Answer
The following conversion can be accomplished by adding $CH_3CO_3H$, then $H_2O$ and then rotating it.
Work Step by Step
The addition of $CH_3CO_3H$ makes an epoxide across the double bond. Then $H_2O$ will attack from the other side on the most substituted carbon. This will open the epoxide breaking the bond and forming O− on the other carbon. Then the H+ adds to the O− and makes OH. Since the epoxide blocks one side, the H2O attacks from the other side. So the addition is anti, but when it is rotated, it becomes a syn addition.
