Dissolve yeast in warm water in a large mixing bowl. Add buttermilk, eggs, 2 1/2 cups flour, 1/2 cup of the butter or margarine, 1/2 cup of the sugar, baking powder and salt. Blend 30 seconds with mixer on low speed, scraping sides and bottom of bowl. Beat 2 minutes on medium speed. Stir in remaining 3 cups flour. (Dough should remain soft and slightly sticky) Knead for 5 minutes, or about 200 turns on a lightly floured board. Cover dough and allow to rest for half an hour.
Divide dough in half and roll each half into a 12x7 inch rectangle. Spread each half with 1 tablespoon soft butter and sprinkle with 1/4 cup of the sugar and 1 teaspoon of the ground cinnamon. Roll up the halves, beginning at the wide side. Seal well by pinching the seams. Cut each roll into 12 slices.
Coat two 9 inch round cake pans with 1/4 cup melted butter, 1/4 cup brown sugar, and 1/2 cup chopped pecans in each pan. Place 12 dough slices in each pan, leaving a small space between slices. Let rise until doubled.
Bake in a preheated 375 degrees F (190 degrees C) oven for 30 minutes. Invert pans onto serving plates immediately.