Access to racemic and enantioenriched 3-methyl-4-chromanones: catalysed asymmetric protonation of corresponding enolic species as the key step
摘要:
Bronsted acids induced the intramolecular cyclisation of 3-aryloxypropanoic esters affording 3-methyl-4-chromanones, which have been transformed into the corresponding racemic benzyl beta-oxoesters. These latter esters, in the presence of hydrogen and catalytic amounts of both palladium and (endo, endo) aminobomeol, led to optically active chromanones with up to 75% ee through a deprotection-decarboxylation-protonation cascade reaction. (C) 2003 Elsevier Ltd. All rights reserved.
α-Aryloxymethylacrylic acids and their derivatives have been found to undergo some novel thermal transformations leading to the formation of ‘ene’ dimers. The structure of the dimer has been revised on the basis of degradation studies, extensive spectral data and isolation of intermediates.