The synthesis of solvent-free glycidic esters from diazoesters and carbonyl compounds catalysed by lanthanide trifiates

Article abstract of DOI:10.1002/1099-0690(200205)2002:9<1562::AID-EJOC1562>3.0.CO;2-Q

The results of the reaction between ethyl diazoacetate and carbonyl compounds catalysed by lanthanide triflates are described. Aldehydes, and α-unsubstituted and α-monosubstituted cyclohexanones react to give the selective formation of α,β-epoxy esters (g

Full text of DOI:10.1002/1099-0690(200205)2002:9<1562::AID-EJOC1562>3.0.CO;2-Q

FULL PAPER
The Synthesis of Solvent-Free Glycidic Esters from Diazoesters and Carbonyl
Compounds Catalysed by Lanthanide Triflates
Massimo Curini,*[a] Francesco Epifano,[a] Maria Carla Marcotullio,[a] and Ornelio Rosati[a]
Keywords: Lanthanides / Diazo compounds / Glycidic esters / Lewis acids / C-C coupling
The results of the reaction between ethyl diazoacetate and of α,β-epoxy esters (glycidic esters), whereas other ketones
carbonyl compounds catalysed by lanthanide triflates are de- are unreactive.
scribed. Aldehydes, and α-unsubstituted and α-monosubsti-
(
Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
tuted cyclohexanones react to give the selective formation 2002)
Introduction
During the last decade rare earth metal triflates have
been found to be unique Lewis acids in that they are water-
tolerant, reusable catalysts that can effectively promote sev-
eral important carbon-carbon and carbon-heteroatom
bond formation reactions such as aldol condensation,[1]
DielsϪAlder and aza DielsϪAlder reactions,[2] FriedelϪ
Crafts acylations,[3] Michael additions,[4] allylations of im-
Scheme 1
ines[5] and carbonyl compounds,[6] the ring opening of ep-
oxides[7] and aziridines,[8] Mannich reactions,[9] the addition
of silyl ketene acetals to nitrones,[10] acetal formation[11] and
heterocyclizations.[12,13] Another interesting application is
the reaction of diazo derivatives with imines leading to the
formation of aziridines.[14]
As part of our ongoing studies to search for new carbon-
carbon bond formation processes using diazo compounds,
we decided to investigate the use of lanthanide triflates as
catalysts in the reaction between ethyl diazoacetate (EDA)
and carbonyl compounds. The Lewis acid-promoted reac-
promoted decomposition of methyl diazomalonate in the
presence of benzaldehyde.[18] The only example of the se-
lective formation of glycidic esters starting from diazo com-
pounds is the reaction catalysed by methylrhenium trioxide
reported by Espenson and Zhu in 1995,[19] although with
some substrates the process was not selective and led to
the formation of ∆3-1,3,4-oxadiazolines as side products in
5Ϫ21% yield.
tion between EDA and carbonyl compounds could lead, in Results and Discussion
principle, to α,β-epoxy esters, also known as ‘‘glycidic es-
ters’’, deriving from a Darzens-type process, or to β-keto
Initially we tested a variety of reaction conditions, em-
ploying different solvents such as methanol, dichlorome-
thane, tetrahydrofuran or acetonitrile, but the best results
were obtained when the reaction was carried out in solvent-
free conditions. We first used aldehydes as substrates and
these results are summarized in Table 1.
