Acetylation of 2-Acyl-1,3-indandiones with Ketene and Determination of the Structure of Products

2-Acyl-1,3-indandiones attracted the interest of chemists as early as forty years ago, since some of them exhibited remarkable physiological, in particular anticoagulant, properties and found use in practice as rodenticides [1—3]. Their chemical properties, however, have been scarcely studied. It is known for example that they exist in a diketoenol form. Nevertheless, existence of two struc­ tures A and ß can be assumed, A representing enolization of an acyl carbonyl group and В an enol form of a carbonyl belonging to 1,3-indandione skeleton. In both enol forms, stabilization via the hydrogen bond and formatton of a fa­ voured six-membered ring is feasible. Evidence gained from the examination of IR spectra demonstrated the preference of the diketoenol form A with an exocyclic enol arrange­ ment [4]. Studying properties of cyclic 1,3-diketones, we were interested lately in their acylation with various acylating agents, as in some cases their behaviour is different from that of acyclic 1,3-diketones. In this paper, our results obtained from acetyla­ tion of 2-acyM ,3-indandiones (acyl = acetyl /, propionyl //, isovaleryl ///, pivaloyl IV, benzoyl V) with ketene are presented. From the theoretical point of view, acetylation of 2-acyM ,3-indan-