Preheat oven to 325 degrees F. Grease and flour a 10-inch fluted tube pan; set aside. In bowl stir together flour, baking powder, baking soda, and 1/4 teaspoon salt; set aside.
In a large mixing bowl beat sugar and oil with an electric mixer on medium to high speed for 1 minute or until evenly moistened. Add eggs one at a time, beating well after each addition; beat until smooth. Alternately beat in flour mixture and buttermilk. Add the 2/3 cup chocolate syrup and vanilla; beat well. Pour into pan. Bake 1-1/4 to 1-1/2 hours or until a wooden toothpick inserted in center comes out clean. Cool on wire rack 15 minutes. Remove from pan; cool completely on rack. Transfer cake to platter; drizzle with Chocolate-Buttercream. Just before serving, drizzle 2 tablespoons syrup around top edge. Makes 12 to 16 servings.
Chocolate Buttercream Drizzle
In large mixing bowl beat butter on medium speed for 30 seconds. Add 1/2 cup powdered sugar; beat well. Beat in chocolate syrup and vanilla. Beat in 3/4 cup powdered sugar. If necessary, stir in milk until mixture drapes.