Total syntheses of stemoamide, 9a-epi-stemoamide, and 9a,10-epi-stemoamide by a convergent A + B ring-forming strategy is reported. The synthesis required a diastereoselective late-stage methylation of the ABC stemoamide core that successfully enabled access to three of the four possible diastereomeric structures. For the natural stemoamide series, the diastereoselectivity can be rationalized both by kinetic and thermodynamic arguments, whereas for the natural 9a-epi-stemoamide series, the kinetic selectivity is explained by the prepyramidalization of the relevant enolate.

中文翻译：

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Stemoamide、9a-epi-Stemoamide 和 9a,10-epi-Stemoamide 的全合成：最终甲基化步骤的不同立体化学

报道了通过收敛的 A + B 成环策略合成茎酰胺、9a-表-茎酰胺和 9a,10-表-茎酰胺。该合成需要对 ABC 茎酰胺核心进行非对映选择性后期甲基化，从而成功地获得四种可能的非对映体结构中的三种。对于天然茎酰胺系列，非对映选择性可以通过动力学和热力学参数来合理化，而对于天然 9a-表-茎酰胺系列，动力学选择性可以通过相关烯醇的预锥体化来解释。