Combine the sugar, cinnamon stick, and 1/2 cup water in a small saucepan. Bring to a boil, stirring to dissolve the sugar. Reduce the heat to low and add the clementine slices. Poach until the clementines are bloated and shiny, about 10 minutes.
Cool completely in the syrup, then carefully remove the clementine slices and drain on a wire rack.
Melt the chocolate according to the package's directions in a small bowl. Using a spoon, dip the curved bottom of each clementine slice into the chocolate. Set on a wax-paper lined pan. Refrigerate until the chocolate hardens.