Make the Syrup: In medium saucepot, heat grapefruit and maple syrup over medium heat until mixture is just warmed through, stirring occasionally. Remove from heat; cover to keep warm.
Make the Pancakes: Preheat oven to 250 degrees F. Place a rimmed baking sheet with wire rack set inside in oven.
In large bowl, whisk flour, sugar, baking powder, baking soda and salt until well combined. In separate medium bowl, whisk egg until beaten. Add buttermilk, butter, grapefruit zest and vanilla bean paste; whisk until smooth. Add wet ingredients to dry ingredients; whisk until ingredients are just combined (do not overbeat; small lumps are fine).
Heat griddle or large nonstick skillet over medium heat. In batches, spray griddle with nonstick spray, then pour batter by heaping 1/4-cupfuls onto griddle. Cook 2 to 3 minutes per side or until golden brown and cooked through. Transfer cooked pancakes to prepared wire rack in oven to keep warm; continue making pancakes with remaining batter.