71 (t, 2 H, J ) 6.9 Hz), 2.11 (s, 3 H); IR (KBr) 2919, 1738,
J. Org. Chem, Vol. 71, No. 14, 2006 5167

Hamaguchi et al.
1493, 1410, 1252, 1155, 1091, 1016, 808 cm-1; HRMS calcd for
C11H13ClO2S 244.0325, found 244.0331.
Anal. Calcd for C15H8O3N2Cl2: C, 53.76; H, 2.41; N, 8.36.
Found: C, 53.71; H, 2.51; N, 8.46.
Reaction of Aryldiazoacetic Anhydride 6a-d with 2,3-
Dihydrofuran. A benzene solution (10 mL) of diazo acid anhydride
6 (0.5 mmol), dihydrofuran (10 mmol), and a catalytic amount of
Rh2(OAc)4 was stirred at 30 °C for 5 h. The NMR spectrum of the
reaction mixture indicated the quantitative formation of single
adducts 18. The reaction mixture was chromatographed over silica
gel using benzene as an eluent. The adducts 18 were recrystallized
from ether/pentane.
2-Methylthioethyl p-chlorophenyldiazoacetate (12b): mp 30
1
°C; H NMR (CDCl3) δ 7.42 (d, 2 H, J ) 8.9 Hz), 7.35 (d, 2 H,
J ) 8.9 Hz), 4.44 (t, 2 H, J ) 6.9 Hz), 2.80 (t, 2 H, J ) 6.9 Hz),
2.17 (s, 3 H); IR (KBr) 2089, 1702, 1495, 1340, 1244, 1155 cm-1
.
Anal. Calcd for C11H11O2SN2Cl: C, 48.80; H, 4.10; N, 10.35.
Found: C, 48.94; H, 4.07; N, 10.31. An etherial solution (20 mL)
of 2-methylthioethyl 4-chlorophenyldiazoacetate (12b) (5.4 g, 20
mmol) and methyl iodide (15 g, 106 mmol) was allowed to stand
for 7 days. Precipitated crystal was filtered and washed with ether
(yield 85%).
7-(p-Nitrophenyl)-6-oxo-2-oxabicyclo[3.2.0]hept-7-yl p-chloro-
1
benzoate (18a): 86%; white crystal; mp 117-118 °C; H NMR
(CDCl3) δ 8.29 (d, 2 H, J ) 8.9 Hz), 7.86 (d, 2 H, J ) 8.9 Hz),
7.83 (d, 2 H, J ) 8.9 Hz), 7.40 (d, 2 H, J ) 8.9 Hz), 5.36 (d, 1 H,
J ) 6.9 Hz), 4.49 (ddd, 1 H, J ) 10.6, 7.3, 3.3 Hz), 3.89 (ddd, 1
H, J ) 9.2, 7.9, 4.0 Hz), 3.17 (td, 1 H, J ) 9.2, 6.9 Hz), 2.21-
2.04 (m, 2 H); IR (KBr) 1789, 1716, 1594, 1521, 1347, 1294, 1097,
1015, 854 cm-1. Anal. Calcd for C19H14ClNO6: C, 58.85; H, 3.64;
N, 3.61. Found: C, 58.65; H, 3.66; N, 3.64.
2-p-Chlorophenyldiazoacetoxyethyl dimethylsulfonium iodide
(13b): mp 119-120 °C; 1H NMR (DMSO-d6) δ 7.56 (d, 2 H, J )
8.9 Hz), 7.50 (d, 2 H, J ) 8.7 Hz), 4.69-4.64 (m, 2 H), 3.73-
3.68 (m, 2 H), 2.94 (s, 6 H); IR (KBr) 2974, 2900, 2094, 1695,
1497, 1381, 1342, 1236, 1162, 1052, 808 cm-1. Anal. Calcd for
C12H14O2SN2ClI: C, 34.93; H, 3.42; N, 6.79. Found. C, 34.96; H,
3.39; N, 6.72.
7-(p-Nitrophenyl)-6-oxo-2-oxabicyclo[3.2.0]hept-7-yl p-meth-
oxybenzoate (18b): 90%; white cubes; mp 112-113 °C; 1H NMR
(CDCl3) δ 8.28 (d, 2H, J ) 8.9 Hz), 7.87 (d, 2H, J ) 8.9 Hz),
7.83 (d, 2H, J ) 8.9 Hz), 6.80 (d, 2H, J ) 8.9 Hz), 5.35 (d, 1H,
J ) 6.9 Hz), 4.49 (ddd, 1H, J ) 10.6, 6.9, 3.3 Hz), 3.91-3.84 (m,
1H), 3.85 (s, 3H), 3.16 (td, 1H, J ) 9.2, 7.3 Hz), 2.20-2.04 (m,
2H); IR (KBr) 1784, 1703, 1606, 1522, 1347, 1289, 1261, 1174,
1090, 854 cm-1. Anal. Calcd for C20H17NO7: C, 62.66; H, 4.47;
N, 3.65. Found: C, 62.79; H, 4.58; N, 3.68.
