Oxazaborolidinones 3, 25, 32, 42, 49, and 53 can be obtained as single diastereomers by
crystallization-induced asymmetric transformation (AT). Asymmetric memory is maintained in the derived
enolates because the stereogenic boron resists equilibration with achiral, trivalent boron-containing species on
the time scale of enolate alkylation with methyl iodide, allyl bromide, or benzyl bromide. Conditions were
found for alkylating oxazaborolidinone enolates derived from phenylalanine (5, 33), alanine (18, 26),
phenylglycine (43), and valine (54) without significant loss of boron configuration. The phenylglycine-derived
oxazaborolidinone alkylation products 44 and 45 slowly undergo boron epimerization at room temperature,
and the C-allyl product 44b partially racemizes during hydrolytic cleavage, apparently by a 2-aza-Cope
rearrangement. These complications were not encountered with phenylalanine derivatives. Preparatively useful
results were obtained with oxazaborolidinones 3 and 32, derived from phenylalanine. AT favors a different
boron configuration in the B-naphthyl analogue 32 compared to 3. This provides access to either
quasi-enantiomeric enolate 5 or 33 by starting from the same phenylalanine enantiomer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.