Both aromatic and aliphatic aldehydes react with EDA
in the presence of Ln(OTf)3 (10 mol %) to afford the corres-
ponding α,β-epoxy esters in 73Ϫ92% yield. All aldehydes
were extremely reactive and the process was complete after
10 minutes. Unfortunately the reaction is not diastereoselec-
tive: in all cases we obtained a mixture of cis and trans
epoxides, which could be separated by silica-gel column
chromatography. As reported in entry 3 carbon-carbon
double bonds were unreactive under these reaction condi-
tions. No homologation (β-keto esters) or carbene dimeriz-
esters, deriving from
a
homologation reaction
(Scheme 1).[15]
The use of boron trifluoride etherate, triethyl oxonium
tetrafluoroborate, tin(II) chloride, titanium(IV) chloride,
zinc dichloride or antimony(V) chloride usually yields only
the corresponding homologation adducts in the reaction be-
tween EDA and aldehydes or ketones,[16] although α,β-
epoxy esters have been obtained as side products in the
boron trifluoride etherate catalysed reaction between acet-
one and EDA at low temperatures[17] or by thermal or CuI-
[a]
Dipartimento di Chimica e Tecnologia del Farmaco, Sezione di
`
`
Chimica Organica, Facolta di Farmacia, Universita degli Studi,
Via del Liceo, 06123 Perugia, Italy
Fax: (internat.) ϩ 39-075/585-5116
E-mail: curmax@unipg.it
1562
WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ193X/02/0509Ϫ1562 $ 17.50ϩ.50/0 Eur. J. Org. Chem. 2002, 1562Ϫ1565

Solvent-Free Glycidic Esters from Diazoesters and Carbonyl Compounds
FULL PAPER
thane, to precipitate Ln(OTf)3, and subsequent filtration. It
could be reused after drying for 2 h at 70 °C. The yields of
the second and third runs of the recycled catalyst were sim-
ilar in all cases to those of the first run. As reported in
Table 1, the catalytic activity of La(OTf)3 was far superior
to that of heavier lanthanide triflates.
Table 1. Reaction between aldehydes and EDA catalysed by
Ln(OTf)3
When ketones were used as substrates a different reactiv-
ity profile was obtained, and these results are reported in
Table 2. Ketones are much less reactive than aldehydes: the
process takes up to 72 h to be complete and, in addition,
many substrates don’t react at all (entries 7Ϫ11 and 13).
Only in the case of α-unsubstituted and α-monosubstituted
cyclohexanones was the process effective, leading to the
formation of glycidic esters. A similar pattern of reactivity
has been reported for the allylation of cyclohexanone and
other cyclic and acyclic ketones with organotitanium spe-
cies.[20] 3-Methylcyclohexanone (entry 14) yielded a 1:1 mix-
ture of stereoisomers, which could be separated by silica-gel
column chromatography; 2-methyl-, 4-methyl- and 4-tert-
butylcyclohexanone (entries 12, 14 and 15) yielded a single
diastereoisomer formed from the thermodynamically more
favourable equatorial nucleophilic attack of EDA at the car-
bonyl function, leading to a pseudo-axial configuration at
the epoxide CϪO bond. The lower yield (25%) obtained
Table 2. Reaction between ketones and EDA catalysed by Ln(OTf)3
[a]
Isolated yield.
ation products (diethyl maleate and/or fumarate), the latter
deriving from Lewis acid-promoted EDA decomposition,
were observed, suggesting that the reaction proceeds by nu-
cleophilic addition of EDA to the lanthanide-carbonyl com-
plex, followed by a nucleophilic SN2 attack of the thus-
formed negatively charged oxygen followed by N2 displace-
ment, as occurs in the Darzens reaction (Scheme 2).
Scheme 2
A similar mechanism was reported by Wang and co-
workers to explain aziridine formation.[14] To confirm that
carbenes or carbenoids were not involved in the process, in
a trial experiment we found that EDA is stable for several
days when mixed with 10 mol % Ln(OTf)3.
The best results were obtained using 0.1 equivalents of
the catalyst; a lower loading resulted in lower yields, while
a higher loading did not significantly reduce reaction times
or increase yields. The catalyst could be easily recovered
from the reaction media by simple addition of dichlorome-
[a]
Isolated yield.
Eur. J. Org. Chem. 2002, 1562Ϫ1565
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M. Curini, F. Epifano, M. C. Marcotullio, O. Rosati
FULL PAPER
CH2Cl2 as eluent. The catalyst was washed with dichloromethane
and dried at 70 °C for 2 h before being reused for several other
experiments without any loss of activity.
using 2-methylcyclohexanone (entry 12), together with the
fact that 2,6-dimethylcyclohexanone (entry 13) is not react-
ive, can be explained by the steric bulk of the α-alkyl sub-
stituents preventing the formation of the lanthanide-car-
bonyl complex., La(OTf)3 also performed as a better cata-
lyst than other lanthanides in the case of ketones.
