This seems to be a challenging reaction due to the easy elimination of HBr from you benzyl bromide with the formation of stilbene byproduct; therefore, I think that the standard conditions like NaH/THF most likely won't be suitable for this substrate. I will suggest trying it with a weaker base like K2CO3 in DMF, at room temperature initially, then with moderate heating if the reaction is slow.

If the elimination of HBr still remains the main reaction, I will consider the alternative ways to make your target compounds.

Hope this helps.

Thanks you Vladimir, I tried few standard conditions and I got elimination product in all cases. In Cesium carbonate / DMF I got elimination product. I will try K2CO3 in DMF lets see.

Thank you.

Namdev,

Thanks for your feedback. Since you already tried Cs2CO3, I am afraid changing it to K2CO3 wouldn't make big difference; perhaps changing the solvent to THF may help.

Also, I would consider using organic bases like 2,6-lutidine or iPr2NEt, lowering temperature to 0°C, or perhaps trying the reaction without the additional base (benzimidazole is a weak base itself, just take an excess of it).

Good luck !

Thank you Vladimir, I used base 2,6 lutidine as a solvent and carried out the reaction in a MW at 140 °C. In this condition, I got the product but conversion is only 10 %.

Thank you.

Congratulations, you seem to be moving in right direction !

Thank you....right direction because of your valuable suggestion...