REARRANGEMENT OF SUBSTITUTED (E)-5,5'-DIPHENYLBIFURANYLIDENEDIONES TO3,7-DIPHENYLPYRANO[4,3-C]PYRAN-1,5-DIONES

The rate coefficients for the rearrangement of substituted (E)-5,5'-di phenylbifuranylidenediones to form the corresponding 3,7-diphenylpyran o[4,3-c]pyran-1,5-diones in ethane-1,2-diol at 30.0 degrees C, catalys ed by sodium acetate, were determined, For the unsubstituted dione, th e rate coefficients for there arrangement in various alcohols at 30.0 degrees C, and for three at 59.8 degrees C, were measured, The reactio ns were first order in both substrate and acetate anion, Rate coeffici ents were also measured for the catalysis of the rearrangement of the unsubstituted dione in ethanol and ethane-1,2-diol at 30.0 degrees C b y a series of sodium meta/para-substituted benzoates, Bronsted-type co rrelations for the latter give alpha approximate to 1.2. Substrate sub stitutent effects on the rates of rearrangement of the diones were not marked, A good correlation was found between the rates of rearrangeme nt of the unsubstituted dione and the solvent effect parameter E-T(30) . This and other evidence indicated a probable mechanism involving a r apid pre-equilibrium between the substrate diones and the carboxylate anion, followed by the formation of an s-trans-enolate anion, The latt er rotates to the s-cis isomer, which then intramolecularly attacks th e second lactone ring, The process is then repeated with the product d ione resulting from loss of the carboxylate anion. (C) 1997 by John Wi ley & Sons, Ltd.