Preparation of p-Chlorophenyldiazoacetic Acid (14b). 2-p-
Chlorophenyldiazoacetoxyethyl dimethylsulfonium iodide (13b)
(4.13 g, 10 mmol) and a small amount of phenolphthalein as
indicator were dissolved in 500 mL of water at 50 °C. A diluted
aqueous sodium hydroxide (1%) solution was added dropwise to
the resultant solution under stirring in ice/water bath until the
solution turned red. After filtration of the aqueous reaction mixture,
the solution was acidified with diluted hydrochloric acid, giving
white crystals. The crystal was extracted with ether and dried over
magnesium sulfate. After evaporation of ether, p-chlorophenyldi-
azoacetic acid was crystallized as yellow powder (82%).
7-(4-Nitrophenyl)-6-oxo-2-oxabicyclo[3.2.0]hept-7-yl acetate
(18c): 74%; colorless cubes; mp 118-119 °C; 1H NMR (CDCl3)
δ 8.24 (d, 2 H, J ) 8.9 Hz), 7.74 (d, 2 H, J ) 8.9 Hz), 5.22 (d, 1
H, J ) 6.9 Hz), 4.37 (ddd, 1 H, J ) 10.2, 6.9, 3.6 Hz), 3.84 (ddd,
1 H, J ) 9.2, 7.6, 4.0 Hz), 3.10 (td, 1 H, J ) 9.2, 7.3 Hz), 2.18-
1.95 (m, 2 H), 2.11 (s, 3 H); IR (KBr) 1790, 1727, 1606, 1533,
1349, 1231, 1074, 1011, 849 cm-1. Anal. Calcd for C14H13NO6:
C, 57.73; H, 4.50; N, 4.81. Found: C, 57.52; H, 4.47; N, 4.82.
7-(p-Chlorophenyl)-6-oxo-2-oxabicyclo[3.2.0]hept-7-yl p-chlo-
1
14b: 82%; mp 109-110 °C dec; H NMR (CDCl3) δ 7.48 (d,
2 H, J ) 8.6 Hz), 7.36 (d, 2 H, J ) 8.6 Hz); IR (KBr) 3285, 2100,
1742, 1672, 1493, 1407, 1235, 1192, 1093, 1014, 834 cm-1. Anal.
Calcd for C8H5O2N2Cl: C, 48.87; H, 2.56; N, 14.25. Found: C,
48.95; H, 2.59; N, 14.23.
Preparation of Aryldiazoacetic Acid Anhydrides 6. Acyl
chloride (10 mmol) in CH2Cl2 (10 mL) was dropwise added to a
dichloromethane solution (20 mL) of aryldiazoacetic acid (10 mmol)
and triethylamine (10 mmol) at 0 °C. After the resultant solution
was stirred for 3 h, the reaction mixture was washed with water,
aqueous NaHCO3, diluted hydrochloric acid, and water and dried
over anhydrous MgSO4. After evaporation of CH2Cl2, treatment
of the residue with CH2Cl2/ether gave yellow crystals of diazoacetic
acid anhydrides.
1
robenzoate (18d): 84%; colorless cubes; mp 119-120 °C; H
NMR (CDCl3) δ 7.85 (d, J ) 8.9 Hz), 7.56 (d, 2 H, J ) 8.9 Hz),
7.41 (d, 2 H, J ) 8.9 Hz), 7.38 (d, 2 H, J ) 8.9 Hz), 5.33 (d, 1 H,
J ) 6.9 Hz), 4.41 (ddd, 1 H, J ) 10.6, 7.3, 3.6 Hz), 3.86 (ddd, 1
H, J ) 9.2, 7.9, 3.6 Hz), 3.13 (td, 1 H, J ) 9.6, 3.3 Hz), 2.17-
1.99 (m, 2 H); IR (KBr) 2877, 1781, 1719, 1595, 1492, 1402, 1296,
1235, 1091, 1014, 826, 756 cm-1. Anal. Calcd for C19H14Cl2O4:
C, 60.50: H, 3.74. Found: C, 60.43; H, 3.83.
p-Chlorobenzoic p-nitrophenyldiazoacetic anhydride (6a):
Reaction of Aryldiazoacetic Anhydride 6a-d with Cyclo-
pentadiene 19. A benzene solution (10 mL) of diazo acid anhydride
6 (0.5 mmol), cyclopentadiene 19 (2.5 mmol), and a catalytic
amount of Rh2(OAc)4 was stirred at 30 °C for 5 h. The NMR
spectrum of the reaction mixture indicated mixtures of 1,3-dipolar
adducts 21 and 22 between 1,3-dioxolium-4-olates 5 and 19 and
[2 + 2] ketene adducts 20. After benzene was removed under
reduced pressure, on treatment of the reaction mixtures with ether,
main products 1,3-dipolar adducts 21 crystallized as white solids.
Ether-soluble part was chromatographed over silica gel using
toluene as an eluent to give acyloxyketene adducts 20. In the
reaction of 6c with cyclopentadiene, 21c and 22c were separated
in a pure state by fractional recrystallization from the reaction
mixture.
