L. Cecchi, F. De Sarlo, C. Faggi, F. Machetti
FULL PAPER
H), 1.59–1.62 (m, 2 H, norb-H), 1.91 (dm, J = 10.4, 1 H, norb-H),
2.16–2.21 (m, 1 H, norb-H), 2.92–2.99 (m, 1 H, norb-H), 3.29 (dd,
J = 1.6 and 7.0 Hz, 1 H,CHCN), 4.14 (d, J = 7.0 Hz, 1 H, CHOH),
7.48–7.53 (m, 2 H, Ph-Hpara), 7.62–7.68 (m, 1 H, Ph-Hmeta), 8.10–
8.16 (m, 2 H, Ph-Hortho) ppm. 13C NMR (100.58 MHz, CDCl3): δ
= 24.4 (t, Norb-C), 28.6 (t, Norb-C), 33.9 (t, Norb-C), 39.3 (d,
Norb-C), 44.9 (d, Norb-C), 45.6 (d, Norb-C), 75.6 (d, COH), 128.7
(d, 2 C, Ar-C), 130.4 (d, 2 C, Ar-C), 134.6 (d, Ar-C), 135.7 (s, Ar-
C), 151.6 (s, C=N), 155.1 (s, C=N), 185.8 (s, C=O) ppm. MS (EI):
m/z (%) = 284 (4) [M+], 267 (40) [M – OH]+, 239 (3), 188 (8), 105
this side reaction path requires a high concentration of both
the base and water; however, enhanced hydrolysis causes
decomposition of the starting material 1 and also of
furoxan 7. Therefore, for synthetic purposes in order to ob-
tain furazanes it is convenient to prepare the furoxan in a
separate step, in the absence of dipolarophile. Subsequent
treatment of furoxan with dipolarophile and DABCO in the
presence of an excess of water affords the corresponding
furazans in fair yields.
(100) [(PhCO)+], 77 (57). IR (KBr) = ν 3484, 3375, 2932, 2867,
˜
1672, 1657, 1597, 1451 cm–1. C16H16N2O3 (284.31): calcd. C 67.59,
H 5.67, N 9.85; found C 67.61, H 5.65, N 10.00.
Experimental Section
Reaction of Benzoylnitromethane with Styrene: After work-up, the
residual oil was subjected to chromatographic purification with
hexane/diethyl ether (10:1). A first fraction (Rf = 0.24) containing
the isoxazoline 4b (80 mg, 75%) was followed by a second fraction
[Rf Ͻ 0.1; Rf (hexane/diethyl ether, 2:1) = 0.23] containing the fur-
azan 5b (31 mg).
General: Melting points were measured on a Büchi 510 apparatus
and are uncorrected. Chromatographic separations were performed
on silica gel; Rf values refer to TLC carried out on 25-mm silica
gel plates (Merck F254), with the same eluent indicated for the
column chromatography unless otherwise stated. 1H and 13C NMR
spectra were recorded with a Mercuryplus 400 spectrometer (op-
erating at 100.58 MHz for 13C). The multiplicity of the 13C NMR
signals was determined by means of APT or HMQC experiments.
Chemical shifts were determined relative to the residual solvent
peak (CHCl3: δ = 7.24 ppm for 1H and δ = 77.0 ppm for 13C).
Mass spectra were obtained in EI mode at a 70 eV ionising voltage;
relative percentages are shown in brackets. Commercially available
benzoylnitromethane was used without further purification. IR
spectra were recorded as solutions in spectroscopic grade CHCl3,
unless otherwise stated, using a Perkin–Elmer 881 spectrophotome-
ter. Elemental analyses were obtained with an Elemental Analyser
Perkin–Elmer 240C apparatus.
