Highly diastereoselective formation of 3,7-dioxabicyclo[3.3.0]octan-2-ones in reaction of 2-arylcyclopropanedicarboxylates with aromatic aldehydes using 1,2-zwitterionic reactivity type

A new reaction of 2-arylcyclopropane-1,1-dicarboxylates (ACDC) with aromatic aldehydes that occurs via generation of a 1,2-zwitterionic intermediate in the presence of GaCl₃ has been developed. This process results in the 3,7-dioxabicyclo3.3.0]octane frame by addition of two aldehyde molecules to an ACDC molecule. The reaction is a complex anionic-cationic cascade process involving the formation of two C–C bonds, two C–O bonds, and five stereocenters. The process occurs with high diastereoselectivity to give only one diastereomer. A probable reaction mechanism is suggested and confirmed by NMR monitoring data.