230
Vol. 38
B. Boutemeur-Kheddis, M. Hamdi, N. Sellier and A. M. S. Silva
3-Methyl-5-(7-methyl-2,5-dioxopyrano[4,3-b]pyran-3-yl)-1-
phenylpyrazole 8a.
was also obtained from the reaction of 11 with phenyl-
hydrazine. The H nmr spectrum of 14 indicates that only
1
one diastereomer, E or Z, is present. The proton resonances
reported by Zaman et al. [5] for phenylhydrazone 7 are
very similar to those which we attributed to compound 14.
However, the melting points values of these two
compounds are very different (222-225 ºC for 7 and
197-198 °C for 14).
A solution of 3 (0.01 mole) and phenylhydrazine (0.01 mole)
in a mixture of ethanol-acetic acid (50 mL) was refluxed for
6 hours. After evaporation of the solvent, the residue was poured
into cooled water to afford a yellow solid, which was collected
and recrystallized from methanol yielding pyrazole 8a (2.7 g,
1
80%), mp 186 ºC; H nmr (deuteriochloroform): δ 2.23 (s, 3H,
7'-CH ), 2.37 (s, 3H, 3-CH ), 6.13 (s, 1H, H-8'), 6.51
3
3
The formation of compounds 10 and 13 from the
reaction of 3 with aromatic amines (Scheme 2) prompted
us to suggest the mechanism depicted in Scheme 4 for
these transformations. However, if we consider that a
retrocondensation can also occur under the experimental
conditions, an alternative mechanism can also be proposed
(Scheme 5). Our results support the first mechanism, but
the results of Castillo et al. [8] showing that compound 15
was obtained from the reaction of 1 with aniline, indicate
that the second mechanism is also possible. As our results
do not exclude the second mechanism, other trans-
formations are being carried out in order get more
information to prove or to eliminate this alternative
mechanism (Scheme 5).
(s, 1H, H-4'), 7.35 (s br, 5H, C H ), 7.64 (s, 1H, H-4); ms (EI):
6
5
+
m/z (relative intensity) 334 (M., 100), 306 (37), 305 (20), 291
(16), 276 (18), 222 (82), 85 (50), 83 (44), 77 (63), 69 (28), 63
(16), 51 (24), 43 (41).
Anal. Calcd. for C H N O : C, 68.26; H, 4.19; N, 8.38.
19 14
2 4
Found: C, 67.96; H, 3.96; N, 8.31.
3-Methyl-5-(7-methyl-2,5-dioxopyrano[4,3-b]pyran-3-yl)-
isoxazole 8b.
A solution of 3 (0.01 mole) and hydroxylamine (0.01 mole) in
a mixture of ethanol- acetic acid (50 mL) was refluxed for
4 hours. After cooling, the reaction mixture was filtered and the
solvent evaporated to dryness. The obtained residue was
recrystallized from toluene to give isoxazole 8b (2.2 g, 83%), mp
1
272 ºC; H nmr (deuteriochloroform): δ 2.35 (s, 3H, 7'-CH ),
3
In summary, we have shown that the reaction of
3-acetoacetyl-7-methyl-2H,5H-pyrano[4,3-b]pyran-2,5-
dione 3 with aniline derivatives and with phenylhydrazine
follows the same pathway, giving 3-(arylaminomethylene)-
4–oxo-6-methyl-2-pyrone derivatives 10 and 13 and
3-(phenylhydrazinomethylene)-4-oxo-6-methyl-2-pyrone
14, respectively. Although these transformations were
carried out under the experimental conditions reported by
Zaman et al. [5], our results are completely different. On the
other hand the reaction mechanism they propose does not
explain the formation of the products that we have obtained.
2.39 (s, 3H, 3-CH ), 6.25 (s, 1H, H-8'), 6.87 (s, 1H, H-4'), 8.50
(s, 1H, H-4); ms (EI): m/z (relative intensity) 259 (M., 100), 205
(18), 134 (13), 120 (17), 106 (16), 85 (47), 83 (63), 82 (46), 78
(17), 69 (21), 63 (16), 53 (17), 50 (17), 47 (14), 43 (68).
