Bring first 4 ingredients to boil in small saucepan, stirring to dissolve sugar. Cool. Do ahead Can be made 1 day ahead. Cover and refrigerate. Combine pomegranate mixture, vodka, grapefruit juice, lime juice, and mint leaves in large pitcher. Fill pitcher with ice. Stir vigorously. Strain drink into Martini glasses. Garnish each glass with mint sprig and serve.