Combine butter, brown sugar, corn syrup, water and whiskey in a large saucepan over medium heat. (Syrup will bubble up so make sure your pan is extra large). Stir constantly until butter is melted. Continue stirring until mixture comes to a boil; boil and stir for 1 minute.
Remove from heat and stir in cinnamon, vanilla and pecans.
Serve immediately or refrigerate until ready to serve. Syrup can be stored for 2 weeks in refrigerator.