Asymmetric Syntheses of APTO and AETD: the β‑Amino Acid Fragments within Microsclerodermins C, D, and E

Efficient asymmetric syntheses of APTO and AETD, the highly functionalized β-amino acid fragments within microsclerodermins C, D, and E, are reported. The conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)­amide to tert-butyl (E,E)-7-(triisopropylsilyloxy)­hepta-2,4-dienoate and in situ enolate oxidation with (−)-camphorsulfonyloxaziridine, diastereoselective dihydroxylation of a 2,3-syn-γ,δ-unsaturated-α-hydroxy-β-amino ester derivative under Donohoe conditions, and a Julia–Kocieński olefination were used as the key steps.本文报道了APTO与AETD的高效不对称合成——二者为微硬海绵素C、D、E中高度官能化的β-氨基酸片段。关键合成步骤包括：将(R)-N-苄基-N-(α-甲基苄基)酰胺锂与(E,E)-7-(三异丙基硅氧基)庚-2,4-二烯酸叔丁酯进行共轭加成，并用(-)-樟脑磺酰氧氮丙啶实现原位烯醇氧化；在多诺霍条件下对2,3-顺式-γ,δ-不饱和-α-羟基-β-氨基酸酯衍生物进行非对映选择性双羟化反应；以及Julia-Kocieński烯烃化反应。