4-(2,5-Dihydroxyphen-1-yl)-crotonic acid and its derivatives, and the preparation of these compounds

摘要

4-(2,5-Dihydroxyphen-1-yl)-crotonic acid and its derivative (I) <IMAGE> I where R1, R2, R3 and R4 are each H or C1-C8-alkyl, R5 is H, C1-C30-alkyl or C2-C30-alkenyl, and R' is H or an organic radical which can be split off hydrogenolytically, and a process for the preparation of the compounds I, wherein a hydroquinone II <IMAGE> II is reacted, in the presence of from 0.1 to 2 moles of a Lewis acid per mole of II, with (a) a vinylglycolic acid derivative IIIa <IMAGE> IIIa or (b) a crotonic acid derivative IIIb <IMAGE> IIIb where X is halogen, hydroxyl or C1-C4-alkoxy or acyloxy.