2,3-取代的 4-氯-2-环丁烯酮,由取代的环丁烯二酮的区域特异性转化制备,经过钯催化与乙烯基和芳基锡烷以及乙烯基锆试剂交叉偶联,形成 4-R unsat -2-环丁烯酮。在热解 (100 o C) 时,这些底物以高产率转化为取代的苯酚。使用这种化学方法以区域特异性方式制备了五取代的芳香族化合物和各种三取代和四取代的芳香族化合物
A general, regioselective synthesis of substituted benzocyclobutenedione monoacetals
作者:James P. Edwards、Damian J. Krysan、Lanny S. Liebeskind
DOI:10.1021/jo00067a029
日期:1993.7
A general, regioselective synthesis of substituted benzocyclobutenedione monoacetals is reported. Palladium-catalyzed coupling of a variety of 4-chlorocyclobutenones with 3-(tri-n-butylstannyl)-3-cyclobutene-1,2-dione 2-(ethylene acetal) and heating up to 70-100-degrees-C produces substituted benzocyclobutenedione monoacetals in good to excellent yields. Thia chemistry is presumed to proceed through palladium-catalyzed formation of a 3-(1-oxo-2-cyclobuten-4-yl)-3-cyclobutene-1,2-dione-2-(ethylene acetal) followed by a thermally induced ring opening to a dienyl ketene and subsequent six-electron electrocyclic ring closure and tautomerization. 2,3-Disubstituted 4-chlorocyclobutenones afford palladium intermediates which couple exclusively at the least-substituted allylic terminus. 2,3,4-Trisubstituted 4-chlorocyclobutenones have not been studied in detail; however, preliminary results suggest that regioselective allylic cross-coupling can be achieved. The methodology described provides an expedient and efficient route to previously difficult-to-prepare benzocyclobutenedione derivatives. These function as important synthetic intermediates in a variety of reactions developed in these and other laboratories.