Department of Chemistry MS 015, Brandeis University, Waltham, Massachusetts 02454-9110, USA.
J Org Chem. 2009 Aug 21;74(16):6245-52. doi: 10.1021/jo901221a.
A Kiyooka aldol condensation of an aldehyde with a trimethylsilyl ketene acetal and the oxazaborolidinone prepared from N-Ts-(S)-valine gives two of the four possible aldol adducts, which were oxidized and deprotected to complete the synthesis of (-)-berkelic acid and (-)-22-epi-berkelic acid. This synthesis establishes the absolute stereochemistry and assigns the stereochemistry at C-22. A biosynthetic pathway is proposed that is consistent with the known absolute stereochemistry at the quaternary carbon of spiciferone A, spicifernin, and berkelic acid and provides a simple explanation for the differing stereochemistry at C-18 and C-19 of spicifernin and berkelic acid.
Kiyooka 醛缩合反应，将醛与三甲基硅基烯酮缩醛和 N-Ts-(S)-缬氨酸制备的噁唑硼烷反应，得到了四个可能的 aldol 加合物中的两个，然后将其氧化和脱保护，完成了（-）-berkelic 酸和（-）-22-epi-berkelic 酸的合成。该合成确定了绝对立体化学，并确定了 C-22 的立体化学。提出了一个生物合成途径，该途径与已知的 spiciferone A、spicifernin 和 berkelic 酸中季碳原子的绝对立体化学一致，并为 spicifernin 和 berkelic 酸中 C-18 和 C-19 的立体化学差异提供了简单的解释。
