Kinetics of base-catalysed condensation of 5-methylfuran-2(3H)-one with 2-hydroxybenzaldehyde

Abstract

Condensation of 5-methylfuran-2(3H)-one (1) with 2-hydroxybenzaldehyde (2), catalysed by triethylamine and yielding 3-acetonylcoumarin (3). was studied kinetically at 45–65°, without any solvent or with small amounts of CHCl₃. Two reaction intermediates were clearly detected, as well as the formation of trans-3-(2-hydroxybenzylidene)-5-methylfuran-2(3H)-one. Concentration versus time profiles are interpreted by a scheme involving basecatalysed condensation of (1) and (2) to form an aldol, which subsequently dehydrates to give trans- and cis-3(2-hydroxybenzylidene)-5-methylfuran-2(3H)-one. The latter is finally converted into (3) by base-catalysed intramolecular acylation. The proposed kinetic scheme is also discussed on the basis of the activation parameters.