Ethyl 3-Methyl-1-oxirane-2-carboxylate (1): Yellow oil. 1H NMR
(cis isomer): δ ϭ 1.33 (t, J ϭ 7.1 Hz, 3 H), 1.42 (d, J ϭ 7.0 Hz, 3
H), 3.19 (d, J ϭ 2.0 Hz, 1 H), 3.22Ϫ3.36 (m, 1 H), 4.26 (q, J ϭ
7.1 Hz, 2 H); (trans isomer): δ ϭ 1.33 (t, J ϭ 7.0 Hz, 3 H), 1.40 (d,
As a knowledge of the factors that drive the process
along one of the two reaction pathways described above J ϭ 6.9 Hz, 3 H), 3.23Ϫ3.37 (m, 1 H), 3.52 (d, J ϭ 4.4 Hz, 1 H),
4.25 (q, J ϭ 7.0 Hz, 2 H). 13C NMR (cis isomer): δ ϭ 14.2, 17.1,
53.9, 54.4, 61.5, 168.7; (trans isomer): δ ϭ 12.8, 14.1, 52.9, 53.4,
61.4, 169.1. GC-MS: m/z ϭ 115, 168, 102, 84, 74, 69, 57. C6H10O3
(130.1): calcd. C 55.37, H 7.74; found C 55.35, H 7.75.
could be of synthetic importance, and because we have cle-
arly shown that a completely different selectivity can be ob-
tained simply by changing the catalyst, quantum chemical
computational studies to gain further insight into the reac-
tion between diazoesters and carbonyl compounds are now
in progress.
Ethyl 3-Pentyl-1-oxirane-2-carboxylate (2): Yellow oil. 1H NMR
(cis isomer): δ ϭ 0.92 (d, J ϭ 7.0 Hz, 3 H), 1.32 (t, J ϭ 7.1 Hz, 3
H), 1.30Ϫ1.85 (m, 8 H), 3.17Ϫ3.24 (m, 1 H), 3.27 (d, J ϭ 1.8 Hz,
1 H), 4.18 (q, J ϭ 7.1 Hz, 2 H); (trans isomer): δ ϭ 0.91 (d, J ϭ
7.0 Hz, 3 H), 1.31 (t, J ϭ 7.1 Hz, 3 H), 1.28Ϫ1.80 (m, 8 H),
3.15Ϫ3.22 (m, 1 H), 3.57 (d, J ϭ 4.0 Hz, 1 H), 4.17 (q, J ϭ 7.1 Hz,
2 H). 13C NMR (cis isomer): δ ϭ 13.8, 14.0, 22.3, 23.0, 25.7, 31.3,
52.8, 57.6, 61.3, 169.1; (trans isomer): δ ϭ 13.8, 14.0, 23.0, 23.1,
27.1, 31.1, 53.0, 58.4, 169.3. GC-MS: m/z ϭ 170, 158, 143, 129,
113, 102, 85, 83, 69, 55. C10H18O3 (186.2): calcd. C 64.49, H 9.74;
found C 64.51, H 9.73.
Conclusions
From the results presented above we can conclude that
lanthanide triflates catalyse the reaction between EDA and
carbonyl compounds, acting as a relatively weak and select-
ive catalyst: they allow only the more reactive compounds
(i.e. aldehydes and cyclohexanones) to react under milder
reaction conditions. The second effect of this ‘‘weakness’’ is
that the carbonyl oxygen, although complexing the lanthan-
ide atom, retains sufficient nucleophilicity to allow the sub-
sequent substitution reaction, making glycidic ester forma-
tion the preferred pathway. Moreover, we have demon-
strated that α,β-epoxy esters can be obtained by Ln(OTf)3-
catalysed reactions of carbonyl compounds with EDA. The
process can be carried out under mild reaction conditions
to afford glycidic esters Ϫ which are important interme-
diates in synthetic organic chemistry as precursors of gly-
cidic acids Ϫ the decomposition of these acids yields one-
carbon homologated aldehydes starting from carbonyl com-
pounds,[21] in good yield, although only from aldehydes and
suitably substituted cyclohexanones. The catalyst can easily
be recovered from the reaction medium and recycled.
