3-STANNYLCYCLOBUTENEDIONES AS NUCLEOPHILIC CYCLOBUTENEDIONE EQUIVALENTS - SYNTHESIS OF SUBSTITUTED CYCLOBUTENEDIONES AND CYCLOBUTENEDIONE MONOACETALS AND THE BENEFICIAL EFFECT OF CATALYTIC COPPER IODIDE ON THE STILLE REACTION

Treatment of 3,4-diisopropoxycyclobutenediones with n-Bu3SnSiMe3/catalytic CN- furnished 3-isopropoxy-4-(tri-n-butylstannyl)cyclobutenedione in 65% yield. This compound cross-coupled with organic iodides attached to sp2- and sp-hybridized carbon atoms and with vinyl trifluoromethanesulfonate esters under the influence of cocatalytic palladium/Cu species to provide 3-isopropoxy-4-substituted-cyclobutenediones in very good yields. Readily accessible 3-isopropoxy-4-methyl 3-cyclobutene-l,2-dione 2-(ethylene acetal) also reacts with n- Bu3SnSiMe3/catalytic CN-, leading to 3-(tri-n-butylstannyl)-4-methyl-3-cyclobutene-l,2-dione 2-(ethylene acetal), which also undergoes the Pd/Cu-catalyzed cross-coupling reaction, allowing the construction of 3,4-disubstituted-cyclobutenedione monoacetals. Highly substituted and functionalized cyclobutenediones can be sythesized by virtue of the mild and neutral reaction conditions of this carbon-carbon bond forming reaction (Stille reaction). © 1990, American Chemical Society. All rights reserved.