Catalysis of the Michael reaction and the vinylogous Michael reaction by ferric chloride hexahydrate

Ferric chloride hexahydrate catalyzes the Michael reaction of 1,3-dicarbony l compounds with alpha,beta -unsaturated ketones under mild and non-basic c onditions with extraordinary efficiency. The chemoselectivity of this Fe(II I)-catalyzed process is superior to that of the classic base-mediated Micha el reaction, since the latter suffers from various side and subsequent reac tions, namely drawbacks such as aldol cyclizations and retro-Claisen reacti ons. Excellent yields and chemoselectivities together with the environmenta lly friendly nature of the Fe(III) catalysis make this an important alterna tive to established methods. An enone-dienol tautomerization of 2-acceptor substituted cycloalkenones is the precondition for the iron-catalyzed vinyl ogous Michael reaction. Herein a gamma -donor formally undergoes conjugate addition to a beta -acceptor to furnish products with 1,7-dioxo constitutio ns. Actually, this process is a sequence initiated by the tautomerization f ollowed by a [4+2]-cycloaddition acid a retro-aldol reaction. When benzoqui none derivatives are employed as accepters, the products of the vinylogous Michael reactions are highly functionalized biaryl precursor compounds.