A general, regioselective synthesis of substituted benzocyclobutenedione monoacetals
摘要:
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.
A new process for the regiocontrolled synthesis of substituted catechols and other 1,2-dioxygenated aromatics: conjugate addition of vinyl-, aryl-, and heteroarylcopper reagents to cyclobutenediones followed by thermal rearrangement
作者:Angela Gurski、Lanny S. Liebskind
DOI:10.1021/ja00067a027
日期:1993.7
A general method for the synthesis of substituted catechol derivatives has been developed utilizing the 1,4-addition of vinyl-, aryl-, and heteroarylcuprates to cyclobutendiones followed by thermal rearrangement. In situ protection with (methoxyethoxy)methyl chloride of the enolate derived from addition of the cuprate yields 2-alkoxy-4-R unsat'd -2-cyclobutenones, which rearrange thermally to substituted