Aldol Reaction and Robinson-Type Annelation Catalyzed by Lanthanoid Triisopropoxides

Abstract

Lanthanoid triisopropoxides are active catalysts for aldol reactions. Aldehydes give the corresponding β-hydroxyaldehydes at low temperatures in good yields, whereas ketones are less reactive, but form condensation products at high temperatures. Exceptionally, γ- or δ-diketones easily undergo condensation to give five- and six-membered unsaturated ketones in high yields. The lanthanoid propoxides, catalyzing the Michael addition of ketones to α,β-unsaturated ketones, which give δ-diketones, are also good catalysts for the Robinson-type annelation. In these reactions, the catalytic activity of the lanthanum propoxide is higher than those of the heavy lanthanoid propoxides, and is almost comparable to that of sodium isopropoxide. Since aluminum triisopropoxide shows poor activity, the lanthanoid propoxides are considerably basic for trivalent metal alkoxides.

Cascade Michael-Aldol reaction: efficient annulation of sulfonamide chalcones into novel cyclohexenones under solvent-free conditions

“…However, these are not supposed to be and Au-catalyzed cyclisation of alkenefunctionalized propargyl acetate followed by base treatment. 28 Robinson annulation of chalcone motif promoted by various catalysts such as lanthanide complex, 29 Rhodium, 30 C-200, 31,32 etc has also been documented. Specifically, addition of β-keto ester to chalcone moiety has also been accessed in the presence of base like sodium ethoxide, 33 potassium carbonate under MW irradiation.…”

Sodium Benzoate as a Mild Base Catalyst for the Tandem Michael-Aldol Self-Condensation of γδ-Unsaturated β-Ketoesters

“…This reaction proceeded via a tandem Michael-Michael addition mechanism (Scheme 2) [11]. The authors reported that the rate of this reaction could be increased by performing the reactions in 2-propanol instead of non-polar solvents like benzene [12]. The self-dimerization of ,-unsaturated ketones to cyclohexenones is less well known [12].…”

“…For base catalyzed annelations, the focus is presently on the use of lanthanide triisopropoxides to induce tandem Michael-Michael annelations [11] and Michaelaldol condensations of ,-unsaturated ketones [12]. On the other hand, we had recently success using lithium carbonate and sodium or potassium benzoate as base catalysts for the synthesis of 2H-pyran-5-carboxylates from ,-unsaturated aldehydes and esters of acetoacetate [13].…”

Aldol Reaction—Homogeneous

“…A significant progress was also made by Feng and co-workers recently; a C-2-symmetric N,N -dioxide-Sc(III) complex has been developed to asymmetric catalytic aldol reaction of α-ketoesters and diazoacetate esters to afford tertiary alcohols in good yields with excellent enantioselectivities (up to 97% ee) (Scheme 54) (208). Lanthanoid triisopropoxides are active catalysts for aldol reactions of aldehydes (209). In addition, it is useful reagent for the preparation of Ln-based heterobimetallic catalysts, such as LLB 160.…”