Stereo- and regiocontrol of electrophile-initiated rearrangement of push–pull 5-substituted 4-oxothiazolidine derivatives

Regioselective α-bromination of (Z)-5-substituted-2-alkylidene-4-oxothiazolidine derivatives affords, under mild experimental conditions, vinyl bromides 3 in good yields. They undergo rearrangement providing a highly efficient route to the stereodefined 4-oxothiazolidine derivatives possessing two fully delocalized exocyclic double bonds at C(2) and C(5) positions. A mechanism of this novel rearrangement reaction via base-promoted proton transfer from one carbanionic site to another, followed by the bromination–dehydrobromination sequence, is proposed.