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González-Gómez JC.
Santana L.
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5 Preparation of 1,4-dicarbomethoxypyridazine[4,5-f]benzo[b]furan(6).
Benzofuran-3(2H)-one (7;
142 mg, 1.05 mmol) was added to a dioxane (4 mL) solution of 3,6-dicarbomethoxy-1,2,4,5-tetrazine
(190 mg, 0.96 mmol) with a catalytic amount of p-TsOH
(10 mg). The reaction mixture was refluxed for 6 h until the red
color of the tetrazine had disappeared. The solvent was removed
under vacuum and the residue was purified by flash chromatography
using 1:2 Hex-EtOAc as eluent, giving pure 6;
yield: 200 mg (73%).
6 For preparation of the trimethylsilyl
enol 3 we followed the general procedure
described in: Lin J.-M.
Liu B.-S.
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1997,
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Guo Zh.
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11 The same regioselectivity on the
amidation of 7 was observed using the Weinreb
protocol: Benson SC.
Ph.D. Dissertation
Boston
University;
Boston MA:
1992.
12 Amidation of 6 in
the absence of MgCl2 afforded mixtures of monocarboxamides
C-4/C-1 in 65/35 for pyrrolidine and
70/30
for N,N-dimethylethylenediamine, as determined by 1H
NMR integration of H-9.
13
Nomak R.
Snyder JK.
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14a An
example of dealkoxycarbonylation on 1,4-diester piridazine systems
was previously described refluxing in 1:1 HCl-HOAc: Wan Z.-K.
Woo GHC.
Snyder JK.
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14b For reviews of dealkoxycarbonylations
see: Krapcho AP.
Synthesis
1982,
822 ; we are currently working on the optimization
of this reaction for the synthesis of related monocarboxamides
14c
Krapcho AP.
Synthesis
1982,
893 ;
we are currently working on the optimization of this reaction for
the synthesis of related monocarboxamides
15 Selected physical and spectroscopic
data of new compounds. Compound 6: mp 218-220 ºC(dioxane). 1H
NMR (CDCl3): δ = 8.87
(d, J = 7.95
Hz, 1 H, H-9), 7.82 (m, 2 H), 7.61 (dt, J = 6.60, 1.70 Hz, 1
H), 4.24 (s, 3 H, OCH3), 4.22 (s, 3 H, OCH3); 13C
NMR (CDCl3): δ = 165.08,
162.57, 157.87, 155.06, 147.87, 140.02, 133.24 (CH), 127.90 (CH),
125.95 (CH), 125.82, 118.48, 113.08 (CH), 54.03 (CH3),
53.94 (CH3); MS (EI): m/z (%) = 286
(M+, 1.9), 169 (100). Compound 8a:
mp 192-194 ºC. 1H NMR (CDCl3): δ = 8.89 (d, J = 8.15
Hz, 1 H, H-9), 7.82 (m, 2 H), 7.60 (dt, J = 6.60, 1.70 Hz, 1
H), 4.24 (s, 3 H, OCH3), 3.88 (t, J = 6.70 Hz, 2 H), 3.74
(t, J = 6.55
