Abstract Heating of dialkyl 2-bromoalkylidenemalonates in boiling xylene resulted in lactonization with formation of 2-alkoxycarbonyl-2-buten-4-olides. Bromination of dimethyl 2- phenylpropylidenemalonate with NBS in CCI 4 gave the corresponding butenolide. However, heating of the 2-bromocyclohexylidenemalonate only afforded the dehydrobromination product.