1
55%; yellow powder; mp 148-149 °C; H NMR (CDCl3) δ 8.30
(d, 2 H, J ) 9.2 Hz), 8.01 (d, 2 H, J ) 8.9 Hz), 7.73 (d, 2 H, J )
9.2 Hz), 7.51 (d, 2 H, J ) 8.9 Hz); IR (KBr) 2113, 1770, 1704,
1592, 1508, 1337, 1260, 1224, 1115, 1036, 1008, 853 cm-1. Anal.
Calcd for C15H8ClN3O5: C, 52.12; H, 2.33; N, 12.16. Found: C,
52.00; H, 2.47; N, 12.23.
p-Methoxybenzoic p-nitrophenyldiazoacetic anhydride (6b):
1
63%; yellow powder; mp 138-139 °C; H NMR (CDCl3) δ 8.29
(d, 2 H, J ) 9.2 Hz), 8.02 (d, 2 H, J ) 8.9 Hz), 7.74 (d, 2 H, J )
9.2 Hz), 6.99 (d, 2 H, J ) 8.9 Hz), 3.91 (s, 3 H); IR (KBr) 2115,
1773, 1601, 1514, 1335, 1260, 1220, 1118, 1020, 996 cm-1. Anal.
Calcd for C16H11N3O6: C, 56.31; H, 3.25; N, 12.31. Found: C,
56.20; H, 3.36; N, 12.37.
Acetic p-nitrophenyldiazoacetic anhydride (6c): 60%; yellow
powder; mp 96-97 °C; 1H NMR (CDCl3) δ 8.28 (d, 2 H, J ) 9.2
Hz), 7.69 (d, 2 H, J ) 9.2 Hz), 2.33 (s, 3 H); IR (KBr) 2111,
7-(p-Nitrophenyl)-6-oxo-2-bicyclo[3.2.0]hept-7-yl p-chloroben-
zoate (20a): 21%; white powder; mp 126-127 °C; 1H NMR
(CDCl3) δ 8.22 (d, 2 H, J ) 9.0 Hz), 7.95 (d, 2 H, J ) 8.4 Hz),
7.59 (d, 2 H, J ) 9.0 Hz), 7.44 (d, 2 H, J ) 8.6 Hz), 5.82 (dq, 1
H, J ) 5.6, 1.8 Hz), 5.29 (dq, 1 H, J ) 5.6, 2.5 Hz), 4.52 (ddd, 1
H, J ) 9.8, 8.4, 2.1 Hz), 4.18 (br d, 1 H, J ) 8.5 Hz), 2.80 (d
quintet, 1 H, J ) 17.8, 2.5 Hz), 2.61 (ddq, 2 H, J ) 17.8, 9.7, 2.5
Hz); 13C NMR (CDCl3) δ 205.15, 163.87, 147.68, 141.18, 140.39,
136.04, 131.22, 128.95, 128.20, 127.81, 127.71, 123.43, 97.45,
60.22, 53.00, 34.78; IR (KBr) 1787, 1717, 1593, 1349 cm-1. Anal.
1801, 1709, 1592, 1509, 1337, 1159, 1092, 1002, 951, 854 cm-1
.
Anal. Calcd for C10H7N3O5: C, 48.20; H, 2.83; N, 16.86. Found:
C, 48.29; H, 2.91; N, 16.51.
p-Chlorobenzoic p-chlorophenyldiazoacetic anhydride (6d):
yellow plates; mp 144-145 °C; 1H NMR (CDCl3) δ 7.99 (d, 2 H,
J ) 8.6 Hz), 7.51-7.39 (m, 6 H); IR (KBr) 2117, 1775, 1700,
1593, 1493, 1280, 1257, 1216, 1092, 1039, 1007, 929, 826 cm-1
.
5168 J. Org. Chem., Vol. 71, No. 14, 2006

Generation of Acyloxyketenes from Mesoionic 1,3-Dioxolium-4-olates
Calcd for C20H14O5NCl; C, 62.57; H, 3.68; N, 3.65. Found: C,
62.72; H, 3.80; N, 3.65.
exo-Adduct (21a): white powder; mp 161-162 °C; H NMR
7-(p-Chlorophenyl)-6-oxo-2-bicyclo[3.2.0]hept-7-yl p-chloro-
benzoate (20d): 11%; oil; H NMR (CDCl3) δ 7.94 (d, 2 H, J )
1
1
8.6 Hz), 7.41 (d, 2 H, J ) 8.6 Hz), 7.34 (d, 4 H, J ) 2.1 Hz), 5.76
(dq, 1 H, J ) 5.6, 1.8 Hz), 5.35 (dq, 1 H, J ) 5.6, 2.3 Hz), 4.46
(ddd, 1 H, J ) 9.9, 8.7, 2.5 Hz), 4.14 (br d, 1 H, J ) 8.6 Hz), 2.74
(dquint, 1 H, J ) 17.6, 2.5 Hz), 2.74 (dquint, 1 H, J ) 17.6, 2.5
Hz), 2.56 (ddq, 3 H, J ) 17.6, 9.9, 2.5 Hz); IR (KBr) 1788, 1722,
1592, 1247, 1228, 1009 cm-1; HRMS(CI+) calcd for C20H15Cl2O3
MH+ ) 373.0398, found MH+ ) 373.0401.
