Enantioselective dynamic thermodynamic resolutions

This reaction showed high enantioselectivity even when (-)-sparteine was added after hthiation of the carboxamide. Also, the racemic lithium carbanion derived from the racemic tin precursor via metal exchange reaction, gave products with high enantioselectivity [Eq. (41)], whereas when the carbanion prepared from the corresponding chiral tin compound was reacted with an electrophile such as TMSCl without (-)-sparteine it yielded racemic product. These results indicate that the reaction of the lithiated 3-phenylpropionamide proceeds through an asymmetric substitution pathway. Furthermore, a warm-cool procedure and then reaction with a substoichiometric amount of an electrophile confirmed a dynamic thermodynamic resolution pathway for this reaction. 

Dynamic thermodynamic resolution has been used to synthesize (i )-(+)-)5-conhydrine by the sequence shown [72]. Quenching the lithiated species with propanal leads to a 70 30 mixture of diaste-reomers with 96 4 enantiomeric ratio. What is the origin of the enantioselectivity in this reaction ... 

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