Long-range Asymmetric Induction

This concept was also applied to the higher homologs to determine the scope and limitations of this process (Table 8.3) [22]. Interestingly, Grubbs s 

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Long-range asymmetric induction controlled by supramolecular interaction of intermediate dilithio species (60) has been shown to account for the selective formation of two (out of four) /(-hydroxy sulfone diastereoisomers on reaction of a-sulfonyl carbanions with benzaldehyde in THF at — 100°C.58... 

Allylation. Long-range asymmetric induction by an oxygen functionality is observed in the reaction of allylstannanes with aldehydes using tin(IV) bromide as catalyst. Irrespective of the original configuration of the allylic double bond, the... 

SCHEME 24.16. Long-range asymmetric induction using the TST-RCM. 

Evans PA, Cui J, Buffone GP. Diastereoselective temporary silicon-tethered ring-closing-metathesis reactions with prochiral alcohols a new approach to long-range asymmetric induction. Angew. Ghem. Int. Ed. 2003 42 1734-1737. 

A new, metal-free protocol involving (heteroaryl)oxazoline catalysts for the enantioselective reduction of aromatic ketones (up to 94% ee) and ketimines (up to 87% ee) with trichlorosilane has been developed. The reaction is characterized by an unusual, long-ranging chiral induction.The enantiodifferentiation is presumed to be aided by aromatic interactions between the catalyst and the substrate.360 Asymmetric reduction of A-arylketimines with trichlorosilane is catalysed by A-methyl-L-amino acid-derived Lewis-basic organocatalysts with high enantioselectivity (up to 92% ee) 61... 

In entry 15 of Table 21.10, it is noted that even a remote hydroxyl group directed hydrogenation by the cationic [Rh(diphos-4)(nbd)]+ catalyst to afford a moderate diastereoselectivity (80 20) [23]. This is an interesting example of long-range 1,5-asymmetric induction. 

Long-range mediation by achiral boronate (IJ-asymmetric induction) in ketone reduction by borane is feasible. Enantioselective reduction of imines with stoichiometric quantities of a cyclic dialkoxyborane prepared from tartaric acid has been reported. 

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