REARRANGEMENT OF SUBSTITUTED (E)-5,5?-DIPHENYLBIFURANYLIDENEDIONES TO 3,7-DIPHENYLPYRANO[4,3-c]PYRAN-1,5-DIONES

Abstract

The rate coefficients for the rearrangement of substituted (E)-5,5′-diphenylbifuranylidenediones to form the corresponding 3,7-diphenylpyrano[4,3-c]pyran-1,5-diones in ethane-1,2-diol at 30.0 °C, catalysed by sodium acetate, were determined. For the unsubstituted dione, the rate coefficients for there arrangement in various alcohols at 30.0 °C, and for three at 59.8 °C, were measured. The reactions were first order in both substrate and acetate anion. Rate coefficients were also measured for the catalysis of the rearrangement of the unsubstituted dione in ethanol and ethane-1,2-diol at 30.0 °C by a series of sodium meta/para-substituted benzoates. Bronsted-type correlations for the latter give α≈1.2. Substrate substitutent effects on the rates of rearrangement of the diones were not marked. A good correlation was found between the rates of rearrangement of the unsubstituted dione and the solvent effect parameter ET(30). This and other evidence indicated a probable mechanism involving a rapid pre-equilibrium between the substrate diones and the carboxylate anion, followed by the formation of an s-trans-enolate anion. The latter rotates to the s-cis isomer, which then intramolecularly attacks the second lactone ring. The process is then repeated with the product dione resulting from loss of the carboxylate anion. © 1997 John Wiley & Sons, Ltd.