Access to racemic and enantioenriched 3-methyl-4-chromanones: catalysed asymmetric protonation of corresponding enolic species as the key step

Brønsted acids induced the intramolecular cyclisation of 3-aryloxypropanoic esters affording 3-methyl-4-chromanones, which have been transformed into the corresponding racemic benzyl β-oxoesters. These latter esters, in the presence of hydrogen and catalytic amounts of both palladium and (endo, endo) aminoborneol, led to optically active chromanones with up to 75% ee through a deprotection–decarboxylation–protonation cascade reaction.