(CDCl3) δ 8.32 (d, 2 H, J ) 8.9 Hz), 7.83 (d, 2 H, J ) 8.9 Hz),
7.60 (d, 2 H, J ) 8.6 Hz), 7.49 (d, 2 H, J ) 8.7 Hz), 5.78 (dq, 1
H, J ) 5.8, 1.8 Hz), 5.01 (dq, 1 H, J ) 5.8, 2.3 Hz), 3.77-3.84
(m, 1 H), 3.59 (ddd, 1 H, J ) 9.7, 7.1, 3.3 Hz), 2.51 (ddq, 1 H,
J ) 17.8, 9.7, 1.5 Hz), 2.07 (dquint, 1 H, J ) 18.0, 3.1 Hz); 13C
NMR (CDCl3) δ 170.35, 147.94, 137.54, 136.46, 135.80, 129.47,
128.95, 127.96, 126.86, 124.20, 123.51, 113.79, 87.61, 56.32, 50.69,
exo-Adduct (21d): white powder; mp 167.5-168 °C; 1H NMR
(CDCl3) δ 7.59 (d, 2 H, J ) 8.7 Hz), 7.57 (d, 2 H, J ) 8.9 Hz),
7.47 (d, 2 H, J ) 8.7 Hz), 7.43 (d, 2 H, J ) 8.7 Hz), 5.73 (dq, 1
H, J ) 5.8, 2.1 Hz), 5.09 (dq, 1 H, J ) 5.8, 2.3 Hz), 3.74 (br d, 1
H, J ) 7.6 Hz), 3.55 (ddd, 1 H, J ) 9.7, 7.3, 3.5 Hz), 2.47 (ddq,
1 H, J ) 17.8, 9.7, 1.3 Hz), 2.04 (dquint, 1 H, J ) 18.0, 2.3 Hz);
IR (KBr) 1793, 1605, 1494, 1372, 1092, 813 cm-1. Anal. Calcd
for C20H12Cl2O3; C, 64.36; H, 3.78. Found: C, 64.07; H, 3.82.
36.31; IR (KBr) 1793, 1605, 1522, 1367, 1351, 1090, 828 cm-1
.
Anal. Calcd for C20H14O5NCl; C, 62.57; H, 3.68; N, 3.65. Found:
C, 62.38; H, 3.60; N, 3.66.
1
endo-Adduct (22a): H NMR (CDCl3) δ 8.32 (d, 2 H, J ) 8.9
Hz), 7.86 (d, 2 H, J ) 8.9 Hz), 7.63 (d, 2 H, J ) 8.8 Hz), 7.49 (d,
2 H, J ) 8.6 Hz), 6.06 (dq, 1 H, J ) 5.7, 2.0 Hz), 5.82 (dq, 1 H,
J ) 5.7, 2.2 Hz), 3.77-3.84 (m, 1 H), 3.60 (dt, 1 H, J ) 9.3, 3.5
Hz), 2.61-2.65 (m, 2 H).
1
endo-Adduct (22d): H NMR (CDCl3) δ 6.00 (dq, 1 H, J )
5.9, 1.8 Hz), 5.78 (dq, 1 H, J ) 5.8, 2.1 Hz), 3.81 (dquint, 1 H,
J ) 9.7, 1.8 Hz), 3.51-3.57 (m, 1 H,), 2.47-2.59 (m, 2 H)
(aromatic protons of 22d were obscured by 20d and 21d).
General Procedure of the Reaction of Aryldiazoacetic An-
hydride 6a-d with Diisopropylcarbodiimides 23a and Dicyclo-
hexylcarbodiimides 23b. A benzene solution (5 mL) of aryldi-
azoacetic acid anhydride 6 (0.5 mmol), carbodiimide (0.55 mmol),
and a catalytic amount of Rh2(OAc)4 was stirred at 50 °C for 1 h.
After evaporation of benzene, treatment of the residue with CH2-
Cl2/pentane gave white crystals.
1-Isopropyl-2-isopropylimino-3-(p-nitrophenyl)-4-oxoazetidin-
3-yl p-chlorobenzoate (24a): 96%; white cubes; mp 209-210 °C;
1H NMR (CDCl3) δ 8.36 (d, 2 H, J ) 8.9 Hz), 8.03 (d, 2 H, J )
8.6 Hz), 7.76 (d, 2 H, J ) 8.9 Hz), 7.50 (d, 2 H, J ) 8.6 Hz), 4.15
(septet, 1 H, J ) 6.9 Hz), 3.47 (septet, 1 H, J ) 8.3 Hz), 1.56 (d,
3 H, J ) 6.9 Hz), 1.53 (d, 3 H, J ) 6.9 Hz), 1.00 (d, 3 H, J ) 6.3
Hz), 0.91 (d, 3 H, J ) 6.3 Hz); IR (KBr) 2970, 1820, 1736, 1704,
1524, 1348, 1274, 1089, 1011, 856, 753 cm-1. Anal. Calcd for
C22H22O5N3Cl: C, 59.53; H, 5.00; N, 9.47. Found: C, 59.47; H,
5.00; N, 9.43.
