Synthesis of an Azido Precursor to (2S,5R)-5-Hydroxylysine Using an Asymmetric Organocatalytic Chlorination/Reduction Sequence

Mechanistic Studies on the Organocatalytic α-Chlorination of Aldehydes: The Role and Nature of Off-Cycle Intermediates

Herein we report the isolation and characterization of aminal intermediates in the organocatalytic α-chlorination of aldehydes. These species are stable covalent ternary adducts of the substrate, the catalyst and the chlorinating reagent. NMR-assisted kinetic studies and isotopic labeling experiments with the isolated intermediate did not support its involvement in downstream stereoselective processes as proposed by Blackmond. By tuning the reactivity of the chlorinating reagent, we were able to suppress the accumulation of rate-limiting off-cycle intermediates. As a result, an efficient and highly enantioselective catalytic system with a broad functional group tolerance was developed.

Facile synthesis of 5-hydroxy-L-lysine from D-galactose as a chiral-precursor

A concise synthesis of (2S,5R) and (2S,5S)-5-hydroxy-lysine was achieved by utilizing D-galactose as a chiral-precursor with stereo retention. This synthetic strategy showcased the potential of utilizing carbohydrates as starting materials to prepare amino acids. Using the diazido intermediate, the derived β-D-galactopyranosyl and α-D-glucopyranosyl-(1→2)-β-D-galactosyl moieties were synthesized.