Preheat oven to 350 degrees F. Butter a 13 by 9-inch casserole dish.
Melt 3/4 cup butter in saucepan over low heat.
Pour the pineapple with juice into the casserole dish and evenly spread blueberry pie filling on top. Cover with dry yellow cake mix and top with pecans. Drizzle with melted butter and bake for 35 to 45 minutes.