Synthesis of benzofurans via acid catalysed transacetalisation/ Fries-type O→C rearrangement/ Michael addition/ ring-opening aromatisation cascade of β-pyrones

Abstract

An unusual and facile approach for the synthesis of 2-benzofuranyl-3-hydroxyacetones from 6-acetoxy-β-pyrones and phenols is presented. The synthetic sequence involves a cascade transacetalisation, Fries-type O→C rearrangement followed by Michael addition and ring opening aromatisation. Versatility of this method was further demonstrated via the synthesis of 4,4a dihydropyrano[3,2-b]benzofuran-3-ones, furo[3,2-c]coumarins, and spiro[benzofuran-2,2'-furan]-4'-ones. The unexpected cascade event would also provide new possible considerations in the β-pyrone-involved organic synthesis.