7-(p-Nitrophenyl)-6-oxo-2-bicyclo[3.2.0]hept-7-yl p-methoxy-
benzoate (20b): 24%; white powder; mp 142-143 °C; H NMR
1
(CDCl3) δ 8.21 (d, 2 H, J ) 9.0 Hz), 7.98 (d, 2 H, J ) 8.9 Hz),
7.59 (d, 2 H, J ) 9.0 Hz), 6.94 (d, 2 H, J ) 9.0 Hz), 5.81 (dq, 1
H, J ) 5.5, 2.2 Hz), 5.28 (dq, 1 H, J ) 5.5, 2.4 Hz), 4.53 (ddd, 1
H, J ) 10.1, 8.6, 2.2 Hz), 4.18 (br d, 1 H, J ) 8.4 Hz), 3.87 (s, 3
H), 2.79 (d quintet, 1 H, J ) 17.8, 2.2 Hz), 2.60 (ddq, 1 H, J )
17.8, 10.1, 2.2 Hz); 13C NMR (CDCl3) δ 205.61, 164.42, 163.94,
147.59, 141.65, 135.87, 132.03, 128.16, 127.99, 123.31, 120.74,
113.85, 97.12, 60.11, 55.55, 53.17, 34.67; IR (KBr) 1778, 1711,
1605, 1517, 1345, 1257, 1169 cm-1. Anal. Calcd for C20H17O6N;
C, 66.49; H, 4.52; N, 3.69. Found: C, 66.46; H, 4.52; N, 3.69.
exo-Adduct (21b): white powder; mp 159.5-160.0 °C; 1H NMR
(CDCl3) δ 8.31 (d, 2 H, J ) 8.9 Hz), 7.84 (d, 2 H, J ) 9.1 Hz),
7.58 (d, 2 H, J ) 8.9 Hz), 7.01 (d, 2 H, J ) 8.9 Hz), 5.77 (dq, 1
H, J ) 5.8, 1.8 Hz), 5.00 (dq, 1 H, J ) 5.8, 2.3 Hz), 3.87 (s, 3 H),
3.79 (br d, 1 H, J ) 6.9 Hz), 3.62 (ddd, 1 H, J ) 9.7, 7.1, 3.3 Hz),
2.53 (ddq, 1 H, 18.0, 9.7, 1.5 Hz), 2.14 (dquint, 1 H, J ) 18.0, 3.0
Hz); IR (KBr) 1791, 1608, 1523, 1349, 1251, 1173 cm-1. Anal.
Calcd for C20H17O6N; C, 66.49; H, 4.52; N, 3.69. Found: C, 66.21;
H, 4.54; N, 3.69.
endo-Adduct (22b): 1H NMR (CDCl3) δ 8.32 (d, 2 H, J ) 8.9
Hz), 7.87 (d, 2 H, J ) 9.1 Hz), 7.62 (d, 2 H, J ) 8.9 Hz), 7.01 (d,
2 H, J ) 8.8 Hz), 6.05 (dq, 1 H, J ) 5.8, 2.0 Hz), 5.81 (dq, 1 H,
J ) 5.6, 2.2 Hz), 3.87 (s, 3 H), 3.77 (dquint, 1 H, 9.3, 1.8 Hz),
3.67 (dt, 1 H, 9.4, 3.5 Hz), 2.50-2.7 (m, 2 H).
1-Cyclohexyl-2-cyclohexylimino-3-(p-nitrophenyl)-4-oxoazeti-
din-3-yl p-chlorobenzoate (24b): 96%; colorless powder; mp 245-
246 °C; 1H NMR (CDCl3) δ 8.35 (d, 2 H, J ) 8.9 Hz), 8.01 (d, 2
H, J ) 8.9 Hz), 7.76 (d, 2 H, J ) 8.9 Hz), 7.49 (d, 2 H, J ) 8.9
Hz), 3.83-3.74 (m, 1 H), 3.65-3.08 (m, 1 H), 2.18-0.97 (m, 20
H); IR (KBr) 2927, 2853, 1833, 1738, 1714, 1594, 1519, 1348,
1273, 1167, 1167, 1091 cm-1. Anal. Calcd for C28H30O5N3Cl: C,
64.18; H, 5.77; N, 8.02. Found: C, 63.92; H, 5.80; N, 7.92.
