1. Combine sugar and rum in a microwave-safe bowl. Microwave at HIGH 1 1/2 minutes or until sugar dissolves. Brush rum mixture evenly over pineapple wedges.
2. Melt butter in a grill pan over medium-high heat. Add pineapple to pan; grill 3 minutes on each side or until grill marks form and pineapple is thoroughly heated. Sprinkle with coconut. Serve with ice cream.