Preheat oven to 350 degrees F (175 degrees C). Grease one 9x5 inch loaf pan.
Measure flour, 1 cup sugar, baking powder, baking soda, 1 1/2 teaspoons cinnamon, salt, buttermilk, oil, eggs and vanilla into large mixing bowl. Beat 3 minutes. Pour into prepared loaf pan. Smooth top.
Combine 2 tablespoons white sugar, 1 teaspoon cinnamon and butter, mixing until crumbly. Sprinkle topping over smoothed batter. Using knife, cut in a light swirling motion to give a marbled effect.
Bake for about 50 minutes. Test with toothpick. When inserted it should come out clean. Remove bread from pan to rack to cool.