Preheat the oven to 350°F Grease a 5-by-9-inch loaf pan. In a medium bowl, whisk together the flour, cocoa powder, baking powder, salt and baking soda.
In a medium saucepan, combine the whole cherries and the sugar. Using a potato masher, crush the cherries. Cook over medium heat, stirring occasionally, for 15 minutes. Transfer to a large bowl and let cool. Whisk in the sour cream and eggs. Stir in the flour mixture.
Fold the chopped cherries into the batter. Gradually stir in the butter. Pour the batter into the prepared loaf pan, then bake until a toothpick inserted in the center comes out clean, about 55 minutes. Let cool in the pan for 15 minutes, then turn out onto a rack to cool completely.