Occult Opportunist

 
Prerequisite(s): Knowledge (arcana) 5+ ranks, Spellcraft 5+ ranks
 
Benefit: You may make an attack of opportunity against an opponent you threaten who dismisses a spell, directs or redirects an active spell, casts a quickened or swift spell, or attempts to turn or rebuke undead. If your attack is successful, your opponent must make a concentration check (DC 10 + Dam Dealt) or lose the action that provoked the attack.
 
Source: Dragon Magazine #340