Synthesis of (2,3-dihydrobenzofuran-3-yl)acetic acids from salicylic aldehydes: Trimethylsilyl as traceless activating group

Salicylic aldehydes were readily alkylated with (chloromethyl)trimethylsilane to give the silylated ortho-methoxy benzaldehydes in 85–96 % yields. These aldehydes were converted into arylidenemalonates in excellent yields. O-(Trimethylsilyl)methyl group was applied as the synthetic equivalent of aryloxymethyl anion in the nucleophilic cyclization at the alkene moiety promoted by cesium fluoride in DMF at 140 °C. In this way, (2,3-dihydrobenzofuran-3-yl)acetic acids and the corresponding esters were synthesized from salicylic aldehydes in 41–70 % overall yields.