Ethyl 3-(9-Decenyl)-1-oxirane-2-carboxylate (3): Yellow oil. 1H
NMR (cis isomer): δ ϭ 1.12Ϫ2.20 (m, 17 H), 2.41Ϫ2.51 (m, 2 H),
3.17Ϫ3.24 (m, 1 H), 3.25 (d, J ϭ 1.8 Hz, 1 H), 4.27 (q, J ϭ 7.0 Hz,
2 H), 5.02Ϫ5.10 (m, 2 H), 5.85Ϫ5.98 (m, 1 H); (trans isomer): δ ϭ
1.11Ϫ2.20 (m, 17 H), 2.39Ϫ2.50 (m, 2 H), 3.15Ϫ3.23 (m, 1 H),
3.57 (d, J ϭ 4.7 Hz, 1 H), 4.26 (q, J ϭ 7.0 Hz, 2 H), 5.73Ϫ5.85 (m,
1 H). 13C NMR (cis isomer): δ ϭ 14.2, 26.1, 28.8, 29.0, 29.1, 29.2,
29.3, 32.0, 33.7, 52.8, 58.5, 61.5, 114.0, 139.1, 167.8; (trans isomer):
δ ϭ 14.0, 25.7, 28.8, 29.0, 29.1, 29.2, 29.3, 31.4, 33.7, 53.0, 57.6,
61.4, 114.1, 139.1, 168.0. GC-MS: m/z ϭ 254, 225, 181, 165, 151,
137, 123, 109, 95, 81, 67, 55. C15H26O3 (254.3): calcd. C 70.83, H
10.30; found C 70.81, H 10.28.
Ethyl 3-Cyclohexyl-1-oxirane-2-carboxylate (4): Yellow oil. 1H
NMR (cis isomer): δ ϭ 1.10Ϫ1.95 (m, 13 H), 2.97 (dd, J1,2
ϭ
1.8 Hz, J1,3 ϭ 6.2 Hz, 1 H), 3.28 (d, J ϭ 1.8 Hz, 1 H), 4.24 (q, J ϭ
7.0 Hz, 2 H); (trans isomer): δ ϭ 1.15Ϫ1.96 (m, 13 H), 2.84 (dd,
J1,2 ϭ 4.7 Hz, J1,3 ϭ 8.7 Hz, 1 H), 3.54 (d, J ϭ 4.6 Hz, 1 H), 4.25
(q, J ϭ 7.1 Hz, 2 H). 13C NMR (cis isomer): δ ϭ 14.0, 25.3, 25.4,
26.0, 28.7, 29.2, 39.4, 51.9, 61.4, 62.4, 169.4; (trans isomer): δ ϭ
14.2, 25.0, 25.2, 28.5, 28.8, 30.5, 36.1, 52.7, 61.2, 61.6, 168.2. GC-
MS: m/z ϭ 198, 141, 125, 115, 107, 95, 81, 67, 55. C11H18O3
(198.2): calcd. C 66.44, H 9.15; C 66.45, H 9.13.
Experimental Section
General Method: 1H NMR and 13C NMR spectra were recorded
in CDCl3 solution on a Bruker AC 200 spectrometer operating at
200.1 and 50.53 MHz, respectively, in the Fourier transform mode.
GC analyses and MS spectra were carried out with an HP 5890
gas chromatograph (dimethyl silicone column 12.5 m) equipped
with an HP 5971 Mass Selective Detector. Flash column chromato-
graphy was performed on 0.040Ϫ0.063 mm (230Ϫ400 mesh
ASTM) Merck silica gel. Elemental analysis were performed on
a Carlo Erba Model 1106 elemental analyzer. Ethyl diazoacetate,
La(OTf)3, Eu(OTf)3 and Yb(OTf)3 were purchased from Aldrich
Chemical Co. and used without any purification.
