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12a
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13
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14d See also: Langille NF.
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Synthesis
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16 Compound 7 was
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Spilman CH.
Yagi Y.
Dinh DM.
Hart KL.
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17
Negishi E.
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18 A 1.5 M solution of t-BuLi
(2.30 mL, 3.45 mmol) in pentane was slowly added to a cooled (-78 °C)
solution of the primary alkyl iodide 8 (575
mg, 1.62 mmol) in diethyl ether (4 mL). After 1 h at -78 °C,
a 1.0 M solution of zinc chloride (2.50 mL, 2.50 mmol) in THF was
added and the resulting solution was stirred for 30 min at r.t.
This solution was added to a mixture of 2,4-dibromothiazole (2, 157 mg, 0.65 mmol), Pd2(dba)3 (15.0
mg, 33 µmol) and dppf (18.0 mg, 33 µmol) in THF
(5 mL). After stirring at r.t. for 16 h the reaction was quenched
by addition of a saturated NH4Cl solution (3 mL). The
aqueous layer was extracted with diethyl ether (3 × 20 mL).
The combined organic layers were washed with a saturated NaCl solution
(20 mL) and dried over Na2SO4. After filtration
and removal of the solvent in vacuo the residue was purified by
flash chromatography (pentane-diethyl ether = 95:5).
Compound 9 (215 mg, 54.8 µmol, 85%)
was obtained as an orange oil. 1H NMR (360 MHz, CDCl3) δ = 0.53
(q, 3
J = 7.9
Hz, 6 H), 0.93 (t, 3
J = 7.9
Hz, 9 H), 1.17 (s, 6 H), 1.42-1.46 (m, 4 H), 1.70-1.83
(m, 2 H), 2.99 (t, 3
J = 7.7
Hz, 2 H), 7.05 (s, 1 H, CHar). 13C
NMR (90 MHz, CDCl3) δ = 6.8,
7.1, 23.8, 29.9, 30.4, 33.7, 44.6, 73.2, 115.6, 124.2, 172.7.
19 The methods we tried included Pd(0)-catalyzed
cross-coupling reactions with bis(pinacolato)diboron or hexamethyldistannane,
halogen-metal exchange reactions and reductive metalations. For
a review on this topic, see: Mongin F.
Quéginer G.
Tetrahedron
2001,
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20
Kelly TR.
Lang F.
J. Org. Chem.
1996,
61:
4623
21 A 1.5 M solution of t-BuLi
(1.80 mL, 2.70 mmol) in pentane was slowly added to a cooled (-78 °C)
solution of the 4-bromothiazole 9 (511
mg, 1.30 mmol) in diethyl ether (10 mL). After 10 min at -78 °C,
a 1.0 M solution of chlorotrimethyltin (2.60 mL, 2.60 mmol) in THF
was added and the resulting mixture was stirred for 2 h at r.t. Subsequently,
diethyl ether (20 mL) and water (5 mL) were added. The organic layer
was dried over Na2SO4. After removal of the
solvent in vacuo crude stannane 10 (620
mg, 1.30 mmol, quant.) was obtained as an yellow oil. The stannane
(90.0 mg, 186 µmol) was added to a solution of iodopyridine 6 (60.0 mg, 186 µmol) and PdCl2(PPh3)2 (6.5 mg,
9.3 µmol) in dioxane (25 mL). After stirring at reflux
for 24 h the solvent was removed in vacuo and the residue was purified
by flash chromatography (pentane-EtOAc-triethylamine = 80:20:5).
Compound 11 (71.0 mg, 140 µmol,
75%) was obtained as a yellow oil. 1H
NMR (360 MHz, CDCl3) δ = 0.53
(q, 3
J = 7.9
Hz, 6 H), 0.91 (t, 3
J = 7.9 Hz,
9 H), 1.17 (s, 6 H), 1.42-1.52 (m, 4 H), 1.76-1.88
(m, 2 H), 3.10 (t, 3
J = 7.8
Hz, 2 H), 3.87 (s, 3 H), 3.95 (s, 3 H), 4.00 (s, 3 H), 7.71 (s,
1 H), 7.89 (s, 1 H). 13C NMR (90 MHz, CDCl3) δ = 6.5,
7.0, 24.0, 29.7, 30.4, 33.6, 44.5, 52.7, 56.1, 60.4, 73.0, 108.3,
120.1, 143.9, 145.8, 146.0, 149.8, 159.4, 165.5, 170.9.
22
Nicolaou KC.
Webber SE.
Synthesis
1986,
453