Reactions of carbonyl compounds in basic solutions. Part 17. The alkaline hydrolysis of substituted (E)-5,5′-diphenylbifuranylidenediones and 3,7-diphenylpyrano[4,3-c]pyran-1,5-diones

Abstract

The alkaline hydrolyses of aseriesof substituted (E)-5,5′-diphenylbifuranylidenediones and 3,7-diphenylpyranq[4,3-c]pyran-1,5-diones have been shown to proceed by biphasic pathways. In both cases, a very rapid primary reaction gives hydrolysis of one lactone ring. This is followed by a less rapid secondary reaction giving hydrolysis of the second ring and identical products from both systems. Rate coefficients for the secondary reactions have been measured in 70%(v/v) dioxane–water at 30.0 °C and, for the parent substrates, at 49.0 °C. The enthalpies and entropies of activation have been evaluated. The effects of substitution have been assessed by means of the Hammett equation. Reaction pathways are suggested and the reactivity is related to the ring size.