Asymmetric Synthesis of 2‑Substituted Oxetan-3-ones via Metalated SAMP/RAMP Hydrazones

2-Substituted oxetan-3-ones can be
prepared in good yields and
enantioselectivities (up to 84% ee) by the metalation of the SAMP/RAMP
hydrazones of oxetan-3-one, followed by reaction with a range of electrophiles
that include alkyl, allyl, and benzyl halides. Additionally, both
chiral 2,2- and 2,4-disubstituted oxetan-3-ones can be made in high
ee (86–90%) by repetition of this lithiation/alkylation sequence
under appropriately controlled conditions. Hydrolysis of the resultant
hydrazones with aqueous oxalic acid provides the 2-substituted oxetan-3-ones
without detectable racemization.