Michael reactions scandium triflate

Several catalytic protocols have been developed for the 1,4-addition of silylcopper reagents to enones and other Michael acceptors. Lipshutz et al.183 treated phenyldimethylsilyllithium with dimethylzinc and used the silylzinc reagent PhMe2SiZnMe2Li thus formed as the nucleophile in copper-catalyzed 1,4-additions to various enones and enals, for instance, verbenone 248 which afforded the desired product 249 in almost quantitative yield (Equation (14)). Interestingly, the rather slow addition reaction is strongly accelerated by catalytic amounts of scandium triflate. 

Rare earth metal triflates are recognized as a very efficient Lewis acid catalysts of several reactions including the aldol reaction, the Michael reaction, allylation, the Diels-Alder reaction, the Friedel-Crafts reaction, and glycosylation [110]. A polymer-sup-ported scandium catalyst has been developed and used for quinoline library synthesis (Sch. 8) [111], because lanthanide triflates were known to be effective in the synthesis of quinolines from A-arylimines [112,113]. This catalyst (103) was readily prepared from poly(acrylonitrile) 100 by chemical modification. A variety of combinations of aldehydes, amines, and olefins are possible in this reaction. Use of the polymer-supported catalyst has several advantages in quinoline library construction. 

The first Lewis acid-catalyzed asymmetric Michael addition in water was developed by Kobayashi et al, who reported ee s up to 83%. Very recent developments show great promise for further improvement of Michael addition reactions in water. In an elegant study, Kaneda and coworkers used montmorillonite-enwrapped metal triflates to execute C—C bond forming Michael additions. When scandium triflate was employed, adducts were obtained in quantitative yield within a 0.5-3 h at or slightly above room temperature. The catalysts were reusable with no appreciable loss in activity.In another recent study, Lind-strdm and coworkers observed a remarkable ligand acceleration effect in aqueous ytterbium triflate-catalyzed Michael additions. A number of 1,2-diamines and 1,2-aminoalcohols were shown to have a positive influence on the rate of the reaction, the most efficient being tetramethylethylenediamine, which induced a nearly 20-fold rate acceleration. 

Enantioselective Michael-type indole Friedel-Crafts reaction with a,P-unsaturated acyl thiazole has been disclosed <07JA10029>. Reaction of indole 127 and 128 in the presence of 10% mol of bis(oxazolinyl)pyridine-scandium(III) triflate complex 129 in acetonitrile at -40 °C affords 130 with high level of enantioselectivity. 

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