Bring juice and 1/2 cup sugar to boil in medium saucepan over high heat, stirring until sugar dissolves. Reduce heat to medium; simmer until mixture is reduced to 2 cups, stirring occasionally, about 25 minutes. Cool to room temperature.
Meanwhile, position rack in center of oven; preheat to 350°F. Stir remaining 3/4 cup sugar and 3 tablespoons water in heavy small saucepan over low heat until sugar dissolves. Increase heat to high and cook without stirring until syrup turns deep amber, occasionally brushing down sides of pan with wet pastry brush and swirling pan, about 10 minutes. Working quickly, divide caramel among six 3/4-cup ramekins or custard cups. Tilt each ramekin to coat bottom with caramel. Set ramekins in 13x9x2-inch baking pan.
Place egg yolks in large bowl.
Whisk in pineapple mixture. Divide custard among ramekins.
Pour enough hot water into baking pan to come halfway up sides of ramekins.
Bake flans until gently set in center, about 30 minutes.
Remove from water; cool. Cover; chill overnight.
Run small knife around flans. Invert onto plates; allow syrup to run over.
