Reinvestigation of the sulfuric acid-catalysed cyclisation of brominated 2-alkyllevulinic acids to 3-alkyl-5-methylene-2(5H)-furanones

Article abstract of DOI:10.1016/S0040-4020(97)10034-5

A synthesis of ethyl-, butyl-, hexyl- and dodecyl-substituted fimbrolides from alkyl-substituted levulinic acid derivatives through bromination and acid promoted lactonisation is described. The underlying reactions have been investigated using levulinic acid as a model, and the effects of varying the bromination conditions and changing acid concentration on product distribution are discussed. Dibromination proceeds best in CHCl₃ and proceeds in EtOH-free CHCl3 without the complication of ester formation. Cyclisation. occurs with concomitant oxidation in 98-100% H₂SO₄ but gives highest yields of fimbrolides in 100% H₂SO₄. The formation of related beckerelide substances is also described.