1
Isoxazoline 4b: Light-yellow oil (ref.[11] light yellow oil). H NMR
(400 MHz, CDCl3): δ = 3.38 (dd, J = 8.8 and 17.8 Hz, 1 H, 4-H),
3.77 (dd, J = 11.4 and 17.8 Hz,1 H, 4-H), 5.76 (dd, J = 8.8 and
11.4 Hz, 1 H, 5-H), 7.29–7.41 (m, 5 H, Ar-H), 7.48 (m, 2 H, Ar-
H), 7.61 (m, 1 H, Ar-H), 8.24 (m, 2 H, COPh-Hortho) ppm. 13C
NMR (100.58 MHz, CDCl3): δ = 41.8 (t, C-4), 84.2 (d, C-5), 125.9
(d, 2 C, Ar-C), 128.4 (d, 2 C, Ar-C), 128.6 (d), 128.8 (d, 2 C, Ar-
C), 130.3 (d, 2 C, Ar-C), 133.6 (d), 135.7 (s, Ar-C), 139.7 (s, Ar-
C), 157.4 (s, C=N), 186.2 (s, COPh) ppm. MS (EI): m/z (%) = 251
(25) [M+], 234 (12), 205 (4), 204 (4), 105 (100) [(PhCO)+], 77 (55).
IR: ν = 3068, 3030, 2926, 2857, 1672, 1652, 1599, 1581,1572 cm–1.
˜
C16H13NO2 (251.28): calcd. C 76.48, H 5.21, N 5.57; found C
76.50, H 5.29, N 5.44.
General Method for Reaction of Benzoylnitromethane (1) with Di-
polarophiles: A solution of 1 (175 mg, 1.06 mmol), DABCO (24 mg,
0.212 mmol) and dipolarophile (0.424 mmol) in anhydrous and eth-
anol-free chloroform (1.4 mL) was stirred for 20 h in a sealed vessel
(Schlenk) at 60 °C. The solvent was then removed and the residue
dissolved in diethyl ether (15 mL) and washed with water
(3×15 mL portions). The organic layer was dried (sodium sulfate)
and concentrated, then the residue column chromatographed on
silica gel.
1
Furazan 5b: Gummy solid. H NMR (400 MHz, CDCl3): δ = 3.48
(d, J = 6.3 Hz, 2 H, CH2CN), 5.15 (t, J = 6.3 Hz, 1 H, CHOH),
7.18–7.40 (m, 5 H, Ar-H), 7.42–7.60 (m, 2 H, Ar-H), 7.61–7.74 (m,
1
H, Ar-H), 8.10–8.20 (m, 2
H, Ar-H) ppm. 13C NMR
(100.58 MHz, CDCl3): δ = 33.2 (t, CH2CN), 72.4 (d, CHOH),
125.5 (d, 2 C, Ar-C), 128.0 (d, Ar-C), 128.5 (d, 2 C, Ar-C), 128.6
(d, 2 C, Ar-C), 130.4 (d, 2 C, Ar-C), 134.7 (d, Ar-C), 135.4 (s, Ar-
C), 142.4 (s, Ar-C), 151.0 (s, C=N), 153.0 (s, C=N), 184.7 (s, CO)
ppm. MS (EI): m/z (%) = 294 (Ͻ1) [M+], 293 (11) [M – H]+, 277
(1) [M – OH]+, 276 (2) [M – H2O]+, 189 (7), 107 (67), 105 (100)
Reaction of Benzoylnitromethane with Norbornene: After work-up,
the residual oil was subjected to chromatographic purification (hex-
ane/diethyl ether, 10:1). A first fraction (Rf = 0.31) containing the
isoxazoline 4a (white solid, 92 mg, 90%) was followed by a second
fraction [Rf Ͻ 0.1; Rf (hexane/diethyl ether, 2:1) = 0.33] containing
furazan 5a (glassy solid, 12 mg, 10%).
[(PhCO)+], 79 (39), 77 (77). IR: ν = 3067, 3032, 2930, 1667 (C=O),
˜
1599, 1580 cm–1. C17H14N2O3 (294.30): calcd. C 69.38, H 4.79, N
9.52; found C 69.00, H 4.73, N 9.76.
