An Unusual Domino Claisen−Conia Reaction Producing 3,5-Dispirodihydrofuran-2,4-diones
摘要:
Allyl tetronates 3 can be selectively converted either (in acetonitrile) into Claisen-rearranged 3-allyltetronic adds 5 or (in toluene) into novel Claisen-Conia-rearranged 3-(spirocyclopropyl)dihydrofuran-2,4-diones 6, featuring up to three new stereogenic centres. The mechanism and the stereochemistry of this process is discussed and an X-ray crystal structure of one of the two diastereoisomers of (+/-)-6c is presented.
Thermal [2,3]-sigmatropicrearrangements 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