D. Donati et al. / Tetrahedron Letters 44 (2003) 9247–9250
9249
Acknowledgements
(CDCl3) l: 1.30 (t, 3H, J=7.2 Hz, COOCH2CH3), 2.64
(s, 3H, 3-CH3), 4.32 (s, 3H, NCH3), 4.43 (q, 2H, J=7.2
Hz, COOCH2CH3). 13C NMR (CDCl3) l: 12.87 (CH3),
13.58
(COOCH2CH3),
39.43
(NCH3),
62.76
This work was financially supported by the University
of Siena, quota Servizi per la Ricerca. The authors
thank Dr. G. L. Giorgi, Centro di Analisi e Determi-
nazioni Strutturali, Universita` di Siena, for the record-
ing of MS spectra and X-ray data collection.
(COOCH2CH3), 112.87 (C4), 156.67 (C3), 160.91 (C5),
162.99 (CO). MS (APCI), m/z: 206/204 (M+).
2-(2,4-Dimethyl-3-phenyl-2H-isoxazol-5-ylidene)malonic
acid diethyl ester 3a: mp 82–84°C; H NMR (CDCl3) l:
1
1.30 (t, 6H, J=7.1 Hz, COOCH2CH3), 1.85 (s, 3H,
4-CH3), 3.40 (s, 3H, NCH3), 4.29 (q, 4H, J=7.1 Hz,
COOCH2CH3), 7.20–7.50 (m, 5H, Ph). 13C NMR
(CDCl3) l: 9.99 (4-CH3), 14.36 (COOCH2CH3), 39.80
References
(NCH3), 59.78 (COOCH2CH3), 85.29 (C6 ꢁC5), 107.43
1. Kotra, L. P.; Mobashery, S. Bull. Inst. Pasteur 1998, 96,
139–150.
2. Del Buttero, P.; Baldoli, C.; Molteni, G.; Pilati, T. Tetra-
hedron: Asymmetry 2000, 11, 1927–1941.
3. (a) Donati, D.; Fusi, S.; Ponticelli, F. Tetrahedron Lett.
2002, 43, 9527–9530 and references cited therein; (b)
Donati, D.; Fusi, S.; Ponticelli, F. Synthesis 2003, in
press.
4. Donati, D.; Fusi, S.; Ponticelli, F. Gazz. Chim. Ital. 1991,
121, 329–334.
5. To a solution of compounds 1a–c (10 mmol) in anhy-
drous benzene (20 ml) was added methyl trifluoro-
methanesulfonate (10 mmol). The reaction mixture was
refluxed for a few minutes, and the solvent was removed
to give a colourless oil which crystallised on treatment
with anhydrous diethyl ether (yield 70–75%).
6. To a stirred solution of compound 2a–c (3 mmol), NaH
60% (3 mmol), dry Et3N (3 mmol) in anhydrous benzene
(15 ml) was slowly added compound 1b. The yellow
solution was evaporated in vacuo and the residue was
quenched with water and extracted with CH2Cl2. The
organic solvent was evaporated in vacuo and the residue
was chromatographed eluting first with CH2Cl2/CH3OH
95/5 and then with CH2Cl2/CH3OH 90/10 to give com-
pound 3a–c (yield 45% for 3a and 3c and 35% for 3b).
7. Becker, D. A.; Anderson, F. E.; McKibben, B. P.;
Merola, J. S.; Glass, E. Synlett 1993, 866–868 and refer-
ences cited therein.
(C4), 126.52, 128.94, 129.29, 130.97 (Ph), 158.31 (C3),
166.54 (CO), 174.05 (C5). MS (EI), m/z: 331 (M+), 286,
259, 212, 187, 144, 118, 103, 91, 77.
2-(2,4-Dimethyl-3-phenyl-2H-isoxazol-5-ylidene)pentane-
2,4-dione 3b: orange oil; 1H NMR (CDCl3) l: 1.80 (s,
3H, 4-CH3), 2.28 (s, 6H, COCH3), 3.79 (s, 3H, NCH3),
7.42–7.60 (m, 5H, Ph). 13C NMR (CDCl3) l: 9.91 (4-
CH3), 28.78 (COCH3), 37.5 (NCH3), 88.11 (C6 ꢁC5), 113.42
(C4), 127.60, 128.40, 128.72, 132.90 (Ph), 156.61 (C3),
164.80 (C5), 194.72 (CO). MS (EI), m/z: 271 (M+), 256,
228, 214, 188, 160, 118, 105, 91, 77.
2-(2,4-Dimethyl-3-phenyl-2H-isoxazol-5-ylidene)-3-oxo-
butanoic acid ethyl ester 3c: orange oil; 1H NMR (CDCl3)
l: 1.21 (t, 3H, J=6.8 Hz, COOCH2CH3), 1.75 (s, 3H,
4-CH3), 2.35 (s, 3H, COCH3), 3.77 (s, 3H, NCH3), 4.14
(q, 2H, J=6.8 Hz, COOCH2CH3), 7.32–7.55 (m, 5H, Ph).
