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For the main references at this
time to obtain 5-indazolyl-boronic acids and esters, see:
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Alberti MJ, and
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Hagihara M,
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For the main references at this
time to obtain 6-indazolyl-boronic acids and esters, see:
<A NAME="RG32908ST-14A">14a</A>
Frazee JS,
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For the main references at this
time about 7-indazolyl-boronic acids and esters, see:
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Shipps GW,
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Huang X,
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Typical Experimental
Procedure for the Synthesis of Indazolylboronic Esters
To
a solution of 1-(4-bromoindazol-1-yl)ethanone (3a,
1.5 g, 6.3 mmol) in 1,4-dioxane (25 mL) were added successively bis(pinacolato)diboron
(1.8 g, 7.2 mmol, 1.15 equiv) and KOAc (2.8 g, 23.8 mmol, 4.6 equiv)
at r.t. The reaction mixture was degassed under vacuum with argon replacement
three times, then PdCl2
(dppf)-CH2Cl2 (0.3
g, 0.5 mmol, 0.08 equiv) was added, and the degassing procedure
was repeated twice. The reaction was heated under reflux conditions
for 15 min then concentrated in vacuo. After the addition of EtOAc,
the organic layer was washed successively with H2O and
brine, dried over MgSO4, and the solvent evaporated in
vacuo. The crude material was purified by flash column chromatography
on SiO2 (EtOAc-cyclohexane, 1:3) to give 1-[4-(4,4,5,5-tetramethyl[1,3,2]-
dioxaborolan-2-yl)indazol-1-yl)ethanone
(7a); yield 1.8 g (98%); pink
solid; mp 128 ˚C. TLC: R
f
= 0.6
(EtOAc-cyclohexane, 1:4). IR (KBr): 2976, 1713, 1601, 1415,
1349, 1325, 1174, 1151, 932, 756 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 1.42 (s,
12 H), 2.80 (s, 3 H), 7.55 (t, J = 8.3
Hz, 1 H), 7.82 (d, J = 7.1
Hz, 1 ), 8.54 (d, J = 7.1
Hz, 1 H), 8.55 (s, 1 H). ¹³C NMR (100
MHz, CDCl3): δ = 23.1, 25.0, 84.2, 118.3,
128.6, 130.6, 132.0, 138.3, 141.7, 171.1. MS (EI): m/z (%) = 286
(53) [M+], 244 (100), 243
(39), 229 (14), 158 (70), 145 (34), 144 (68), 134 (67). Anal. Calcd
for C15H19BN2O3: C,
62.96; H, 6.69; N, 9.79. Found: C, 62.39; H, 6.48; N, 9.23.
For Suzuki-Miyaura cross-coupling
reactions using K3PO4 as base in DMF, see:
<A NAME="RG32908ST-26A">26a</A>
Cailly T.
Fabis F.
Rault S.
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Watanabe T.
Miyaura N.
Suzuki A.
Synlett
1992,
207
For Suzuki-Miyaura cross-coupling
reactions using Na2CO3 or Cs2CO3 as
base in dioxane, see:
<A NAME="RG32908ST-27A">27a</A>
Song YS.
Lee
Y.-J.
Kim BT.
Heo J.-N.
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Heo Y.
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Littke AF.
Fu GC.
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<A NAME="RG32908ST-28">28</A>
7-(4-Methoxyphenyl)-1-(tetrahydro-2
H
-pyran-2-yl)-1
H
-indazole (17)
Yield
0.3 g (73%); white solid. TLC: R
f
= 0.1
(EtOAc-cyclohexane, 1:10). IR (KBr): 3428, 2932, 1611,
1497, 1245, 1078, 1032, 824 cm-¹. ¹H
NMR (400 MHz, CDCl3):
δ = 1.37-1.42
(m, 2 H), 1.76-1.78 (m, 1 H), 1.90-1.95 (m,
1
H), 2.56-2.58 (m, 1 H), 2.91-2.96 (m, 1 H), 3.74-3.80
(m, 1 H), 3.91 (s, 3 H), 4.04-4.07 (m, 1 H), 5.00 (dd, J = 12.7, 2.2
Hz, 1 H), 7.02 (dd, J = 7.3,
1.4 Hz, 2 H), 7.18-7.19 (m, 2 H), 7.23-7.26 (m,
2 H), 7.64-7.70 (m, 1 H), 8.12 (s, 1 H). MS (EI): m/z (%) = 308
(22) [M
+
],
224 (100), 209 (26), 192 (2), 182 (8), 154 (7), 85 (8). Anal. Calcd
for C19H20N2O2: C, 74.00;
H, 6.54; N, 9.08. Found: C, 74.30; H, 6.74; N, 9.28.
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Schumann P.
Collot V.
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Dauphin F.
Sopkova J.
McKenzie ET.
Duval D.
Boulouard M.
Rault S.
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The use of Oxone® (2KHSO5-KHSO4-K2SO4)
as oxidative reagent in the presence of Na2CO3 in
a mixture of H2O-acetone (1:1) at 0 ˚C
led to the desired compounds but in lower yields.