Synlett 2001; 2001(6): 0723-0732
DOI: 10.1055/s-2001-14578
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Catalysis of the Michael Reaction and the Vinylogous Michael Reaction by Ferric Chloride Hexahydrate

Jens Christoffers*
  • *Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany; Fax + 49 (0)711/685 4269; E-mail: jchr@po.uni-stuttgart.de
Further Information

Publication History

Publication Date:
31 December 2001 (online)

Ferric chloride hexahydrate catalyzes the Michael reaction of 1,3-dicarbonyl compounds with α,β-unsaturated ketones under mild and non-basic conditions with extraordinary efficiency. The chemoselectivity of this Fe(III)-catalyzed process is superior to that of the classic base-mediated Michael reaction, since the latter suffers from various side and subsequent reactions, namely drawbacks such as aldol cyclizations and retro-Claisen reactions. Excellent yields and chemoselectivities together with the environmentally friendly nature of the Fe(III) catalysis make this an important alternative to established methods. An enone-dienol tautomerization of 2-acceptor substituted cycloalkenones is the precondition for the iron-catalyzed vinylogous Michael reaction. Herein a γ-donor formally undergoes conjugate addition to a β-acceptor to furnish products with 1,7-dioxo constitutions. Actually, this process is a sequence initiated by the tautomerization followed by a [4 + 2]-cycloaddition and a retro-aldol reaction. When benzoquinone derivatives are employed as acceptors, the products of the vinylogous Michael reactions are highly functionalized biaryl precursor compounds.