In my textbook, the addition of alkaline $\ce{KMnO4}$ to fumaric acid (trans) is stated as a syn-addition even though $\ce{OH}$ is present on opposite sides in the product.

Addition of electrophile and nucleophile on the available sites on the same side of molecule.

Note that there are two rotations in this: the first step includes a rotation of fumaric acid by $90^\circ$ so that I can draw the five-membered ring in a plain. After cleaving off $\ce{MnO4^3-}$ (which further reacts to $\ce{MnO4^2-}$ in basic conditions) I arrive at the syn-product.