Hz, 2 H), 1.96-2.08 (m, 4 H); MS (EI): m/z (%) = 325
(M+, 23), 70 (100). Compound 8b:
mp 168-171 ºC. 1H NMR (CDCl3): δ = 8.89
(d, J = 8.15
Hz, 1 H, H-9), 8.72 (s, 1 H, NH), 7.87 (m, 1 H), 7.82 (m, 1 H),
7.60 (m, 1 H), 4.23 (s, 3 H, OCH3), 3.68 (t, J = 5.75
Hz, 2 H), 2.62 (t, J = 6.10 Hz, 2 H), 2.33
(s, 6 H). Compound 9a: 1H
NMR (CDCl3): δ = 11.00
(s, 1 H, NH), 8.84 (d, 1 H, J = 8.25 Hz, H-9), 7.57
(m, 2H, H-6/H-7), 7.37 (m, 1 H, H-8), 4.29 (t, J = 6.50 Hz,
2 H), 4.14 (s, 3 H, OCH3), 3.77 (t, J = 6.55 Hz, 2 H), 1.95
(m, 4 H); MS (EI):
m/z
(%) = 324
(M+, 15), 168 (100). Compound 9b: 1H
NMR (CDCl3): δ = 10.83
(s,
1 H, NH), 8.92 (d, J = 8.25 Hz, 1 H, H-9),
8.84 (s, 1 H, NH), 7.70 (m, 2 H), 7.49 (m, 1 H), 4.22 (s, 3 H, OCH3),
3.69 (m, 2 H), 2.64 (m, 2 H), 2.34 (s, 3 H), 2.33 (s, 3 H). Compound 10a: mp 190-193 ºC. 1H
NMR (CDCl3): δ = 8.42
(d, J = 7.90
Hz, 1 H, H-9), 7.75 (m, 2 H), 7.55 (m, 1 H), 3.80 (m, 8 H), 2.00
(m, 8 H); MS (EI):
m/z
(%) = 364
(M+, 29), 70 (100). Compound 10b:
mp 161-162 ºC. 1H NMR (CDCl3): δ = 9.27
(d, J = 8.15
Hz, 1 H, H-9), 8.76 (t, J = 4.80 Hz, 1 H, NH),
8.56 (t, J = 4.80
Hz, 1 H, NH), 7.88 (d, J = 8.45 Hz, 1 H), 7.77
(dt, J = 7.20,
1.35 Hz, 1 H), 7.58 (t, J = 8.18 Hz, 1 H), 3.73
(m, 4 H), 2.63 (m, 4 H), 2.33 (s, 6 H), 2.32 (s, 6 H). Compound 11a: 1H NMR (CDCl3): δ = 8.34
(d, J = 8.10 Hz,
1 H, H-9), 7.65 (m, 2 H), 7.40 (m, 1 H), 4.35 (t, J = 6.40 Hz, 2 H), 3.88
(m, 4 H), 3.56 (t, J = 6.50 Hz, 2 H), 2.00
(m, 8 H); MS (EI):
m/z
(%) = 363
(M+, 4), 70 (100). Compound 11b: 1H
NMR (CDCl3): δ = 10.86
(s, 1 H, NH), 9.35 (d, J = 8.20 Hz, 1 H), 8.73
(m, 2 H, 2NH), 7.65 (m, 2 H), 7.44 (m, 1 H), 3.75 (m, 2 H), 3.68
(m, 2 H), 2.67 (m, 2 H), 2.63 (m, 2 H), 2.35 (s, 6 H), 2.34 (s,
6 H). Compound 12: 1H
NMR (CDCl3): δ = 9.86
(s, 1 H, H-1), 8.13 (d, J = 7.80 Hz, 1 H, H-9),
7.75 (m, 2 H), 7.56 (m, 1 H), 3.86 (t, J = 6.80
Hz, 2 H), 3.76 (t, J = 6.50
Hz, 2 H), 2.00 (m, 4 H); 13C NMR (CDCl3): δ = 162.29,
156.91, 152.28, 146.09, 145.02, 131.80 (CH), 125.45 (CH), 124.49,
122.66 (CH), 119.56 (CH), 113.67 (CH), 49.11 (CH2), 46.99
(CH2), 26.67 (CH2), 24.56 (CH2). Compound 13: 1H NMR (CDCl3): δ = 10.62
(s, 1 H, NH), 9.76 (s, 1 H, H-1), 8.15 (d, J = 7.95 Hz, 1 H, H-9),
7.57 (m, 2 H), 7.36 (m, 1 H), 4.30 (t, J = 6.40
Hz, 2 H), 3.77 (t, J = 6.50
Hz, 2 H), 1.90 (m, 4 H); 13C NMR (CDCl3): δ = 163.25,
143.07, 140.42, 138.96, 135.26, 128.66 (CH), 121.06 (CH), 120.88,
120.21 (CH), 118.41 (CH), 111.55 (CH), 49.16 (CH2), 46.98
(CH2), 25.90 (CH2), 22.57 (CH2).
16
González JC.
Lobo-Antunes J.
Pérez-Lourido P.
Santana L.
Uriarte E.
Synthesis
2002,
475
