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HETEROCYCLES, Vol. 75, No. 1, 2008
hexane/EtOAc). Mp 139-140 ºC (lit.,9a 141-142 ºC) (hexane). 1H NMR (400.16 MHz, CDCl3): δ 7.49 (dd,
J = 5.2, 1.8 Hz, 2H), 8.46 (d, J = 5.2 Hz, 2H), 8.60 (d, J = 1.8 Hz, 2H). 13C NMR (100.62 MHz, CDCl3): δ
124.8 (CH), 127.4 (CH), 134.0 (C), 149.8 (CH), 156.0 (C).
Method b: 4-bromo-2-trimethylstannylpyridine (11): In a dry Schlenk flask, Pd(PPh3)2Cl2 (0.075 g,
0.105 mmol), LiCl (0.015 g, 0.3 mmol) and toluene (5 mL) were placed and purged with argon. Then
Me6Sn2 (1.2 mL of a solution 0.97 M in toluene, 1.15 mmol) was added followed by 2,4-dibromopyridine
(1a) (0.250 g, 1.05 mmol). The reaction mixture was stirred at 90 ºC for 16 h, then washed with aqueous
saturated KF and extracted with CH2Cl2. The combined organic layer was separated, dried over Na2SO4
and the solvent removed under reduced pressure. Purification by distillation afforded
4-bromo-2-trimethylstannylpyridine (12a) (220 mg, 65%) along with a compound identified as
1
2-bromo-4-trimethylstannylpyridine in a 20:1 ratio. H NMR (400.16 MHz, CDCl3): δ 0.36 (s, J119Sn-H
2
=
2
3
56.2 Hz, J117Sn-H = 53.7 Hz, 9H), 7.33 (dd, J = 5.4, 2.1 Hz, 1H), 7.61 (d, J =2.0 Hz, J119Sn-H = 22.3 Hz,
3J117Sn-H = 18.4 Hz, 1H), 8.53 (d, J = 5.4 Hz, 1H). 13C NMR (100.61 MHz, CDCl3): δ -9.8 (CH3), 89.8 (C),
125.3 (CH), 131.8 (C), 134.0 (CH), 150.8 (CH). MS (FAB+) m/z (%): 322 ([M+1]+, 6). HRMS (FAB+)
1
calcd. for C8H13NBrSn 319.9244, found 319.9247. 2-Bromo-4-trimethylstannylpyridine: H-NMR
(400.16 MHz, CDCl3): δ 0.35 (s, 2JSn-H = 55.4 Hz, 9H), 7.32 (d, J = 4.5 Hz, 3JSn-H = 37.8 Hz, 1H), 7.56 (bs,
3JSn-H = 39.6 Hz, 1H), 8.26 (d, J = 4.5 Hz, 1H). MS (FAB+) m/z (%): 322 ([M+1]+, 43).
Stille coupling: Pd(PPh3)4 (0.4 g, 0.035 mmol), CuI (135 mg, 705 mmol),
4-bromo-2-trimethylstannylpyridine (12a) (0.11 g, 0.35 mmol) and 2,4-dibromopyridine (1a) (90 mg, 0.4
mmol) were heated in degassed THF (4 mL) at 100 ºC for 96 h under argon. The reaction mixture was
allowed to cool to 25 ºC, the solvent evaporated and the residue was taken up in CH2Cl2. Then a 30%
NH4OH (1 mL) and EDTA (0.18 g) were added and the mixture stirred at 40 ºC for 1 h. The organic
phase was separated and the aqueous layer was extracted with CH2Cl2. The combined organic layers were
dried, the solvent removed and the residue purified by chromatography in alumina grade III (10:90
CH2Cl2/hexane) to give 4,4’-dibromo-2,2’-bipyridine (2a) (63 mg, 57 %). 2,4’-Dibromo-4,2’-bipyridine:
1H-NMR (400.16 MHz, CDCl3): δ 7.55 (dd, J = 5.2, 1.2 Hz, 1H), 7.83 (dd, J = 5.2, 1.6 Hz, 1H), 7.94 (d, J
= 1.6 Hz, 1H), 8.10 (d, J = 1.2 Hz, 1H), 8.49 (d, J = 5.2 Hz, 1H), 8.56 (d, J = 5.2 Hz, 1H). 13C NMR
(100.61 MHz, CDCl3): δ 120.1 (CH), 124.5 (CH), 125.6 (CH), 127.5 (CH), 134.0 (C), 143.2 (C), 147.8
(C), 150.7 (C), 150.8 (C), 154.3 (C). MS (EI+) m/z (%): 317 ([M+1]+ 81[Br], 6), 316 ([M]+ 81[Br], 53), 315
([M+1]+ 79[Br] [Br], 13), 314 ([M]+ 79[Br] 81[Br], 96), 313 ([M+1]+ 79[Br], 7), 312 ([M]+ 79[Br], 54).
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HRMS (EI+) calcd. for C10H6N2Br2 311.8898, found 311.8891. 4,4”-Dibromo-2,4’:2’,2”-terpyridine:
1H-NMR (400.16 MHz, CDCl3): δ 7.52 (dd, J = 5.1, 1.6 Hz, 1H), 7.54 (dd, J = 5.2, 1.8 Hz, 1H), 8.01 (dd,
J = 5.1, 1.4 Hz, 1H), 8.13 (d, J = 1.8 Hz, 1H), 8.54 (d, J = 5.1 Hz, 1H), 8.59 (d, J = 5.2 Hz, 1H), 8.70 (d, J
13
= 1.6 Hz, 1H), 8.81 (d, J = 5.1 Hz, 1H), 8.94 (d, J = 1.4 Hz, 1H). C NMR (100.61 MHz, CDCl3):