In a small bowl, combine the walnuts, sugar and cinnamon; set aside. Grease a 13-in. x 9-in. baking dish with some of the melted butter. Unroll phyllo dough sheets (keep dough covered with plastic wrap while assembling).
Place one sheet of phyllo in baking dish; brush with butter. Top with a second sheet; brush with butter. Fold long ends under to fit the dish. Sprinkle with about 1/4 cup nut mixture. Repeat 18 times, layering two sheets, brushing with butter and sprinkling with nut mixture. Top with remaining dough; brush with butter. Cut into 2-in. diamonds with a sharp knife.
Bake at 350° for 45-55 minutes or until golden brown. Meanwhile, in a saucepan, combine the syrup ingredients; bring to a boil. Reduce heat; simmer, uncovered, for 10 minutes. Pour over warm baklava. Cool on a wire rack.