Preheat oven to 400 degrees. Line a standard 12-cup muffin tin with paper liners. Toss together strawberries and 1/3 cup sugar. Using a potato masher, lightly mash berries; set aside.
In a large bowl, whisk together flours, baking powder, baking soda, salt, and cinnamon. In a glass 2-quart measuring cup or a medium bowl, combine buttermilk, oil, egg, and vanilla; whisk to combine.
Make a well in the center of the flour mixture and pour in the buttermilk mixture and the berry mixture (with juice). Fold just until combined. Using an ice cream scoop, divide the batter among the muffin cups. Sprinkle the tops with remaining sugar.
Bake until a toothpick inserted in the center of a muffin comes out clean, about 17 minutes. Cool 5 minutes in the pan, then transfer muffins to a wire rack to cool completely.