1,2-Dioxo-3-isopropyloxy-4-methyl-3-cyclobutene as a nucleophilic synthon. Synthesis of Sq-containing cinnamic acid derivatives

An enolate-like intermediate A derived from 1,2-dioxo-3-isopropyloxy-4-methyl-3-cyclobutene (6) has proven to be a novel nucleophilic synthon for an aldol condensation reaction with an arylaldehyde to give a variety of 4-hydroxy-2,3-dioxocyclobut-1-enyl group (Sq group)-containing cinnamic acid derivatives.