Ethyl 3-Phenyl-1-oxirane-2-carboxylate (5): Yellow oil. 1H NMR
(cis isomer): δ ϭ 1.07 (t, J ϭ 7.0 Hz, 3 H), 3.52 (d, J ϭ 1.9 Hz, 1
H), 4.25 (q, J ϭ 7.0 Hz, 2 H), 4.38 (d, J ϭ 1.9 Hz, 1 H), 7.23Ϫ7.50
(m, 5 H); (trans isomer): δ ϭ 1.32 (t, J ϭ 7.1 Hz, 3 H), 3.78 (d,
J ϭ 4.6 Hz, 1 H), 4.26 (q, J ϭ 7.1 Hz, 2 H), 4.40 (d, J ϭ 4.6 Hz,
1 H), 7.27Ϫ7.55 (m, 5 H). 13C NMR (cis isomer): δ ϭ 13.8, 56.8,
57.9, 61.5, 125.8, 128.0, 128.6, 129.0, 129.3, 167.8; (trans isomer):
δ ϭ 14.1, 55.8, 57.4, 61.2, 126.63, 128.4, 128.4, 129.2, 129.9, 133.4,
167.6. GC-MS: m/z ϭ 192, 163, 119, 103, 77. C11H12O3 (192.2):
calcd. C 68.74, H 6.29; found C 68.76, H 6.27.
General Procedure: A mixture of carbonyl compound (1.0 mmol)
and EDA (1.2 mmol) was stirred with Ln(OTf)3 (0.1 mmol) at
room temperature for the appropriate time (see Tables 1 and 2).
CH2Cl2 (5 mL) was then added to precipitate the Ln(OTf)3, and
Ethyl 1-Oxaspiro[2.5]octane-2-carboxylate (6): Yellow oil. 1H
NMR: δ ϭ 1.25 (t, J ϭ 7.2 Hz, 3 H), 1.35Ϫ1.90 (m, 10 H), 3.25
the catalyst was removed by filtration under reduced pressure. The (s, 1 H), 4.20 (q, J ϭ 7.2 Hz, 2 H). 13C NMR: δ ϭ 14.1, 24.6, 24.9,
residue was purified by silica-gel column chromatography with
1564
25.1, 28.5, 34.7, 59.3, 61.1, 64.6, 168.2. GC-MS: m/z ϭ 184, 167,
Eur. J. Org. Chem. 2002, 1562Ϫ1565

Solvent-Free Glycidic Esters from Diazoesters and Carbonyl Compounds
FULL PAPER
[1]
156, 144, 138, 127, 111, 99, 81, 67, 55. C10H16O3 (184.2): calcd. C
65.19, H 8.75; found C 65.21, H 8.72.
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371Ϫ373.
[2] [2a]
S. Kobayashi, I. Hachiya, M. Araki, H. Ishitani, Tetrahed-
[2b]
Ethyl 4-Methyl-1-oxaspiro[2.5]octane-2-carboxylate (7): Yellow oil.
1H NMR: δ ϭ 0.81 (d, J ϭ 7.0 Hz, 3 H), 1.23 (t, J ϭ 7.2 Hz, 3 H),
ron Lett. 1993, 34, 3755Ϫ3758.
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C. Marcotullio, O. Rosati, Heterocycles 2001, 55, 1599Ϫ1604.
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2169Ϫ2172.
[3]
3.40 (s, 1 H), 1.50Ϫ2.40 (m, 9 H), 4.15 (q, J ϭ 7.2 Hz, 2 H). 13C
NMR: δ ϭ 14.1, 14.0, 23.3, 24.5, 168.5, 27.1, 32.5, 35.5, 57.5, 61.0,
66.5. GC-MS: m/z ϭ 198, 183, 170, 141, 125, 113, 107, 95, 81,
67, 55. C11H18O3 (198.2): calcd. C 66.64, H 9.15; found C 66.63,
[4] [4a]
S. Kobayashi, I. Hachiya, H. Ishitani, M. Araki, Synlett
[4b]
1993, 472.
