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

Semi-empirical AM1 and PM3 molecular orbital calculations on the mechanism of the hydrolysis of unsaturated lactones: substituted (E )-5,5′-diphenylbifuranylidenediones and 3,7-diphenylpyrano[4,3-c]pyran-1,5-diones

“…Experimentally, addition of the nucleophile to the enol 8 has been proposed as the rate-determining step in the alkaline hydrolysis of the bifuranylidenediones 5. 8 This is exactly what is found with the AM1 calculations. Moreover, the calculated activation energies for this step give an excellent correlation with the measured 8 rate coefficients (Fig.…”

“…The respective transition states [see structure (b) in Fig. 1] are also very similar to TS (7)(8). According to PM3 calculations ring opening of the enol adduct 9 to the dienolic carboxylic acid 10 should require a higher activation energy than addition of H 2 O except for the m-NO 2 derivative.…”

“…2230 i cm Ϫ1 ), indicating an analogous mechanism. In the latter ones a stabilising intramolecular hydrogen bond between one H-atom of the approaching water molecule and the keto carbonyl function is present, leading to a lower activation energy (3-4 kcal mol Ϫ1 ) for TS (11-12) as compared to TS (8)(9). As for the opening of the first lactone ring AM1 calculations also lead to a significantly lower activation energy for opening of the second lactone ring [TS (9-10) and TS (12)(13)] than for addition of the nucleophile, especially for the enol tautomer.…”

“…Given the close resemblance between the systems treated in ref. 8 and those described by us 3 we found it worthwhile to investigate these reactions in more detail with the aid of computational methods. In view of the very general importance of nucleophilic addition reactions on carbonyl compounds a number of theoretical papers either at the ab initio 10 or the semiempirical 11-13 level have already been published.…”

Coordination Programming of Photofunctional Molecules

“…Its structural isomer, 3,7-diphenylpyrano[4,3-c]-pyran-1,5-dione ( P 66 -Ph , Scheme 2 a) was produced by thermal isomerization under basic conditions in the Pechmann dye [ 101 ]. P 66 -Ph is also a good dye molecule, showing a strong absorption at approximately 430 nm [ 102 ]. There are two more possible isomeric forms of Pechmann dye, P 56 -Ph and P 55 ’-Ph [ Scheme 2 (a)].…”