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A. Kotschy et al. / Tetrahedron 60 (2004) 3421–3425
poured into cold water. The resulting precipitate was filtered
off, washed with cold water and dried. The crude products,
which consist in each case of a mixture of three isomers
(syn,syn; syn,anti; anti,anti) were used in the subsequent
step without further purification.
2H, J¼7.7 Hz), 7.59–7.40 (m, 12 H), 6.90 (t, 1H,
J¼11.7 Hz), 6.86 (d, 1H, J¼12.1 Hz), 6.84 (t, 1H,
J¼12.0 Hz), 6.45 (t, 1H, J¼9.0 Hz), 5.93 (d, 1H,
J¼14.7 Hz), 5.56 (d, 1H, J¼9.0 Hz), 5.07 (t, 1H,
J¼11.9 Hz), 3.24–3.20 (m, 4H), 3.38–3.34 (m, 4H),
1.91–1.87 (m, 4H), 1.84–1.80 (m, 4H).
12a: Yield: 0.91 g (97%), yellow solid; 12b: Yield: 0.90 g
(96%), yellow solid.
15b: Yield: 0.28 g (92%), yellow solid, a 40:60 mixture
of E,E–E,E and Z,E–E,E isomers; 1H NMR (CDCl3):
(E,E–E,E) 8.28 (s, 4H), 7.57–7.38 (m, 12H), 6.87 (d, 2H,
overlapping signals), 5.91 (d, 2H, J¼14.8 Hz), 5.06 (t, 2H,
J¼12.1 Hz), 3.25–3.21 (m, 8H), 1.90–1.84 (m, 8H); (Z,E–
E,E) 8.32 (d, 2H, J¼4.8 Hz), 8.27 (d, 2H, J¼5.1 Hz), 7.59–
7.40 (m, 11 H), 6.87–6.84 (m, 3H), 6.46 (dd, 1H, J¼11.0,
10.2 Hz), 5.91 (d, 1H, J¼14.8 Hz), 5.53 (d, 1H, J¼11.0 Hz),
5.06 (dd, 1H, J¼14.8, 10.2 Hz), 3.39–3.35 (m, 4H), 3.23–
3.20 (m, 4H), 1.98–1.93 (m, 4H), 1.89–1.84 (m, 4H).
4.1.5. 1,10-m-, and 1,10-p-Phenylenebis(3-phenyl-
[1,2,3]triazolo[1,5-a]pyridinium) bis-fluoroborate 13a
and 13b. Solutions of 2,4,4,6-tetrabromocyclohexa-2,5-
dienone13 (1.05 g, 2.5 mmol) in dichloromethane (3 ml) and
of the appropriate hydrazone 12a or 12b (0.20 g, 0.4 mmol)
in dichloromethane (2 ml) were mixed and stirred at
ambient temperature for 30 min. Ether was added to the
resulting mixture and the precipitate was filtered off,
dissolved in nitromethane and the solution treated with
cyclohexene (1 ml). Ether was then added to the solution,
and the resulting precipitate was filtered off; the crude
bromide salt was converted into the tetrafluoroborate by
addition of acetonitrile (3 ml) followed by 40% tetrafluoro-
boric acid (4 drops). The resulting solution was diluted with
water and extracted with nitromethane. The combined
organic extracts were dried, the solvent evaporated and the
crude product recrystallised from dimethylformamide–
water.
16a: Yield: 0.265 g (88%), yellow solid, a 90:10 mixture
of E,E–E,E and Z,E–E,E isomers; 1H NMR (CDCl3):
(E,E–E,E) 8.10 (1H, t, J¼1.5 Hz), 8.07 (4H, d, J¼7.7 Hz),
7.71 (2H, dd, 7.7, J¼1.5 Hz), 7.49 (1H, t, J¼7.7 Hz), 7.39
(4H, t, J¼7.7 Hz), 7.22 (2H, t, J¼7.7 Hz), 7.16 (2H, dd,
J¼15.2, 10.9 Hz), 6.65 (2H, d, J¼13.2 Hz), 6.18 (2H, d,
J¼15.2 Hz), 5.09 (2H, dd, J¼13.2, 10.9 Hz), 3.12 (8H, t,
J¼6.8 Hz), 1.81 (8H, t, J¼6.8 Hz); 13C NMR (CDCl3):
146.60, 145.30, 142.10, 140.40, 135.90, 132.30, 129.50,
129.30, 128.40, 128.35, 127.00, 118.90, 106.00, 99.30,
49.30, 25.70.
13a: Yield: 0.15 g (59%), white solid, mp: 268–269 8C
(dec); IR 1624, 1492, 1124, 1084, 1039, 694 cm21 1H
;
NMR: 9.40 (d, 2H, J¼7.0 Hz), 9.04 (d, 2H, J¼8.8 Hz), 8.70
(br s, 1H), 8.47 (d, 2H, J¼7.7 Hz), 8.41 (br t, 2H,
J¼7.6 Hz), 8.09–8.01 (m, 7H), 7.89–7.86 (m, 6H), 7.75;
13C NMR: 141.47, 136.21, 134.58, 134.13, 133.72, 131.70,
131.08, 130.31, 129.18, 128.11, 127.63, 126.20, 124.79,
121.55; Anal. Calcd For C30H22N6B2F8: C, 56.29; H, 3.46;
N, 13.13; found C, 55.90; H, 3.55; N, 13.40%.
