Can you use Lightning Rager when you sleep?

Hello,
I have a question about a Lightning Rager. Somebody want do a coup de grace on Barbarian when he sleep. Can he use a feat Lightning Rager before a attack or he is helpless and he die?

He is helpless, and if a coup de grace (full-round action) is being performed it isn't a surprise round and lightning rager does not apply, even if you could take an immediate action while asleep. Even if you could enter a rage via lightning rager the feat says nothing about cancelling other conditions including sleep.

A coup de grace isn't quite an auto-kill though. There is still a fortitude save involved.

Well after looking at the rules:
1) He is sleeping so he is helpless by definition,
2) However, if he has uncanny dodge, he is not flat-footed, unless he is immobilized, so can use an immediate action,
3) Lightning Rager grants a 2 point AC bonus during the surprise round.

Personally, I would allow him to use it provided he "notice" the thread with a penalized Perception check. But that's my interpretation and I can see it go both way.

He cannot do it. He is asleep, he is helpless, he is unaware of the situation. He cannot take an action to stop something he is unaware of (unless the ability says otherwise.)
Even if he could, a Coup de Grace is an auto-hit and his AC makes no difference whatsoever.

I can add this sleep is not a spell effect is normal sleep in night time. This is stupid situation.

well.. id' say perc check to see if he wakes up and notices

if not.
he's getting coup'd and he better hope he survives the rolls.