Synthese von bromosubstituierten Butenoliden II

Synthesis of Bromosubstituted Butenolides II . Methyl 4,4′-dibromosenecioate ( 2 ) was prepared by double N-bromosuccinimide bromination of methyl senecioate ( 1 ) and converted to methyl 4,4′-diiodo-senecioate ( 3 ) with sodium iodide and to 3-bromomethyl-2-buten-4-olide ( 4 ) with aqueous hydrobromic acid. A mixture of methyl (Z)- and (E)-4-bromosenecioate ( 8 and 9 ) yielded 3-methyl-2-butenolide ( 5 ) with aqueous hydrobromic acid and a mixture of (Z)-and (E)-4-methoxy-senecioic acid ( 10 and 11 ) with methanolic potassium hydroxide. N-Bromosuccinimide treatment of the butenolide 5 afforded 4-bromo-3-methyl-2-buten-4-olide ( 6 ) and 4,4-dibromo-3-methyl-2-buten-4-olide ( 7 ).