NOVEL CHEMOSELECTIVE AND DIASTEREOSELECTIVE IRON(III)-CATALYZED MICHAEL REACTIONS OF 1,3-DICARBONYL COMPOUNDS AND ENONES

Iron(III) chloride hexahydrate catalyses the Michael reaction of 1,3-d icarbonyl compounds with alpha,beta-unsaturated ketones under mild and neutral conditions with extraordinary efficiency. The chemoselectivit y of this Fe-III-catalysed process is superior to that of the classic base-catalysed Michael reaction, since the latter suffers from various side reactions, namely drawbacks such as aldol cyclisations and ester solvolysis. Excellent yields and chemoselectivities; together with th e environmentally friendly nature of Fe-III catalysis makes this an im portant alternative to classic base catalysis. Moreover, the reaction procedure is reasonably easy: Fe-III catalysis does not require inert or anhydrous conditions, and in most cases no solvent is needed. In te rms of diastereoselectivity, the Fe-III-mediated reaction may also pro ve superior to a base-catalysed one. In at least one example, Fe-III c atalysis forms a diastereoisomer as the major kinetic product, which i s disfavoured in the base-mediated Michael reaction, where a thermodyn amic mixture is obtained. The relative configuration of the diastereoi someric Michael products has been determined for two examples by synth esis and structure elucidation of the cyclic aldol derivatives.