Access to 2-alkyl chromanones via a conjugate addition approach

The introduction of alkyl substituents at C-2 of chromanones via conjugate addition of silyl enol ethers to a variety of chromenones is reported. In most cases racemic 2-alkyl chromanones were obtained in good yield in the presence of TMSOTf. The copper(II)-promoted conjugate addition of silyl enol ethers to chromenones was also carried out, albeit in low yields and no selectivity. Reliable syntheses of the chromenones via acylation of the corresponding β-diketo-compounds are also described.