A Photochemical Route to 3- and 4‑Hydroxy Derivatives of 2‑Aminocyclo­butane-1-carboxylic Acid with an all-cis 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.本文报道了2-氨基-3-羟基环丁烷-1-羧酸的两种对映异构体，以及具有全顺式构型的2-氨基-4-羟基环丁烷羧酸的两种对映异构体的克级简短合成路线。该合成序列采用高内型选择性的[2+2]光环加成反应，随后通过连续操作或一锅法方案完成完全区域选择性的开环/霍夫曼重排/氮保护步骤，最后借助手性恶唑烷酮实现高效拆分。