RAMP and SAMP hydrazones

An alternative to hydrolysis is cleavage of the RAMP- and SAMP-hydrazones by ozonolysis which takes place without epimerization or racemizationA This is a reliable method of obtaining the alkylated ketone products with high de and ee selectivity. ... 

The easiest way to make oxidizable silanes is by condensation of an organolithium with the inexpensive dimethyldimethoxysilane. If enolates have to be silylated, it may be preferable to use the more reactive chlorodimethylalkoxysilanes. Introduced by Dieter Enders, a-lithiated RAMP- and SAMP-hydrazones (e.g., 78) are enolate-like species having an impressive track record for stereocontrolled synthesis. The chiral auxiliary enables the stereoselective introduction of the silicon substituent. Having oxidatively cleaved the hydrazone to restore the original carbonyl function, the latter may be diastereoselective reduced to either an (/ )- or (5)-alcohoI. The ultimate silicon/oxygen displacement thus produces either a meso- or a dl-Aio (Scheme 1-55). ... 

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