16b: Yield: 0.235 g (78%), yellow solid, a 85:15 mixture
of E,E–E,E and Z,E–E,E isomers; 1H NMR (CDCl3):
(E,E–E,E) 8.17 (4H, d, J¼7.7 Hz), 7.91 (4H, s), 7.50 (4H, t,
J¼7.7 Hz), 7.33 (2H, t, J¼7.7 Hz), 7.26 (2H, dd, J¼15.3,
12.7 Hz), 6.78 (2H, d, J¼12.9 Hz), 6.27 (2H, d, J¼15.3 Hz),
5.19 (2H, t, J¼12.7 Hz), 3.25 (8H, t, J¼6.2 Hz), 1.94 (8H, t,
J¼6.2 Hz); 13C NMR (CDCl3): 146.6, 145.2, 142.1, 140.4,
135.9, 131.6, 129.5, 128.8, 127.0, 118.9, 106.0, 99.1, 49.3,
25.7.
13b: 0.18 g (70%), white solid, mp: .290 8C; IR 1627,
1494, 1427, 1126, 1060, 850, 742 cm21; 1H NMR: 9.38 (d,
2H, J¼7.0 Hz), 9.05 (d, 2H, J¼8.7 Hz), 8.46 (s, 4H), 8.40
(dd, 2H, J¼8.9, 7.0 Hz), 8.13–7.98 (m, 8H), 7.91–7.87 (m,
4H); 13C NMR: 141.27, 136.20, 134.80, 134.56, 134.14,
133.75, 131.70, 130.29, 128.10, 126.24, 124.79, 121.55;
Anal. Calcd For C30H22N6B2F8: C, 56.29; H, 3.46; N, 13.13;
found C, 56.44; H, 3.32; N, 12.91%.
4.1.7. General procedure for the inverse electron-
demand Diels–Alder reaction of bis-dienamines
(14a–b, 15a–b) with dimethyl 1,2,4,5-tetrazine-3,6-
dicarboxylate (3). The tetrazine diester 314 (0.070 g,
0.35 mmol) was added in one portion to the slurry of the
appropriate bis-dienamine 15a–b or 16a–b (0.097 g,
0.16 mmol) in dichloromethane (5 ml) and the mixture
was stirred for 6 h. After evaporation of the solvent the
residue was washed with ether and the crude product
recrystallised from aqueous dimethylformamide.
4.1.6. General procedure for the ring opening of the bis-
triazolopyridinium salts (8a–b, 13a–b) with pyrrolidine.
The synthesis of bis-dienamines. Pyrrolidine (0.7 ml) was
added to a slurry of the appropriate bis-salt (0.32 g,
0.5 mmol) in acetonitrile (5 ml) and the resulting mixture
was stirred at room temperature for 3 days. The precipitate
which formed was filtered off, washed, and dried to give the
crude dienamine, which was used without further purifi-
cation in the subsequent step.
17a: Yield: 0.15 g (59%), white solid, mp: 215–216 8C
(dec.); IR 1730, 1499, 1264, 1137, 772, 693 cm21 1H
;
NMR: 8.86 (s, 1H), 8.48 (s, 2H), 8.22 (d, 2H, J¼8.3 Hz),
8.06 (d, 2H, J¼16.1 Hz), 7.73–7.61 (m, 11H), 7.37 (d, 2H,
J¼16.1 Hz), 4.00 (s, 6H), 3.98 (s, 6H); 13C NMR: 165.46,
164.92, 164.50, 161.64, 153.10, 153.00, 152.15, 135.79,
130.67, 130.46, 130.21, 128.25, 126.39, 126.29, 124.50,
124.07, 122.91, 54.23, 54.09; Anal. Calcd For
C42H32N10O8: C, 62.68; H, 4.01; N, 17.40; found C,
62.34; H, 4.16; N, 17.32%.
15a: Yield: 0.30 g (99%), yellow solid, a 70:30 mixture
of E,E–E,E and Z,E–E,E isomers; 1H NMR (CDCl3):
(E,E–E,E) 9.01 (s, 1H), 8.22 (d, 2H, J¼7.7 Hz), 7.59–7.40
(m, 13H), 6.86 (d, 2H, J¼12.1 Hz), 5.93 (d, 2H,
J¼14.7 Hz), 5.07 (t, 2H, J¼11.9 Hz), 3.25–3.20 (m, 8H),
1.92–1.87 (m, 8H); (Z,E–E,E) 9.09 (s, 1H), 8.26 (d,
17b: Yield: 0.18 g (70%), white solid, mp: .290 8C (dec.