Synthesis of (R)- and (S)-Allyloxiranes via Enantioselective Allylboration of Bromoacetaldehyde. Transformation of (R)-Allyloxirane into (–)-(R)-GABOB (GABOB = γ-amino-β-hydroxybutyric acid)

Enantioselective allylboration of bromoacetaldehyde with allyl(diisopinocampheyl)borane 2 or allyl(diisocaranyl)borane 3 has been used as a key step in the first synthesis of (+)-(R)-6 [89% enantiomeric excess (e.e.)] and (–)-(S)-allyloxirane 7 (92% e.e.), respectively; in two steps, oxirane 6 was converted into (–)-GABOB [(R)-4-amino-3-hydroxybutyric acid] 9 (89% e.e.), which is both a neuromodulator of the mammalian central nervous system and a drug.