Adjust oven rack to middle position and heat oven to 475 degrees. Half squash through stem, seed and cut each half into 4 wedges. Toss squash, oil, sugar, salt, pepper in large bowl. Arrange squash cut side down in a single layer on rimmed baking sheet. Bake until bottoms of squash are golden brown, about 25 minutes.
Meanwhile, bring syrup to boil in a small saucepan over medium-high heat. Reduce heat to medium low and simmer until slightly thickened, about 3 minutes. Off heat, whisk in butter and cyenne until smooth. Cover and keep warm.
When bottoms are deep and golden, remove from oven. Flip and brush 6 tablespoons glaze. Bake, rotating baking sheet, until squash is tender and deep golden all over, about 15 minutes. Flip and brush with remaining glaze, serve.