Aldol condensation stereoselectivity

Stereoselective aldol condensation. The stereoselectivity of the reaction of 1 with the ester 2 can be controlled by the choice of the metal enolate. The products are intermediates to 1-methylcarbapenems. 

In principle, stereoselective aldol condensations can be carried out under two distinct sets of conditions. Under the influence of acid catalysis, stabilized enol derivatives of defined geometry (M = SiMea,... 

The studies just cited demonstrate several important design features pertaining to the objective of achieving highly stereoselective aldol condensations with Group I-II metal enolates. 

Stereoselective Aldol Condensations of Dialkylamide Lithium Enolates... 

In large measure, the problem associated with the execution of a stereoselective aldol condensation has been reduced to the generation of a specific enolate geometry. The recent results of Kuwajima (66a), which demonstrate that enolsilanes may be transformed into boryl enolates without apparent loss of stereochemistry (eq. [53]), should enhance the utility of vinyloxyboranes in stereoselective synthesis. The only current drawback to this procedure is associated with the presence of trimethylsilyl triflate (69), which must be removed from the reaction medium before the aldol condensation. It has recently been established that 69 is an effective catalyst for the aldol process (4). 

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