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H 9.17.
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[6]
Ethyl 5-Methyl-1-oxaspiro[2.5]octane-2-carboxylate (8): Yellow oil.
[7]
1H NMR (isomer 1): δ ϭ 0.84 (d, J ϭ 7.0 Hz, 3 H), 1.22 (t, J ϭ
7.2 Hz, 3 H), 1.40Ϫ1.85 (m, 9 H), 3.25 (s, 1 H), 4.15 (q, J ϭ 7.2 Hz,
2 H); (isomer 2): δ ϭ 0.87 (d, J ϭ 7.0 Hz, 3 H), 1.23 (t, J ϭ 7.0
Hz, 3 H), 1.45Ϫ1.85(m, 9 H), 3.26 (s, 1 H), 4.18 (q, J ϭ 7.2 Hz, 2
L. Favero, F. Macchia, M. Pineschi, Tetrahedron Lett. 1994, 35,
[7c]
433Ϫ436.
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62, 3575Ϫ3581.
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12929Ϫ12938.
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M. P. Doyle, M. A. McKervey, T. Ye, Modern Catalytic
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W. T. Tai, E. W. Warnhoff, Can. J. Chem. 1964, 42, 1333Ϫ1336.
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4952Ϫ4954.
H). 13C NMR (isomer 1): δ ϭ 14.1, 21.8, 23.1, 23.2, 30.5, 33.8,
42.3, 59.2, 61.1, 64.0, 168.0; (isomer 2): δ ϭ 14.1, 21.9, 23.2, 27.4,
30.4, 33.6, 35.9, 59.1, 61.1, 63.9, 168.1. GC-MS: m/z ϭ 198, 183,
170, 141, 125, 113, 107, 95, 81, 67, 55. C11H18O3 (198.2): calcd. C
[8]
[9]
[10]
[11]
66.64, H 9.15; found C 66.61, H 9.16.
[12]
Ethyl 6-Methyl-1-oxaspiro[2.5]octane-2-carboxylate (9): Yellow oil.
1H NMR: δ ϭ 0.90 (d, J ϭ 7.1 Hz, 3 H), 1.23 (t, J ϭ 7.2 Hz, 3 H),
1.52Ϫ1.90 (m, 9 H), 3.28 (s, 1 H), 4.20 (q, J ϭ 7.2 Hz, 2 H). 13C
NMR: δ ϭ 14.1, 21.7, 27.4, 31.4, 32.2, 32.3, 33.7, 59.2, 61.0, 63.9,
[13] [13a]
168.2. GC-MS: m/z ϭ 198, 183, 170, 141, 125, 111, 95, 81, 67, 55.
C11H18O3 (198.2): calcd. C 66.64, H 9.15; found C 66.65, H 9.15.
[14]
[15]
Ethyl 6-(tert-Butyl)-1-oxaspiro[2.5]octane-2-carboxylate (10): Yel-
low oil. 1H NMR: δ ϭ 0.90 (s, 9 H), 1.23 (t, J ϭ 7.2 Hz, 3 H),
1.40Ϫ1.90 (m, 9 H), 3.30 (s, 1 H), 4.20 (q, J ϭ 7.2 Hz, 2 H). 13C
[16]
NMR: δ ϭ 14.5, 24.8, 24.9, 27.4, 27.6, 32.5, 34.4, 47.1, 59.2, 61.1,
64.2, 168.2. GC-MS: m/z ϭ 240, 225, 183, 167, 155, 137, 123, 107,
93, 81, 67, 55. C14H24O3 (240.3): calcd. C 69.96, H 10.07; found C
[17]
69.97, H 10.05.
[18]
[19]
Z. Zhu, H. Espenson, J. Org. Chem. 1995, 60, 7090Ϫ7091.
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[20]
Acknowledgments
[21]
`
The authors wish to thank MURST and Universita degli Studi di
Perugia, Italy for financial support.
Received September 22, 2002
[O01454]
Eur. J. Org. Chem. 2002, 1562Ϫ1565
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