Sequential treatment of a 1,2-disubstituted olefin with m-CPBA, Br₃CCO₂H, and DBU results in the one-pot, stereospecific conversion of the olefin to the corresponding disubstituted cyclic carbonate (1,3-dioxolan-2-one). The reaction proceeds via an initial epoxidation followed by S_N2-type epoxide ring opening by Br₃CCO₂H and subsequent base-promoted carbonate formation upon elimination of bromoform. When a solution of a secondary allylic or homoallylic amine and Br₃CCO₂H is sequentially treated with m-CPBA then DBU, the product of the reaction is a cyclic carbamate (1,3-oxazolidin-2-one or 1,3-oxazinan-2-one).