Compounds of the formula I, II, III, IV or V ##STR1## in which Ar, X, Y, Y', R.sup.1 to R.sup.5 and R.sup.1' to R.sup.5' are as defined in claim 1, can be used as photoinitiators for the photopolymerization of unsaturated compounds. They can be prepared by a Diels-Alder reaction and/or a Grignard reaction.
式I、II、III、IV或V的化合物##STR1##中,其中Ar、X、Y、Y'、R.sup.1至R.sup.5和R.sup.1'至R.sup.5'如权利要求1所定义,可用作不饱和化合物的光
引发剂。它们可以通过Diels-Alder反应和/或Grignard反应制备。