Base-promoted cyclization of halohydrins is one of the main synthesis pathways for epoxides. Competing reactions such as elimination reactions are also possible and must be monitored. However, in this problem we will focus on epoxide formation and ignore the competing elimination. This base-promoted cyclization method takes advantage of the fact that alkoxide groups are good nucleophiles and that halide ions are good leaving groups. Recall that halide ions are good leaving groups, because they are electron-withdrawing, polarizable, and stable after departing the molecule. The first step in the base-promoted halohydrin cyclization mechanism is the deprotonation of the halohydrin OH group by the base, generating a halogenated alkoxide ion. The second step is an internal nucleophilic attack of the carbon bonded to the halide from the alkoxide. This forms the epoxide ring and causes the cleavage of the halide leaving group.
Provide curved arrows, draw the missing intermediate, and draw the product for the base-promoted cyclization of the indicated bromohydrin to its corresponding epoxide.
Draw all missing reactants and/or products in the appropriate boxes by placing atoms on the canvas and connecting them with bonds. Add charges where needed. Electron-flow arrows should start on an atom or a bond and should end on an atom, bond, or location where a new bond should be created.