Polymetallic asymmetric catalysts

Lanthanide Bimetallic and Polymetallic Asymmetric Catalysts 683 Table 13.29 Catalytic enantioselective weso-epoxide ring-opening with TMSCN... 

Lanthanide Bimetallic and Polymetallic Asymmetric Catalysts 687 Table 13.32 Catalytic asymmetric conjugate addition of cyanide to a,p-unsaturated imides (S,S)-[(salen)AI]20 (2 mol%)... 

In 1999, Shibasaki et al. reported on the direct catalytic asymmetric aldol reaction (Scheme 8.36), which was not necessary to preconvert the ketone moiety into the more reactive species such as an enolate ion and enol ether." The addition of bulky aldehyde 248 into the mixture of ethyl methyl ketone 249 and LaLi3tris(/ -binaphthoxide) [(/ )-LLB)] afforded aldol adduct 250 in excellent stereoselectivity. However, this reaction required a large amount of ketones (50 equiv), and catalyst (20 mol%) were required. They improved the conditions to reduce the amount of ketone (5 equiv) and catalyst (8 equiv) by using the hetero-polymetallic asymmetric catalyst (Scheme 8.37). The addition of the catalytic amount of potassium bis(trimethylsilyl) amide (KHMDS) and H2O was found to be effective to the catalysis. Adduct 253 was converted into ester 254 by the... 

New asymmetric polymetallic catalysts were reported for the ring-opening reaction of ffieso-aziridines with TMSCN <07T5820>. Three contiguous tertiary stereocenters were generated via the reaction of active methylene nucleophiles with tosylated aziridines under mild phase-transfer catalyzed conditions. For example, reaction of aziridine 61 with the anion derived from 62 provided substituted cyclopentane 63 in excellent yield <07OL4677>. 

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