The thermal rearrangements of methylenecyclopropanecarboxylic acids

Abstract

Substituted methylenecyclopropanecarboxylic acids (6) and (7) rearrange thermally in the liquid phase to mixtures of the lactone (10) and the dihydrofuranone (13). The product ratios depend on the positions of the substituents. The parent acid (5) and Feist's acid (1a) decompose thermally in the presence of water to give ethyl methyl ketone and levulinic acid respectively. The mechanistic rationale of the above reactions is based on a competition between ring cleavage and electrophilic addition to the exo-double bond.