Dissonant Whispers and Warcaster

I wanted to make sure that I read this right. Let's say that I'm a GOO warlock with warcaster and spell sniper, and an enemy runs up to 5ft of me. On my turn, I can cast Dissonant Whispers and if the enemy fails, they trigger an attack of opportunity and I can unload an Eldritch Blast on them as Reaction?