Abnormal Claisen rearrangements of tetronates and stereoselective ring opening of intermediate spirocyclopropanes

Thermal [2,3]-sigmatropic rearrangements of allyltetronates proceed via 3-(spirocyclopropyl)dihydrofuran-2,4-diones; in some cases these could be isolated and their cyclopropane rings stereoselectively opened with alcohols or water to give 3-(β-syn-alkoxy)tetronic acids. Treatment of a 5,5-disubstituted benzyltetronate with LDA also produced a 3-substituted tetronic acid by an anionic [1,3]-rearrangement.