1-Isopropyl-2-isopropylimino-3-(p-nitrophenyl)-4-oxo-azeti-
din-3-yl p-methoxybenzoate (24c): 90%; white cubes; mp 179-
180 °C; 1H NMR (CDCl3) δ 8.35 (d, 2 H, J ) 9.2 Hz), 8.04 (d, 2
H, J ) 9.2 Hz), 7.77 (d, 2 H, J ) 9.2 Hz), 6.96 (d, 2 H, J ) 9.2
Hz), 4.15 (septet, 1 H, J ) 6.6 Hz), 3.48 (septet, 1 H, J ) 6.3 Hz),
1.56 (d, 3 H, J ) 6.6 Hz), 1.53 (d, 3 H, J ) 6.6 Hz), 0.98 (d, 3 H,
J ) 6.3 Hz), 0.92 (d, 3 H, J ) 6.3 Hz); IR (KBr) 2971, 1821,
7-(p-Nitrophenyl)-6-oxo-2-bicyclo[3.2.0]hept-7-yl acetate (20c):
14%; white powder; mp 109.5-110.0 °C; 1H NMR (CDCl3) δ 8.18
(d, 2 H, J ) 9.1 Hz), 7.50 (d, 2 H, J ) 9.1 Hz), 5.77 (dq, 1 H,
J ) 5.6, 2.1 Hz), 5.23 (dq, 1 H, J ) 5.6, 2.3 Hz), 4.42 (ddd, 1 H,
J ) 10.1, 8.4, 2.3 Hz), 4.02 (br d, 1 H, J ) 7.9 Hz), 2.74 (d quint,
1 H, J ) 17.8, 2.3 Hz), 2.56 (ddq, 1 H, J ) 17.8, 10.1, 2.0 Hz),
2.15 (s, 3 H); IR(KBr) 1780, 1733, 1606, 1524, 1347, 1253, 1236
cm-1. Anal. Calcd for C15H13O5N; C, 62.72; H, 4.56; N, 4.88.
Found: C, 62.58; H, 4.53; N, 4.82.
1721, 1700, 1604, 1531, 1512, 1459, 1347, 1264, 1167, 1078 cm-1
.
1
exo-Adduct (21c): white powder; mp 157-158 °C; H NMR
Anal. Calcd for C23H25N3O6: C, 62.86; H, 5.73; N, 9.56. Found:
C, 62.62; H, 5.82; N, 9.44.
(CDCl3) δ 8.28 (d, 2 H, J ) 8.8 Hz), 7.73 (d, 2 H, J ) 8.8 Hz),
5.82 (dq, 1 H, J ) 5.7, 2.0 Hz), 4.96 (dq, 1 H, J ) 5.6, 2.3 Hz),
3.67 (br d, 1 H, J ) 7.2 Hz), 3.17 (ddd, 1 H, J ) 9.8, 7.2, 3.3 Hz),
2.66 (ddq, 1 H, J ) 17.9, 9.8, 1.6 Hz), 2.41 (dquint, 1 H, J ) 17.9,
2.8 Hz), 1.88 (s, 3 H); IR (KBr) 1790, 1605, 1525, 1401, 1353
cm-1. Anal. Calcd for C15H13O5N; C, 62.72; H, 4.56; N, 4.88.
Found: C, 62.47; H, 4.49; N, 4.79.
1-Cyclohexyl-2-cyclohexylimino-3-(p-nitrophenyl)-4-oxoazeti-
din-3-yl 4-methoxybenzoate (24d): 96%; white cubes; mp 205-
206 °C; 1H NMR (CDCl3) δ 8.33 (d, 2 H, J ) 8.9 Hz), 8.03 (d, 2
H, J ) 8.9 Hz), 7.77 (d, 2 H, J ) 8.9 Hz), 6.97 (d, 2 H, J ) 8.9
Hz), 3.89-3.74 (m, 1 H), 3.89 (s, 3 H), 3.15-3.10 (m, 1 H), 2.17-
1.05 (m, 20 H); IR (KBr) 2932, 2856, 1822, 1700, 1604, 1522,
1347, 1263, 1166, 1082 cm-1. Anal. Calcd for C29H33N3O6: C,
67.04; H, 6.40; N, 8.09. Found: C, 67.05; H, 6.42; N, 8.11.
1-Isopropyl-2-isopropylimino-3-(p-nitrophenyl)-4-oxoazetidin-
1
endo-Adduct (22c): white powder; mp 154-155 °C; H NMR
(CDCl3) δ 8.30 (d, 2 H, J ) 8.8 Hz), 7.80 (d, 2 H, J ) 8.9 Hz),
6.00 (dq, 1 H, J ) 5.7, 1.9 Hz), 5.74 (dq, 1 H, J ) 5.7, 1.9 Hz),
3.63 (dquint, 1 H, J ) 9.0, 1.9 Hz), 3.18 (ddd, 1 H, J ) 9.2, 8.2,
4.8 Hz), 2.47-2.52 (m, 2 H), 1.88 (s, 3 H); IR (KBr) 1792, 1605,
1524, 1402, 1348 cm-1; HRMS(CI+) calcd for C15H14NO5
MH+ ) 288.0872, found MH+) 288.0876.
