Yield:-

Reaction Conditions:

Stage #1: 2,5-dimethyl-3-bromopyridinewith n-butyllithium in hexanes;diethyl ether at -78; for 1 h;Inert atmosphere;
Stage #2: with Triisopropyl borate in hexanes;diethyl ether at 20;
Stage #3: with ammonium chloride in hexanes;diethyl ether;

Steps:

99.4

n-BuLi (1.6 M in hexanes, 6.7 ml_, 10.8 mmol, 2.0 equiv) was added dropwise to a cold (- 78°C) solution of 3-bromo-2,5-dimethyl-pyridine (Bulletin de Ia Societe Chimique de France, 1972, (6), 2466-81 ) (1 g, 5.38 mmol) in Et₂O (20 ml_), under an argon atmosphere. The reaction mixture was stirred for 1 h at -78°C. Triisopropyl borate (3.7 ml_, 16.1 mmol, 3.0 equiv) was then added. The reaction mixture was allowed to warm to rt, quenched by addition of a saturated solution of NH₄CI (1 ml_), and concentrated. The residue was diluted with EtOAc/H₂O and the pH adjusted to 7. The aqueous layer was separated and extracted with EtOAc. The organic phase was dried (Na₂SO₄), filtered and concentrated to afford 170 mg of the title compound as a beige solid (batch 1 ). The aqueous layer was concentrated, the residue combined with batch 1 and dissolved in EtOH (5 ml_). This solution was added to a mixture of 5,8-dibromo-quinoxaline (800 mg, 2.8 mmol) (Step 1.5), PdCI₂(dppf) (1 13 mg, 0.1 mmol, 0.05 equiv), Na₂COs (2 M solution in H₂O, 5.6 ml_, 1 1.1 mmol, 4 equiv) in toluene (30 ml.) at 105⁰C, under an argon atmosphere. The reaction mixture was stirred at 105 ⁰C for 4 h, allowed to cool to rt, diluted with EtOAc and H₂O, and extracted with EtOAc. The organic phase was washed with H₂O and brine, dried (Na₂SO₄), filtered and concentrated in vacuo. The crude product was purified by silica gel column chromatography (Hex/EtOAc, 1 :4) to afford 250 mg of the title compound as a purple solid: ES-MS: 314.0 / 316.0 [M+H]⁺; t_R= 2.63 min (System 1 ); R_f = 0.09 (Hex/EtOAc, 1 :4).

References:

WO2009/141386,2009,A1 Location in patent:Page/Page column 121