A Photochemical Route to 3- and 4‑Hydroxy Derivatives of 2‑Aminocyclo­butane-1-carboxylic Acid with an <i>all-cis</i> Geometry

Short gram-scale syntheses of both enantiomers of 2-amino-3-hydroxy­cyclo­butane-1-carboxylic acid and of 2-amino-4-hydroxy­cyclo­butane­carboxylic acid with an all-cis geometry are described. The sequences feature highly endo-selective [2 + 2]-photocycloaddition reactions followed by fully regioselective ring opening/Hofmann rearrangement/nitrogen protection, in a consecutive or one-pot protocol, followed by efficient resolution using a chiral oxazolidinone.