Die Wohl-Ziegler-Bromierung von Tiglin- und Angelika-säureestern

The Wohl-Ziegler bromination (with N-bromo-succinimide = NBS) of methyl tiglate ( 1b ) gave a 2:1 mixture of methyl γ-bromotiglate ( 3b ) and methyl β′-bromotiglate ( 5b ). This ratio of γ- to β′-bromination was unaffected by changes of solvent, catalyst or size of the ester alkoxy group. The same products were obtained from the NBS treatment of methyl angelate ( 2b ). This NBS-bromination appears to be thermodynamically controlled, since both angelic and tiglic acid as well as their methyl esters were brought into equilibrium ( 1 ? 2 = > 9:1) with catalytic amounts of NBS.