Synlett 2014; 25(09): 1291-1294
DOI: 10.1055/s-0033-1341230
letter
© Georg Thieme Verlag Stuttgart · New York

Ruthenium-Catalyzed C–H Silylation of 1-Arylpyrazole Derivatives and Fluoride-Mediated Carboxylation: Use of Two Nitrogen Atoms of the Pyrazole Group

Tsuyoshi Mita*
a  Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan   Fax: +81(11)7064982   Email: tmita@pharm.hokudai.ac.jp   Email: biyo@pharm.hokudai.ac.jp
,
Hiroyuki Tanaka
a  Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan   Fax: +81(11)7064982   Email: tmita@pharm.hokudai.ac.jp   Email: biyo@pharm.hokudai.ac.jp
,
Kenichi Michigami
a  Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan   Fax: +81(11)7064982   Email: tmita@pharm.hokudai.ac.jp   Email: biyo@pharm.hokudai.ac.jp
,
Yoshihiro Sato*
a  Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan   Fax: +81(11)7064982   Email: tmita@pharm.hokudai.ac.jp   Email: biyo@pharm.hokudai.ac.jp
b  ACT-C, Japan Science and Technology Agency (JST), Sapporo 060-0812, Japan
› Author Affiliations
Further Information

Publication History

Received: 27 February 2014

Accepted after revision: 24 March 2014

Publication Date:
28 April 2014 (online)

Abstract

Carboxylation of 1-arylpyrazole derivatives was developed using a ruthenium-catalyzed ortho silylation in conjunction with fluoride-mediated carboxylation with carbon dioxide. The two nitrogen atoms of pyrazole play crucial roles in promoting ortho silylation via the formation of a five-membered ruthenacycle and in accelerating aryl anion formation by lowering the electron density of the aromatic ring.

Supporting Information

 
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  • 16 General Procedure for the One-Pot Carboxylation Into a 10 mL sealed tube was placed substrate 1j (47.5 mg, 0.3 mmol, 1.0 equiv), and then the tube was evacuated and backfilled with argon (3×). To the reaction tube were added toluene (0.15 mL, 2.0 M), norbornene (141.2 mg, 1.5 mmol, 5.0 equiv), RuH2(CO)(PPh3)3 (5.6 mg, 0.006 mmol, 2 mol%), and HSiEt3 (174.4 mg, 0.24 mL, 1.5 mmol, 5.0 equiv). The system was closed and stirred at 100 °C for 20 h. The reaction mixture was directly pumped up at r.t. to remove volatile materials such as toluene, HSiEt3, and norbornene, followed by the introduction of CO2 (balloon). To the residue were added DMF (3.0 mL, 0.1 M) and flame-dried CsF (136.7 mg, 0.9 mmol, 3.0 equiv). The system was closed again and stirred at 100 °C under 1 atm of CO2 for 16 h. The reaction mixture was then cooled to r.t. and treated with Cs2CO3 (117.3 mg, 0.36 mmol, 1.2 equiv) and MeI (51.1 mg, 22.4 μL, 0.36 mmol, 1.2 equiv) followed by stirring at r.t. for 30 min. H2O was added, and the mixture was extracted with EtOAc (3 × 10 mL). The combined organic layer was washed with H2O (1×) and brine (1×) and then dried over Na2SO4. After removal of the solvent under reduced pressure, the residue was purified by silica gel column chromatography (hexane–EtOAc, 7:1) to afford the corresponding ester 3j (54.9 mg, 253.9 μmol, 85% yield); white solid; mp 64.3–66.0 °C. IR (Nujol): 2924, 2854, 1731, 1589, 1518, 1301, 1199, 1149, 1114, 747 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.74 (d, J = 7.7 Hz, 1 H), 7.71 (d, J = 1.7 Hz, 1 H), 7.52 (d, J = 2.3 Hz, 1 H), 7.46 (d, J = 8.3 Hz, 1 H), 7.40 (dd, J = 8.3, 7.7 Hz, 1 H), 6.44 (dd, J = 2.3, 1.7 Hz, 1 H), 3.63 (s, 3 H), 2.10 (s, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 166.2, 140.1, 138.8, 136.9, 134.2, 131.3, 129.6, 128.7, 128.2, 106.0, 52.2, 17.3 ppm. HRMS (EI): m/z calcd for C12H12N2O2 [M]+: 216.0899; found: 216.0895.