| Summary: | Enantiopure ε-O-silyloxy- and ε-O-benzyloxy-α,β-unsaturated esters derived from d-ribose, each containing a cis-dioxolane unit, display excellent (≥95:5 dr) levels of diastereofacial directing ability upon conjugate addition of achiral lithium N-benzyl-N-isopropylamide. In contrast to the corresponding enantiopure ε-O-silyloxy-α,β-unsaturated ester derived from l-tartaric acid, which contains a trans-dioxolane unit, the conjugate additions of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to its cis-configured counterpart result in doubly diastereoselective 'matched' and 'mismatched' reaction pairings in which the inherent reagent control serves to augment or oppose, respectively, the established substrate diastereocontrol. © 2014 Elsevier Ltd. All rights reserved.
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