1
3-yl acetate (24e): 92%; colorless cubes; mp 116-117 °C; H
NMR (CDCl3) δ 8.30 (d, 2 H, J ) 9.2 Hz), 7.66 (d, 2 H, J ) 9.2
Hz), 4.09 (septet, 1 H, J ) 6.6 Hz), 3.42 (septet, 1 H, J ) 6.3 Hz),
1.50 (d, 3 H, J ) 6.6 Hz), 1.48 (d, 3 H, J ) 6.6 Hz), 1.06 (d, 3 H,
J. Org. Chem, Vol. 71, No. 14, 2006 5169

Hamaguchi et al.
J ) 6.3 Hz), 0.97 (d, 3 H, J ) 6.3 Hz); IR (KBr) 2965, 1825,
1756, 1700, 1527, 1348, 1218, 1049, 1009 cm-1. Anal. Calcd for
C22H22Cl2N2O3: C, 58.78; H, 6.09; N, 12.10. Found: C, 58.78; H,
6.09; N, 12.10.
dl-(2R,3S)-2-(p-Chloroprene)-3-(p-nitrophenyl)-4-oxo-1-p-
tolylazetidin-3-yl p-chlorobenzoate (27): 15%; a white crystalline
solid; mp 120-121 °C; 1H NMR (CDCl3) δ 8.30 (d, 2 H, J ) 8.9
Hz), 7.87 (d, 2 H, J ) 8.9 Hz), 7.57 (d, 2 H, J ) 8.9 Hz), 7.40 (d,
2 H, J ) 8.6 Hz), 7.31 (d, 2 H, J ) 8.9 Hz), 7.30 (d, 2 H, J ) 8.6
Hz), 7.24 (d, 2 H, J ) 8.3 Hz), 7.11 (d, 2 H, J ) 8.3 Hz), 5.70 (s,
1 H), 2.30 (s, 3 H); IR (KBr) 1767, 1732, 1595, 1520, 1388, 1349,
1266, 1092, 1014, 844, 756 cm-1. Anal. Calcd for C29H20O5N2Cl2:
C, 63.63; H, 3.68; N, 5.12. Found: C, 63.78; H, 3.75; N, 5.23.
1-Cyclohexyl-2-cyclohexylimino-3-(p-nitrophenyl)-4-oxoazeti-
din-3-yl acetate (24f): 90%; colorless cubes; mp 123-124 °C;
1H NMR (CDCl3) δ 8.29 (d, 2H, J ) 8.9 Hz), 7.67 (d, 2H, J ) 8.9
Hz), 3.73 (m, 1H), 3.07 (m, 1H), 2.25 (s, 3H), 2.09-1.00 (m, 20H);
IR (KBr) 2931, 1820, 1762, 1705, 1522, 1345, 1224, 1028 cm-1
.
Anal. Calcd for C23H29N3O5: C, 64.62; H, 6.84; N, 9.83. Found:
C, 64.32; H, 6.91; N, 9.73.
Rh2(OAc)4-Catalyzed Decomposition of 6a in the Presence
of Methanol. A benzene solution (10 mL) of diazoacetic anhydride
6a (211 mg, 0.6 mmol), methanol (86 mg), and a catalytic amount
of Rh2(OAc)4 was stirred at 40 °C for 1 h. After evaporation of
benzene, methyl 2-p-chlorobenzoyloxy-p-nitrophenylacetate was
recrystallized from CH2Cl2/ether.
Methyl 2-p-chlorobenzoyloxy-p-nitrophenylacetate (28a): 92%;
white needles; mp 133-135 °C; 1H NMR (CDCl3) δ 8.29 (d, 2 H,
J ) 8.6 Hz), 8.06 (d, 2 H, J ) 8.6 Hz), 7.77 (d, 2 H, J ) 8.6 Hz),
7.46 (d, 2 H, J ) 8.6 Hz), 6.28 (s, 1 H), 3.78 (s, 3H); IR (KBr)
2959, 1759, 1724, 1591, 1515, 1435, 1401, 1346, 1260, 1218, 1166,
1103, 1040, 1012, 968, 856 cm-1. Anal. Calcd for C16H12O6NCl:
C, 54.95; H, 3.46; N, 4.01. Found: C, 55.04; H, 3.50; N, 4.02.
1-Isopropyl-2-isopropylimino-3-(4-chlorophenyl)-4-oxoazeti-
din-3-yl 4-chlorobenzoate (24 ): 95%; colorless cubes; mp 176-
177 °C; 1H NMR (CDCl3) δ 8.01 (d, 2 H, J ) 8.6 Hz), 7.52-7.44
(m, 6 H), 4.11 (septet, 1 H, J ) 6.6 Hz), 3.53 (septet, 1 H, J ) 6.3
Hz), 1.54 (d, 3 H, J ) 6.6 Hz), 1.50 (d, 3 H, J ) 6.6 Hz), 1.02 (d,
3 H, J ) 6.3 Hz), 0.90 (d, 3 H, J ) 6.3 Hz); IR (KBr) 2969, 1820,
1732, 1699, 1594, 1491, 1400, 1273, 1092, 1050, 1011 cm-1. Anal.
Calcd for C22H22Cl2N2O3: C, 60.98; H, 5.12; N, 6.46. Found: C,
60.82; H, 5.14; N, 6.44.
