Lithium hexamethyldisilazide, reaction with esters

A saturated amino acid can be functionalized to serve as a good synthetic precursor to an unsaturated amino acid, via a jy/t-elimination reaction. Reaction of 1.242 with lithium hexamethyldisilazide gave the ester enolate and reaction with p 1.2.5 eq. LiN(SiMe3)2 p... 

This reaction can sometimes be useful in synthesis. In the Honda et al. formal synthesis of securinine,2h N-benzylamino-ketone (97) was treated with lithium hexamethyldisilazide and then sorbic anhydride. This gave dienyl ester 98 by O-alkylation of the initially formed enolate anion. When the nitrogen protecting group was... 

The (Z)/( ) stereoselectivity of enolate formation is dictated by the structure of the starting carbonyl compound and the base used for deprotonation. Compared to LDA, Lithium 2,2,6,6-Tetra-methylpiperidide usually favors ( )-enolates whereas Lithium Hexamethyldisilazide preferentially leads to (Z)-enolates (eq 10). With a caveat for any generalization, enolate configuration usually determines the stereochemical result in the product for example, using a hindered ester and a bulky aldehyde combination, excellent stereoselectivities in aldol reactions are observed (eq 11). ... 

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