Isoxazoline 4a: Colourless crystals, hexane, m.p. 49–50 °C. (ref.[10]
50–51 °C). 1H NMR (400 MHz, CDCl3): δ = 1.09–1.16 (m, 1 H,
norb-H), 1.18–1.24 (m, 1 H, norb-H), 1.29–1.36 (m, 1 H, norb-H),
1.38–1.44 (m, 1 H, norb-H), 1.49–1.62 (m, 2 H, norb-H), 2.58–2.61
(m, 1 H, norb-H), 2.62–2.66 (m, 1 H, norb-H), 3.51 (d, J = 8.4 Hz,
1 H, CHC=N), 4.64 (d, J = 8.4 Hz, 1 H, CHON), 7.39–7.48 (m, 2
H, Ph-Hpara), 7.52–7.59 (m, 1 H, Ph-Hmeta), 8.11–8.14 (m, 2 H, Ph-
Hortho) ppm. 13C NMR (100.58 MHz, CDCl3): δ = 22.7 (t, Norb-
C), 27.2 (t, Norb-C), 32.3 (t, Norb-C), 39.3 (d, Norb-CH), 43.1 (d,
Norb-CH), 56.3 (d, CC=N), 89.4 (d, CON), 128.2 (d, 2 C, Ar-C),
130.2 (d, 2 C, Ar-C), 133.3 (d, Ar-C), 136.4 (s, Ar-C), 158.2 (s,
C=N), 186.7 (s, C=O) ppm. MS (EI): m/z (%) = 241 (36) [M+], 212
Reaction of Benzoylnitromethane with Phenylacetylene: After work-
up, the residual oil was subjected to chromatographic purification
with hexane/diethyl ether (13:1). A first fraction (Rf = 0.30) con-
taining the isoxazole 4c (60 mg, 57%) was followed by a second
fraction (Rf = 0.17) containing the furazan 5c (8 mg, 6%).
Isoxazole 4c: White solid, m.p. 84–85 °C (89–90 °C;[12] 84.5–
85 °C[13]). 1H NMR (400 MHz, CDCl3): δ = 7.03 (s, 1 H, 4-H),
7.42–7.50 (m, 5 H, Ar-H), 7.60–7.63 (m, 1 H, Ar-H), 7.80–7.83 (m,
2 H, Ph-Hortho), 8.32–8.38 (m, 2 H, COPh-Hortho) ppm. 13C NMR
(100.58 MHz, CDCl3): δ = 100.2 (d, C-4), 126.0 (d, 2 C, COPh-
Cortho), 126.7 (s, COPh-Cipso), 128.5 (d, 2 C, Ph-Cmeta), 129.1 (d, 2
C, COPh-Cmeta), 130.6 (d, 2 C, Ph-Cortho), 130.7 (d, COPh-Cpara),
134.0 (d, Ph-Cpara), 135.7 (s, Ph-Cipso), 162.4 (s, C-3), 170.7 (s, C-
5), 185.7 (s, C=O) ppm. MS (EI): m/z (%) = 249 (17) [M+], 105
(11), 174 (3), 105 (100), 77 (72). IR (KBr) = ν 2967, 2875,
˜
1653 cm–1. C15H15NO2 (241.29): calcd. C 74.67, H 6.27, N 5.80;
found C 74.46, H 5.99, N 5.72.
(100) [(PhCO)+], 77 (94). IR: ν = 1662 (C=O), 1450 cm–1.
˜
Furazan 5a: Colourless crystals, hexane/diethyl ether (1:2), m.p. 99–
100 °C. 1H NMR (400 MHz, CDCl3): δ = 1.22–1.32 (m, 3 H, norb-
C16H11NO2 (249.27): calcd. C 77.10, H 4.45, N 5.62; found C
77.50, H 4.81, N 5.56.
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Eur. J. Org. Chem. 2006, 3016–3020