Photochemical bromination of methyl (E)-2-methylbut-2-enoate with N-bromosuccinimide: formation of 4-bromo-2-methylbut-2-en-4-olide

Bromination of methyl (E)-2-methylbut-2-enoate (4) with N-bromosuccinimide under irradiation with light was described. The formation of 4-bromo-2-methylbut-2-en-4-olide (8) in fairly good yield together with the desired methyl (E)-4-bromo-2-methylbut-2-enoate (5), methyl (E)-2-(bromo-methyl) but-2-enoate (6), and methyl 2,3-dibromo-2-methylbutanoate (7) was clarified.Methyl (E)-4-(p-formylphenoxy)-2-methylbut-2-enoate (16) was smoothly subject to catalytic hydrogenation using Wilkinson complex, while the rate of the hydrogenation of its geometrical isomer (17) was extremely retarded.