REGIOSPECIFIC PREPARATION OF CYCLOBUTENEDIONE MONOACETALS

Treatment of 2,3-diisopropoxy-4-hydroxy-4-organyl-2-cyclobuten-l-ones, prepared by addition of nucleophiles (H-, C-sp3, C-sp2, C-sp) to diisopropyl squarate, with Me3SiOCH2CH2OSiMe3 and catalytic trimethylsilyl triflate in THF induces a regiospecific monoacetalization, providing the 3-isopropoxy-4-organyl-3-cyclobutene-l,2-dione 2-(ethylene acetal) in high yield. These compounds react with a wide range of nucleophiles to give 1,2-adducts that can be converted into 3,4-disubstituted-3-cyclobutene-l,2-dione-2-ethylene acetals under mild conditions. By changing the order of introduction of substituents, this sequence of reactions provides access to a variety of isomeric cyclobutenedione monoacetals in a regiodefined fashion. © 1990, American Chemical Society. All rights reserved.