13C NMR (CDCl3) l: 9.96 (4-CH3), 14.47
(COOCH2CH3), 29.61 (COCH3), 38.08 (NCH3), 58.97
(COOCH2CH3), 85.01 (C
128.84, 129.45, 131.59 (Ph), 157.51 (C3), 167.87
6 ꢁC5), 111.10 (C4), 124.62,
(C6 OOCH2CH3), 169.80 (C5), 192.43 (C6 OCH3); MS
(APCI), m/z: 324 (M++Na), 296, 281, 188, 118.
3-Ethoxy-5,7-dimethyl-6-oxo-1-phenyl-2-oxa-7-azabicy-
clo[3.2.0]hept-3-ene-4-carboxylic acid ethyl ester 4: mp
113–115°C (cyclohexane–ether); 1H NMR (CDCl3) l:
1.11 (s, 3H, 5-CH3), 1.27 (t, 3H, J=7.1 Hz, OCH2CH3 or
COOCH2CH3), 1.43 (t, 3H, J=7.1 Hz, COOCH2CH3 or
OCH2CH3), 2.85 (s, 3H, NCH3), 4.16 (q, 2H, OCH2CH3
or COOCH2CH3), 4.48 (q, 2H, J=7.1 Hz, COOCH2CH3
or OCH2CH3), 7.24–7.51 (m, 5H, Ph). 13C NMR (CDCl3)
l: 13.10 (COOCH2CH3 or OCH2CH3), 14.08 (OCH2CH3
or COOCH2CH3), 15.20 (5-CH3), 24.01 (NCH3), 59.23
(COOCH2CH3 or OCH2CH3), 66.83 (OCH2CH3 or
COOCH2CH3), 69.65 (C5), 83.01 (C1 or C4), 99.33 (C4 or
C1), 126.11, 128.82, 129.82, 131.44 (Ph), 164.11
8. All new compounds gave satisfactory analytical data
(within 0.3%). 1H and 13C NMR spectra were recorded
with a Bruker AC 200 spectrometer at 200.13 and 50.33
MHz, respectively. 13C assignments were established
based on chemical shift considerations and DEPT experi-
ments. APCI MS specta were recorded with a LCQ-
DECA Thermo Finningan instrument and EI MS spectra
were obtained with a VG 70 250S instrument. The
reported yields are relative to the isolated product.
5-Chloro-2,3-dimethyl-4-phenylisoxazol-2-ium trifluoro-
(C6 OOCH2CH3 or C3), 165.81 (C3 or C6 OOCH2CH3),
170.90 (C6). MS (EI), m/z: 331 (M+), 258, 230, 212, 118,
77.
1
methanesulfonate 1a: mp 83–86°C; H NMR (CDCl3) l:
9. A solution of 3a (1.5 mmol) in CH3CN (40 ml) was
irradiated for 15 h in a pyrex tube with a Rayonet
apparatus operating at 355 nm.. Chromatographic purifi-
cation on a silica gel column eluting with diethyl ether
gave compound 4 (yield 60%) as a white solid.
10. Crystal data and structure refinement of compound 4:
2.87 (s, 3H, 3-CH3), 4.31 (s, 3H, NCH3), 7.38–7.52 (m,
5H, Ph). 13C NMR (CDCl3) l: 12.02 (CH3), 39.42
(NCH3), 121.44 (C4), 123.09, 129.19, 130.36 (Ph), 154.27
(C3), 161.47 (C5). MS (APCI), m/z: 210/208 (M+).
5-Chloro-2,4-dimethyl-3-phenylisoxazol-2-ium trifluoro-
1
methanesulfonate 1b: mp 70–72°C; H NMR (CDCl3) l:
C18H21NO5, MW=331.36, monoclinic, a=9.228(2), b=
3
2.14 (s, 3H, 4-CH3), 4.26 (s, 3H, NCH3), 7.51–7.74 (m,
5H, Ph). 13C NMR (CDCl3) l: 7.58 (CH3), 40.21
(NCH3), 117.14 (C4), 121.50, 129.44, 129.92, 133.47 (Ph),
156.52 (C3), 161.52 (C5). MS (APCI), m/z: 210/208 (M+).
5 -Chloro-4-ethoxycarbonyl-2,3-dimethylisoxazol-2-ium
trifluoromethanesulfonate 1c: mp 86–89°C; 1H NMR
,
,
9.625(2), c=20.872(4) A, V=1826(5) A , space group
P21/n, Z=4, F(000)=704, Dcalcd=1.205 g cm−3, v(Mo
Ka) 0.088 mm−1. The data were collected on a Siemens
P4 four-circle diffractometer with graphite monochro-
,
mated Mo Ka radiation (u=0.71069 A) in the range
−15h512, −15k513, −295l529. Three standard