Highly Diastereoselective Epimerization: Stereodivergent Synthesis of α-Hydroxy-β-amino Isopentanoic Acid

Oxazolidinones and 2,5-Dihydrofurans via Zinc-Catalyzed Regioselective Allenylation Reactions of l-α-Amino Aldehydes

The simultaneous control of diastereoselectivity and regioselectivity in Zn-catalyzed allenylation reactions of N-protected l-α-amino aldehydes is reported. A reversal in diastereoselectivity could be realized by variation of the α-amino aldehyde protecting groups. A range of 1-allenyl-2-amino alcohols were obtained with excellent regioselectivity and converted to oxazolidinones and dihydrofurans. Many of which could be isolated as single diastereoisomers and without significant erosion of ee, making this a practical catalytic synthesis of highly functionalized heterocycles.

New building block for polyhydroxylated piperidine: total synthesis of 1,6-dideoxynojirimycin

(3R,4S)-3-Hydroxy-4-N-allyl-N-Boc-amino-1-pentene 10, an important precursor for the synthesis of polyhydroxylated piperidines, has been achieved as a single diastereomer without racemization via vinyl Grignard addition to N-Boc-N-allyl aminoaldehyde 9, which was derived from an enantiopure natural amino acid. Having forged a tetrahydropyridine ring scaffold 13 from 10 in 85% yield via RCM using Grubbs II catalyst, we were able to effect its stereodivergent dihydroxylation, via a common epoxide intermediate to yield a range of interesting hydroxylated piperidines, including ent-1,6-dideoxynojirimycin (ent-1,6-dDNJ) 1 (28% overall yield) and 5-amino-1,5,6-trideoxyaltrose 2 (29% over all yield) in excellent dr. To the best of our knowledge, our synthesis of ent-1,6-dDNJ 1 is the most expeditious to date.