Process for the preparation of substituted indanones

A process for the preparation of a compound of the formula III or the isomer thereof of the formula IIIa ##STR7## in which R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are identical or different and are hydrogen, (C.sub.1 -C.sub.20 )-alkyl, (C.sub.6 -C.sub.14)aryl, (C.sub.1 -C.sub.10)alkoxy, (C.sub.2 -C.sub.10)alkenyl, (C.sub.7 -C.sub.20)arylalkyl, (C.sub.7 -C.sub.20)alkylaryl, (C.sub.6 -C.sub.10)aryloxy, (C.sub.1 -C.sub.10)fluoroalkyl, (C.sub.6 -C.sub.10)haloaryl, (C.sub.2 -C.sub.10)alkynyl, an --SiR.sup.8.sub.3 radical in which R.sup.8 is (C.sub.1 -C.sub.10)alkyl, or are a halogen atom or a heteroaromatic radical having 5 or 6 ring members which may contain one or more heteroatoms, or the adjacent radicals R.sup.1, R.sup.2, R.sup.3 and R.sup.4, together with the atoms connecting them, form one or more substituted or unsubstituted rings, which comprises reacting a compound of the formula I ##STR8## with a compound of the formula II ##STR9## in which R.sup.9 is straight-chain (C.sub.1 -C.sub.20)alkyl, and R.sup.1 to R.sup.7 are as defined above, in liquid, anhydrous hydrogen fluoride.