Stir together cranberries, sugar, 1 cup water, orange juice, salt, and cinnamon in a large saucepan; cook over medium, stirring occasionally, until cranberries are softened but mostly retain their shape, 14 to 16 minutes. Pour cranberry mixture through a fine wire-mesh strainer set over a medium bowl; let cool completely, about 30 minutes. Reserve syrup for serving or another use, if desired.

Preheat oven to 325°F. Grease a 12-cup Bundt pan with butter, and sprinkle with flour; set aside. Sift together flour, cinnamon, salt, and baking soda in a medium bowl; set aside.

Combine brown sugar and orange zest in bowl of a stand mixer fitted with the paddle attachment. Rub zest and sugar using your fingers to release oils. Add butter and half of vanilla bean seeds. Beat on medium speed until light and fluffy, 3 to 5 minutes. Add eggs, one at a time, beating well after each addition. Beat batter on medium speed 1 minute. Reduce speed to medium-low; add flour mixture in three additions alternately with 1 cup buttermilk, beginning and ending with flour mixture; beat until just combined after each addition. Fold cooled cranberries into batter. Spoon batter into Bundt pan, and spread into an even layer.

Bake cake in preheated oven until a wooden pick inserted in center comes out clean, about 1 hour. Let cake cool in pan 10 minutes. Invert cake onto a wire rack, and remove pan. Let cool completely, about 2 hours.

Whisk together powdered sugar, remaining vanilla bean seeds, and remaining ¼ cup buttermilk in a bowl. Place cake on wire rack over a baking sheet; pour glaze evenly over cake, allowing glaze to run down sides of cake. Let harden 10 minutes. Serve cake with cranberry syrup, if desired.