1-Cyclohexyl-2-cyclohexylimino-3-(p-chlorophenyl)-4-oxoaze-
tidin-3-yl p-chlorobenzoate (24h): 92%; white cubes; mp 221-
222 °C; 1H NMR (CDCl3) δ 7.99 (d, 2 H, J ) 8.6 Hz), 7.53-7.43
(m, 6 H), 3.81-3.69 (m, 1 H), 3.23-3.12 (m, 1 H), 2.17-0.92
(m, 20H); IR (KBr) 2935, 2856, 1828, 1731, 1705, 1592, 1491,
1401, 1271, 1173, 1092, 1011 cm-1. Anal. Calcd for C28H30-
Cl2N2O3: C, 65.50; H, 5.89; N, 5.46. Found: C, 65.24; H, 5.89;
N, 5.45.
Reaction of p-Nitrophenyldiazoacetic p-Chlorobenzoic An-
hydride 6a with N-p-Chlorobenzylidene-p-toluidine 25. A ben-
zene solution (5 mL) of 6a (173 mg, 0.5 mmol), N-p-chloroben-
zylidene-p-toluidine 25 (122 mg, 0.53 mmol), and a catalytic
amount of Rh2(OAc)4 was stirred at 50 °C for 2.5 h. The reaction
mixture was chromatographed over silica gel using benzene as an
eluent, giving two crystalline products. They were recrystallized
from CH2Cl2/pentane.
dl-(2R,3R)-2-(p-Chlorophenyl)-3-(p-nitrophenyl)-4-oxo-1-p-
tolylazetidin-3-yl p-chlorobenzoate (26): 39%; a white crystalline
solid; mp 187-188 °C; 1H NMR (CDCl3) δ 8.06 (d, 2 H, J ) 8.6
Hz), 7.99 (d, 2 H, J ) 8.6 Hz), 7.59 (d, 2 H, J ) 8.6 Hz), 7.44 (d,
2 H, J ) 8.6 Hz), 7.25 (d, 2 H, J ) 8.6 Hz), 7.17 (d, 2 H, J ) 8.6
Hz), 7.11 (d, 2 H, J ) 8.6 Hz), 7.08 (d, 2 H, J ) 8.6 Hz), 5.82 (s,
1H), 2.30 (s, 3 H); IR (KBr) 2923, 1767, 1732, 1594, 1517, 1492,
1348, 1296, 1174, 1092, 1014, 854, 756 cm-1. Anal. Calcd for
C29H20O5N2Cl2: C, 63.63; H, 3.68; N, 5.12. Found: C, 63.69; H,
3.68; N, 5.11.
Methyl 2-p-anisoyloxy-p-nitrophenylacetate (28b): 98%; white
1
needles; mp 133.5-134.5 °C; H NMR (CDCl3) δ 8.29 (d, 2 H,
J ) 8.9 Hz), 8.08 (d, 2 H, J ) 9.0 Hz), 7.78 (d, 2 H, J ) 8.6 Hz),
6.96 (d, 2 H, J ) 8.9 Hz), 6.26 (s, 1 H), 3.88 (s, 3 H), 3.77 (s, 3
H); IR (KBr) 2951, 1747, 1709, 1602, 1517, 1425, 1350, 1260,
1170, 1101, 1010, 970 cm-1. Anal. Calcd for C17H15O7N: C, 59.13;
H, 4.38; N, 4.06. Found: C, 59.05; H, 4.32; N, 4.08.
Methyl 2-methoxy-p-nitrophenylacetate (28c): 95%; white
needles; mp 90.5-91.0 °C; 1H NMR (CDCl3) δ 8.25 (d, 2 H, J )
8.9 Hz), 7.68 (d, 2 H, J ) 8.9 Hz), 6.05 (s, 1 H), 3.75 (s, 3 H),
2.24 (s, 3 H); IR (KBr) 2960, 1766, 1724, 1607, 1524, 1443, 1402,
1348, 1212, 1074, 1011, 983, 880 cm-1. Anal. Calcd for
C11H11O6N: C, 52.18; H, 4.38; N, 5.53. Found: C, 52.14; H, 4.32;
N, 5.47.
Methyl 2-p-chlorobenzoyloxy-p-chlorophenylacetate (28d):
1
99%; white needles; mp 81-2 °C; H NMR (CDCl3) δ 8.04 (d, 2
H, J ) 8.6 Hz), 7.50 (d, 2 H, J ) 8.4 Hz), 7.43 (d, 2 H, J ) 8.9
Hz), 7.40 (d, 2 H, J ) 8.5 Hz), 6.12 (s, 1 H), 3.75 (s, 3 H); IR
(KBr) 2958, 1744, 1720, 1593, 1492, 1439, 1405, 1291, 1176, 1119,
1093, 1013, 850 cm-1. Anal. Calcd for C16H12Cl2O4: C, 56.66; H,
3.57. Found: C, 56.53; H, 3.56.
JO060074E
5170 J. Org. Chem., Vol. 71, No. 14, 2006