The general procedure for the synthesis of [2,3'-bipyridin]-6'(1'H)-ones from 2-bromopyridine and 2-hydroxypyridine-5-boronic acid pinacol ester was carried out as follows: firstly, the synthesis of [2,3'-bipyridin]-6'(1'H)-one was carried out by Suzuki coupling reaction of 2-bromopyridine (18) with 6-hydroxypyridine-3-boronic acid pinacol ester catalyzed by Pd(PPh3)4, with Na2CO3 as the base and CH3CN/H2O ( 1/1) as solvent and reacted at 75 °C to afford intermediate 20 in 70% yield. Subsequently, intermediate 20 was converted to thio analog 21 in 71% yield by reaction with P2S5 in pyridine at 120 °C. Finally, intermediate 21 was alkylated with 2-methylbenzyl bromide in DMF in the presence of K2CO3 to give the target product 22 in 76% yield. This synthetic route is also suitable for the preparation of other analogs for assessing the effect of phenyl and pyridyl substituents on the pyridazine ring.