3
+
Anal. Calcd. for C H NO : C, 60.23; H, 3.47; N, 5.40. Found:
13
9
5
C, 60.43; H, 3.30; N, 5.20.
3-Methyl-5-(7-methyl-2,5-dioxopyrano[4,3-b]pyran-3-yl)-
pyrazole 8c.
A solution of 3 (0.01 mole) and hydrazine (0.01 mole) in a
mixture of ethanol and acetic acid (50 mL) was refluxed for 3
hours. After cooling, the solvents were evaporated to dryness and
the residue was recrystallized from toluene to yield pyrazole 8c
EXPERIMENTAL
1
(1.8 g, 70%), mp 230 °C; H nmr was not registered due to the
insolubility of 8c in common solvents; ms (EI): m/z (relative
+
intensity) 258 (M., 100), 230 (18), 109 (15), 106 (18), 105 (14),
Melting points were determined in an Electrothermal
1
13
89 (16), 85 (29), 83 (33), 77 (17), 69 (14), 63 (18), 55 (11), 43
apparatus. H nmr and C spectra were recorded on a Bruker AC
200 and an ARX Bruker WM 300 instruments; the chemical
shifts are expressed in δ (ppm) values relative to tetramethyl-
silane as an internal reference. Mass spectra were recorded on a
Nermag R10-10C quadrupole mass spectrometer.
(57), 39 (13).
Anal. Calcd. for C H N O : C, 60.46; H, 3.87; N, 10.85.
Found: C, 60.26; H, 4.02; N, 11.02.
13 10
2 4
Synthesis of Compounds 9 and 10.
3-Acetoacetyl-7-methyl-2H,5H-pyrano[4,3-b]pyran-2,5-dione
3a and its Enolic Form 3b.
A solution of 3 (0.01 mole) and 2,4-dimethoxyaniline
(0.01 mole) in a mixture of ethanol and acetic acid (50 mL) was
refluxed for 1 hour. After cooling, the mixture was filtered and
the solvent was evaporated. The obtained residue was washed
with hot ethanol giving a soluble fraction which corresponds to
pyranopyran-2,5-dione 9 (1.6 g, 40%), whereas the rest was
recrystallised in ethanol giving pyran-2,4-dione 10 (1.1 g, 38%).
3-[3-(2,4-Dimethoxyphenylimino)-1-oxobutan-1-yl]-7-methyl-
A solution of 4-hydroxy-6-methylpyran-2-one 1 (triacetic
lactone) (0.02 mole) and triethyl orthoformate (9 mL) in ethanol
(30 mL) was refluxed for 4 hours. The precipitate was collected
and recrystallized from ethanol or toluene to yield compounds 3
1
(1.8 g, 70%), mp 192-193 °C; H nmr (deuteriochloroform): δ
2.23 (s, 3H, 7-CH ), 2.40 (s, 3H, H-4'), 4.11 (s, 2H, H-2', dione),
3
1
2H,5H-pyrano[4,3-b] pyran-2,5-dione 9, mp 270 ºC; H nmr
6.23 (m, 1H, H-8), 6.61 (s, 1H, H-4), 8.76 (s, 1H, H-2', enol),
15.74 (s, 1H, OH, enol); ms (EI): m/z (relative intensity) 262
(deuteriochloroform): δ 2.06 (d, 3H, 7-CH ), 2.21 (s, 3H, 3'-CH ),
3
3
+
(M., 32), 247 (14), 219 (6), 205 (100), 150 (8), 95 (11), 84 (6), 69
3.75 (s, 3H, OCH ), 3.84 (s, 3H, OCH ), 6.19 (s, 1H, H-8), 6.56
3 3
(25), 67 (5), 57 (9).
Anal. Calcd. for C
59.55; H, 3.80.
(m, 2H, C H ), 6.85 (m, 1H, C H ), 7.00 (s, 1H, H-4), 8.92 (s, 1H,
6 3 6 3
2'-H); ms (EI): m/z (relative intensity) 397 (M., 100), 396 (29),
340 (18), 285 (17), 282 (30), 84 (27), 59 (12), 55 (13), 43 (28).
+
H
O : C, 59.54; H, 3.82. Found: C,
13 10
6