Abstract
A new synthesis of chromones and flavones based on the ortho-directed metalation of methoxymethyl aryl ethers with alkyllithium reagents is described. It entails reaction of the ortho-lithiated intermediates with a conjugated unsaturated aldehyde followed by oxidation of the allylic alcohol product with «periodinane» to yield an ortho-allylic ketone. The latter on heating in acetic acid undergoes loss of the methoxymethyl protecting group and cyclization to a chromanone (or flavanone, if a β-phenyl substituent is present). Dehydrogenation by treatment with pyrrolidone hydrotribromide (PHT) in dimethyl sulfoxide yields the corresponding chromones (or flavones). This synthetic approach appears general in its applicability
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