Azaallyllithium reagents silylation

Silylation of azaallyllithium reagents derived from hydrazones unlike silylation of enolates seems to occur mainly on cartwn. While chiral (S)-l-amino-2-methoxymethylpyrrolidine (SAMP) aldehyde hydrazones (c/. equation 4) alkylate to a greater extent on nitrogen to form an azaallylsilyl reagent, ketones give predominant C-silylation. In the case of chiral ketone hydrazones derived from (5)-(4), a-silylated ketone hydrazones are produced in these reactions with consistently high ee ( 6%) ... 

Corey, Enders and Bock were among the first to describe the utility of lithium dimethylhydrazone anions for crossed aldol reactions. In the reaction shown in equation (14), an azaallyllithium reagent derived from an aldehyde dimethylhydrazone was first silylated with trimethylsilyl chloride to yield a silyl aldehyde dimethylhydrazone. Subsequent lithiation using lithium diethylamide at -20 C for 1 h generated the silylated azaallyllithium reagent (29). Subsequent addition of one equivalent of an aldehyde or ketone at -78 C and warming to -20 C then yielded the product a,p-unsaturated aldehyde dimethylhydrazone in yields of 85-95%. Hydrolysis produced the unsaturated aldehyde in 75% overall yield. 

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