In a bowl stir together the flour, baking powder, salt, and baking soda. In a second bowl whisk together the buttermilk, eggs, and vanilla. In a medium bowl, using an electric mixer, cream the butter and sugar on medium-high speed until lightened, 2 to 4 minutes. On low speed, add the buttermilk mixture and beat until mixed. Gradually add the flour mixture and beat until smooth, scraping down the sides of the bowl as needed. Spread the batter evenly over the pineapple slices.