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 degrees 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.