1. Between 2 pieces wax paper, pound chicken breasts to flatten slightly.
2. In shallow bowl, mix together flour and 1/4 teaspoon salt and 1/4 teaspoon pepper. Dredge chicken in mixture to coat lightly.
3. In large frypan over medium heat, place oil. Add chicken and cook about 5 minutes on each side or until light brown and fork can be inserted in chicken with ease. Remove chicken to platter and keep warm.
4. Whisk grapefruit juice into frypan and simmer until reduced by half. Whisk in wine and sour cream; cook about 5 minutes or until hot and bubbly. Remove from heat and add butter, whisking. Add sugar and remaining salt and pepper. Stir in grapefruit and chopped cilantro. Return chicken to pan and stir to coat. Arrange on serving platter and garnish with grapefruit slices and cilantro sprigs.